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Old 26 June 2019, 16:09   #1
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Country: UK - Scotland
Town: Inverness
Make: Avon
Length: 4m +
Engine: Yamaha 40hp
Join Date: Jun 2012
Posts: 9
Prop for Yamaha 40hp ?

I have a 4m Avon rib and an old (90's) Yamaha 2-Stroke 40hp engine. Myself and a friend had it at 31mph and with a lighter person and calmer weather we have had 36mph from it.
I am needing a new prop. Is there anything out there a bit more modern or am I already at the speed limits of this set up ?

At one end of the bushing there is a 25 stamped at (12 o'clock) and the letter A at (6 o'clock). What does this mean ? Reason asking is I have seen a similar prop but it is stamped with 20 and A.

On the other side I have 48-73136-13 and printed on the side is 48 73136 A40 13P


If I find a prop for sale do all of the above numbers need to match ?


Sorry for the Novice Questions, I just want to buy the correct part or even a more modern prop, Thanks.

Is this the prop I need to buy ?

https://www.ebay.co.uk/itm/Mercury-4...s/273901485325
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Old 27 June 2019, 02:06   #2
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Country: UK - Scotland
Town: Isle of Lewis
Boat name: Macleod Special
Make: Ceasar Thundercat
Length: 4m +
Engine: Yamaha 70ces
Join Date: Jul 2010
Posts: 853
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That's actually a mercury prop you've got on there, 13p. 10.5" diameter aluminium
Pretty much any 13 spline prop will fit that Yamaha, yamaha mercury and tohatsu all use the same splines and gearbox size for 40/50hp.

Depending on how the boat is performing you can change pitch, higher will give more top end, lower less top speed but quicker acceleration. If you're after better all round performance you should upgrade to a stainless prop, some of the best ones are made by Yamaha themselves, the "G" series semi cleavers. You can get them in 13-16p but the 15 and 16 are 400 odd, the 13G is 180 and 14G is 140. I've got a couple 14G for sale if you're interested, or can get new 13G's still
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Old 27 June 2019, 12:13   #3
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Country: Other
Town: Lima-Peru
Boat name: Nautile
Make: Sea Rider 450 Rib
Length: 4m +
Engine: Tohatsu 5/18/30 HP
Join Date: Sep 2007
Posts: 1,826
Bad music and dangerous for motor to play with pitches without counting with a installed tachometer which seems you don't have, right ? Safe wot rpm range is all, MPH is relative.

To prop right your motor there's 2 choices, running middle wot rpm for top end speed whichever the max MPH was achieved, max wot revs for top hole shot, both scenariost as usually loaded. Will need to check what's the min-max wot rpm range factory stated for your motor and play safely with prop pitches when doing recreational boating.

Happy Boating
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Old 27 June 2019, 14:07   #4
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Not neccesary here, this is a well known and tested setup, no need to reinvent the wheel
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Old 27 June 2019, 14:54   #5
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Country: UK - England
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I put a 40V on a 4m searider and it struggled to get max revs with a 13p, went much better with a standard 12” Yamaha 6H5 alloy cupped blade type (actually quite similar to the Mercury design)
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Old 28 June 2019, 06:56   #6
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Country: USA
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Make: AB
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I have a Yamaha f40 on a ABNautilus 12 ft that weighs around 900 total. To get into the 5 to 6 k RPM sweet spot I have to use a 12 or 13 pitch prop. That gets me to around 34 miles per hour. I've tried a 14 pitch stainless steel prop but that was too heavy and too tall. Oddly enough there is not enough torque for that engine to pull that prop properly. I would not recommend the stainless steel for an engine that's small.
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Old 28 June 2019, 08:20   #7
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Quote:
Originally Posted by Roflhat View Post
Not neccesary here, this is a well known and tested setup, no need to reinvent the wheel
Who's post were you referring to, mine or yours ? Sorry mate, each motor/boat combo it's a unique instalation doesn't matter if using same type and HP motor. Hull shape, deck load, weight distribution, lower leg/transom height, trim angle, prop shape could be different from one installation to any other one, lots of variables accounts for more or less wot rpm difference. A 12-13 pitch prop will power the boat, only a tach will tell which one is better suited for motor to run safely inside its wot rpm range factory stated.

Like playing with prop pitches myself, but doing so with an induction tach it's a night day difference than by ear tach, doesn't matter iif having a musician ear. With a tach will be able to fine tune any prop in a half pitch size to slightly increase/decrease wot rpm if needed.

If you guys like boating with any HP motor while olympically ignore at which rpm the motor is revving up at full speed simply ignore this post and keep boating as you've been doing so far...

Happy Boating
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Old 30 June 2019, 07:22   #8
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Country: UK - Scotland
Town: Inverness
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Thanks for the replies, still somewhat confused, can anybody share a link to the exact prop that came with the engine when it was built or a link with the prop that will best suit my needs ?, it's a bit of a minefield out there.

Thankyou in advance for the time taken to point me in the right direction !
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Old 30 June 2019, 08:22   #9
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Country: UK - Scotland
Town: north ayrshire
Boat name: charlie girl
Make: reiver 3.8/regal3760
Length: 10m +
Engine: 40hp 2st 2x6lp 315
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Quote:
Originally Posted by nousername View Post
Thanks for the replies, still somewhat confused, can anybody share a link to the exact prop that came with the engine when it was built or a link with the prop that will best suit my needs ?, it's a bit of a minefield out there.

Thankyou in advance for the time taken to point me in the right direction !
As has been said there is no one size fits all, no such thing as a standard prop. To get the correct prop for your boat you need to know the rpm flat out with your average loading. Engine needs to reach as close as possible makers max rated rpm.
You can buy a small induction tach off ebay for around a tenner which will do to work out your required size.
A stainless prop will always be more efficient and you often need to use a lower pitch if going stainless as the extra efficiency can result in less wot rpm but a stainless prop probably speced will give a small performance advantage over ally, wether its worth the extra cost is a decision for you.
Take the boat out measure the wot rpm with your current prop and people can advise accordingly anything else is guesswork
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Old 30 June 2019, 13:14   #10
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Country: UK - Scotland
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Length: 4m +
Engine: Yamaha 40hp
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Quote:
Originally Posted by beamishken View Post
As has been said there is no one size fits all, no such thing as a standard prop. To get the correct prop for your boat you need to know the rpm flat out with your average loading. Engine needs to reach as close as possible makers max rated rpm.
You can buy a small induction tach off ebay for around a tenner which will do to work out your required size.
A stainless prop will always be more efficient and you often need to use a lower pitch if going stainless as the extra efficiency can result in less wot rpm but a stainless prop probably speced will give a small performance advantage over ally, wether its worth the extra cost is a decision for you.
Take the boat out measure the wot rpm with your current prop and people can advise accordingly anything else is guesswork

My current prop has sustained damage, it has a crack on one blade and a 2 size it missing from another blade. I can buy the tach, I hope my damaged prop doesn't alter the rpm much but will reply in due course, Thanks
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