Gen Set as auxilary propulsion

[George.]

Has anyone else toyed with the idea of using a 12.5KVA generator ( which I happen to have already installed and plumbed) with fuel and cooling .
An reversible electric motor and rheostat, along with a sailboat type of folding prop to propel a 45 ft twin that weighs 38000 lbs.
I am thinking a double wide chain and sprocket drive system that would allow easy ratio changes ,motor to mounted off center to allow for sprocket changes during experimental stages. Any ideas on the propellor thrust blocks?
I am thinking the folding prop under the swim grid , so that is not impeding during displacement cruising and would be fully out of water during planning.
I am hoping that existing rudders (and autopilot)would be sufficient for steering control
The objective here is for salmon trolling at 2-4 knots without having to use either of the big Cummins.

 

[O C Diver]

Assuming your generator isn't 3 phase, 10 HP would be about as much as you will get single phase 220 volt. A very big gear reduction ratio will be required. Doubt the rheostat could be used for speed control. Probably won't be able to start the motor without some form of clutching devise. Probably a better bet with an electric outboard like an Epropulsion.

Ted

 

[Arc]

After all said and done you might get 3-4 HP out of the prop. I’m not sure it would be effective in anything but calm water

 

[DDW]

Probably a better bet with an electric outboard like an Epropulsion.

Ted

I keep threatening to try that but haven't found the time and opportunity. Maybe beginning of next season. I think even my little 1KW ePropulsion will move my small trawler at maybe 2 knots in calm conditions. It would do that nearly forever on the genset. To get reasonable trolling I'd need a bigger outboard, I'm just thinking of slowly making my way back towards civilization in a power-out scenario.

 

[rslifkin]

Assuming you could actually get 10hp out of the setup, it could likely be made to work.

Doing a little math based on my own boat, this seems pretty plausible if you can spin one or both of the main shafts (ideally both would give the best low speed steering control).

My own boat does ~5 kts at ~900 engine RPM in calm water. That's ~350 shaft RPM in my setup. A little calculation (assuming a 2.7 prop curve exponent) extrapolates that spinning my shafts at that speed should take about 5.3 hp each. Spinning them at idle speed of 700 rpm (272 shaft RPM, ~4 kts boat speed) should take ~2.7 hp each. Figuring that at low shaft speeds like that, you might double your power requirement once you factor in drag in the shaft bearings, etc. I'd expect a pair of 5hp electric drives would do fine at giving me ~4 kts. You're talking about a bigger, heavier boat, so 10hp might only get you 3 kts in calm water.

How much power you could really extract will depend on the motor(s) you use and how they're controlled. In theory a 12.5 kva generator is good for ~16.75 hp with perfect motor and controller efficiency. Knock that down to 75% to get more realistic and to keep the generator below max load and you'd be looking at 12.5hp. So 10hp is definitely realistic, a little more might be possible. Depending on the generator engine size vs actual electrical output, a hydraulic pump and motor setup might also be a possibility.



The whole setup strikes me as not the most practical thing you could do, however.

 

[Airstream345]

Wesmar and Kobelt make hydraulic get home systems that utilize a generator driven PTO that powers an around-the-shaft hydraulic motor. You could add one to one side, skip the extra folding prop and associated fabrication and troll your heart out.

I priced a system from Kobelt last year and it wasn’t terrible. Our main use case would be get home given we’re in a single.

 

[O C Diver]

I keep threatening to try that but haven't found the time and opportunity. Maybe beginning of next season. I think even my little 1KW ePropulsion will move my small trawler at maybe 2 knots in calm conditions. It would do that nearly forever on the genset. To get reasonable trolling I'd need a bigger outboard, I'm just thinking of slowly making my way back towards civilization in a power-out scenario.

One of the hurtles to overcome is building a battery to run the outboard that can be simultaneously charged. The Epropulsion line doesn't offer what could be referred to as a hybrid battery for their electric motors. The batteries are designed to be charged slowly. I think their Navy 6.0 (9.9 HP) with the bigger diameter propeller would be a good choice.

