Designing to Steve Clark's proposed new rules

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Steve Clark
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Post by Steve Clark » Mon Jun 19, 2006 11:01 pm

Oh, Jim, give us more credit for playing around than that! There have been some pretty small dagger boards that stalled quite happily. When the board area gets down around .15 m^2 it gets hard to keep things hooked up. Particularly in a slop, off a starting line or in a pinching pile up at a weather mark. In the open field these small blades might be fine, but when you race you often have to sail 'incorrectly" for periods of time for tactical reasons. Often the places gained and lost in these situations are larger than anything you might gain optimizing according to the theory.
SHC
Beatings will continue until morale improves

Phil Stevenson
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Post by Phil Stevenson » Tue Jun 20, 2006 11:57 am

On the latest subject I believe that excessively small centreboards, like rudders with excess weather helm work at too high an angle of attack to achieve required side force and as a result work in at much higher drag coefficient than appropriate size and balanced foils.

I think a boat just does not feel like its going until the helm is neutral.

This tallies with Steve's assessment that a minimum centreboard size is required. I measured mine and was pleased it is well over the .15m^2 nominated.

On the subject of my new DC there are more photos on my Yahoo site now. With the deck on it now weighs 24kg, so with 5kg mast, 2kg boom, 6kg seat, 4kg for CB and rudder, there should be a fair bit to spare for gloss finish and gear. Big smile!!
Design perfection is achieved, not when there is nothing else to add but when there is nothing else which can be taken away.
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jimc
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Post by jimc » Wed Jun 21, 2006 11:48 am

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Steve Clark</i>Oh, Jim, give us more credit for playing around than that!<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">

You have to forgive us new guys Steve, what I don't know I tend to ask... I've never heard of someone running into the excessively small daggerboard problems other than when I did it myself. It wouldn't be the first time I'd made a mistake everyone else was smart enough to avoid...

Karl Wittnebel
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Post by Karl Wittnebel » Mon Jun 26, 2006 3:48 pm

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Steve Clark</i>
<br />Well, when Oliver broke the shaft in RedShifts rudder, he sailed 4 miles upwind in force 4-5 with the rudder blade stuffed in the slot and sort of held in place with a bungee. Not that this wasn't semi tough and there were more than a few uncalled for tacks and swims.
My current rudder has a root chord of 150 mm and a tip chord of 50 mm and is 850mm deep. Or at least it was, during Sunday it mysteriously became a shallower blade.
The biggest hindrance to making the blades narrow is fitting a shaft that is big enough and not letting the section get too fat. We can go round and round.
But the point is that many ICs are very well balanced and can be sailed hands off for a long time and that the rudders can be and have often been quite high aspect ratio foils. As always the trade offs are personal preference and sometimes driven by how things turn out. For example my rudder is now shallower. I will fair in the new tip instead of building a new blade, I don't expect a big performance change....
SHC

<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
Karl Wittnebel
NC USA 193 (Lust Puppet)

Karl Wittnebel
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Post by Karl Wittnebel » Mon Jun 26, 2006 4:01 pm

Red Shift story proves point: can't get upwind without something generating lift in the stern, bungified or whatever.

Tall rudders work, but are less practical, particularly down here in the Chesapeake with our shallow water. Just depends what you want to put up with in terms of launch/recovery procedures.
Karl Wittnebel
NC USA 193 (Lust Puppet)

Oliver Moore
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Post by Oliver Moore » Tue Jun 27, 2006 3:59 am

Definitly did 4 or 5 circles added to swimming with nothing in the back before I realized that it wasn't going to work like that. But I was fully ramped upon the end of the seat steering with heel alone, pretty damn cool.

Well my 15 minutes are up, time to go spray another coat on the acat.

