When to trim up?

1

1974merc

Cadet
Joined
Aug 21, 2009
Messages
20
I saw something that said that for my type of stern drive I'm not supposed to trim up after I get underway. Is this true I thought that all stern drives were supposed to.

I have a 1974 140 HP I/O mercruiser. I had to adjust the trim tabs because it was listing to the right. Now i'm not sure if I should trim up after I get on plane. Help!!
 
1

1974merc

Cadet
Joined
Aug 21, 2009
Messages
20
Re: When to trim up?

Also, if I remove the trim tabs off the transom, how will that affect ride performance? Thanks so much.
 
ziggy

ziggy

Admiral
Joined
Jun 30, 2004
Messages
7,473
Re: When to trim up?

your supposed to trim while underway w/ the drive ya got. i'll go so far as to trim up while under full load, hammer down start. as soon as i'm on plane i'll start trimming up. that's when i'm testing hole shots with/against my buddy's. which i don't do often. since i know i can beat them now, i don't have to need to do that much anymore. but ya get the idea. trim at will.

others know more about tabs than me. but i'l ask. what kinda tabs. smart tabs, elec./hyd. tabs, stationary tabs? tabs lift up the back of the boat. keeping the bow down generally speaking when deployed.
 
1

1974merc

Cadet
Joined
Aug 21, 2009
Messages
20
Re: When to trim up?

They're mechanical tabs that you use a wrench to adjust. When I had the boat out yesterday, the boat was listing to the right when I got on plane. Also, it was tough to turn the wheel to the right. Basically if I wanted to go right I had to slow down to get the wheel to turn hardly at all. I checked the tabs when I got home and noticed the port side trim tab was adjusted much lower than the other. So I adjusted them so that they were equal. Hopefully that will help.
 
QC

QC

Supreme Mariner
Joined
Mar 22, 2005
Messages
22,783
Re: When to trim up?

Steering effort is controlled by the vertical trim tab above the prop. Take a look at the FAQs, as there is a description of how to adjust there. You need to also read up on the difference between trim and tilt. In the case of a Merc, trim and tilt are only differentiated by range. Trim is limited to adjustments close to all of the way down, below "neutral" is called negative trim and above neutral is called positive trim, neutral is considered propshaft parallel to the bottom. Tilt is used for higher settings for trailering, beaching etc.

I am guessing if you take your trim tabs off she will porpoise, because I am also guessing that's why the previous owner put them on . . . ;) Porpoising is the rythmic "bouncing" of the bow up and down at planing speeds. Negative trim helps that, trim tabs help that, weight moved forward helps that. However, boats are usually fastest right at the point of porpoise, so it is good to set them up to porpoise at high speed and positive trim, then you control the porpoising with the tabs. Lots to read up on if you want to completely understand this. With "fixed" tabs your options are somewhat limited. The only way to confirm is to take them off and try it.
 
1

1974merc

Cadet
Joined
Aug 21, 2009
Messages
20
Re: When to trim up?

QC, was this the vertical trim tab you were referring to? If so, I got home last night and noticed that it was almost an inch off line. So I quickly adjusted it back to center.

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