Diesel outboard as 'get me home' option?

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2savage

2savage

Senior Member
Joined
Feb 21, 2017
Messages
278
Location
USA
Vessel Name
Savage
Vessel Make
Seaton 50 expedition trawler
Just hypothesizing here. If a swim ladder were to have a strong outboard engine mount, could a diesel outboard be used in an emergency? What does everyone think?
 
The brief answer is "yes". If you have a strong enough engine mount and either a nice gas or diesel outboard motor, it may very get you 'home' or close enough so you could contact a towing service but, in what time fame? Maybe you can get 1/2 to 2 mph but at least you, are making head-way in the desired direction of "HELP". :rolleyes:

Historically, in the last 20 years, I recall some owners of inboards, installing such an option so it they damaged the running gear, they still had the option of the outboard.
I never did read of anyone actually taking advantage of this modification.
 
Well, use of this would be a last resort. Gas powered is out of the question due to fuel quantity needed.

The scenario for use would be when you are halfway to Bermuda and, say, the prop falls off (a metaphor for serious main engine failure). Two MPH is better than no MPH even if it takes weeks to get to safety.
 
Problem is, there are no small diesel outboards and few large ones (which weigh far too much). My thinking instead was to use an electric outboard, powered by 110 or 220. I have a diesel genset on board and effectively unlimited fuel for it. It doesn't take much power to push a small trawler at 2 knots, in calm conditions. 2 knots is 50 miles closer to civilization each day. Probably not useful in a mid ocean breakdown, but could be quite useful in SE Alaska or upper BC, water is sheltered but remote, 100 miles could put you back in port and save many thousands of dollars in tow fees (there are essentially no tow services there).
 
It's been 20 years since I actually laid eyes on a diesel outboard. It was a large chunk of iron. Given the compression ratios of diesel, not exactly a pull-start affair either.

As previous post suggested, you'd get more use out of investing in some sort of electric motor. Expense would be in batteries and generator. But at least those are useful.

Get home power is vexing. No good options.

Peter
 
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There's the old Yanmar 18hp (D18, D27 and D36). They aren't cheap, but what diesel is!

The propping on any outboard probably means you're not getting the same hp and thrust as 18hp on whatever your existing shaft & prop is, but it could be an excellent get-home - assuming you haven't stopped due to bad diesel!
 
Put me as a “no”. I think it would be entirely impractical. Like a sailboat auxiliary on steroids. Think it through. A mount that’s strong enough to not be ripped off in snotty seas, and hold 100 pounds of dead weight but be able to be lifted clear when not used. How would you start and steer it. An annual dues to BoatUS or Seatow is much more useful and reliable.
 
2savage said:
Trawler has Westerbeke 12.5Kw genset. So, what sort of electric motor has a propeller that can move a trawler?

Yanmar Diesel Outboard Motors
Click to expand...

If you can be happy with 3, maybe 4, knots, then the prop size doesn't matter as much and the electric power needed is quite manageable for most boats (maybe 1-2.5kW). You could get away with a much smaller genset, even the one already on the boat if there is one. If the genset was DC, it is possible to direct connect the motor to the genset, although unusual, so inverters and battery still need to usable.
 
LOL
No one said it would be practical.
 
BandB said:
Mercury 175 hp weighs 528 pounds.
Click to expand...

Come on folks, we are looking for a massive engine to give you near "hull speed". We are looking for an emergecy solution.
 
High Wire said:
Put me as a “no”. I think it would be entirely impractical. Like a sailboat auxiliary on steroids. Think it through. A mount that’s strong enough to not be ripped off in snotty seas, and hold 100 pounds of dead weight but be able to be lifted clear when not used. How would you start and steer it. An annual dues to BoatUS or Seatow is much more useful and reliable.
Click to expand...

First, Seatow would not (and could not) go hundreds of miles offshore to tow a boat weighing well north of 60,000 lbs.

Second, you should assume that the engine mount is sufficient for the task at hand. I did indicate that it would be up to the job. Boat and swim platform are steel.
 