Ted

 

[mvweebles]

Willard 40s were frequently equipped with a 3-phase 12kw generator with a very heavy 5hp electric motor chain-driven to the prop shaft. I know of no instance where they were needed. Replacing a 3-phase motor is expensive with very limited choices. And a 12kw generator is oversized for most W40s. Overall, a lot of compromise for a "what if" that rarely happens (if ever). Most owners abandoned this over the years.

As others have said, better option would be a hydraulic motor off a generator PTO.

Peter

 

[Peter B]

Welcome to TF, and as your query is rather electrical and propulsion specific, I have moved your thread now from Welcome Mat to the best area relative to your issue.

 

[Bmarler]

Actually, three phase motors are not difficult to come by, and your 12 kw genset could run an inverter/frequency drive to supply that motor. You get fwd/rev, variable speed, etc… clutch it to a main shaft. It would probably be best to do both shafts with smaller drives and motors than do one big one.
Two 5 or 7.5 hp drives and motors might do what you want, as long as the transmissions can handle being driven that way.
Hard to say how effective it would be though. It’s a big boat to push with electric drive.
It would have to be something I was going to do a lot of to justify the expense.

 

[Pete Meisinger]

The electric outboards are getting bigger, more powerful and better all the time.

The higher hp models are pricey but the set up you are debating will be expensive also.

pete

 

[mike66]

https://www.kobelt.com/products/get-home-drives

This seems like s good solution without re inventing the wheel

 

[twistedtree]

As other have suggested, the hang up with such an approach usually comes down to the power requirements. The power available from a reasonably sized generator will only move the boat very slow, and only in calm conditions. And to get enough power for more reasonable propulsion pushes you into a hugely oversized generator for normal use.

 

[KnotYet]

Has anyone else toyed with the idea of using a 12.5KVA generator ( which I happen to have already installed and plumbed) with fuel and cooling .
An reversible electric motor and rheostat, along with a sailboat type of folding prop to propel a 45 ft twin that weighs 38000 lbs.
I am thinking a double wide chain and sprocket drive system that would allow easy ratio changes ,motor to mounted off center to allow for sprocket changes during experimental stages. Any ideas on the propellor thrust blocks?
I am thinking the folding prop under the swim grid , so that is not impeding during displacement cruising and would be fully out of water during planning.
I am hoping that existing rudders (and autopilot)would be sufficient for steering control
The objective here is for salmon trolling at 2-4 knots without having to use either of the big Cummins.

A 9.9(+) hp electric outboard (or a pair if needed) would be one approach and
has the advantage of needing no hull mods beyond a readily available bracket(s).
Your generator could be charging a spare battery or two while underway. Clean.
Really, though, a regular outboard would probably move your boat a lot better.

If you really want to roll your own electric drive system, I would be tempted to
avoid any through-hulls and use an external surface drive or longtail set-up like
the ones from Beavertail, Backwater, Mud-Skipper, etc.
These can be transom mounted and adapted to the electric motor of your choice.
AC motor controls are available to match most motors as are phase converters.

 

[DDW]

One of the hurtles to overcome is building a battery to run the outboard that can be simultaneously charged. The Epropulsion line doesn't offer what could be referred to as a hybrid battery for their electric motors. The batteries are designed to be charged slowly. I think their Navy 6.0 (9.9 HP) with the bigger diameter propeller would be a good choice.

Ted

You don't need the battery at all. Even for the little 1Kw outboard, ePropulsion offers a cable to run it from any 48V source. A 48V DC power supply of sufficient capacity is in the $200 - $300 range. Of course for a 6Kw or 10Kw outboard, everything gets more expensive, including the outboard.

