Outside the box design for recreational inboard propulsion using lawn mower engines.

[preventec47]

Outside the box design for recreational inboard propulsion using lawn mower engines.

I am seeing a great availability of used "industrial" motors from Briggs Stratton, Kohler, Honda etc. between 8hp and 30hp and other
than paddle wheel drives I am not seeing any cheap easy solutions to get thrust from my preferred source......spinning propellers .
We need to rob cheap stuff off the shelf like drive shafts from cars and their U-joints or the mechanisms from front wheel drive
cars.... I think referred to as CVS ( constant velocity shaft?) . Also how bout centrifugal clutches used in go-karts and
maybe chain drive and sprockets and GoKart rear axles sticking through the transom with props connected to the wheel
hubs etc etc.

If we can figure out how to do this with perhaps scavenged parts off cars etc we can have complete prop propelled water
vehicles for hundreds of dollars instead of tens of thousands of dollars. Sure this stuff wont be "Marineized" but always
pulling it out of the water after use and slathering of oil and grease on the critical parts should slow the corrosion
down. We have to get creative! What are your thoughts ? I am not familiar with the old days but how did
the early pioneers build inboard shaft drive units ?

 

[gm280]

:welcome: to iboats preventec47. You need to take a look at this thread;

http://forums.iboats.com/forum/engi...0069857-26-briggs-aircooled-yamaha-50-project

 

[Scott Danforth]

Welcome aboard..... While I understand your desire, air cooled is not a solution unless your running an airboat or a long-tail mud motor

The resultant explosion or fire would make it a bad day. Marinized motors have a maximum exterior temp under 200 degrees to prevent ignition (fire)
Air cooled motors are as hot as 400 degrees on parts of the block as well as over 1600 degrees for the exhaust.

You can play with an outboard lower and mount a vertical shaft mower motor to it, that keeps the potential for fire limited to hanging off the back of the transom.

 

[Ned L]

There are countless ways to do just what you are talking about (going all the way back to the 1920's - 30's), some good, some not so good.

 

[shrew]

There is a fine line between thinking out of the box and wasting your time. Energy spent pursuing this line of thinking falls in the latter category.

 

[gm280]

preventec47, actually you are a little later to that game. Some earlier "Outboard Engines" were air cooled. Sear sold some under the names of Eska, Ted Williams, and even the Sear brand. And they were air cooled as well. I actually own an old Ted Williams, if I remember the name correctly now, and it was a 7.5 HP air cooled engine. It really looked like a typical lawn mower engine under the cowling. It did what it was designed to do but not much else. I had it on a 12 foot Feather Craft "V" bottom aluminum bat. And while it did get me around, when I replace it with a 9.8 Mercury OB, the difference was night and day with the performance level. The boat came alive with the Mercury engine. But the TW did its job.

 

[GA_Boater]

Unlike an air-cooled outboard, using an air-cooled motor for an inboard isn't very safe. A water cooled motor is a safer way to go.

But you still have the same problems with devising some form of transmission and drive shaft to turn the prop. The drive shaft and prop can't stick out of the transom, it needs to be below the hull.

 

[preventec47]

Thanks for the many well intentioned suggestions and to clear the air I need to mention that I have been
given a horizontal shaft 25hp VTwin Kohler. This will be used in an inboard installation but not enclosed
so there will be plenty of cooling. Those not aware should realize that these engines in commercial lawn tractors
run all day every day at full throttle in the hot summer. They are also run faster than full throttle in racing
go karts and have proven their durability. Anything you thought you knew in the old days about air cooled
motors is not applicable to the new technoligy by Honda, Briggs and Kohler and a few others. They are tough.
and one fourth the cost of an equal hp outboard motor. Regardless mine is free and I want to use it.

I dont need neutral or reverse as that is what oars and engine cut off switch are for.
Further many of you may not be aware of the class racers in the northeast that are using
20hp VTwin inboards in crab skiffs and appear to be having a blast and experiencing solid
reliability. I just cannot seem to track down the specific mechanical details of the components being
used. I'm on it though like a bird dog with the detective work.

 

[boltonranger]

I think that what some are saying is related to safety within the boat. Not necessarily the safety of the motor. I would not want an orange to cherry red muffler where oil or God forbid gas fumes often are.

 

[airshot]

I don't think the posters intention is to take the family for a summer cruise, just something to play around with for a hobby. As a matter of fact those pics are really neat....now ya got me thinking about about those little hot rods. I gotta say they sure look like fun. People have always dabbled in creativity, I have often thought about adding a lawn mower engine to an old outboard leg just for $hits and giggles....

 

[boltonranger]

I do think that one outside the boat could be fun. Saw "man with golden gun" the other night and they had a v8 egg beater contraption on there that looked like a hoot.

 

[frantically relaxing]

Well, if they can mount V8's to chainsaws and make 'em work...

That said, there must be a zillion water cooled motorcycle engines of various sizes kicking around. Still have to cool the exhaust...

 

[preventec47]

There are countless ways to do just what you are talking about (going all the way back to the 1920's - 30's), some good, some not so good.

I/we only need one or two of the ones that worked good. Lets hear how you would do it if we cant copy
those in the past. Go back fifty years and I think there was a whole lot of inboard smallish run-abouts
before they invented Personal Watercraft. Besides what would you rather work on/ get-parts-for ....
a Johnson/Evinrude or a BriggsStatton ?

