Am I trimming up too much?

bcj.jones

Seaman
Joined
Nov 17, 2017
Messages
72
I have a 2005 Fisher Pro Hawk 180 (essentially a Tracker 175txw) with a 90 horse Merc on it. Under full power if I trim up just one or to "clicks" too much the boat tries to turn left on its own? Anyone experience that before? I just trim back down and it'll bite and correct itself, but i'm curious as to why it does it?
 

dwco5051

Commander
Joined
Sep 14, 2008
Messages
2,326
My Nitro does the same thing when running flat out and trimmed out where it is just running on the pad. I assumed that it was caused by the boat heeling slightly to counteract the prop torque. Without playing with the trim tab or weight distribution my solution is to not run it flat out. As I am approaching 80 years on this earth I not only realize I don't have the reflexes to control a boat at that speed I am never in that big of hurry to get anyplace. I just trim and than add a couple of hundred rpms past the point it stays on plane. At today;s gas prices speed isn't my biggest concern.
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
27,030
Pulling left is a sign of high trim. However, since you only trim a bit, maybe the motor is mounted too high.
 

Fed

Commander
Joined
Apr 1, 2010
Messages
2,457
i'm curious as to why it does it?
It does it because when over trimmed the angle of attack on the Port side blades is greater than that on the Starboard side.
The reverse is true when you're under trimmed.
 

jimmbo

Supreme Mariner
Joined
May 24, 2004
Messages
12,944
It does it because when over trimmed the angle of attack on the Port side blades is greater than that on the Starboard side.
The reverse is true when you're under trimmed.

That's pretty much the explanation.
In addition, most engines rotate clockwise when viewed from above. Newton's 3rd law says that the engine block will try to spin the opposite direction, this torques the engine in the direction that will steer the boat to starboard

Just be aware that if the engine is suddenly slowed down or quits, while at hi speed and trimmed out, the boat might veer to port very sharply.
 

Fed

Commander
Joined
Apr 1, 2010
Messages
2,457
And it's the engine torque (usually Starboard, counter clockwise when viewed from above) that the little fin is on the motor to counteract, that's why it's turned to the Starboard to push the motor back towards the Port.

It's quite the balancing act when you nut it all out eh jimmbo?

I like to start with arranging weight to get the boat level & fast plane with a shallow 3 to 5 degree attitude as they say that is the best.

Then move on to the engine torque by adjusting the little motor trim tab and finally use the T&T to even out any steering torque. I don't try or need to change the boat attitude much with the trim at all.

All in all it's like herding cats when you put engine height & various props into the mix.
 

Texasmark

Supreme Mariner
Joined
Dec 20, 2005
Messages
14,544
Don't remember what i used to do. May have been tweak my trim tab for where I liked to run which was flat out whenever possible and at max trim. On my '89 Ranger I'd get on the pad and trim out till I started loosing speed and rpms started increasing. Don't recall what if anything I had for a TT....too many boats over the years. On the alum padded boat in my avatar (my last boat) the transom pitch was too steep and I never could trim out far enough to get the prop surface ventilating so I don't know there. I was running a 24 pitched prop on there and had the thin Quicksilver tab and had to notch it just a bit to get the blade tips to clear.

In short, I'd play with your TT first. When standing at the rear of the engine, turn your tab in the direction that the boat wants to go.....if it wants to to to starboard (right) turn the rear of the tab to the right.... How far? Trial and error.
 
Top