Converting power catamaran to sailing catamaran

[Suijin]

Originally Posted by tiopirata

Both Rob Denney and myself have designed or engineered large multihulls, we have also sailed these, we probably have more than 80 years seagoing between us. This is not the difficult project some of you allege, but doing it requires a bit of 21st century thinking. Most responses here can't get past the 19th century notion of shrouds, stays, triangular sails etc. I also have a rigging company, no way will any yacht of mine ever have cable rigging supporting a spar, never again.

That's great. He should get the design and build specs for you and you can design a solution.

Can it be done? Of course it can be done. But possibility should not be mistaken for feasibility which is a function of many factors, including engineering, budget, skillset and knowledge. The "box" you speak in this case has nothing to do with what the rig design looks like. It has to do with the remainder of Ranchero's requirements, his budget, and his knowledge base.

He is is looking for cost estimates. There is no way anyone here can give him what he needs in order to make a decision about moving forward without the benefit of design and build specs of the existing boat and new rig design.

[StuM]

Originally Posted by cal40john

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.

+1

Fore/aft hull design for a sailboat with a COE part way up the mast needs to be entirely different to that of a powerboat which is pushed from below the waterline. (Just look at the way a sailing cat under full engine power digs it's stern in ) .

[wyb2]

What is the boat in question? Pictures?

I certainly can't answer your question, but I think anyone who can will also need to know: what is your budget?

[roland stockham]

The only sensible answer to this question is "talk to the designer" if they go pale and reach for a drink you have your answer. If they say "yes, it was also produced in a sailing version' you may be on to something.

[ranchero76]

Thanks for all replies. I actually was smiling when reading some of them.

First of all, to these who "trying to stop me". It's not like I'm "ready to jump on it". It's more like brain exercise, looking at possibilities.

Regarding "talk to the designer" - I already answered this question earlier - there's no real designer, it's mixed design with Tennant hulls.

I totally agree with these who tell "to think outside the box". Firstly, you have to forget word "North America". If you do that, you realize that there are countries where
highly skilled engineer of most trades has MONTHLY salary is $400-$600.
In first post I stated that I would do all or most work myself, so most spending would be on engineering, used mast of proper size and materials, hardware, right?
That's answer to these who "can't even estimate conversion cost" but still want to know my budget.

I was trying to figure out what would be involved if I would jump on it.
I really appreciate the answers from these who has real experience - hands-on building or engineering. That's your opinion guys I was really interested in.

[james247]

Originally Posted by ranchero76

I have silly question.

I've heard about dismasted cats converted to be power cats. That would be easy - just discard all "extra hardware" and you all set - you have slow power catamaran.
What about other way around?

Here's why I'm asking this question.
There's power cat, 50-something ft. I was told it has Tennant hulls, but cat is highly customized, not something "standard". It has unique layout, I simply love it. Not just inside layout, but overall layout of the boat. No sailing cat have anything close to that layout. I mean - to buy sailing catamaran and convert it to something similar in terms of layout will most likely cost more than to build new one. Unfortunately, I'm not feeling like building boat from scratch, for many different reasons, at least for now.

Hulls are displacement hulls, so there are no problems with that.
Pricewise...Let's put price of the boat aside for now. Let's say it's free.
I'm willing to do ALL or most modification work myself. I'd use used mast of proper size.
I'm engineer, but not a naval engineer.

So the question is - what would it take to create proper compression post with adequate reinforcements, mounting points for chainplates etc. on such big boat?
I especially would like to hear opinions from these who had built their catamarans from scratch.

Purpose is the question. We see huge kites deployed on ships to enhance their fuel economy. The average square rigged sailing ship or dhow went to windward very poorly.
Many a motor launch in years gone by had sails for down wind cruising.
The effort to convert a motor cat to an efficient windward sailing boat would be a whole lot different than to convert it to an efficient down wind sailing boat.
If it's extended cruising you are contemplating then unless your a masochist 90percent of cruising is down wind. The loads for downwind sailing from an engineering perspective are totally different.
A pair of headsails rigged on rolling foils would give max boat speed with little effort and at a much lower cost than a full conversion.

[billknny]

Originally Posted by ranchero76

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!

My background and expertise matters not a jot.

You have the answers you like, so just go with them, buy the boat, and do the conversion.

[ranchero76]

Originally Posted by james247

Purpose is the question. We see huge kites deployed on ships to enhance their fuel economy. The average square rigged sailing ship or dhow went to windward very poorly.
Many a motor launch in years gone by had sails for down wind cruising.
The effort to convert a motor cat to an efficient windward sailing boat would be a whole lot different than to convert it to an efficient down wind sailing boat.

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

[StuM]

Originally Posted by ranchero76

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

Which will require considerable modification to the hull shape and buoyancy distribution

[Franziska]

While I principally agree with Stu regarding buoyancy and the like and have mentioned that previously, it's worth mentioning that you can use kites for tacking upwind to some degree. They have even be used to cross oceans.
Still anywhere close to shore big kites can be burdensome and difficult to handle (unless a kite board is at the lower end).
But then again you have powerful engines which you could use close to shore or in busy waterways.

One more issue though. It is difficult to adjust kites to the force of wind. What do you do in a sudden squall?

Would I personally get the joy of sailing from a kite rigged sailboat?
Probably not, but that's a personal preference.

[ranchero76]

I don't see much difference from sailing catamaran hull. It even has mini-keels, even though strange ones, very long. Would be good for beaching I guess

[CatNewBee]

for winward performance / pointing you need noteworthy keels or at least daggerboards. This hull would work eventualy from beam reach with some drift to leeward down to dead downwind.

[Franziska]

Looking at the above, the forefoot looks fairly low volume, the sterns pretty full.
Exactly as to be expected on a power cat.
I doubt that the forward volume will be enough for a rig. Still without seeing a linesplan this is guesswork based on a photo.

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 .

[valhalla360]

Originally Posted by ranchero76

highly skilled engineer of most trades has MONTHLY salary is $400-$600.
In first post I stated that I would do all or most work myself, so most spending would be on engineering, used mast of proper size and materials, hardware, right?
That's answer to these who "can't even estimate conversion cost" but still want to know my budget.

Where are you finding these $500/month engineers? I do some work with our foreign branch offices (not marine engineering). Some of the lower tier engineers just starting out make around $1500/month. They are nice guys but not even close to the same level as I would expect in a western country at the same experience level...they take direction well but thinking outside the box is not even close.

Cobbling together a quality system that will sail well from a bunch of used junkyard material...yeah, that's the ticket...

[valhalla360]

Originally Posted by ranchero76

I don't see much difference from sailing catamaran hull. It even has mini-keels, even though strange ones, very long. Would be good for beaching I guess

That picture isn't much more than our Gemini showed when the boards were retracted. First time we took it out sailing, we did 3-4 tacks trying to go upwind and making at track on the GPS 90 degrees to the wind direction...then we remembered to put the boards down.