Jack Plate question

[Twidget]

I have a 16 ft fiberglass V hulled boat. I replaced the old Merc. 950 with a newer Johnson 90 and now have cavitation problems. Never had the problem with the Merc.<br /><br />The old motor used to sit quite a bit lower than the 'new' one. The Merc AV plate was about 2" below the hull, the Johnson AV plate is even with the bottom. The Johnson is also as far down as it will go. <br /><br />Would a jack plate help this situation at all? Do they adjust downward also? Would the setback compensate in some way for the height difference?<br /><br />Thanks in advance.

 

[Dhadley]

Re: Jack Plate question

The problem you describe points to prop issues more than anything else. What prop are you running? What condition is it in?

 

[Twidget]

Re: Jack Plate question

Its a new Michigan Match 19 pitch aluminum.

 

[Dhadley]

Re: Jack Plate question

The first thing I would try is a ss prop like a Stiletto. That will "bite" much better and hold water longer.<br /><br />To answer you original question -- yes, a jackplate lowers the motor somewhat. The transom is on an angle. So the further back you go the further down the AV plate is. Plus the water coming off the back of the hull is going on an upward angle.

 

[Twidget]

Re: Jack Plate question

Thanks Dhadley. I'll give that a try. Should I stick with a 19 pitch, or drop to a 17?

 

[Dhadley]

Re: Jack Plate question

Thats a question that can only be answered with testing. But a V4 on a 16' boat I'd say a good 19 is a real good starting point.