Prop difference?

C

cfelton

God
A couple of weekends ago my buddy took his 85 v20 with a 170 hp mercruiser out while I had my 77 V20 out. We ran them together all day and I noticed these differences. When starting off my V jumped way out in front of his but after a half a mile he began to over take me. We ran them wide open for a few miles and he gradually pulled away. My V ran 42 mph and his ran 44. He was taching 4400 rpm, mine tached 3500. The V's have identical engines , hulls, and both are cuddys. The only differences I know of are I have an Elite SS prop with unknown pitch( no numbers or markings) and his is a Quicksilver SS19 pitch and he is running his timing a lot higher than I do. Do you think its the prop or the timing or both making this difference. Also noticed I burnt more fuel per hour than he did. What do yall think?
 
Spare and Ferm can answer the timing problem, but from where I sit I think that you're over-propped. Look at the differences in the RPM's. I don't know what Mercury recommends for WOT for your engines, but if they are both the same engine, then they should be turning (close to) the same RPM's at WOT. I would bet that your prop is either a 21 or 23 pitch. That would account for the better hole shot, and also the increased fuel burn.
 
The prop probably has something to do with it but your talking 900 rpm diffrance and your running a 19 inch pitch.You don't say if either boat is kept in the water or not or if any bottom paint is used on either.It could also be your older boat could be getting water logged. I beleive all these things are all possable reasons why.I would happy to see my 77 cuddy hit 35 mph
 
if your boat jumps his, and you are only showing 3500 at WOT, your tach is bad(or miss adjusted). What pitch is he running? BTW, base timing should be no higher than 4 degrees BTDC if you are running 87 octane . I've run them as high as 9 degrees but that was with good 89 no ethanol fuel in a light boat with a different carb, protonix ignition, colder plugs, and a very special prop
 
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Well I pulled the prop again and the only number I found is stamped way inside the web and it is 22.My buddys prop is a new Quicksilver 19 pitch prop. Never heard of a 22 pitch prop but who knows its an Elite 1. Im running 93 octane non ethanol fuel, with the timing at 4 degrees and a Pertronix ignition. The tach is the factory installed tach so it could be off some. My neighbor gave me a quicksilver 23 degree prop but I think that would make it worse. I guess Ill try to get my hands on a 19 pitch prop and try that. Both boats stay on trailers but Im wondering what the weight difference is between a 77 and a 85 V20. The stern of my boat sits about 3 inches lower than the 85 at rest, and at WOT both of us were trimmed up to almost porposing Thanks guys!
 
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I agree with spare, sounds like your tach is off. If your jumping on plane, but not keeping up on the top end while burning more fuel, then you probably have a prop without alot of rake, and a good bit of cup. Prop design has alot to do with how a boat runs out and planes. I'm a fan of the large diameter 3 blade props myself, but they don't normally reccomend them for smaller engines due to the amount of bite they get down low in the RPM range. You need to take your prop to a prop shop, and let them tell you what pitch it is. Most any prop shop will have a pitch gauge to check it. If he has the old style generic quiksilver, that is a pretty crude and basic stainless prop, with ALOT of room for improvement. Or if it is one of the newer quiksilver props, it could be just about anything since MERCURY changed and used QUIKSILVER as there generic prop series. All I could find for the ELITE SS is it is a name they include with most of MERCURYS props now, so without a cup series number, who knows what it is.

A good example of prop series differences would be like when I changed from a HIGH FIVE to a TROPHY PLUS on my flats boat I had. Both props were 21 pitch props, both were basically teh same diamter, and both props tached out close to each other on the top end. The high five topped out around 5300RPM's at 51 MPH, and the TROPHY plus topped out at 5600 RPM's and 62 MPH before the wife made me let out of it(it was still climbing). Or the SEA RAY I did a few years back. Ran it with a 17 pitch old style quiksilver prop and it redlined at 5000 RPM's and only hit about 25 MPH. Swapped over to a large diameter MIRAGE style prop of 16 pitch, and it topped out at 4700 and ran upper 30's. Less pitch turned less RPM's, and was faster.
 
