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Old 10-07-2014, 11:12 AM   #1
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"Tuning" props for salt vs. fresh water.

Anybody ever heard of having two sets of props, one set "tuned" for fresh and another set "tuned" for salt?
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Old 10-07-2014, 12:13 PM   #2
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Some planing hull boats behave differently in fresh vs salt, especially if barely planing. The difference in density can be pretty profound there.

At trawler speeds, no real differences.
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Old 10-07-2014, 12:21 PM   #3
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Cold vs warm water and air temps cause reduction in HP so that is a reason for less pitch in FL than Maine for planing boats. Boats set up for cold areas may not reach wot in FL.

Hot air, water and fuel can reduce performance several %.
Sea water is 2% denser than fresh so the boat displaces less volume, same weight, but I suspect that the temperature issues will be more significant that density issues.

All nice in theory but marine growth will be a biger change for a freshwater boater.
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Old 10-07-2014, 02:05 PM   #4
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Anybody ever heard of having two sets of props, one set "tuned" for fresh and another set "tuned" for salt?
We operate in an environment with both fresh and saltwater. Never heard of it.
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Old 10-07-2014, 04:32 PM   #5
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Anybody ever heard of having two sets of props, one set "tuned" for fresh and another set "tuned" for salt?
I have never heard of that. Where did you hear of it?
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Old 10-07-2014, 04:57 PM   #6
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The owner of the boat I'm currently delivering said his spare props were tuned by the prop shop for salt water. I've never heard of it either. But apparently there may be some validity to it. At least for some types of boats do to the density of salt water vs. fresh.
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Old 10-07-2014, 05:16 PM   #7
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The owner of the boat I'm currently delivering said his spare props were tuned by the prop shop for salt water. I've never heard of it either. But apparently there may be some validity to it. At least for some types of boats do to the density of salt water vs. fresh.
Do you suppose they charged him extra for that?
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Old 10-07-2014, 05:35 PM   #8
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Do you suppose they charged him extra for that?
Perhaps.

But as I mentioned, for some types of vessels, like higher speed planing vessels, there may be something to it. So I'm not ready yet to dismiss it as marketing.
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Old 10-07-2014, 07:48 PM   #9
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I think it may be a bit like changing the air in your tires for summer or winter. At least as far as this prop shop goes.
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Old 10-07-2014, 07:52 PM   #10
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Believe any difference would be minimal. Me worry?
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Old 10-07-2014, 08:24 PM   #11
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I'd think there would be a greater effect due to water temperature than salinity

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Old 10-08-2014, 06:29 AM   #12
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I think it may be a bit like changing the air in your tires for summer or winter.

Never!

We have a 1996 and ONLY use 1996 air !!
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Old 10-08-2014, 06:56 AM   #13
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Operated a twin water jet vessel in fresh water for a few days a couple of years ago. Max speed dropped from 29 to 27 knots when in fresh water .

BTW: Do fresh water vessels have sea water strainers or fresh water strainers?
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Old 10-08-2014, 12:20 PM   #14
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We see a significant drop in our waterline from seawater to freshwater, we loose some performance, but not something to warrant a real pitch change for, we already have some margin of error in seawater anyway.
Interesting side story, by sisters boat with twin gas 454's would overheat the transmissions when in fresh water and full load of fuel, in sea water never see it.
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Old 10-08-2014, 01:01 PM   #15
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The most memorable example of this was an old Bertram 54 with 12-71 Detroits. It was old and water logged and owner had packed it full of junk. When I ran it it would kinda sorta plane at 2100 and make about 19kts, full tabs. That was in sea water. I did not dare run the motors harder than 2100 as I feared they'd blow.

Came in Cape Fear river from offshore, hit the fresh water and boat started settling. Down to about 15kts and plowing like crazy. Still at 2100. Had to shove it to the pins to get back up and then 19kts was then 2150.

Couple days later came back out to sea and it was back to 19kts at 2100.

Unique example as boat was right on edge of falling off plane on a good day.
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Old 10-08-2014, 01:23 PM   #16
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BTW: Do fresh water vessels have sea water strainers or fresh water strainers?
Sea water but they have much longer hoses.
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Old 10-08-2014, 05:15 PM   #17
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Sea water but they have much longer hoses.
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