I'm Hoping Someone Can Check These Statistics.

Those seem reasonable, so given the source they are probably correct.

I'm not quite sure what you are planning through. There are a lot of things that can impact fuel efficiency. If you are looking for about 11 meters of boat there are a lot of different vessels out there to chose from that will each have their own performance curves to consider.

As OPCN said figures seem valid. Keep in mind however that a diesel engine is a very finicky beast. Everything effects fuel consumption. Marine growth, bottom paint condition, prop pitch, engine condition and fuel filter cleanliness as well as fuel quality. Plus a few dozen other things. That being said, the numbers you have shown should serve you as a very reliable guide as to what one could expect. Good luck.

There are a LOT of variables in this game. And many, if not all on this forum will tell you fuel is the least of your operating costs.

And then there's the fact that having two motors is a REALLY warm and fuzzy feeling when one craps out.

Certainly it takes less fuel to power 1 x 291hp versus 2 x 192hp (384hp total).

Include the adding resistance for a second shaft/prop/rudder, and yes the single shaft is more efficient - there is just fewer mechanical losses and less hardware to "drag" through the water. But what about redundancy / back-up in case of an engine failure? That is the trade-off.

I would venture to say that the comparison could have been designed better - compare diesels of same make (and preferably same rpm), and same hp = 2 x 146 hp = 229 hp). You could also add a free-wheeling feature on the twin engine set-up which would require a gearbox that could operate with the second engine off and freewheel in neutral, which would require a separate cooling system (a bit more complex) or a robust shaft brake system that would allow you to lock one shaft in place during single engine operation. This would close the gap, but you would never beat the efficiency of the single shaft system.

Commercial vessels can safely use single engine designs because they use engines that are designed to operate as the single source of power - these are typically rated for full time operation at full or near full loads, basically the most rigid duty cycles. The rpms are the lowest offering for that engine life, and the system robustness is matched to the application. They then take the redundancy factor out of the equation, and will provide the proper resources/capital for scheduled and preventative maintenance (usually).

Larger ships can use gearboxes that allow for two inputs - one output. The two inputs can be engines or a combination of engines and electric motors. Or they have systems that can allow and electric motor drive to "clamp" on the shaftline downstream of the gearbox and provide a second "get home" propulsion device, typically an electric motor driven by additional generator capacity.

See examples:

http://www.industry.siemens.com/dri...-specific-gear-units/ships/Pages/Default.aspx

I agree with this as well. But the difference is, are you looking for best fuel efficiency and travelling at slower speeds (11.4 knot cruise) with the single CAT, or much easier dockside maneuvering with twins and a 14.5 knot cruise speed.

I agree it could've been a better comparison, quite frankly I'd rather have seen the boat equipped with a single 3126 CAT with 350 or 425hp, and the twin volvo's. If I was looking for efficiency at slower speeds, I'd rather have the larger single CAT with more cruise speed. But, these are probably the 2 engines the builder offered. Cruise speed would be pretty close with a single 3126 cat and the 2 volvo's.

The problem with a large wind turbine on a boat is that the center of effort from the wind is really high, up at the hub of the turbine. A consequence of this is that it's got tremendous leverage trying to pull the boat over. A negative consequence of which is that your turbine won't be facing into the wind when you're heeled and you'll get more drag and less power. In order to get the righting moment you'd need out of a monohull like a trawler you would have to put so much weight into the bottom of it that you'd be looking at turtle speeds. There is a catamaran out there that successfully uses a wind turbine to enable it to sail 360deg with respect to the wind.

You might also look into the dynarig used on the sailing yacht Maltese Falcon. With its in mast furling and sails constructed of smaller panels it's less physical work to operate when sailing, and the center of effort can be lower which means that you don't need as much weight in the keel.

Well building the dynarig of the MF would be expensive, but a smaller dynarig could be managed. Two masts with two or three panels each, built from fiberglass or aluminum. sized for a vessel you might feasibly own, and you are in a cost bracket that is very competitive with a custom built wind turbine. The only way you are going to get the wind turbine cheaper is if you buy one "off the shelf" and (possibly illegally) take advantage of tax credits that various nations put on windturbine construction to offset fossil fuels in production of electricity for the grid.

Batteries are not idea ballast, because you cannot pour them into a keel. Really you want your batteries up off the floor on a low shelf for servicing them, but at the very least you are looking at building a flat spot high enough out of the keel to support them and that is going to shorten your lever arm substantially. You have to remember that for righting arm what matters is the distance between the metacenter and the center of mass. At rest the metacenter is going to be at the center of buoyancy which is well below the waterline. If you raise your ballast 30% up from the keel to the waterline you might make it 60% less effective, and need 150% more of it. Really for a big wind turbine you have to maintain a very low heel angle which just isn't feasible in a monohull given the drastically lower initial stability, unless you build out a barge and then your windage is going to make any kind of controlled movement under "sail" very difficult. By turtle speeds, I meant by comparison to other vessels. So if you consider someone sailing along at 7 knots to be doing turtle speed already, you should really think hard about how fast you can expect to move. Really I think a monohull under turbine power is going to move at a maddeningly slow pace, even for people used to traveling slowly under sail in motor sailors. Just bust out a map and figure out how long it would take you to get from your marina to some of your favorite cruising spots at 3 knots, and decide if a monohull is worth that to you, or if a multihull is something you can live with.

As to using an electric drive train versus a geared mechanical drive train, I suspect that difference is less than important to the point I was making. I actually prefer the concept of an electric drive train too, and wrote that in my first post but deleted that portion out because I figured it wasn't important. Mechanical and electric systems each have their advantages and disadvantages, but how you deal with the dynamic loads of sailing are more what matters.

To state things differently, the figures quoted in the resource are nowhere near accurate for a monohull that is sporting a wind turbine to generate power.

I ran a 34' Luhrs FB that someone put a wind generator on and it didn't seem to effect the boat too much. It was mounted directly above the hardtop.

I suspect quite strongly that you are talking about a wind turbine that is under or around a 4' diameter, rather than the 60'+ diameter wind turbine that you would need to generate 300 horsepower reliably.

No, I'm talking about a wind generator that is 4' in diameter. Not a wind turbine that is 60' in diameter

I was, on reflection, being really generous suggesting that a 60' turbine could get 300 HP even at peak windspeed. Really looking around and using an envelope a more realistic peak for such a turbine would be 100 horse. But to get that hundred horse you need to have about 5 metric tonnes of gear supported 90' above the waterline. That could be managed on a multihull, but man it would be a challenge for a monohull, even neglecting the drag that you are going to experience from the rotor in the wind. So you downsize for the 35' boat, to a 15' rotor 30 feet over the waterline. Now you are looking at the equivalent of a 5 horsepower system, to drive a heavy displacement craft. If you tried to keep it light, and built some system that could angle your turbine based on heel angle (maybe put the rotor downwind and used the generator windings as an upwind counterweight and gave it and additional pitch axis gimbal to move on to match the heel) you might get a boat that was tolerable at under 10 tons. I pencil that out at around two and a half knots, that is slower than most people walk, and I still feel like that rotor is too big for a 35' monohull.

^^^ A good one that completely slipped my mind!

I don't buy the lower end numbers on the single engine. Perhaps in a brief test of some sort they were achieved but the 17.4 nmpg I don't believe is achievable in a real life environment. I'd have to see it to believe it. Obviously, I can't disprove those numbers but I'd perhaps believe something in the range of 8 nmpg at 7 knots and 4 or 5 at 8.5 knots.