The Bench

The Vysion displays are up and running on a few boats now, and all who have used them are quite happy. They are highly visible, can be almost infinitely customized, and have several features not found on any other display.

We now have a demo program available that can be run on any PC. It requires a source of Ockam data to run properly. If you have the OckamSoft 4.07 driver installed on the PC, you can place it in simulator mode, and the Vysion program will read the data. It can also read live data that is pitched over UDP broadcast from an Ockam system (like from a 051L LANBridge or the OckamSoft driver).

The demo program requires registration, which uses the usual Ockam unlock key exchange. The operating time is limited, but is variable and determined by us when the registration key is issued. Typical allowances have been in the range of 2 weeks.

Write to me, Dan Chesson, at the "repairs" email address to obtain a link to download the demo application.

Comments (0)

So what’s new here at Ockam? A few things…

First, the new Vysion system has now been installed on a few boats. We’ve encountered some growing pains with these, but that’s the price to pay for bleeding-edge technology! We continue to improve the system, and all involved seem to be pretty happy with the results. I’ve even heard from other boats racing against the boats with the Vysion displays, and all remarks have been very positive. One person remarked that he could easily read the Vysion display on the boat… from another boat over 100 feet astern in direct sunlight! There’s even an example program that simulates the Vysion output that you can install here (please use Internet Explorer for this link) or download a zip file here for later use.

We continue to refine the DeWiggler program. There are many refinements for the program now. One major refinement is that there are many "flavors" of DeWiggler available. There is the original Analyst version, which requires collection of data to be sent to Ockam for analysis and report generation. This can produce corrections for compass, boat speed, and wind inputs. There is a sub-version of analyst that produces reports for just compass and boat speed, the test for which can be done under motor (no crew required). There is also an "instant gratification" version avaialble: DeWiggler Realtime. This version can produce corrections for all the same things as the Analyst version, except for Upwash Slope. These corrections are available immediately after running the tests. There is no human to judge the validity of data, so this test may not produce as good results as the Analyst version, but it is still much improved over the initial results that one can expect from a regular human-only calibration. Finally, there is now a tack analysis program available. This program analyzes the boat’s performance during tacks, and allows the crew to determine areas of inadequacy that might be addressed to improve racing performance.

Our 051L LANBridge continues to gain momentum. There are now several boats with this interface installed. Data input to a PC is much simpler, and now multiple computers can read the instrument data without the hassle of a distributing multiplexer! We have also been involved in some very advanced (for a boat) network architecture, and have created a telemetry system using a 051L LANBridge with some additional hardware. Can hacking another boat’s instrument system be too far off?

We are working on an updated version of the venerable 001 CPU. We were forced to twilight production of the popular CPU after many years of production due to difficulty in obtaining parts in reasonable quantities. Initially, we believed that the T1 CPU would adequately address demand for an Ockam system, as the T1 has easily outsold the 001 since its introduction. However, there is still the cadre of older boats with the 001 system that need support, and now many sport boats are looking for the performance of an Ockam system without the processing features of the T1. We are currently developing the new CPU, and are hopeful for a spring 2010 release.

We would love to hear from you if you have any questions or comments regarding these new developments… drop us a line!

Comments (0)

The story of one boat having calibration problems was recently relayed to us. The crew was having difficulty obtaining reasonable numbers from their instrument system, so they began to "calibrate" the instruments. I used quotes because what they were doing was not actually calibration, but fiddling and guessing. After a race or practice, they would talk over the numbers they saw while sailing, and then adjust the instrument according to what they thought they should be. They were getting frustrated because the instruments would constantly show inconsistent numbers, and needed adjustment after every race. The instruments became worse than useless - they became unnecessary weight and a source of frustration and distraction.

There have also been cases where we have been told that the instruments must be wrong, since the driver knew he could go faster than that or the boat couldn’t possibly sail like it did in the conditions indicated by the instruments. After much discussion where we made the case that the instruments need to be calibrated correctly, the crew went ahead and adjusted the calibrations to reflect what they thought were the correct calibrations. This of course created false data which in turn led to bad decisions, and many poor finishes. If I recall correctly, it also led to one boat being sold in frustration. The new owner of said boat calibrated the instruments correctly, and was very happy with the results.

The hazards of engaging in this behavior should be obvious. Anyone trained in science can tell you that forcing the data to fit your own perception or assumption leads to incorrect conclusions. Pilots are very familiar with this - there have been many documented crashes where the pilot chose to follow perception rather than hard instrument data and pranged the aircraft (often with fatalities). A well-calibrated instrument system may sometimes give odd figures, but these may be indications of conditions that can give an advantage when recognized, such as wind shear.

The numbers used for calibration should not be created by guessing or by the T-LAR method (that looks about right). We have a well-established routine for calculating the calibration numbers. The Ockam System Manual contains a detailed step-by-step process for manually calibrating the instruments. It even has work sheets that guide the user through the whole process - what I call the "plug and chug" method. The numbers are plugged into the various formulae, and the then the answers are chugged out. However, some people are simply frightened by math, and avoid doing this. I think this is a bit ridiculous, since the math used is no more advanced than what you might use to balance your check book.

