TO ALL UNIRIG SAIlORS and friends,
<br>1. I did the final test today, brought along another driver, so we could compare notes( Tom has a I-20)
<br>2. Put new standing rigging on I-17(..from Murrys Marine,..note*front bridles came 1/2 inch longer than factory rigging*)
<br>3. Rake..Set front plate at hole #2 from TOP
<br>4. Mast speaders @ 3.5 inches ,..tight ( prebend)
<br>5. Mast rotation @ 20% (...pointing @ hull to crossbeam intersection)
<br>6. Set boards @ 12 inches UP on run #1,...full DOWN in run #2
<br>7. Wind @12,..waves small 1 foot,...driver #1 @ 230 lbs,...rider # 2 @ 180 lbs.]
<br>8. downhaul just to make sail tight ( 3 inches)
<br>9. outhaul released 1 inch
<br>10. traveller set at 4 inches
<br>RESULTS
<br>BOARD UP 12 inches
<br>DRIVER # 1 and DRIVER # 2 same report.
<br>- boat handles great
<br>- took puff...rose hull...stayed @ 1-2 foot above water,....needed NO adjustment,..did not touch msheet, traveller or dhaul
<br>- speed,...excellant in all conditions
<br>- neutral helm w a touch of weather
<br>- tacked well
<br>
<br>TEST # 2....Board down full
<br>
<br>Both drivers reported the same
<br>- slow
<br>- boat out of balance
<br>- raised hull fast and irractic
<br>- a general bad ride in all condiitons
<br>
<br>OK,..thanks to all. i could not have done it without everyone. I am thankful
<br>
<br>NExt,...downwind Wild Thing
<br>
<br>regards,
<br>Bruce
<br>St. Croix<br><br>

Wouter<br><br>

Peace brother
<br>regards,
<br>Bruce<br><br>

Bruce,
<br>
<br>I wish you the greatest of success with the boat.
<br>
<br> We just got a second I17R in our fleet as of today. I am looking forward to it's arrival this Friday.
<br>
<br>What you saw was the " tripping over the boards " that I have come to also see. It also never seems to be the same twice.
<br>
<br>Do you have the chute for the boat?
<br>
<br>As to Wouters comment ... have you ever thought about counciling? It might help!
<br>
<br>Bruce, keep sailing !
<br>
<br>
<br>
<br><br><br>CR, Inter 17R USA 107

Bruce,
<br>Just as an interesting side issue.
<br>Jim Boyer on several occassions pointed out his concern regarding the possibility of tripping over long boards. (For this reason his boats don't have long boards by modern standards)
<br>
<br>I was about to experiment by making a set of longer boards
<br>for my Taipan. Maybe you've just save me a whole lot of trouble.
<br>Thanks.
<br>Phill<br><br>

On the other hand I-17 board are huge compared to taipans. Thruth might be somewhere in the middle. And bear in mind that Board of I-17 were designed for the I-18 and copied to the I-17 to save costs. I-17 board at 70 % length which still is about 0,7 mtr. which is more than Taipan full down. BTW I'm not saying that Taipan board aren't at their optimimum, I just look at A-cats (Auscats ?) and some other optimized boats like Stealth and see that Taipan went a totally different direction and wonder which of the two is best.
<br>
<br>I can imagine that rather high aspect (which is not always the same as long !!! ) is better but that I-17 had to much total area for the boat and that Taipan's ratio area to aspect ration is better. Maybe Auscat ratio is even better still. ?
<br>
<br>Wouter<br><br>

Chris, Wouter Phill and others,
<br>I NEVER thought that the boards would be that big a factor. I was wrong. Oh, I have sailed the boat well with them full down,...but, man, what a difference.
<br>Once you think about it,...the I17, I18, I20,...each are such different designs in respect to one another,.......how can they have the same underwater foils?????,.....I wonder now at the reasoning by PErformance Catamaran,....it would be nice to hear there point of view.
<br>Phill, exactly,..I am thinking about building a set of boards at the correct lenght now,...save some weight too!
<br>Like I said,...on to WIld Thing now,....no, Chris,...no chute yet,...???
<br>regardss,
<br>Bruce<br><br>

