Scott06
Admiral
- Joined
- Apr 20, 2014
- Messages
- 6,972
mercruiser has set up drawings on their website of the X dimension that is height off the bottom for the crank center line and thus keyhole. I doubt its off as if it were too low your front motor mounts would be bottomed out on the stringersWell, turns out the vibration I'm getting is due to cavitation. It's putting cavitation burns on the prop.
Prop guy wonders if the prop sits too low in the water. His theory makes since. This boat you can't hardly even use the trim unless you're going below 10mph.
I was wondering if it was a balance issue, but maybe this motor and drive are installed to low. Looking into this.
Clearly the boat has the power to get me up with 6 people on the boat.
If you cant use any trim try a prop with more bite with some cupping. As an example I have a tested Merc Vensura 21" (also called offshore), Enertia 22", and Revolution 4 21". Like you I have 21 ft fairly azz heavy boat. With the Vensura I also couldn't trim much.
On paper I should have highest top speed with the Enertia. I was able to net best top speed with the Rev4 because I cab fully trim out. As you trim more you can see the spray line off the hull walking aft and wake size reduces.
The vensura had best holeshot because the smaller blades allow the engine to spin up in its power band faster, but slip was like 20% at WOT. The Rev4 is almost too much prop for good holeshot, but the vent plugs help on it. I do geta vibration from the cavitation in the mid 2000 rpm range that goes away.
bottom line big diff with these props over the Aluminum ones.
If you can get up slalom with 6 ppl in the boat with 200hp I think you are doing pretty good. Like you I fight bowrise I just dont want to bother with trim tabs.