props

[searover2]

Hi all, i hope. ive put this,, on the right forum. i have a avon 5.6meter rib with a 115 hp. motor 4 stroke. my question is , does a prop, 21 pitch and 14 diamiter 3 blade, sound right for this set up . or could anyone with similar set up, advise me . as my prop is nacked, and on the boss it says, 3x21x14. as i have just bought this boat, i cant tell u max revs with this set up and i would rather if pos, buy the best dia and pitch set up as i can. at 200 quid a prop. thanks for reading this , i know someone out will be able to help, cheers all, and happy sailing........

 

[carlton]

In the absence of any other replies, I'd suggest you post the same question on the ribnet forum (clicky).

 

[ulyden]

You have to know some datas!

Boat maximum speed!

VOT engine rpm

Gear ratio!

An example!

Boat maximum speed! 40 knots

VOT engine rpm! 5000rpm

Gear ratio! 1:2

Propeller: 10% slipp means 44.5knot propeller speed or 915 inch pr second

Propeller rotating 5000rpm/gear ratio/60= 41.5r/sec

Pich 915inch/sec/41.5r/sec = 22 inches!

 

[MapisM]

my question is , does a prop, 21 pitch and 14 diamiter 3 blade, sound right for this set up

Yes.
Mind, it's impossible to say if it's dead right, based only on the info you gave us, but it does sound reasonable.

 

[moonraker 36]

all depend's on how fast you want to get onto the plane(water skiing)or if you want to cruise at a high speed with out the engine reving its nut's off.smaller pitch will give you faster pick up .i wouldnt go higher in pitch then you already have.
if you go for more blades on the prop such a 5 blade's come down in pitch 2"" or so.

 

[ulyden]

You can only select propeller that gives you speed between the upper and lower VOT range for your engine. Most manufacturers have a 10% vot speed span you should be able to achieve.
For an engine that runs about 5500rpm you can choose a propeller that gives you from 5000rpm to 6000rpm max speed! (Yamaha F115)

Select 5000 rpm gives you an economical boat with slow acceleration and low margin of load changes. Select 6000rpm provides quick acceleration, often higher speed and higher consumption!

If the speed is above 6000 or below 5000, you change propellers!

Finding optium propellers can be difficult. You must know what you want and buy something that fits exactly. A steel propellers often provide the best properties