Prop for Barrus Shire 45

[vontel57]

Is a 17 x 11 Prop Suitable with a Barrus Shire 45E engine with a 150 hydrualic gearbox, for cruising on rivers. There is also another prop with this boat which is a 18 x 12 but at 1000rpm it has a slight humming noise. Comments would be appreciated.

[RobinJ]

Is a 17 x 11 Prop Suitable with a Barrus Shire 45E engine with a 150 hydrualic gearbox, for cruising on rivers. There is also another prop with this boat which is a 18 x 12 but at 1000rpm it has a slight humming noise. Comments would be appreciated.

You don't say what the boat is, but the 17 should be ok if a little low on pitch, the 18 is probably slightly over propped. At the end of the day it will be what your happy with on revs when running against the current!

[steelaway]

Is a 17 x 11 Prop Suitable with a Barrus Shire 45E engine with a 150 hydrualic gearbox, for cruising on rivers. There is also another prop with this boat which is a 18 x 12 but at 1000rpm it has a slight humming noise. Comments would be appreciated.

 

 

Hi

 

 

On this setup I have a 19x12 and runs at 16/1800rpm at cruising speeds

 

A 19x10 might also be OK - but also consider the blade form - some have much more 'blade'

 

You can some times cure the humming (cavitation) by grinding a knife edge the leading edge.

 

 

Alex

[Flyboy]

Barrus recommend 18x10 for the Shire 45 ( 2:1 gearbox). My choice would be 17x14 or 17x13 if I was buying a new prop. Your 18x12 should be fine but maybe it's not giving you enough clearance between the tips and the hull/skeg which may cause ringing. Do you have an anti cavitation plate under the weed hatch?

[steelaway]

Barrus recommend 18x10 for the Shire 45 ( 2:1 gearbox). My choice would be 17x14 or 17x13 if I was buying a new prop. Your 18x12 should be fine but maybe it's not giving you enough clearance between the tips and the hull/skeg which may cause ringing. Do you have an anti cavitation plate under the weed hatch?

 

 

Hi

Why would you choose a smaller prop? Surely you are going to have to use more revs for any given speed.

 

The bigger the pitch the more likelyhood of prop cavitation/ring

 

Alex

[Flyboy]

Hi

Why would you choose a smaller prop? Surely you are going to have to use more revs for any given speed.

 

The bigger the pitch the more likelyhood of prop cavitation/ring

 

Alex

A smaller diameter prop. with a larger pitch does not nessessary mean more cavitation. One of our forum members, Billy Pownal was not happy with the revs. he needed to get a good cruising speed ( Barrus Shire 45/18x10 prop). He changed it for an 17x14 and used 200rpm less to get the same speed. An increased clearance between the prop. tips and counter reduces the risk of debris getting trapped and improves the flow through through the prop. reducing cavitation. A good rule of thumb is 2" on the pitch = 1" on the diameter. Propellor selection seems to be more of a black art than scientific IMHO.