Catamaran hull difference sail / power

[Fanie]

Thanks all, Tuks you have outdone yourself with these links ! Looking at the article on the hull shapes, why doesn't sailing catamarans also adapt the Bobcat hull with HySuCat foils ?

[tuks]

You mentioned foils, Douglord will be here soon. I think for sophisticated and highly developed craft foils might be an option, but im a firm believer in the KISS principle. Less stuff to maintain and replace when it breaks.

I hope those links will help. I find this stuff very interesting and have learnt a little bit of the basics of why hulls are shaped the way they are.

I found it interesting is to look at drawings of existing boats to see the difference between hullforms of powercats and sailingcats. The rockerline is very different. There are a bunch of drawings on the the Schionning designs website. www.schionningdesigns.com.au

[Fanie]

After some reading and more reading and then some I've come to the conclusion that it would be better to keep the sailing hull's. While you may not be able to plain the cat at speed with outboards, the water piercing shapes of the sailing hull's still can make good time.

The next question would be what size outboards should one use. Yeah yeah I've seen the new 300'ds, but hardly peactical in my case

It seems most of the cats have 9 or 10 hp outboards, but that probably is just for maneuvering, still, it would be nice to know what speeds a couple of those can achieve on a cat.

Smaller motors tend to be more fuel efficient and easier handled if you don't have power trim and tilt and I don't think one needs to overpower the idea. I was thinking in the range of two 28 to 40hp motors. Don't worry about the steering for now, I'm sure there's an easy way to do it.

Could any one dare an opinion as to the speed one can expect ? 8m x 5m sailing cat hull

[Basjan]

Hi Fanie

First get the design you like and then worry about motors.

The hull design would be the factor that influence your decision iro the amount of power required to move the boat.

In general most local manufacturers will advise that minimum power for a 21' powercat is 2 x 50hp.
I'm no expert, but it stands to reason that a sailing vessel will require less power to get moving than a power boat and you would therefor be able to down scale on the motors.

PS - If you realy want your boat moving, bring her down here. We have wind, fish, sunshine, wind, wind, wind and more wind.

[Fanie]

Hi Basjan, I'm attempting to bring a couple of things and ideas together to paint the picture. Be patient, there's a lot of unknowns that still needs coloring in. I have in principle already decided what I want, but not carved in stone.

Personally I hate the wind. When lure fishing it is the only single element that can bugger your day up. Now I know it's different at the coast. If there's no wind there's no fish. If the wind blows the fish bites, so it's different. Best sea fishing ever was in rainy, wind blowing, really miserable weather. Never been so wet in my life Amazingly how much water some clothing can hold. Best way to lose weight quickly is to get undressed.

Bottom line is if you keep the wind down there where it counts I'm happy with it.

I still have the question - What speed can one expect with wat size motors on an 8m x 5m sailing cat hull. Surely someone must have an idea of at least their own rig ?

[Basjan]

Hi Fanie

Were trying to get rid of the wind here, can i send you a couple of truck loads to get you started?

[Fanie]

Getting rid of the wind is really easy !

Just put up anything that will work off the wind, like a wind generator - the wind won't blow for at least three days.

[Basjan]

Their planning to build a windfarm here to generate electricity so maybee we will have more nice fishing days.

Have a gander at Super Cat's new "Sliver 29". It's a displacement cat but resembles a sailing cat. Minimum is 2 x 25hp, the test model was fitted with 2 x 40hp and reached 22 knots.

http://www.supercat.co.za

[Fanie]

Thanks Basjan, nice link and I must say nice boats too. I'm not even going to ask what such a boat retail for. My Yamaha 115's CDI packed up and I'm really PO about it. After working the rubber potting away I can see about 6 solder joints that was never soldered. The spares used will probably come to R100, yet a replacement CDI is around 5K ! Pathetic and rediculous.