I see two major problems with using an AC motor coupled to the shafts: A large AC motor, like 5 or 10 hp designed for continuous use is very large and heavy. It has to be coupled to the shaft with a chain or belt with sufficient ratio to reach rated speed and still turn the shaft. That maybe results in 500 rpm as has been guessed above. Now you fire the main engine and run the shaft at 1500. That AC motor will explode. So you have to also have a clutch or disconnect. Even then, if the disabling event involved the prop or shaft, the whole thing is useless.

 

[Comodave]

Way too much complexity. Go with an electric outboard or throttle down the main engine. Or put a trolling valve in the transmission.

 

[fgarriso]

Not to be a spoil sport, but it sounds like you could buy a new 10HP outboard for less than it would cost to rig up your generator.

 

[grandbanksbayfield]

Yup, 10 hp outboard.

Not to be a spoil sport, but it sounds like you could buy a new 10HP outboard for less than it would cost to rig up your generator.

Having a GB32 with one engine, I am always concerned about being dead in the water in the St. Clair River with a 1000-foot freighter bearing down on us. I built a easily attached bracket to hook onto the back side of the swim platform -- about one minute to install. The 6 hp Johnson we use on the Zodiac can be mounted on it in short order. It actually pushes the boat along at about two knots, enough go get out of the way or slip into a marina and tie up.

 

[Sailinggod]

Think about a hydraulic drive

I’ve seen a “get home” arrangement using a hydraulic PTO off the gen set, with a fan belt around the prop shaft that can be engaged when needed. Requires two hydraulic drives, one the gen set powers, and one that drives the fan belt arrangement on the prop shaft.

 

[mvweebles]

I’ve seen a “get home” arrangement using a hydraulic PTO off the gen set, with a fan belt around the prop shaft that can be engaged when needed. Requires two hydraulic drives, one the gen set powers, and one that drives the fan belt arrangement on the prop shaft.

Also requires a GenSet with a PTO. Last I checked, smallest Northern Lights was a 9kw, larger than what I'd expect to include on a GB32.

Peter

 

[Pirate]

When I bought my Krogen in 1996 it had that set up. There was a sprocket on the shaft. If you needed it had to put the chain on the sprockets and insert a link. The theory was ok for a get home solution but only as a solution for an engine problem which are very rare in well maintained Ford Lehman. It would not solve a transmission problem or a prop issue. I removed it because it was a poor design that blocked access to the stuffing box.

 

[Bmarler]

When I bought my Krogen in 1996 it had that set up. There was a sprocket on the shaft. If you needed it had to put the chain on the sprockets and insert a link. The theory was ok for a get home solution but only as a solution for an engine problem which are very rare in well maintained Ford Lehman. It would not solve a transmission problem or a prop issue. I removed it because it was a poor design that blocked access to the stuffing box.

I have that exact setup. I hate how it blocks the stuffing box too. Previous owners have been lax with keeping the boxes adjusted properly and the sprocket is rusty. I’m going to have a heck of a time removing it. I doubt it’s ever needed to be used. I might make up a two piece sprocket to keep on board, but not high priority for my cruising grounds.

 

[Pete Meisinger]

OK, I'll just "skirt" the twin engine debate here for a second, (without getting into it).

If a diesel engine fails, no matter if you have a single or twins. The problem is most often fuel. So if you have some bad or dirty fuel your genny will fail also.

A curious thing about a "get home" engine is that it will probably fail also. That is why I like having an outboard along, either gas or electric. It will not get me home in all probability but it will get me out of the shipping lane, to a safe anchorage or hopefully to the lee side of an island so I can change filters.

"Any port in a storm"

pete

 

[slowgoesit]

When I bought my Krogen in 1996 it had that set up. There was a sprocket on the shaft. If you needed it had to put the chain on the sprockets and insert a link. The theory was ok for a get home solution but only as a solution for an engine problem which are very rare in well maintained Ford Lehman. It would not solve a transmission problem or a prop issue. I removed it because it was a poor design that blocked access to the stuffing box.

