The Bench

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.

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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.

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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.

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Here’s a term that is bandied about in sailing, but is commonly misunderstood: upwash. Many people think they understand what it is, but are wrong by 90 degrees. What do I mean by that?

Most people hear the term upwash and take it for face value. It is the motion (or wash) of a fluid over something; in effect, the opposite of downwash. In the case of sails, the fluid in question is air. However, the misconception lies in what people assume to be "up" in relation to the wash direction. People assume that upwash refers to the motion of air up and over the top of the mast as the boat moves through the air (or the air moves around the boat). While this does occur, it is not what the term "upwash" is referencing. If we are to be pedantic, this motion of air up and over is termed axial flow (amongst many terms used).

So what actually is upwash? Let’s explore where the term comes from, and that should provide an insight into what it actually is.

As most people may know, sails on a modern boat form an airfoil shape, like those found on heavier-than-air aircraft. This realization didn’t come until the science of aerodynamics had been well-established to service the aircraft industry. Airfoil shape strongly determines an aircraft’s performance, so the flow of air around the airfoil has been very extensively studied. Air primarily moves in two directions around an airfoil: under and over. The difference in air speed between the two paths results in the Bernoulli effect, which is the conventional source of lift.

The portion of the air that travels over the top of the airfoil is called upwash. Airfoils are typically oriented so that one surface faces down and one faces up, so it’s natural to reference the flow of air according to this. When we apply the science of aerodynamics to sails, we are presented with a small problem: the frame of reference is rotated 90 degrees. What was once "up" is now to the side - in the case of sails, to leeward. So instead of flowing up and over the sail, the air is flowing to the leeward side and around.

Czesław Marchaj wrote a seminal book in the mid-1960’s titled "Sailing Theory and Practice." In it, he applied many of the principles he had learned as an aeronautical engineer to the design of sailing yachts and sails. He established the convention of calling the leeward flow of air around the sail "upwash", as a convenient way of marrying the worlds of aeronautical and nautical design. Since many boat and sail designers studied his work, upwash kept Marchaj’s frame of reference.

On the Ockam system, the upwash calibration allows the user to remove the effect of the sail plan and rig on the apparent wind angle. Since the air is forced around the sail, the apparent angle bends as it travels around the sail. Since the wind angle sensor is embedded in this distorted flow, it is necessary to remove this distortion to properly figure the true wind solution. The additional calibration of upwash slope allows the value of the upwash calibration to change with wind speed. The effect of upwash is lessened at higher wind speeds as the air travels closer to the sail before turning. This requires that the base upwash calibration is de-rated which is what upwash slope does.

The ability to correct for the effects of upwash haven’t been commonly found on sailing instrument systems, so it is not a term that is commonly understood by the sailing community. It is a term that is worthwhile to understand however, since it so strongly affects the way a boat sails.

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Wind shear… it’s that mysterious quality of the wind that can make or break your strategy in a race. Many people refuse to believe in the existence of wind shear, never mind its effects on sail trim. Much has been written on wind shear, especially here at Ockam. We have a web page devoted to discussing wind shear and gradient.

It is a very real phenomenon that can be seen in sail trim (especially jib cars) and the wind information from an Ockam system. Many other instrument systems cannot reliably display the angle offsets that provide clues as to the presence of wind shear due the the method of calculating the wind solution, so many people refuse to believe its existence. The moment of epiphany for the Ockam system’s ability to detect shear came back when the America’s Cup was still in Newport, and it was a Block Island Race Week year. One syndicate was using SODAR to image the wind field prior to the warning signal. They also had the Ockam system installed. Several boats racing at Block Island (13 miles south of the Rhode Island coast) also had Ockam instruments. The boats with Ockam systems were seeing absurd tack-to-tack differences in wind angles, and the users were declaring them "useless pieces of junk." However, the SODAR was imaging vertical wind shear at the same time. It dawned upon the shore crew analyzing the data that the tack-to-tack differences in wind angles were due to the effects of wind shear! After a little more examination of the data over many sailing days, it was determined to be a real effect. The crews who were able to recognize the existence of vertical wind shear went on to gain a tremendous advantage in racing.

Short of using a SODAR, how can the ordinary person see wind shear? One of our customers has come up with a simple but ingenious device to demonstrate the absence or presence of vertical wind shear. He calls it the "Shear-O-meter", and a short write-up can be found as a PDF on our web site. It requires hauling a line up the mast without sails present, so it is most useful just before the race.

During a race, it’s not practical to drop sails to check for shear. Also, some boats leave the harbor with the main already up to reduce problems out on the water. So how can these people check for shear? Shear can be discovered while sailing, but there is a simpler way. There is an atmospheric mirage phenomenon called Fata Morgana. The conditions that produce Fata Morgana are also ideal for producing vertical wind shear! Chances are, if you can see a Fata Morgana mirage, then there will be vertical wind shear. The conditions that form a superior mirage also tend to produce shear, although it may not be as pronounced. An inferior mirage indicates conditons opposite those that tend to produce vertical shear, but they are rarely seen over water. The absence of these optical phenomena does not indicate the absence of vertical wind shear. Their presence indicates the presence of the atmospheric structure that strongly promotes vertical wind shear - stratified surface layers with laminar flow.

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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.

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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.

