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Math formula or algorithm to fine Tune my prop size

Rssuttle

Rssuttle

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Someone on this site has a formula on how to fine tune a prop.
Looking for prop diameter and pitch that can add to my current prop

21’ Bennington SSX pontoon with no added packages or under shield or lifting stakes.
2020 Yamaha f115 four stroke
Gear ratio 2.15:1
Rpm range 5300-6300 want to be 5900-6000 wot Yamaha says 5500 is when the 115 horse power.

Pontoon Weight 2,300lb + motor 377 lb + 2 people 500lb which includes other things I’ve added. Rod reels cooler etc. Total 3,100lb and 16 gallons gas.

Yamaha k aluminum prop came on it 13.5 x 15 running 5800 rpm’s 26 mph. Prop Has no cupping or rake just simple straight prop. If I add 3 people still at 5800 rpm 22 mph

Bought 2 props from turning point and these have some cup added to make it more aggressive for top speed and hole shot.
. 13.75 x 15 5100 rpm’s 27mph
Add 3 more people 5000 rpm’s
23 mph

14 x 13 6300 rpm’s 24 mph add 3 people 21 mph Eats Gas.

I’d like to stay with aluminum because I don’t have any thing to compare one too

My thinking is to take the 13.75 x 15 and change the diameter to 13.25 or 13. Should Bring rpms up 300-500 or roughly 5600 rpm. I could lower the pitch to 14 but probably loose mph but not sure

The 14 x 13 if I change it to 14x14 and be 5900-6000 rpm’s.

I know the boat has two toons I know but I feel like I could get more.

If I have to I’ll go to a ss but I’d be starting over.

I’ve looked through all the Yamaha Bullintens but can’t get one close enough to compare.

I know this is long. Maybe I’m chasing a rainbow. And No I can’t go buy a 150. Lol

Really hoping someone can use there math skills and help out.
 
LOL and LOL again! None of the props you have are appropriate for YOUR pontoon. Also, you already have data far more useful than any math formula can deliver.

The only choice that does not have excessive slip is the Turning Point 15p AND, because it actually "grips" the water well, it is too much pitch for your application. Worth noting that you did not mention motor height. For some props, that significantly alters results.

Rather than tinkering with existing poor choices, consider a likely less expensive path and buy ONLY unmolested props that are specifically pontoon rated. Expect a 15p Nemesis would be too much of a good thing for your use, so try the pontoon rated 13p. If you prefer to stick with Yamaha props, try a 14p Talon. The current versions have the SDS hub that most people really like. (Even the 14p Talon may not be quite prefect, but it should be, overall, better than what you have so far)

No math skills are needed beyond plugging numbers into a slip calculator, like the one below. In general for pontoons like ours, slip above 20% at WOT means something could be better.

Prop Slip Calculator | Mercury Racing

Quickly determine slip for Mercury Racing propellers using our prop slip calculator.
www.mercuryracing.com www.mercuryracing.com

Yamaha rates motors like ours @~5500 RPM. That said, people with the means to test that have claimed that peak HP is closer to 125 for your motor at a bit more RPM. However, if you use the ponies, expect to have to feed them.
 
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Given the 115 HP, two tubes and no lifting strakes I don't think you'll be getting more than high 20's. As PartyBarge noted you already have the data you need to indicate what improvements can be made.

You need more diameter to overcome the plowing of your tubes that are sitting deeper in the water without strakes. 14+ is what I would recommend or else you could be losing efficiency and grip. Yes more diameter hurts top speed but these are the tradeoffs in any prop selection. Go too small on the diameter and you're just wasting gas especially under load (more people, towing tube).

Better prop design is also key - trialing a Talon SS or Turbo would be the first step for me as these are made to handle heavier boats while considering top speed as a goal.
 
On the sheet Bennington provides to the dealers for rigging on a 115 HP 21 ft , 13 1/4 X 17
 
PartyBarge said:
LOL and LOL again! None of the props you have are appropriate for YOUR pontoon. Also, you already have data far more useful than any math formula can deliver.

The only choice that does not have excessive slip is the Turning Point 15p AND, because it actually "grips" the water well, it is too much pitch for your application. Worth noting that you did not mention motor height. For some props, that significantly alters results.

