Mercury prop code

[Ron Noco]

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

[jyasaki]

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

[paintman]

^^^^^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.

[Ron Noco]

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

[Poly]

Originally Posted by Ron Noco

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?

[jambo]

You beat me to it Poly I agree something doesn't add up.


Sent from my iPhone using RIB Net

[Ron Noco]

Originally Posted by Poly

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

[Dirk Diggler]

Originally Posted by Poly

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

[Ron Noco]

Originally Posted by Dirk Diggler

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

[jyasaki]

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

[Ron Noco]

Originally Posted by jyasaki

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

Mmm....Interesting... 😕

Also is there anyway to check that the throttle end stop screw is set correctly? Voltage or ?
Seems to me there's another 6-8mm of travel left after the stop hits...

Only have the one prop at present, but I was thinking if I trimmed it up higher than normal just for a few seconds it should allow it to spin up the revs whilst still getting some cooling...?

If it can Rev to 5500 then it must be the prop?

Bad idea or OK for a few seconds...

Cheers

[Ron Noco]

Ok back with some data.... 🤔

Total weight down to 480kg approx

Did a good few runs varying the trim but the max I could get was WOT - 5760rpm = 26kts, wasn't ideal conditions but normal for what I'll be out in ... Actually 26kts was more than felt comfortable, scary when trimmed up as the steering changes a lot
Plane hole shot was <5 seconds, needed 14kts to stay up...

From what I can find online throttle max 5500-6000...


Won't be always fully loaded (800kg+) 4500 revs @ 16kts

Rarely be on my own (480kg) 5760 revs @ 26kts

So a prop to suit 650kg average?

Thanks for any help

Cheers
Noel

[Poly]

Originally Posted by Ron Noco

Ok back with some data.... 🤔

Total weight down to 480kg approx

Did a good few runs varying the trim but the max I could get was WOT - 5760rpm = 26kts, wasn't ideal conditions but normal for what I'll be out in ... Actually 26kts was more than felt comfortable, scary when trimmed up as the steering changes a lot
Plane hole shot was <5 seconds, needed 14kts to stay up...

From what I can find online throttle max 5500-6000...


Won't be always fully loaded (800kg+) 4500 revs @ 16kts

Rarely be on my own (480kg) 5760 revs @ 26kts

So a prop to suit 650kg average?

Thanks for any help

Cheers
Noel

Looks like you are pretty well set up for your light load. I'd want to load it at 650kg and get some data on speed, rpm, holeshot with the current prop and different trim settings before spending money on an experimental prop.

[Roflhat]

The Mercury will likely have a gear ratio around 1.84, I would be going down to 11" pitch and see how it goes. On a heavy boat with 40hp that's about right.
The standard Mercury props decrease in diameter as the pitch increases, to account for the reduction in load on the engine. So an 11" pitch prop will usually be over 11" diameter whereas a 15" pitch will be around 10" diameter.
Comparing prop pitch and engine rpm against anything that isn't a similar setup won't help too much

[Ron Noco]

Hopefully drag some passengers "ballast" out tomorrow to see what the result is for a usual load

Ya I think an 11" pitch sounds like what I'll end up with

Although it'll be slower, it'll suit why I bought the boat better :-)

Cheers lads

[Ron Noco]

Sea Conditions not good at present, but in the meantime I've been researching props...
From the data I have at present it sounds like a 3 blade 11" pitch should be the best choice
But would a 4 blade 10" prop actually be a better idea?

Reason I'm thinking along these lines is...
Rarely get flat clam seas around here, so top end max speed isn't a priority
Being able to plane and stay up at a slower speed would definitely be a bonus
Websites mention "stern rising" as a plus for 4 blades, what's that mean in real life? Bow comes down? That would be good as my boat catches enough wind to stop her planning fully loaded

Any comments, good or bad as I've only limited experience with planning boats

Thanks lads

[Ron Noco]

Also, boat insured to 25kt max