Ours is set up similar to the above. The 12.5k generator is powered by a hydraulic motor. Hyd pressure is supplied either by a pump off of the main engine, or off of an Isuzu standalone engine.

That engine drives a separate hydraulic pump, which can be selected to either provide pressure to 1) generator, 2) hyd motor which attaches by chain to the main shaft.

Put main transmission into neutral, hook up chain to main shaft, start auxiliary engine, and use controllable pitch propeller for fwd or reverse. I've yet to hook it up and try it, but it's on our list of things to do prior to heading South.

 

[Pirate]

OK, I'll just "skirt" the twin engine debate here for a second, (without getting into it).

If a diesel engine fails, no matter if you have a single or twins. The problem is most often fuel. So if you have some bad or dirty fuel your genny will fail also.

A curious thing about a "get home" engine is that it will probably fail also. That is why I like having an outboard along, either gas or electric. It will not get me home in all probability but it will get me out of the shipping lane, to a safe anchorage or hopefully to the lee side of an island so I can change filters.

"Any port in a storm"

pete

EXACTLY. I worry more about keeping my fuel clean. When you eliminate fuel as an issue diesel failures are very rare. Transmission failures are probably more common. If your transmission fails then this whole turn the shaft solution is mute because you lost the forward shaft bearing.
- Tom

 

[mvweebles]

EXACTLY. I worry more about keeping my fuel clean. When you eliminate fuel as an issue diesel failures are very rare. Transmission failures are probably more common. If your transmission fails then this whole turn the shaft solution is mute because you lost the forward shaft bearing.

- Tom

So.....while clean fuel is no doubt important, it's largely manageable. I know of two recent shut downs - one due to a cracked diesel line to the injection pump. The other a broken shaft on a water pump that seriously overheated the engine . These are the types of issues I worry about as I contemplate heading south through Mexico with my single engine Willard. A get-home off a generator would work.

Psneeld recently observed singles are fine within tow-range. Beyond that --- twins (I hope I paraphrased him correctly). While I am not an adherent, I understand the logic. If you have a single, you really want to close-off extraneous mechanical risks.

Peter

 

[DDW]

While dirty diesel might be responsible for a lot of diesel failures, in the drive SYSTEM, I don't think it dominates. Prop, shaft, log, transmission, electronics, engine all contribute. But that is exactly why an outboard (or some propulsion independent of all of the above) is a better bet. I've only run diesels a few thousand hours, the few failures I've had were fuel related but not bad fuel. Rather a fuel delivery problem that would not have affected a genset.

 

[rslifkin]

Even if the failure is bad fuel affecting all engines, they likely won't all die at the same time. Which means filters can be changed on one while another is still running.

 

[Airstream345]

I think about this a little differently.

Assuming a well maintained vessel, fuel, filters, maintenance, etc a failure” on the main is more likely to be a wearable accessory component such as a raw water pump (or impeller), alternator, fresh water pump, belt etc.

Ensuring you can maintain steerage in a seaway or offshore while you swap the spare is far more likely (in my mind) than a total fuel system contamination/failure. Yes a fouled prop would reduce both systems to paperweights but I think it’s about managing likely risks and failures with preventative maintenance and onboard spares.

This makes me think our ketch rig make more and more sense.

 

[AndrewAdams]

Photo of electric get-home motor over main shaft

I have one of the Willard 40s that Peter mentioned shipped with a get-home system. It's single-phase, three belts, tabernacle fitting, flip a lightswitch and it comes on. As long as your 7.5kW genset is running, of course. I'm replacing the 7.5kW Onan that's not reliable enough with a used 8kW Northern Lights that will hopefully be more reliable.

I've never once (knock on wood) had to use it in real life, just testing it in the harbor. The prop wash is quite strong and the boat strains against its lines. A 1977 magazine review said "five honest knots" in San Diego harbor.

I'm glad it's there, but also glad the Perkins keeps perkin'

Andrew