Pontoon Proping, Why the 400-600rpm rule per 2" don't work!

[rancherlee]

I've noticed a lot of people giving the same old "2 pitch change will give you 400-600rpm gain/cut in WOT speed" and for high speed bass boats or tri-toons that may be true. That might be a good rule of thumb but it just doesn't wash out for the majority of tooners in the 40-115hp range swinging 9-15 pitch props. I know some people don't like math but it really is simple math. Lets take a look at the Percentage of change between pitches as that is the Percentage of change in RPM you should see between them on identical brand/type props.

9 pitch to a 11 pitch 9/11 = 18% drop in rpm! Say your over revving slightly at 6200rpm with the 9 pitch and want to drop your rpm a bit so you purchase an 11 pitch of the same brand/style prop. Now you load you toon up, head to the lake, and find out that your only turning 5075rpm! That's right, that "little" 2 pitch change just cost you over 1100rpm and your lugging that engine. "But that guy on the forum said I'd loose 400-600rpm with a 2 pitch change" you say, well here is why that rule hangs around. Lets take a bass boat that is over revving at the same 6200rpm with a 21pitch prop. He orders up a 23 pitch, slaps its on, heads to the lake and now turns 5650! He his happy and the 400-600rpm worked great for him, only a 550rpm change.

Here is a run down of the percentage changes between common pontoon pitches and try to correct a slight, but not horrible lightly loaded 6200rpm WOT on a 5000-6000 rated power band.
9 to 11 = 18% Drop 6200 to 5075 which is BAD, keep the 9
11 to 13 = 15% 6200 to 5250 In which case I'd prefer the over revved 6200 with a light load
13 to 15 = 13% 6200 to 5375 I'd personally still take the over revved 6200, but the 5375 might return better economy and is OK
15 to 17 = 12% 6200 to 5474 Granted this is in the higher HP tri-toon range but there is STILL a 700rpm drop in the 2" change!

Lets go the other way, say your motor is chugging along with a heavy load and only turning 4800rpm with a 5000-6000rpm power band.

17 to 15 = 13% Gain 4800 to 5450 GREAT Idea, slap a 15 on her for heavier loads
15 to 13 = 15% 4800 to 5550 Great again, but might start over revving with light loads, but 4800rpm isn't good for the engine
13 to 11 = 18% 4800 to 5675 Perfect but over rev will happen with a light load, should consider changing props back and forth depending on the expected load.
11 to 9 = 22% 4800 to 5875 good only for a heavy load day!

Most people should be running at least a 2 prop system as in this pitch range its going to be hard to find one pitch that works well will all loads unless you are lucky and your engine happens to turn right at or slightly above the top end of the rev range. You carry a spare prop anyway, RIGHT? why not have it be a different pitch than your main prop! I've also noticed that some manufactures do make in between "even" numbered pitch props which is a great help if you can find one that fits your engine. Also stainless steel props tend to perform 1" higher then they are labeled as in a 13 pitch stainless will run like a 14 pitch aluminum so that can also help you in finding a good prop for your toon. My stainless is a perfect example, I hit 6300/rev limiter with 13p aluminum, turn 5500 with my 15p aluminum, and nail 6000-6100 with my 13p stainless with a light load.

[Shopguy]

This might be a waste of words but here goes.
Your right on with the math, and have a very good point. Two props are the way to go if your load varies quite a bit.
I think... and here we go.... one of the reasons the 2" rule applies is because of the other variables involved in prop designs like cup, rake, and diameter. Usually when shopping for a prop you'll see a diameter change along with the pitch as you look down the list of selections.
I'm running a 14 3/4 x 17 and a 15x15. My normal load is 8-9 passengers and the boat came with a 17p on it which ran fine with just a couple on it at around 5400. A touch over 5 grand with the larger normal load. So I bought the 15x15 and it still runs in the low 5's but...with the 8-9 people. I should buy a 14 3/4 x15 next time to get the R's up closer to 5500. That quarter inch is worth something too.
Diameter, cup, and rake are also relative to the slip factor. A prop spinning water is not the same as a tire connected to the asphalt. Discussing slip percentage is a long story but that's the jist of it.
You are correct in that if you only changed pitch, the percentages are big in difference. But I think the fact that diameter, cup, and rake changes with pitch selection is the reason the 2" pitch rule applies on the average. It's gonna be close.

