Flashman666
Recruit
- Joined
- Aug 2, 2010
- Messages
- 5
I am new to this forum, and have been greatly impressed with the wealth of information that is available here.
I have a question to do with the proper height of the cavitation/AV plate to the keel. I?ve read a number of threads on this topic and have gleaned much helpful information.
I have a 30 year old 14? Sears Gamefisher open aluminum boat with a 15? (measured) transom. I recently purchased a more or less new 15 hp Yamaha short shaft to go on the back. However, on my first sea trial, it porpoised badly and water literally gushed up the back of the transom when I opened her up. On closer inspection, I could see that the cavitation plate was a full 3? below the keel (this seems to be because the distance from the cavitation plate to the clamps is 15?, but a full 18? to the top of the motor mount ? thus, putting the motor flush on the transom puts the cavitation plate far too low in the water).
When I raised the motor up close to an inch and trimmed her out fully, things improved. The gushing of water over the transom stopped, but the boat continued to porpoise (albeit not as badly, but I still had to have my passenger sit on the rear bench seat as we ran).
I?m thinking what I need to do is replace and refurbish the transom and raise it up a full 3? (this way, the motor would sit flush on the top and the cavitation plate would be at the same height as the keel). I?d reinforce it on both the inside and outside of the transom.
So, does anybody have any reason to say this is not a good idea? Tips? Many thanks in advance.
I have a question to do with the proper height of the cavitation/AV plate to the keel. I?ve read a number of threads on this topic and have gleaned much helpful information.
I have a 30 year old 14? Sears Gamefisher open aluminum boat with a 15? (measured) transom. I recently purchased a more or less new 15 hp Yamaha short shaft to go on the back. However, on my first sea trial, it porpoised badly and water literally gushed up the back of the transom when I opened her up. On closer inspection, I could see that the cavitation plate was a full 3? below the keel (this seems to be because the distance from the cavitation plate to the clamps is 15?, but a full 18? to the top of the motor mount ? thus, putting the motor flush on the transom puts the cavitation plate far too low in the water).
When I raised the motor up close to an inch and trimmed her out fully, things improved. The gushing of water over the transom stopped, but the boat continued to porpoise (albeit not as badly, but I still had to have my passenger sit on the rear bench seat as we ran).
I?m thinking what I need to do is replace and refurbish the transom and raise it up a full 3? (this way, the motor would sit flush on the top and the cavitation plate would be at the same height as the keel). I?d reinforce it on both the inside and outside of the transom.
So, does anybody have any reason to say this is not a good idea? Tips? Many thanks in advance.