Engine trim tabs

Scousedeli · 03 September 2009, 09:28

I need to off set the trim tab on a 75 mariner but I cannot remember which way to off set it, anyone know which way it goes?

Cheers

Lee

9D280 · 03 September 2009, 10:56

That depends what your steering feels like!

If it pulls to port, turn the tab to starboard a bit, & vice versa. The actual angle will depend on your boat, prop, speed, etc etc etc.

Best bet is get a cheap socket with an extension, go for a spin. make a small adjustment (hence the cheap socket, coz if you drop it.......) try again. When it's all nicely balanced, put the plastic cap over the access hole & job done!

SPR · 03 September 2009, 11:19

ermm....i might be wrong here, i thought you always turned the tab to the direction of error.

ie ...if it pulls right adjust to right, if it pulls left adjust to left.

S.

alystra · 03 September 2009, 11:52

Quote:

Originally Posted by SPR

ermm....i might be wrong here, i thought you always turned the tab to the direction of error.

ie ...if it pulls right adjust to right, if it pulls left adjust to left.

S.

That's always confused me too. However, it depends on which way you're facing - in the boat or out of it.

I still don't know, but mine's ok anyway.

9D280 · 03 September 2009, 12:15

It doesn't actually turn the boat, all it does is loads the steering one way or t'other.

The high level version is move it one way - if it gets worse - move it the other!!

Scousedeli · 03 September 2009, 20:47

Thanks for all the replies.....I think! Next time I'm out I'll give all your ideas a go!

Lee

wavelength · 03 September 2009, 21:04

I seem to remember being told by a man who knows about these things that you offset the engine and turn the trim tab both in the direction of prop rotation. Not that I've ever found adj of the trim fin alone of any use at all.

JSP · 03 September 2009, 21:08

I've been told if your bow is wondering to the right you adjust the trim tab to the right (your right if your out of the boat and facing the transom), same goes for the left.

alystra · 03 September 2009, 21:41

Quote:

Originally Posted by JSP

I've been told if your bow is wondering to the right you adjust the trim tab to the right (your right if your out of the boat and facing the transom), same goes for the left.

Yep! Says something like that in my instruction book too. It seems illogical.
Can anyone explain the physics of it?

Maybe it's quantum physics.

wavelength · 03 September 2009, 21:48

well I was told its cos its not a rudder-as there is a pivot in front of it on the engine leg. But as you are normally fighting the prop torque I have always found offsetting the engine to be the answer.

PeterM · 04 September 2009, 09:13

My understanding is (I'll use port & Stb to avoid left/right confusion) - if you have to apply port steering, then you want to get the trim tab to do this for you . As the trim is at the back of the outboard you need to force the back of the engine to port - so to do this you turn the trim tab over to the stb side of the boat .

The trim tab will try & run straight through the water rather than at an angle that is created with the motor straigt ahead (for the same reason that your prop pushes you forward, wings get lift etc etc) - so will try & push the back of the leg to port to acheive this. And vice-versa ...........

Hey presto the tab is now providing the force so you dont have to on the helm !

(I think.................)

jyasaki · 04 September 2009, 15:15

The trim tab (well, mine does, anyway) also has a bit of an airfoil shape, though, so will try and pull a bit to the arched side. So it doesn't try to run in a true straight line, but a slight offset.

jky

alystra · 06 September 2009, 15:14

Quote:

Originally Posted by Blackroady

My understanding is (I'll use port & Stb to avoid left/right confusion) - if you have to apply port steering, then you want to get the trim tab to do this for you . As the trim is at the back of the outboard you need to force the back of the engine to port - so to do this you turn the trim tab over to the stb side of the boat .

The trim tab will try & run straight through the water rather than at an angle that is created with the motor straigt ahead (for the same reason that your prop pushes you forward, wings get lift etc etc) - so will try & push the back of the leg to port to acheive this. And vice-versa ...........

Hey presto the tab is now providing the force so you dont have to on the helm !

(I think.................)

Ah! Yes. (I think).

Many thanks.

phillnjack · 27 September 2009, 19:51

The main object of the trim fin is not to turn the boat at all.

The whole idea is to help the steering effort required.
If you can steer easy to the right but its hard to steer to the left then you adjust the
tab to help against the torque effect.

Unless an engine is offset on the transom it will walk to one side no matter how much
trim you give it.

In an ideal world the outboard should be able to steer to left and right with the same
amount of effort required.

phill