Catamaran from two single hull boats

Revisit original Question

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

 

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

 

twin mast

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

 

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....

 

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.

 

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.

 

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.

 

Catamaran Motor "Sailor" Houseboat from Mono Hull

I am not well versed in Catamarans. I like (love) the general idea... However it combines some of the worst of both worlds. I have read a statistic that some high amount (60% or 75%) of the effort and expense is after you have the hull and deck built. Show us a drawing (know anyone who does CAD or sketch up?)

Two identical boats (27 to 35') with added salon and new helm station built on top.

The nay sayers see it as a waste of money. What if for $25k you get an odd looking but large house boat? It doesn't have to look like a house boat, but it is wide and tall because it has interior space for living. And as a bonus it motors at a very low cost, and once in a while you can turn off the motor and go for a downwind reach?

The "what if for 25k?" is the part then, can you really budget the right amount to get this done and have it warm, weather tight, water tight, and motoring away from the dock at this price?

It will never be the same value as an $80k cat, but if you had to sell it, or if you wanted to sell a test run, would it be worth $5k or $15k as a liveaboard? People in the city are always trying to find a way to dodge $12k in apartments rents.

It is an interesting use of surplus boats. There are a huge amount of old fiberglass boats that are being scrapped. From 22 feet to 34 feet this is very very common. There are not trailers for all of them, they need new sails, new motors, and under a pile of expenses they get parted out to other boat owners.

The draw backs;
Building the deck house and beams will take on most of the qualities of building from scratch. Wiring, cabinetry, plumbing, rudder controls, motor controls. Maybe you want to do some drawings and get it bid from a couple boatyards. Some cats end up at 14' beam, but unless you choose narrow boats and maybe cut off some of the widest mating surfaces? This creation could end up wide. Will you moor it on a dock? Will the width fit in a slip?

Variations;
(1) choose smaller racing hulls to increase speed? Soling 27, Schock 25

My ideas;
For a single efficient motor your primary engine could be an outboard (diesel or gas). HOWEVER, can you retrofit the inboard motors to be electric (golf cart motors?), and keep them for maneuvering? Even if they only had small or folding propellers would be fantastic control.

 

Two thirty footers seems not a workable idea from all the advice read here.

How about FOUR twenty four footers?

Narrow beam hulls, cheap and plentifull used, 48 ft over all when done.

Four masts. redundant parts galore, spare rudders, ect.

Lots a room for WIFE. and hopefully at least ONE of them will stay afloat if you break up, to use as a life boat.

 

Catamaran for Blue Water travel...

Does anyone make an asymmetrical sailing catamaran? I know of at least one maker who makes one for power boating, with a single screw in the larger hull.

http://www.aspenpowercatamarans.com/pages/technology.html

http://www.ecofriend.com/eco-boats-...icient-catamaran-powered-by-solar-energy.html

http://forum.woodenboat.com/showthread.php?163777-Lug-yawl-cruising-design

http://www.duckworksmagazine.com/11/outings/scenes/

http://proafile.com/magazine/article/the-arcsail-proa

Maybe it would be possible to make a monohull lighter and faster? by adding one hull (smaller and narrower)... you could subtract ballast greater than the weight of the structure you are adding. maybe you would need to move the mast over towards the new hull. (moving your center of effort toward the center of resistance).

The original post is a great question. Solar motor, extra wide. I keep throwing modifications at it.

http://bwsailing.com/cc/2013/09/04/solar-boat-hits-milestone-on-the-great-loop/

http://blog.boattrader.com/2008/11/dse-hybrid-is-first-truly-green.html

http://archives.starbulletin.com/2008/03/17/news/story05.html

http://www.mooseislanddesign.com/telstar48.htm

http://forum.woodenboat.com/archive/index.php/t-126136.html

This is absurdly tall and absurdly wide.... but I like it.

http://www.dailymail.co.uk/news/art...t-Sussex-boat-designers--controlled-iPad.html

 

while I meant it as a joke, actually might have some feasibility, if you paired the hulls stern to stern and faired them.

Your two long narrow hulls would be double ended.

 

An Asymetrical Catamaran is called a proa. Been around a long time.
Still has to have slim hulls to be of any use.

http://www.clcboats.com/shop/boats/wooden-sailboat-kits/proa/madness-31-foot-pacific-proa.html

http://harryproa.com/index.php/design/15/new-visionarry

And many others

 

Joining hulls together, or extending them, is more suited to metal boats than other types, where it would rarely be a worthwhile exercise.