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

I just paid over £800 to service my two 40hp yanmars.

There's one big reason to consider any single engine options such as one engine with two drives driven by hydraulics.

Cheers

Garold
 
This note is opening a two year old thread, so please excuse if wrong place for it.
Discussion of Cat engine configuration- most helpful, thanks.
During the discussion, one person inquired about twin outboards off the transom.
Another member responded that engines off transom are difficult to brace [bracket] adequately, difficult to raise/lower. No further comments were offered. This post is to request more detail, please:

Questions:
Should one be able to adequately engineer brackets for both cat hull transoms, and should he rig a reliable raising method [mechanical or electrical]- what then are thoughts regarding twin outboards?

Here are the advantages I can imagine:
free crawl thru space [no diesels];
more room in cockpit [no single outboard];
less noise;
less fumes and smoke;
advantage of twin engine redundancy;
cheaper to repair;
cheaper to replace;
probably no more expensive to run;
most compelling of all: simplicity compared to diesels and
adequate power battling a sea over a bar.

Here are the problems I can imagine:
-WEIGHT ON TRANSOM
I do not currently own a cat, my experience is monohulls exclusively.
But i have learned that weight, and perhaps more to the point, weight distribution, is of prime importance. In case of twin outboards, you have significant weight, plus leverage, clinging outboard of the stern- like having two men standing on edge of a boat's swim platform.
Could this be disastrous- slowing stern from rising to steep waves, or lowering stern to breaking following sea?

Another consideration: the transoms are not designed for supporting engines.
Perhaps they would need beefed, at hull/transom joints, hull/deck joints, etc?

May I ask for any and all comments, suggestions, warnings or experience.
All opinions most welcome- am looking at an Heavenly Twins that needs repower.
[Yes, I know they are plodders- but plodders compared to other cats or plodders compared to equal length monohull?]

Thanks to all.
 
4Henry said:
This note is opening a two year old thread, so please excuse if wrong place for it.
Discussion of Cat engine configuration- most helpful, thanks.
During the discussion, one person inquired about twin outboards off the transom.
Another member responded that engines off transom are difficult to brace [bracket] adequately, difficult to raise/lower. No further comments were offered. This post is to request more detail, please:

Questions:
Should one be able to adequately engineer brackets for both cat hull transoms, and should he rig a reliable raising method [mechanical or electrical]- what then are thoughts regarding twin outboards?

Here are the advantages I can imagine:
free crawl thru space [no diesels];
more room in cockpit [no single outboard];
less noise; Expect twin engines to generate more noise, not less.
less fumes and smoke; Probably more.
advantage of twin engine redundancy;
cheaper to repair; Outboard engines generally have half the life of diesel.If not specifically designed and tuned for this application.

cheaper to replace; Have you looked at the price of outboards including running cost, indtruments and other fittings like trim tabs.
probably no more expensive to run;The cost petrol and the economy is much cheaper with diesel.
most compelling of all: simplicity compared to diesels and adequate power battling a sea over a bar.

Here are the problems I can imagine:
-WEIGHT ON TRANSOM Only when static, trim tabs control the amount if lift under power.
I do not currently own a cat, my experience is monohulls exclusively.
But i have learned that weight, and perhaps more to the point, weight distribution, is of prime importance. In case of twin outboards, you have significant weight, plus leverage, clinging outboard of the stern- like having two men standing on edge of a boat's swim platform.Trim tabs.
Could this be disastrous- slowing stern from rising to steep waves, or lowering stern to breaking following sea? Trim tabs.

Another consideration: the transoms are not designed for supporting engines.
Perhaps they would need to be beefed up, at hull/transom joints, hull/deck joints, etc? Best if designed that way first, but impossible to retro fit.

May I ask for any and all comments, suggestions, warnings or experience.
All opinions most welcome- am looking at an Heavenly Twins that needs re power.
[Yes, I know they are plodders- but plodders compared to other cats or plodders compared to equal length monohull?]

Thanks to all.
Click to expand...

We have atwin engine cat, each engine compartment has it's fore and aft bulk head, access is via a large deck hatch, air suply is via individual dorades, not even wiff of oil or diesel on board.

Good luck and fair winds.
 
A belated reply to Lazy Kipper, the only time a Heavenly Twins is faster than an Anderson is off you drop the HT from a Hercules...maybe a case of dodgy PY's again.

4Henry,

other problems I foresee are,

the outboards would be vulnerable to following seas & pooping, they would also be vulnerable to damage in port, and may well collect things like shore lines when rafted up; I have seen the controls torn off a transom hung outboard when shore lines got it as the tide went out alongside a wall.

The fuel consumption will of course be a great deal higher too.

However if you understandably baulk at the cost of two diesels, the twin outboards seems an idea worth pursuing; at my club there's a big modern ' Maldives ' cat with a central outboard, and manouvering is a nightmare - one might as well use a ouija board !
 
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Twin outboards on the stern is a bad idea I'm afraid. On the HT the transom is a long way above the water but the outboard pod in the centre is much lower, better to investigate a cockpit mounted o/b similar to the standard HT o/b configuration.

Early diesel HT's were fitted with just one diesel and it needs a tiny amount of rudder to correct the turning force.

