Smallest boat with an inboard?

[maa. melee]

So what is the smallest (shortest length) boat with an inboard you have seen or read about? Any limitations to boat length besides shaft angle and space?

[rbgarr]

The 'push boats' for the Maine Windjammer schooners are about 14 feet long with honking great engines, and LIBERTY, a Hodgdon built commuter yacht has an inboard dinghy maybe 12' long. Beautiful lapstrake, with a beamy Whitehallish shape. The shaft (tiny prop!) passes almost level through the deadwood and the outboard rudder is cut out to clear the wheel. It's so lightweight that I think the crankshaft-to-propshaft connection may be bicycle chain and gears to get the shaft low and level... but I'd have to check on that.

I imagine that electric motors could make a very small inboard possible in a similar way.

[paladin]

Jay Benfords 8 1/2 foot steam dink....

[P.I. Stazzer-Newt]

These are short

[Keith Wilson]

For traditional designs, Weston Farmer's aptly named 10' "Irreducible". Here's a link to the original article in the Rudder: http://www.duckworksbbs.com/plans/wf...ible/index.htm

[maa. melee]

That is exactly what I had in mind. It sure is a cute one. What I wouldn't give to have a 1.5-3 HP one-lunger make and break...

[Thorne]

You may need to define the question further to get what you are looking for -- are you asking in an historical sense, or regarding modern motors and designs?

From the various discussions on the forum, it seems that motors have gotten larger and produce higher rpm's than 100 years ago, thus limiting their use as inboards in small boats. They seem to be being replaced with electric motors nowadaze -- does that count?

;0 )

[maa. melee]

I'm really leaning towards traditional applications...and I cringed a little at that picture of the jetski. With so many small boats, it's very hard finding a good small boat inboard engine of the traditional kind, something along the lines of a raw water cooled one cylinder gas engine (or even air cooled). Lawmower engines just dont have the stroke and the RPMs are way too high...

[outofthenorm]

The introduction to our host's Fifty Wooden Boats has the lines, construction and offsets for the Irreducible. It's written by Weston Farmer.

Norm

[Thorne]

There has been some interesting discussions on how to use belts to reduce the rpm on inboard engines on the Rescue Minor threads here -- well worth checking out! Going to the agricultural machineshops sounds like a great idea for belt and pully setups that would really work.

[paladin]

BIL modified a weedwhacker motor and fitted it inside an 8 foot dink that I built back in '69......he used it as a fishing boat for years...

[kc8pql]

I built on of these about 1964. Eight feet long. Had two inboard chainsaw engines.

[maa. melee]

So there is an easy way to get low rpms, high torque, and steady running speeds out of a short stroke 2 stroke engine without re-maching crankshafts etc? How did you tune the rpm's down and keep the torque high enough to turn a wheel? I love Irreducible...it's finding an engine that suits the boat that's hard to find. Maybe a small 2-3HP lawnmower engine with a flywheel to steady, mounted in a housing with a fat duct to scoop up air...something quick and dirty...

[TR]

Strikes me that far more satisfactory power for Irreduible would be an electric trolling motor embedded in the rudder.

Course...then you miss all the noise, smoke, stink, and expense of an infernal combustion plant.

Tad

[John E Hardiman]

So what is the smallest (shortest length) boat with an inboard you have seen or read about? Any limitations to boat length besides shaft angle and space?

About 6"....



http://www.sciencetoymaker.org/boat/index.htm

[Keith Wilson]

Some further inspiration - here's another Weston Farmer design for a sweet little 16' double-ended launch, bizarrely named "Assassin", with a similar motor. Look here: http://www.duckworksmagazine.com/sto...ssin/index.htm
One could certainly use a trolling motor in the rudder (or instead of the rudder for maximum simplicity), or alternately a DC motor in place of the inboard gas engine. The latter would require a certain amount of thinking to work out the batteries and speed control, but it would work fine and be almost silent. Electric Propulsion For Boats by Charles Mathys, or Electric Boats by Doug Little (now out of print but available used) cover the subject. OTOH, the experience of electric power is very different from running a small slow-turning gas engine - better or worse is your call.

[TR]

This one is 13'6" overall, with a beam of 5'7". Her power is a 7HP BMW single cylinder diesel turning a 12" by 8" three blade prop.





That would be the designer at the helm, I'm not really unhappy just trying not to scratch the varnish.

Tad

[paladin]

dogonnit Tad....build a glass box around that one....

[maa. melee]

Wow what a boat...that pic should be on the label of a can of varnish.
As for electric boats...them are horses of a different color...
I prefer the sound, smoke, grease, and rugged-stouborness of a small gas engine.

[Paul Pless]

So what is the smallest (shortest length) boat with an inboard you have seen or read about?

I once saw a yawl boat for one of the oystering skipjacks, similar to the boat pictured below. The yawl boat was less than ten feet long and had Buick 455 cu in inboard in it.

[Cuyahoga Chuck]

Clark Craft offers plans for Heckle and Jeckle. About 8' long. One is powered by a 250cc motorcycle engine that sits amidship between the pilots knees. Because the motor has an integral gearbox you can lock it in whatever gear gives you the proper propeller RPM range.

