Converting power catamaran to sailing catamaran

[Dennis.G]

Maybe a side-by-side unstayed mast arrangement would be a good solution on this. No bridge loading from a central mast to design for. A fellow here in Mexico has one of these and it sails very well.

https://www.boatdesign.net/proxy.php...bca31cb171e096

[Gaia]

We sailed with Pete Hill on his double masted junk rigged catamaran China Moon (one mast on each hull) and it gives a whole new meaning to wing on wing sailing! She was or is, I am not sure what became of her, much smaller and not directly comparable but was fun to sail on. Certainly much easier to sail downwind as the sails do not interfere with on another.

Jim

[Mike Banks]

I wouold simly fit two bipod masts and make her a schooner ior ketch, depending on hull.

This simplifies a lot of things and when fitted with furlers, makes sailing a simple matter. The ancient Egyptians used this rig on their reed boats because it put the least stress on the "Hull".

This will probably be the easiest to manage because it too will put the least strress on the hulls, and reinforcing the deck shelf and running an extra frame to the keelson to support the deck shelf where the mast legs meet the deck pivot clevis (for (for easy lowering or raising of masts) Could see you sailing in less than a month. It all depends on the hulls, and doing it this way will not involve any interference with the deck cabins or saloon, with heavy beams. It will however involve fitting a comparatively light tension fitting where the furlers for each sail are affixed. This strain will be MUCH less than the strain on any chain plate, because this kind of mast distributes its forces into the vessel without the need for high tension loads to keep the rig stable.

The only real loads it gets are from the wind itself.

[CapnBazza]

Would you be destroying that “unique layout” that you love about this cat by having to build in extra load-bearing bulkheads? There is a reason why sailing cats do not have “anything close to that layout”.

[ranchero76]

Originally Posted by CapnBazza

Would you be destroying that “unique layout” that you love about this cat by having to build in extra load-bearing bulkheads? There is a reason why sailing cats do not have “anything close to that layout”.

Well, it definitely would need to be modified to accommodate stick, but not drastically.

There's actually sailing cat which has SOME of the features of cat in question. It's 20m "Euro Catamaran 2000". Its owner is member here.
It cost him little fortune to build it, and he doesn't sell it anyway .

http://www.bruceroberts.com/public/H...escription.htm

[44'cruisingcat]

Originally Posted by Gaia

We sailed with Pete Hill on his double masted junk rigged catamaran China Moon (one mast on each hull) and it gives a whole new meaning to wing on wing sailing! She was or is, I am not sure what became of her, much smaller and not directly comparable but was fun to sail on. Certainly much easier to sail downwind as the sails do not interfere with on another.

Jim

Friends of ours have a biplane rigged cat, and certainly it's excellent DDW. It loses out a bit around beam reaching though, because on those angles the sails do interfere with each other. Swings and roundabouts...

A stayless biplane rig might be the easiest option for the OP though. IMO it would still be very advisable to consult with a multihull designer, because the placement of the masts is critical to getting the sailplan balanced.

[Tricolor]

I've been in the naval engineering business for over 40 years doing many conversions to sea going vessels, if we had listened to all the self proclaimed specialists minimal half of our work hasn't been done.

To answer your question is not a simple one, the existing catamaran has to be evaluated and calculations have to be made. Maybe its possible, maybe even straightforward but without an evaluation of a naval engineer its all talking to just make noice. So my advice get a specialist on the site and listen what he/she has to say.

On this forum you will not find your answer.....

[billknny]

Originally Posted by Tricolor

On this forum you will not find your answer.....

Realistically, the OP doesn't want an "answer", he wants validation. He wants people to line up and say, "Wow! What a great idea! How come nobody has thought of this before!"

The long string of people telling him, "No Problem! Just use an unstayed rig!" are no better. It's true, an unstayed rig avoids the downward thrust of a stayed rig, but ALL the other loads and issues are still there, and some are larger... You still need to PUSH the boat from a place it was not designed to be pushed from. But hey, you can sail downwind just great! Any piece of trash sails downwind.

As you know, there is a reason navel architecture is a real profession and not just a hobby. When it comes to boat design, at least I know what I don't know. So many people haven't a bloody clue.

[ranchero76]

Originally Posted by billknny

Realistically, the OP doesn't want an "answer", he wants validation. He wants people to line up and say, "Wow! What a great idea! How come nobody has thought of this before!"

