Confusion over prop size

[Chambuzz]

I'm still a relative noob to the boating world, so forgive me for not knowing how to go about this properly.

I purchased 1999 Tracker 25' pontoon with 75hp motor back in 2010 (original post here - viewtopic.php?f=2&t=5944). We've recently spent some money fixing up the boat (pics to follow after this weekend) and we're trying to get it in tip top shape for the summer. Unfortunately, our prop has seen better days. Some wood in the shallow water of my in-laws' cove has taken its toll and we'll likely need to replace the prop, or at least have it reshaped.

I called the Tracker boat center at Bass Pro near me and got some info from their parts department. I was never sure if our outboard was a Merc or a Force, as the cover says both, but the parts guy looked up the serial number and informed me it's a Force. He said the prop size for that motor is 11.25 x 10. Does that sound right to anyone? He looked up the info for the Merc motor of the same year and hp and it's a 13.75 x 15. How could there be such a large discrepancy?

I'll get a visual confirmation tomorrow when I'm out on the boat to see what's stamp on the prop, but I'm leery of putting a 11.25 x 10 on there. Am I worrying over nothing? Does that sound right for a 25' boat?

[Bamby]

He said the prop size for that motor is 11.25 x 10. Does that sound right to anyone? He looked up the info for the Merc motor of the same year and hp and it's a 13.75 x 15. How could there be such a large discrepancy?

I'm far from a prop expert but neither one of them actually sound right to me, at least. If you're boat does take a 12" dia prop I'm guessing it a 12X13 may be about right. If it accepts a 14" prop I'm guessing it may take a 14X11 or maybe even 13 but if it appeared right before why not just replace it with a like prop that was on it. After all Farting around with props can get pretty pricy after awhile.

[Chambuzz]

He said the prop size for that motor is 11.25 x 10. Does that sound right to anyone? He looked up the info for the Merc motor of the same year and hp and it's a 13.75 x 15. How could there be such a large discrepancy?

I'm far from a prop expert but neither one of them actually sound right to me, at least. If you're boat does take a 12" dia prop I'm guessing it a 12X13 may be about right. If it accepts a 14" prop I'm guessing it may take a 14X11 or maybe even 13 but if it appeared right before why not just replace it with a like prop that was on it. After all Farting around with props can get pretty pricy after awhile.

Not sure if it necessarily performed "right" before, but I'm not sure what's normal for a boat of my size with a 75hp motor. I'm going to take some measurements this weekend and will report back. Looks like the folks at the iboats.com forums are pretty helpful with these types of questions as well, so I might impart their advice.

Thanks!

[grizzdu]

If that motor is not a bigfoot lower unit, the smaller size may be right. If it is, the larger diameter would make more sense.

[rancherlee]

If it is a relabeled "Force" then it probibly does take the smaller prop. Force outboards were NEVER converted to prop rated HP like all other brands were in the mid 1980's. A 75hp Force would be around 65hp at the prop and I don't be leave they ever made a Bigfoot Force. Force became Mercury's "Bargin Basement" brand after they purchased them.

[curtiscapk]

To small in my opinion... I have a 24' 94....

It is heavy!!

See my sig for performance.

[Chambuzz]

Well, I have some numbers to report after a HOT weekend out on the boat. Unfortunately, I couldn't find any sizing info anywhere on the prop. I probably spent 5 minutes looking at every square inch I could see without taking it off, but nothing. Also, if it does only have a 11" prop, there's definitely not room to go any bigger (I didn't get a chance to measure with a tape when I was looking at it).

WOT - 4,600 RPM
Top Speed - 19 mph (measured with GPS on calm water with light load)
Force manual says recommended WOT RPM is 4,750 - 5,250

The prop has some damage, so I'm not sure how much better it would perform if repaired or replaced with the same size. I think we're going to take it in and see if we can get a replacement and have the old repaired for a spare.

[Bamaman]

If you're around Gwinnett, checkout Georgia Prop (770 945 1961) in Buford.

He can tell you what the pitch is, and either fix your current prop or sell you a propeller that will improve your performance. Prop shops' expertise is free--with a purchase.

[Chambuzz]

If you're around Gwinnett, checkout Georgia Prop (770 945 1961) in Buford.

He can tell you what the pitch is, and either fix your current prop or sell you a propeller that will improve your performance. Prop shops' expertise is free--with a purchase.

Must've gone down with the economy. Phone number is no longer in service.

[Bamaman]

If you check around, I'm sure there's a prop shop somewhere around Atlanta. It's the biggest boating market I've ever seen--with two big lakes in the city.

I cannot help that there's one somewhere around Lake Lanier-Buford-Gainesville. Any of the boat dealers should be able to refer you to one, as they use'em too.

[southern7]

Port City Propeller Service in Ft. Smith, Arkanasas does some good work on repairs at very reasonable prices www.portcityprops.com I had them put a new hub in a stainless prop off my 50 hp Nissan on my fishing boat, and my father in law had them repair an aluminum prop with a broke blade on a Merc 50. I think we paid around $35.00 each for those repairs.

[screwball]

We just bought a new 18' Sun Tracker Party barge. It came with a 13.75 X 13 and would do 24mph. It would over speed, so I replaced the 13 pitch with a 15 pitch stainless. Big mistake, the prop 'slipped' at anything over 4000rpm. Then tried a 13.75 X 17. Get about the same speed, but engine won't turn over 4200 rpm. Soooo, I guess a 17 pitch is too much, and a 13 a little too low. I'm having the 13 pitch redone to a 15, which should be just right. I should get another 400 to 600 rpm and a couple miles per hour. When I get the prop back from the prop Dr. I'll let ya know.

[Chambuzz]

Finally got a chance to take off the prop today and measure the diameter - 14". The local marina near us didn't have any 14" props in stock that would fit our Force, but they did recommend a 11" pitch based on the boat size. Still wasn't able to find any information stamped on ours, so no clue what the pitch currently is. Crossing my fingers the Michigan Match prop I just ordered for $130 shipped turns out to be the "right" one.

Thanks to everyone for your help!

[Chambuzz]

Thought I'd post the conclusion to my prop saga...

Installed the new 14"x11" prop on Saturday and things are running great. WOT is now at 5,000 RPM and vibrations seem to be gone. Top speed is still under 20 mph, but I wasn't expecting any appreciable gains.

The little ones seemed to enjoy the boat as well.

[cwag911]

Doesn't get any better than that!