Some people insist on using a professional calibrator, but their services are not necessary to produce good calibrations. A dedicated amateur can produce results as good as a professional. The difficulty in using professional calibrators is that they are hard to find and difficult to schedule. They also tend to charge for their services and expenses. In my opinion, only the largest or most specialized boats really benefit from their services. Some calibrators are also professional sailors, so it may be possible to get a "two-fer" when hiring one, and have them sail in an important regatta. Not everyone can afford to do this, though.

The DeWiggler program can also produce excellent calibration data. I’ve written previously about what DeWiggler can do, and some of the information we’ve gleaned from the results. DeWiggler is probably the least intensive method of running the calibrations. The computer program is set up and run, and it guides the user through the entire calibration process. Depending on the version used (Realtime vs. Analyst), results may be available immediately, or in a few weeks. Not every boat has a computer available to run the DeWiggler program, but those that have run the program have been extremely happy with the results.

Even with good calibration, it is possible to fudge the numbers to produce the desired result. One top-level sailor would adjust the polar data weight during practices so he wouldn’t have to push the boat (and himself) every day sailing. He would make it appear as if they were always hitting or exceeding the performance numbers by de-rating the polar data (i.e., the boat did not have to go as fast to reach the theoretical speed). It didn’t really matter in the end, as he and his crew did quite well. However, anyone of lesser talent would have just been cheating themselves by not measuring performance honestly. How can you improve your performance if you don’t know what you’re doing wrong?

An excellent white paper has already been written on the politics of calibration, and is available on our web site. It discusses the types of personalities encountered on boats with problematic calibrations, and has suggestions on improving the situation.

Comments (0)

We’re entering the second year of public release of DeWiggler, and there is now enough data to make some general conclusions. Probably the single most important conclusion gleaned from the data analysis concerns the compass.

The first half of the DeWiggler tests calibrate the boat speed (V_s) and compass heading (M_s), so it is referred to as the V_sM_s test or "viz-miz." This test only requires motoring around in a pre-defined pattern (no sails), so it has been performed more than the other half. This test also has the greatest initial effect on the operation of the instrument system. That is, only if the apparent wind calibrations aren’t too far off. Using previously valid or the default wind settings are usually a good start.

From the data gathered, the median value of existing compass peak-to-peak deviations was 6 degrees. The interesting discovery was that on compasses with deviations above the median, no amount of compensation would sufficiently remove the error. The error was thus due to the installation area, and not the lack of automatic compensation. To correct the problem on these compasses, it is necessary to move the compass location to eliminate the source of error, and then re-run the automatic compensation.

For instance, one boat had horrible deviation values, and no amount of compensation was removing that error. The compass was moved, and the compensation improved immediately. The owner spoke to the builder and designer, and found out that steel reinforcements had been embedded in the fiberglass under the original location of the compass! There was no external evidence of this to alert the installer, so the only way to really discover this was by examining the quality of data from the compass with DeWiggler.

An aside on installing compasses: I find that using a hand-bearing compass to scout installation locations works pretty well. By moving the compass in and out of the proposed installation area, you can see the deflection caused by any ferrous materials in the area. If the compass needle moves a lot, that is probably not a good location.

It is important to remove as much deviation as possible, as any compass deviation is completely carried into the wind direction figure calculated by the instrument system. That means that 10 degrees of deviation will create a 10 degrees error in the wind direction.

For the complete analysis of the first season’s DeWiggler results, see the document at http://www.ockam.com/dewiggler/DeWigglerReport.pdf

We have also thought about how DeWiggler is used. There are likely to be some refinements in the coming months, especially in regards to changing calibrations before a race. It’s been well-noted that racers get really nervous about changing things just before a big regatta, so some changes in DeWiggler will be made to reduce the jitters caused by changing the calibrations. Also as previously mentioned, the V_sM_s test is by far the easiest portion of the DeWiggler test suite to perform. There is now separate pricing to run only the V_sM_s test.

Comments (0)

Our current favorite compass for use with the Ockam system is the Maretron SSC200. It is a 3-axis turn-stabilized electronic compass, and is relatively inexpensive. It is also widely available, so it can be obtained fairly easily (including through our Web Store). It can also be calibrated for deviation using a variety of methods, so it is rather flexible in actual use, unlike many other compass types.

One method requires a connection to a PC for serial communications. However, this method is not very practical unless you are very comfortable with working with this type of low-level hardware configuration. It requires a certain familiarity with electronic hardware and software, so it is not suitable for everyone. Even those who are well-versed in this type of work find it to be a bit of a bother. Personally, I avoid this method when possible.

Another method requires the use of one of Maretron’s proprietary displays. This method has the clear advantage of ease-of-use, but the display itself is a little expensive (USD 800 retail price). Some people have installed this display as a heading repeater for the steering station (like with the KVH AC100) and gotten the additional calibration functionality as a bonus. Most people do not want to incur the additional expense, so this is not usually a viable method. Some servicing dealers happen to have a DSM200 for use in calibration, so you may be able to arrange something with them if you want to go this route.

