Fuel Consumption of Larger Yachts

Its cheap --1 shaft is cheaper. Many engines mean as long as one keeps going your happy . Landing craft in battle have a life of what,---one landing perhaps would be sufficient

 

I was thinking of 6/12/18 for high speed motorsailer

and probably with two props, but connected through gears, so the smallest engine would still drive two props.

This would be for fast motorsailer 1 or 2 40' container(carrying the boxes, not fitting inside the boxes...LOL) capable cargo/expedition/charter 50M boat I'm sketching. Two props for maneuverability and shallow water operations. Multiple power settings for loaded or unloaded motoring.

A hull able to motor reasonably fast and power train able to serve as efficient 'helper' when under various amounts of sail.

Yeah, I know it is gonna cost more than one motor on one prop, but with CAD/CAM those things are getting better and cheaper all the time, but fuel just keeps going up and up.

OK, those things seem to be getting better, not some much cheaper. Actually they are getting cheaper, due to runaway inflation. Oil to gold price isn't changing, just oil to US dollar changing.


Also be nice to have a smallish engine to run HVAC etc

I think one reason for multi-engines on one shaft was convince. When they were slapping landing craft together they could get more smaller motor easier than big engines. Isn't there sort of a big jump from Detroit X-71 class engines to "real ship" engines, cost and availability wise, not to mention hoisting them in and out of boats? Some class of Canadian? Coast Guard fishing patrol ships had two engines on one shaft as "cost saving" measure.

 

It's the navy Halifax class frigates-and it's for range and I think the US navy has started it. Several others do it.
8000 hp diesel to cross oceans and stay out for months,and the 50,000 hp turbines are clutched in for 30 knot emergencies.
IIRC all they have to do in emergency is hit a button,turbines fire,clutches, engage,the CPP shift and they can be at full power in 10-15 seconds.

I saw them do it once,putting along at 10 knots,a bunch of noise and it was cool to see a 450' ship just hunker down and take off at 30+ knots.

The Iroquois sub destroyers are similar,they run off about 12,000 hp tubines but can switch over to an extra 100,000 hp for emergencies

 

The problem has to do with a prop that works at 6-12-18 cyl.

A simple solution would be an auxilary gear box on the smaller engine.

A bit of math could have the usually higher speed of a smaller engine converted into more torque , that could spin the main shaft for a SL 1 cruise.

With the extra gear box , the smaller engine could power the vessel hotel loads or hyd system when not in use for propulsion.

FF

 

Hey thanks Tad and westvanhan for the helpful info!

Tad-don't know how you found that..I used google and couldn't.

Westvanhan-thanks for the direct experience-thats actually better than what I thought it would be-that is an acceptable range as we'd only use it 50 to 100 hours a year and not even every year.I'm wondering if you know what would happen if one engine was turned off. I hear what you say about one being changed with a Cummins.
Also know about variable pitch props,would it be a good idea for one of these?
All this talk about shafts and differnttrans sounds too complicated and expensive,and we don't want to burn through tons of fuel and are happy with slow speeds.

With a 700 to 800 nm range that is plenty.There's a Sunseeker here in town??? Whereabout is it?? But yes I imagine they are probably hoping for the moon and 94 is too big.

Thanks again guys

 

Jim:

-I turned off one engine,and with that big prop dragging and the rudder,it was a very noticeable drag.
You'd get worse mpg IMO.

-as for variable pitch AKA CPP I would say so BUT the bigger Sunseekers and many of the others are V-drives.
I doubt it would even be possible to fit it. Maybe a feathering Autoprop? If you could cut the drag of a dead prop I could see it really helping.

-yes,like I said-when one of the engines blows or will cost a ton to fix,throw in a reman Cummins QSM11 or even 5.9 for cheaper,reprop and use that as your main engine. The other V12 would be back up and have the feathering prop.
That's what I'd do.

the SS 94? North side of False Creek,just west of Cambie bridge-if you drive south on the bridge and are not in a car you should see it. Marina at the foot of Davie,forget the name.