Single offcenter rudder for a cruising cat?

[rayaldridge]

Thom, on Slider, the daggerboard goes down the side of the hull, so only takes up about 4 inches of space on that side. This is not enough to interfere with the seating-- the seats rest on rails that run the length of the cockpits so that the seats can be quickly moved to any part of the cockpit, turned front to back, or two seats can be placed in the same cockpit.



In the new boat, so far I've placed the board in the hull with the two bunks, and it doesn't take up enough room to interfere much with the aft bunk. The bunk flats are about 26 inches wide at the head-- the case narrows the head of that bunk a little. The board will emerge from the side of the cabin just above deck level, so it's well-supported, and can be shorter than a board that extends up through the cabin roof.

[dstgean]

Originally Posted by rayaldridge

The problem with centrally mounted foils, in my opinion, is the lack of endstopping. It's the reason I'm dubious about leeboards on fast multis. As an example, the Stiletto originally came with a central board, and it just wasn't as fast as Stilettos with daggerboards in the hulls.

Hey, if I was worried about acceptance, I'd have never built Slider. I might call the new boat Slammer-- it's intended to be a much faster boat, since it will have a lot more sail area and beam. Of course, the word has some negative connotations for sailors, so maybe not.

Ray,

How fast do you imagine it will be? 10 knots? 15? On the one hand you mention cruiser with the intent to never fly a hull, and the other you mention Stiletto's and "it's intended to be a much faster boat". Which side of the spectrum do you think it will fall on? Like the idea of the boat though regardless of the answer to that one though, as I think trailerable multis are ideal for lots of cruising folks like myself who prefer to to go fast, stay reasonably level, and have a huge party platform at the anchorage for the size of the boat.

I've been taken recently by the Dachew's later cats also maned Beowolf that were literally ply boxes with shaped foam (by Micky Munoz) bottoms. Kinda low tech for a really fast boat. Fixed beam and not too trailerable though.

As for the single rudder issue--there is a loss of redundancy. Most mono's deal with that my making it REALLY bomber. Balance the boat up and you should be able to steer with the sails in the event of rudder loss. Having a rudder on one hull and the outboard on the other makes some pragmatic sense for setup time.

Me? I'd say anything you can do to get the boat set up quicker is a good thing. Trailering with everything attached is one way to get this thing together quicker too. If the rudder is powerful enough, you won't notice the effect of the altering of the CE/CLR. Like Phill, I do like to have a pair of rudders surfing downwind though.

How big do you imagine the cabins will be? Larger than the Jones boats? How about compared to the the K650?

Dan

[garydierking]

Either move the leeboard aft or move the mast forward, whichever is easiest.

[rayaldridge]

Hey, Dan. I don't know how much faster the new boat will be. I thought Slider was going to be only a little faster than a monohull open cruiser and was pleasantly surprised. But, I figure maybe a lightship weight of 800 pounds, and max displacement of 1800, with about 235 sq. ft. of sail. It's LOA is 19' 8". It won't be as fast as a beach cat, except maybe in heavy air (I'm aiming for a beam of 13 feet.) But it should be able to hit the mid teens in the right conditions.

The cabins are smallish. But there are two good bunks in one hull, each 26" wide at the shoulder end and 6.5 feet long. The ends of the bunks form seats, with 40 inches of sitting headroom over the flats. The other hull contains the galley, with an 18" deep counter and storage, a two or three person settee with fold-down table, and space for a porta-potti. The galley hull also contains most of the storage, in compartments fore and aft.

The houses are quite low, if you look at the drawing I posted upthread. They don't need to be very high to give sitting headroom, because the hulls have a lot of freeboard-- the strakes yield the most freeboard you can get out of a 4 foot wide piece of ply. But somehow the narrowness of the hulls seems to take a little of the curse off the high freeboard, visually.

To sort of give some context, the boat is meant to be about the smallest trailerable cat that could take two people to the Caribbean via the Thorny Path. Not an ocean crosser-- just a Gulf Stream in really settled weather crosser.

The original concept was for a boat that could be built with a donor rig from a beach cat, and that would still work fine, because. the folding mechanism uses a central spine, so moving the mast would be no problem. But I've had such good luck with Slider's sprit/sloop rig that I'm tempted to do it again. The mast would be cheap to build, and easier to get up and down, and would function well in a tabernacle. (I'm thinking about the EC here.)

Well, soon the weather will start to cool down, and if a hurricane doesn't blow us away, I'll get started.

[aussiebushman]

I may be getting senile, but I recall Roger Simpson specifically advising against single rudders, The 9.1 metre Signwave that I built to his plans had twin rudders connected by a simple alloy cross beam. Sure, it is more work to build two and there is a bit more weight but the major benefits seem to be safety in the event of one being damaged also much cleaner and more even flow over the surfaces.
Alan

[rayaldridge]

Originally Posted by aussiebushman

... the major benefits seem to be safety in the event of one being damaged also much cleaner and more even flow over the surfaces.
Alan

Alan, I don't understand why the flow would be cleaner over two rudders compared to one. Could you explain?

[Alex.A]

You are straying into proa teritory? - Gary Dierking knows this area - good advice?

[rayaldridge]

No, definitely not proa territory. The only difference between this and a conventional cat like Slider would be one less rudder.

[Richard Woods]

How do you plan to steer the boat? Always sitting on one side?? Personally I hate steering from the lee side, especially when its windy or I am sailing fast. And I always sail slower when I cannot see the wind and waves properly.

But if you aren't going to be on one side all the time how have you designed the tiller?? Just curious

As far as which is better, one rudder or two, I agree with Catsketcher, as always.

Richard Woods of Woods Designs

www.sailingcatamarans.com

[aussiebushman]

Ray - in answer to your question, I probably expressed it badly, but Phil already provided the answer, namely:

"the time I most like deep twin rudders is downwind in a swell. With the swell on the quarter you often get the windward rudder almost half out of the water just before the boat starts to surf down the wave. If the single rudder was the windward one it would be heavily loaded and half out of the water at the same time - bad combination"

[rayaldridge]

Originally Posted by Richard Woods

How do you plan to steer the boat? Always sitting on one side?? Personally I hate steering from the lee side, especially when its windy or I am sailing fast. And I always sail slower when I cannot see the wind and waves properly.

But if you aren't going to be on one side all the time how have you designed the tiller?? Just curious

I'm thinking about a push-pull tiller. The perpendicular arm could extend to the centerline of the boat, and the tiller itself could swing to either side. Big leverage, at least.

The problem with a rudder lifting downwind seems like a pretty plausible objection to the idea. How do tacking outriggers handle this problem? Are they more prone to broaching than cats?

[BriggsMonteith]

What is your objection to a large centerline rudder again? I would think you'd rather have your motor offcenter.
-Briggs

[rayaldridge]

Originally Posted by BriggsMonteith

What is your objection to a large centerline rudder again? I would think you'd rather have your motor offcenter.
-Briggs

The idea was to put the single rudder on one hull, and the outboard on the other. One of the problems with outboards and small cats is that usually you have to hang it on a beam, where it's exposed to spray and waves break over it, etc.

I don't think there's anything wrong with a centerline rudder-- it and a centerline board might be slightly less efficient than a board end-stopped by the hull and a rudder in the entrained water aft of the transom, in my opinion.

However, this is meant to be a folding cat, and it already has a narrow central spine. You could add a rudder and a case to that spine, but the wider the spine, the narrower the cabins must be. It would also, I think,add weight and complication. The offcenter case I used for Slider (see pic upthread) is simple, strong, and takes up little room. A transom makes a strong mounting point for a rudder.