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Old 04 August 2007, 16:14   #1
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prop sizes

I have a v4 115hp evinrude with 14x19 prop hits about 4700 to 4900 rpms. We tuned it up not much changed. Loaded with dive equipment or passengers she"s(politically incorrect) slow out of the water. Been told a dozen different things, so today bought a 13.25x17 prop try it tomorrow Question is I know many have gone through this so should I look for a 14x17 prop or is there much of a difference. Or should we look deeper into the engine
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Old 04 August 2007, 16:23   #2
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You should get a few more revs than that. Also it helps if people move forward to get it on the plane - then move aft as speed increases.
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Old 04 August 2007, 16:32   #3
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When it is my dive buddies we move back and forth, but when the "little woman" is aboard she is white knuckling it and to get her to move ain't happening. So it sounds like we should look a little deeper into the engine?
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Old 04 August 2007, 22:17   #4
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Originally Posted by 603doug View Post
When it is my dive buddies we move back and forth, but when the "little woman" is aboard she is white knuckling it and to get her to move ain't happening. So it sounds like we should look a little deeper into the engine?
No the prop change should govern the rpm - also engine height can make quite a difference.
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Old 06 August 2007, 11:51   #5
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Quote:
Originally Posted by 603doug View Post
I have a v4 115hp evinrude with 14x19 prop hits about 4700 to 4900 rpms. We tuned it up not much changed. Loaded with dive equipment or passengers she"s(politically incorrect) slow out of the water. Been told a dozen different things, so today bought a 13.25x17 prop try it tomorrow Question is I know many have gone through this so should I look for a 14x17 prop or is there much of a difference. Or should we look deeper into the engine
I have the V4 Johnson 115 which I am guessing is the same engine?

Mine (before I bent the prop) got 5200rpm 39kt with a 19" prop, I have the 17 back on there now (new 19 arrives this week yay!) and you get more revs but less speed on my boat - 36kt at 5500rpm. I can't honestly say I noticed the hole shot improved when I switched back either. Not sure about a laden boat, it might be different then.
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Old 06 August 2007, 16:33   #6
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When I first got the rib changed plugs etc did about the same 39 kts. at 5000, loaded (2 divers and extra gear) 35 at around 4900.But started to notice longer to get up on plane and lost a few rpms, the reason for the tune up. Went out sunday to try the prop bendex on the starter came apart so will try again later this week. Also same engine v4 115
thanks for the info
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Old 08 August 2007, 16:37   #7
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We changed from a three bladed 19" ally to a four blade 21" SOLAS from steel developemnts on a Humber 5.5 Extreme with a 115 Evinrude/Johnson V4 on her arse. Correctly trimmed we got over 40kts quite happily.

Got any ideas about Suzuki DF175 on a Ring 685? Carries a 3x15x31 at the moment and over revs madly.
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Old 12 August 2007, 15:02   #8
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Tried my 13.25x17 prop today, 2 divers and gear got up on plane faster and seem to have midrange speed where before it was all or nothing. I still have to check out rpms only manage 4500.
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Old 15 August 2007, 10:38   #9
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Tried my 13.25x17 prop today, 2 divers and gear got up on plane faster and seem to have midrange speed where before it was all or nothing. I still have to check out rpms only manage 4500.
Max rpms will vary with load. It will also be affected by how much water is in the hull, where the load is situated, how much fuel, etc.

You want to prop for max-rpm-within-mfgr's-spec at a "normal" load, with the engine trimmed up. In my case, I propped for full load of fuel, with 2 people on board, and just accepted the rpm drop with dive gear (and more divers.) If I expect to have a lot of divers and gear on board, I swap to a much lower pitched prop.

General rule is about 200 rpm per inch of pitch, all other things being the same (though it's kind of a black art, and never goes quite the way it's supposed to.) Other general rule is about 100 rpm per quarter inch of diameter.

Figure out a baseline for testing (as far as load goes) and work it up from there; you can't tell anything if you're testing under constantly changing conditions.

jky
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