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Are You At Optimum Trim



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Are You at Optimum Trim Arvel Gentry tells how to make your own Sailboat Performance Recorder By Arvel Gentry SAIL Magazine March 1974 Ocean racing skippers are relying more than ever on wind velocity and direction indicators and a speedthe many different types of marine instruments Wind recorder that continually recorded boatspeedspeed boatspeed and wind direction indicators have Two years ago I wondered if I couldnt use this samebecome almost indispensable on allout racing machines December 1999 approach as I started to equip my own 23 MORC boatnot only for general navigational purposes but to help the Excellent marine sensors and indicators were and crew keep the boat performing at its best But but the most important part of the system the speedanother important and new use for these instruments is to recorder was not I would have to build up my own Thehelp the crew tune a boat and adjust the sails for best results of my efforts are shown in Figure 1 it is a device Iperformance call the Sailboat Performance Recorder However even with all this equipment sailboat Now dont get me wrong Im not trying to is still subject to many variables Wind speed anything You can do just as I did make up your ownand direction sea conditions sail trim the helmsmans recorder using the available components Im about are all constantly changing These describe The cost Only a little more than what you make it very difficult to gather good pay for one of your other marine instruments well data at any instant of time All the needles are a small boat budget After two years of using the moving and an eyeball averaging process is Performance Recorder Im firmly convinced that its thenecessary to get a reading most important piece of equipment on my boat But what Now this is not too bad if you are only interested in is it How is it used And how can you make your ownknowing if you are going about five knots But what if you The Sailboat Performance Recorder is an instrumenthave changed helmsmen and you want to know if the new that records the boatspeed on a continuous strip of paperone is really sailing 110th of a knot better Or youre trying and once every minute it automatically switches to recordto see if a change in sail trim or maybe a sail change is a short record of apparent wind speed It gets its inputwhat is giving you that 110th of a knot instead of perhaps signals from the boats conventional knotmeter and windan increase in wind speed Ocean races are won and lost by speed instruments Other important information such astenths of knots apparent wind angle sail trim conditions sail In the 1970 Americas Cup campaign Bill Ficker faced combinations etc are written by hand right on the strip ofthese same problems on Intrepid Without the use of a pace paper as it goes through the recording window or on theboat as a trial horse he and his crew relied upon careful viewing extension The signal traces on this strip of testing using an onboard paper can then be examined to determine very This consisted of boatspeed indicators apparent the average boat speed and windspeed for the sailing Figure 1 Sailboat Performance Recorder mounted in portable box Figure 2 Typical output from strip can be marked to show when changes in trim took present extension and the paper stayed within the recorder it is This check of the record can be made just after the not so useful in a real sailing are recorded or many hours later when a great At the end of a test day I take the paper from thenumber of records can be evaluated and compared A recorder and study and compose the records If a giventypical output strip from the recorder is shown in Figure 2 change in sail trim between two records gives an is linear and can be read directly from the grid in average boatspeed and the recorded wind speeds havelines However the wind speed is nonlinear because of the not changed significantly then I have found a way ofoutput signal from the Telcor wind instrument that I used making the boat go faster Each test condition is usuallyWind speed is read with a small calibration scale and this repeated several times to verify the actual amount of speedhas turned out to be an advantage because it gives good improvement The same type of procedure is used inaccuracy at the lower wind speeds where you need it testing different sail combinations The Sailboat Performance Recorder consists of a The Sailboat Performance Recorder is also used incommercially available strip recorder control and filter actual racing conditions All sail selection and trim to prepare the boat instrument signals for the are checked before and after they are made by reading therecorder a relay switching circuit to change automatically average boatspeed and wind speed from the strip recorderthe recorded signal and a housing box to protect the This is especially helpful on longer races when there are noinstrument as well as make it portable The recorder I used other boats close by to compare with visually On short daywas a 10 millivolt DC Rustrak recorder which is used in races I leave the strip recorder running during the entiremany nonboating electronic applications The rest of the race It is very interesting to look back on these records andrequired electronics the control filter and switching see if the boat was sailed up to its full potential and to seecircuits are very simple and you can wire them up how much time was lost in bad spinnaker sets etcyourself Or if youre not so inclined you can have your A strip recorder makes it very easy to gather the datalocal marine radio repairman do it for you necessary to construct a complete speed polar for your I use the Sailboat Performance Recorder in boat Such a polar will help in making the proper sessions and in actual races The procedure selection for different wind conditions The recorder is alsoused in the testing sessions is simple and useful in making a direct and accurate comparison of theOnce the boat is stabilized for a given set of sail and boat performance of different helmsmen During very shorttrim conditions the recorder is turned on It then races the cassette magnetic tape recorder can be used records the boatspeed on a continuous strip record supplementary data such as apparent wind anglesof paper Periodic short wind speed records are also made sail trim changes and crew positionsby the automatic switching system The main use of the