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

[monte]

my 30hp yanmars weigh 130kg each, tanks are 100kg each. the 15hp model is 20kg lighter x2. Do you suggest halving the HP to save 40kg? Not too sure about the point of the thread. One engine plus tank is just the weight of one of my fat friends. Probably be more efficient to sail solo

[Roy M]

I have a forty-foot trimaran, weighing about 12,000 pounds when loaded for cruising. The engine is a Yanmar 3GM30F, which moves the boat at hull speed (about 8 knots), for a weight of less than 300 pounds. This engine replaced the Volvo MD2B 25 HP engine that weighed in at over 500 pounds. The engine has a one-inch shaft (17 feet long, with intermediate pillar block bearings) and a folding Martec Mark III prop (16DX10P). The fuel tank is 55 gallons, weighing about 500 pounds when full. That provides a powered cruising range in excess of 1500 miles.

While, perhaps, over-stocking on the motorized options of fuel, it does offer a cruiser the chance to explore more isolated areas where wind may not be as available or where tidal currents must be reckoned with, for example, the Pacific Northwest's extensive fjordlands and islands.

If I'm in a racing mode (virtually never), I can always forego most of the fuel to reduce weight.

[David M]

Still, nothing beats Diesel for stored energy per pound (other than nuclear)...and stored energy per volume for that matter. It's not even close.

[Juniper]

I think it depends on if you are using one inboard diesel or two outboards, a pair of outboards gives you some good manuvering and could use a bit less HP, one inboard trying to dock in unfavorable winds could be tricky if under powered.

[nimblemotors]

Originally Posted by David M

Still, nothing beats Diesel for stored energy per pound (other than nuclear)...and stored energy per volume for that matter. It's not even close.

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

[Cheechako]

It depends on your intention. If you are a stalwart sailor (like th Pardeys) Then the most you need is something to get you out of the marina. a 4hp outboard will likely do it. OTOH, most cruisers just want to get from point A to Point B in a reasonable amount of time and comfort. My 42 ft catamaran had Yanmar 3GM30 engines and max props. These engines are really not 30 hp. They are more like 18 hp at reasonable RPMs. They were not enough for the boat at times. In strong wind gusts there were times when I could not turn the boat into the wind.... this gets kind of dicey when your anchor drags and there are boats all around you! If you cant respond to anchors dragging and wind properly because you choose to go "old school" with an engine that's only good to get you out of the slip on a calm day, then you should keep that in mind in anchorages and stay away from the crowd.

[ArtM]

This recalls my old complaint about how this "Cruisers" forum is often hijacked into a "Sailors" forum. Though I also greatly prefer sailing to motoring, the fact is that "Cruising" is about living and traveling on a boat, and it doesn't really matter how that is accomplished as long as it meets the needs and interests of the cruiser.

On past forums, I've referred to the "performance" of Lagoons, which has drawn some derisive commentary, but that fact is that a Lagoon is a big, luxury cruising yacht that is capable of traveling under sail alone. As you've pointed out, not all "sailing" cats are capable of that!

I've also said that if they made solar-powered motor boats, many "cruisers" would have no trouble giving up the sails. In fact, that is proving to be a reality as there are now people taking the masts off of cruising catamarans and creating solar-powered cruising boats

So sailing is sailing, and cruising is cruising, and often they overlap but they are not one and the same.

[Cheechako]

Originally Posted by ArtM

This recalls my old complaint about how this "Cruisers" forum is often hijacked into a "Sailors" forum. Though I also greatly prefer sailing to motoring, the fact is that "Cruising" is about living and traveling on a boat, and it doesn't really matter how that is accomplished as long as it meets the needs and interests of the cruiser.

On past forums, I've referred to the "performance" of Lagoons, which has drawn some derisive commentary, but that fact is that a Lagoon is a big, luxury cruising yacht that is capable of traveling under sail alone. As you've pointed out, not all "sailing" cats are capable of that!

I've also said that if they made solar-powered motor boats, many "cruisers" would have no trouble giving up the sails. In fact, that is proving to be a reality as there are now people taking the masts off of cruising catamarans and creating solar-powered cruising boats

So sailing is sailing, and cruising is cruising, and often they overlap but they are not one and the same.

Well said. My Lagoon 42 kept up neck and neck with a Perry designed 48 mono aluminum cutter even to destinations that were to weather. Dead to weather they had a slight edge, but if one tack was favored not so. Both boats heavily loaded. Not too sure about the newer Lagoons though.

[David_Old_Jersey]

Originally Posted by Caracal

Sorry, the rest is also good points, but I wonder if in such a big boat where weight still matters, but you have a very deep centerhull compared to a mono, if it would be an idea to consider not only a small (diesel) generator coupled to a (smallish) LFP battery bank, and coupled to a really miniscule electric motor. I mean, the torque in an electric motor is there from 0 rpm, so you wouldn't need to "oversize" as you would with a combustion engine.

