It seems many multi's today are motor boats with auxiliary sails...

[FLLCatsailor]

I would say 90% of cruising boats are "motor sailors".

[Kettlewell]

Sheesh, I guess my 135 HP on a 30 ton boat is just overkill then.

Keep in mind the Hiscocks first circumnavigated in Wanderer III, displacing around 9 tons, with a 4 HP 2-stroke gasoline (petrol) inboard!

[motion30]

have you ever heard anybody complain ..........my boat has too much power ?

[44'cruisingcat]

IMO it's just a reflection on how people use boats these days - generally on weekends and holidays, so time limited. There's a percieved need to be able to get to places in a timeframe regardless of the weather.

[downunder]

The Neel trimaran has 75 HP so I suspect that is a minimum starting point for a 60ft trimaran.

I would venture perhaps 100hp is needed.

[Jim Cate]

Originally Posted by Factor

It isnt just the size, its also the placement of the weight, some boats have their motors so far back that props are behind the rudders and the the 50hp 200kg lump that far back needs ridiculously fat hulls. But it makes for lovely aft cabins. To each his own, but I am with you Pipeline, a sail boat should be a sail boat. I have 10hp (9.9 actually - yammie outboards) a side, its plenty and being outboards means I can have big meaty props and not worrying about drag when sailing.

There is no doubt many of the current crop of boats are designed around charter and or carrying unneeded crap. If thats your bag then fine, but i often wonder why some boats bother with a mast.

So, Factor, it seems that you endorse the one h/p per tonne theory... I think.

And to support that endorsement, you note that your cat has "only" two 10 h/p outboards.

I didn't realize that Seawind 1000 cats weighed 20 tonnes!

In reality, I reckon that you have something nearer 3 h/p per tonne, perhaps even more if you keep her light.

Just sayin'...

Jim

[valhalla360]

It seems many multi's today are motor boats with auxiliary sails...

And that's bad because?

We are looking to ship our Gemini to Europe in a year and are seriously thinking about leaving the mast at home since our plan would be to spend most of our time exploring the canal system with just short periods on the Med.

We've been full throttle going up a 30' wide 1/2 mile channel into a marina making 2kts vs 40kt head wind. No chance of tacking up the channel. If we replaced our 25hp with an 8hp, I think we wouldn't have made it up the channel. I suppose if you want to take the purist approach, we shouldn't have been staying at a marina in the first place.

[Factor]

Originally Posted by Jim Cate

So, Factor, it seems that you endorse the one h/p per tonne theory... I think.

Nope

And to support that endorsement, you note that your cat has "only" two 10 h/p outboards.

Simply to indicate that it has less than some of the more sedate cats

My point isn't so much the HP - its the weight of the engines and the placement of that weight.

[44'cruisingcat]

Originally Posted by downunder

The Neel trimaran has 75 HP so I suspect that is a minimum starting point for a 60ft trimaran.

I would venture perhaps 100hp is needed.

You could be right. Wild Oats 11 has a 150hp engine, and it only uses that for "sailing".

[tuskie]

Originally Posted by Factor

My point isn't so much the HP - its the weight of the engines and the placement of that weight.

I agree.

Read books by the Pardeys and Hiscock and sail wooden boats sealed with Stockholm tar. Eschew all things electronic! Lead lines instead of echo sounders. Hemp not that new fangled stuff! Sail into and out of moorings and flog the crew if they can't! Real engines are diesel and made by Perkins, Gardner or Thornycroft.

The real world, the 21st century, cruising multihulls, reliable outboards and lightweight diesels (such as Monte's) are still unimagined.

Avast, me Pardeys!

[TeddyDiver]

Originally Posted by nimblemotors

Gasoline. A direct-injected 2 stroke engine is 1/4th the weight of a diesel.

It was not about the engine weight. It's the stored energy ie batteries vs diesel vs gasoline etc
BR Teddy

[downunder]

Originally Posted by 44'cruisingcat

You could be right. Wild Oats 11 has a 150hp engine, and it only uses that for "sailing".

[Jimbo485]

It's about windage on a multi, not the displacement.

Twin 8 HP, 5.5 or 6 tonne displacement, means at least 2.7 HP/tonne. And yet we can't motor directly into a consistent 30 knots. We have to tack or sail. Why? Because it is the windage, not the displacement, that matters and our outboards are small.

[Caracal]

I don't see a problem with people poking a bit at modern boats being defacto motorsailers. Pipeline, the OP, has obviously chosen a sailing machine for himself (I'm not envious. No, not at all, lol), and I bet he uses it for sailing first and foremost. However, he is talking about engine and sizes of engines, and I don't see him poking fun of "motor sailers".

What I'm saying, is that a discussion like this, where we are in effect talking about some "sweet spot" with regards to weight vs. power (weight of engine and weight of boat), of course things like "sail when you can" crops up. I don't see these comments as bad. Not at all - even if the OP has a real machine designed for sailing.

However, he is also one who wants enough of a mechanical push for his boat when he's not sailing, but at the same time doesn't want to carry unnecessary weight around. Being a perfectionist myself, loving to think out "best solution scenarios", I can definately relate.

Could you (Pipeline) perhaps go back to the designer of your boat and ask about (windage) area of the boat when dead on, 15 degrees off of the bows, 30 degrees and 45 degrees off of the bow, in order to get some working numbers that one could compare to windspeed forces? I mean, with that in hand, it should be possible to calculate rather precisely just how many kWs of "push" was needed at the propeller, and by extension what kind of horsepower was needed to achieve that.

[nimblemotors]

That your boat? Is there more pics or description, would like to know more about it!!

If you have gone to all the expense of carbon fiber to save a little weight, why would you put some big old fashion heavy diesel engine lump in it? If not electric, at least something light. This 120hp jetski motor I have is 95lbs,
and of course, you don't need to use 120hp from it.