WOT RPM's and Prop Pitch

[Bridgetsdad63]

I was given a 20ft pontoon with a 2010 Mercury Bigfoot 60hp, that only has about 5 original hours on the engine since installation about 9 years ago. Well one high pressure fuel pump later I'm cruising the lake and the engine runs great, except I only get 5000 rpm at WOT with an 11P prop and almost 20mph speed. I found out the RPMs for this motor should be between 5500-6000. So I took my prop in to change the pitch to 9, and guess what I slowed down by 4mph but my rpm's didn't change. I checked my tach and it is supposedly set correctly to the engine, since it was installed new with the new engine. Now my next experiment is I'm getting another prop with a pitch of 13 to see what effect that has on the RPM. Yes this is a 4 stroke fuel injected engine, and what I am wondering is if the throttle cable is set correctly? It shifts into forward and reverse correctly, but the throttle is slow, meaning I have to move the lever quite a bit to get the boat moving, especially in reverse, I almost have to go to the stops. Any suggestions?

[bigi]

3 or 4 bladed props. Also what is the load in terms of people, gear and fuel?

[ROLAND]

I don't have the exact set up that you do, but close. I also have a 20 footer but instead of a 60 I have a Yamaha 75 hp four stroke. Actually had my boat out yesterday so I know what I'm saying here is factual. I'm guessing you should be getting close to 6000 rpm's. On my boat I believe they told me the limiter would alarm at around 6250 rpm's. Yesterday after she warmed up good, I had her at WOT on the way back to the boat ramp and the tach showed me that she was holding steady at 6100 rpm's... as far as the prop, I believe it's a 13 pitch ( no positive about that, but I think so ).. I do know it's just a 3 blade aluminum prop. weight wise on the boat just me and the wife, a cooler, a bunch of fishing gear and about 16-17 gallons of fuel.. Obviously with a 75 hp motor we're not setting any speed records. I believe when the boat was BRAND NEW, nearly 9 or 10 years ago I could get 24 to 25 mph if the lake was smooth as glass.. I'm sure she's lost a mph or two in the last few years...like I said, not exactly the same set up, but close enough that it might give you something to compare to.

[riplipper]

bought my boat brand new and rpms were driving me crazy..
Dealer did not help at all and was pretty worthless.
Called Mercury technical folks and again no help.
After some digging around on the Hull Truth, found that my tack might be set wrong. Never knew there was such a thing.
Called Mercury back and they pretty much said "oh yeah, that could be the problem."
Set my tack to what they said and all is well.
BTW, mine had multiple choices to choose from on the back of the tack.

[riplipper]

bought my boat brand new and rpms were driving me crazy..
Dealer did not help at all and was pretty worthless.
Called Mercury technical folks and again no help.
After some digging around on the Hull Truth, found that my tack might be set wrong. Never knew there was such a thing.
Called Mercury back and they pretty much said "oh yeah, that could be the problem."
Set my tack to what they said and all is well.
BTW, mine had multiple settings to choose from on the back of the tack.

[Bridgetsdad63]

Well I got my new 13P prop and it performed poorly. RPM at WOT went to 4200 and I could only get 14 mph out of the boat. It was loaded with 4 adults 2 kids and 1 dog. I landed on an island and reinstalled my 9P prop and it went to about 4800 RPM and 16 MPH which is about right considering the weight onboard. It looks like the original 11P was the best prop, but yet I still haven't gotten over 5000 RPM with just me on the boat. The tach is set to the 6P position on the back which is correct for my engine, and the engine idles at about 750 RPM which is about right. Still confused, about RPM's at WOT. Is there a limiter setting somewhere I don't know about or is it my throttle cable?

[bigi]

Are these 3 or 4 blade props?

[Bamaman]

Sometimes you just have to accept the performance of a boat. Buying numerous propellers chasing the optimum speed gets expensive.

Also, raising and lowering motors on the transom can be another part of the puzzle. It may or may not help with your performance. Top speed and redlines are a balance between the proper engine height and the proper propeller.

I once had a Yamaha 115 hp 2 stoke on a Starcraft 24' pontoon with U Tubes. I could only get 4900 rpm's out of it, but it ran plenty fast with a 15 pitch propeller. And it accelerated like a bass boat--fast out of the hole with immediate planing off. I knew I needed another 900 rpm's out of the motor, but I was otherwise satisfied with it.