110 V electric get-home motor ?

"In my opinion, best option along these lines is a hydraulic pump off the PTO of a generator -

You bet , The hyd could also power the bow thruster (no short operating tine) and the windlass (no white smoke from large loads) .

If hyd is installed , use it as much as you can !!!

I think the key to making this work, either via electric or hydraulic, is the power requirement for acceptable propulsion. It doesn't take much to make a boat move in calm water, but that goes up a bunch (I don't know how to quantify how much) in rough water. And if you need a get-home motor, there is a very good chance that the need is accompanied by rough water.


To me, the threshold is 4-5kts in calm water. Anything below that and I think you will not make progress against any sort of weather.



The OP said 5hp which is very doable with an 8kw generator as a power source. But I don't know what the 5ph is based on.


I looked at something along these lines for our 68, and concluded it didn't really work. Why? Because it took more power to move the boat than any reasonable size generator could produce. The standard wing engine that drives a shaft and folding prop is 160hp. That seems like a lot, but it moves the boat about 5kts. I suspect there is quite a lot of loss in the off-center prop and shaft, and in the small, folding prop. For comparison, the folding prop is 24" diameter where the main prop is 46" diameter. When you size a generator to produce something even close to 160 hp, you end up in the 100kw range which is way more than you would ever need or want on a boat that size. Again just to put it in perspective, our generators are 12 and 25kw. The 25kw could probably power around a 20-25hp get home motor which is a far cry from the 160hp that it takes to move the boat 5kts.


Now on smaller boats, the propulsion power requirement is less, and perhaps the natural sizing for a generator doesn't drop as rapidly as the propulsion power need such that for some size boat a reasonably sized generator could also provide get-home power. I don't know, but it seems this is what's required fro this to actually work acceptable.


BTW, I know of a couple of boats that have done hydraulic get-home drives powered off the generator. Both do the job, but just barely. But both also drive the main shaft and main prop which is much more efficient that an offset folding prop. I think that's what makes them work, though their performance is marginal in my opinion. But as a retrofit you have constraints, and I think they took the best possible approach. And there is of course a down side; if the main is disabled because of a drive line problem, say a destroyed shaft seal, fouled prop (seems to be the most likely case), or other disabling of the prop, then the get-home is useless too. This is where the independent shaft and prop comes into play in many get-home schemes.


Trade-offs, trade-offs, trade-offs.

I've been studying hydraulics the past few days. My boat is going to have a simple open loop system. I agree that driving a hydraulic pump off the genset crankshaft and powering a hydraulic motor would be the better solution. Chain to driveshaft coupler would be the easier way, IMHO. The chain wouldn't take long to install with a master link set up, if you have easy access to the coupler. Any hydraulic shop should be able to do the math to get the components needed to make the conversion.

diver dave said:

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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My choice would also be a hydraulic solution, but you'd need a power takeoff (pto) on your genset to run a hydraulic motor. If that was possible, you could turn the main shaft by a belt or chain. I have seen this done for get-home power.

ben2go said:

I've been studying hydraulics the past few days. My boat is going to have a simple open loop system. I agree that driving a hydraulic pump off the genset crankshaft and powering a hydraulic motor would be the better solution. Chain to driveshaft coupler would be the easier way, IMHO. The chain wouldn't take long to install with a master link set up, if you have easy access to the coupler. Any hydraulic shop should be able to do the math to get the components needed to make the conversion.

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Keep in mind that a hydraulic drive system will require cooling. This typically means a heat exchanger with hydraulics on one side, and raw water on the other. And the raw water will need a pump, inlet, and discharge. Circulating pump can be AC powered, DC powered, or hydraulically powered. Most of the ABT systems use a hydraulic pump to circulate raw cooling water since it will run anytime the hydraulics are active. Without cooling, it will overheat very fast. So hydraulics aren't necessarily all that simple to add. And have you priced a PTO for a generator? $5k, and now perhaps more.

twistedtree said:

Keep in mind that a hydraulic drive system will require cooling. This typically means a heat exchanger with hydraulics on one side, and raw water on the other. And the raw water will need a pump, inlet, and discharge. Circulating pump can be AC powered, DC powered, or hydraulically powered. Most of the ABT systems use a hydraulic pump to circulate raw cooling water since it will run anytime the hydraulics are active. Without cooling, it will overheat very fast. So hydraulics aren't necessarily all that simple to add. And have you priced a PTO for a generator? $5k, and now perhaps more.