[rancherlee]

I'm mainly coming from my experiences helping many people prop lower HP pontoons, including mine. IMO the 40-60 HP range is the hardest to prop, especially if they have a standard gear case instead of a Bigfoot/High Thrust/Ect. The ever popular Evinrude/Johnson V4 for example, The 9, 11 , and 13 all have the same 14" diameter prop in which the diameter doesn't drop until 15 pitch. Same goes for the smaller gear case twins, the diameter doesn't drop until 15p. What brought this up is a guy at the landing had just come in, running an older 40hp Rude, and wasn't happy that his shinny new 13 pitch prop wasn't turning the RPM's he expected. He had wrecked his one and ONLY 11 pitch prop a few weeks back (carry a SPARE DUDE) and had a slight over rev. Now his new 13 pitch was at the bottom of his range with a light load and he had lost almost 1000rpm and 2mph and his engine wasn't happy. He was pissed because he use the good old 2" rule he had been told about on the internet. Experiences are the same for my pontoon, I started with 14x11 pitch when I still had two pontoons and had a slight over rev @ 20mph and didn't loose any RPM with a heavy load because I simply had too much torque and not enough clean water for the prop to bite. Added my 3rd pontoon and the 14x11 was WAY under proped, hit the rev limiter with ease @ 23mph JUST up on plane. Switched to a 14x13 and now hit the rev limiter @ 27mph and the math told me that what I should have expected. Found a 13.75x15p and dropped to 5500rpm @ 28mph which is exactly where the math puts it again, almost Identical slip % between the 3 and I had lost 800rpm between the 13p and 15p props, both older OMC props in good shape. 15 pitch was too much for a loaded pontoon though, it would drop into the high 4000rpm range with a full capacity load. Add in my new Turbo Stainless 14x13 pitch and RPM's are just over 6000rpm @ 29-30mph which puts it right about where a 14p aluminum would have put it and she is now happy turning 5300rpm with an 8 person load (maximum). My pontoon came with 28spl originally and props were available in 1" increments for that engine, I had a 10x9 10x10 and a 9.5x11 and each 1" was over a 500rpm difference!

[Shopguy]

I see what your sayin. That does put a guy in a tight spot if his boat lands in between two props. I hate prop shopping. I did that with our last boat. It was a Caravelle 232 Interceptor. I wanted the nose down at lower RPM's for tubing and tried four props till I settled on one. Anyway, good point.

[Ryan]

Good descussion, I just got online to shop for a prop for my F115 Yammy. It came with a 13.5x15 alum. 3 blade. It will turn ~6300 with myself, wife, and twin 5 year olds; the way its loaded 75% of the time. I just throttle it occoringly knowing to not twist it to tight during a fast run across the lake. Well we tubed this weekend for the first time and had us plus 5 more aboard and it just sounded like the prop was slipping and couldnt stay hooked up. The engine is lowered to the very last holes already so no option there. Max rpm with all the friends onboard and even while tubing [didnt seem to change things at all] was around 5750-5800. My gut tells me to see If thiers a 14x17 but it may be a big mistake to make 2 changes at the same time so does a 13.5x17 make more since or even such a critter? Thanks


Ryan

[curtiscapk]

My 2¢ props stuck! Mine runs 5k with 8 aboard and 2 coolers 20 mph, 3 aboard 1 cooler 5200 (5250 is max) 22 mph, 14 /13 prop mine is sweet spot, but my old ass toon weighs around 3500 lbs... You all have fun I was happy with 20

[rancherlee]

Good descussion, I just got online to shop for a prop for my F115 Yammy. It came with a 13.5x15 alum. 3 blade. It will turn ~6300 with myself, wife, and twin 5 year olds; the way its loaded 75% of the time. I just throttle it occoringly knowing to not twist it to tight during a fast run across the lake. Well we tubed this weekend for the first time and had us plus 5 more aboard and it just sounded like the prop was slipping and couldnt stay hooked up. The engine is lowered to the very last holes already so no option there. Max rpm with all the friends onboard and even while tubing [didnt seem to change things at all] was around 5750-5800. My gut tells me to see If thiers a 14x17 but it may be a big mistake to make 2 changes at the same time so does a 13.5x17 make more since or even such a critter? Thanks


Ryan

I think a 15 pitch 4 blade Aluminum or a 15 pitch 3 blade Stainless would put you where you want to be, a 14x17 would probably drop you all the way to 5500rpm but hook a tube up or put a few more people on board and you might drop below the 5000rpm bottom end. Its nice to have a bit of over rev on these 4 strokes with a light load but it sound like you have a bit too much over rev and can't go WOT with a light load. I know, at least on my engine, that is make 70hp from 5000-5500rpm since Suzuki posted a chart when they first came out comparing the HP/TQ curves to there own 65hp two stroke. At the 6100 rpm I turn at WOT my hp is around 65hp and Its like having a spare 5hp in reserve so when I load it up and drop RPM I actually gain HP. I'm willing to bet your F115 is probably down 10hp @ the 6300rpm your turning so you have power in reserve also.

[Shopguy]

Whatever you decide don't go witha smaller diameter. Pontoons like big props. =more thrust, less slip. Mine would cavitate gurgle, and slip when doing tight turns. Two options, drop the motor or use a hydro-foil to help get the prop into cleaner, less turbulent water.
See how much room you have between the cav plate and the prop blade and put the largest prop you can on it. Then pitch accordingly. Lots of folks like the Enertia props...Hmmm..probly cause there BIG. Solas usually has a nice selection of big aluminum props to look at and compare to.

