Does anyone know what the standard drive shaft length should be on a Yamaha 300 outboard that powers a Grady White Fisherman 257? I bought a used 2019 Fisherman 257 last summer and the 300 hp engine, which I was told was purchased on the boat new, seems to cavitate when getting up to speed or making sharp turns. It revs loudly but seems to not be going anywhere like it’s not getting enough water at the engine to properly move the boat forward. One mechanic suggested that the 25” drive shaft is too short and not the correct pairing for the boat. He suggested that it should have a 30” drive shaft, but I’m struggling to understand that a boat would come from the factory with the wrong size drive shaft. How do I tell what the correct drive shaft length should be? Any help would be appreciated.
Fisherman 257 Yamaha 300 Drive shaft length?
- Thread starter TDub
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Mustang65fbk
GreatGrady Captain
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It appears as though the 257 Advance had a name change in the early 2010's era and then became the 257 Fisherman shortly thereafter. All of the specs appear to be the same from one boat to the other, though most of the newer brochures don't give the outboard shaft length for some reason. Which is why I had to go back to 2009 and use the 257 Advance for reference, which shows on it as being a 30" shaft on a single outboard and 25" shafts on twin outboards... or at least that's what the brochure states. How many hours are on the motor? I suppose it could've been repowered, though pretty unlikely on a motor that's just barely 6 years old at this point.
You can measure on the outside of the engine for the shaft length.
But... how does the anti-ventilation plate compare to the hull bottom? Put a straight edge on the hull.
FYI, you're most likely experiencing ventilation, not cavitation. They're actually two entirely different things.
If the vent plate is at the proper height, also look to the prop hub for the issue.
But... how does the anti-ventilation plate compare to the hull bottom? Put a straight edge on the hull.
FYI, you're most likely experiencing ventilation, not cavitation. They're actually two entirely different things.
If the vent plate is at the proper height, also look to the prop hub for the issue.
I did some research and I am pretty sure a single motor on that hull should be a 30 inch.
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