Propulsion system for a high speed trimaran

[boat88]

Hello,
I try to find the best propulsion system for a high speed planning boat,its a trimaran with these characteristics

Length=10m
Beam=5m
Maximum speed=60 knots
Cruise speed=50 Knots
Weight=4.5 ton

but i have problem to decide between stern drive and outboard propulsion systems.
Also i want to know how many propulsion systems is more proper for this situation(i.e. 2 or 3)?
Thank you.

[Jameswright4]

A sterndrive is much preferable.

We have two outdrives on the outer hulls of our yacht and the problems are as follows:

1. 40% Power is lost by the distance frm the shafts to the legs to the engine in the aft cockpit (Yanmar 55 which drives the two legs which hydraulically are raised and lowered)

2. Noise is increased via vibration as transmitted through the drive shafts. ..Makes more noise than the engine!

3. In a heavy sea the legs often come out of the water yet the props still spin
and thuis makes for more inefficiency.

A sterndrive with moveable twin props takes care of all these woes.

To see my boat enter LARINKA into Google and up she comes or check out
www.planesail.com and see the utube video.

Hope this helps James Wright

[boat88]

Dear james,
Thank you for your reply, you helped me so much, would you tell me which outboard motor do you use?

[Jameswright4]

Do not even think about it......Volvo and Vetus combination
and all non standard as not meant to lift and lock in positions designed.

Focus only on Stern drive and if possible depending on size also fit a bow thruster.

A fixe wing evne when feathering doe have a little bit of movement in tight manouvering such as coming in to dock. ..takes experience from inside control cockpit to judge width for our boat is 9 metres wide.

[Speng]

for 60 knots you probably want to go with a surface piercing drive like Arneson or something like that. Like the offshore powerboats use.