Yes, it's a tad more complex than a direct drive diesel, but there might be a weight savings all up. And the diesel would definately live a bit longer, all things equal.

I really like the idea of Electric Power - just not (yet) enough to give it a go myself .

At least on 60 foot of tri would have plenty of room for solar!, might not even need the generator (unless wanted to power the domestics)..........the rest I guess would be down to weight and use and area (some sun!).....won't get 1500 miles of range in a straight line, but if yer can live with far less plus endless easy "refuels" then maybe. maybe..........

But for tried and tested likely that the Roy M approach (30hp of modern diesel in a tri) would be the winner - to shift a mono of similar length at hull speed would likely have approx 60hp onboard, and probably also be a bit thirstier.

Or Nuclear .

With boats lots of choices to mull through to find own solution - the trick to being happy with own choices is to not be oversensitive about what others do and what works for them.........internet and real life.

[Lucky Larry]

I'm still pretty green but when I heard that "gentlemen don't sail to windward" I took it to mean I needed the bigger optional engines to go to the places of my choosing. After all, they don't say we don't motor to windward.

We sail when the wind is blowing in our direction. If not, we cruise.


Lucky Larry

[Kettlewell]

I hate to say it, but in some ways a 62-foot tri needs a powerful engine more than a mono of the same length. The deeper mono won't blow around as much when going slow, and that's when some additional oomph is needed. Plus, with your beam you cover a lot of territory in a crowded harbor, and you just don't have as much room for error when say the anchor breaks free, the bow starts to blow off to leeward with a gust, and you don't have the horsepower to quickly get things under control. On the other hand, a cat with twin outboards can have good control with light weight, while still not dragging around props and shafts under sail. I think an outboard makes a pretty good auxiliary if you want to be closer to a sailing purist. I used a 9.9 HP Yamaha on a 32-foot cat for more than a dozen years. It was always a great feeling to turn off the motor and pull it out of the water when under sail--you could feel the instant gain in speed.

"gentlemen don't sail to windward"

I soon learned I'm no gentleman, because it seems like I do a lot of sailing to windward.

[Pipeline]

Thx for the comments, folks. You know, reading Hiscock (not that he is THE engine expert, by any means), but he recommended 1 hp for every ton of displacement in "Crusing Under Sail", yet in his later book, "Sou'West in Wanderer IV", he had a 61 hp Ford diesel installed in his boat which displaced 20 tons (though he added 2 additional tons to the keel, later). So, if my figures are correct, that's significantly more than 1 hp per ton.

[Kettlewell]

The Hiscock's final boat, Wanderer V, which they had designed and built for themselves, was about 39 feet, 11 tons, and they specified a 20HP engine. In Two Yachts, Two Voyages (copyright 1984), they wrote:

We believed that with a weatherly and easily driven hull, we did not need a very powerful engine, and working on the old British assumption (which I fancy is now quite out of date) that for an able sailing yacht one horsepower per ton of displacement should be enough, and that two horsepower per ton would be generous, we decided on a 20-horspeower engine for our 11 tons.

[P1PEL1NE]

Originally Posted by Kettlewell

I hate to say it, but in some ways a 62-foot tri needs a powerful engine more than a mono of the same length. The deeper mono won't blow around as much when going slow, and that's when some additional oomph is needed. Plus, with your beam you cover a lot of territory in a crowded harbor, and you just don't have as much room for error when say the anchor breaks free, the bow starts to blow off to leeward with a gust, and you don't have the horsepower to quickly get things under control. On the other hand, a cat with twin outboards can have good control with light weight, while still not dragging around props and shafts under sail. I think an outboard makes a pretty good auxiliary if you want to be closer to a sailing purist. I used a 9.9 HP Yamaha on a 32-foot cat for more than a dozen years. It was always a great feeling to turn off the motor and pull it out of the water when under sail--you could feel the instant gain in speed.



I soon learned I'm no gentleman, because it seems like I do a lot of sailing to windward.

I agree with you, Kettlewell. The tri is a carbon fiber cruiser/racer (45' beam), with a very clean bottom, i.e, few through hulls, no thruster etc...clean. So, the folks here are starting to convince me that by adding another 60 lbs of weight, I get a four cyl. - Beta (Kubota) 38 (38 hp) vs. 3 cyl. Beta 30 (30 hp). Maybe I can put my crew on a diet, and make up that 60 lbs...

[minaret]

Originally Posted by Kettlewell

The Hiscock's final boat, Wanderer V, which they had designed and built for themselves, was about 39 feet, 11 tons, and they specified a 20HP engine. In Two Yachts, Two Voyages (copyright 1984), they wrote:

Sheesh, I guess my 135 HP on a 30 ton boat is just overkill then. Except that it allows me to motor near hull speed at lower RPMs, where the engine is more efficient and will live longer. Every diesel has a sweet spot it likes to be run at, and if that RPM range of highest efficiency happens to push the boat quite well, that's a good thing. Another advantage of the big, heavy mono. Engine weight is a tiny fraction of the total displacement, so going big is no big deal.