Removing the diesels doesn't free up any useable space on an HT before the Mk4 because the space is used for bulkheads and supports, you won't get a crawl space in there.

An HT is a plodder compared to some other cats of its era e.g. an Iroquois which is a bad design that requires a float at the masthead and is almost solely responsible for the mistaken fear people have that a cruising cat will capsize. But hard on the wind it makes far too much leeway and even an old Anderson 22 will overtake you, hard on the wind and in a seaway my dog doing the doggy paddle will overtake you. But crack it off to 50 degrees and she comes alive and it's fun and rewarding sailing but with very little of the feedback you get from a monohull. Nice boats, about 500 made which tells its own story, unlike some marques where production fizzled out at about 100 :eek:
 
I would suggest that desirability for engine ranking on cats is 1 twin diesels with shafts/saildrives 2 An outboard with power trim/tilt and steeering linked to the rudders 3 a sonic leg and diesel outboard. Modern outboard engines are almost as economical as diesels on fuel usage and cost much less when you take account of drive shafts, gearboxes, intake filters and exhaust systems.
 
4Henry... Not a good idea at all. In big seas the engines would probably be getting swamped one second and then the props out the water the next. There are very good reasons why 99% of cats have twin inboard diesels.
 
dancrane said:
I must have been half-asleep for three weeks...the point I'd meant to make latterly, was that a Heavenly Twins I saw for sale, has a pretty big (20hp) centrally-mounted diesel, which powers a pair of hydraulic drives, one in each hull.

View attachment 22640

So...great engine access (it's in the cockpit), no vulnerable outdrive-leg, full manoeuvrability of a folding propellor in each hull, but a lot less weight than a pair of smaller diesels. Plus this option frees the considerable hull-space the diesels take up in twin engine versions...

...I'm just wondering how effective/efficient/reliable the hydraulic drive is? They're certainly compact. Not common, though.
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Fiend with Heavenly Twins binned the central outboard and fitted twin hydraulic drives with Beta inboard as you describe. Said it transformed it.
 
If I were designing a new cat I think I would go for twin diesel outboards mounted on the rear beam just inboard of each hull so they can be lifted out the water both by way of normal tilt and also raising/dropping the actual mount. ... assuming there is a bit of a distance between the aft beam and the back of the transoms... That way you would have a clean underwater when sailing and be able to drop the motors down for motoring.

There was a cat called Sula with this sort of arrangement next to us im Plymouth a couple of years ago. They had designed the cockpit to use the engine covers as part of the working space so the whole arrangement was very neat..
 
GrahamM376 said:
Fiend with Heavenly Twins...
Click to expand...

There's a lovely irony in that. Sounds like a sex-murder headline. ;)

Can't believe it's two years since I started this thread. I'd lately persuaded myself that a Heavenly Twins would be most economically, space-efficiently & weight-efficiently powered by a 20hp Tohatsu turning a big prop, mostly at half-revs. The weight of a pair of Yanmar 1gm plus their batteries and tankage must be a quarter-tonne, and the HT hates weight.

But, respect to Lazy Kipper who has answered many of my queries about the Heavenly Twins. And I'm sure five minutes spent berthing two catamarans, one with a prop in each hull, the other with just one amidships, would overwhelmingly justify the two-prop decision, whether by hydraulic drive or two separate engines.
 
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Jeannius said:
4Henry... Not a good idea at all. In big seas the engines would probably be getting swamped one second and then the props out the water the next. There are very good reasons why 99% of cats have twin inboard diesels.
Click to expand...

Agreed, our central o/b was about 6 foot back from the stern and in big steep seas the prop would leave the water at limes, on the stern with a cat's hobby horsing it would be a nightmare.
 
Have a look here.

http://www.schionningdesigns.com.au/

I know this guy well and have races some of his mono hulls, bloody fantastic builder and designer, was stationed in Mackay Queensland Australia many years ago.

Have a look at the Prowler power cat and other models shown.
Go down to the drawings and design details.
You can purchase the panels and build one yourself or have built for you. I had a but more thab hand in building two of them.

Also look at the pec's. 650 mm draft, up to 22 knots and 1.90 mm head clearance in the hulls and saloon as well as a fly bridge., sleeps 7 on 3 doubles and one single. filly moulded interior fit-out.

And they look very nice not like most power cats.

Yes I an a big fan of Geoff's work.

Good luck and fair winds.

PS. some of his cats have outboards, some mounted internally like sail-drives.
 
Lovely to have lots of ideas on these questions. If I may be bold, however,

Personally, I don't think the answer matters too much, whatever you got, it's practice (as always).

Personally, I sailed thousands on a couple of different Prouts. Enjoyed every bit, using that out drive leg was a challenge but as I learned, grew to enjoy every mooring challenge!

Sailed twin engine cats, delivered one, for example, St Lucia to Croatia, several pit stops, two engines. Lovely, similar to twins in a Mobo. But all take practice.

I would choose the boat I like and make it work for me.

Good luck with whatever you choose!!
 
Tomahawk said:
Seajet...

you need to get your head round the fact that 22 ft is the ideal beam not length..
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bigwow said:
I would agree, that is until it's time to find a travel hoist!:disgust:
Click to expand...

Not a problem!

launch.jpg
 
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