40hp Force Prop Question for 21' Sun Tracker Pontoon

[GoFastr]

Just recently picked up a 1999 Sun Tracker 21' Party Barge pretty cheap, but needs some TLC otherwise pretty decent shape and motor runs good though troubleshooting a starting issue.

On this black colored outboard which sez "Tracker" on the cowling and by Mercury. There's a sticker on the power head that sez it's a 40hp Force too. At the bottom of the shaft just above the cavitation plates on the trailiing edge, there's a sticker/lable that indicates 13 x 26 and 2.00:1. I'm thinking the 2.00:1 indicates the gear ratio of the motor? Does the other indicate the prop size as in 13" diameter x 26" pitch?

I would like to maximize the prop bite for this small motor on the boat. The prop that came with it is in pretty gnarley shape and I want to replace it, but can't find any part numbers or size info on it.

Also, what is the proper wide open throttle RPM range for this motor?

If the numbers above aren't what i think they are, then any info on this motor and/or boat would be greatly appreciated.

 

[steelespike]

Re: 40hp Force Prop Question for 21' Sun Tracker Pontoon

13/26 is another way to write the ratio.Devide 13 into the 26 for 2.00:1
Your prop size should be under the prop nut.The good thing is I believe the Force uses a Merc leg that year.
I'm guessing about a 9" pitch.

 

[Frank Acampora]

Re: 40hp Force Prop Question for 21' Sun Tracker Pontoon

You know: I just worked on a 24 foot 'toon for a fellow. It also had a Force 40 and was severely underpowered. I put on a 125 for him and he was much happier. (The toon was rated for 125)

If you intend to simply putter around with not too many people, the 40 will be fine. Otherwise, consider stepping up to at least a 70.

Pontoon props are a much larger diameter and much lower pitch than regular outboard props. For example: Your 40 on a 14 foot planing hull would use the Mercury 10 inch diameter X 15 inch pitch prop. The pontoon prop would be more like 11 1/2 - 12 inch diameter by 9 inch pitch.

WOT RPM range is probably similar to other Force engines---4500-5500. You certainly won't go wrong if you prop it for 5000.

 

[GoFastr]

Re: 40hp Force Prop Question for 21' Sun Tracker Pontoon

Well I fixed a starting problem by replacing the starter solenoid. Now it starts so fast it's surprising without even doing the push in to choke thing. Cleaned up the original prop which didn't turn out so bad except one of three blades is chipped at the end/tip, and took it for a little check ride. Motor purred except for a little occasional vibration from the prop. WOT I got 47/4800 RPM. My best guess is the prop is a 10.5" diameter by (using a ruler) 9 pitch. I'm now thinkin' maybe the pitch is more because with a relatively small diameter this thing is biting a chunk at maybe 10-12 pitch? Cause at 9p with 10.5" diameter one would think this thing should bangin' top rpm range? Again someone's info with this motor/boat setup experience and experimentation would be awesome.

 

[steelespike]

Re: 40hp Force Prop Question for 21' Sun Tracker Pontoon

Measure from the center of the bore to the tip of one blade and double it for the diameter. Diameter is usually about 12 or 12 1/2".
Rpm rating is 4750 to 5250. It would be good to know your load and gps speed. Some cells have a gps app.A lightly loaded run would be interesting.
Weight placement and elimination is critical for best speed. A 4 blade pontoon dedicated prop should help.
Merc may have one and your leg is a Merc.
An increase in horsepower will add a little speed but the bigger gain would be you could run the motor at a reduced rpm and still go as fast as the 40.The bigger motor would be loafing when the 40 would be blowing its guts out.

 

[GoFastr]

Re: 40hp Force Prop Question for 21' Sun Tracker Pontoon

I went out yesterday for a quick out and back run with a little less than half a tank (26 gallon max) and one other 185 pounder. Thru the no wake area i got an intermittent vibration from the prop which has a little piece missing off the end of one of the three blades, and I'm sure the vibration stems somewhat from that. Otherwise i sanded it up pretty nice and put a nice coat of paint on it until I found the actual for sure specs of the off showroom floor model with this boat motor combo. Anyway after throttling up I maxed at 4800 rpm and 9mph on my iphone gps. There's a little gunk on the bottom that will need to be cleaned off and I'm sure that will help a tad. Anyway, I still haven't tracked down the builder/mfr specs for the prop for this 1999 Force 40hp pushing a 21' Sun Tracker.

 

[steelespike]

Re: 40hp Force Prop Question for 21' Sun Tracker Pontoon

Pontoon speeds are all over the place.9mph is really slow.It figures out at about 56% slip normal pontoon slip is around 25%
runabouts about 10-%.is considered reasonable. Is your gps set for mph? Your prop size should be under the prop nut.
Very likely a Merc number beginning with 48.
If I understand your statement ,you feel the motor/prop has a good grip on the water.That could indicate the tach is not accurate.
For instance 4800 rpm, 9" at 25%slip is about 15 mph.

