1988 40 hp Mariner revs 6,100 @ WOT

The more I read, the more I learn. By reading I've found that I should be in the 4500-5500 RPM @ WOT area - however, I push over 6,100 on the tach (and it sounds it too). Since this is a used 1988 boat/motor combo I'm assuming the prop has been changed somewhere along the line. I don't know how to identify a prop so here's what I've got: It's 3 bladed, 6" from the center of the prop shaft to the tip of 1 blade. There's no writing, or stamped info on the prop that I can see. I wouldn't be able to tell the pitch by eye unless there's a way of measuring.

The rig is a "Tracker" Pro-17, fitted with the 40 HP Mariner. I'm happy with the way she moves and planes, just concerned with the over-rev @ WOT.

What prop should I be looking for and would I be better off with a 3 blade or 4 blade?

Thanks folks.

Yes, you are running way too high and that is not good for the motor or performance. You need a higher pitched prop but without knowing what you have now it is hard to recommend one. You have a common setup so hopefully someone else that has one can chime in here.

Thanks Bill, that's what I was thinking too. I would order another prop if I knew what this one was --- I have no base-line to go by. I have a manual but there's nothing listed about the pitches or size.

If it helps, I have a 1978 40hp Mariner on a 16'-6'' Alumnacraft. I was running a bit over at 5700rpm with a 10 1/2" x 12P aluminum prop. I switched to a 10 1/8" x 13P stainless which brought it down to 5400rpm.

Thanks Mr. H.I., That gives me some sort of a baseline to look at now. I'm still at a loss to figure out what I have on it now -- sounds like you zero'd in right at the rpm I'd like to be at. Thanks for the info.

A prop shop can tell you what you have.

Thanks Bill, good thought. Problem here is that there are no Prop Shops in this area! We are in a real 'void' part of the country as far as 'services' go. The nearest store is 8 miles. I've asked 2 boat dealers (80 mile round trip) about the pitch and I got blank looks. They both were really RV Dealers who know EVERYTHING there is to know about boats until you ask a question that's not answered on a brochure. I've talked with a few of the fellows at the lake we fish and they tell me the same thing, real knowledge is hard to find locally. I've learned more by reading a LOT of these threads than from the dealers/service managers. They don't want to talk to people unless they want to buy new boats from them. The way I learned about the blended oil system was to pose as a new boat buyer and asked questions ---- and (honestly) some of the answers I got from the 'sales-person' were totally wrong. I'm not complaining, just explaining why I have to ask folks such as yourself for help. God knows I need it and I'm smart enough & old enough to know that you folks have knowledge & experience that is worth it's weight in gold. I've bought the manual, a parts book, a few marine magazines, and am reading everything I can find that would give me a bit more of an education. I've found the math calculation for measuring the prop/pitch but it's way over my head. It's frustrating, but I keep the faith... For now I'll keep the RPMs under 5500 and go on with my rewiring. Oh, if anyone needs the actual wiring diagram for a Tracker Bass Pro-17 (1988), I have it! I got it from Tracker Mfg via e-mail. I was going crazy, never thought of calling the mfg until I read a thread here and another fellow said he'd called them & they emailed his info.... I called, they did! So many great ideas shared here, so many.... Thanks for the thought Bill.

H. I. McDunnough said:

If it helps, I have a 1978 40hp Mariner on a 16'-6'' Alumnacraft. I was running a bit over at 5700rpm with a 10 1/2" x 12P aluminum prop. I switched to a 10 1/8" x 13P stainless which brought it down to 5400rpm.

Click to expand...

Sorry Floyd, I gave you some wrong info. I went from a 13P to a 14P,not12P to 13P.

I'd take a wild punt and assume the prop you have is close to stock. So, find out what the motor came with originally and see if you can locate one somewhere close by to look at.
Generally though, for a good all round prop on an average boat of that size, 14" is really close to where you'd want to be, 15" is getting a bit performance oriented and 16" definitely is.

Regards, Andrew.

Thanks Mr. H.I. for taking the time to correct that size/pitch.

Mr. Andrew, Sounds like the 15"/pitch would be the best 'general' pitch for me to start with. I'll be doing some 'on line shopping' for the next few days and give it a shot.

Thanks to all for the help on this one, I'll do a 'result' post as soon as I can get a prop and hit the lake with it.

f.