By far the most popular method is the simple power-on calibration method. The SSC200 will perform a calibration after power-on when a few simple steps are followed (see page 11 of the current SSC200 manual). This is probably the simplest method, but feedback can be a problem. The compass will indicate a successful deviation calibration by sending the compass headings 000, 090, 180, and 270 each for two seconds, followed by the actual heading. If you had a direct indication of the compass heading, this would not present much of a problem. However, the Ockam system typically has some sort of averaging set for the display data, so this confirmation message can get masked by the display averaging.

The best way to get around this is by setting the display averaging for heading to zero on a T1 processor. This forces the system to display the information as it receives it. The display averaging for heading can be set through a computer connected to the Ockam system; this option is unfortunately not available through a Matryx display. The command to set heading to zero display averaging is A23=0 with a direct command through a terminal session. Display averaging can also be set on the OckamSoft driver through the Control tab under the Avgs radio button by entering 0 in the Val box and clicking the Execute button.

The 001 Unisyn processor cannot have a display averaging value set lower than 0 or anything other than an integer, so the lowest value is 1. You may be able to catch the Maretron confirmation sequence with this, but it is not likely.

Regardless of the processor used, you should set the display averaging back to the value it was before. The default value for heading averaging is 1 second, so the command is A23=1 if setting by direct entry.

Comments (0)

I wrote the following letter to the editor in response to the article titled "Keep Your Insurance Paid Up" in Scuttlebutt 2747:

A lightning strike contains an impressive amount of energy. Temperatures in a lightning bolt can easily exceed those found on the surface of the sun, and the electrical current can exceed 40 kiloamperes! Even if the electronics survive a lightning strike, they should be treated with suspicion, as the component parts have probably been subjected to induced voltages or currents outside their specified maximum tolerances.

Lightning protection on boats is used to minimize structural damage, not to protect electronics. Protection for electronics against lightning strikes would have to be similar to what the military uses to harden installations against nuclear electromagnetic pulse (EMP): a Faraday cage with electrically isolated power and signals. On a racing yacht, the weight and power required for that is prohibitive. Without protection against EMP, even a nearby lightning strike may induce enough current in the yacht’s wiring to damage on-board electronics. I have encountered many instances where a boat was not directly struck by lightning, yet had several electronic items fail.

As mentioned in the article, the best strategy is to get insurance coverage for your electronics, and keep up on the premiums. There’s little that can be done to repair an item when lightning has burned through the circuit board!

Comments (0)

We have a new product here at Ockam, as you may have noticed on our main web site. It’s called the LANBridge, model number 051L.

What does this product do? It attaches to the Ockam bus with the standard BNC connector, and provides all the data available on the Ockam bus (Ockam format and NMEA 0183) to a connected Ethernet LAN by UDP broadcast. This is similar to what the OckamSoft 4 driver could do, but no computer is required. The system can send the data out by UDP itself! It can also accept data input from a device attached to the LAN.

What is special about this? First, if you have a PDA running Ockam Eye, you no longer need a PC running below deck. All you need is a wireless access point (either dedicated WAP or integrated with a router) to provide the WiFi radio. Second, it eliminates many of the common problems found using RS-232 on board a boat if you are using a PC.

As usual, this new interface is backwards compatible. It will work with all previously produced Ockam Instrument systems. How about that… You can put this on a system built in 1983 and expect it to work! It will work with both the older 001 Unisyn based systems and the newer T1 Tryad based systems. The interfaces already in the field have been working flawlessly since first power-up! Tactical and navigational programs such as OckamSoft 4, Expedition, and Nobeltec VNS can accept UDP broadcasts as data sources.

We are also investigating a wireless (WiFi) version of this interface, as well as many other "flavors" of the concept. So far, the interest has been resoundingly in favor of the wired LAN version, but I expect to see the wireless version take off as well. We will continue to produce and support the 050 RS-232 interface and the RS-232 connection on the T1 processor, as the RS-232 signal format is robust and well-established in the electronics world, and is not expected to disappear any time soon.

Comments (0)

Putting the boat away for the winter…It’s a sad time of year in the Northern Hemisphere. Unless you’re one of those die-hard few that keeps sailing your big boat in the winter, it’s time to put away the big toy until next spring.

Most people are very aware of the mechanical preparation given to putting away boats. There’s the adding of antifreeze where needed, the fall service for the engine, the fuel stabilizer added to the fuel tanks, clearing out the fresh and waste water tanks, and the general clean-up before closing everything tight against the weather. But how many people give attention to the electronics? In my experience, not many.

First, be sure to remove any displays that are outside and bring them home with you. It’s likely that you won’t see the boat much over the winter, so you’re not going to catch any small problems that can lead to bigger problems. Freezing water expands, so if there’s a little water left on the displays, it can force open the seals and cause leaks. I’ve gotten more than one display in for repair that has been subjected to a freeze/thaw cycle, and has let in water to damage the electronics. I’ve also had one case where differential cooling caused the glass on a display to crack - the display was mounted in a custom metal pod that twisted the display and broke it! It easiest to just remove the display, cover any holes with tape, and then reinstall the displays in the spring.

