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-   -   Prop advice (http://www.rib.net/forum/f36/prop-advice-72268.html)

Motoxmental 31 May 2016 07:11

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,

paintman 31 May 2016 13:20

What's the WOT range specified by Mercury for your engine?
What WOT rpm are you currently getting with the boat normally loaded?

Motoxmental 31 May 2016 13:54

Prop advice
To both your question, im sorry I have no idea! 🙈

jeffstevens763@g 31 May 2016 14:07

You need info on performance you have now as paintman has said, engine serial number etc.

Roflhat 31 May 2016 14:41

How is it performing just now?
is the current prop stainless?

Motoxmental 31 May 2016 15:27

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"

Roflhat 31 May 2016 16:04

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

Fstarocka 02 June 2016 16:12

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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Fstarocka 02 June 2016 16:15

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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