Wouter,
<br>The Auscat and Taipan Boards may look very different.
<br>You probably already know that there is some scope for variation under the class rules but the A &T boards made by AHPC that I've measured (unfortunately I don't have the figures with me but)shows there's really not much in it. The Auscat is something like two inches narrower and 2 inches longer.
<br>
<br>Phill<br><br>

He guys, your logged on too ! I just attented a stupid meeting where no-one seemed to be able to think.
<br>
<br>Phill, 2 inches smaller = 50 mm on a board that is at 230mm wide. This comes out at 22 %
<br>
<br>2 inches longer at 630 mm max length comes out at 8 %.
<br>
<br>Ratio in aspect ratios is (630/230) / (680/ 180) = 2,74 / 3,78 = 73% or Taipan board ratio to Auscat ratio = 73 %. A few inches here and there can make a big difference !
<br>
<br>Surface area ratio 0,1449 / 0,1224 = 118 %
<br>
<br>I wonder what exactly causes the Board tripping feeling ? Do you have any suggestions ? Is it the board area or the steaper efficiency graph ?
<br>
<br>Wouter
<br><br><br>

Wouter,
<br>My personal view .for what it's worth. Length times thickness as opposed to wetted surface. But it is very possible that I'm wrong as I've never really analysed the situation.
<br>Most Taipan sailors leave their boards down on all points of sail. They say they can get away with this because they are so thin (ie depth of chord not length of chord).and the drag is so low that its not worth pulling them up even when they have to sail flat.
<br><br><br>

Well, maybe we should redefine the situation :
<br>
<br>Which board performs better when the total wetted surface area and thickness remain the same :
<br>
<br>Personally I don't know either, just as you Phill, but it is an interesting (side) issue. It caught my interest when I reread the our earlier comments with respect to board size change of the Stealth. Their was something funny there that I couldn't explain right away. I must also admit that I haven't been able to give it much thought due to my other time consumming activities, but it pops up from time to time and facinates me.
<br>
<br>Ofcourse with brobu I took the simple approach and calculated the ratio of the boards area with respect to the righting moment ratio and it obviously was found to have strong relations to the real behaviour of the boards and overal boat performance. This maybe a point to remember. Really facinating.
<br>
<br>Stealth old ***** width = 0,122 wetted length = 0,450 area = 0,0549 aspect = 3,69
<br>Stealth R (new) width = 0,188 wetted length = 0,750 area = 0,141 aspect= 3,99
<br>
<br>I propose three important stages :
<br>
<br>* Low speed where maybe overall area is important and lift characteristics realatively unimportant. Actually I suspect that both a rather unimportant here because of the low ratios between thrust and heelingforces due to the low speeds.
<br>* Medium speed around just lifting a hull where a transition characteristic can be expected and lift is most importent
<br>* High speed where lift characteristic is important, length and aspect ratio but where area is of secondary importance. MInd you importance of length and aspect ratio can go both ways !!! Bear in mind the extremely small boards c.q. fins that the surfboards use
<br>
<br>What do you think ?
<br>
<br>Taipan 4.9 boards :
<br>
<br>width 0,230 length 0,63 , area = 0,1449, aspect ratio = 2,7391
<br>
<br>Looks like Taipan has the same surface area but at a much lower aspect ratio. Now the Two boats being almost equal under F16 HP rule will make a performance comparison between them rather accurate !
<br>
<br>Wouter
<br>
<br><br><br>

Is it possible that with the full length down the boards are not stiff enough and are deflecting or twisting?<br><br>Keith Chapman, Annapolis, Md.
<br>H-18
<br>Northstar 500 (monoslug)
<br>WRCRA - www.wrcra.org