recorder in all these applications is At the end of the test run I turn the recorder off change to determine accurate average boatspeeds and windthe sail settings and repeat the procedure on the next test speeds over a period of sailing time This is very difficult toOther significant information is written right on the strip do just by looking at the knotmeter and wind speed dialspaper with a pencil and this usually includes the compass Most important of all the strip recorder provides aheading relative wind direction and any sail setting data permanent record for later study under more relaxed nondistance off spreader genoa car position halyard tension sailing conditionsetc Sometimes this information is written on a separate My recording instrument itself is a Model No 2194test log sheet or is recorded on a cassette magnetic recorder Rustrak Recorder range 0 to 10 millivolts with a 12volt DCfor subsequent correlation with the strip recorder wind unregulated drive motor 10 rpm The actual paper chartspeed and boatspeed traces speed is determined by the drive motor rpm and the The strip recorder has a viewing extension so that about gear train selected Rustrak gear train 1510 minutes of the strip record is in view before the paper and the 10rpm motor gives a paper speed of 75 per hourfeeds back into the recorder takeup spool I consider this After trying several different paper speeds this speedan important feature If the recorder did not have this seems to be best for most applications With the 75hr 2paper speed one roll of paper will last 10 hours The other the circuits are all electrolytics and are used to help smoothRustrak item needed is the Model 223 Chart Viewing out and filter the signals to minimize the trace wiggles TheExtension The total cost of the Rustrak recorder and different amounts of filtration and the different is approximately 250 Rustrak Instrument Div of the boatspeed and wind speed traces makes it very easyGulton Industries Manchester New Hampshire 03103 to tell which is which The only other item is the chart paper itself A number Once the input signals are ready for the strip recorderof different recorder chart paper styles are available from you need a means of automatically switching the signalsRustrak I use style WB chart paper which gives a full scale for the recorder is only able to record one signal at a timereading of 75 knots with grid lines at 110 knot intervals The circuit for this is shown in Figure 5 To activate the Once you have the strip recorder and your knotmeter switching circuit I use the flange on the Rustrak recorderand wind speed instruments youll have to build circuits to takeup spool itself I added a small contact point insulatedhook the recorder and instruments together This consists from the recorder frame and that rides on the spool flangeof circuits to finetune the recorded signals so that they The circuit is broken whenever the contact point is lifted bymatch the marine instruments and to dampen the a piece of tape on the flange Splicing tape used forrecorded traces to aid in giving a better average boatspeed magnetic recording tape seems best for thisand wind speed readings The boatspeed circuit is shown The width and number of tapes on the spool flangein Figure 3 The variable resistance at R2 is the control used control how often the switch is made between boatspeedto adjust the recorded signal trace so that it matches exactly and wind speed Two 14 pieces of tape give about 12the knotmeter instrument reading The value of resistor R1 seconds of wind speed every minute The depend upon which knotmeter you use I used a Telcor switching circuit shown in Figure 5 controls the relay thatknotmeter with the R1 value shown in Figure 3 actually switches the signals being sent to the Rustrak The wind speed connection circuit is shown in Figure 4 recorderAgain the Telcor wind speed indicator was used and R3 To drive the recorder and switching relay circuit youhad a fixed value of 33K However with other brands I need a 12volt battery source Normally the recorder canwould recommend that R3 be variable as shown Consult be powered by the boats 12volt battery However withyour own instrument manufacturer for the proper values the Telcor windspeed instrument the Rustrak recorderto use for resistors R1 and R3 in these circuits or calculate had to be driven by a separate 12volt source because of thethem yourself using the equation given in the Rustrak 6volt reference voltage used by Telcor Because of thisowners manual and the desire to make the unit completely portable I These resistors must step the marine instrument included a Rustrak rechargable battery pack model 154Asignals down so as not to exceed the maximum 10 millivolt 12400 though a regular 12volt dry cell can be used just assignal tolerated by the Rustrak recorder The capacitors in well The final task is to build a box to hold and protect the recorder and control circuits from the marine environment I attached a small hatch board to the box so that it could be conveniently positioned in the companionway Since the unit is portable I can take the whole box home after a race to remove the paper and recharge the battery Figure 3 Boatspeed circuit The top of the box is a hinged piece of Plexiglas to keep out spray A manual switch is added at the battery source to turn the recorder on and off I also added a double throw switch so that I could record boatspeed only wind speed only or have the signals switched on automatically Figure 6 shows all the unit components the battery is in the bottom of the box Then the two circuit boxes go in on top and they are followed by the Rustrak recorder The battery and circuit boxes lie underneath the chartviewing Figure 4 Wind speed circuit extension If making your own recorder connecting and switching circuits is too much work for you contact Signet Scientific Company 129 E Tojunga Ave Burbank California 91503 I believe they now are selling strip recorders for use with their instruments at about 500 per single channel device I am told that some of the new large oceanracing boats are ordering as many as four and five of these recorders to record everything from wind speed Figure 5 Switching circuit 3 Figure 6 Detail of Sailboat Performance Recorder heading rudder angle probably even theheartbeat of the helmsman However if you are on a smallboat budget you can make your own Recorder as I did and still have virtually thesame equipment as the big boys 4

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