setback trouble

[E-rudesoldier]

I gave my dad my old manual jack plate that is 4 inches of setback, he put it on his 1987 startcraft thruster, with his evinrude 90. When I went to visit him I helped him raise and lower the stupid thing all the way up and all the way down, funny thing is the best performance is with it all the way down but that is still two miles an hour slower then before it went on. Has anyone ever heard of setback hurting perfromance?

[Jay R.]

why did you add a jack plate? usually you only add that when you have to use positive trim to get the hull to air out. but that really isn't that kind of hull. That said, a jack plate could help if set up right. should be put it on and lift the engine up till you start to loose water pressure. Then lower it back down till you get water pressure again. then you have to mess with the trim until you get the hull to fly and keep the engine level.

[Forkin' Crazy]

What prop?

[E-rudesoldier]

the hull gets its top speed up on full trim, only way to get the nose up. I really only gave it to him with the intention that a few inches of setback would get the motor to cleaner water would help all around. its no performance boat and its old, so mostly we did it to tinker with it.

[Jay R.]

Well if it only got full speed when trimmed all the way up then the jack plate should work for ya. if you are slower all the way up and down. I would say you need to lower the jack plate down a few holes so you can get in the water a little more.

[E-rudesoldier]

I took it all the way up and have it now set at the very bottom, it only went 47 mph before and is now going 45 so no big loss I just was kinda stumped by why it would slow down.

[Jay R.]

They usually have a few mounting holes. Is best speed with it down or up? I would think down. You should probably remount so it is the lowest it can go. Then try again.

[E-rudesoldier]

its all the way down on both the jackplate and on the motors mounting, its old and not worlth alot of effort but we will mess with it next time I am up there.

[transomstand]

Has anyone ever heard of setback hurting perfromance?

Yes

If it's too much setback, the hull loses it's "pivot point" (the rear edge of the pad), a smaller engine doesn't have the grunt to overcome this, and only drives the back of the boat deeper.

[E-rudesoldier]

I had never heard of that and I think that is what I have done to my Dads boat. If I cant talk him into a bigger motor I will help him take it off.

[Wizard]

That cleaner water thing is bunk! Setback does only one thing and that is change the leverage point. An adjustable jackplate also allows you to raise or lower the engine which is an added benefit. Also consider that that you added probably 1/3 of the weight of the motor to the back of an already light boat. The 90 probably does not have the guts to lift the bow with the further back leverage point. Dump the plate and put it back on the transom. 2mph is a hefty loss with no other appreciable benefits. :cheers: