Sail Catamaran Engines - Diesel v's Outboard

[Cruisin Cat]

I've done quite a bit of single handed ocean sailing in cats with diesel engines...but never sailed a cat with "outboard" engines. I'm looking at buying a 40ft cat with outboard engines and would be very interested to hear from people who have experience with outboard engines on cats...what are the pros and cons of outboard engines, eg little or no prop wash on the rudders? In a big following sea, waves coming up through the outboard boxes? etc

[catsketcher]

Gday cruisin

You will get widely varying opinions on this question as it really does come down to the boat and the sailor.

I have a 38ft 4000kg daggerboard cat. I am a dinghy racer. For me outboards are a no brainer but my situation is a bit unique.

I started off in my cat with a single outboard on a pivoting nacelle. The nacelle pivoted really high out of the water when not in use. The system worked well for our first 3 year cruise - we sailed almost all the time and spent almost no time getting in and out of marinas.

Then someone stole the outboard with the nacelle. I built a new one to better suit our different cockpit - it was pretty terrible. It did not lift up when sailing and would bang in waves. The new outboard got wet offshore - I hated it.

So I made it lifting - but with the new cockpit I could only lift it 30cm above the motoring position - it was much better than nothing but still got me cranky sometimes.

So in the end I made two high lifting nacelles at either side of the bridgedeck which lift totally clear of the water under sail. They work beautifully although they take up some interior space - but I am very happy.

I love outboards as they are cheap, reliable and easy to service, but if your system is badly designed or built, then it could be a real problem. It depends on the system, even on the same boat.

[Captain Bill]

I've not personally owned one but have done a bit of sailing on a friend's Mainecat 30. His biggest issue was servicing them when something did go wrong. Getting access to them down in the wells was not easy getting them out of the wells was a real problem when away from home. When at his home dock he had an A-frame that he used but it was not practical to keep on the boat while cruising. Because of the lack of a true transom the electric tilt system seemed to give him no end of trouble as it was being constantly immersed in seawater. Propwash over the rudders was not a big issue when both engines as you could turn using engine thrust. One engine operation was a real problem until you got enough speed up for the rudders to bite. He replaced both engines once in the 10-11 years he owned it and as I recall he figured he got about 2000 hours out of them. The good thing was they were relatively cheap compared to a diesel. I don't know what cat you're looking at but I would definitely be concerned about service access and the ability to lift the engine out of the well unless you want to have the boat hauled every time you need to change the impeller or the lower unit oil.

[fxykty]

We have a cat with props about 70cm below the waterline and 1m ahead of the sterns (rudders behind the props). In rough sea conditions the props will ventilate as the boat pitches. With outboards the props are even more shallow, so unless you can move them forward so that they’re at the pitch centre - generally about 2/3 of the way back from the bows) - I’d be concerned with using them in rougher conditions.

That’s a question for those who have outboards on their cats.

[Tupaia]

As previous posters have said it depends on the boat. There are also diesel outboards and petrol inboards. Pros and cons of fuel type are secondary to that.


I have had experience of all four combinations and they were appropriate for the cat.

[catsketcher]

Originally Posted by fxykty

We have a cat with props about 70cm below the waterline and 1m ahead of the sterns (rudders behind the props). In rough sea conditions the props will ventilate as the boat pitches.
That’s a question for those who have outboards on their cats.

Again a problem with bad installations. With fixed nacelles you have duelling considerations of lifting the nacelles for better performance sailing and lowering for better performance in chop. That being said - I am surpised Fxykty motors much in a chop. Outboard cats often have daggerboards ansd nice rigs so they usually have good windward performance - so they don't motor much in chop - they sail. A slug with outboards would be a bad bet. I get some ventilation but we don't motor much in big chop offshore so it is not much of a prerequisite.

Some of the nicest installations are the ones in Bob Oram cats that have the outboard pod integrated into the chamfer panel - gets it low and protected from the waves in the tunnel.

[fxykty]

Originally Posted by catsketcher

…Iam surpised Fxykty motors much in a chop. Outboard cats often have daggerboards ansd nice rigs so they usually have good windward performance - so they don't motor much in chop - they sail...

Have to make a correction regarding how much we motor in chop - NOT a lot, because we do sail well in all conditions. But sometimes, a narrow pass or other situation precludes sailing so you do motor in waves. Or when picking up an anchor when the conditions have worsened. Was just making the point that rough waves can be an issue for relatively shallow props.