Also remove any sensors that are exposed to the elements. These usually include the masthead unit, the speed sensor, and the depth transducer. It’s not usually practical to remove a load pin, but if one is installed, make sure that it is covered - especially the cable. Plastic and rubber tend to get brittle at lower temperatures, so a knock that may not do any harm in the summer may shatter the object in the cold of winter. Just be sure to place the blanking plugs in the through-hull fittings if you take out the speed sensor and depth transducer. It is also a good idea to protect the connector for the masthead unit (a small bag taped over this is usually enough).

The items that are kept below deck - the processor, interfaces, and compass - are fine if left in place. Just be sure that they will stay dry, as freezing water can cause a lot of damage.

These are some general suggestions to decommission your electronics for the winter. Some boats require a little more preparation, but the suggestions given here should help most boats get through storage without too much of a problem.

Comments (0)

There are many sources of noise on board a boat. Once the motor is off and the boat is under sail, things quiet down. Most of us don’t actively think of noises on the boat unless they become worrisome or annoying. The crew can be the most immediately annoying, especially if they don’t like the provender and drink in the galley (or cooler, depending on your boat). However, there is a type of noise that many sailors don’t think about that can adversely affect the operation of the boat: electrical noise.

How do you know that there is electrical noise? It’s usually noticed first on anything to do with audio, so the radios are the first place that electrical noise gets noticed. There might be a hum on the stereo, or whistling on the VHF, or buzzing on the SSB. But there are other places that electrical noise can cause problems. One common place on the Ockam system is the boat speed reading - especially on the 015 "black box" type interface. Electrical noise can cause all sorts of silly values here. Another place is the wind speed; the value for wind speed usually just stays put at or above a particular value if there is a noise problem. I’ve seen a boat with wind speed stuck at 52 knots because of AC induction from an inverter.

Electrical noise is typically only noticed when it starts affecting the normal operation of the boat’s electronics, but it’s almost always present to one degree or another. If you suspect there is a problem, you can try a few things to isolate the source.

First, turn off any generators and inverters. Also turn off any battery chargers. Finally, disconnect any shore power or communication connections (cable TV, telephone, etc.). These are very common sources of electrical noise. If the bad behavior goes away once you have removed these potential sources, then you know that one of them is likely responsible for the noise. Re-attach or turn them on one by one to see when the bad behavior comes back; you should be able to figure out the source.

But what to do about it? In some cases, simply providing a good ground connection can solve your problems. There are also a variety of noise filters available to help remove noise from the voltage supply of a boat. I have found that good battery isolation between banks (again, there are a variety of products that do this) can help immensely, especially on boats that use more than one house bank.

The Ockam system can also be a source of noise, especially the older systems operating with an SSB on the boat. The paper at this link covers several strategies to eliminate this noise. I have found that most boats don’t even get past the first two remedies before the problem is reduced to a level where it is no longer a problem. On the newer systems, the components produce far less electrical noise, so reduction of RFI is rarely an issue.

Comments (0)

Most of us don’t do a whole bunch of night sailing, except for the occasional distance race or when trying to make good distance on a cruise. Sailing at night opens up a whole bunch of new issues, and since we don’t get much practice doing, the solutions aren’t always obvious.

One tremendous issue is the visibility (of lack thereof). People rarely realize how dependent they are on sight as the primary sense until it is taken away by darkness. We key so much of our world to sight, and being deprived of that sense interferes with our ability to operate normally. It’s at best annoying, and at worst, terrifying.

Being able to see your instruments helps alleviate some of that terror. You can at least be reassured by the same numbers that you see while sailing during the day, and compare your situation against that. Any aircraft pilot will tell you that no matter what you think you feel while flying, the instruments rarely lie. Your body might tell you that you’re in a slow ascent, but the instruments will tell you for certain if that’s true. Basing your decision off a gut feeling while flying can easily get you killed.

For instruments to be visible in the dark, some sort of lighting is required. On old analog type displays, there was often a dimable incandescent bulb inside the unit that provided a nice dull glow. Some analog instruments also had luminescent paint to augment the visibility. Most digital instruments (ours included) use LEDs for back lighting.

The problem with instrument back lighting is that your eyes adapt to the dark, but the lighting level typically doesn’t change unless you control it. Human eyes reach one plateau of dark adaptation around 9 minutes, and another hours later. Instrument lighting levels at one point in the cycle may be completely wrong for a later point. Fortunately, it is possible to control the system lighting level (see "Set Light Level") and the lighting level for individual disaplays (see "Remote displays commands: @Jn" section) on the Ockam system. Note that the system light level will control the maximum brightness of all the displays, while the individual display control can dim individual displays down from the system maximum.

