88Glastron
Seaman Apprentice
- Joined
- Nov 11, 2008
- Messages
- 34
I have the Black Max mounted to a 1980 Robalo 20' Center Console. I bought the motor last summer and have gone over that thing with a fine tooth comb. It started with maintenance but became:
new waterpump
new thermostats and tubing
new flywheel
stator
switch boxes
trigger
ignition coils
new plugs and wire
rebuilt fuel pump
rebuilt carbs
The compression is great (can't remember numbers off the top of my head) and the motor runs like a top. Only problem that I am having is the boat performance. I mounted the motor directly to the transom with the bottom hole in the transom bracket because that put the cavitation plate right inline with the keel. When I finally got the boat in the water and up on plane I noticed that not only did I only get 4200 at WOT, but there was a lot of splashing going on in the transom and the boat topped out at 28 mph SOG. I did attempt to trim the motor out and was able to get the bow down to what I believed to be the correct height but the transom splashing continued.
I am currently using the 4 blade black diamond 15x16 prop that came with the motor. Mercury makes the prop but has no detailed information about it so I am not sure how to calculate for speed or slip with this prop. I have an se300 hydrofoil ready to be installed but I was thinking that there may be more to this than just adding the hydrofoil. I hear great things about 4 blade props but I am not impressed so far. My question is how should I attack the problem? Bring the motor down a hole or two or swap the prop for a 3 blade stainless spare that I have? Both? Something else completely? Any input would be greatly appreciated.
new waterpump
new thermostats and tubing
new flywheel
stator
switch boxes
trigger
ignition coils
new plugs and wire
rebuilt fuel pump
rebuilt carbs
The compression is great (can't remember numbers off the top of my head) and the motor runs like a top. Only problem that I am having is the boat performance. I mounted the motor directly to the transom with the bottom hole in the transom bracket because that put the cavitation plate right inline with the keel. When I finally got the boat in the water and up on plane I noticed that not only did I only get 4200 at WOT, but there was a lot of splashing going on in the transom and the boat topped out at 28 mph SOG. I did attempt to trim the motor out and was able to get the bow down to what I believed to be the correct height but the transom splashing continued.
I am currently using the 4 blade black diamond 15x16 prop that came with the motor. Mercury makes the prop but has no detailed information about it so I am not sure how to calculate for speed or slip with this prop. I have an se300 hydrofoil ready to be installed but I was thinking that there may be more to this than just adding the hydrofoil. I hear great things about 4 blade props but I am not impressed so far. My question is how should I attack the problem? Bring the motor down a hole or two or swap the prop for a 3 blade stainless spare that I have? Both? Something else completely? Any input would be greatly appreciated.