Catamaran from two single hull boats

[Kalagan]

Hi,

I have been considering building a Cat from two monohulls for awhile also. my idea was to get two flush deck Monohulls with bolt on Keels (like Columbia 34 or 43) and attaching them. If you take the Keels off, which saves a lot of weight, plus reduces the surface area and drag (no keel and higher out of the water), add a center section (bridge deck) that turns into a Pilot House and attaches to both hulls in 3 places, deck height, half way down hull and under the water, with a foil from old keel location on one hull to the other.

It would seem that taking this approach would create a cat that is structurally stronger than manufactured Cats, because the under water foil would not allow any movement between the hulls. Basically, the connecting structure between the two hulls would be a squared off Capitol "A" on Top, with curved sides (that match the hull curve) and a closed bottom, which would be the Under water Foil. Seems like it would be stronger? Am I off base?

Also, if I was going to take this approach, I was considering leaving the rigging of both boats intact. So, you would end up with two masts/booms and 4 sails. if the Head Sail for each Masts was setup as a Roller Reefer, then you would have the ability to control how far out the Jib came, depending on which side the wind was coming from.

I have seen smaller Cats and Tris with twin Masts and it seems like a good setup. What are the negatives and positives of this twin mast approach?

Please consider it on its merits and don't dismiss it only because it is not a common setup.

Thanks
Kalagan

[whitepointer23]

Originally Posted by nimblemotors

actually I don't care to loose the $50k on resale since the plan is to die in this boat eventually, of natural causes, not boat failure.
I would hope to build the ghetto cat for $20k, so the loss not nearly as much, specially compared to what I'd have to pay to get a good one in the end ($150k) I get it that its a bad idea. I've looked for unfinished projects, hasn't seen much resembling anything affordable. There just are not older cats to fixup, they are too new, at least the good ones.

My woman will not put up with a monohull, to get enough room and stability its too big to single-hand, so as much as I'd want to go that route and get an older one with my $50k, ain't gonna happen.

I appreciate the feedback.

it sounds like you should look at the wharram cat designs, cheap and simple to build and proven offshore cruises.

[Sand crab]

Part of the benefit of cats is that they are lighter and therefore faster generally than monos. Even with the keels removed you will still have more weight due to the redundancy of systems like 2 galleys, gensets etc. Furthermore the hull shape of a mono is much different than a cat and has much more beam so you would probably end up with the slowest cat around. The bridge deck salon would require extensive mods to each mono hull because you would surely want to get from one hull to the other without being in the weather. That means that half of the existing rigging will be in the way. I'm not sure why you feel a need to strap the keels together because it would be stonger. I've never heard of a modern production cat breaking up due to structural design or construction. In fact several that were abandoned because of severe weather were found afloat even months later. There are a few double masted cats. Check out Cat2fold and Cata Roll's. These are unique rigs but show it can be done. Also go to Constellation Yachts and click thru their pics on the construction of the gaff rigged schooner cat. They show a relatively simple method of attaching the cross beams using carbon fiber straps. What I'm trying to say is if you want a cat then start with a cat. There are plenty of kits, plans, and unfinished projects to give you a nice affordable start. Anyway, good luck. BOB

[nimblemotors]

just to emphasis a point, the work needed to make the two monohulls work would make the savings in not building the hulls insignificant.
so ending up with a poor cat, but still having to spend a lot of time and money, makes the idea not workable. now if you want to just have something that floats and LOOKS like a real ghetto boat, then it might work,
but it won't be a real sailboat. I've given up the idea.

My current idea is using two jet fuselages as the hulls....

Originally Posted by Sand crab

Part of the benefit of cats is that they are lighter and therefore faster generally than monos. Even with the keels removed you will still have more weight due to the redundancy of systems like 2 galleys, gensets etc. Furthermore the hull shape of a mono is much different than a cat and has much more beam so you would probably end up with the slowest cat around. The bridge deck salon would require extensive mods to each mono hull because you would surely want to get from one hull to the other without being in the weather. That means that half of the existing rigging will be in the way. I'm not sure why you feel a need to strap the keels together because it would be stonger. I've never heard of a modern production cat breaking up due to structural design or construction. In fact several that were abandoned because of severe weather were found afloat even months later. There are a few double masted cats. Check out Cat2fold and Cata Roll's. These are unique rigs but show it can be done. Also go to Constellation Yachts and click thru their pics on the construction of the gaff rigged schooner cat. They show a relatively simple method of attaching the cross beams using carbon fiber straps. What I'm trying to say is if you want a cat then start with a cat. There are plenty of kits, plans, and unfinished projects to give you a nice affordable start. Anyway, good luck. BOB

[rayaldridge]

Originally Posted by Sand crab

Generally a 30' cat is too small for blue water cruising. The Catalac 10M is still a bit on the small side. The highly succesful Gemini 105mc is about this size and they specifically do not call their own boat a blue water cruiser. Most people consider about 36' to 40' the minimum size for true blue water cats. You need a larger size to get rid of the low bridgedeck pounding. The Catalac and the Gemini both suffer from this.

I don' think that's due to their size so much as their design brief, which was to get as much accommodation in the length as possible. Much smaller cats do not pound if their bridgedecks are high enough-- for example, even relatively small open bridgedeck Wharrams don't pound.

Many cats smaller than 30 feet have made trans-atlantic passages safely-- one, a Tiki 21, circumnavigated and recently competed very well in the Jester Challenge.

Bigger is better, of course, but smaller is cheaper.

[oldsailor7]

In the 18th century the British Navy experimented with two sailing ships of the line attached together with massive wooden cross beams.
They encountered all the negative aspects described in this thread and went no further. It wasn't until Francis Herreshoff designed his catamarans with slim, light hulls that catamaran design made any progress.

[Steve W]

Oldsailor, i think it was Nat Herreshoff, not Francis who figured out the formular which had been embraced by the pacific islanders for centuries.
Steve.

[oldsailor7]

Originally Posted by Steve W

Oldsailor, i think it was Nat Herreshoff, not Francis who figured out the formular which had been embraced by the pacific islanders for centuries.
Steve.

Yes Steve you are right. My mistake.