Another problem is wavelength perception. The human vision sytem perceives some wavelengths of light as brighter than others. Two light sources of identical physical luminosity but different wavelengths are perceived as having different brightnesses. Pure red light appears to be dimmer than other colors, but that’s not the reason that most night lighting is red. Most night lighting is red because that’s what was used in photography dark rooms (remember those?). Red light was used in dark rooms because black and white film had poor response in the red part of the spectrum, so being exposed to red light would not ruin developing photographs like other colors of light. Red lighting for night use came into common use during World War 2, but the reasoning behind it was not well understood - they just did it that way because it worked in the dark room. It was serendipity that the human eye didn’t change dark adaptation as quickly when exposed to red light.

All displays on the Ockam system now use red back lighting. Some of the older Matryx displays have a green backlight. The Matryx displays with green backlights can be converted to red back lighting if desired however. The green back light shouldn’t interfere too badly with night vision, as the Matryx displays can be individually dimmed lower than the system lighting level.

Comments (2)

Ever hear someone talking about hitting their targets at the post-race party, and wonder why they were shooting at people? They’re not trying to shoot the competition, they’re just using polar plots of the boat’s performance to judge how they are performing against the boat’s potential in the conditions.

Many people are familiar with polars as the table and graph documents that detail the boat’s performance in a variety of wind speeds at wind angles from dead downwind all the way up to in irons (at least the good polars cover this range). It’s not very convenient to whip out some sheets of paper while racing, so the better instrument systems (Ockam included) can compute and display polar performance information on the fly. This may seem like overkill to win a race, but all the best racing programs use polars. To paraphrase a recent sailing forum post: "How do you recognize people who use polars? They’re standing up front with the trophy in their hand."

I’ll not go into the nitty-gritty details of plotting polars - that’s covered pretty well elsewhere. However, there are a few important details that are worth noting.

First, everyone should be aware that polars use true wind angles and speeds. This is what the boat "sees" as the basis for its speed, as true wind is independent of the boat’s motion through the water (unlike apparent).

Almost all polar sets, or at least the initial model runs, assume optimal conditions. This means that there is no accommodation for bad sails, bad trim, bad driving, bad weather, or bad luck. If you have old sails, it should be pretty obvious that you will not be reaching your polar targets. For those people inexperienced with the use of polars, it may not be as obvious that bad weather will also prevent you from reaching your polar targets. If you have to reef, or if you are pounding through waves, the boat will not be driving to its potential speed for the given wind speed.

A boat isn’t precluded from having more than one polar file. Many high-end programs will have the initial prediction file from the designer as a basis for starting measurement, and then also build a file from observed performance. One aside: building a polar file from observed performance can be difficult since it’s hard to winnow out bad data. Performance analysis is typically done off the boat much after the race, so it can be hard to determine when the boat is responsible for a particular data point, or if an external factor is at work (e.g., bad helming, collision avoidance, weather, etc.). A good alternative polar file built from observed data can provide a way to compensate for weather and sea state. It takes a lot of concerted effort by the person doing the analysis and a large data set in a wide range of environmental conditions to provide a good foundation for analysis. Some boats also have multiple rig or sail configurations that strongly affect performance, and require separate polar files for different configurations. The Ockam system has always allowed for the use of several polar files. On the 001 CPU with 037 Performance Index, there was a hardware switch to set the desired polar file. On the T1 CPU, the polar file can be selected with a software command.

Another detail that should be obvious, but really isn’t: you need good instruments to use polars effectively. Your instruments must measure the boat and its environment accurately and precisely to give you a good idea of the actual performance. This means that you must have instruments with reproducible results, and must have any measurement errors corrected (i.e, calibrate the instruments). The more astute reader will have realized that since true wind is the basis for polar performance, then good calibration of the instrument system is a must. Some instrument systems have no capability for calibration, and are completely unsuitable for using polars. Imagine driving a car with a speedometer that worked differently each time you drove - bad instruments are like that. It’s pretty impossible to know how well you’re doing from day to day if you don’t have reproducible results.

It may not be completely obvious, but GPS-based SOG should NOT be substituted for speed through the water! "Why?" you ask… SOG does not take into account any current. Those of you who have sailed in foul current (such as The Race in Long Island Sound) know how frustrating it is to trim the sails perfectly in good wind, only to make 1.0 knot headway over the ground. Now imagine if your polar performance was based off SOG. Assuming you have decent wind speed and a good point of sail, the polar performance would show you making some paltry low percentage of your expected performance! There would be much gnashing of teeth, since it seems like you’re doing everything correctly and not making any speed. However, if you use speed through the water, it will at least show that you are making the best speed through the water possible for the wind conditions. The Race is an extreme example, but it illustrates the point that current can significantly affect your speed over ground, thus rendering SOG a poor indicator of performance.