Phil Stevenson
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Post by Phil Stevenson » Tue Jun 27, 2006 4:46 am

In moderate 5-8kt winds I can sail my moth with the rudder in place but with the tiller extension thrown over the back. By using heal it is possible to tack and gybe almost at will as well as sail pretty any course except square. This is with the rudder free swinging from normal gudeons/pivot forward of the leading edge. In this case it can not be taking any lateral load nor can it be providing any longitudinal stability (airplane tail effect) to the centreboard, but maybe the deep narrow hull is helping a lot in both counts.

After a breakage, I also tried sailing it with no rudder at all in 25kts and that was impossible.

Obviously Olivers blade mounted neutral, provided him with just the same stability, but as it was centralised it would not necessarily have been contributing greatly to lateral resistance.

My DC is narrow up front like a moth but flat at the back like an IC so I think the rudder will be needed for stability but hope it will not be contributing to lateral resistance which would result in weight on the tiller.
Design perfection is achieved, not when there is nothing else to add but when there is nothing else which can be taken away.
http://philscanoes.blogspot.com/

jimc
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Post by jimc » Tue Jun 27, 2006 7:33 am

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Phil Stevenson</i>
Olivers blade mounted neutral ... as it was centralised it would not necessarily have been contributing greatly to lateral resistance<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">

Feel free to correct me, but it seems to me that if the rudder is bang on the centreline it must be operating at the same angle of attack as the daggerboard and thu creating sideforce. For it to be completely neutral wouldn't the tiller be pointing very slightly to leeward to match the leeway angle of the boat? Whether its possible to observe such fine distinctions from the end of the sliing seat is another matter (unless like Oliver you can't move the rudder). I don't think I could.

Karl Wittnebel
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Post by Karl Wittnebel » Tue Jun 27, 2006 5:41 pm

All I know is that when you are hooning along upwind and the rudder breaks off you don't go straight anymore. Lots of ICs are set up with neutral rudder post position so you can pretty much let go of the tiller on the fly, but the thing is still surprisingly loaded up. I was off the end of the seat on LP, going in a straight line, when the very hokey rudder made by previous owner broke off at the post, so it must have been reasonably loaded; instant dunk, round up and capsize. And capsize. And capsize...

Same thing happened to me at Worlds on Bill's boat, because the carbon on the post had not infused completely and it just sheared off. Stern goes sideways and you go from end of the seat to swimming to boat on top of you.
Karl Wittnebel
NC USA 193 (Lust Puppet)

Phil Stevenson
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Post by Phil Stevenson » Sun Jul 30, 2006 8:31 am

I launched my beast yesterday.

Sailed initially in maybe 12kts which faded to a total drift after an hour or so. Very hard to say how it goes when you are in a mixed fleet in those conditions, but both with pressure and without, I did sail away upwind from the contender as would be expected.

I could not expect to stay with the 49ers, 18s, As, T, and F18s, but did spend about an hour and a half going downwind in company with a 49er, Hobie Tiger and Capricorm, because they had to sail such high angles to keep the kites full, and I probably had a lot less wetted surface.

So the hull does seem slipery enough, and as everyone expected including me, it will take a while for an old moth sailor to learn how to tack and gybe it while moving the seat across. Fortunately it was a warmish winters day and I did not get too wet and cold.'

There was no breakage or damage, but the unstayed mast seems slightly softer than needed as in the biggest gusts I only needed to get to the feet to gunwale position, maybe only 75% potential righting moment. I have a stiffer mid mast section on order.

Sorry no photographers on hand that I know of.
Design perfection is achieved, not when there is nothing else to add but when there is nothing else which can be taken away.
http://philscanoes.blogspot.com/

jimc
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Post by jimc » Sun Jul 30, 2006 8:27 pm

Good one Phil. That all sounds very promising, especially to someone who hasn't worked out how to stop an RS600 coming past his Nethercott downwind in f3 and less...

