B/S Motor to drive out board motor lower unit

& where will you get this mythical abundant hydrogen?

.........from expensive dirty (CO2 wise) electricity I expect!!!!!

We had went down this dirty road a couple of weeks ago when someone asked about putting an electric drive on a fishing boat. If you need a supply of HHO gas, get some solar panels and a tank for a separator, add water, tubing to collect the HHO, And pump it into your motor. There is much more detail to go into that, but that is the jest of being on the open water for a never ending supply of HHO.

Yeah but, you guys don't think I will have any problem with putting a B/S Riding lawn mower motor on the outboard ? I think it will work alright like I said b4 I am after longevity not power for getting on a plane.

Yes sir I do think it can be done .I would recommend putting a gear reduction on the final drive . If you are after the pushing not the speed . It would be much less load on the motor and you can increase the pitch on the prop. If you capp the RPMs around the 4000 mark you should be able to get a reduction that can handle that input. In trying this you sound as though you neck is red. There are not many necks redder than mine so , I am going one step farther to say the transmission off a tiller to convert the power to the water. that would allow a good reduction but keep the torque

I will thank you very much for recognizing me as I am and dare I say proud of it. But why would you put a gear reduction on this and not be directly on the spline's of the drive. Only asking no offense meant.

NO sir no offence at all . I was just hoping to take a bit of load off the motor, and not let RPMs do all the work. I would say with reduction you can increase your torque.The water is going to have a bunch of resistance. And a four stroke needs RPMs to work. I would even go as far to put a fly wheel on it to smooth it out thru the the range.

Well thank you for that I have taken the liberty of torching the original crank shaft with the end of the interior splines to fit on the drive splines in order not to have to use a motor couple. But ho do I go about attaching the motor to the base and using the gear reduction to couple to the crank spline and will I have to worry about water coming up from the bottom as for the centrifuge is still attached to the lower unit. Also for now I will not go about using hydrogen as long as I can get this going at all, which I feel pretty good about doing.

OK let me get it in my head . Is this a vertical or horizontal shaft motor? I can work with both and it may take some true shade tree engineering, but we can get thru this. And also what HP are we talking about? I'm thinking that we could use a flex coupler or if you have the tools we can cut a new key way or a taper lock to allow for a nice pulley system and ditch the reduction gear and go with some much cheaper and more available v- belt drive. I see things in my head now... images are comming...

We may be able to help you with the engine conversion. Can you tell us some of the parameters of the original set up like HP, RPM, what is the reduction ratio, propeller pitch, etc. That way the new engine can be operated in a useful output range with suggested propeller or other changes.

How many HP is the new motor. If its "lawn mower like" I suspect it's designed to operate at a max of 3600 or 4000 RPM.

The original motor or power head was approx. 115 hp Evinrude motor the pitch of the prop I don't know I think it is 30 degrees maybe less maybe alot less I think it is a standard 10 inch prop. and the motor to go onto this is a 10 horse riding lawn mower motor. As far as the gear reduction I don't know at this point.

I seriously doubt that this will work with some extra gearbox installed to cut the revs by about 80%.

Think about it, the props size and the gearing were for a 115 HP motor, a 10 HP motor will just keep stalling trying to turn that thing!!!

So you probably need to reduce the revs via a gearbox by about 80% as I said.

You would be better off buying a small petrol outboard with a 10 HP motor already in it!!!

If the prospective power-head is a 15Hp B&S engine, it is rated at 3600 RPM. It will probably require a 10x8 or flatter pitch prop to allow the engine to reach 3600 RPM. The original 115 Hp Evinrude was rated at probably 6000 RPM and would drive a 10x18 or coarser prop.

Since the new engine output is in the range of 1/10 the HP of the original there are some issues as the above posts have pointed out. Not only would I try to reduce the output shaft speed and possibly reduce prop pitch but if I did these kind of "guesstimate" calculations I would also look at the relationship between HP, speed, and HULL DISPLACEMENT. That can get you to the resultant propeller RPM, torque and pitch so you can back into the reduction you need for the new motor. By doing "guesstimates" these two ways you can see if there is agreement and therefor a possibility to succeed (meaning your going in the right direction).

To find the overall gear reduction of the lower unit just count the shaft rotations of the input compared to the output (prop).

To me personally, this is another proof of the fact that many non-engineers try and use CR4 to do impossible things against impossible odds without the benefit of any brain cells. Its simply completely stupid....and totally worthless.....whats new?

The original poster would be better off by far by buying a much smaller outboard, in a working condition......sorry to be so critical.....but thats life, ain't it?

