1990 140hp evinrude
16' cape horn
See attached. It's porpoising a lot and I was told by a local prop shop that my motor is mounted too low. I went there because the awful porpoising started after i swapped from the V6 gearcase that was on the motor when I bought it, to the V4 gearcase it ought to have. I first ran it without the fins (I had them on the previous gearcase and it had about zero porpoising) but it was unbearable without them. Now it's acceptable with them but still needs something done about it. Figured maybe i was just propped horribly wrong for the different gearcase? It's a 15" 17p on there right now. Other than on smooth water at high throttle, trimming up just sends it into a terrible fit of porpoising.
They told me that my porpoising was because the motor is mounted way too low, and also gave me a 14" 21p prop. Said my RPMs should come up with a proper mounting. (it runs great at 5600 with the current setup)
Right now the cavitation plate is set right around the bottom of the keel. This is where the shop I bought the motor from mounted it. These guys at the prop shop told me that it needs to be set so the cavitation plate is level with the spot where the transom dips in toward the keel, where it rides when it's on plane.
I'm going to make the changes later today when I can get some extra hands over here, but would appreciate any feedback on whether I'm headed in the right direction.
16' cape horn
See attached. It's porpoising a lot and I was told by a local prop shop that my motor is mounted too low. I went there because the awful porpoising started after i swapped from the V6 gearcase that was on the motor when I bought it, to the V4 gearcase it ought to have. I first ran it without the fins (I had them on the previous gearcase and it had about zero porpoising) but it was unbearable without them. Now it's acceptable with them but still needs something done about it. Figured maybe i was just propped horribly wrong for the different gearcase? It's a 15" 17p on there right now. Other than on smooth water at high throttle, trimming up just sends it into a terrible fit of porpoising.
They told me that my porpoising was because the motor is mounted way too low, and also gave me a 14" 21p prop. Said my RPMs should come up with a proper mounting. (it runs great at 5600 with the current setup)
Right now the cavitation plate is set right around the bottom of the keel. This is where the shop I bought the motor from mounted it. These guys at the prop shop told me that it needs to be set so the cavitation plate is level with the spot where the transom dips in toward the keel, where it rides when it's on plane.
I'm going to make the changes later today when I can get some extra hands over here, but would appreciate any feedback on whether I'm headed in the right direction.
