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Old 07 June 2016, 18:14   #11
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Originally Posted by jyasaki View Post
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
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Old 10 June 2016, 17:16   #12
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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
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Old 10 June 2016, 17:35   #13
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Quote:
Originally Posted by Ron Noco View Post
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.
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Old 10 June 2016, 19:06   #14
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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
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Old 11 June 2016, 11:12   #15
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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
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Old 16 June 2016, 10:53   #16
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Mercury prop code

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
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Old 16 June 2016, 15:28   #17
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Also, boat insured to 25kt max
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