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My ancient Vosper hydraulic stabilizers have the heat exchanger inline in the engine raw water intake - no additional pump required. I just had the exchanger replaced as part of replacing a bunch of hoses and pumps on my 50-year old boat in prep for heading 500 nms to Ensenada where my boat is being refit. The exchanger was only about $150 or so.

Going with the kite idea. Here is a example which is a little more complicated than I would like.

https://youtu.be/Qy3IayvR_SQ

Another sail option.

OMEGSAILS : Kites for Stand Up Paddling, canoeing and boating

twistedtree said:

Keep in mind that a hydraulic drive system will require cooling. This typically means a heat exchanger with hydraulics on one side, and raw water on the other. And the raw water will need a pump, inlet, and discharge. Circulating pump can be AC powered, DC powered, or hydraulically powered. Most of the ABT systems use a hydraulic pump to circulate raw cooling water since it will run anytime the hydraulics are active. Without cooling, it will overheat very fast. So hydraulics aren't necessarily all that simple to add. And have you priced a PTO for a generator? $5k, and now perhaps more.

Click to expand...

My hydraulics are going to be in with my other keel cooled accessories. An open loop system doesn't usually build up heat unless flow control valves are used or there is a high duty cycle with the equipment. With that being said, even though my system will only power my winches/windlasses, dinghy crane, bow thruster, and possibly a get home option. The get home option will win out because it would be a 100% duty cycle system. The rest wouldn't need cooling because they are only used in short bursts. The fluid running through the system wouldn't build much heat. The hydraulic system I'm planning is an on demand system, not a continuous running system. I will have an accumulator and a pressure/flow switch to activate the hydraulic pump's clutch when the system's pressure or flow drop. A continuous running system would require cooling even if the hydraulic equipment is low duty cycle. I won't activate my hydraulic system until I have a need for it. It will mostly be laying in wait until needed. I will have full instrumentation for my hydraulic system.

mvweebles said:

My ancient Vosper hydraulic stabilizers have the heat exchanger inline in the engine raw water intake - no additional pump required. I just had the exchanger replaced as part of replacing a bunch of hoses and pumps on my 50-year old boat in prep for heading 500 nms to Ensenada where my boat is being refit. The exchanger was only about $150 or so.

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I had my Grand Banks set up the same way, for the same reason (no need for another pump). But that approach wouldn't work for a get-home where the main engine is presumably dead.

ben2go said:

My hydraulics are going to be in with my other keel cooled accessories. An open loop system doesn't usually build up heat unless flow control valves are used or there is a high duty cycle with the equipment. With that being said, even though my system will only power my winches/windlasses, dinghy crane, bow thruster, and possibly a get home option. The get home option will win out because it would be a 100% duty cycle system. The rest wouldn't need cooling because they are only used in short bursts. The fluid running through the system wouldn't build much heat. The hydraulic system I'm planning is an on demand system, not a continuous running system. I will have an accumulator and a pressure/flow switch to activate the hydraulic pump's clutch when the system's pressure or flow drop. A continuous running system would require cooling even if the hydraulic equipment is low duty cycle. I won't activate my hydraulic system until I have a need for it. It will mostly be laying in wait until needed. I will have full instrumentation for my hydraulic system.

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I agree that the real cooling demand will come from operating the get-home, so that's what you need to size/design for.


And I agree that your open-center approach will generate the least heat of the various approaches. The worst is closed center with fixed displacement pump with all fluid either doing work or being pushed through a relief valve. That's what I had on my Grand Banks for just stabilization. Next best to open-center is closed center with a variable displacement pump. Those only pump a small amount of fluid to maintain pressure, but otherwise de-stroke the pump to zero flow. Then when there is demand they stroke up to whatever capacity is required. They are move complicated, but have the advantage to always maintaining pressure, and stabilizers seem to want that.

