Waterjet Catamaran Powering

I am working on a catamaran project which is 18 meter long, 6 meter wide (Hull breadth is 2.00), draft is 0.8 meter. I have derived resistance data by Hullspeed using Savitsky planing hull prediction.

Got confused when contacted some waterjet manufacturer. The resistance data suggests to use 680 hp (Total, for the whole catamaran, I used the full model of cat, not half of single hull or full single hull) for a speed of 25 knots.

All are proposing to use more than 02x650 hp. Is it too much?

My question is what margin should I keep when using waterjets?

Any help? I suppose the experts in this forum will be able to help me before I come back from dinner

 

The all up weight?

Does the "Hullspeed" you use really include an algorithm for catamaran resistance? In older versions you could only check one (symmetrical) sidehull; no compensations available for wave interference in tunnel and so forth.

 

Savitsky method is for planing monohulls of shapes close to prismatic and can't be used for catamarans without corrections. You should look at Muler-Grag or Molland methods but those are not included in this 'magic software', have to develop Your own software or do it by hand.

Generally, for 18x6m cat displacement would be about 25,000kg that gives power requirement of 2x500HP minimum for 25kts of cruising speed if propellers are used. With jets, one needs even more power on such speed...