I am going to ask here, I have a merc 90 on my tracker boat, it runs out at 6100 RPM, it was mentioned that my motor is over reving at the top end, i am running a 17 degree prop, which is strait from the dealer, and I am starting to figure that I have gotten the wrong prop. the motor is an 05, new, just curious as to what other people thing, should I go up to a 19 or 21 or just let it run at 6100 and only get about 43 MPH?
thanks for the input and opinions.
shane 
Is alumanum? if so I would think a 17 stainless would be a nice choice, probably drop a few rpm’s and mayve some speed, from the idea in my head…
Coming from a guy who’s never changed props on anything 
How many rpms is the motor suppose to run according to owners manual?
good question, seeing how I canot seem to find that page in there anywhere, maybe I need to look when I am not half asleep. I just thought I would ask out here and see what other poeple thought, I am thinking that 43 with a 90 isn’t bad, but my neighbor has a 4 stroke 50 on a 22′ pontoon and he is getting 40 with that. just don’t seem right to me.
shane
In my 2000 Mercury manual. 90 hp full throttle is 5000 – 5500 rpm’s
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but my neighbor has a 4 stroke 50 on a 22′ pontoon and he is getting 40 with that. just don’t seem right to me.
Not possile to have a 50HP on a 22 FT pontoon hitting 40 MPH. I run a 182 TS with a 135 Opti and top end fully loaded 4 people live wells full is 44 MPH GPS
Just geussing but I think you should be running 5400 to 5800 RPM. Is this Merc a 4 stroke? 4 Strokes do run higher RPM`s
first off your tach probally hasnt been calibrated so 6100 could be 5900 as well as 6300. I would think 6100 is purty close. I think the mercs tend to run a little higher. I beleive my yamaha is suposed to run at 5800. For every size you drop you will change about 200 rpms. for example if you are running a 19 and switch to a 21 you should loose about 200 rpm’s and vise versus if you go the other way. You will gain a little speed say 2-4 mph. and your hole shot will be another sec. slower. How long does it take for your boat to get up on plain with 2 people full gear and a full live well? Should be no longer than the count of 5.????? Also there is alot to do with where your motor is mounted on your transom too.
So to sum up my opinion I would say if you have a good hole shot (3 or less) I would go up one pitch if you choose to stay aluminum. if you choose to go with stailess stay with the same pitch to start, any shop will alow you to trade until you find the perfect one not sure if they will do that with aluminum.
Probably speedo speeds, I guess…
Another thing is it’ll depend on how the boat is loaded too, 1 person no gear as light a possible versus the whole family and a cooler of snack for the kids changes things for the boat…
Seen a bunch of props in the bargin cave at Cabela’s in Owantanna… 
Also have to watch dia. off the prop as well. Lots of variables.
43 mph with a 90 horse and 17 pitch at 6100?
If thats what you claim to be true then yes, yes, yes go with a 19 pitch cupped prop.
The biggest diameter prop must be utilized for best preformance. The correct 19 pitch cupped prop should lower your rpm’s to 5700 & raise your top end to darn near 50 if what you say is true. Some select Merc dealers will let you try out props till you find one that works best for your boat. Ask your prop provider.
This is what pitch means; well at least one old river rat told me.
17 pitch=one revolution of the prop, the boat moves 17inches.
hope this helps,
Brian
well I am looking at the gauges on the dash, 43 mph at 6100rpm, the gps shows me at 39 to 40. my 90 is a 2 stroke, oil injected. I can be up on plain right now in about 3 seconds, so I do have some room to go down.
shane
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but my neighbor has a 4 stroke 50 on a 22′ pontoon and he is getting 40 with that. just don’t seem right to me.
Not possible, I have a 20′ monarch with a 90 4-stroke, top speed is 23mph (gps) unloaded and just myself in it.(which is fast enough) I almost flipped it 
40 mph in a poontoon is dangerous and I would think impossible, without alot of modifactions which would make the poontoon illegal.
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40 mph in a poontoon is dangerous and I would think impossible, without alot of modifactions which would make the poontoon illegal.
There’s some big Premiers that are rated for 300HP outboards 
that is correct,
40 mph in a poontoon is still hard for me to belive and if there is one that goes that fast, do not put it into a turn at that speed or you will be swiming.
100 hp is max on my boat and we have a 90 (because merc doesn’t make a 100 4-stroke) and that is fast enough in my book.
Not to derail this any more, but I’m going to
Don’t kid yourself there are some wicked fast pontoons out there, crusing on our lake last summer I run into one that do an honest 50mph, he couldn’t quite keep up with me, but I wasn’t losing him by much, that pontoon was an i/o Looked to be somewhat of a trihull, and the first 1/4 or so of the pontoons were out of the water at full speed.
Back onto topic I was saying the pontoon was speedo speed.
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