Board Thinkers,
<br>Here is some data,....in the St. Croix Internatoinal, the I-20's were pulling there boards UP in the 25+mph winds! The ones that did,..were passing the ones that did not (UPWIND)!
<br>
<br>Down here, the I-20's have a habit of snapping the boards in half,...I do not know if it is because of the speed ( ie -force) generated downwind ( speed 20+knots) or what,...but they do snap those boards...Comment?
<br>Bruce<br><br>

First of all; Boards were designed for the I-18 and it could well be that the I-20 puts more load on the boards. On the other hand I believe that this is not the case for the overall width of the boat is equal to the I-18 and therefor they are both equally limited in righting moment and thus in maximum sailforce. That unless you sail the boats 3-up which is sometimes done in heavy air here. (Not in races though !)
<br>
<br>I think they did it for the same reason as you did it, they've must have felt the tripping effect and I also believe that long boards are not needed at high speeds and only create more drag.
<br>
<br>Visulize it like this. An aircraft wing (foil) has one optimal set of working conditions when it is not fitted with extras like flaps and slats. Going slower means not having enough lift from the wing so the angle of attack needs to be increased drasticall = drag. At higher speeds the wing produces to much lift, so angle of attacked must be decreased making the ratio lift /drag a bad one. On wings they use flaps and sorts to alter the lift characteristics of the wing and adjust it to different speeds. You can 't do that with boards. You can however change the total surface area by pulling the boards up or pushing them down.
<br>
<br>In effect what your doing is adjusting the surface area in such a way that the optimal angle of attack is needed in order to get the lift you need. A board at a optimal angle of attack will nearly always produce the smallest overall drag.
<br>
<br>Ofcourse the lift characteristic is dependend on velocity squared so there are big differences to be found at even small speed differences.
<br>
<br>I'm still working out of more accurate model of the boards but I assume that this goes some way in explaining why they reduce board area in higher winds.
<br>
<br>BTW, most sailors assume that more board in the water is always better. This is understandable but errornous. Lift and drag characteristics are similr to parabolic graphs they have an optimal workingpoint and drop of on both sides. Adjusting the boards is a must. Often asked question why don't the Tornado guys do it ? THis is because they have centrebaords and an centreboard that is partly "pulled" up leaves a gap in casing and this is more draggier than leaving the boards down.
<br>
<br>Pulling boards up or fitting smaller boards in common in dinghy and skiff classes.
<br>
<br>Wouter
<br>
<br><br><br>

Comment on 50% of the I 20's down here breaking the centerboards??
<br>
<br>Bruce
<br>
<br>St. Croix<br><br>

About how many boats are we talking here I mean 50 % of only two boads can still be a one -off accident.
<br>
<br>Wouter<br><br>

I think you will find most people around here are pulling thier boards up around 1/2 way going downwind on the Inters. This seems to eliminate snaping boards. I only run my N 6.0 boards down 3/4 of the way in winds over 20 knots.
<br>Eric<br><br>

On the I17R I only run the boads so approx. 6" is showing below the hull. Works fine.<br><br>CR, Inter 17R USA 107

I sailed my I20 with 3 crew (600 lbs) in 20 - 30 kts during a storm in March in San Diego Bay. We kept the boards down the whole time, upwind, reaching, and downwind, hitting 25 kts at times downwind with the spinnaker. We had absolutely no problems steering (or anything else).<br><br>While I agree it might be a slightly less drag to partially raise them on a long downwind or reaching leg, I have not found any steering- or handling-related reason to do so. <br><br>Alan Thompson<br>I20 - San Diego<br>http://www.whitecaps.net<br><br>P.S. I have never heard of anyone breaking a board, except during the Worrell 1000<br><br>

Board stuff...
<br>
<br>I've broken 2, I think John 1, and Terry one. Plus Simon from St. Marrten broke one in Rolex. That sound like a good spread?
<br>
<br>Mongo
<br>Team Ocean Spray VI
<br>
<br>