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03-28-2015, 09:48 AM
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#1
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Senior Member
City: Blaine
Vessel Name: Slow Bells
Vessel Model: Marine Trader 38
Join Date: Nov 2013
Posts: 327
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"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.
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03-29-2015, 07:08 AM
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#2
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Guru
Join Date: Oct 2007
Posts: 22,553
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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.
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03-29-2015, 09:56 AM
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#3
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Guru
City: gulf coast
Join Date: Jun 2014
Posts: 3,440
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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.
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03-30-2015, 01:16 AM
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#4
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Senior Member
Join Date: Feb 2011
Posts: 305
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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.
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03-30-2015, 07:07 AM
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#5
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Senior Member
City: Blaine
Vessel Name: Slow Bells
Vessel Model: Marine Trader 38
Join Date: Nov 2013
Posts: 327
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Quote:
Originally Posted by FF
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.
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03-30-2015, 07:50 AM
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#6
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Guru
City: Carefree, Arizona
Vessel Name: sunchaser V
Vessel Model: DeFever 48 (sold)
Join Date: Apr 2008
Posts: 10,186
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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 ----
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03-30-2015, 08:47 AM
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#7
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Guru
City: I need a bigger boat!
Vessel Model: Cheetah 25' Powercat.
Join Date: Aug 2014
Posts: 925
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Quote:
Originally Posted by seattleboatguy
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.
__________________
Peter.
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03-30-2015, 08:56 AM
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#8
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Moderator Emeritus
City: Chicago, IL
Vessel Name: Bay Pelican
Vessel Model: Krogen 42
Join Date: Oct 2007
Posts: 2,993
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Quote:
Originally Posted by seattleboatguy
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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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.
__________________
Marty
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