Does anyone recognise this SIB?

[kubcat]

Took out our SIB for the second time and was a little disappointed at the performance with an older 15hp. It didn't seem that fast and was wondering if I should get the short shaft motor higher as there was lots of spray.

This boat planed with a 3.5 on it's first outing a year ago.

It has an inflatable keel and floor which I had at about 8psi. The tubes were at 3.5psi as per the compliance plate. I seem to recall that the floor and tubes should be 11psi but have lost the manual.

Amy suggestions?

[Calne Diver]

If there was a lot of spray, shouldn't you lower the motor? Maybe I missed something, sorry!

[thornbackflound]

Most sibs are short shaft designed,sounds like you may have had the leg at an angle?if it planed with a 3.5 ,very small hp?,would of thought you would of got on the plane with a 15hp,my 10hp get's my heavy 4m on the plane no prob

[kubcat]

No problem getting on the plane, just wasn't a Lot faster. Maybe I am expecting too much.

I tried different trim settings and can't go down with the engine so thought I might try up till it cavitates. Probably makes more sense to go down buy that is not an option.

I think the problem is more likely to be not enough air pressure but don't know how high to go on the floor and keel.

[thornbackflound]

Originally Posted by kubcat

No problem getting on the plane, just wasn't a Lot faster. Maybe I am expecting too much.

I tried different trim settings and can't go down with the engine so thought I might try up till it cavitates. Probably makes more sense to go down buy that is not an option.

I think the problem is more likely to be not enough air pressure but don't know how high to go on the floor and keel.

I might try up till it cavitates. Not to good for the engine,shakes the hell out of the gear box

[Pete7]

The sib colour schemes and square bow make it look like a Suzuki often sold under their Suzumar label.

Pete

[Pete7]

Next thought is you may have too much weight at the stern? Shift the seat to the middle position. You might need one of those aftermarket tiller extentions to reach but an old broom and some gaffer tape would do to confirm the problem first.

Pete

[John Kennett]

Originally Posted by kubcat

I think the problem is more likely to be not air pressure but don't know how high to go on the floor and keel.

If you're not sure then the floor is almost certainly not inflated enough. Get that sorted first before you muck about with the engine.

Floor should be something like 10psi which is a lot more than you think it is. Keel doesn't need so much, but does need more than the tubes. Perhaps someone with a similar boat like a Quicksilver airdeck could see what their book says.

[Fenlander]

I'd go for 10psi in the floor as in this Quicksilver manual...

http://www.mercurymarine.com/media/m...-899194001.pdf

It is unthinkable that performance would be similar between a 3.5hp and 15hp... something very wrong here.

[John Kennett]

Originally Posted by Fenlander

It is unthinkable that performance would be similar between a 3.5hp and 15hp... something very wrong here.

Agreed, but let's make sure the boat is set up right first. A floppy floor will lead to prop ventilation and lousy performance whatever the motor.