Converting an outboard to an inboard

[simcott]

Hello
I have just joined and I thought that I would ask if anyone has converted a small,(~8hp fourstroke), into an inboard engine.
Why you ask, I have a fine clinker wooden boat that would be spoiled by an outboard motor. As this boat is rigged for sailing as well, it requires a good sized rudder to have steeridge.
At present the boat has a 7HP Vire 2 stroke. I have spent a great deal of time reducing the engine noise with a well padded engine box, the end result is that I still have to put up with the noise and considerable vibration.
To my knowledge no one makes a quiet 4 stroke water cooled engine of this size, so I am looking to use a Merc 8 or 9 hp four stroke and re-configiure it to drive the prop shaft.
Outboard manufacturers have put a great deal of work in perfecting these current engines and I wished to apply that research to my needs.
I have looked into electric, but to have 5 hours run time the battery mass would be prohibitive.
I thank you for your forum and hope that someone can shed some light on this.
Regards
simcott

 

[Willyclay]

Re: Converting an outboard to an inboard

Welcome to the iboats.com forum. The experts here, which I am not, can help you with any question about a boat, motor and trailer. I believe it is the best single resource for recreational boaters. Good luck with your project.

 

[Home Cookin']

Re: Converting an outboard to an inboard

I would wonder if the motor will run on its side (I'd think not) so you'd have to manufacture a right angle transmission to link the prop shaft with the motor. You'd be tearing apart an expensive piece of equipment and discarding half of it., just to eliminate some, but not all, noise, adn I don't think the 2 v 4 stroke would affect vibration especially in a home made rig.
Sounds like you want the smallest 4 stroke automobile/lawnmower motor to convert rather than chop up an outboard, especially if you are on fresh water.
Just guessing. Welcome aboard. Are you in England?

 

[Silvertip]

Re: Converting an outboard to an inboard

4-stroke outboards are designed to run with the crankshaft in a vertical plane. As such the oil pan or "sump" is at the bottom of the engine between the engine block itself and the lower unit. If you installed that engine in a boat in a "V-drive" orientation the crankshaft now operates in a horizontal (almost) plane so something would need to be done to create an oil pan or sump and oil pump pickup that is lower than the engine. A dry sump system could be designed but you are now talking a fair amount of money and machine/fabrication work. A water pump and plumbing for the water cooling would also need to be fabricated since on an outboard the water pump is in the lower unit, not on the engine.

 

[kenmyfam]

Re: Converting an outboard to an inboard

Just got to be some better options out there than this.

 

[trendsetter240]

Re: Converting an outboard to an inboard

Hey Simcott, welcome to iboats!

Have you tried installing some better bushings on the engine mounts for your current motor? Obviously the most simple solution is making your current setup quieter.

I do not believe you will find it a viable option to mount an outboard power-head on your existing drive-train.

I have seen some sailboats with an outboard mounted vertical with the leg straight though the hull in front of the rudder. Is that an option for you?

 

[simcott]

Re: Converting an outboard to an inboard

Hi
Thanks to you all for your thoughts, I am aware of the pitfalls of this venture.

I would not consider an air cooled lawnmower engine as a likely option in this case. It may be OK in a cold climate but as we are facing a few days above 38C, more heat in the boat is not desirable. Liquid cooled engines suitable for this are not designed for salt water cooling. A heat exchanger could be used of course, but that is another thing do deal with.

I origanaly thought of positioning the engine so as to offer the output shaft in a horizontal plane but as you point out the oil sump would have to be reconfigured. Also the carburater and exhaust would more than likely be challenges too difficult to re-arrange. So keeping the engine in it's normal position would be better.
Of course the gear housing would supply both the shifting and re-direction of the engine output and so address the drive issues. However it may also be that the gear housing requires water immersion to keep it cool.
I have purchased the workshop manual to study up and I have a chance to view one of these engines as it is going to be fitted to a boat at the dealers.
I have been promised a look see when the engine is in place to check out noise levels and all relevent dimensions etc.
Steps I have taken with the existing engine are considerable, with tight sealing and a well padded engine box. Unfortunately this has produced a heat problem as far as the intake is concerned, after some time the fuel vaporizezs and leans out, the motor overheats and one has to open the lid to allow the engine to resume normal running. Then you get to hear the engine more loudly. I have also made a fuel cooler but it is the air temp that is the problem I fear.
The carbureter intake is one of the most noisy aspects of a single pot two stroke. To this end I have fabricated a specialy padded induction silencer with some good effect.
I have also used a pair of VW CV joints to make a fully floating drive shaft connected to a thrust bearing inboard of the shaft seal, this is to avoid alignment hassles. This has permitted the use of soft engine mounts but the rather poorly balanced engine still shakes the floorboards, different parts of the boat at different revs. We also have the disgusting fuel oil mix that produces smoke.
The use of a "sail drive" system with a prop leg hanging out of one side is out of the question.
I have a well fitted workshop so machining etc. so machining is not a problem.
Admittedly it seems that buying an engine and scrapping most of the parts is questionable, but as most of you would know buying the pwerhead plus all the other bits to get a working engine would cost more than a complete outboard. There is also the opportunity to offer many of the not required parts for sale, we all know how expensive they are.
You know it might also be that I am looking for a nice winter project to avoid jobs I don't want to do.
Cheers from Perth West Australia.

