Kind of a long story but I am perplexed and could use some help.
First of all, this is my 2005 2520XL with modified vee and 2005 Yamaha F250. Everything was fine and dandy for 5 years (I'm the second owner) until August. I replaced the lower unit then when the gears ground themselves up. I installed a brand new genuine Yamaha lower unit. When I installed the new anode on the cavitation plate I did not have the old position to reference so I took a guess and just placed it at a slight tilt to starboard if you look at it from the back.
After break in of the new lower unit, it felt like the prop was starting to slip. On flat water with no wind, I would be at say 4200 rpm and the rpm would rapidly increase without the throttle being moved. Rpm would increase to 5000 quite rapidly and the boat speed would slow slightly. This had never occurred during the previous 5 years. So, I thought the prop hub must be starting to slip. The prop shop replaced the hub but said the old one was very difficult to press out and the rubber did not show signs of slip.
Re-installed the prop, did the break in. Same rpm increase occurs. Only happens at 4000 rpm and above and does not happen during hole shot.
Could this possibly be that the angle of that little anode is causing cavitation? Or...when we replaced the lower unit, we took the opportunity to upgrade to a CHIRP fishfinder and new chart plotter. We installed a transom mount transducer just starboard of where the Armstrong bracket meets the transom. Could that be causing high speed cavitation?
What's the best way to sort this all out? I'd appreciate your ideas on how to approach this. Thanks! John
First of all, this is my 2005 2520XL with modified vee and 2005 Yamaha F250. Everything was fine and dandy for 5 years (I'm the second owner) until August. I replaced the lower unit then when the gears ground themselves up. I installed a brand new genuine Yamaha lower unit. When I installed the new anode on the cavitation plate I did not have the old position to reference so I took a guess and just placed it at a slight tilt to starboard if you look at it from the back.
After break in of the new lower unit, it felt like the prop was starting to slip. On flat water with no wind, I would be at say 4200 rpm and the rpm would rapidly increase without the throttle being moved. Rpm would increase to 5000 quite rapidly and the boat speed would slow slightly. This had never occurred during the previous 5 years. So, I thought the prop hub must be starting to slip. The prop shop replaced the hub but said the old one was very difficult to press out and the rubber did not show signs of slip.
Re-installed the prop, did the break in. Same rpm increase occurs. Only happens at 4000 rpm and above and does not happen during hole shot.
Could this possibly be that the angle of that little anode is causing cavitation? Or...when we replaced the lower unit, we took the opportunity to upgrade to a CHIRP fishfinder and new chart plotter. We installed a transom mount transducer just starboard of where the Armstrong bracket meets the transom. Could that be causing high speed cavitation?
What's the best way to sort this all out? I'd appreciate your ideas on how to approach this. Thanks! John