Boat leaning while underway

[captain red beard]

Hi all, I am after some suggestions as to why my mates boat leans to left while underway. It is a 4.2 Blue fin tinnie with a Yamaha F40 tiller steer.
It is fine at rest and isn't as noticeable while going slow but while cruising at 3/4 throttle you can definately notice the boat leaning towards the left. We have tried to shift most of the weight to the right hand side of the boat which does make it better but is still noticeable.
I was thinking that the prop diameter may be too big? Its a 11 5/8 x 11-G.

Any other ideas?
Cheers Red Beard

[wirlybird]

any trim tabs on it?

like engine annode possibly

[Noelm]

first off, does the steering pull to one side? reckon it does, you will need to adjust the little fin just above the prop, but be careful, you adjust it to steer the motor, not the boat, it is the reverse of what yoi think, do it a bit at a time.

[captain red beard]

Thanks guys I will have a play with it. Marking it first as I have learnt in the past.
Wasnt sure if this would be the problem as the boat seems to drive nice and straight, just leans to the left.

[Moonlighter]

Sometimes boats that have the motor set too low (ie too deep) can have this problem.

So suggest you also check your motor height. Lots of boats have the engine set too low. Because dealers either don't know, don't care, or just want to be extra safe and avoid any possibility of the prop losing grip and cavitating.

Does the boat have any tendency to cavitate, lose prop grip in turns? If it doesn't, then there are quite a few advantages of lifting it one or more holes higher. Better running angle, more revs, better top speed and better fuel economy.

The only way to check that your engine is at the optimum height is to have a look at the cav plate when you are travelling at a decent cruise speed, if it is fully underwater, engine is too low and should be lifted one hole and checked again. Also check it in some turns and if it doesn't cavitate or is the same as it was before lifting, it should be fine. Subject o it not losing grip, the higher, the better, for reasons as stated earlier.

Have a look at this link for advice from the experts about engine heights:
http://www.veradoclub.com/smf/index.php?topic=137.0


Cheers

ML

[Jarrah Jack]

There was an interesting thread on another site about the same problem. It turned out in the end that the boat wasn't made true and so a new hull was the answer. Hopefully with this problem it will be an easy answer. Has it been doing it since new?

[captain red beard]

There was an interesting thread on another site about the same problem. It turned out in the end that the boat wasn't made true and so a new hull was the answer. Hopefully with this problem it will be an easy answer. Has it been doing it since new?

That was the first thing I told him, but he told me that was the incorrect answer.

[captain red beard]

Only just bought the boat second hand. The engine is not the original, pretty much brand new.
We will have a play with it and see what happens.
Thanks for the replies.

[Blusta]

if it was a windy day blowing onto one side in particular, this may cause the boat to lay over in that particular instance; dropping the side the wind blows on.

[Blusta]

perhaps the engine is not perfectly vertical/ parallel with the centreline of the boat

[Lancair]

In addition to the above, I learnt a LOT from driving a 40hp tinny with TnT.
If the motor is trimmed in too far, you will need to be holding a fair bit of force to stop the tiller moving away from you, this in turn will cause the boat to lean to the left due to prop torque. When a tiller steer with electric TnT is trimmed correctly the force on the tiller will be nuetral, ie: You should be able to take your hand off the handle and it keeps going straight.
Do you have electric tilt and trim ? If so you need to trim out more when on the plane. Or, if you dont, then as suggested the trim tab on the underside of the AV plate needs adjusting or you need to lift the trim bar so the motor sits higher/further out from the transom.

[bluefin59]

The battery isn't sitting on the same side he sits I'd hope...Matt

[gofishin]

I notice you say ‘we’, as in two or more in the boat, and I assume the skipper is sitting to the STB side as normal? By ‘shifting the weight’, what & how much/heavy – people, bait tank, esky etc? Is it the same when both are sitting on the rear thwart and other loads are distributed evenly?

As per suggestions in some posts above, especially re prop torque, engine height & motor-centre/plumb placement, but I would also look very carefully along the bottom sheets, comparing the port and starboard sheets, for what are called ‘hogs’ and ‘rockers’ in the sheets. A hog is where the sheet curves up, i.e. into the boat, and a rocker is where the sheet curves down, i.e. into the water. A keen eye can also pick problems from looking at the ribs, from inside the boat- but only if there is no floor.

A hog acts like a tim tab, forcing the bow down, a rocker sucks the transom down and forces the bow high. Depending on the size & type of open tinny, they are generally always made with a little rocker – but both sides should be the same! In your case look for a hog or flat STB sheet (especially close to the transom) and a slight rocker in the port toward the stern. When there is a difference further forward, or around mid-ships, it can also be opposite. If uneven etc they could have been like that from new (bad!), but more likely from an incorrectly adjusted trailer and/or being overloaded at the same time – which can easily cause a hog.

It could also be from a hook in the keel, ie the keel is not straight and curvesto the right or left if you look along it. This causes the boat to want to steer to the left or right, and hence you need a slight adjustment of the tiller to compensate – which causes the boat to lean.

It sounds severe – so it could be a combination of things too.
Cheers
Brendon

[WalrusLike]

Jeez, anytime I start to think I know a little bit about boats I find some guys saying something like this info in the above posts and I realize I am only at square one...

Good informative posts Brendan and others..... well done fellas and thanks for the start of an education.

[Fed]

The Captain's mate has ruled out hooks & rockers on the bottom of the hull & uneven balance being the cause.