 

[stormin94]

Re: Converting an outboard to an inboard

I believe they make liquid cooled go cart engines that are around 9 horsepower, possibly more like 18. I believe they are verticle shaft. You could rig up something fairly simple with one of those, just make sure you place the radiator somewhere where it can get airflow, and possibly mount an electric fan to it. Then you could rig up a drive shaft to a propeller. It seems like it would be much simpler to just keep it direct drive rather than to mess around with a transmission. I've seen an inboard motor made from an aircooled 12 hp motor mounted in a wooden boat. It was pretty neat, and also surprisingly quick due to the better weight distribution of a more forward mounted motor. The guy who made it did an excellent job on it. If you could get enough airflow around the motor, you could go aircooled. It gets over 105 (43C) here every year and he has had no problems cooling it in those conditions.

 

[Bondo]

Re: Converting an outboard to an inboard

Ayuh,... Crazy thought,... Look into a shaft-drive, water cooled Motorcycle motor...

 

[Silvertip]

Re: Converting an outboard to an inboard

Check your local auto salvage yards for a Suzuki Swift (or the Chevy derivative the name of which escapes me at the moment). These were three cylinder engines that were relatively bullet proof and small (1.5L as I remember). Seems to me that would make an excellent candidate. It could even be canted a bit to port or starboard if height is an issue. Since you have a nice shop, modifying the oil pan and pump pickup should not be an issue.

 

[Home Cookin']

Re: Converting an outboard to an inboard

Seems like an awful lot of work to soften a little noise--are you planning to sneak up on someone? Looks like you might reconsider electric.

I personally like a little engine noise in the boat, maybe it's comforting to me b/c there are too many times when my motors wouldn't make noise, so I got paddle noise instead!

BTW I had a great stay in Perth many years ago; it's a lot like my hometown. I'd like to come back--this time not by bus across the Nullaboor!

 

[BaDucK]

Re: Converting an outboard to an inboard

how about finding a small onan style generater.....already set up for salt water use, and takes all the headaches out of installing....

connect a small hydraulic pump to the genny, and plum hydraulic lines to a slave pump thats connected to prop shaft shaft...or even a stout dc motor ran right off the genny itself

the small self enclosed gennys are very quiet, and designed to be crammed down into dark damp locations, the running of hydraulic lines or electric lines to a pump/motor located where you need it or it fits best will cut down virtually all drive train vibrations....and those small gennys run smooth and vibration free...

you can get them right down to just a couple of HP and in a very compact self contained unit

navy ships and big cruise ships for a long time have run this "diesel/electric" combo...

this would be the best way to do it in my opinion......

you would be using parts meant to be used the way your using them, and the engineering aspects would be like a night and day difference to the better..

and you might even find doing it this way would be cheaper.......plus, you would be using diesel.....far superior for inboard applications


thanks,
Bruce

 

[Willyclay]

Re: Converting an outboard to an inboard

...connect a small hydraulic pump to the genny, and plum hydraulic lines to a slave pump thats connected to prop shaft shaft...Bruce

Excellent suggestion! We have been running a piece of equipment with a hydraulic pump/motor system powered by a low-HP, air-cooled, gasoline engine for many years at my workplace and it has been super reliable with just regular-interval PM. Only problem encountered was the OEM hydraulic motor mounting-plate cracked after who knows how many forward/reverse cycles and we had to fab a new plate. It uses a chain for the connection to the drive shaft.

 

[stormin94]

Re: Converting an outboard to an inboard

Excellent idea for a hybrid boat motor. It would make things much simpler since you wouldn't have to worry about a transmission, you could just reverse the current, and then you would have a reverse "gear" too. Maybe rig something up from an electric golfcart controller for the speed control, and reverse/forward/neutral.