2savage said:
First, Seatow would not (and could not) go hundreds of miles offshore to tow a boat weighing well north of 60,000 lbs.

Second, you should assume that the engine mount is sufficient for the task at hand. I did indicate that it would be up to the job. Boat and swim platform are steel.
Click to expand...

Not sure the answer would be no....probably more like it depends on a few factors whether you vcould get commercial towing. Sea Tow would reimburse up to $5000 if the pieces fit.
 
High Wire said:
An annual dues to BoatUS or Seatow is much more useful and reliable.
Click to expand...

There are plenty of places where your annual dues to BUS or ST won't even get them to pick up the phone. I was only about 15 miles off the coast of Maine and was told "several thousand dollars, could be a lot more" and it isn't even that remote. Up in SE Alaska they don't even have a phone number to call. And if you read the fine print "unlimited tow" does not mean unlimited tow.

Every diesel outboard I have seen is WAY too heavy to even consider. But to move at 2 knots, a 1500 watt electric would be adequate I think. This would be easily powered - effectively forever - by the small diesel genset I already have on board. No batteries needed, just an extension cord. The motor mount required would be very light weight and easily attached to the swim platform. Again, not a solution to drive back from Bermuda, but to get 5 miles to an anchorage for the night and then work your way back to a port in a day or three in sheltered water, watching the weather. Not going to make way against the tide, or against much wind.

The only thing that has prevented me from doing it is you really need a submersible motor, like a trolling motor or small electric outboard. A continuous duty AC electric motor of 1500 watts is itself pretty heavy, partly because of the cooling requirements. Most of the trolling or electric outboards are BLDC or PMAC motors, so you'd need a power supply capable of feeding it continuously. That is hard to find off the shelf, something like 48V @ 40 amps. e-Propulsion for example makes the Navy 3.0, Victron makes a 48V/50A power supply that would power it at about 2/3 throttle indefinitely. Could be used as the dinghy motor otherwise. You'd be out about $4000 for the setup.
 
Most boats that are at home cruising "off shore" have some sort of gen set.

There are multiple ways of using this power for propulsion as a get home.

Most are practical , not as expensive a purchasing and maintaining a seldom used motor.
 
I tried it with a log shaft 9.9 gas O/B on a bracket I fabricated and fastened through the slats in the teak platform "sandwiching" a large section of platform. Structurally was no a problem, ultra calm water was not a problem, any kind of chop or sea = Problem :banghead:

Even with the long shaft, and the platform low enough that the engine lower unit was fully and well submerged, in any kind of chop or sea the prop would cavitate so bad I could not make headway. It was so bad that I determined that even if I modified the bracket to lower the engine it would still not be enough to improve thrust to be acceptable without the engine taking a dunk every cycle. I was never able to create enough way to steer with the rudder. At the kind of slow speed we are talking about pitching is so bad in any kind of sea that just wasn't going to work.

The Mainship 34 is a semi-displacement downeast style hull. Fine entry forward doesn't provide a lot of buoyancy forward, and full flat bottom with hard chines aft and lots of buoyancy just bounce the hull right back forward in pitch. On a full displacement hull might work better as buoyancy would be better balanced fore/aft, but in a sea I think doubtful this is workable.

$0.02 :socool:
 
Keysdisease, Thank you for relating your experience.
It answers LOTS of question.
So much for Plan A. Time for Plan B. Call home for a rescue.
 
Thinking about get home setups is an entertaining mental exercise. But thinking about why you might need a get home setup and deal with those scenarios rather than install a full separate power and steering system that won't be used much and may not work when needed due to lack of use / maintenance is a better mental exercise.

It's been my experience listening to the radio and the few assistance tows I've done along with my own system failures the causes are in this order.

Perhaps Psneeld will log in with his extensive assistance towing background.