[Ron Carter]

maa. melee, e-mail me. I can direct you to such an engine if you are interested.

[win_wood]

Hey Cuyahoga,
I have been building Jeckyl......for several years. One of these days I am going to finish it. I have been too busy working on our house project and putting my workshop together. I need to get ahold of that Glen-L book about inboard installations. The hull is about done except for finishing but I have kind of let the motor and hardware installation stall my progress.

[Cuyahoga Chuck]

Win,
I remember.
You were looking to use a snowmobile engine which is about 3 times bigger than what they recommended. And because those motors have no transmissions I suggested there was no easy way to get the prop RPM's down to workable levels.
That's the chink in any small motor installed in a boat. If you try to run the prop at motor speed the boat is rather uncontrollable in tight places and the prop may be going too fast to drive the boat well in the open.
I don't think Glen-L is going to help you. An inboard installation in an 8' hull doesn't allow much room for interpretation. Whoever designed that set-up had to have figured out how to make the bike engine work in a boat. If he didn't proove it was practical the design wouldn't be saleable.
Jeckyl is so unusual that everything you need to know should be on your plans. If it isn't you've got a problem.

[sfrancis36]

This is a picture of my 12 ft 4in Tewksbury, with a 1968 Palmer PW27 8hp inboard. I use it all the time. It's the smallest inboard I know of.
http://www.oldmarineengine.com/discu...54/134943.html

Win,
I remember.
You were looking to use a snowmobile engine which is about 3 times bigger than what they recommended. And because those motors have no transmissions I suggested there was no easy way to get the prop RPM's down to workable levels.
That's the chink in any small motor installed in a boat. If you try to run the prop at motor speed the boat is rather uncontrollable in tight places and the prop may be going too fast to drive the boat well in the open.
I don't think Glen-L is going to help you. An inboard installation in an 8' hull doesn't allow much room for interpretation. Whoever designed that set-up had to have figured out how to make the bike engine work in a boat. If he didn't proove it was practical the design wouldn't be saleable.
Jeckyl is so unusual that everything you need to know should be on your plans. If it isn't you've got a problem.

[Jamie Orr]

So what is the smallest (shortest length) boat with an inboard you have seen or read about? Any limitations to boat length besides shaft angle and space?

Maybe not quite the shortest, but definitely the coolest, would be Alpha, the 12 foot clinker built dinghy with a steam engine. See http://www.northweststeamsociety.org for more.

Jamie

[Peerie Maa]

I have seen small, with a Stuart Turner inboard, maybe a 10' clinker stem motor boat.

[Garret]

I used to have a 12' plywood lapstrake launch with an 8HP Yanmar in it. It now lives the next peninsula down from the original poster. Really fun boat for tooling around the Maine coast.

[Clarkey]

I always liked the Dutch opduwertje - used as push boats for sailing barges, usually with a chunky diesel or hot bulb engine. Steel, of course.

[Garret]

Nice clean wake from that.

Not so much..... Pushing her beyond hull speed?

[Clarkey]

Nice clean wake from that.

Not so much..... Pushing her beyond hull speed?

I think that is the inevitable consequence of a short, heavy boat with loads of power, a huge prop and no hope in hell of planing! Still, must have moved those barges around pretty well.

[robm]

Hydraulic drive may make it feasible to make a small high speed engine turn a big prop slowly. It also means that prop angle is not the same as engine angle (level is better for oil pickup etc.) and the engine can be placed just about anywhere it will fit in the boat. Reverse is also very easy to arrange. I am not sure about cost, but I bet a system sourced from low-end industrial supplier (Princess Auto, e.g.) would be pretty competitive with any kind of marine gearbox.

One drawback is efficiency. 80% is about maximum efficiency from end to end on the hydraulic system. However, the higher efficiency of a large, slow prop may make up for this to some extent. It also needs a reservoir, which will take up room and add weight. Also, the low-end industrial stuff may not last well in a marine environment.

It might be fun to try, though.

[Outlaw]

I think one of the designer on here built a little tug with a inboart not too long ago. can't remember. maybe tad roberts I think.

Outlaw

[TR]

the engine can be placed just about anywhere it will fit in the boat.

Unless you come up with an engine that weighs nothing, the only place to put the engine in a very small boat is right in the middle. Anything else is bad design. It is tempting to move the engine forward, to be countered by crew weight aft.....But the boat sits nose down when empty which looks like a mistake....

[Wooden Boat Fittings]

What I wouldn't give to have a 1.5-3 HP one-lunger make and break...

That's what I had on my 12' clinker putt-putt Serenity -- a single-cylinder Blaxland (traditionally painted red, not blue) --

It had a dog-clutch which allowed you to move it from neutral to forward. That was all. If you needed to go in reverse you stopped the engine altogether, then started it again by pulling the flywheel round backwards -- instant reverse....

You removed the magneto altogether and took it ashore with you to stop the vessel being stolen.

Mike