Most of the folding or feathering props are made for modern sailboats that require very little push for a modest speed.

The Luke props are old style , made to push a heavy sailing vessel with an offset wing engine.

Lots more blade area and good sized diameter , just what is needed .

Automatic Feathering Propellers, P. E. Luke. Full Service ...

www.peluke.com › marine-hardware › boat-props

twistedtree said:

I agree that the real cooling demand will come from operating the get-home, so that's what you need to size/design for.


And I agree that your open-center approach will generate the least heat of the various approaches. The worst is closed center with fixed displacement pump with all fluid either doing work or being pushed through a relief valve. That's what I had on my Grand Banks for just stabilization. Next best to open-center is closed center with a variable displacement pump. Those only pump a small amount of fluid to maintain pressure, but otherwise de-stroke the pump to zero flow. Then when there is demand they stroke up to whatever capacity is required. They are move complicated, but have the advantage to always maintaining pressure, and stabilizers seem to want that.

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I see we're on the same page.

Dwsmith69 said:

Another sail option.

OMEGSAILS : Kites for Stand Up Paddling, canoeing and boating

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This looks like the inflatable sail that our French friends used to cross the Atlantic in their powercat. They started out in France and used the sail for the long downwind passages that they could not do under power due to fuel limitations. After crossing the Atlantic and going through the Caribbean they spent a couple of years in Panama before going up the Pacific coast (not sailing that stretch) to El Salvador where we met them.



-Sven

I would be curious to learn how many pounds of force (thrust) is generated by that kite in various winds. That way one could estimate what speed could be achieved.

Trawler_traveler said:

This looks like the inflatable sail that our French friends used to cross the Atlantic in their powercat. They started out in France and used the sail for the long downwind passages that they could not do under power due to fuel limitations. After crossing the Atlantic and going through the Caribbean they spent a couple of years in Panama before going up the Pacific coast (not sailing that stretch) to El Salvador where we met them.

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Hi Sven,
I would like to know more - I have found the brief story from Omega (and got a quote as well), but I'd like to know some more details like was it worth it, what speeds did they average, difficulty, etc. Do you know more, or have a contact?
We were thinking of using one for tradewinds crossings and an ultimate get-somewhere-with-the-wind option.
They were on a Lagoon 43 I believe, which was for sale about a year ago from the pictures which still included the kite attachment.
Thanks

Sven I posted the same on FB for you not too far back but to get some additional opinions I thought I’d post it here too.

As a new single engine trawler owner that has sails as get home propulsion AND a large generator and hydraulic system this intrigues me.

https://www.powerandmotoryacht.com/maintenance/auxiliary-propulsion-unit



Not truly redundant as it reuses the main engine shaft and prop but on a single with a protected prop it seems like a reasonable risk. Carry a spare prop and your risk is even lower.

Wesmar says they offer it in hydraulic or electric driven hydraulic. The electric version would make it much easier in.
a boat without existing hydraulics.

Can a 5HP electric motor turning a main shaft/prop do much to move a 40ft vessel except in mill stream conditions? Our 65HP Yanmar back-up could only do 4-5 kts on a 47ft. Even in its most efficient propulsion form (outboard) 5HP will only move a small 2-person dinghy. While I am sure to get lots of differing opinions, and I am sure there are theoretical answers, I just question the practicality of this approach.

5hp is ridiculously small, but a 12+ kW genset driving an efficient electric APU (like that Wesmar) could very well push a small trawler downwind. Coupled with that kite sail, or even an old used jib, and in an emergency, Bob’s your uncle!

Anyway, 1 or 2 knots downwind is better than sitting still going nowhere. Downwind usually leads to land, right [emoji846]?

Honestly I don’t see why it’s necessary to have a 160hp backup so you can maintain 5kts upwind at sea, for an emergency backup that likely may never be used. But everyone has their own comfort levels for risk, and their own budgets, to work with.

I began a post about the same subject awhile back, still planning to do it as time permits. I've purchased a British Seagull outboard with that in mind. Japanese outboards usually have the power head pretty tightly integrated into the leg, with a lot of extraneous metal. The British Seagull power head can be removed with two bolts (Whitworth!), the remaining leg is minimal, about 16 lbs, has a high reduction and a large 5 bladed prop.

My plan is to get a 1 or 1.5 hp 1ph washdown motor (because they are SS bodied) and make an adapter for the power head. Simply run a cord inside and plug it into the wall. More sophisticated would be a phase converter, that would make the motor a bit lighter (3ph, no start windings). The Franken-outboard would be hung on the swim platform when needed. I'd expect to get about 2 knots in calm conditions.

Is that useful? Not in the open ocean, not against much current, nor against much wind. But up in the PNW, you can wait for good conditions and get them. 2 knots doesn't sound like much, but it is 50 miles in 24 hours. In 3 days you could be back to civilization from anywhere up there. If you read the fine print, "unlimited" tow service isn't really, and up there, there is very little commercial tow presence - nearest one could be hundreds of miles away. You may find a Good Samaritan to give you a tow, much more likely if you are at least a bit mobile (there are many inlets that are blind to VHF).

An alternative might be a trolling motor, Minn Kota has a double 160 lb thrust version intended to attach to an outboard leg, be easy to build the leg. But you would need a very large DC power supply to run it, and it isn't clear what happens if you run one at full chat for days. Another possibility would be a 220V motor, could be 3 hp then but it is heavier and would require restrapping the genset to 220V to use, special circuits, etc.

makobuilders said:

Honestly I don’t see why it’s necessary to have a 160hp backup so you can maintain 5kts upwind at sea, for an emergency backup that likely may never be used. But everyone has their own comfort levels for risk, and their own budgets, to work with.

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I'm guessing this is in reference to my boat? If so, let me correct/add a few things. The 5kt speed on the wing engine is in calm conditions, and speed will of course be less into seas and wind. How much less? I'm not sure, but think a loss of 2-3 kts is very possible yielding a net speed of 2-3 kts. That's pretty slow, but you will at least make progress. This is why I think 4-5kts in calm water is the minimum target for any sort of backup propulsion.


And that wing engine also doubles as the hydraulic APU, so gets regular use. On our last boat I found that the biggest hydraulic load was when weighing anchor in rough conditions. You have the anchor wash running, the windlass running, and intermittent thruster operation to keep the nose towards the chain line. On this boat that adds up to about 80 hp. And docking using both thrusters is around 70hp. So the engine gets a work out.

I"m quite enamored with a dual purpose stern thruster. There have been installs with a fully pivoting design to double as a forward thruster. You have the advantage of a water cooled motor, like a trolling motor, but it also lends well to hydraulics. It is well underwater, to avoid the outboard short leg issue. They hide under the swim platform easily. Not much ER space for support. Plus, it get used and tested with docking. Not sure why they are not more common.

There were only 2 occasions in 8 years that we ever needed the back-up engine (for short periods) but when we did we really needed it to perform as a real engine with genuine thrust. Thinking that you can plod away for days on end to get home at 0.5 kt provided wind and current are not a problem is not worth the effort. Better to invest in a satellite phone and call for help.

The Willard 40 had a get-home setup with an electric motor belted to the propshaft. The ones that I've read about used a 7.5hp three-phase motor. It was factory installed, so I assume the engineering was solid.

One simple rule of thumb is a good prop will produce 20 lbs of push from a single HP.


Perhaps having a buddy tow your boat at different speeds with a scale in the tow line will give an idea to what is needed.

ABfish said:

The Willard 40 had a get-home setup with an electric motor belted to the propshaft. The ones that I've read about used a 7.5hp three-phase motor. It was factory installed, so I assume the engineering was solid.

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musta had a pretty fancy VF electronic motor controller. That or a rare multi-phase generator for a 40' boat.