Rudder Question

[Doug Lord]

Originally Posted by CutOnce

At under 12 feet, hull speed is about 5 knots, regardless of how much power is developed. A short dinghy like this is going to be stuck in it's own waves, and will probably never be able to climb out of the trough and plane.

Sure, the Laser blade could work, but it certainly would not be as positive a control as the larger barn door - because it will never get the laminar flow necessary to develop superior lift. Huh?!

The cool part about having a working headstock that fits the boat is that BobBill can tweak the larger rudder's size down a little at a time to optimize the feel and performance.

Dinghies, unlike keelboats are really sensitive to the lateral area provided by rudders - and it's location in terms of overall CLR. Balanced rudders with a portion of the area in front of the pintle/gudgeon axis may change the overall CLR enough to affect handling - worsening actual weather helm, but desensitizing the effect from the person holding the tiller. Although you may not "feel" the weather helm, you will have more turbulence developed - and hence slower speed.

All the reasons for balance rudders are good - but only if they don't create other problems. Whatever you end up with should be considered in terms of the original design and real world testing. A tiller that "feels" better but causes a drop in speed isn't worthwhile.

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CutOnce

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That is waaaay too much rudder area for that boat! Looking forward to hearing BB's experience with the white rudder. If it is a Laser rudder it should work fine-Kite SA is slightly less than a Laser. Worse case scenario it might need slightly more area but the Laser aspect ratio appears ideal.


Kite with two aboard ,planing:
click on image-

[BobBill]

Sorry. I made this confusing.

Doug, the unfinished rudder on left has not been shaped...the Laser II (white) would work, but it would be a bad choice. The new kick up will be somewhere in between.

As CO observed, we do not want to go slower, just have a kickup, but if we can make a tweak to pick up some agility or half a knot, why not...?

We are all on the same tack...

CutOnce, that little boat is a fooler. It will creep up on a Laser in equal pressure. It planes in about 10 knots of pressure and does it actually too easily for my old bones. But, unlike Laser, one can flop around all stretched out on a balmy summer day, with a case of brew.

Imagine a shorten Finn...with far fewer strings etc. That is with stretched old 73 sail. I have new sail and spar set that is a few square feet greater, but too much for real windy sailing.

You can look up its rating, if that means anything.

[Doug Lord]

Originally Posted by BobBill

Sorry. I made this confusing.

Doug, the unfinished rudder on left has not been shaped...the Laser II (white) would work, but it would be a bad choice. The new kick up will be somewhere in between.

As CO observed, we do not want to go slower, just have a kickup, but if we can make a tweak to pick up some agility or half a knot, why not...?

We are all on the same tack...

CutOnce, that little boat is a fooler. It will creep up on a Laser in equal pressure. It planes in about 15 knots of pressure and does it actually too easily for my old bones.

Imagine a shorten Finn...with far fewer strings etc.

You can look up its rating, if that means anything.

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Just out of curiosity: why would the white rudder be a bad choice-is it not a kick up rudder? UPDATE: I clicked on the picture and it looks like it is a kickup-no lead ,though. Even so, it looks like it should work-have you tried it?

[BobBill]

Doug, the Laser is too small area-wise. Hangs higher than it looks.

Would have to r&r gudgeons to try out and that precludes using barn door in meantime. Too much BS.

The Laser rudder head has pintles set closer together.

[Doug Lord]

Originally Posted by BobBill

Doug, the Laser is too small area-wise. Hangs higher than it looks.

Would have to r&r gudgeons to try out and that precludes using barn door in meantime. Too much BS.

The Laser rudder head has pintles set closer together.

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BB, you know that one of the advantages of moderate aspect ratio like the Laser rudder is that it can produce the same lift or more than the original kite
rudder with less area, right? That is the advantage of a shape like that as compared to the original rudder: same or more force with less area resulting in less wetted surface and less total drag assuming a well designed section. I would use a rudder with the same underwater area and planform as the white rudder-no more. You should at least try it since you have it- if you can modify it to work at the rudder head.

[BobBill]

Doug, I will do as you suggest. When I reposition the gudgeons, I will use the blade first and if it is satisfactory, but I think it will be a bit short, and that is where the new one can be custom whittled to do the task of both.

Boat is in storage now, the leaves beckon as winter looms in Minnesota, to my dismay.

Will post the results late spring.

[bruceb]

Way too many years ago I sailed a season in a Penguin class dingy, a hard chine design, but quite similar in concept to the Kite. The Penguin was also a very capable boat- this was before the Laser was even a dream so I have no direct comparison, but very good for a 12' boat. Its rudder also had to be somewhat "oversize", both to overcome the balance issues of a long boom, and the lifting at the transom both from heeling and quite a bit of rocker. Sculling is also more effective with a broader blade B