 

[GoFastr]

Re: 40hp Force Prop Question for 21' Sun Tracker Pontoon

I called spoke with the Sun Tracker folks in Missouri and the local dealer. Both were conflicting but agreed the rpm range was 4750-5250 for this setup. Finally went to a reputable local prop shop (after calling ahead) that deals with boat props of all shapes and sizes. I took the current prop in with me and it turned out to be a 10.7/8 x 11. In discussion about use, avg number of passengers etc, they gave me a 12.5" x 8 prop that appeared a bit larger mostly in the size of the blades themselves (big dog ears). I was told when out by myself it might over rev a bit, but as i added passengers/weight or pulled a tube it would come down and be the most beneficial overall. So I'll find out how it does over the weekend. If there's a disappointment, they said bring it back and they would give me an adjustment prop according to the results.

 

[steelespike]

Re: 40hp Force Prop Question for 21' Sun Tracker Pontoon

That sounds like an excellent shop, you certainly have a good starting point and the option to adjust.
It sure sounds like a pontoon dedicated prop.

 

[GoFastr]

Re: 40hp Force Prop Question for 21' Sun Tracker Pontoon

Well after some delays i finally tried the new prop out. The results were disappointing with RPMS maxing out at 4600 and speed on the GPS was around 13-14mph. The load was two males and one female counting myself or roughly a little over 500 lbs and 3/4 tank of a 26 gallon tank. RPM range for this motor is 4750 - 5250. So tomorrow i'm gonna take the prop back to the shop we'll see which prop to try next. The original prop was 10.5 x 11p, and of course the one I just tried was 12.5 x 8p.

 

[steelespike]

Re: 40hp Force Prop Question for 21' Sun Tracker Pontoon

I wonder if you may have something more than prop selection going on.
Imo your 40 should do better with a 8" pitch. at least get some rpm.
I think you should be able to get 15 to 17 mph.
Be sure the motor is in excellent tune.Throttle opening all the way.
Bottom clean. Be sure there is no water in the tubes.
The 40 Force isn't known for its power but your struggle seems excessive.

 

[GoFastr]

Re: 40hp Force Prop Question for 21' Sun Tracker Pontoon

Called the prop shop today and they seem to think the results were not right, especially the rpm's. So they said before we go chasing the prop angle anymore they want me to check/ensure the tachometer is reading right and to also ensure the motor is running well and tuned up nicely, which it seems to be. I pulled the plugs and found the them in great shape except they were Champion L78V's vice the L76V's called for. Don't think it will make a difference, but I replaced those with the proper plugs. I also changed a cruddy looking fuel filter and blasted out the carburetor with carb/throttle body cleaner. I also inspected to be sure the throttle was full open and it was. I also went ahead and ordered a main jet (.96) for 50hp to see if any notciable change occurs. What the heck, $7 + shipping.

Now gotta figure out how to check the rpm gauge. Unfortunately won't be able to trial run her until Sunday due to commitments tomorrow/Saturday.

 

[steelespike]

Re: 40hp Force Prop Question for 21' Sun Tracker Pontoon

A quick prop calculator check Using 14 mph and 8" prop 2.00 ratio I got about 19% slip Not rediculess but decidedly low for a pontoon.
Perhaps the tach is a little low. 14 Is on the low end Of what I feel you should be able to do but again not rediculess.
Further prop calculator check:: at 5250 2.00 ratio,8" prop 10% slip on a planing hull indicates about 17.9 mph.I don't know if this makes your 14 mph look really good or un realistic?
It would be nice to see your results with a really light load.
Are the tubes clean?

 

[GoFastr]

Re: 40hp Force Prop Question for 21' Sun Tracker Pontoon

Tubes when i got it were barbacled up. Sincve no trailer I first got in the water and scraped them all off and did touch up once i configured my standard boatlift to hold it. They're pretty clean except for needing a good sanding but shouldn't have any affect at such a low speed. Both nose cones had leaks and had water drain once i raised it out of the water. I then temporarily patched them up with combination of epoxy, layers of fast cure 5200, and a couple coats of spray polyurathane. Again as a temp fix.

I checked the tach settings and connections on the back and all was set/looked good (see attached pic). So other than verifying the tach correctness, all things appear normal.

 

[steelespike]

Re: 40hp Force Prop Question for 21' Sun Tracker Pontoon

Sometimes if you note the position of the tach switch and operate it a few times to clean the contacts it helps.
Also make sure connections at the motor are clean and tight.