Catamarans: better with an engine in each hull, or a retractable sail-drive?

Greenheart

Greenheart

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I was looking at two old Prouts for sale. The larger of them had a diesel in each hull, shaft-driving props in the conventional way. The other had a single, centrally-mounted diesel and a saildrive-leg that swings out of the water. Is one way markedly better than the other?
 
dancrane said:
I was looking at two old Prouts for sale. The larger of them had a diesel in each hull, shaft-driving props in the conventional way. The other had a single, centrally-mounted diesel and a saildrive-leg that swings out of the water. Is one way markedly better than the other?
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The single engine will possibly sail quicker but the twin diesel one will be better in the marina unless the single engine one has a bow thruster.
 
Grey hairs

I'd imagine cost is a factor too; however I know someone with a big modern cat with one engine on the aft beam, he had an interesting time getting it through the French Canals...
 
It is unlikely you will get proper counter rotating props on a small engine and gearbox... So yes you get better manourvability with two engines but not as good as it cound be...
 
We have twin engines with sail drives and counter rotating stainless props, very easy to control in close quarters like marinas and picking up moorings etc.

The single engine would sail a little better with less drag with the prop out of the water, but cats are very prone to windage with high sides and very little in the water.

Good luck and fair winds. :)

PS They will happily run on one engine if the other fails.
 
dancrane said:
Is one way markedly better than the other?
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Yes!

A twin-engine setup is vastly superior for several reasons:

  • With saildrives and folding props the extra drag of a second gear leg is negligible.
  • Two props set a long way apart (in my case 17 ft) mean you can turn in your own length. You can also make the boat go sideways. A steerable centre leg does help but will never be as good as twin props.
  • Props slung under the hulls never cavitate so you can motor to windward in any weather. A central leg will pop out from time to time however deep it is.
  • Twin engines mean there is another to use if one fails.
  • For economical motoring or motor-sailing you can run on one engine (the windward one when motor-sailing)
 
dancrane said:
I was looking at two old Prouts for sale. The larger of them had a diesel in each hull, shaft-driving props in the conventional way. The other had a single, centrally-mounted diesel and a saildrive-leg that swings out of the water. Is one way markedly better than the other?
Click to expand...

had one with a Sillette outdrive leg. Found it was excellent at marina manoeuvres - after a bit of practise I could effectively move the boat sideways if there was little wind. And it had three major plusses:

1/ only one engine to service , repair etc
2/ prop out of water added half a knot min
3/ easy to deal with rope or net round prop.

Only disadvantage was that it was a bit agricultural.
 
I have owned both. Frankly the sillette legs are a bunch of **** engineering wise. They are always in need of service regarding pivot points and locking mechanism and are very very noisy. The only advantage of the damn things is that you can raise them when not sailing and if you get a rope around the prop. However, be warned that I once got a rope around a prop and it tore the leg completely off its yoke. The castings are very poor and pourus and break easily! Twin engines are far better but like all sail drives you need to be assured that the rubber gaskets are in good condition and there is no water getting in the engine bay because it can corrode the sump and cause big oil leaks. For manouvering the twin engine configuration is also far better and you dont need contra rotating props with them that far apart. The ideal set up IMHO is twin engines with brunton autoprops. Perfect!!
 
boatmike said:
The ideal set up IMHO is twin engines with brunton autoprops. Perfect!!
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Mr Brunton himself advised me not to fit his props to my boat. When feathered they still produce a lot of torque and, at speeds easily achieved when surfing, could bump-start the engines!

The price for two of them is pretty scary too.
 
snowleopard said:
Mr Brunton himself advised me not to fit his props to my boat. When feathered they still produce a lot of torque and, at speeds easily achieved when surfing, could bump-start the engines!

The price for two of them is pretty scary too.
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Interesting, especially as I had a good experience with them. The sailing performance was easily as good with them fitted as the old saildrive duck bills and simply putting the engines in gear kept them feathered OK but yes they are extremely expensive but as your boat is more high performance than my Prout was then that might make a difference. As the question was regarding a Prout though my opinion, based on experience would not change.
I see we agree entirely regarding twin engines though which was indeed the OP question.
Also I might add that although not a fan of the Sillette leg there is absolutely no chance of it coming out of the water on a Snowgoose!
 
snowleopard said:
Yes!

