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Old 05 June 2016, 17:36   #1
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Mercury prop code

Hi all,
I have a Mercury 40hp efi
Prop has a code embossed in it = 73136A40P13, guessing the "13" is pitch? when out with the whole family ( max load) I noticed it Rev-ed out to only 4600 , from what I've found out it seems I'm over propped?
There will be occasions where the load will be less but I think it's still way over???

Ideally like to get it up close to 5500



Any help appreciated

Cheers
Noel
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Old 05 June 2016, 21:31   #2
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I've got my boat propped to turn 6100 when lightly loaded and fueled. When heavily loaded, it may turn less than 5000, and really take some time to get on plane. I have a 2" shorter prop for when I know I'm going to heavily loaded.

Select your pitch based on how you normally load the boat. Google says your current prop is 10.38" dia x 13 pitch.

jky
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Old 06 June 2016, 04:14   #3
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^^^^^What he said.
Test at WOT with your normal load. If it's OK & within range then I wouldn't worry about it.

It's the part number for your prop. You are quite right that P13 is the pitch of the prop.
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Old 06 June 2016, 10:19   #4
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Yesterday she took a while to plane at full revs 4600, once up I dropped it back to 4200 for passengers comfort, made good progress, covered 16nm in just over an hour

On the return journey I couldn't her to plane as the wind had picked up, wasn't head on but enough to resist

Going by that should I get an 11" pitch prop with the same diameter?

Thanks lads

Noel
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Old 06 June 2016, 10:54   #5
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Quote:
Originally Posted by Ron Noco View Post
Yesterday she took a while to plane at full revs 4600, once up I dropped it back to 4200 for passengers comfort, made good progress, covered 16nm in just over an hour

On the return journey I couldn't her to plane as the wind had picked up, wasn't head on but enough to resist

Going by that should I get an 11" pitch prop with the same diameter?

Thanks lads

Noel
Something doesn't makes sense to me, I can run an 11" prop, with 20HP albeit on a slightly smaller boat, but doing 18+ knots with a reasonable load at WOT. With double the power you shouldn't be struggling to get just a little bit bigger prop to turn, on a slightly bigger boat and achieving <16 knots....

Is your tacho definitely set right?
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Old 06 June 2016, 10:58   #6
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You beat me to it Poly I agree something doesn't add up.


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Old 06 June 2016, 12:04   #7
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Quote:
Originally Posted by Poly View Post
Something doesn't makes sense to me, I can run an 11" prop, with 20HP albeit on a slightly smaller boat, but doing 18+ knots with a reasonable load at WOT. With double the power you shouldn't be struggling to get just a little bit bigger prop to turn, on a slightly bigger boat and achieving <16 knots....



Is your tacho definitely set right?

Not sure to be honest, it's one of those can bus smartcraft combo gauges, tick over is showing 930-960 rpm which sounds about right...

The 450 is a heavy yoke when full
Hull & bolt on extras = 230kg
Fuel = 25-30kg
Battery= 20kg
Anchor= 6kg
Outboard= 106kg
Auxiliary = 25kg
Miscellaneous = 10kg
Passengers = 400kg
Total = 800kgs +

Moving the passengers around yesterday did help planning but it isn't easy to put the heavier ones on the bumpy seats :-)


I'll need to take it out on my own and see if the revs are much higher...

I had a 30hp last year and that Rev-ed to 5800 with half the passengers we got 22kts @ WOT, can't remember the prop specs but changed to the 40hp as it felt under powered...

Cheers
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Old 06 June 2016, 12:18   #8
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Quote:
Originally Posted by Poly View Post
Something doesn't makes sense to me, I can run an 11" prop, with 20HP albeit on a slightly smaller boat, but doing 18+ knots with a reasonable load at WOT. With double the power you shouldn't be struggling to get just a little bit bigger prop to turn, on a slightly bigger boat and achieving <16 knots....

Is your tacho definitely set right?
different lower ratio's I suspect
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Old 07 June 2016, 05:02   #9
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Originally Posted by Dirk Diggler View Post
different lower ratio's I suspect

Final drive on the 40hp = 2:1
Yamaha F30 same ratio

After a bit of digging I found the old Yamaha prop box...

For comparison , same boat, different engines, similar loads

Yamaha F30 - 5600 revs , prop 12.25 X 9 = 20kts

Mercury 40 - didn't have tach, prop 10.75 X 13 = 22kts

Try and get out on my own soon and see difference then
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Old 07 June 2016, 11:06   #10
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From my recollection, 1/2" diameter affects rpm about the same as 1" pitch, so the props are not as different as you'd think by looking at the numbers.

jky
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