maximum down position of outdrive

[todd d]

Newly purchased 1988 Mach 1, 16ft, 3.0 inline 4cyl, alpha 0ne drive.
How far down should the outdrive go? When fully down, my prop actually points down toward the rear of the boat. In other words, the force from the prop is pushing the bow down into the water. If I held a straight edge on the cavitation plate, should it be parallel to the bottom of the hull?

The boat takes a long time to get up on plane, and will top out at 25mph with the drive fully down. I can get it up over 30mph if I raise the drive a little. I know that trim tabs will help with the planning issue, but wonder if an adjustment to the engine angle will help.

 

[Fishermark]

Re: maximum down position of outdrive

The purpose of the tirm system is to get the outdrive in the best position to get on plane and then maintain at the most efficient position. It takes a little "ear" and practice. But no, you don't just go all the way down and keep it there.

 

[Don S]

Re: maximum down position of outdrive

Here is a link to an owners manual for 2000. While it's newer than yours, the basics are the same on what the trim does. Go to page 32 of the manual for details.
http://www.boatfix.com/merc/Owner/gas/86017101.pdf

 

[Fishermark]

Re: maximum down position of outdrive

Don - I find it interesting that Mercruiser acknowledges the necessity on occasion of using the trailering button to overide the trim for some situations:

the Power Trim system Trailering feature allows the operator to raise
and lower the drive unit for trailering, beaching, launching and low speed (below 1200 rpm engine speed), shallow water operation.

Here in SW Florida we have many places of extreme shallows - usually sandy or mucky bottom - not rocks. I often find myself having to raise the outdrive pretty far up to negotiate these areas. Low speed of course, as mentioned. But it is nice to see it in print that the practice has official authorization and sanction.