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96 Ski Nautique Propeller sizing |
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Dean96Ski 
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Joined: January-03-2020 Location: NE Indiana Status: Offline Points: 8 |
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 Topic: 96 Ski Nautique Propeller sizingPosted: January-06-2020 at 3:19pm |
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This past Fall I purchased a 96 Ski Nautique with the GT-40 engine. The previous owner used it primarily for knee boarding. So with only 330 hours on the boat the engine should have plenty of pep left in her. I believe the red line RPM is 4400 RPM. I ran it only twice this past fall. I calibrated one of the speedometers and 36MPH felt like 36MPH when I skiied. So I believe the speedo is correct. Running wide open I am seeing 5000RPM and only about 40MPH. This was with a 14x16 4 blade propeller. I switched to the spare 14x17 3 blade propeller with similar results. It seems that these propellers are under pitched. Or the tachometer is reading wrong. I NEED INPUT FROM OTHER OWNERS as to what propellers they are running. I will be pulling barefooters at 39MPH so I really do not wish to be taching these high revs. Thank you for your input!
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Still Skiing even though I shouldn't be.
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TRBenj
Grand Poobah 
Joined: June-29-2005 Location: NWCT Status: Offline Points: 21107 |
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Posted: January-06-2020 at 3:58pm |
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I wouldn’t worry about those revs... recommended HO WOT RPM is 4800-5000 (not 4400, that’s the non-HO). The 351w can spin that safely all day long.
That said your top end numbers are poor and do not align with the rpm you’re indicating. So either the props are junk, or one or both readings are inaccurate. Ideally we’d like to get good baseline numbers before making a hard recommendation but props on that hull have been pretty well characterized... if it were my money I’d be ordering an Acme 1442, but the 422 is also a decent choice. |
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Dean96Ski
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Joined: January-03-2020 Location: NE Indiana Status: Offline Points: 8 |
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Posted: January-07-2020 at 12:06pm |
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Thank you for your input. Yes I agree speed/RPM just do not add up. Another person suggested improving on the grounding across the gauges, mentioned that a loose ground connection may result in erroneous gauge readings. I am planning on borrowing a friends prop who is reporting 45MPH at around 4500 RPM on a naturally aspirated 94 ski. It is still winter here for a few more months.
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Still Skiing even though I shouldn't be.
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8122pbrainard
Grand Poobah
Joined: September-14-2006 Location: Three Lakes Wi. Status: Offline Points: 41040 |
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Posted: January-07-2020 at 12:15pm |
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Dean,
A GPS speed and a shop tach will confirm your RPM's and speed. |
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TRBenj
Grand Poobah
Joined: June-29-2005 Location: NWCT Status: Offline Points: 21107 |
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Posted: January-07-2020 at 1:50pm |
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45-47 is about what I’d expect for speed if all is healthy... the NWZ hull becomes less efficient over 40mph and the 1:1 speed vs rpm (with a stock 14x16 or equivalent like the 422) that you see at 25mph through slalom speeds will typically drift away a little. 46mph at 4800-5000 is pretty typical.
1442 will raise RPM across the board by 200rpm which will keep you near peak power at WOT with a bigger load (like some barefooters). |
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Hollywood
Moderator Group 
Joined: February-04-2004 Location: Twin Lakes, WI Status: Offline Points: 13510 |
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Posted: January-07-2020 at 2:13pm |
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What was your RPM at 36mph?
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Jonny Quest
Grand Poobah
Joined: August-20-2013 Location: Utah--via Texas Status: Offline Points: 2840 |
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Posted: January-07-2020 at 11:06pm |
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My 1994 SNOB runs an ACME 654 - 4 Blade 12.5" x 15" Propeller. I'm at 4,400 feet of elevation and my tug can get to 43 MPH on the GPS speedo at 5,000 RPM. Not a true apples-to-apples comparison as you have a GT-40 and mine is a warmed-up carbureted High-Output mill. If all is well with your engine and drivetrain, I should reasonably expect to achieve 45 MPH plus.
JQ |
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Current
2003 Ski Nautique 206 Limited Previous 2001 Ski Nautique Open Bow 1994 Ski Nautique Open Bow Aqua skiing, ergo sum |
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MrMcD
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Joined: January-28-2014 Location: Folsom, CA Status: Offline Points: 3590 |
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Posted: January-08-2020 at 4:48am |
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My 1995 GT40 has been run with 4 props now.
A 224 Acme that I purchased from TRBenj was my favorite, unfortunately it was damaged and fixed the first time, that prop pulled quite well and the boat ran 48 to 50 while taching up to 5,200 or so, there is old posts that will show the numbers recorded but that prop ran fast for me. It was damaged again and after 2nd repair I lost 3 MPH was not as smooth and still tached up but was not as fast. Disappointed I purchased a new Acme 422 and it is very smooth and pulls hard, no complaints on this choice but I have not seen more than 46-47 with this prop yet and I think top RPM is right at 5,000 but it has been a while since I checked. We normally ski at 1,500 ft elevation. I have not pulled bare-footers on the 422 yet but it pulls hard so I expect it would do fine at near sea level. Tim has tested and tried most prop combinations with stock and high horsepower engines and his advice on props is hard to beat. The last few times I bare footed I went 37 MPH on purpose, I can't slide around as much but the falls are a little softer when they happen but I am old and it is still bare footin! |
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Dean96Ski
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Joined: January-03-2020 Location: NE Indiana Status: Offline Points: 8 |
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Posted: January-08-2020 at 6:10pm |
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To all. Thanks. You gave the kind of input that I was looking for. I was thinking the 1:1 speed to RPM ration is a good rule of them. Note that when I said that the one working speedometer was calibrated using a speed app on a smartphone. I am leaning towards propellers that were good enough for the previous owner but not good for my needs.
This is the third Nautique that I have owned. Bought brand new 1986 Ski, Then traded for a 1999 Sport. Then due to an unfortunate period in life I went about 7 years without a ski boat. Now I am finding that this 65 year guy still has a little left to give on a slalom ski. |
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Still Skiing even though I shouldn't be.
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