25 Merc Outboard Tiller Pulling Hard

[DavidJinPa]

My Father has a 99 merc tiller outboard (no power trim/pull start only) that pulls very hard (tries to make boat turn hard right). We've adjusted the trim tab to every possition, and also put on a new factory prop to try to correct. Nothing fixes the problem. The motor is properly centered on the transom of a 1998 16'.6" Alumacraft boat. Anyone have any idea what the problem could be here???? HELP

 

[Laddies]

Re: 25 Merc Outboard Tiller Pulling Hard

If you have turned the trim tab all the way to the direction that the engine pulls and that won't correct the problem, some times it is the motor isn not trimed properly and if that don't work there is a longer tab availlable, I think that it's listed for Mercrusier--Bob

 

[DavidJinPa]

Re: 25 Merc Outboard Tiller Pulling Hard

Can anyone else think of a way to explain this besides what Laddies has to say?

 

[Virago85]

Re: 25 Merc Outboard Tiller Pulling Hard

Well He11 If Laddies says it, Its pretty much gold He gave you about the only answer there is

 

[skiffer]

Re: 25 Merc Outboard Tiller Pulling Hard

The torque is a result of the lower blades of the prop being in greater pressure water than the upper blades, simply because they are in deeper water where the pressure is greater. Seems like the pressure difference between the upper and lower blades should be insignificant but it it enough to cause the sideways torque on a spinning prop. <br /><br />The trim tab is able to correct for this up to a certain point. I suspect the prob here is the prop is not deep enough in the water possibly because you are using a short shaft motor or maybe it has something to do with the hydrodynamics of the boat. <br /><br />Sometime what happens is you trim the tab to nul the torque at low speeds when the prop is deep in the water but when you speed up the hull starts to plane, then the bow goes down and the transom comes up raising the prop so the upper blades are so near the surface the pressure balance is upset.<br /><br />I would try either a larger trim tab if you can find one or lowering the motor is possible. If the motor is a short shaft, try a long shaft.

 

[WillyBWright]

Re: 25 Merc Outboard Tiller Pulling Hard

Put the tab close to straight, but slightly to stbd on the trailing edge. Radical settings get radical variances in control with different trim angles. You'll never get rid of it no matter what you do. Every tiller motor on the planet does it to some degree. That's why they have steering friction devices on tiller models. If your dad's doesn't have that feature, find out why. It's supposed to be there.

 

[DavidJinPa]

Re: 25 Merc Outboard Tiller Pulling Hard

Ok, Thanks for all the insight. This is a longshaft motor, and it just really has me confused due to it not happening for the first two years he had the motor (on the same boat). Hmmmm, anyways. You guys know where I could find the "larger trim tab" online??? I searched n searched but could find what I think your descibing to me.<br />Smooth boating to ya all, and thanks for all your help.

 

[Motor Boater Bill]

Re: 25 Merc Outboard Tiller Pulling Hard

The steering friction is usually adjustable--perhaps yours has loosened over time. That would account for why it pulls more now when it didn't before. Maybe the prop doesn't pull more but you just feel it more. Just a thought. Ask yourself what else might have changed--hit a rock and bent the skeg a bit? Something dragging on the boat? Changed the location of the tilt pin?

 

[jimp37]

Re: 25 Merc Outboard Tiller Pulling Hard

I have the same problem on my 2001 20hp short shaft.I've tried everything but no luck.Pulls so hard at times ,if I were to let go of the handle at top speed the boat would defenetely throw me.

 

[Laddies]

Re: 25 Merc Outboard Tiller Pulling Hard

Has the tilt pin setting been changed that will effect torque on the steering---Bob

 

[DavidJinPa]

Re: 25 Merc Outboard Tiller Pulling Hard

No the tilt pin hasn't been moved at all. Its been at the same place since the motor was set on the transon. The boat plains out nice, and level where its been back to when the problem wasn't existent. Also the skeg is 100% A-OK factory straight, and Yes pgm this ones the same way. Would throw you in a second. Anybody have any idea who has those longer tabs (net wise)?