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Prop Question
https://www.smwebhead.com/phpBB3/viewtopic.php?f=11&t=4591		 Page 1 of 1
Author:  Aquadisiac [ Sat Sep 19, 2009 7:25 pm ]
Post subject:  Prop Question
2000 235 sundowner 5.7gsi sx drive. It has the recomended prop from FW 14.5 x 19 wot RPM 4800 as long as the tach is correct, 2 adults 2 kids full of fuel will hardly hit 43mph on gps and according to FW it should be closer to 48-51mph but anything over 45mph would be more realistic...any thoughts?
Author:  230 Mike [ Sun Sep 20, 2009 12:23 am ]
Post subject:  Re: Prop Question
What altitude? Gear ratio? Fresh fuel?
Author:  Aquadisiac [ Sun Sep 20, 2009 2:06 pm ]
Post subject:  Re: Prop Question
ratio is 1.51, 70 - 110 masl several tanks of premium
Author:  Walt [ Sun Sep 20, 2009 7:55 pm ]
Post subject:  Re: Prop Question
It seems to me you are not hitting WOT RPMs. Since the boat is a few years old, I would go through first and get a tune-up, as well as fresh fuel filter, if not already done. If your boat is running the recommended WOT RPM and prop for the drive, then you should be getting close to advertised WOT RPM and speed. Once that's done, start getting some detailed numbers, and plug them into this....

http://www.go-fast.com/Prop_Slip_Calculator.htm

That should tell you where your "slip" is (not where you park the boat :roll: ), and you should be able to identify the ideal prop pitch for your desired needs and RPM range. Again, make sure you are using your GPS.

Good luck!
Author:  Aquadisiac [ Mon Sep 21, 2009 7:00 pm ]
Post subject:  Re: Prop Question
From what I can tell my slip is 0.25, not sure what that all means or what to do with it, also been looking around and it looks like the proper ratio for a 5.7gsi is 1.43 and mine is 1.51 which it says is for a 5.0 not sure why or if it has been replaced, or even how to compensate with prop.
Author:  Walt [ Mon Sep 21, 2009 8:50 pm ]
Post subject:  Re: Prop Question
Your "slip" should be relatively constant for your hull. With that, you can plug in different prop pitches and see what you get for top end. Or work backwards as I do to find the ideal prop for the desired top-end and WOT RPM. Remember, as you prop-up, your WOT RPMs will actually drop, and may not actually improve top end. Also, the more blades, and/or lower pitch, the prop dia tends to be smaller.
Author:  ht32bsx115 [ Thu Sep 24, 2009 1:31 pm ]
Post subject:  Re: Prop Question
Aquadisiac wrote:
From what I can tell my slip is 0.25, not sure what that all means or what to do with it, also been looking around and it looks like the proper ratio for a 5.7gsi is 1.43 and mine is 1.51 which it says is for a 5.0 not sure why or if it has been replaced, or even how to compensate with prop.



Your slip is 25% using your numbers. Since you're using GPS, your other numbers could be incorrect. RPM is usually the other inaccurate number. Tachometers are frequently WAY off.

Also, depending on where you got the drive, (it's a 1998 model?) if you didn't buy it new, someone may have either replaced or rebuilt the drive with whatever parts they could find cheap. The ratio may not be what you think it is. The prop-slip calculator is pretty accurate if you plug in accurate numbers.

Quote:
Your "slip" should be relatively constant for your hull
YES. and if your slip is higher than about 15-18% for most sport-runabout, under 25' boats, then something is causing the drag....... I.E. the boat is WAY HEAVY (waterlogged), the bottom is covered with barnacles or other stuff, or you're dragging an anchor!!!


To determine the problem, you should get another (known) tach. and accurately determine your drive ratio. If you cannot read it off the drive, pull your spark plugs, and use a wrench to turn the crankshaft exactly 3 turns. If it's really a 1.51:1 drive, the prop will turn 2 turns (- a little but you won't see it unless you use a protractor!!)

if it's a 1.43:1 drive, 3 engine turns will result in 2.1 prop "turns".....0.1 turns is about 35 degrees so the reference blade will go about 35 degrees PAST 2 turns and you can easily see that.

