Putting a new transom on 17′ lund fisherman with a merc 125. Owner says he has little to no trim before the motor cavttates. Motor is mounted in the second hole down. Was thinking of dropping the motor one hole which would be the top one, or maybe a prop change.
Only one way to find out……
Hole 2 is a pretty common hole for Lund to have hung a engine as far as height. I had a long winded answer and deleted it so we don’t get to far in the weeds. Not knowing the history of the boat, and not being able to see the setup myself here are some things that may have change. However like Crappie said you may just need to try it because you and the owner may not know the history either.
-Engine replaced at some point with a different length(20″ vs 25, or L vs XL) because someone got a deal.
-Engine replaced at some point with same advertised length engine, but not all 25″, or XL, engines are the same length. Definitely trips people up sometimes on repowers because it can require a change to mounting height.
-Rocker or hook in the bottom of the boat.
-Transducer mounted low and too close to the engine causing turbulent water to the prop.
As a general rule I tend to think of props as more of a fine adjustment once I pretty well have the engine height nailed down. Certain four blades can be ran a hole higher than some 3 blades. Stainless can also often times be ran slightly higher than aluminum.
Hole 2 is a pretty common hole for Lund to have hung a engine as far as height. I had a long winded answer and deleted it so we don’t get to far in the weeds. Not knowing the history of the boat, and not being able to see the setup myself here are some things that may have change. However like Crappie said you may just need to try it because you and the owner may not know the history either.
-Engine replaced at some point with a different length(20″ vs 25, or L vs XL) because someone got a deal.
-Engine replaced at some point with same advertised length engine, but not all 25″, or XL, engines are the same length. Definitely trips people up sometimes on repowers because it can require a change to mounting height.
-Rocker or hook in the bottom of the boat.
-Transducer mounted low and too close to the engine causing turbulent water to the prop.As a general rule I tend to think of props as more of a fine adjustment once I pretty well have the engine height nailed down. Certain four blades can be ran a hole higher than some 3 blades. Stainless can also often times be ran slightly higher than aluminum.
Thanks for the indepth the owner is not the original owner so not sure on the motor. Since the motor is already off the boat it’s not a big deal to try the lower setting. I would think that the problem has a better chance of getting better then worse. I will report back when we get the boat back on the water.
Does anyone now how high the cavitation plate should be from the bottom of the boat?
Does anyone now how high the cavitation plate should be from the bottom of the boat?
I usually see that it should be within 1″ of the bottom. I think the actual answer though look at it while running on a calm day with a usual weight in the boat and get it so that it’s just skimming the water.
I raised my motor 2 holes and if I remember right I’m closer to 2″ above bottom of boat now and when my boat is light it’s too high.
I confirmed the engine would have been hung in hole 2 by Lund. 1″ up should be a good starting point. Make sure the cavitation plate is parallel to the boat bottom when measuring.
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