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Old 03-02-2014, 06:41 AM   #12
Tony B
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City: Joe Wheeler State Park, Al
Vessel Name: Serenity
Vessel Model: Mainship 36 Dual Cabin -1986
Join Date: Jul 2011
Posts: 1,251
Quote:
Originally Posted by psneeld View Post
.... you talking cavitation/antiventilation plate? YES. Tony B

Unless you are talking pretty high performance...being a couple inches too low really doesn't hurt a lot unless you are talking speeds way over 10-12 knots where the increased drag becomes more of an issue. YES. Tony B

What HP and speed are you talking about? 7.2 HP top speed unknown. Probably 15 or 20 maybe more. Tony B

My quick stab is I would go steel if down in the 1/4inch range and make sure you get 2 rows of bolts on both sides of the motor and a few inch overlap with the original transom....up the speed slowly and watch what it does (see how solid she stays). That is my thinking. Tony B
Yes, I am talking about the anti-ventilation plate/cavitation plate. The dimension I am talking about is "B" and it is 17".
I have a Tohatsu 9.8 4 stroke. I have the short shaft. The owners manual calls for a transom height of 17.1 inches. I have also measured the dimension "B" with a tape and it is 17+ inches.

This all came about when I put the motor on the dinghy and started using it. This is before I took any measurements. I felt like the cowl was sitting too low in the water. Could be a combination of motor weight (88 lbs) which should be well under the dinghy specs, the gas tank placement and my fat ass.
I tried moving the gas tank up forward and also took a passenger (the admiral) to balance the load. O/B cowl still looked too low. The drag around the cowl was also very evident. So, my problem is not in engine draft but in engine drag. I want to raise engine a few inches to reduce drag on the cowl. The drag is so great that the dink wont plane.
Dinghy specs call for max of 10 HP. I have the 9.8 engine which I believe is actually 7.2 Hp. I also think that the new O/B of 88 Lbs is less weight than a 1994 version of a 10 HP. I could be remembering wrong.
As for skill level, I'm OK on that. I am short on tools but still do-able. I was wondering if a quick fix like a steel plate was a viable choice. I'm sure if the aluminum plate wont work, that a steel plate will. I wanted the quick fix not for ease and speed so much but also to be able to readily un-do.
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