Resolving wind speed and angle to predicted performance can be a problem if you have a very coarsely granulated polar file. In the past, the Ockam system required very strict data ranges to provide polar information through the 037 Performance Index. Wind angles had to be provided from dead downwind (180 degrees), all the way up to extreme pinching (ideally around 15 degrees) in 2 degree increments. Winds speeds were provided from 0 to 25 knots in 0.5 knot increments. These rather strict requirements were due to the limited processing power of electronics back then. Remember when 33 MHz processors with 16-bit busses were the leading edge for PCs? More powerful processors have opened the door to better functionality; the more powerful processor in the Ockam T1 has loosened the requirements for the polar files. It can interpolate values with far less data points than before. However, the polar file shouldn’t be too sparse on data points if any sort of accuracy is desired. Data points every 10 degrees and 5 knots are a good minimum standard for the T1 processor, but higher data resolution is always better. Areas of the performance plot that have large changes in a small region should have data point higher resolution to capture the predictions accurately.

For most instances of simple performance comparisons, polar plots that cover the range from close-hauled to dead down wind will suffice. When using VMC sailing and Wally, having more information past close-hauled becomes important. VMC sailing becomes especially important when going to a mark that is not directly in line with the wind (typically some sort of distance race). It becomes even more important if the wind is shifting over time, such as is found in almost every distance race. The performance information for the region above close-hauled allows computation of the possible VMC benefit of sailing both above and below the rhumbline. This allows comparison of the distance advantages between sailing on a conventional rhumbline course and sailing off the rhumbline (either above or below) at the fastest VMC speed. Without the data above close-hauled, possible advantageous sailing is eliminated from the calculus of the fastest route! That would be like only allowing your trimmers to adjust sails while on only one tack, and hobble you from your possible best performance.

Sailing with polar performance comparison can induce a lot of headache, and has a pretty steep learning curve. Many people simply don’t have the time to fully comprehend all the nuances of using the performance analysis with their instrument systems. However, many of the more common functions can be easily incorporated into the tactician’s tool kit with a little study and practice.

Comments (0)

Alas, the plight of the ignoble load cell: doomed to ride for eternity at the point of a knife, dunked in salt water ever and anon, but expected to work flawlessly.

Load cells are a tremendous help when tuning the rig for different conditions. They are especially important on fractional rigs, where it can be hard to judge the headstay tension based on the backstay (unless you have done your math ahead of time). Load cells are also used frequently on larger yachts to judge rig tension all around, as it would be pretty difficult to use your typical Loos gauge on 3/4" PBO.

On land, load cells are pretty much indestructible. They are used widely in industrial and transportation applications with nary a problem. However, put them in the marine environment, and forget about that eternal reliability, especially when put on a yacht. Load cells, especially load pins, have some important considerations that are frequently ignored, leading to failure.

The load cell is basically a Wheatstone bridge. The actual configuration of the measured circuit can vary, but they are all essentially the same. Bending stress on the special printed circuit causes a change in resistance in one or more legs of the circuit. This change in resistance unbalances the Wheatstone bridge, and this is measured by the amplifier. The amplifier then converts the measurement into something usable by external devices, typically in RS-232 or NMEA 0183 format.

One of the most frequent failures I have seen involves the cabling. A well-sealed cable keeps out salt water and prevents infiltration into the electronics. Once this cable is damaged, ether through a nicked sheathing or a pulled-away seal, failure is sure to follow in short order. Salt water will wick throughout the wire by capillary action, and will also seep into the actual sensing portion of the load cell. As we all know, salt water and electronics don’t mix. I have received items back where the entire cable has corroded inside the sheathing due to one nick in the rubber.

Another common failure has to do with the way that the load pin is constructed. Many of them have a preferential strain direction due to the internal configuration of the individual strain gauge circuits. The preferential direction is usually indicated by an arrow etched on one end of the pin. If the pin is mounted in such a way that the strain is applied in a different direction than indicated, the printed circuit foil inside is either ripped off its mounting, or simply tears and breaks continuity. Either way, you end up with a non-functioning load pin.

Load cells are also susceptible to lightning damage. They are mounted to the mast and rigging, which are almost always made of a conductive material. This forms a large antenna on the boat, which can lead to damage to the load pin through induced current by a nearby "splash" strike - the lightning doesn’t even have to directly hit the boat! It’s usually pretty obvious when this happens, as there are a few other things on the boat that stop working as well. However, I have been on at least one boat that had a load pin fail due to lightning, but left everything else intact.

There are also the typical bug-a-boos of electronics: weak connections, bad power, et cetera. If the amplifier isn’t powered, or if wires aren’t connected, chances are that the load pin won’t work.

A load pin can be connected to the Ockam system through a variety of interfaces: the older 066, the newer 067, or the T2 (among others). Read the individual manual sections in these links for some
troubleshooting information specific to the interface; some of these
troubleshooting items are repeated below.