Also, if you don't have accurate RPM and ratio data, you're wasting your time with the prop slip calculator.
It's important to know this because that slight difference in drive ratio can really make a significant difference in performance with a given prop.

Regards,


Rick
Author:  Aquadisiac [ Sat Sep 26, 2009 5:55 pm ]
Post subject:  Re: Prop Question
The drive says it is a 1.51, but I think the timing is too far advanced whether that would make a difference in my top end or not I'm not sure. I am going to change plugs and wires and set the timing and see if that makes much of a difference. The prop that is on it is the one four winns put on it and I am turning 4800 at wot whether you believe the crappy vdo gauges and the recomended range is between 4600 and 5000. I am planning on putting a stainless prop on in the spring, but if I am not getting anywhere near the advertised speeds said by Four Winns for this boat and current current prop, I need to get that sorted out before anything. As for it being waterlogged, I will need to get a moisture meter and see, but man I hope not, but the way things have gone with the dealer I would not be surprised if I am stuck with a piece of #&%$!
Author:  DaleG [ Mon Sep 28, 2009 2:08 pm ]
Post subject:  Re: Prop Question
Boat weight is also a bigger variable than often thought. I am sure when Four Winns established that number that the boat was pretty light. Over time boats tend to get anchors.chain -- extra parts -- extra lifejackerts and much much more. If you really want to compare to the Four Winns data --- lighten the boat as much as possible -- all the gear we add adds weight --
Author:  ht32bsx115 [ Tue Sep 29, 2009 2:09 am ]
Post subject:  Re: Prop Question
Aquadisiac wrote:
The drive says it is a 1.51, but I think the timing is too far advanced whether that would make a difference in my top end or not I'm not sure. I am going to change plugs and wires and set the timing and see if that makes much of a difference. The prop that is on it is the one four winns put on it and I am turning 4800 at wot whether you believe the crappy vdo gauges and the recomended range is between 4600 and 5000. I am planning on putting a stainless prop on in the spring, but if I am not getting anywhere near the advertised speeds said by Four Winns for this boat and current current prop, I need to get that sorted out before anything. As for it being waterlogged, I will need to get a moisture meter and see, but man I hope not, but the way things have gone with the dealer I would not be surprised if I am stuck with a piece of #&%$!


You will probably get better performance with a SS prop. Your best bet would be to go over to the local truck stop and run it over the scale. (weight your tow vehicle first) that way you can get a ball park figure for your boat.

You should get another tach and try it so you can rule that out.

I'll also assume you're trimming the drive for best speed at WOT?
Author:  Aquadisiac [ Tue Sep 29, 2009 5:39 pm ]
Post subject:  Re: Prop Question
ht32bsx115 wrote:
Aquadisiac wrote:
The drive says it is a 1.51, but I think the timing is too far advanced whether that would make a difference in my top end or not I'm not sure. I am going to change plugs and wires and set the timing and see if that makes much of a difference. The prop that is on it is the one four winns put on it and I am turning 4800 at wot whether you believe the crappy vdo gauges and the recomended range is between 4600 and 5000. I am planning on putting a stainless prop on in the spring, but if I am not getting anywhere near the advertised speeds said by Four Winns for this boat and current current prop, I need to get that sorted out before anything. As for it being waterlogged, I will need to get a moisture meter and see, but man I hope not, but the way things have gone with the dealer I would not be surprised if I am stuck with a piece of #&%$!


You will probably get better performance with a SS prop. Your best bet would be to go over to the local truck stop and run it over the scale. (weight your tow vehicle first) that way you can get a ball park figure for your boat.

You should get another tach and try it so you can rule that out.

I'll also assume you're trimming the drive for best speed at WOT?




I intend on getting a stainless prop, just not sure if I can stay with same size that is on there right now. This boat does 43mph with the stock aluminum prop, which I don't think is too bad for a boat of this size and loaded up with fuel, people and all the gear it probably weighs in at around 5000lb+, I am more into the cruising anyway, but I would like to know that it is running at its potential with this prop. I have even thought of a four blade stainless from hill marine, they say pitch for pitch, but maybe a 3 blade would be a better all around prop.
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