Pro slip

[peteR75]

I have a 9.8 Tohatsu on a Wetline 300 Air RIB (extended airdeck)

The engine is fine at slow speeds and high speeds.

Somewhere in the middle the engine revs but doesnt get anywhere.

Like a clutch slip in a car.


I have tried to turn the prop in gear and the prop will turn 1/4 turn before the engine turns over.

Has the rubber hub/bush failed ?


Or is it cavitation from the air rib, there is a large v floor which I think is causing too much cavitation.

A mate has suggested a new prop as the current one my be slipping.

I can change weight distribution in the dinghy and it will get a grip most of the time.

Any ideas, is it a trim issue or is the prop damaged.

[jyasaki]

If it holds during the hole shot and at high rpm , I doubt it's the bushing.

A different prop *may* make a difference if you're ventilating, a hydrofoil should help, as will trimming in or lowering the engine (which can be a job if the motor's already as low on the transom as it will go.)

Make sure your tube and floor inflation pressures are correct (while on-water; not on the trailer or parking lot) before you go too crazy making changes.

jky

[peteR75]

Originally Posted by jyasaki

If it holds during the hole shot and at high rpm , I doubt it's the bushing.

A different prop *may* make a difference if you're ventilating, a hydrofoil should help, as will trimming in or lowering the engine (which can be a job if the motor's already as low on the transom as it will go.)

Make sure your tube and floor inflation pressures are correct (while on-water; not on the trailer or parking lot) before you go too crazy making changes.

jky

Thanks, that makes sense.

trimming in did help

My bravo pump is not getting the floor hard enough and I havent adjusted the pressure after submerging in cold water.

I'll try that first.

[willk]

Was the boat loaded much (i.e. two adults plus kit?)

If so, I think that it's possibly just trim, weight distribution and power (or lack thereof)

On my rig (same engine, 2.7m airdeck) I need to keep the leg well down - the second hole up, IIRC. At that, it runs well but with two on board, but the motor can bog down a bit if the weight is too far back. The pressure of the airfloor is critical too - if it is too soft, a lot of energy gets wasted there.

When I'm one up with kit, I don't notice any problem at all.

[peteR75]

yes, it was well loaded self and two large kids, it was very rough with swell.

It wasnt struggling to get on the plane , the prop was slipping, I'm hearing the air deck pressure and I accept that I havent really being getting that up to pressure.

Will try harder and report back

Thanks for your help.

[Fenlander]

This is something inflatables can do more than a hard hull and air decks seem much more prone.

I've found they are sensitive to prop type/condition more than a rigid floor. If your prop is an OE type and not obviously badly out of shape it should be fine though. 1/4 turn of slack in the transmission sounds about right.

As discussed you can't make any judgement unless the floor pressure is spot on.

[peteR75]

Originally Posted by Fenlander

This is something inflatables can do more than a hard hull and air decks seem much more prone.

I've found they are sensitive to prop type/condition more than a rigid floor. If your prop is an OE type and not obviously badly out of shape it should be fine though. 1/4 turn of slack in the transmission sounds about right.

As discussed you can't make any judgement unless the floor pressure is spot on.

I think you have all solved it, thank you.

The more i think about it the problem has been when someone is sat on the floor which will distort it.


It lives on davits, it gets hot and is upto pressure in the sun.
as soon as I drop it in the water the cold water will be dropping the pressure.

I will pump it up after Ive launched it and hopefully it will be fine and no need for a new prop/gearbox.

[peteR75]

update
thanks for everyones help.

It was indeed the pressure of the deck at fault.

I had been filling it with warm air, putting it in cold water and loosing pressure as the temp dropped.

I added pressure after I launched yesterday and i couldnt believe the difference thanks.