Outboard mounting height too High?? Older larson with new motor

zarillus

zarillus

Petty Officer 1st Class
Joined
Jan 29, 2009
Messages
252
:confused:Guys-I have a 67 Larson All-American 16ft with an 20 inch 89 110hp evinrude.I am trying to figure out the proper mounting height.When i took it for a lake test it seemed very unstable at high speed.Sorts like driving an old Ford pickup with bad ball joints on the freeway.Hard to control at high speeds.Would this be because the motor is too high on the transom?

Anyhow back to the question, what is the proper height?? cavitation plate level with very bottom of keel? Currently its about 1/2 inch to 3/4 inch above keel.

THanks:D
 
JB

JB

Honorary Moderator Emeritus
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Mar 25, 2001
Messages
45,907
Re: Outboard mounting height too High?? Older larson with new motor

Most boats can handle the anti-ventilation plate up to an inch higher than the keel, zarillus. Sounds like you are fine, but have a squirrely boat. You may also be overpowered. What is your boat rated for??

If you mount the outboard too high the prop will ventilate and over-rev the outboard.
 
ondarvr

ondarvr

Supreme Mariner
Joined
Apr 6, 2005
Messages
11,527
Re: Outboard mounting height too High?? Older larson with new motor

There is no exact right height, it's a trial and error type thing. Level with the hull would be the absolute lowest point, but it should be higher, maybe an inch or so depending on several variables. So right now at 1/2 to 3/4 above is fine, but you might be able to go higher, you just need to try it and see it.

A 110 may be too large for your boat too.

It may just be that your hull design isn't all that stable, but you need to experiment to find out.
 
ondarvr

ondarvr

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Apr 6, 2005
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11,527
Re: Outboard mounting height too High?? Older larson with new motor

I must type slow.
 
smokeonthewater

smokeonthewater

Fleet Admiral
Joined
Dec 3, 2009
Messages
9,838
Re: Outboard mounting height too High?? Older larson with new motor

slop in the steering???? If so tighten it up

Do you have a hydrofoil????? If so take it off...

are you adjusting trim for best speed/handling/ride?
 
GA_Boater

GA_Boater

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May 24, 2011
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49,038
Re: Outboard mounting height too High?? Older larson with new motor

I'm with smoke on the steering and adjusting the trim. Trim too high or too low makes for a bad handling boat. The motor height usually is more performance tuning than anything else.
 
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