  1. Out of fuel. Simple fix, don't run out of fuel.
  2. Dirty fuel, plugged filters. Set up switchable dual filter system. Carry spare elements. Monitor the fuel system and if even the tiniest bit of water shows up deal with it before you put to sea again.
  3. Soft part failure. Impellers, hoses, belts etc. Proactively replace them, carry spares.
  4. Cooling water flow blockage. Install alarms, monitor sea strainers.
  5. Running gear fouled by pot lines. Watch where you're going, have your shaft fitted with spurs if you must frequently run in pot infested waters.
  6. Control system failure. Old mechanical, modern electronic or any of the less common systems. Learn the work arounds. If at sea beyond tow range disconnect the control from the input shaft, governor or transmission. Manually put it in gear at a decent RPM and fix the control shaft with anything handy and that position. Run until within towing range and call for a tow into the harbor.
  7. Drive saver or other soft part between transmission output and shaft failure. Replace them proactively. If you're really concerned carry a blank and bolts. Or better yet, don't use them.
  8. Total steering system failure on a single screw boat. Before you ever head to sea or into remote areas make sure you have emergency steering. Even a good idea for twins.
Now what's left?

Total failure of the main engine or transmission. Very unlikely if you've taken care of business. But it can happen. With a good gen set there are a number of ways the shaft can be turned to provide get home capability in the event of loss of main engine or transmission.

Loss of shaft or prop are the only things I can think of that will leave you completely stranded unable to help yourself. That's the only time a fully independent get home drive and steering system will be of use.

Failure of electronic engine controls. I don't mean throttle and shift, I mean the engine's systems. That's another can of worms all together and if you've got such a system needs serious thought and preparation. My total experience with electronic engines is 3 boats. Two have suffered failures at sea. Not a good track record.

The first was low voltage. The result of a failed battery isolator. A straight forward work around once the problem was identified.

The second was uncertain. Lots of time and money spent to solve the issue. Open, clean and close all connectors, new wiring harness, new ECU.
 
Keysdisease, how fast would the OB push the boat in flat calm conditions?

I would not expect an outboard to work in much of a seaway, there is just too much resistance even if the prop can be kept in the water. I don't think an OB is a good get home strategy from offshore.

A mechanical diesel can be jury rigged for many failures. An electronic may not be. I ran into a guy in Bella Bella who'd been there a week waiting for an oil pressure sensor. Engine would not run without it, and not as simple as just jumping across it.
 
If you have a 12 KW generator, why not install a hydraulic pump on the front of the engine (done on some boats to power a bow thruster). Then take a lower unit from a 200 HP outboard, marry a hydraulic motor to the input shaft of lower unit, and fabricate what you need for a bracket. You would need a volume control to regulate the propeller speed. Add some male hydraulic quick disconnects to the transom and females on the hoses attached to the motor.

You won't go very fast, but the prop will be big enough to push the boat.

Ted
 
I’d like to have a nickel for every hour I have spent in planning, laboring and just generally worrying about the breakdown/get-home scenario. I modified my boat in numerous ways to accommodate several possibilities, none of which I’ve really acted on. The first required reinforcement of the inside of my transom for a swim platform it was never meant to have, installed eight beefy 3/8” SS flat bar brackets, then cored a custom swim platform with coosa board to hold a 5/16” SS C-channel in the center with a heavy SS ladder, all this with the intent to bracket my 9.9 Merc should such a scenario arrive.

I also yanked my genset from beneath my galley (a terrible location) and made a new hatch for it in the veranda, where the crank pulley of the genset is centered directly over the shaft of my single main engine which could easily be belt or chain coupled to turn the existing prop using an idler pulley or cone coupling to engage or disengage.

My concern is less for having to get-home than it is for steerage in rough seas or swift currents. Being able to control roll & pitch gives me a better chance to repair or service whatever is broken. Even if I can’t get more than a knot, I’ll have some directional control. I’m not planning any big time ocean travel and should be in range for our towing insurance 99% of the time.

All the above planning and labor/expense is interesting but far less practical than a decent towing contract. If I can make enough headway to at least steer, I can probably keep myself out of trouble and/or limit my contribution to trouble for anyone else. I’ve looked at diesel and propane outboards but it seems to me that an electric option mounted on the platform would provide the lightest and most practical leverage to perform that service.
 