Been looking around and now Im confused on what prop to try. Pretty sure I need a 19 pitch but what diameter? They range from 13, 14, 14.1/2,14 5/8,15 and so on. Ive got the old alum prop that probably came on the boat but its not in too good a shape. Its been painted a dozen times and I cant see anything on it. What do you all suggest I try.
 
What do you want out of the boat? I think the large diameter props are good for all aorund useage, and really good for cruisng efficiency. Props with alot of rake are good for lifting the bow and top speed, but not always good for planing out and cruising as they tend to popoise at cruise on some hulls. 4 blade props have great holeshots, good cruisng efficiency, but tend to lack on the top end because they tend to lift the stern and not air the bow out on the top end.

I like the MIRAGE style prop for offshore boats as they have so much bite, hold so steady in the water, while maintaining good cruisng efficiency. You may need to drop down to a 18 pitch with a large diameter prop as the larger diameter increases bite and reduces prop slip, which makes the prop run like a prop of a larger pitch.
 
spareparts said:
Swap props with your buddy. Run them both again and see what happens. Is that elite a four blade prop?
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X2 That was going to be my suggestion, but Spare beat me to it. But I'm still sticking to my original comment about too much pitch. I agree with everything that everyone else has said about cupping, rake, timing, weight, drag, etc, but I also believe in the KISS principal. (Keep It Simple Stupid) And right now, the simplest thing is to switch props with a known 19P prop and see how your boat (and your friends) performs with the prop change. It's a simple check and it costs nothing and that's always a good thing.
 
How about the diameter, does 15 inch sound right? I'll probably go with a 19 pitch for speed and economy. I don't pull skiers or a tube very much so I guess Im trying to get more milage and top end speed. My engine kinda sounds like its straining running WOT. If my buddy will swap props for a day maybe Ill try that and see how that does. I know his prop is a 19 pitch, not sure of the diameter.
 
cfelton said:
How about the diameter, does 15 inch sound right? I'll probably go with a 19 pitch for speed and economy. I don't pull skiers or a tube very much so I guess Im trying to get more milage and top end speed. My engine kinda sounds like its straining running WOT. If my buddy will swap props for a day maybe Ill try that and see how that does. I know his prop is a 19 pitch, not sure of the diameter.
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Only downside to the 15" diameter is you will most likely have to trim your trim anode or go with a smooth one to clear it. And be prepared to step down in pitch as the larger diamter bites better with less slip.
 
C... I have a Mirage 15.5x17 that gave me 38mph at 4600 WOT, a little too much RPM for the 2-barrel, I now have a 15.25x19 Mirage that I hope to try soon. And yes you will have to trim a regular trim tab. I did try a 19p aluminum that gave me 4300 WOT and engine sounded happy there no lugging or overturning but it had been ground too thin and cracked. BTW timing is 5/6 degrees, pertronix and 89 non-ethanol.
If you would like to try the 17p Mirage you are more than welcome to, also have a 21p ss not sure of make it gave upper 3's in rpms.
 
I love the mirage prop for the v20, if you get a chance try an enertia. I gained 3.5mph switching from a mirage plus 15p to enertia 17p turning close to the same rpm's.
 
If I can find one I might give that a try! Asked my buddy and I don't think he was too keen on swapping props for a day. He did say it was a 19 pitch and he got it from The Prop Shop up in Virginia, next to Portsmouth Trailer Service. Said he paid 250.00 for it.
 
This is a old vertical reed 1987 Merc 175hp powerhead pushing my 23 seacraft with a 17p enertia in a little chop.

https://www.youtube.com/watch?v=jg7cdv1w1vE&feature=youtu.be

With the 15P mirage plus WOT bounced b/w 39-40 with a full tank.

with the 17p enertia I had no problem hitting 42-43
44_G.jpg
 
Looked up the Enertia prop on ebay, found a few but they ain't cheap are they. I'll try to find a used one. Do you remember the diameter? That 175 had that boat in the wind! looks like it performed very well!
 
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