 

[gm280]

Obviously he wasn't asking about an air cooled engine for a typical fishing boat setup seeing the pictures posted now. And I can see his interest in such little boats with lawn mower type engines. There is a following for such things and I can see his issues. I think we all thought about a standard boat setup with a lawn mower powering the boat and not these little custom boat runners. I say go for it. But do post your pictures along the project for us to see. :thumb:

 

[minuteman62-64]

In the old "Small Boat Journal" (the 1980's, I think) they had a few articles about setting up a B&S (or similar) motor to propel a small craft. I don't remember the types of drives that were used or proposed. Maybe there is an archive of back issues some where.

​When I was growing up, back in the early '50s, my dad had a 3/4 HP, air cooled, Neptune. It actually pushed our 12' row boat pretty well across the pond. But, sure was and adventure getting it started every Spring - I learned a lot of my curse words listening to my Dad pulling on that starter rope

 

[R055]

Add a propeller to a weed wacker and you've got yourself an outboard

 

[ricohman]

I see, this is for small hobby boats. But like garden tractor racing, lets not discuss how much money it takes to keep our hobbies going. Some will see it as a giant waste of cash and others will think its a lot of fun. Most hobbies are expensive if they involve engines.
Post pics of your little racing craft once your get going. I'd like to see some.

 

[airshot]

In the old "Small Boat Journal" (the 1980's, I think) they had a few articles about setting up a B&S (or similar) motor to propel a small craft. I don't remember the types of drives that were used or proposed. Maybe there is an archive of back issues some where.

​When I was growing up, back in the early '50s, my dad had a 3/4 HP, air cooled, Neptune. It actually pushed our 12' row boat pretty well across the pond. But, sure was and adventure getting it started every Spring - I learned a lot of my curse words listening to my Dad pulling on that starter rope

You got me to thinking....back in the 60's when I was a young lad, my aunt and uncle had a small wooden boat with an aircooled engine in the middle with a pull rope to get her started. Inboard with only forward and neutral, no reverse. We would push off the dock and pull our butts off until it started then putt around the river at about 8-10 mph for hours on end. That little one cylinder had about a gallon size tank on her but would putt away for hours. Boat was probably around 12-13 ft in length. Don't recall the brand name but appeared to be a factory build.

 

[Ned L]

Air cooled outboards up to about 4 hp were very common in the 50's & 60's. Louder and hotter,... Yes, but they were fine running (and lasting) engines. I still have a 2 hp West Bend (air cooled) outboard that my dad bought new in 1964. We ran the heck out of it for decades and it still starts easily and runs fine. I have a couple of others too.
I think a small air cooled onboard could be a lot of fun. As I mentioned above, there have been lots of ways to do it for decades. In the 40's & 50's Briggs & Stratton and Wisconsin had "marine engine" offerings where they put reverse gears on their small air cooled engines. In the 50's, Lawson and some others offered marine 'kits' (their small air cooled engine, a shaft, strut, prop, stuffing box and rudder) for do it yourself builders. All these are very collectable today.
For a good 40 years I have been thinking this would be fun to do.
I have seen some nice home built setups done. I've seen v-belts and pulleys with a pivoted idler pulley used to give forward and neutral.
I will say that if you want to do it all "properly", the biggest obstacles are a USCG approved flame arrestor for the carb, and a way to eliminate the gravity feed fuel tank (not USCG permitted).

 

[preventec47]

It has been more than 45 years since my family enjoyed weekends at the lake and on the water with a 40 hp runabout and a big 75hp 23ft cabin cruiser.
Today I am disgusted to see the 100+ / 200+ HP personal watercraft that must gulp hundred dollar bills at the gas pump for a little scootin around
on a Saturday. This is more than insane when I know that smallish boats can be pushed along nicely by 20 and 30 hp motors.
(To be completely honest there is a class of small racers that skim the watertops with only 8HP outboards. yes I said "Eight" so I know
we would have to be happy with 20 or 30hp.)

Indeed todays
largest evolved V-Twin horizontal shaft industrial engines used on commercial lawnmowers and other implements range up to 1 liter and close to 40
hp and I know that these engines when new cost only one fourth of an equivalent power outboard engine. For those with tons of money stop reading
here. This is not for you. I'm saying that there were craft 45 years ago we can copy today with these inexpensive engines if we can only figure out
where to get a prop shaft, with some ten dollar axle bearings to fit and a couple of neoprene "O" rings or other rubber seal to keep the water from traveling
through the prop shaft tube to enter the boat. Probably add in there a few ten dollar u-joints and a propeller to complete a super entertaining rapid transit
floater that might be able to run sun-up to sun-down on a 20 dollar bill.

No offense to the authority figures here ( since they can kick me out ) but I would rather not hear from the nannys and naysayers.
My request to posters is to mix a batch of "can do" juice and chug it before you post. Again, it is not like we are inventing anything.
Others are doing it.... NOW. and have been doing it in some fashion for a hundred years.

I am seeing several hulls or combinations in design of about 11 feet in length and about 52 inches wide with a hull only weight of 160 to 200 pounds
and capable of passenger carry in a side by side layout. Add in engine and mechanicals and I see a total empty weight of approx 350 pounds
and expect to see maybe 35 mph max solo or 25mph with passenger at 80% cruise rpms all day long. This with a 25 hp motor.

Further, I think there is a thousand lawnmowers for every boat in the world and I dont hear of them exploding .... EVER. So I am not worried.
Mufflers- I am not happy about in mowers but there is as much space in a boat as in a car so why not an automotive muffler?

I see riding lawnmowere at Home Depot for less than $1000 with all kinds of speeds forward and reverse with v-belts and it would be fantastic
to use some of that in a smallish boat but I dont want to hold up development as I can always get out the paddle for reverse.