Drive options for displacement powercats
Bob, et. al.
Do the Volvo Penta IPS and Cummins Zeus drives fit within the same category as the outdrive, with respect to most of the advantages and disadvantages you discussed? Yes, it is my understanding that they cannot be lifted out of the water while moored or docked, and the corrosion potentials may yet be unknown.
Do they have trim capability? Does one lose efficiencies if the drives are protected by a skeg in a fashion similar to standard inboard propulsion arrangements for trawlers? Some tug bots have Z-drives; how are these drives protected from the occasional dead head or submerged shipping container?
The fore-aft trim problem would seem to be better resolved with a Zeus type of arrangement, as there would seem to be greater design freedom for the naval architect with respect to engine placement.
The photographs that I have reviewed also show a more spacious engine room with this design, due to a more compact propulsion unit.
Thoughts and comments greatly appreciated.
Gill
--
The Volvo IPS drive units are bronze not aluminum, so corrosion should not
be an issue. They do not trim, only rotate, but the clever control system
means they can drive the boat in any direction, no thrusters are needed.
They only suit fast boats at the moment as the smallest units are in the 300
HP range, and they only come as twins.
The propulsive efficiency is about the best you can get, due to the forward
facing props, as in most prop driven aircraft. But they are very vulnerable
to damage from grounding or debris. Volvo says they are designed to break
away in such an event, without leaving a hole in the boat. All very well,
but how costly it must be to replace that beautifully machined lump of
bronze!
My own choice is a true inboard with an enclosed shaft in front of a rudder
which is hung top and bottom. In other an arrangement similar to what most
single screw trawlers have. It can be applied to any type of boat if
considered at the design stage. It should be able to take the ground without
damage.
Kind Regards,
Grahame Shannon
2101 Philip Avenue
North Vancouver, BC V7P 2W5
Some years ago, some of the better RIB's (Otech Marine for example) were putting a diesel in the center console with a jack shaft to an out drive to provide much improved balance and weight distribution. Not likely an option in "cats" due to space utilizations, but in commercial applications maybe. Made all the difference in the world in rough weather, high performance use. A little more maintance for a jack shaft, but well worth it.
-----Original Message-----
From: gill.tt@comcast.net
To: power-catamaran@lists.samurai.com
Sent: Sun, 27 Apr 2008 11:36 am
Subject: [PCW] Drive options for displacement powercats
Bob, et. al.
Do the Volvo Penta IPS and Cummins Zeus drives fit within the same category as
the outdrive, with respect to most of the advantages and disadvantages you
discussed? Yes, it is my understanding that they cannot be lifted out of the
water while moored or docked, and the corrosion potentials may yet be unknown.
Do they have trim capability? Does one lose efficiencies if the drives are
protected by a skeg in a fashion similar to standard inboard propulsion
arrangements for trawlers? Some tug bots have Z-drives; how are these drives
protected from the occasional dead head or submerged shipping container?
The fore-aft trim problem would seem to be better resolved with a Zeus type of
arrangement, as there would seem to be greater design freedom for the naval
architect with respect to engine placement.
The photographs that I have reviewed also show a more spacious engine room with
this design, due to a more compact propulsion unit.
Thoughts and comments greatly appreciated.
Gill
--
Power-Catamaran Mailing List