Mounting height

[Freeball]

I've got a question with regard to the mounting height of an outboard motor. I know its essential to get it right, but am unsure as to how and why. Can anyone explain the difference between mounting too high and too low, and what the correct height below the transom is?? I'm sorry if it sounds like a rookie question, but i'm really green when it comes to this. Its all learning right?

 

[Dunaruna]

Re: Mounting height

Too low creates unnecessary drag and will effect performance. Too high can create a situation where surface air has easy access to the prop, this is known as ventilation.

The ideal location is for the anti-ventilation plate to be level or slightly above the lowest part of the 'V'. If the outboard mounting holes are drilled correctly, there should be provisions to move the motor up or down by using the multi mounting holes in the outboard.

 

[tashasdaddy]

Re: Mounting height

too high also can effect cooling water pick up, and the motor runs hot. most of us run with the AV plate 1-2 inches above the keel, deepest part of the V of the transom, if transom is flat, above that. if you are running a 1950-thur early 1970 motor they need to be deeper due to water pick up.

 

[5150abf]

Re: Mounting height

Get the motor set at 1-2'' above the bottom as TD said then play with it to get it to the best place for your boat.

run it at that setting then try running it one hole higher and see what happens, if it cavitates easily put it back down and you are there, a gps or speedo is really required to see the results.

I run a 6'' set back on mine so I can run the motor 1 hole higher than if I didn't have the setback.

You do want the motor as high up as posible without cavitating.

 

[Freeball]

Re: Mounting height

Thanks guys, seems as though ive got to raise this motor. May need to drill some new mounting holes though as the previous owner said he fitted it himself. One quick question with regard to the lower mounting holes, what kind of sealant is recommended to avoid leakage??

 

[tashasdaddy]

Re: Mounting height

3m4200, as it is removeable, 3m5200 is permantent, and nearly impossible to break apart. use 3m4200 on anything screwed to the transom.

 

[Freeball]

Re: Mounting height

got it! Thanks again!!

 

[steelespike]

Re: Mounting height

Usually the antivent plate about even with the bottom of the boat is considered a starting point. Raise it a little at a time to a point just before venting becomes a problem.Some tollerate a little venting to get the best performance.Be sure it pumps water.Don't drill any holes untill your sure you
have chrecked for any adj. holes on the motor.

 

[F_R]

Re: Mounting height

Usually the antivent plate about even with the bottom of the boat is considered a starting point. Raise it a little at a time to a point just before venting becomes a problem.Some tollerate a little venting to get the best performance.Be sure it pumps water.Don't drill any holes untill your sure you
have chrecked for any adj. holes on the motor.

I agree. Get that sucker too high and you will hate it. It will be great for top speed or idle and a PIA at mid range. Every boat and motor combination is different and hard to predict.

 

[Dhadley]

Re: Mounting height

The actual correct X dimension or height will depend greatly on what style / brand prop you choose, how it reacts with your hull design and your intended use. I use 3 props on my flats boat that run at totally different heights. With 2 I can run the jackplate all the way up and take off in shallow water. One of those has to be dropped as the boat gets on plane. The other prop stays hooked up at that height but the motor can't pump water that high. The 3rd prop can be set at about 1/2 way on the plate and left alone.

There is no one height that's correct for any given boat. However, if the motor is too low you'll get a spray of water back up and over the transom. Plus it won't be efficient at all.

 

[woody614]

Re: Mounting height

I have noticed the rule of 15" to 17" Transom = a 15" short shaft outboard
and 19" to 22" Transom = a 20" long shaft out board. I am going to buy a New Mercury 40hp but it is going on a Starcraft Explorer 14' with a 18" transom. Can anyone give me which motor size I need? Short or Long?

Thanks,

Mike