Converting power catamaran to sailing catamaran

[ranchero76]

Originally Posted by Franziska

The skegs might be useful for beaching. Still they will not be of help when going to windward.
These hulls will not provide good upwind performance without added short low aspect stub keels or at least on one side a dagger- or centerboard .

IF such project would be undertaken, building dagger boards (and/or enlarging the rudders) wouldn't add much to amount of work already needed
It would be nice to keep extra shallow draft though - imagine places you can go to with such draft!

[Franziska]

Lol I do not need to imagene that.
I do it on Lady Rover all the time.
Lady Rover just has one centerboard on port side. That's working fine for us.
Still I'd prefer a daggerboard because of simpler mechanics.

[rabbi]

Originally Posted by ranchero76

Of course the target would be to create decent sailing boat, not something strange to sail only downwind.

If you just want to do downwind passages under sail, that should be much easier.
Build a 15m A frame from scrapyard stuff and stick it somewhere on the hulls. Raise a spinnaker or maybe sails on roller furlers and call it a day.

Similar to Bernd Kohler's KD122.




To arrive at a "decent sailing boat" will definately require a different and more complex approach, especially a knowledgeable professional naval architect. Otherwise you won't get boyancy, lateral resistance, sail CE, etc right to achieve this goal and of course you still have the structural issues to handle the loads.
Even if you succeed I doubt it will be "decent sailing" compared to a cat that was born as a sailboat.

Just that naval architecct kow-how will cost you a fortune, if you can find it at all. No credible naval architect wants his name associated with converting a motorcat that was built loosely based on someone elses plans into a sailing cat.

All this won't be cheap and your resale value will be marginal.

Do it cheaply yourself and live with the limitations, or loose money.

[ranchero76]

Wait a sec - is A-Frame mast only good for downwind sailing?

[VBsail]

Is this the boat in question?





2008 Malcolm Tennant Passage Maker, Ormond Beach Florida - boats.com

[ranchero76]

$1M? No, for that kind of money I'd order new Majestic 530 Fly with all modifications I would imagine )))) That's nuts to pay that kind of money for 10yr old power boat. It's nice cat...but not 1M nice.

[rabbi]

Originally Posted by ranchero76

Wait a sec - is A-Frame mast only good for downwind sailing?

Not necessarily. I may be wrong but from my gut feeling I'd say it's less efficient than a normal mast on other points of sail. Two masts, spreaders & wires between, all cause drag. I doubt there is much data available but I'm no expert.
To me the A frame just looks like the easiest way to rig a spinnaker for downwind work which would be my choice.


Why I think the downwind is the the way to go (if you want to go forward at all):
A spinnaker can be cut & rigged so its mostly pulling at deck level. As a result you have relatively small loads on the mast. Smaller compression loads require smaller structural changes required to fit the mast. Also smaller turning forces trying to flip / turn over the boat lead to smaller or no changes in buoyancy distribution required.
Downwind lateral resistance is not important, beam vs length ratio not important, keels not important, CE not important, etc. Even with the small keels a cat will sail downwind like on rails.


To me most important: Very few people want to buy a "modified tennant hull motor cat with unaproved modified layout converted into a sailing cat by someone". So once you stick a mast ontop of this cat it will cost money, and actually lose in resale value at the same time. Unless the motor cat is free or dead cheap this project is just burning money.
So I'd keep the outlay as small as possible, and try to make my changes mostly reversible. The A frame looks like a way to achieve this.

The monetary difference between a cheap & simple conversion into a downwind motorsailor cat vs the expensive "decent sailing cat" conversion will pay for decades of diesel.

Last but not least: downwind is the major part of a circumnavigation, this is what we need sails for (range & cost!). On a cat its the comfortable fun part. For many folks the upwind part sucks anyway. I suppose this cat has a decent motoring range so why not use the engines and get over the upwind part as quickly as possible in comfort.

Overall downwind is the low hanging and most rewarding fruit.

[wyb2]

Originally Posted by rabbi

Similar to Bernd Kohler's KD122.

As drawn, the mast would come down if the mainsheet is released. Odd design.

[rabbi]

Originally Posted by wyb2

As drawn, the mast would come down if the mainsheet is released. Odd design.

As drawn the Genoa is just flapping around with no sheet. Or may be it's just a sketch and not a detailed plan.

[danielamartindm]

Don't let your affinity for a given hull move you to take on a costly project that should likely include plans drawn up for it by an architect. The forces on sailing cats are HUGE. Why try to re-invent the wheel?

[wyb2]

Originally Posted by rabbi

As drawn the Genoa is just flapping around with no sheet. Or may be it's just a sketch and not a detailed plan.

Fair enough.

Given the context I thought it was supposed to be a mast/rig design sketch. I was hoping that a lack of any backward support wasn't being touted as part of the simplicity of an A-frame setup.

[hpeer]

Was recently admiring this. Watched it sail by today for anout 38 seconds, then it was GONE!!

[Cadence]

I am sure if you have enough people answer you here, you will get the answer you want to hear... but it will be wrong.
I'd agree with this if your looking for an answer you want rather than some, not all, that make sense.

[Franziska]

It's a Chris White Atlantic 47 mast foil design.
Hardly a converted power cat.

The main reason for this rig is that it can be very fast reefed by a small crew.

Originally Posted by hpeer

Was recently admiring this. Watched it sail by today for anout 38 seconds, then it was GONE!!

[tiopirata]

That's not a Chris White mastfoil rig, it's a tandem schooner rig, which may work well. I used to work with Malcolm Tennant as engineer and I think I know the vessel to which the original poster refers and can unequivocally say that that boat will sail well with such a rig. He would need to install a centerboard in one hull but that vessel can easily handle the rigs and centerboard in structural terms. I have sailed such rigs and can tell you all that they are the equal of conventional rigs, indeed they have many advantages.