300 HP shaft size

traditions

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A lot of the old 42 Brunos had 1 1/2 shafts,and had more than 300 hp..Aquamet 22 is pretty strong.Some has to depend on how big of wheel you have and how much reduction.If its Aquamet, a 1 3/4 would be fine,but 1 1/2 could also work.
 

captainlarry84

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Reduction gears break shafts not so much HP. The rule of thumb is over 22: pitch on a single screw DE needs 1.75 shafting.
a 300 HP motor with a 1.5 shaft will most likely work as the wheel will be 22 or less. same HP with a 1.75 or 2:0 the load goes up to over 23" you will need a 1.75 shaft.
 

jojobee

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Engine torque and RPM in addition to what Capt Larry said. All of our yanmar 6LP's with a 2-1 were recommended to use a 1.5" shaft (Aquamet 22 without some crazy shaft length). Some Bertram 31 owners that had a 1 3/8" shaft used a 1.5-1 reduction. I never heard of one breaking. The same engine with a 2.5-1 reduction jumped up to a 1.75" shaft.
 

sidejob

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sorry to interfear but i have a 300 hp jd with a 5 blade prop what is the safest rpms i should run thanks for the info
 

captainlarry84

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sorry to interfear but i have a 300 hp jd with a 5 blade prop what is the safest rpms i should run thanks for the info

We need to know:
Shaft size
wheel size
reduction gear
WOT RPMs rate
WOT RPMs that you get
 

Brooksie

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Prop diameter divided by 14, round up.
 
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