The long string of people telling him, "No Problem! Just use an unstayed rig!" are no better. It's true, an unstayed rig avoids the downward thrust of a stayed rig, but ALL the other loads and issues are still there, and some are larger... You still need to PUSH the boat from a place it was not designed to be pushed from. But hey, you can sail downwind just great! Any piece of trash sails downwind.

As you know, there is a reason navel architecture is a real profession and not just a hobby. When it comes to boat design, at least I know what I don't know. So many people haven't a bloody clue.

I really appreciate your opinion. Sounds very professional. Just one question - how many boats you had built with your own hands? Some of the posters above actually had built boats WITH THEIR OWN HANDS and some even naval engineers, and at some reason they're not so negative. But what do they know? I'm sure you have vastly more experience, tell us about it!

[cal40john]

What about hull shape? A powerboat's thrust is pushing from under the center of drag, a sailboat is pulled from above. Seems a sailboat needs more buoyancy up forward.

A power cat typically has bigger engines, more weight aft, so more volume aft.

[ranchero76]

Originally Posted by cal40john

What about hull shape? A powerboat's thrust is pushing from under the center of drag, a sailboat is pulled from above. Seems a sailboat needs more buoyancy up forward.

A power cat typically has bigger engines, more weight aft, so more volume aft.

Actually, most information provided in first post. Hulls are displacement hulls, same as on sailboats, not planing hulls.

[Franziska]

That's got very little to do with displacement or planing hull form.
But much more with Archimedes Law. If the center of the overall weight will not match the center of the underwater volume the boat will correct itself until it finds that balance.

Now if your hullshape is not designed to carry all that extra weight far forward you'll end up with a boat floating at a funny angle.
You could perhaps reduce this by repositioning very heavy items on board and keeping that rigging very very light (which will be expensive to do!).
Adding underwater volume at the proper location could help too but tends to be much more involved as it has to be lighter than the water displaced, structurally integer, faired in, and watertight to achieve the desired effect.

Further your hulls will sink in considerably deeper than designed.

A heavy multihull will always be slow.
Sometimes that's acceptable if one gains other advantages from it, but most tend to prefer speed.

Still these influences can not be property judged without seeing the boat, its lines and doing some calcs on it.

Good luck.

[cal40john]

Originally Posted by ranchero76

Actually, most information provided in first post. Hulls are displacement hulls, same as on sailboats, not planing hulls.

Pull forwards on a string attached 1/3 of the way up the mast, friction from water is low on the hulls, so pull backwards with a string attached low on the hulls. The bows go down.

Where do the strings go on a powerboat?

Hobie 16s with low bow volume pitchpole a lot. Modern beach cats have lots of bow volume, much harder to pitchpole.

Not saying you're going to pitchpole, but boat trim and balance under sail could be odd.

[valhalla360]

Originally Posted by 44'cruisingcat

Oh yeah, and it would probably need bigger rudders.

Probably needs some sort of keel added if it was designed from the ground up as a power boat.

Realistically, you have two choices:
- Stick a mast on it and hope for the best.
- Hire a qualified naval architect and pay a lot of money to have him do a full analysis and it still may or may not be viable.

An unstayed mast may be a little easier to do but since you haven't told us what boat it is or what you really like about it, the initial assumption is now you have a big old post in the middle of the hull living space.

Also, what is your sailing expectation? If it's just getting "some" propulsion, it's certainly possible but if you expect great performance, in particular to windward, it's a much more challenging problem.

Throw enough money at the problem and accept a lot of compromises and it's always possible to do something...even if it's not a very good solution.

Another thought:

what's your goal with adding sails? If it's just to counter range limitations, could you throw a couple hundred thousand into a massive solar array covering the entire deck (it's not like adding a rig to a 50' sailboat is going to be cheap). On a 50'x26' boat, you might be able to fit 20kw of solar panels. If you accept a slow offshore speed and keep a generator for backup, you can probably get 2000-3000mile range running the geneator at night and using the solar panels during the day.

For shorter coastal hops, you might be able to do everything with solar and battery if you accept limited speeds. If you get 5hr of the rated output per day and 20kw gets you 5kts speed, that's 25miles per day you can motor.

[CatNewBee]

If you are looking for ideas outside of the box, you can go for a huge kite sail. There were experiments to use kite like parasails to reduce costs for commercial vessel, but they remain just prototypes.


For dead downwind sailing it might work well...