Power cat with sail hulls

[2farnorth]

Hi to all,
Is it feasible to use the hulls of a sailing cat in a power application? I do not want to plane, but was wondering about weight distribution and such. I assume I would just want to keep the weight centered and just aft of amidships? I want to build a trawler type cat, nothing fancy, just simple and reliable. Or is this a stupid question and I should just go back to my room.

[Manie B]

What size?
aplication?
power / speed requirements?

maybe we can get a better idea of what you are planning

[2farnorth]

36-40 foot, electric propulsion with a large solar array (see "SUN21") with a generator backup, 6-8 knot cruising speed, liveaboard for my wife and I.

[sabahcat]

Yep, that should work as it should have worked when it had a mast on it (assuming the original hulls would motor at around 6-8 knots)


This is, I believe, what Gen 1 French powercats basically were from the big production yards as they already had the moulds.

I am doing a similar thing with diesels, and in the last 15% of the hull, started pulling the underwatershape down so as to have a horizontal flat about 200mm underwater in the last 5 feet of boatlength to help prevent any tendency to squat in the 10-14 knot (max) range

[2farnorth]

[quote=sabahcat;243706]Yep, that should work as it should have worked when it had a mast on it (assuming the original hulls would motor at around 6-8 knots)


I guess the only thing I am concerned with (maybe I shouldnt be) is moving the cabin a bit foward and adding a flybridge. Just do it, right?

[sabahcat]

Ermmm, I found low speed powercats that were in production with similar hulls and displacement, that worked, then errmm, massaged their styling and cabin/ bulkhead positions somewhat to suit what I want.

I justified the moving the cabin Forward, 400mm from original sailing position, to be balanced by the slightly heavier engines.

I justified the extra cabin, engine and diesel weight by the lack of rig and winches and making boat 24 feet wide instead of the 28ft in sail format

[2farnorth]

sabahcat, sounds like if I justify everything in my head, she should float right on her lines No, I know what you mean. I think maybe I am over thinking this whole deal....I just need to build it and be done with it.

[Nolan Clark]

Have you takena look and the cats the Gougeon Brothers built. They based the hull shape on what they learned building Tris.
http://www.westsystem.com/ss/birth-of-the-gougmarans/
Download the article and check it out.
Nolan

[Steve W]

What sailing cat hulls do you have in mind? I assume you are thinking of using some existing hulls.If you go to Malcom Tennants website and read some of his articles you will find that he uses sailing cat hull shapes for powercats under about 10 meters. I see you just a few hours away from me.
Steve.

[2farnorth]

Nolan, thanks for the link, very informative. Those hulls would work perfect for the next 10 years as we will be restricted to week-end and short vacation cruising on the rivers up here in Minnesota/Wisconsin.

Steve W, I was looking at K-Design 860 because of the price of the plans and hoping to be able lengthen the hulls.

[MarboMan]

Check out PDQ Yachts.

The main problem that you will run into is in rough to moderately rough conditions, the props will be lifted out of the water.

[sabahcat]

Originally Posted by 2farnorth

Steve W, I was looking at K-Design 860 because of the price of the plans and hoping to be able lengthen the hulls.

This ?

http://www.ckdboats.co.za/kd860.asp

I'd be inclined to something like the pic if it was me (this is a KD860)

[Ernie Travers]

Hello 2farnorth,
basically the answer is "NO"
A lot of professional builders have done that with disastrous results, although they never realise it.
If you want to go over 11 knots, you should have planing hulls. Then you get efficiency. Displacement hulls only work on big long power catamarans.
Light weight good design is critical. Then you experience pleasure.

[2farnorth]

Hey Ernie, thanks for the reply, I ahve been off the thread for a while. I am not looking to go fast, If I got 10 knots out of a twin electric motor setup I would be happy. Does that change your opinion?

[PortTacker]

Originally Posted by MarboMan

Check out PDQ Yachts.
.

Im my opinion not a good example. The hulls are very flat aft and at any speed just dig and squat.