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Old 19-08-2010, 01:13   #16
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I was wondering if it is possible to upgrade the engines on a catamaran to ones with a higher cruising speed.
Back to the original question. If you want a cruising speed above hull speed, then you are really going to pay in weight and fuel.

Whata didn't ask about riding out a hurricane, he just wants to go faster.

George
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Old 19-08-2010, 01:46   #17
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Not to many sailing cats work that well as faster speed powered cats as they tend to squat in the bum.

This can and has been overcome on some production cats that have been modified for power (lightwave, perry as an example) by reversing the rocker in the last couple of metres and making a flat.

This is what I have done to my hullshapes, plan on 10 knot cruise @1800rpm 55hpx2, 14knots on the perfect day at full noise 2600rpm 65hpX2

Even so, these vessels work best at up to 14 knots, after that, you really need to change hull-shape to a full blown displacement powercat type (double canoe ends with bustle)like Tenants IMHO.

There is a good article that I will try to find by Tenant where he discusses performance of sailing cats under power and where they start to become inefficient

here it is
Quote:
http://www.catamarans.com/news/2006/...comparison.asp

and a snippet from the article

"When many of the French catamaran companies decided to get into power cats they just fitted larger engines into their sailing hulls, probably because being production boats they had the moulds handy. This is fine as long as you are not going to exceed around 15 knots. Beyond this speed the hulls start squatting and assuming a bow out attitude. The sailing boat hull form is not really suitable for a displacement power cat with any performance or long range aspirations. They are essentially trying to go up hill and require increasingly large amounts of horsepower to move."
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Old 19-08-2010, 15:44   #18
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I have the upgraded engines in my cat, though that's a matter of small degrees. The options are 18 hp each or 30 hp each. Glad I have the 30's, but I don't think I'd need much more...
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Old 21-08-2010, 04:34   #19
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Originally Posted by winds aloft View Post
I have the upgraded engines in my cat, though that's a matter of small degrees. The options are 18 hp each or 30 hp each. Glad I have the 30's, but I don't think I'd need much more...
I have a pair of 1GM10 Yanmar diesels and would be absolutely thrilled to increase the engine weight by 27lbs an engine by installing 2YM15s and consider the issue solved. However, I will agree that increasing emergency power is one thing and trying to turn a sailboat into a power boat is a completely different kettle of fish.
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