rudder size

[Gary Baigent]

Paddy, in this day and age of rapid net communication throughout the world, patents are a waste of time ... because someone, somewhere, for sure has already thought of "your" invention/solution. I'm doing the finishing touches on a book on Jim Young, iconoclastic designer from Auckland - and he has a very inventive mind, way outside the proverbial box - and he patented a few of his innovative ideas but gave up because of the hassle involved in chasing copy cats down. And this was before the net.
For sure, again, rudder/boards/foils is an area worth communicating over because it is a wide open subject. My thoughts are to check out nature, fish and sea mammal fins and tails.

[bruceb]

I think checking out mermaid's tails would be particularly interesting- but we are fresh out of them here in the US with global warming and all. Got any down there? B

[rayaldridge]

Originally Posted by oldsailor7

Over the 55 years of modern multihull development, there has emerged a basic rule of thumb for efficient leeway reduction. It is round bottom hulls...

I'd agree with everything else you say, but this doesn't seem to be correct, in that the most recent America's Cup winner (and loser) did not seem to have round bottom hulls.



Since windward ability is so critical in match racing, I would assume that there's some reason the designers have moved away from the lowest possible wetted-surface hulls.

[Doug Lord]

One thing discovered in the Moth class just prior to foils flying the whole boat was that a higher L/B ratio(skinnier hull) trumped a lowest wetted surface hull.
There may be another aspect as well: the ama foils can lift a huge proportion of the weight of the boat-on old ORMA tri's it was up to 70% or so-as it is on the new Mod 70's. That leaves the ama supporting just 30% of the boats total weight which is the sole method of pitch control on most of these boats.
The squared off back ends could provide better pitch damping and, as the foil supports more of the weight in higher wind perhaps allow the aft sections to plane.

PS- just a note-the picture of USA 17 shows a center daggerboard. After extensive tesing they removed it and the boat was raced with just the curved lifting daggerboards.

[oldsailor7]

Originally Posted by rayaldridge

I'd agree with everything else you say, but this doesn't seem to be correct, in that the most recent America's Cup winner (and loser) did not seem to have round bottom hulls.



Since windward ability is so critical in match racing, I would assume that there's some reason the designers have moved away from the lowest possible wetted-surface hulls.

And the reason is a reduction in pitching motion. Hence the flattened buttocks.

All hull design ---or for that matter all sailboat design is about trade offs. Round bottom hulls do not have to be a circular section, even though that is technically the lowest drag shape. Experience has shown that ovoid shapes , either horizontal or vertical,( often both in the same hull), are the best for all round performance. Deep V hulls are the worst when the hull it'self is expected to provide all the leeway resistance. The early Wharram boats were a perfect example.
The ideal hull would have no leeway resistance, leaving the leeway prevention to a well designed, non ballasted, fin of some sort, retractable or otherwise..

[rayaldridge]

Originally Posted by oldsailor7

And the reason is a reduction in pitching motion. Hence the flattened buttocks.

It looks to me as if the flattening goes well forward. If the only reason were pitch damping, that could be achieved by fuller sections, without the flattening, or so I opine.

I would assume that these hulls were tested extensively in the tank. I wonder if the explanation has to do with the relative effects of skin friction and wave-making drag at the higher speeds these boats are designed for. It could be that semi-circular sections are best for reducing skin friction, but not optimal for reducing wave-making resistance.

[gonzo]

These are boats designed for a very narrow set on conditions.

[cavalier mk2]

The German subchasers in WW2 with their round hull were faster in the rough water than the V hull boats the British used which had the edge in calm conditions. This illustrates the combination of wavemaking resistance with resistance through the waves. The wider performance envelope should be faster overall.

[Gary Baigent]

Mermaids, you ask, Bruce? Only if you're breathing an excess of epoxy fumes ... which is what I'm doing - so yes, plenty of fantastical mermaids in Auckland. I'm incorporating their sophisticated tail design into Sid's wing. Cheers.

[rayaldridge]

Originally Posted by gonzo

These are boats designed for a very narrow set on conditions.

I'm sure that's true, but how does that relate to the question of windward ability? The Cup racers don't go out in much wind, but how is that hull shape less suitable for bigger seas and more wind?

[Silver Raven]

Originally Posted by Gary Baigent

Mermaids, you ask, Bruce? Only if you're breathing an excess of epoxy fumes ... which is what I'm doing - so yes, plenty of fantastical mermaids in Auckland. I'm incorporating their sophisticated tail design into Sid's wing. Cheers.

G'day Gary. "Sid's wing" - is that the 15.6 X .6 wing mast on 'Waterblaster' or something else? More info please. Has anyone done the - auto altering wing yet? We did that back in the late 60's & not many noticed what was going on but it sure worked. In 6 years - only 2 X's out of the first 2 places - in any fleets of 'B' class racing in Australia. Have a great weekend (sailing of course), Ciao, james

[Gary Baigent]

James, have you got some photographs of your big wing, sounds very interesting and well ahead of its time.
There is a load of stuff on Sid (the last couple of pages relate to the rig) here under "alternative to marvelous Buccaneer 24."

[HASYB]

Sam, I addition to all scientific and philosophical advice above I would say; "be the rudder, be the boat" and of course don't forget the birds.

Cheers

[Samnz]

I am going to test the rudders the length they are, one is nearly a metre longer than the other. (but same section) The short one is about the same size as the 8.5m cats are using so will be fine.

I will keep you posted on the speed difference between port and starboard Tack.

I actually think the bigger one will provide better VMG upwind if I have the perfect amount of weather helm.

I will also put the bigger one on the starboard side to give better control when on Port (give way boat)

[cavalier mk2]

Chuck Kanter wrote a article in Multihulls mag some years back where he shortened the rudders of his Karmin cat but increased pointing and leeway resistance with an end plate. He described it as a definite improvement.