If a load pin is connected to an Ockam system, and it doesn’t seem to work, here are a few things to try:

• Check that the interface is sending data on the expected tag. It is possible to change the data tag on many Ockam load cell interfaces. If the display is set to look at the wrong data tag, then you will not see data. Also check that the data tag is not used by another interface on the system (for instance, a position interface).
• If connected to a T2, check that switch S3 is set to accept load cell data.
• On the T2 and e-Series (square box) interfaces, check that the data input light is blinking as though data is being periodically transmitted. If not, the signal cable or power cable for the amplifier box may be loose or disconnected.
• Check that the amplifier box is configured correctly. The Diverse Yacht Services load pin amplifier (the yachting world’s de facto standard for many years) has two internal rotary switches that need to be configured correctly. Refer to the documentation included with the amplifier for the correct settings.
• Check that the load pin is zeroed. With no tension on the backstay, the forestay load pin should read right around zero. If not, try re-zeroing the amplifier.
• Check the resistance on the unloaded pin. There are five wires from the load pin. One wire is connected to the shield and can be disregarded. The resistance between any two of the remaining wires should be 350 Ohms. The resistance should be the same for all possible pair combinations. If it is significantly different than 350 Ohms, then the pin is damaged and must be sent in for repair.

Beyond this, it can get complicated. Don’t hesitate to contact us if you have a load pin problem on your boat that you can’t resolve.

Comments (0)

For those of you who have raised children, you know how much a wet diaper can irritate a baby’s bottom. Changing the diaper is one of the "baby care triumvirate" when trying to soothe a little one (aside from feeding and nap time). Think of all those times that you have sat on the rail during a race and had a wet bum - it gets pretty uncomfortable after a while.

Likewise, wet electronics are unhappy. Marine electronics are surrounded by water, so it’s especially difficult to keep everything dry, but it’s worth the effort. It’s highly recommended to keep the CPU and interfaces in a sheltered location to prevent any contact with water. Special attention should be paid to the location of the interfaces by the mast. Many boats douse the spinnaker through the forward hatch, so it’s possible to get water on the interfaces if they aren’t sheltered properly. The CPU is usually safely located behind the nav station or in a similar location, so exposure to water isn’t usually a concern. All bus and sensor cables should be routed away from water where possible. This means that cables shouldn’t be run through the bilge (except possibly depth and speed transducers, because there’s not much choice). The displays are typically pretty immune to water, so they aren’t as much of a concern, although they also have some special considerations.

The mounting angle of some displays can cause water to accumulate along the bottom edge of the bezel near the glass. This isn’t a problem in the short term, but water shouldn’t be allowed to stand there for long periods. If you have an older display with a weak gasket seal, you may find yourself with a failed display once the water seeps in and corrodes the electronics.

Another issue that typically crops up in the spring and fall is the presence of condensation or misting inside the unit. This usually happens when there is a small amount of moisture trapped inside the display. The more extreme temperature cycles found in the spring and fall (warm days followed by cold nights) will really show the tiniest amount of trapped moisture. This moisture is easily removed from the Ockam displays. All displays (005, 007, and 044) have a blue plug on the rear of the unit. This plug contains desiccant that removes moisture from the inside of the display. The desiccant does need to be recharged every once in a while, but this can be very easily accomplished.

If there is a lot of condensation, you may also want to remove the display from the boat and bring it indoors. After removing the desiccator plug, place the display on the windowsill with the glass facing out towards the sun. This will help drive the moisture out of the enclosure. Then take the desiccator plug and place it in a WARM, not hot, oven. I find that a toaster oven at the lowest setting works pretty well. Leave the desiccator in the warm oven for 1-2 hours. Let the desiccator cool to room temperature before replacing it in the display, and then put the display back on the boat. DO NOT UNDER ANY CIRCUMSTANCES PUT THE DISPLAY IN AN OVEN - IT WILL MELT!!!

If you are doing this on one display, you might as well do it on as many displays as you can. This way, you know that you have dried out the interior of the display, and recharged the desiccator plug. It’s just one less thing to worry about. You may even consider adding it to your commissioning/decommissioning routine.

Comments (0)

On most mechanical systems, you can tell when something absolutely needs more grease. It starts to squeak and things don’t work as well. You add grease, and everything gets better (most of the time).

Do you need grease on electronics? You bet, especially on marine electronics! Now why would you use grease on electronics?

The major reason to use grease on marine electronics is to protect the connections. Connections are the weakest point of any electronic system. You might have the most robust, bulletproof displays and interfaces, but if the connections are weak, then nothing will ever work for any amount of time. You can usually tell when the connections in a system are weak when nothing seems to work consistently anymore. Since connectors must use metal to conduct electricity, they are susceptible to corrosion - at least until someone invents a practical room-temperature ceramic superconductor!

Another thing to note is that you must use the correct grease. Some grease for mechanical systems has detergent as an additive. This type of grease can cause electrical problems because of the slightly ionic (and thus conductive) nature of detergents, so it is best to use a grease specifically formulated for protective use on electronics; this is called dielectric grease. This type of grease is usually labelled as silicone or Teflon type grease, although is can also be labelled specifically as dielectric grease.

There are three or four places on an Ockam system that could use a dab of grease, depending on the system vintage.

The first place that can use protective grease is at every BNC junction, especially on mast displays and any other displays where the back connector is exposed to salt water. BNC connectors can actually freeze together through corrosion if left alone for years. Usually, I just smear some grease around the female BNC connector first, then connect the male BNC on to it, and then smear some more grease around the whole thing. It usually pays off to make sure that everything is clean and dry before you do this, because whatever is on there tends to stay there once the grease is applied. I prefer using grease rather than self-vulcanizing tape since it’s easier to see what’s under the grease. Tape tends to trap water and salt inside.