A twin-engine setup is vastly superior for several reasons:

  • With saildrives and folding props the extra drag of a second gear leg is negligible.
  • Two props set a long way apart (in my case 17 ft) mean you can turn in your own length. You can also make the boat go sideways. A steerable centre leg does help but will never be as good as twin props.
  • Props slung under the hulls never cavitate so you can motor to windward in any weather. A central leg will pop out from time to time however deep it is.
  • Twin engines mean there is another to use if one fails.
  • For economical motoring or motor-sailing you can run on one engine (the windward one when motor-sailing)
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Good answer...would you be kind enough to explain why one would motorsail with the *windward* engine? Obviously to counter weather helm and point higher but how exactly? Thanks. I am not arguing just interested. I live on a mono but crewed 2000M on an Outremer 55 and loved it,a 10 ton boat with daggers with Porsche 911 acceleration! Cheers Jerry
 
jerrytug said:
...would you be kind enough to explain why one would motorsail with the *windward* engine?
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I wondered about this too...doesn't it make more sense to run the leeward engine, whose prop will never break the surface?

Presumably, there are folding propellors (other than the Brunton), which can be persuaded not to rotate in the flow? Can't a shaft-brake be applied, or a sailing clutch?

The more I look at catamarans, the more I'm always persuaded of their advantages. But I'm surprised that when the opportunity exists to enjoy the dependability & versatility of twin auxilliaries, most buyers (despite spending large amounts on new cats) plump for a single.

Has anyone tried running an Aquair generator at twenty knots, behind a cat? :eek: :D
 
Thread drift, out of a blue sky...

...not such a drift; still talking catamarans.

Reading about a big old Prout Quasar Espace, I see that the accommodation provides four double en suite staterooms...nice...

...but the bridgedeck saloon expects all eight to sit round one cramped little dinette...

View attachment 22139

...plus, the dining area's floor is 8" above the floor astern! Necessarily, I daresay, but presumably there's not much headroom around the table? An enormous 49' catamaran, 23' wide with a large rectangular bridgedeck area...yet the sitting space is like a 32' AWB. Why?

I know it was considered appealing, to locate the galley on the bridgedeck, rather than putting cook in one of the hulls. Appealing to SWMBO, who really had to be obeyed? Imagine how the saloon might be laid out, if the galley (bridgedeck, port side) was moved...

...suddenly there'd be room for a couple of well-spaced chesterfields and a decent-sized dining table, big Persian rug maybe? Individual chairs rather than GRP moulded benches? Something approaching style, instead of the cramped bargain-basement fit-out. :mad:

End of rant. I'd love one of those...to spend 18 months turning it into a 4-berth Gatsby-esque gin-palace. :rolleyes:

Ah! Just looked at the other photos of the same Quasar...which did put the galley elsewhere. Well done that man. The whole bridgedeck is improved thereby. :)
 
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dancrane said:
Has anyone tried running an Aquair generator at twenty knots, behind a cat? :eek: :D
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Not Aquair and not at 20 knots, but we did use a Duogen on our Prout quest 31 which put in more than enough wiggly amps at ordinary speeds and by the time we got over ten knots the batteries would be brimming so we would lift it from the water and go a little faster without the drag.
 
dancrane said:
I wondered about this too...doesn't it make more sense to run the leeward engine, whose prop will never break the surface?
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Heavens to Murgatroyd old chap, if your windward prop breaks free of the water on a Prout then you have a lot more than cavitation to worry about!

Two engines are the way to go because she's a cruising cat - lots of compromises, most of them very good ones.
 
How does J Wharram manoevre in the marina,strip off and request assistance. On a cat,it's all academic below 50',your cruising kit will over load her never mind 2 diesels. Trimmed badly by the arse end for easy turning=waste,but economical steaming through the doldrums,coool man
 
dancrane said:
......Reading about a big old Prout Quasar Espace, I see that the accommodation provides four double en suite staterooms...nice......but the bridgedeck saloon expects all eight to sit round one cramped little dinette......
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Older Prout designs made poor use of the space inside the boat, and look really dated now. The Prout Quasar when it was new I seem to recall a magazine article which said something like

loads of space and accomodation, unfortunate that a lot of the space appears to either be unuseable or still kooking for a purpose​

I think the 45 was their best design, and quite liked the Escale, but the interior was still old fashioned Prout. I suspect that is one of the reasons that the sales went down. Take a look at the Prout Manta 38 and its equivalent the Broad Blue 38, and then look at the Broad Blue 385
 
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