[Ryan]

Thanks guys. Ya still undecided and not purchased just yet. I think the advise on going larger in dia. is very sound. Not found much for 14" 3 blade alum. though; which will fit but would def. be the largest dia. poss. The factory 13.5x15 has ~1/2" of clearance, so spliting that other 1/2" will only raise me a 1/4" and leave just a bit for comfort. I found a site that listed "Pontoon Props" which sounded good.... and ya they were all 14" dia. but what I found odd was that they were all smaller pitch like maybe 9-11; wonder why they dont offer that in a 13,15 17,19,21 etc.... I know for certain I would'nt go with a SS prop for reason that all our lakes are stumpy and dont want that on my mind every trip out. Id go for either a 14x15 or 14x17 at this point and see how it did If I could find one. That 1/2" might make all the diff. making a 14x15 a great choice......quess Im off looking again. Thanks again guys


Ryan

[Doctordeere]

... wonder why they dont offer that in a 13,15 17,19,21 etc...

Merc's Black Max series offers 14" in damn near every pitch from 9 on up. They have a Flo-Torq hub kit that mates them to Yamaha (and others).

[curtiscapk]

Ryan try TP props they have a good prop wizard.

http://turningpointpropellers.com/

Mine has been flawless for 3 years.

14 x 13 bought from iboats.

[Ryan]

Whatever you decide don't go witha smaller diameter. Pontoons like big props. =more thrust, less slip. Mine would cavitate gurgle, and slip when doing tight turns. Two options, drop the motor or use a hydro-foil to help get the prop into cleaner, less turbulent water.
See how much room you have between the cav plate and the prop blade and put the largest prop you can on it. Then pitch accordingly. Lots of folks like the Enertia props...Hmmm..probly cause there BIG. Solas usually has a nice selection of big aluminum props to look at and compare to.

Well Ive had all I can stand on this for today, lol. Ive spent hours on the phone with no result, how frustrating. Rockwall Marine, Plano Marine, James Propeller, and a couple others all say there is NO such thing as a 14" Yamaha propeller and that thats the wrong direction to go anyhow, they recc. going down to a 13x19 or even a 12.75x21. Nope not going for a change that drastic when Im not that far off. Then when I do find a 14" prop online the biggest p is a 13? I think at this point Id try a 13 3/4x17 or a 14x15 or 14x17 nothing else makes any since to me knowing where my factory 13.5x15 is now. Also, from what I gather only the "Yamaha" props use this pressed in rubber insert made into the prop, is this what most would recc. stick with or fine to use the Merc. style with an adaptor? I like the idea of sticking with Yamaha stuff but whats yalls opinion? Thanks

[Ryan]

Ryan try TP props they have a good prop wizard.

http://turningpointpropellers.com/

Mine has been flawless for 3 years.

14 x 13 bought from iboats.

Thanks for the link. They showed a 14x13 for Sport Perf. and 14x11 for heavy load. Still seems like a long ways from where Im at now though with the 13.5x15. All everyone on the phone wants to say is that dia. has little to no effect on it.... thats its all in the pitch. If thats the case then to go from what I have now to a 14x11 sounds silly does'nt it, I mean I can hit 63-6400 now with light loads and with looking at the paint on the prop you can tell its fighting bad to stay hooked up. More pitch makes since to me not less.

[Ryan]

Whatever you decide don't go witha smaller diameter. Pontoons like big props. =more thrust, less slip. Mine would cavitate gurgle, and slip when doing tight turns. Two options, drop the motor or use a hydro-foil to help get the prop into cleaner, less turbulent water.
See how much room you have between the cav plate and the prop blade and put the largest prop you can on it. Then pitch accordingly. Lots of folks like the Enertia props...Hmmm..probly cause there BIG. Solas usually has a nice selection of big aluminum props to look at and compare to.

But it looks like all the enertia props are SS is this correct? Do you think they make a 14x 15p or 17p 3 blade alum?

[Ryan]

... wonder why they dont offer that in a 13,15 17,19,21 etc...

Merc's Black Max series offers 14" in damn near every pitch from 9 on up. They have a Flo-Torq hub kit that mates them to Yamaha (and others).

Im looking into this next. Could you explain more about the Merc. hub setup and adapting that to a Yamaha? Ive heard of some props having to slid these little staws in between the hub and it being a real pain to switch at the lake and such but have no first hand exp. with it at all. I removed mine today just to see, and its nothing more than the cotter pin and the 1 1/16" nut, remove the prop then theres a heavy brass washer/spacer behind it.

http://mercury-props.org/mercury-black-max-prop/