Daggerboard catamarans

[ejlindahl]

Just,

I'm not understanding your comment below. Catanas have 2 main sheets, (maybe you know that and I'm not getting it). You see them on the vid; one is near vertical on the stbd side and the other is "closer to horizontal" on the port side of the boat. (there is no traveller). They are doubled so you see 4 lines going up to the boom end (two from each aft corner of the boat). You trim both in concert to get the proper athwartship location of the boom end and also to get the right amount of tension in the leach. If Yelola's leach tell tails are flowing I'd assume his trim is good. What am I missing?

Your comment: "The best way of improving performance on that video would have been by preventing the main from stalling low down. The boom was a lot closer to centerline than it should have been at 80+ apparent wind angle based on the angle of the mainsheet, closer to horizontal than vertical. It should have been at least 20 degrees closer to vertical for max performance."

[Seaslug Caravan]

Originally Posted by 44'cruisingcat

I tested mine. Motoring in glassed out conditions board up was 1/2 knot faster at 6 knots.

Have you checked to see if your board is in the case "leading edge forward"??

I suspect if its generating that much drag its either badly fouled or simply not shaped correctly.

[44'cruisingcat]

Originally Posted by Seaslug Caravan

Have you checked to see if your board is in the case "leading edge forward"??

I suspect if its generating that much drag its either badly fouled or simply not shaped correctly.

How much difference do you see on your boat? What design is it? (If it exists.)

[MikeFergie]

Look I can't comment on big racing cats but when I raced tornados we kept the main as tight as possible and used the traveler for speed and depowering the main

[SVNeko]

Originally Posted by catsketcher

I think the reason Catana may specify reduced board area is because of engineering constraints. The shock loading, by waves, onto the board is greatly increased in large waves. Also the increase in rig drag and wind loads increases the loads in the boards. You could design them to handle these loads but the boards would be very heavy so designers go for the middle ground - pull them up in heavy winds.

Yes, this. I know of at least 2 Catanas that broke boards merely sailing the boat.

[yeloya]

Originally Posted by SVNeko

Yes, this. I know of at least 2 Catanas that broke boards merely sailing the boat.

Do you have more info, which model, when, where ?

Thanks

Yeloya

[Factor]

Originally Posted by Seaslug Caravan

Have you checked to see if your board is in the case "leading edge forward"??

I suspect if its generating that much drag its either badly fouled or simply not shaped correctly.

Typically rude insulting comment.

[SVNeko]

Originally Posted by yeloya

Do you have more info, which model, when, where ?

Thanks

Yeloya

I believe both were 47's. One is of a guy on Mh4Us and another is a Chilean boat based in Shelter Bay Marina, Plan B. One Switch had a board break crossing the Atlantic and replaced both with CF. The Switch boards are absolute bears - taking 4 guys struggling to carry and cored with hardwood. They still float however.

[yeloya]

Originally Posted by SVNeko

I believe both were 47's. One is of a guy on Mh4Us and another is a Chilean boat based in Shelter Bay Marina, Plan B. One Switch had a board break crossing the Atlantic and replaced both with CF. The Switch boards are absolute bears - taking 4 guys struggling to carry and cored with hardwood. They still float however.

Isn't better to break the board rather than the case when you hit something ? On the other hand, they shouldn't be so weak to break without hitting something..

Yeloya

[brownoarsman]

Originally Posted by 44'cruisingcat

Why on earth would you want board down on a run?

I think he meant as a temporary way of unloading the board to change its position, then getting back on prior angle immediately after the board is fixed.

[rom]

Hey there, though I have never sailed a cat with daggerboards I am following this thread with lots of interest ! At the risk of being OT again, what angle would you set your AP when sailing upwind (to a destination straight upwind) in wind mode ? Could anyone show an actual trace and explain the boat & pilot settings ?

[Stumble]

Originally Posted by yeloya

Isn't better to break the board rather than the case when you hit something ? On the other hand, they shouldn't be so weak to break without hitting something..

Yeloya

Long thin boards that are strong and stiff enough to handle side loads in big wind are difficult to manufacture in anything other than carbon fiber. So it is somewhat common for designers to just spec that the boards have to be pulled up as the wind builds in order to ease the preassure on them. It has nothing to do without what's faster, or preferred in general, and a lot to do with trying to save money by building boards from glass instead.

[44'cruisingcat]

Our autopilot has a VMG optimiser function. It usually settles on 30 degrees apparent, but may go as far as 32' in very light wind.

We'll usually tack through 90 - 100 degrees.

[valhalla360]

Originally Posted by yeloya

Isn't better to break the board rather than the case when you hit something ? On the other hand, they shouldn't be so weak to break without hitting something..

Yeloya

In theory, that's true but it's tricky designing to be strong enough not to fail during heavy but normal use but weak enough to fail when you hit something.

That's one of the advantages of a rotating center board. Hold it down with a friction clutch and it will pop up if you hit something. If it does manage to come up during normal operations, it can simply be redeployed.

Of course the downside is it's hard to set up a high aspect ratio foil without a big slot adding performance robbing turbulence. Probably more hassle then it's worth for most cruising boats but I would some sort of rubber cover that closes off the slot when retracted but is pushed aside when deployed would seem to address the slot issue.

[Seaslug Caravan]

Originally Posted by rom

Hey there, though I have never sailed a cat with daggerboards I am following this thread with lots of interest ! At the risk of being OT again, what angle would you set your AP when sailing upwind (to a destination straight upwind) in wind mode ? Could anyone show an actual trace and explain the boat & pilot settings ?

Here U go....

Upwind Catamaran Sailing onboard ROAM — Sail Surf ROAM

Surf Sail Roam with a beautifully equipped 48 foot performance cat with daggers.

The theory pales into insignificance when you gotta nurse the boat to windward so as not to batter the crew around too badly. Averaging 8 knots and tacking through 110 to 115 degrees gives a VMG directly to windward of around 4.5 knots.

Good luck pushing one of those "jobbies" with flat bottoms too windward that hard.

French mini keels and motoring suddenly start to make sense.