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Old 10-20-2019, 08:59 PM   #1
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110 V electric get-home motor ?

I'm still considering options for a get-home engine/motor using our 8 kW Onan. I see quite a few 110V industrial motors in the 5 hp range which would be near perfect if it could be geared right. The motor would be installed on a dedicated shaft for full redundancy.

I'm wondering if any of you have a similar arrangement or have pointers to installations like that?

Thanks.

-Sven
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Old 10-20-2019, 09:15 PM   #2
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I am wondering what the concern is, how old is your boat and did it ever need a get home motor? I would spend the money on clean fuel, etc. And have unlimited towing insurance.
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Old 10-20-2019, 09:25 PM   #3
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I am wondering what the concern is, how old is your boat and did it ever need a get home motor? I would spend the money on clean fuel, etc. And have unlimited towing insurance.
The engine appears to be in top shape, but there is only one and we don't carry a spare crankshaft (as just a silly example). The fuel is clean and we filter/polish it just to make sure. The designer who put in the paravane rig did away with the mast so there is no way to install a drift-somewhere sail.

We have unlimited tow assistance but that stops at 200 NM off-shore and is only usable in the US (I think, maybe Canada ?).

We have every intention of getting back to cruising and Alaska, Mexico and Central America are all hoped-for destinations.

We really believe in being self-sufficient if at all possible and not have to hpe for some fellow sailor to ruin their plans just to tow us back in range of Vessel assist.

Thanks for the question.



-Sven
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Old 10-20-2019, 09:35 PM   #4
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Ok, then have you thought about a Dickson stern thruster? They run off hydraulics which could be mounted on your genset. The stern thruster can be rotated to fore and aft to give a get home capability. Not sure how much thrust they provide but it would be a benefit as a stern thruster for the 99.9% of the time it wasnít needed for get home. Might be a win economically and practical as a stern thruster... No affiliation.
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Old 10-20-2019, 09:40 PM   #5
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Ok, then have you thought about a Dickson stern thruster? They run off hydraulics which could be mounted on your genset. The stern thruster can be rotated to fore and aft to give a get home capability. Not sure how much thrust they provide but it would be a benefit as a stern thruster for the 99.9% of the time it wasnít needed for get home. Might be a win economically and practical as a stern thruster... No affiliation.
Interesting idea (without having looked at the specifics) !

I'll have to look into PTO options for the Onan to see if it is an option without tearing a hole in our wallets :-)

Thanks again,



-Sven
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Old 10-20-2019, 09:47 PM   #6
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No idea on costs or how fast it would move the boat but something to look into. And you get the added benefit of having a thruster. I wouldnít think it would be more than adding a second drive train.
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Old 10-21-2019, 07:39 AM   #7
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I have a Dickson stern thruster. It is not supposed to be operated at more than 1000 RPM. Yes you could size the pulleys on a generator to max out at that, but at that power level mine would not help much in a get home situation in my opinion.
Of course Dickson might say otherwise, but they want to sell them.
I think you'd be better served by rigging a 8 hp outboard engine.
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Old 10-21-2019, 08:49 AM   #8
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That could work if you are confident that 5hp of propulsion would do the job. In seas it takes a lot more than in flat water. Perhaps experiment with an outboard either pushing or towing the boat?

Anyway, a 5hp motor is about 4kw, so you should have enough power.

But a 5Hp motor is most likely 3 phase, and your generator single phase. But thatís probably all for the better since using a VFD (motor driver for the 3 phase motor) you will also gain speed control and reverse capability. VFDs need to be pretty significantly oversized when powered from single phase. I donít recall exactly how
Much, but itís order 2x.
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Old 10-21-2019, 08:55 AM   #9
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Thinking about it, the electric motor get-home could be useful in another situation if it could be implemented in a reasonable package. Put one on each shaft of a twin. As much as you can run on one engine if you have a failure, being able to power the dead engine's shaft would be a huge benefit when it comes time to dock somewhere to fix the thing.
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Old 10-21-2019, 09:41 AM   #10
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Second the post about using a three phase motor and VFD. Input to the VFD can be 240v single phase from genny, output completely variable 3ph through VFD. Allows soft starts and full authority over rpm and direction.

No way would I want to start a 5hp single phase motor with prop attached with an 8kW. The startup load would stomp the genny.
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Old 10-21-2019, 10:07 AM   #11
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I like the idea of an electric motor as a backup. You will probably need to incorporate an Aquadrive or something similar as most electric motors aren't designed to handle end shaft load on the bearings.

