find correct motor height for outboard

[joseph L]

I have a 1981 20 foot pursuit with a 150 mercury. I would like to know how you can tell if the motor is at the right height. The motor is at the lowest position. And the cavatation fin (don't know if this is the correct name) is
2 1/2 inches above the hull. Is this correct? I heard it should be level with the hull or a little above. What is a little? I would like to fix it if it is wrong because I am putting a new transom in. I would like to fix the problem now so I can put the new engine mounting holes in the right spot.

 

[walleyehed]

Re: find correct motor height for outboard

If the engine is all the way down on the transom now, there is no need to drill any holes.
What holes are the top bolts in now?
Is there a built-in set-back in the transom?

 

[jcsercsa]

Re: find correct motor height for outboard

If the engine is all the way down on the transom now, there is no need to drill any holes.
What holes are the top bolts in now?
Is there a built-in set-back in the transom?

Hi uuummm walleyehed, are you saying that if the mount is all the way down that I dont need to bolt it down ?? I not quit sure I am fallowing , I also am putting a new transom in and I was wondering the same thing ??? thanks john ps what is a set-back ??

 

[mpsyamaha]

Re: find correct motor height for outboard

so the motor is in the lowest hole on the mounting bracket?


if the motor performs well, doesnt ventilate easily, i would leave it the same when you re-do the transom.

 

[walleyehed]

Re: find correct motor height for outboard

I'm not talking about trim...I'm talking where the engine is mounted on the transom...Is it clear down against the mount brackets? Yes, it needs bolts, but if it's clear down against the transom and the ANTI-VENTILATION PLATE is still 2-1/2" above the hull, either the transom is too tall, or the design sets the engine back farther than normal, ie, set-back.
The engine must be trimmed so the AV plate is parallel to boat bottom, not trimed all the way in.

 

[jcsercsa]

Re: find correct motor height for outboard

Thanks walleyehed, I was going to put the bolts in anyway, I didnt want anyone else to think you didnt need them , thats just the way I took it sorry !!!! Thanks John

 

[joseph L]

Re: find correct motor height for outboard

Would it perform better if the antirention is at the bottom of the hull. The boat perform well. I would like to get more speed out of it

 

[joseph L]

Re: find correct motor height for outboard

Need help ///

 

[steelespike]

Re: find correct motor height for outboard

The best height is the highest position that has minimum venting problems and still pumps water.A little occasional venting may be tolerated in order to get the best performance.Generally the more motor in the water the more drag thus less speed.If you presently have no venting problems you may be able to raise the motor even more.You may want to add a jack plate when you rebuild the transom.This will give you some setback (set back gets the motor in cleaner water)as well as make fine tuning the height easier.
The rule of thumb "antivent plate even with the bottom"is considered a starting point.A stainless prop will make it easier to get that ideal height.

 

[joseph L]

Re: find correct motor height for outboard

What is & what do I look for when the motor is venting? Do I adjust the motor just before venting.

 

[steelespike]

Re: find correct motor height for outboard

Venting is the prop losing its grip actually becoming airbound.motor revs boat may actually slow.The idea is to get the motor as high as possible with minimum venting.Some want no venting at all others will tolerate some in order to get that fine edge.
Many say they aren't interested in speed.Keep in mind the best speed will also produce the best mileage when operated at cruising speeds.
Don't forget when adjustng the height to be sure it pumps water.