Speed help- 2004 Crest XRS III 140 HP Johnson- only 24mph

[busatom]

SO I just bought a 2004 Pontoon with a 140 HP Johnson on it. It has a 13.75X15 Prop on it, and at WOT Im at 5600RPM. My WOT range is 5600-6200. On GPS Im only doing 24.2MPH with about 8 people. I saw a link on here for a prop recomendation, and for water sports & fully loaded boat I have the recomended prop. I have 2 jetskis for watersports, and would like to "maximize" the speed of my toon. The prop recomendation says to use a 13.25X17 for maximum Speed & performance????????????????????? If I wanna go up to the 6200 WOT range, actually 6000 is where Id like to be, so Im just under the 6200 why would I go up in Pitch? Is the .50 Diameter that much difference & will give me more rpm, to get the best top speed? What speed should I get out of a 25' toon with a 140hp 4 stroke? Thanks,

Tom

[dockholiday]

Welcome
Is that an alum. prop you have now. think 15p is going to be a ball park for your motor although results vary even between 15" props. Merc makes about 10 diff props, http://www.westmarine.com/webapp/wcs/st ... mpleSearch

think there is a little info in there about props. I am getting 40.5 with the tritoon with the 150 an the dealer told me he is getting 35mph with a 150 on his two log boats (now that is not with 8 people) The dia of the toons will also have a bearing on speed, although a 2004 should have the larger toons, I think. Best to work with a dealer or prop shop to find the right one for your boat, so you can try different ones.
doc

[toondog]

Eight people is a lot of weight. What speed/RPMs do you get with maybe just 2 or 3 people?

[busatom]

It is an aluminum prop. I have 26" cans. I def wanna go ss prop. I found a 13x19 ss prop for 100 bucks might try it. That prop link said 13.25x19 for max speed and performance up to 8 people so a 13x19 is close. I would think closer to 35 mph is what I should get with a 140hp 4stroke. ?????? Thanks appreciate all the input I can get

Tom

[Kitchen363]

Is your toon underskinned?? This may help. My friend just got a 25' Premier with a 150hp 4 stroke (underskinned). They say it really helps with fast pontoons with larger motors hanging off the back. It keeps water from catching on the braces under the boat and slowing you down!

[dockholiday]

It is an aluminum prop. I have 26" cans. I def wanna go ss prop. I found a 13x19 ss prop for 100 bucks might try it. That prop link said 13.25x19 for max speed and performance up to 8 people so a 13x19 is close. I would think closer to 35 mph is what I should get with a 140hp 4stroke. ?????? Thanks appreciate all the input I can get

Tom

You could give the 19p a try for a 100 bucks, but I could only turn 5300rpm with a 17p which was the first prop I tried. Thinking you will be less than 5k rpm wot with the 19p. I gained about 600 rpm or so going from the 17p to the 15p and picked up about 2mph.
doc

[busatom]

I know, going from a 15 to 19 should give me less RPM, and I want to gain about 400 rpm, but it is .75 inch smaller diameter, so would that get me the extra rpm being a lil smaller? The prop calc said 13 3/4 X15 for water sports and 13 1/4 X 19 for speed & performance, so the 1/2 inch must make a HUGE diference in rpm, is that correct?
Thanks,

Tom

[busatom]

Anyone else have any input? Thanks

Tom

[busatom]

Now that I think about it I get the same top speed from just under 4000 rpm or 5600 rpm. The toon is 6 yrs old but only had 58 hours on the engine and I believe original prop from 2004. Can the wear out over age and get a ton more slip? Is it better to go ss or at speeds under 40 does it not matter? Ss in my baja I just got rid of with a 454 magnum made a huge difference. Thanks

Tom

[busatom]

Ok took it out this morning by myself, and got 5800 rpm and 29.1mph out of her. MY WOT is 5600-6200 so I think I am going to go from a 13.75X15P to a 13.5X13P so I can max the rpm at just under the 6200 or right near there! I think I will be able to get to just over 30mph! What are your thoughts? Thanks,

Tom

[bb king]

I think your good right where you are, the 13 pitch probably will not gain you any speed but will obviously raise rpm's, if you already have the 13 it wouldnt hurt to try it just to be sure.

[dockholiday]

Ok took it out this morning by myself, and got 5800 rpm and 29.1mph out of her. MY WOT is 5600-6200 so I think I am going to go from a 13.75X15P to a 13.5X13P so I can max the rpm at just under the 6200 or right near there! I think I will be able to get to just over 30mph! What are your thoughts? Thanks,

Tom

Sort of got lost, are we still with the alum? My goal was 5800 even though they give a range similar to what your WOT.
My guess is you will pick up one mph at the most two an you may over rev with the 13.
Here are the results of the two props I tried
Mercury mirage plus 17p max rpm was 5300@ 38mph
Merc enertia 15x15 5800 or better at 40.5
Actually unless you have a gps you would not notice the diff between the two. I was just wanting to get the rpm to the 5800
doc

[busatom]

Hey guys thanks for the replies! Doc when I'm at load I only get around 5200-5400 max rpm, that's why I wanna try the 13p to gain those 5-600 rpm. I think I will get to over 30, and with a 2 log no strakes, that's pretty good. I don't have a spare prop anyway so his is a good reason to buy one, and if pitched to low, I just need to watch tach, but I'm never alone so I should be good! Thanks

Tom

[WaltF]

So youre running a 13.25x17 now?
If your running a 13.25 pitch now, going to 13 isnt gonna get you 5-600 more rpm. Infact, it wont do much at all...Id be surprised if you see 100 more.
Been there, done that...

If it was me, id go 11x16. That would give you about 400 more rpm and youd hit 6000.
Also, youre not gonna reach WOT with 8 peeps on board. Prob 4 at the most...

Either way, to get MORE rpm ya need LESS pitch.

Also, id be surprised if you could beat 30 mph. If you had strakes, then ya, but no strakes, your top speed will be close to 30 mph.

But does it really matter? Its not a speed boat..

[busatom]

I have a 13X15 now and am going to go to a 13.5X13, which should easily give me 400 more rpm. I dont see why I cant get over 30mph when today by myself I hit 29.1mph. Thanks for all the replies

Tom

I have typed in lifting strakes 10 different ways & I must be retarted cause I cant find them anywhere???