Another place to use protective grease is on the external switch contacts on the rear of the Matryx and Magnum displays. These displays have the screw terminals to attach N/O momentary switches to change the displayed data. On mast displays in particular, salt water can wash over the terminals and short them, causing the display to flip through data pages. Lightly coating these terminals with grease helps prevent accidental page switching. I’ve also seen a few displays where spray-on or brush-on waterproofing varnish has been applied. This will work to protect these terminals, but it can be very difficult to remove the varnish later. Grease just wipes off when you need to remove it.

The mast cable for the wind sensor can also use a bit of grease. I usually goop some inside the connector with the pins, and then just squish the two together and wipe off the excess. This is especially helpful at the top of the mast. Realistically, you don’t go up there and clean off the connector after every race, so salt does accumulate up there and cause corrosion if you’re not careful. It’s a pretty nice feeling knowing that the connector is fairly safe up there and that you aren’t going to be sending someone aloft to fiddle with the wind sensor.

The last place that typically can use some protective grease is only found on older Ockam systems. The 015 Boatspeed interface uses a TNC screw-on connector to attach the boatspeed transducer to the interface. Applying a bit of grease here helps prevent the connectors from corroding together, and helps keep any salt water out. Just a little salt water inside this connection can cause the boatspeed reading to be quite far off, as salt water is conductive and will prevent the correct propagation of the boatspeed signal.

Dielectric grease can be obtain through a variety of sources. It can be purchased directly from Ockam, from a marine supply store, or through many industrial supply stores. Just remember when purchasing, that dielectric grease must be used, not just any grease!

Comments (0)

As many of you may have noticed, most laptops (and even desktops!) don’t come with a DB9 connector for RS-232 serial anymore. That’s a problem, since so many pieces of electronic equipment use RS-232 as means of communicating with a computer. USB has pretty much supplanted RS-232 in the PC world, but I doubt it will ever do so in the industrial and wider electronic world due to several design considerations (I’ll leave that discussion for another day).

So how do you get RS-232 data into a computer that doesn’t have an RS-232 port? Currently, the simplest way is to use a USB to RS-232 adapter. These are widely available, but you’ve got to be sure to get a quality adapter for use on a boat. Don’t just pick up any old adapter from Radio Shack and expect it to work - my experience is that they don’t! I’ve assembled a list of adapters that have worked well for me in the past:

Edgeport For several years, Edgeport was the only way to go. Their apaters are mounted in robust housings, the electronics never seem to fail, and the software and drivers provided with the units are excellent. Other companies have caught on to the idea that a USB to RS-232 adapter needs to be well-made, but I’d say that Edgeport is still the best for multi-port adapters.

Sea Level Systems Although tailored towards the industrial end of the market, Sea Level Systems makes an excellent product. I have seen their products used extensively on board some very high-end yachts with stellar results. It’s not as common to find their products on your typical racing boat, but I see no reason not to consider them.

Keyspan If you only need one USB to RS-232 adapter, you can’t beat the USA-19HS for price. It’s the one I use myself. You can usually find these online for a bit less than the list price.

ShipModul The products from ShipModul require a little more effort to install (they use bare wires), but are capable of some pretty neat stuff. They can filter out unwanted data based on port source and destination, and some have Bluetooth connectivity.

Regadless of the type used, you should try to get the software driver for the adapter to always assign the same COM port number to the adapter. This way, you don’t have to reassign the connections each time you use the adapter.

Comments (2)

Every once and a while, I get a Matryx display with a broken lens. It usually happens when someone puts a knee into the glass to brace themselves while pulling on a winch. I’ve even done it. The way I figure, each crew member will only do it once, but it’s still a hassle when it happens. There’s a few options on how to handle it:

• Put the displays where this won’t happen. Depending on the boat, it might not be an option due to limited space.
• Make the crew member(s) in that position aware of what they can do with their knee if they’re not careful.
• Carry a spare Matryx lens to replace a broken one. We will gladly provide one if asked.
• Call Jeff Udell at Custom Offshore about the plexiglass overlay we helped him develop. It’s basically a piece of clear plastic that attaches to the Matryx and covers the glass, but allows access to the buttons.

If the lens does get broken, remember that the unit is no longer waterproof! I’ve received more than a few Matryx displays with unrepairable water damage because nobody took steps to secure the display after it was broken. The simplest thing to do is to cover the glass with tape to keep out the water. You can also remove the display, but this usually leaves a big hole in the boat (unless you’re fortunate enough to have a spare display).

In a lot of cases, the LCD module is fine, but may have a few surface scratches. It’s usually pretty obvious when there’s a problem requiring replacement. When you send the display back in for repair, we take a good look at the LCD and replace it if required.

So, that’s all for now. If anyone has a suggestion on what they would like covered here, email me at dan@ockam.com. I appreciate comments about the blog color, but that doesn’t give me much to write about!

Comments (0)