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O C Diver said:
If you have a 12 KW generator, why not install a hydraulic pump on the front of the engine (done on some boats to power a bow thruster). Then take a lower unit from a 200 HP outboard, marry a hydraulic motor to the input shaft of lower unit, and fabricate what you need for a bracket. You would need a volume control to regulate the propeller speed. Add some male hydraulic quick disconnects to the transom and females on the hoses attached to the motor.

You won't go very fast, but the prop will be big enough to push the boat.

Ted
Click to expand...

I avoid hydraulics like the plague, because they leak. The sort of setup you describe might move the boat OK, but is would be quite heavy to install when you are broken down.

What I had planned to do was remove the power head from a British Seagull (which I have) as they separate easily and cleanly (unlike all modern outboards). Then just machine an adapter for an AC motor. The Seagull has a large 5 blade prop and a pretty high reduction in the bottom end. Run an extension cord inside and plug it in.
 
It was a very long time ago and I didn't run for long because even the wake from a passing boat would cause pitch/cavitation. As I remember I don't believe I even had steerage and at best maybe 3-4 knots, which would have been fine for get-home, if it could have been sustained in even moderate conditions.

The engine was a Yamaha 9.9 hi-thrust from my Sailing Catamaran, a MacGregor 36. With 2 x 9.9HP on the back that Cat would run 10knots + in most conditions. The brackets were infinitely adjustable and cavitation was rare. Different hull shapes, and at speed the transoms stayed in the water. Of course in any real sea we were sailing

:socool:


DDW said:
Keysdisease, how fast would the OB push the boat in flat calm conditions?
.
Click to expand...
 
2savage said:
Just hypothesizing here. If a swim ladder were to have a strong outboard engine mount, could a diesel outboard be used in an emergency? What does everyone think?
Click to expand...

Attached to the swim LADDER? NO

Can an outboard be used as a GetHome engine? Maybe, it depends on it's cruise speed, the current or tide and the direction of the current or tide. If you can only make 3kts and your bucking a 3kt current, you're not going anywhere.

My thoughts are that one should regularly inspect, and properly service and replace parts. The "I think I can get some more life out of this item" (and deferred maintenance) is how props fall off.
 
Keysdisease said:
It was a very long time ago and I didn't run for long because even the wake from a passing boat would cause pitch/cavitation. As I remember I don't believe I even had steerage and at best maybe 3-4 knots, which would have been fine for get-home, if it could have been sustained in even moderate conditions.
Click to expand...

Thanks for that info. I'd be extremely happy with 3-4 knots. But that was a 9.9.

The thread has me looking at this again. I can get a 1HP PMDC motor and power supply/controller for <$500 it looks like. the motor weighs only 32 lbs so the whole thing would be <50. Wonder if I could get 2 knots with that. A couple of the rule-of-thumb type calculators suggest I could.
 
At second look, this could be easier than I thought. I already have an e-Propulsion 1KW outboard on the dinghy. The issue with using it was battery life of only 1 hour and recharge time of 6. Turns out I can get an external battery cable for it, and a 48V power supply capable of running it forever for around $300. Mounting it on the swim platform will be easy, it is waterproof (submersible) so not too many worries there. Only question is will it actually push the boat? That'll be something I'll have to try at launch time in the Spring.
 
How big of a Diesel outboard are you thinking?
I've personally never seen one so I just googled. The only ones that come up on a quick search are as others have pointed out...rather large
there's a 175 HP Mercury. Something like that?

I wonder, if you're talking about a tiny little engine running at a good clip just to barely crawl the boat along it seems like that wouldn't be very fuel efficient...and therefore the mission is defeated right away.
If it's a larger one...such as the 175 HP I found....running at a slow efficient speed to barely move the boat, how efficient would that be?
 
This thread is making me wonder if our 4hp Yamaha dinghy motor can move the mother ship at all if I mounted it to the swim step somehow. Moves the 65 lb dinghy pretty well. Not sure about 27,000 lbs. I suppose I could try to tow the mothership with the dinghy first, that might be hilarious. Better choose a glass-smooth day next spring. I have this vision of a mouse in a harness trying to budge a locomotive.
 
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