Shaft Size on 39' ers

[sdonx]

I've broke a shaft twice (I've hit once also).
The Propeller people are telling me my shafts 2"
are too small for the 32x40 5 blades that came with the boat. I'm running 30x40 4 blades now, which they say are borderline, but would like to switch back to the 5's at some point. What do other 39' boats have? shaft size and wheel diameter??

[divernc]

How much HP are your engines?

[divernc]

www.boatdiesel.com has both a prop and shaft calculator. (you do have to join for $25 to use).

[Barry E Sweet]

Shaft diameter is 2 1/4" - Wheels are 5 blade 32x41. I started with 32x44 but had to take 3" out to get speed. Tops out at 2550rpm but I usually cruise at 2050-2100

[sdonx]

Thank You for the reply
450 hp Cummins C series-Diamonds
I can do the calc, but I want to know what others have and there experience

[sdonx]

What engines do you have?

[Barry E Sweet]

My engines are Detroits 6-71TI rated at 465 hp

[Hatt36]

The recommended product of propeller shaft diameter divided into propeller diameter is 12-14.
Richard

[hmacdonald]

I broke a shaft on a 36 right after props had been changed by a diver. I'm pretty sure that prop wasn't adequately tightened. That's another factor to consider. By and large your're not going to find Hatteras undersize anything like a shaft.

[edgewalker]

I own a 96 39 express and the shafts are 2"1/4 and I also had to remove pitch out of my 32 5blades.Before I was getting 2350 out of my 671 ,now like Barry Im getting 2550.The engines are more efficient now and I picked up some speed,but most important the engines are now running in the rpm range they were meant to.I only heard of one another 39 with Cummings and they were 420hp that boat was in montauk and I don't remember him breaking any shafts.But then again he may have had the 2and1/4.