Paul Scott
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Post by Paul Scott » Tue Aug 01, 2006 11:02 pm

Sounds really promising, Phil
"Exuberance is better than good taste" -Flaubert

Steve Clark
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Post by Steve Clark » Wed Aug 02, 2006 9:15 pm

Good news Phil.
Look forward to more info as you develop the boat.
How did you end up on weight?
My concern about the Skate style seat is that it may be hard to manage because it can swim around so much. I think I am pretty used to having a fairly rigid connection so that thje seat can act as an outrigger if things get messy. Time will tell.
Nice work.
SHC
Beatings will continue until morale improves

Phil Stevenson
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Post by Phil Stevenson » Wed Aug 02, 2006 10:44 pm

Steve,
I am really pleased with my boat so far. It was a delight to sail but I see a challenge in learning to handle the sliding seat, and boat handling in general as it gets windier. But I think that must have always been part of IC sailing.

I have not weighed it since it has been finished. I know the hull gained weight in rails, deckskin, finish coats and a few fittings since I last checked. It was 24 then so I think it should not have gone over 30kg. The seat is 7kg which is a bit more than I expected because I used too much glass, and once I stiffen the mast it will be more like 6kg. I think the boom is 2, fin 1.5 and rudder 2.5 which all adds up to 49. I will check everthing on the weekend and get a final tally.


WRT the skate seat. I agree with you fully with the potential for it to slew. This makes it tricky sometimes to get it across swiftly and I think I have to address this problem. Maybe the skates use shorter rails, but mine are long because I did not know where I would need to put my weight on the new boat and I wanted to be able to trim it properly.

I did some bad tacks because I could not slide the seat swiftly. I will initially try some relocatable stoppers to try some fixed locations and then see just how much fore and aft movement is needed. In the variable breeze last week I did not move it fore and aft at all and found when I was most powered up on a beam reach the bow was lifting rather than being driven down. But I know things will be different when it is really blowing.

In the end I may need to make some form of carriage just to keep the seat square to the boat. I have installed the rails parrallel so that the carriage/guide/square can run under them, while the rails still take the loads. So hopefully that 49kg is generous.

The freeboard and spring seem about right, it leaves a very clean wake, passes waves easilly and has almost no bow wave.

It ended up about 860mm width at the deck, while still 750 at the chines. It will float upright by itself and I had no problems getting on board. It certainly was a lot nicer and less strenuous to sail downwind in sub 5kts than my moth. But it feels a lot like the moth in the way it heals and accellerates to the slightest increase in breeze. But unlike the moth, without the leeward wing, excess heal does not put the brakes on.

Design wise there was a fair bit of cut and shove during construction but none the less I have a pretty good record of the final ply shapes and how it went together, I am putting all this in a spreadsheet so anyone with the inclination and skills can make a similar boat. When I get it tidied up I will send it to Christian for the Aus IC web site. No hurry yet, obviously one day's sailing is nothing and there is a lot more yet to test, prove, develop or ammend.

Thanks everyone for your interest. Thanks to the IC class for providing the oportunity to make one of my fantacy designs. (I thought a long moth would be awesome as a big person's singlehander but have a hatred of people starting new classes)

Phil S
Design perfection is achieved, not when there is nothing else to add but when there is nothing else which can be taken away.
http://philscanoes.blogspot.com/

Paul Scott
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Post by Paul Scott » Fri Aug 04, 2006 1:55 am

A few questions-

1) If the seat does not slide, that is it extends out 2040mm on both sides, does it still have to weigh in at 12Kg?

2) Is it legal for leeboards to slide or pivot through the seat?

3) Is it OK to have the leeboards outside of the 1100mm max beam? Or,

4) Are leeboards considered part of the hull?

5) If leeboards are angled out, do the tips have to be within the 1100mm max beam when the hull is at rest?

Hey Phil- interest is easy- this is cool stuff.

Paul

"All inquiries carry within them some element of risk." -Carl Sagan, 'Broca's Brain: Reflections on the Romance of Science'
"Exuberance is better than good taste" -Flaubert

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