motor height question

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brappley

Seaman Apprentice
Joined
Apr 17, 2011
Messages
33
I just put a new motor on my 19 foot bayliner, i lowered it on the mounting bracket as far as it will go so it sits down in the water, problem is it seams to be sucking air into the prop, does anyone know the dimentions for setting up a new motor and how far down into the water the prop should be, please let me know.
 
fireman57

fireman57

Captain
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Aug 24, 2004
Messages
3,811
Re: motor hight question

Re: motor hight question

Welcome to iboats. What you are seeing is known as cavitation. You need to lower it until it stops. Usually the starting point is to have the fins level or barely above the bottom of the keel. You may need a different jackplate.
 
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Chris1956

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Mar 25, 2004
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27,136
Re: motor hight question

Re: motor hight question

Actually sucking air into the prop is called ventilation. What is the measurement between the top of the antiventilation plate (flat plate above prop) to the part of the transom bracket that sits on the transom? Now measure the height of the transom from the center of the hull. Normally these measurements will be close to 15" or 20" or 25" or 30". if the motor measurement and the hull measurement are close, something strange is going on. However, I will bet that the motor is shorter than the hull.

You did not say if you have a jackplate, so I am assuming not.
 
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brappley

Seaman Apprentice
Joined
Apr 17, 2011
Messages
33
Re: motor hight question

Re: motor hight question

No jackplate, did find out the antivent plate is almost 2 1/2 inch above the bottom of the lowest part of the hull, i was told they had to be at the same plain or as close as possible, unfortunatly i cant lower it any further, the mount is sitting 1/2 inch above the transum. Any idea's?
 
Bob_VT

Bob_VT

Moderator & Unofficial iBoats Historian
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May 19, 2001
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26,022
Re: motor hight question

Re: motor hight question

Well first you might have the wrong shafted motor.... :(

When you say you lowered the motor was it by removing the bolts and lowering the mounting all the way? The plate above the prop should NOT be any higher then about 1" above the keel point.

If the motor is sitting about 1/2" high on the transom then it needs to go down. Is this a new motor to this boat?
 
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brappley

Seaman Apprentice
Joined
Apr 17, 2011
Messages
33
Re: motor hight question

Re: motor hight question

Yes , the motor is new, the old one died. i did not put it on, the other owner did, i just got it a few weeks ago and found th problem after the fact. It runs great, just sucks air and the motor rev's up at full throttle , sucks air when it hits plain, or turn a corner, i was told to cut the transom down 2 " , then it would be 1/2 not 2 1/2. I do have the room to cut it but would rather not.
 
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Chris1956

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Re: motor hight question

Re: motor hight question

2.5 inches too short is a funny measurement. There were some Johnnyrudes made with a 22.5" shaft length. If you had one of these moors on a 25" transom, that would match your observation. The motor model number will tell us if this is the case.

A jackplate could solve your issue. Lenghtening the motor shaft will fix it also, as will cutting down the transom.
 
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brappley

Seaman Apprentice
Joined
Apr 17, 2011
Messages
33
Re: motor hight question

Re: motor hight question

the model # is 1057HF 1974 chrysler 105 HP, been told its a salt water motor, problem is i cant find parts so lenghtening the shaft would be almost imposible. If i use a jackplate ill have to remove the trim tilt , unless there is a way to use it with it still attached,
 
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Chris1956

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Mar 25, 2004
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27,136
Re: motor hight question

Re: motor hight question

I am not familar with your motor, but most PTT units will work with a jackplate. The control cables and steering need to have enough length.
 
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