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Old 21 May 2007, 04:15   #1
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Prop for Yamaha 4 HP 2 Stroke

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
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Old 23 May 2007, 17:37   #2
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Any takers or am I going to have to buy one of each to test for the best option?

Chris
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Old 24 May 2007, 03:58   #3
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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
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Old 24 May 2007, 04:32   #4
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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
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Old 24 May 2007, 05:38   #5
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Try Steel Developments in SW18. They are brilliant and very helpful.

http://www.steeldevelopments.co.uk/Prop_Repairs.html
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Old 24 May 2007, 06:11   #6
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Quote:
Originally Posted by Chris1573 View Post
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
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Old 24 May 2007, 17:04   #7
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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
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Old 11 June 2007, 09:18   #8
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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
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