Short shaft or long shaft.

[MasterofHera]

I bought a long shaft 4hp johnson as a back up for my Folkboat onboard engine. What effect if any will it have if I use the long shaft on a tender? Apart from the obvious need to tilt earlier coming onto a beach.

 

[Otter]

As I recall you effectively suffer a power loss but I can't remember the percentage - it maybe 25%. As you're bound to hit the bottom by mistake it may be worth buying some spare shear pins!

 

[MasterofHera]

I would put up with 25% power loss from a 4hp motor. Dont realy want to shell out on another short shaft if this one will do.

 

[Lakesailor]

4hp is plenty on a tender so a little loss of oomph is hardly going to matter.

 

[VicS]

The excessive draught is one thing but the fact that the exhaust outlet will be much more deeply immersed than it should be may make it difficult to start. A bridge to cross when and if you come to it but be warned!

It's on boats that are designed to plane that things become critical from the performance point of view. Should you decide to go for a 100 hp or something so that you can tow a couple of water skiers behind the dinghy then youll need to mount it so that the cavitation plate is about 3/4 or 1" below the bottom of the transom. /forums/images/graemlins/grin.gif

 

[MasterofHera]

Thanks VicS I will bear the hight of the exhaust in mind. Possibly could extend the transom up if it is a problem. Tender not purchased yet.

 

[leomagill]

They can usually be converted if you can get hold of a shorter drive shaft, normally there is an extesion housing on the leg that can be removed, the water pickup pipe and gear rod is easily shortened but the driveshaft takes a bit more technical knowhow to keep the splines on each end and keep it straight.
I've converted a yamaha 8hp longshaft to short shaft and it works fine on a dinghy so it can be done.

 

[VicS]

[ QUOTE ]
They can usually be converted if you can get hold of a shorter drive shaft

[/ QUOTE ] But he wants the longshaft for his Folkboat

 

[leomagill]

Doh! In my defence I have been drinking all day!
/forums/images/graemlins/smirk.gif /forums/images/graemlins/blush.gif

 

[retsina]

I use a 6 hp long shaft Tohatsu which i bought last year on my inflatable tender. It makes no difference what so ever. It is just few inches longer that is all.

 

[William_H]

Yes it will be perhaps worth while to extend the transom up higher to get the prop higher. About 10cms I imagine.

We have this race here in West Oz down a river known as the decent of the Avon. It is for canoeists and outboard powered boats up to 10HP.
Most sane yachties would regard the motor boating as insane. They bounce from rock to rock, capsize and get thrown out.

The boats are purpose built a bit like a punt in shape usually Aluminium. They invariably have a very high transom. I suspect they use LS motors so that the leg kicks back away from rocks at a better angle. I don't think they use any protective cage around the prop but certainly carry spare props and shear pins.
The boats are crewed by 2 people. One to steer and one to balance the boat. (and help recover the boat in a spill.

good luck olewill

 

[VicS]

[ QUOTE ]
It is just few inches longer that is all.

[/ QUOTE ] 5 inches I think you will find. Standard shaft engines are for a transom height iof 15" long shafts are for 20" extra long where they exist are for 25".