Folding prop for outboard ?

[Javelin]

I have an 8hp outboard, housed in a well.
The issue is that when sailing, not only is the noise of water sloshing around in the well annoying, (let alone the drag it must create) but the outboard prop causes drag and disturbs the flow over the rudder.
I have made a couple of baffles that fit round the leg of the outboard at waterline level and this has killed the noise, though they need removing when I start the engine to allow the cooling water to drain.

Of course on option is to lift the engine out of the well but this is a hassle and on a 23ft boat there is then an issue of where to put it.
Yes I guess it could be hung off the pushpit but the 8hp is not that easy to manhandle and I'm not keen on hanging that sort of weight any further aft than I really have to.
It could also be dumped below but again there's not much space as it is and if I need the engine in a hurry it could be a problem.

So the answer, or at least a good chunk of it, would be to have a folding prop.
But does such a thing exist for an outboard and if not why not.
I realise that a % of the exhaust exits through the prop but surely this is not an insurmountable problem.

Any thoughts ?

 

[sarabande]

I have not come across any folders for outboard ... yet !

Wonder if there is any possibility of making a plastic 'cone' on a rigid stick, shaped so that it encases the lowest part pf the leg and the prop ? That way you could leave the motor in position for ready use, and use the cone to act as a shield round the prop when you are not motoring. Something shaped like one pointed end of a rugby ball might work. Perhaps if you can reach the prop a rugby ball with a slit in it would stay on by hydrodynamic force and a piece of string ?

 

[duncan]

not sure how a folding prop is going to help here because of the shape of the blades on a high speed prop as used on OBs, rather than the, generally, low speed ones used on shafts.

overall I suspect there is significantly less drag from the freely rotating existing one than could be achieved by any folding one

the drag from the OB overall is the bigger issue, but it's designed to be as efficient as possible for the necessary bulk - so adding a cone etc is unlikely to reduce the drag and very likely to add to it.

one possible solution would be a sliding plate system (as used on racing power boats to raise and lower the OB on the transom - not tilt) but you are not likely to get the whole thing clear of the water this way.

 

[VicS]

In addition to the speed ( rpm) issue I wonder if the dog clutch normally used in outboard gear boxes would also be a factor.

Gear engagement on shaft drive gearboxes and even sail drives is by cone clutches I believe. Outboards have dog clutches so gear engagement is sudden, not at all gentle or progressive. That would perhaps have to be catered for in the design of a folder.

 

[prv]

I find it unlikely that folding outboard props would exist, because the market for them must be tiny.

Most outboards are on pure powerboats, motor dinghies, etc, so strike them out. Of the remainder, most can be tilted out of the water in situ - they don't want to buy folders. Of those still left, some will get the leg out of the water by other means - dismounting the outboard, or some cunning lifting device. Of the people not yet covered, who have a sailing boat with an outboard leg unavoidably stuck in the water, many will not care, or care a little but not enough to spend the money. The final group left, which you are in, must be miniscule.

Hence no folding outboard props.

Pete

 

[William_H]

Outboards

As said forget folding prop idea. I personally prefer the transom mounted bracket that allows the o/b to be both tilted and lifted. And frees up a lot of cockpit floor. But then I usually keep my o/b at home and sail without motor. Easy conditions here. A pair of paddles seems to suffice if wind drops. Which it doesn't.

Anyway I have admired some boats where the o/b is in effect in a pit but the aft end of the pit is open right through to the transom so motor can tilt up and away. This boat was called a Marauder 24. The rudder is ahead of the o/b. Another version of the same boat had a motor on the transom itself in a well a bit like many small power boats. Aft but not as far aft as on a bracket.

I would suggest you consider a bracket arrangement that will lift the o/b on a curved track so that in lifting it swings forward in an extended well so that prop can come inside the hull then slide aft inside the hull. A plug could drop into the hol;e in the hull and another cover over the huge well.
Or try a transom mounted bracket. You could compare all the pros and cons for yourself before sealing up the hole in the hull. As some of my friends have done. good luck olewill

 

[Javelin]

Ok, so that looks like a non starter.

So the other option is to find a small inboard of some description.

Anyone know of a physically small 6 to 8hp engine for low cost ?

I've got a 8hp Honda engine here from a farm pump but of course no gearbox so no reverse, which is a shame as it would fit nicely.
I've even thought about turning it into a generator and running an electric motor for propulsion.

 

[simonfraser]

i down graded my o/b from 6hp to 2.3, aircooled, less bits to go wrong.
the 6hp never had to be used at full power.

the 2.5 drives my boat into 20knots of wind and the tide at 2.5knots of boat speed. not a lot, but then i dont have to go far. i have not tried to motor into a nasty chop yet . . . .

much easier to handle and store.

 

[Javelin]

What make is the engine ?

 

[fergie_mac66]

back in olden days

the wells had a plug shaped to fit the hole sort of the shape of the hull it was split and a shaped hole was made to fit the leg produced a sort of saildrive leg .. they werent that hard to make .. .. er the water outlet was piped over board . That stopped the sloshing and reduced cavitation.... I assume the outboard is a long shaft or you would get a lot of sloshing and not much motoring