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Old 10-21-2019, 10:10 AM   #12
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I think you'd be better served by rigging a 8 hp outboard engine.
I think fuel range would quickly become an issue, particularly if you are cruising in Alaska, he is unlikely to carry enough gasoline to get very far and diesel outboards are virtually non-existent.

I don't know what the largest electric outboard available, or what service ratings one might have, but that could be a viable solution to avoid modifying the existing generator and not need a new fuel source. It would be an interesting and pretty low cost project to find a junked 10-15hp outboard with a bad power head and swap it for the electric motor of your choice with some bracket work, an adapter to the top of the driveshaft to a lovejoy coupling to the new motor. You could even retain the water pump, build a water jacket of sorts for the electric motor and make it water cooled to boost efficiency. The ideal donor motor would be the "big foot" type trolling motors with better gearing and configured to allow a larger diameter prop.
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Old 10-21-2019, 10:13 AM   #13
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In my mind, water cooling the electric motor would likely be necessary. Not so much for efficiency, but because it would allow the size of everything to be a bit smaller compared to an air cooled motor that needs to handle continuous running at high power. Plus, water lines are easier to route than air ducts big enough for forced air cooling.
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Old 10-21-2019, 10:34 AM   #14
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Ok, so if you acquired say a dead 50 HP outboard with hydraulic trim, removed the engine and raw water pump, installed a 5 HP 1,750 RPM electric motor, started it trimmed up, and then lowered it into water. Obviously the size outboard and propeller pitch would have to be worked out. Probably need to waterproof the electric motor. But on the plus side, you could get a reasonable diameter propeller, all be it with a very flat pitch.

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Old 10-21-2019, 10:54 AM   #15
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While they are hard to come by, some small trolling motors in the 10-15 hp range have electric power tilt (mercury I believe), and even the hollow tilt rods that accept push-pull steering cables. I believe they are primarily marketed for lake fishing, slow trolling market. Of course these would be much harder to come by. I think an easier approach would be fix mounting it on a vertical track on the back of the boat. Raise and lower it with block and tackle. A larger outboard would be just more weight and grossly exceed the size of the electric motor a 8kw generator would support.
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Old 10-21-2019, 11:32 AM   #16
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A larger outboard would be just more weight and grossly exceed the size of the electric motor a 8kw generator would support.
Most outboards are designed to run at 5,000+ RPM. Between a flat pitched prop and a 1,750 RPM electric motor, I think you could be in the neighborhood power wise. 10 to 15 HP outboards will mostly cavitate because of a too small diameter prop.

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Old 10-21-2019, 11:37 AM   #17
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It's not a cheap solution, but what about something like buying one of the bigger Torqueedo or other electric outboards and building a rectifier / voltage regulator to power it directly from the generator instead of the normal battery supply?
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Old 10-21-2019, 12:26 PM   #18
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Most outboards are designed to run at 5,000+ RPM. Between a flat pitched prop and a 1,750 RPM electric motor, I think you could be in the neighborhood power wise. 10 to 15 HP outboards will mostly cavitate because of a too small diameter prop.

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I bet I could find a half dozen dead Force 50hp outboards in an hour's time.
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Old 10-21-2019, 12:54 PM   #19
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That generator should have a crank output of around 16 hp I think. In the interest of getting the most possible horsepower to an auxiliary shaft, I would consider fluid power over electric power. It should be possible to couple a pump to the non electrical end of that generator engine, switch the load off of the electrical end, and run a nice orbit motor coupled to this auxiliary drive shaft for propulsion. You would need to find room for a hydraulic fluid reservoir supply.
I am in over my head here on the engineering of the hp conversion, but this is how I am set up and it seems to work fine in relatively benign sea states when I exercise it. I am not at all sure how it works but I do have a toggle at the helm that changes me from forward to reverse as well. Steering becomes manual helm obviously.
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Old 10-21-2019, 01:11 PM   #20
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Just one word, and its not "plastics". Its hydraulic. If the genset doesn't do it, find one with a PTO option. I've designed in VF drives for some electric motors, but all with essentially fixed loads. I wouldn't think an ac induction motor, or its drive, will be happy with prop loads underway. From recurring high negative to high positive loads due to seas. Something will overheat on a passage. Hydraulic motors are the ticket for this application.

Not keen on outboards either, but mostly due to the shallow prop position at the "end" of the boat. Obviously, seas are not usually flat.
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