Catamaran propulsion setup

[kingfisher]

Following a discussion in "Why have a forum", I always wanted to post the following question:

With cats, why not use the following setup:
A central diesel engine that delivers electrical/hydraulical power to two units in each of the hulls. Would this not be a more economical option then a diesel engine in each hull?

Or a diesel in one hull that drives a prop and provides electrical power to an electrical engine in the other hull.

 

[snowleopard]

yes, it does work and it is done reasonably frequently. some Heavenly Twins models were built that way.

the disadvantages are: when you put one gearbox in neutral the other doubles its speed which can make manouvering exciting. the engine has to be mounted high up affecting stability, making it difficult to get the cooling water to it (impeller pumps don't have much suck) and taking up cockpit space.

there are efficiency losses, also the capital cost can be high.

 

[jamesjermain]

It's a good question. Various alternatives for powering cats have been experimentedd with over the years but builders have always returned to the diesel in each hull configuration for anything other than small cats when either a central outboard or twin outboards are the preferred option. Even Prout eventually abandoned their steerable central leg.

One problem with a single, central engine is finding a suitable place for it. The bridgedeck is usually not deep enough unless an intrusive box is created. Noise and vibration are greater. Also in British waters, the heat of a diesel under the after cabin bunks is a bit of a bonus!

The losses in the hydraulic drive and/or electrical connections would be significant and hydraulic motors, though generally reliable are not cheap to fix when they do go wrong.

The advantages of having two engines is also a factor. If one breaks the other will get you home, plus you have two charging circuits, two fuel systems etc.

 

[mikewilkes]

Catfishers were built with a single engine, on the bridgedeck just inside the accomodation.
I use a single outboard in a well just fwd of the transom. But I am trying to find a decent mounting system on the transom so that I can fit 2 engines.

 

[ShipsWoofy]

When I replaced the engines on my Heavenly Twinge in 2002 I looked at hydraulic drives from a single motor mounted in the cockpit.

I asked on many forums including the owners association and no one said it is a great idea. As well as the intrusion and weight issues that JJ stated I was told the drives were inefficient and required a much larger engine to obtain the same power as two small inboards. The drives are also very noisy apparently. There were no real weight gains for this set up either.

There may be new quieter more efficient drives, but with my budget twin 1GM10's was the cheaper option.