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Many people are familiar with weather reports through a variety of media. We all supplement our day-to-day weather awareness with forecasts from the newspaper and TV news. The Internet has become a very popular way to get sailing weather, as it delivers the right information at the right time. And as always, The Weather Channel and NOAA Weather Radio are big favorites with sailors. But how many people get weather information through the phone? Not many, I would venture. However, this is a fast and easy way to raise your weather awareness while out on the water, simply using any cell phone. While you can frequently get detailed weather data using wireless web browsing, it’s not always available due to limited time, limited hardware, or poor signal strength. The information here applies to the United States, although many other countries have similar systems in place for public weather information.

One way of obtaining current weather information is through the FAA/NWS METAR network. Almost every airport in the United States has an automated weather station now (called either ASOS or AWOS). Every airport that has an automated station also has a voice line to call for automated weather information. In highly populated areas, such as Long Island Sound, there are many airports near the usual sailing areas, so it’s easy to get a good mental picture of the weather conditions over a wide area. You may be able to see things like the sea breeze filling in, or an expected wind change starting to work through the area. There are a few important limitations to note when using the METAR reports. First, the observations are only reported once an hour some time in the ten minutes preceding the top of the hour. Second, airports are infrequently sited directly on the water, so there is typically some difference from the airport observations and conditions on the water. Third, these observations are from automated weather stations that are following reporting algorithms created for aviation, so they may not tell you exactly what you’re accustomed to hearing.

Another method of getting weather information by telephone is through the NOAA National Data Buoy Center Dial-A-Buoy program. This automated information line gives you the current conditions from the network of oceanographic data buoys maintained by NOAA NDBC. It can also provide the current NWS marine forecast for that location. Location is selected by one of two methods: you either need to know the buoy ID, or the approximate latitude and longitude in degrees and minutes. The buoy ID number can be found by clicking on the map on the front page of the NOAA NDBC; there are instructions on the Dial-A-Buoy page to enter buoy IDs with letters. It may be handy to have a small list of local buoys when calling the Dial-A-Buoy line. Otherwise, entering the lat/lon may not give you the buoy you wanted. The major drawback to getting data from the NDBC is the poor spatial resolution. There are not many data buoys out there, so the one closest to you may be some distance away. However, they are frequently located away from land, so you will see less of any land effect than if you check the airports. You also get sea state information from many of the buoys.

A third method of getting information is through the PORTS network. The PORTS network is limited to only 15 areas right now, but these areas also happen to have a lot of sailing activity. Some areas only have a few stations, but most have several. The availability of information varies by PORTS station; the web site details what is reported from each station. In addition to meteorological data, water data is also reported for most stations.

This list is by no means comprehensive. There are many automated information systems available for call-in access. The outlets listed here are a good start, and cover a large area of the United States. While checking out the web links here, click around to see what other weather and oceanographic resources are provided by the US government - maybe you can find something interesting!

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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.

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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.

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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!

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Key West Race Week 2008 is rapidly approaching. Unfortunately, I will not be in attendance, but Alan McGlashan (our new VP of Sales), and several dealers will be there. Paul Roell and Jeff Udell will be available to assist boats encountering problems with electronics in Key West; their contact details can be found on our dealers page in the main web site. We will be here as always to assist with technical advice, quick-turn repairs, and loaner units to replace broken items.

Here’s some tips to get the most out of your instruments during a race:

• During the pre-start, you can set the stopwatch to run when the previous class starts. Just add five minutes for each class before you. This way, the stopwatch is running when it’s your start, so if there’s a slight panic on your boat when the gun goes off, you don’t miss the RC signal. The reset function of the stopwatch will synchronize the stopwatch to the nearest minute when it’s running so you can match up with the race commitee if you’re off by a few seconds.
• When going upwind, it’s pretty useful for the helmsman to have Apparent Wind Angle and Boatspeed visible. Other functions are useful to the tactician/navigator, but the helmsman should use apparent wind to get the boat in the groove (since that’s what drives sail lift), and boatspeed to see how each course adjustment affects the overall speed. Polar data is also useful, but those that concentrate on polars exclusively tend to burn themselves on VMG to the mark. See the Ockam U manual for the full discussion of VMG sailing.
• When going downwind, watching boatspeed is (of course) essential. True Wind Angle is more important than Apparent Wind Angle to watch downwind, as it gives a clearer picture of the boat’s relationship to the wind. I find that a peek at Wind Direction (geo-referenced true wind) is handy at least 10 boat lengths before the mark rounding so you can plan your exit angle and set up gear accordingly. It also gives you a chance to see if there’s been a persistent wind shift since the last rounding. Nothing stinks worse than getting stuck on the wrong side of the course because you didn’t bother to check what the wind’s doing!
• Let the helmsman set what he (or she) needs on the mast displays. It’s hard for the helmsman to successfully steer and look down at a display, so letting him have priority on determining the mast display data is key. Everyone else can spare the time and attention to look down at a display to get the data they need.
• The helmsman shouldn’t be the one worrying about what the instruments are doing. If there’s a problem, assign someone else to handle it! There’s nothing worse than a distracted helmsman trying to tell someone what to do - the boat goes all over the place, and that’s not fast!

There’s plenty more I can say, but most of it is covered in the Ockam U Manual, which explains it far better than I could here. To those of you going to Key West: Good Luck!

Dan

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