Prop for Yamaha 4 HP 2 Stroke

Chris · 21 May 2007, 09:15

Hi,

The prop on my newly aquired Yamaha 4A 1990 engine is the standard 7 1/4 x 7 B.

This prop needs replacing as it is looking worse for wear and the options are either:

7 1/4 x 5
7 1/4 x 6.5
7 1/4 x 7 (current)

as this engine will be pushing a 5.5 metre RIB I am not sure whether to go for a lower pitch prop. The current prop is crap anyway so I cant really use it as a yardstick to check performace.

Can anyone recommend from experience oh and the bugger of the smaller pitch prop is that is twice the price of the standard one at £56.00

Chris

Chris · 23 May 2007, 22:37

Any takers or am I going to have to buy one of each to test for the best option?

Chris

Pete7 · 24 May 2007, 08:58

Stick a new standard one on it and chuck the boat in a nearby canal for a trial. If the engine sounds like its pulling max revs then you have cracked it with the standard prop and not spent a fortune. A beer says its 3 knots tops.

Pete

Chris · 24 May 2007, 09:32

Pete I got 3.5 knots with the short shaft which was cavitating like mad, so I reckon you may be dusting off your wallet.

I am going to try the 6.5 first and see how I get on.

Chris

JABS · 24 May 2007, 10:38

Try Steel Developments in SW18. They are brilliant and very helpful.

http://www.steeldevelopments.co.uk/Prop_Repairs.html

Pete7 · 24 May 2007, 11:11

Quote:

Originally Posted by Chris1573

Pete I got 3.5 knots with the short shaft which was cavitating like mad, so I reckon you may be dusting off your wallet.
Chris

a ha, hadn't realised you had changed it. Viv has got all my money now, the days of being single with pocket money are a distant faded memory

Revised estimate 5 knots then, you could run a sweep stake on this

Chris · 24 May 2007, 22:04

Hi Pete,

Yeas I did a straight swap with a longshaft. Will be going out tomorrow hopefully for a test so will let you know the results with the exisitng slightly worse for wear 7" prop tomorrow. Have also got a 6.5" on order so will be interested to see the difference.

Chris

Chris · 11 June 2007, 14:18

Pete 5 knots seems to be about right I have had 5.3 out of it.

The 6.5 inch prop makes all the difference, it does not look upto the job really as it is a different style and shape to the 7" however to my suprise it gave me another 1.5 knots over the standard prop.

Chris