Got The Cavitation Problem Fixed With A Stainless Prop...Now To The Partial Full Throttle Issue
A stainless 19p prop completely eliminated the cavitation, it allows trim that goes beyond the optimum trim that allows the best speed and ride, which the aluminum props simply would not do. The other thing is that when it's trimmed best it will easily turn without cavitating and jumping the rpm up...I'm jazzed that the problem is gone and it's such an easy fix.
The issue now is that full throttle is only 5200 rpm, everything else has been running at a WOT of about 5600 tops, so I'm thinking that if the extra throttle is fixed that this prop will run at at least 5600rpm. Even though the engine is only turning 5200rpm the speed was at 46mph, and the mid level cruising speeds are really good for the rpm it takes to do them. I'm really happy with this performance, it's just that part of tuning a boat with the right prop is being able to know where the line is in terms of what pitch allows the engine to develop full max rpm's...then you know you are good to go up one size or more.
The mechanic I found that seems to be the most knowledgeable has done a fair amount of work on these 115 Mercury's, he says they should be able to pop the rev limiter at 6200 with a 17p prop, and be at least 5800 or so with a 19p.
Technically speaking, the mechanic is going to open up the throttle body and manually see what the full throttle position looks like, and then make sure the cable is making it do that. He said he could not do it under warranty like the dealer could, and I told him the dealer's mechanic was having a difficult time understanding the problem, and seemed to think if he could rev it up to 6000rpm without a load there was no problem, he rolled his eyes and said he would never under any circumstances rev an engine up like that without a load on it...I said exactly.
There are a lot of boat mechanics out there that are fairly clueless about a lot of things...I talked to a total of four mechanics about this problem, and only found one that sounded like he had a clue how to home in on a simple matter of the throttle cable or engine throttle mechanism not allowing full throttle.
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