"get home" system powered from generator

I would be interested in hearing from anyone with some experience with "get-home" systems using a power take-off from the generator. They sound like a great emergency back-up system for a single screw boat, but I get the impression that they are very expensive, and not all generators can be adapted to them. I read the Passage Maker article from May 3rd, 2013. If there is another good thread on this topic, please send me the link. Thanks.

Offshore boats are sometimes designed around a get home system.

The noisemaker is located where a chain or belt drive can turn the shaft after the engine is uncoupled ,
this requires a thrust bearing at the end of the shaft.

Some noisemakers can use a conventional shaft and drive , if a proper folding power boat prop is selected .
This requires a robust enough engine that full electrical power can be taken from the front. A DD 2-71 perhaps.

Hydraulics on the noisemaker run into the same hassle , how much power can be taken from the front of the usually small engine.

Big bucks (but worth it ) to have a hyd pump on the main engine and noisemaker , to operate a hyd generator head, bow thruster, windlass , get home and all the rest.

Putting 30-50HP to a prop is easy with a shaft or hyd , but first the unit must be over 50 hp, usually far too large for a cruiser that is not large and with 24/7 electric , with a $100-$250 a day fuel bill.

For the usual TT ,,Sea Tow is the least costly option.

generators typically are very low powered compared to mains.




746 watts equals 1 HP so you can figure your equivalent get home power.




Then there will be heavy losses from gearing, prop shaft seals, bearings and motor so there will be a lot less available at the prop.

Some Willard 40's used a 3 phase generator and a 3 phase 5hp motor with a belt drive to a big sheave on the prop shaft just behind the gearbox coupling. The belts were off the sheaves normally, but as a get home drive you installed and tightened the belts, and started the motor. A modern variable frequency drive would be an interesting addition to this system.

FF said:

For the usual TT ,,Sea Tow is the least costly option.

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It sounds like the bottom line is that there are very few of these installations in the average cruising fleet. I guess it's a great theory that just didn't turn out to be very useful or affordable. But, thank you for the feedback.

SBG

I have seen several get homes powered by hydraulic motors mounted on the generators with separate shaft. The gensets as I recall were in the mid 20 KWh range. Selenes and Northern Marine come to mind. Check out the Wesmars website.

If you have the space a separate diesel makes more sense to me. Look at a smaller Nordhavn on how to do it right. I priced one out 3 years ago on a single engined 52' trawler - $40K minimum. either way not cheap but since boating is for the rich ----

seattleboatguy said:

It sounds like the bottom line is that there are very few of these installations in the average cruising fleet. I guess it's a great theory that just didn't turn out to be very useful or affordable. But, thank you for the feedback.

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I'm sure you have petrol (gasoline) on board for the dingy, so why not put a larger OB on the dingy and use it as a standby motor; people have been doing this for years on smaller boats used for fishing/recreation.

How would the engine mount on your transom and be able to tilt up?
Bolt a jacking plate to the transom; the OB will move vertically up out of the water. Cheap, off the shelf, electro/hydraulic.

Fitting time : 1 hour.

I think about 5hp/ton of displ will push you along at hull speed with a fine pitch prop.

seattleboatguy said:

It sounds like the bottom line is that there are very few of these installations in the average cruising fleet. I guess it's a great theory that just didn't turn out to be very useful or affordable. But, thank you for the feedback.

Click to expand...

The majority of the less than 60 foot trawlers that visit the Caribbean have auxiliary / wing engines. The Yanmar 27 or 40 hp are popular.