Well maybe you shouldn't ought to be so critical and just try to read about everyone else's dream's and if they can't be brought to fruition and you know it in your heart and soul say so.

Unless you are the type of person that says what he want's without any consideration of anybody's feeling's at all.

Hello Michael, I did a little research and found the final drive (engine RPM to propeller RPM) is 2.07:1 for the Mercury 115 Hp outboard. I'm making a guess here but maybe your unit's ratio is about the same. That being the case lets look at some of the design issues.

The first is the gear reduction proposed by Logix101, Dave B, Keith E Bowers, and Andy Germany. According to specifications your Briggs and Stratton engine produces 10 HP at 3600 RPM.

Now it's obvious that 10 horsepower at 3600 RPM will not spin a loaded propeller designed to absorb approximately 60 HP at 1739 propeller RPM (3600÷ 2.07). You'll need to increase the torque by reducing the RPM delivered to the old engine 's drive shaft by at least 4:1.

Therefore I suggest installing a 3" diameter pulley on your engine and a 12" pulley on the drive shaft. This will net you about 434 rpm at the propeller with your engine running at 3600 RPM. I'm not sure of the size of you boat but on our family 18' runabout with a 115 HP Mercury, 450 propeller RPM around (1000 RPM on the tach) pushes the boat about 6 to 8 miles per hour.

According to B&S fuel burn spec's for a 10 HP Generator set you should expect to burn about 1 gallon per hour.

As far as mounting the engine, without some photos or a drawing of the lower half of the outboard you have we can't really help you except to say find a machine shop and let them mount the unit.

As to your desire to operate using hydrogen as a fuel I suggest you research the internet and find out about converting your engine to some gaseous fuel such as propane or natural gas. This will give you some idea of what you'll need to use hydrogen as a fuel as the carburetors designed for these fuels might also work with hydrogen.

A word of caution here, hydrogen is extremely volatile and will ignite readily so read all you can about using this fuel safely. Also these small engines do not have much of an oil reservoir so you must not tilt the engine more than a few degrees or else you may uncover the oil squirter pickup and burn a bearing or worse.

Thank you very much for the needed input of this mess I seemed to find myself in. I have done alot investigating of hydrogen fuel usage and for the most part the internet is where I found out that it can be done. As for actually doing it at this point i find myself up a tree. But it will not scare me away as for the power ratio I thank you again and didn't really know what it would be, but the one thing we are not looking at is whether or not the centrifuge will continue to work bringing fresh water from the bottom and whether it is needed for this lower unit to cool the existing drive unit but also can I use it to a fresh water bait well for fishing or do I need to cap it off totally?

The water pump ("centrifuge") is only there to pump water to cool the original engine and since the original engine is gone there is no need for the water pump.

There are a series of screws when removed will allow you to separate the lower propeller drive unit from the vertical portion containing the drive shaft. You'll find the water pump impeller on the drive shaft. It is made of rubber and can be easily removed off the end of the shaft. The water pump contributes to parasitic losses and merely blocking it off does not stop the waste of energy required to spin it.

While you are there you might want to grease the input spline to the lower unit and check for corrosion. A little preventative maintenance here will extend the life of the all important seals. If you have access to a maintenance manual for that particular brand and model of outboard motor I strongly advise you to follow the maintenance instructions for maintaining the lower unit.

I have an old 2 hp evinrude foot . I took a 31/3 hp briggs and stratton lawnmower engine ( 4 stroke) and drilled hole bigger where a mower blade used to be screwed onto and slid it over the driveshaft going down into the foot then drilled a hole through them and bolted together...Problem was the 4 stroke under too much load to start while connected to foot. So I am thinking a flywheel will help it start and run as well as offering stability to the boat while running. But not sure of this idea. Other thought is and I will probably go this route is putting a centrifical clutch ( like used on a go cart) and putting between motor driveshaft ( crank shaft) and foot driveshaft especiaslly since the foot has no nuetral or reverse but rather forward gear at all times, I like that because less to go wrong lol. The centrifical clutch will allow startup of the motor and then when you rev motor up it will catch traction thus spin driveshaft of the evinrude foot.I will then have a nuetral when its idling. I would say the centrifical clutch would work for years cause it sure wont be under stress a go cart puts on it . I could be wrong about all this but I beg all and anyone to correct me if you see flaw in this idea...I would in fact greatly appreciate all input..

I think you are on the right boat now mate. Anchors away! But what size is the boat that you will use and why such a small motor? Also will you use the HHO for fuel with or without gasoline as I have seen in the past some will use gasoline with HHO.