How to operate trim

[Dilluzionz]

1985 Four Winns Horizon 190. OMC 3.8L V6 I/O.
Replaced faulty trim pump. Now, how does it work? I have separate tilt which I understand.
My trim raises and lowers the front of the engine. When I push the up trim, the front of the motor goes all the way down, which I believe makes the outdrive trim up? If this is the case, I'm not sure why I need it, as before I replaced the pump, the front of the motor was all the way down, so trim was all the way up? Boat ran and runs fine in that configuration. Gets up on a plane, doesn't cavitate. What is the proper way to use the trim?

 

[Lou C]

Trim is used to get the angle of the boat at the optimal angle to the water, which will improve both performance and handling. Normally with a conventional trim system, you start with the outdrive all the way down (or in) and start to accelerate on plane. As the boat planes out, the bow will drop down a bit lower than is optimal. So now you tap the trim up button a couple of times to lift the bow and at the same time you can feel the rpms rise a bit because the boat is traveling through the water with less resistance. When properly trimmed it will perform and steer better. So on the stringer drive, I think you'd start with the engine all the way up (that lowers the outdrive) and then as you come up on plane you lower the engine a bit (that raises the outdrive). Make sense? I have an OMC Cobra on which the trim works exactly the same as a Mercruiser or Volvo SX system.
On a boat with a straight inboard, you use trim tabs to achieve the same goal and tabs can be used on boats with outdrives and outboards to provide additional trim options (side to side trim).

to answer your question, the boat will get up on plane faster if you start with the drive all the way down. The engine will labor more trying to plane out with the drive all the way up. So proper use of the trim also reduces the load on the engine.

 

[Dilluzionz]

That makes perfect sense. I'm taking it out tomorrow and will experiment with it.
Thank you!

 

[Dilluzionz]

Wow, what a difference! Almost instantly on plane and then trim up. I had no idea that trim would make such a difference in performance.
Thanks Lou!

 

[Lou C]

Glad it worked out, good thing you asked!
I think I had our boat a season before I discovered trim, my brother asked why aren't you trimming it out...and I'm like what's that lol. A very long time ago. I was starting with the drive down like you are supposed to but never trimmed up to lift the bow, so the boat tends to plow a bit, there is an optimal angle for the hull to have to the water. This is one of the main advantages of both I/Os and outboards vs straight inboards. Inboards have to use trim tabs to get the same effect, but I/Os and outboards are still more efficient since the prop shaft angle is adjustable and can be much closer to optimal. Of course a straight inboard boat is a lot simpler to maintain though.
Most boats will struggle trying to get the boat up on plane if the drive is up. The idea is to reduce the stress on the drivetrain, save fuel and get better performance.