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Old 31 May 2016, 08:11   #1
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Country: UK - Scotland
Town: Scotland
Boat name: Barry
Make: Avon
Length: 4m +
Engine: 50hp Mercury
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Prop advice

Hello, I have an old merc thunderbolt 50, current prop is 10 1/4 x 14. Struggled to find a replacement anywhere. Its on a 4.5m avon waverider.

I am looking at new props, in particular a 10 1/2 x 12 replacement.

Is there any striking advantages or disadvantages here? Will I see a conplete reduction in performance?

Many thanks guys,
Jamie
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Old 31 May 2016, 14:20   #2
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Country: UK - England
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Length: 5m +
Engine: 135hp Mercury
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What's the WOT range specified by Mercury for your engine?
What WOT rpm are you currently getting with the boat normally loaded?
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Old 31 May 2016, 14:54   #3
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Country: UK - Scotland
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Prop advice

To both your question, im sorry I have no idea! 🙈
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Old 31 May 2016, 15:07   #4
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Country: UK - England
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You need info on performance you have now as paintman has said, engine serial number etc.
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Old 31 May 2016, 15:41   #5
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How is it performing just now?
is the current prop stainless?
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Old 31 May 2016, 16:27   #6
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Prop advice

Il need to find the engine number etc its an older thunderbolt blueband.

At the moment it has an alu prop but its like grannys teeth with cracks and dints in it. My main concerns would be going from a 14 inch diameter to a 12"
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Old 31 May 2016, 17:04   #7
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that's pitch, the 12 and 14" are pitch, both have similar diameter.
So with a 14" pitch your top speed will be higher (more distance covered for same RPM) but acceleration slightly slower. Going to a 12" pitch you will have better acceleration but lower top end, assuming you are getting correct WOT (Wide Open Throttle) RPM.

Generally for heavier boats you want more diameter and less pitch, lighter boats require less diameter and can plane with higher pitch props.
Unless you are unhappy with the performance just now then go for a replacement of the same prop. There's a 13" pitch on gumtree just now - https://www.gumtree.com/p/boats-kaya...rd-/1170051087
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Old 02 June 2016, 17:12   #8
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Go to the mariner prop selector, excellent. I just went thru this for my 80s mariner 60hp.. Ended up with a spitfire prop 14 pitch, mines a 4.2 rib solid hull..

I wouldn't go 12.. Ull over rev.. If u are carrying weight in rough water go 13.. All round 14 best, light weight and economy long range go 15.. I wd say 13-14.. It's not only wot rpm but gear case ratio, boat weight, gear/luggage and intended use..

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Old 02 June 2016, 17:15   #9
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13 will give best holeshot and be slightly safe in rough water with a load.. 14 in my results came up as the recommendation for 90% of my calculations on the mariner prop selector.. FYI they only go back to 1990 so check your gear case ratio and pick the oldest motor with same ratio.. They do show it..

Aldo the mercury props can be used on all makes so u can reuse these props

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