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ContinuousWave: Whaler Performance
Prop Question From a Noob
|Author||Topic: Prop Question From a Noob|
posted 02-10-2004 12:04 PM ET (US)
Where do I look on the prop to determine its specifications, i.e. width and pitch? A related question: I'm running at the lower end of the RPM range when at WOT (4500-5500) on my 70 Evinrude with only myself and about a half-tank (12gal capacity) of fuel, is this a function of the prop being improper for the boat configuration, or something else? The engine runs pretty good, a TAD slow on the holeshot, but not too bad, and very smooth at top-end. Again, I'm new to this end of boating and appreciate any and all advice and information. The prop is a steel one (not stainless, it rusts a little on the leading edges when not in use for a few days) and I'm assuming it's the OEM one that came with the motor, but it's a '83 model, so it might be after-market. Thanks again,
posted 02-10-2004 12:11 PM ET (US)
Not sure how to edit my post, but I also would like to get some feedback on suggested prop specs for my boat, it's a 15'CC '83 model, with (as posted earlier) a 70 Evinrude 3cyl 2-stroke, also an '83 model. I'm in class in Tallahassee, and the boat is at my home in Panama City, so I don't have access to Serial Numbers right now...can post them later though if necessary. Thanks again, this forum is the absolute best resource for Whaler owners, I'm SO happy I stumbled onto it.
posted 02-10-2004 12:25 PM ET (US)
Check out www.ptprop.com. Powertech props. They will answer your email questions pretty fast. I have a powertech prop on a '99 Dauntless. Very happy! Tell them what you want to achieve. Holeshot, top speed, economy, whatever. They also have a pretty decent exchange policy if a prop doesn't work for you. Its nice to get an email from a human from a web site.
posted 02-10-2004 01:09 PM ET (US)
If engine is running good and tach is ACCURATE, a 19" prop should be what you run in SS. Your prop is SS, they all rust a bit. To see what pitch you have you may need to remove the nut and look at the top of the prop. should read 13x19 or 13 3/8 x 17 or 12.75x21. You want the 19" and should be at your redline or close. I ran a 20" on my 1990 which redlined at 6000 and I would hit about 5900. My gear ratio was different though.
posted 02-10-2004 04:08 PM ET (US)
The markings on the propeller itself may or may not be interpretable for pitch information; it depends on the manufacturer. Sometimes they have the pitch stamped on the propeller, and sometimes justs a long product code that you have to use a reference to look up the actual pitch.
The diameter is reasonably deduced by measurement from a blade tip to the center of the shaft. This is the radius and the diameter would be twice that measurement.
There is no way do deduce the pitch from the blade shape except perhaps by very careful measurements. There are machines that can do this. Or the pitch can be deduced by fitting of "pitch blocks" or gauges to the blades.
If you are lucky, the propeller will have a number stamped on it that makes sense. My YAMAHA propellers say "17K" which I interpret to mean 17-inch pitch. The "K" stands for something--I don't know what.
posted 02-10-2004 06:12 PM ET (US)
Is there any way to determine whether or not my tach is accurate? I never considered this possibility, it seems to increase pretty linearly as I throttle up, but can the mechanic put it on a machine to tell, or can you do it with a timing light or something? Thanks again,
posted 02-10-2004 08:06 PM ET (US)
If the prop's been "worked on", (very likely in the life of a 20 year old motor), the performance characteristics may have been changed,(pitch, rake etc) so you can't blindly assume the numbers on the prop are accurate.
How can you tell if your prop's been worked on? You got me.
Point is, assume nothing.
posted 02-11-2004 10:48 AM ET (US)
Usually when a prop is reconditioned it makes it smaller. What I do see is a seller has a boat, prop is bad, goes to a place and buys a used one, puts it on, you buy boat, prop is WAAAAYYY too big but was cheap because dealer/mechanic could not unload it for 2 years. Best way to tell if prop is accurate is to ask someone here what size they run on their 15' with a pre 1986 70hp OMC and what rpm they hit. Then get that prop and see if you get there. You might want to do a compression test as well. If one cyl is low, she will run fine but only at say 80% and then you have your answer......time to repower;(
posted 02-11-2004 12:22 PM ET (US)
As usual Biggie, you've hit on something I hadn't considered. When I bought the rig, I was given a mechanic's certification that all three cylinders were within specs and basically even, but I'm planning on getting the motor a check-up anyway, so I'll know the status of the compression of the old girl pretty soon. I think I'll follow your other piece of advice, assuming the compression is good, and ask around to see what prop other 15' owners are running with the same motor and just go buy one to match it. Again, thanks to everyone for the great feedback, I love this community!
PS-Cross your fingers, I don't want to have to re-power yet!
posted 02-11-2004 04:04 PM ET (US)
Rick, that 70 hp should blast you out of the hole like a rocket if the prop is the right pitch.
It sounds to me being your rpms are at the low end [ wish you said how many rpms ] that your 4" to much pitch, such as it must be a 21 or a 23 pitch & you need either a 17 or 19 pitch, either way, your 4" over on your pitch.
Your prop is marked somewhere.
If it isn't, bring the prop to a prop shop & have them set it in a mold that will tell you the amount of pitch & diameter of the prop, then come back here & we will put you on the right tract.
posted 02-11-2004 07:11 PM ET (US)
It is also possible that the engine is not performing for another reason other than the prop. The linkage and synchronization and timing advance can all affect the top end. When you get the check up, I would ask them to check the "link and sync", although I would assume that they would have anyways.
posted 02-11-2004 08:12 PM ET (US)
For what it is worth, I run a 19 inch pitch aluminum prop (Michigan Wheel) on my '89 15' GLS with '94 Evinrude 70 HP. Not sure if the engines translate with each other.
RPMs max out at 5400 and 42 MPH...I will be raising the engine up one hole this spring to see if I can crank up the RPMs a bit, as I think it is lugging a little.
Not sure what the compression was when I hit those numbers...engine is in for an overhaul right now (compression was approximately 132, 128, 72 - bad #3 cylinder). She still felt strong when I brought her in, only a stutter at idle, so I'd imagine that she'll scream once I've broken her in from the rebuild.
posted 02-14-2004 01:10 PM ET (US)
I have taken numbers stamped on my prop, threw in the word merc or prop and put it in google. It found out my prop specs...FWIW....
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