Should motor be higher or lower

[lanezupkov]

I have a 1985 avanti boat w/ 1986 115 hp merc. How do you know how high to mount the motor on the transom. I took the boat out for the first time today and didn't really know what to look for. It went forward and got me back to the dock, but I just want to be sure I'm running this rig correctly. Later to come is the prop questions. I need to see what kind I have on it now. Thanks for the help! you guys saved me hundreds on the last postings.

 

[studlymandingo]

Re: Should motor be higher or lower

The motor should be mounted so that the anti-cavitation plate is level with the bottom of the boat.

 

[imported_Curmudgeon]

Re: Should motor be higher or lower

The motor should be mounted with the ventilation plate just out of the water when at speed. While even with the bottom may be a starting point, usually the most efficient height will place the plate 1-3" above the bottom.

 

[DJ]

Re: Should motor be higher or lower

Start with the cav. plate level with the keel or just slightly above.<br /><br />Record your wide open throttle tach. reading. That is your baseline.<br /><br />Raising the engine and/or prop. selection come after that.<br /><br />Let us know.

 

[lanezupkov]

Re: Should motor be higher or lower

I will do a search to see what the cav plate and the ventilation plate is unless you guys are still around and can tell me those are? I didn't even realize that would make a difference, until I started reading these posts. Thanks!!

 

[Solittle]

Re: Should motor be higher or lower

The cav plate & the ventilation plate are the same thing. It is the horizontal plate just above the prop. The lower it is the more drag. The "ideal" is as high as you can get it without the prop venting or sucking air through the water pick-up for the water pump. When adjusting it is best to do it one hole at a time and record the results after each run.<br /><br />Post back the results and tell us what prop you are running.

 

[calwldlif]

Re: Should motor be higher or lower

Generally speaking<br />raising the anti vent above the <br />bottom of the transom promotes speed and fuel<br />savings. Drawback is prop could ventilate,<br />some possible following seas instability.<br />Possible hole shot slip.<br /><br />Lowering it gives more bite in hole shot,<br />general better handling in rough seas.<br /><br />The sweet spot in found by trial and error.<br />To add to the confusion, prop has a big influence<br />on the sweet spot.

 

[Silvertip]

Re: Should motor be higher or lower

Raising the engine can also cause loss of water pressure if carried to extreme so installation of a water pressure gauge is a good idea when playing with engine height.

 

[lanezupkov]

Re: Should motor be higher or lower

I'm starting to think the motor is not set right. I'll have to look at it later. It seems to plow through the water until higher speeds. I guess this could be the prop too. O man where to start.