Rather than tinkering with existing poor choices, consider a likely less expensive path and buy ONLY unmolested props that are specifically pontoon rated. Expect a 15p Nemesis would be too much of a good thing for your use, so try the pontoon rated 13p. If you prefer to stick with Yamaha props, try a 14p Talon. The current versions have the SDS hub that most people really like. (Even the 14p Talon may not be quite prefect, but it should be, overall, better than what you have so far)

No math skills are needed beyond plugging numbers into a slip calculator, like the one below. In general for pontoons like ours, slip above 20% at WOT means something could be better.

Prop Slip Calculator | Mercury Racing

Quickly determine slip for Mercury Racing propellers using our prop slip calculator.
www.mercuryracing.com www.mercuryracing.com

Yamaha rates motors like ours @~5500 RPM. That said, people with the means to test that have claimed that peak HP is closer to 125 for your motor at a bit more RPM. However, if you use the ponies, expect to have to feed them.
Click to expand...
The slip calculator. How does it work without putting the weight of pontoon or any boat.
PartyBarge said:
LOL and LOL again! None of the props you have are appropriate for YOUR pontoon. Also, you already have data far more useful than any math formula can deliver.

The only choice that does not have excessive slip is the Turning Point 15p AND, because it actually "grips" the water well, it is too much pitch for your application. Worth noting that you did not mention motor height. For some props, that significantly alters results.

Rather than tinkering with existing poor choices, consider a likely less expensive path and buy ONLY unmolested props that are specifically pontoon rated. Expect a 15p Nemesis would be too much of a good thing for your use, so try the pontoon rated 13p. If you prefer to stick with Yamaha props, try a 14p Talon. The current versions have the SDS hub that most people really like. (Even the 14p Talon may not be quite prefect, but it should be, overall, better than what you have so far)

No math skills are needed beyond plugging numbers into a slip calculator, like the one below. In general for pontoons like ours, slip above 20% at WOT means something could be better.

Prop Slip Calculator | Mercury Racing

Quickly determine slip for Mercury Racing propellers using our prop slip calculator.
www.mercuryracing.com www.mercuryracing.com

Yamaha rates motors like ours @~5500 RPM. That said, people with the means to test that have claimed that peak HP is closer to 125 for your motor at a bit more RPM. However, if you use the ponies, expect to have to feed them.
Click to expand...
first off it not lol.
How does a slip calculator work with out knowing the weight or if it’s a pontoon or bass boat etc.
 
If you look at the link, the calculation is independent of even the type of boat. The only parameters needed are those shown in the fill-in boxes and are the only ones needed to learn how well the prop is hooking.

Jack M said:
On the sheet Bennington provides to the dealers for rigging on a 115 HP 21 ft , 13 1/4 X 17
Click to expand...
Wow, that is clearly a misprint or for a motor with a non-Yamaha gear ratio! Like maybe a Suzi running 2.5 to 1?

Thye show common boat/motor configurations, how they perform and with which prop. I found one "similar" to your setup: https://yamahaoutboards.com/en-us/h.../f115/f115/pb_bnt_22ssx_f115lb_2014-10-28_pnt

The above is NOT a similar pontoon. Those with elliptical toons are significantly faster! Running the much more expensive Pontoon Performance SS is a very good thing for pontoon speed too. Worth noting that the calculated slip for that combo is (supposedly) -2%! Really? That is one mighty fine prop!
 
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Rssuttle said:
Someone on this site has a formula on how to fine tune a prop.
Looking for prop diameter and pitch that can add to my current prop

21’ Bennington SSX pontoon with no added packages or under shield or lifting stakes.
2020 Yamaha f115 four stroke
Gear ratio 2.15:1
Rpm range 5300-6300 want to be 5900-6000 wot Yamaha says 5500 is when the 115 horse power.

Pontoon Weight 2,300lb + motor 377 lb + 2 people 500lb which includes other things I’ve added. Rod reels cooler etc. Total 3,100lb and 16 gallons gas.

Yamaha k aluminum prop came on it 13.5 x 15 running 5800 rpm’s 26 mph. Prop Has no cupping or rake just simple straight prop. If I add 3 people still at 5800 rpm 22 mph

Bought 2 props from turning point and these have some cup added to make it more aggressive for top speed and hole shot.
. 13.75 x 15 5100 rpm’s 27mph
Add 3 more people 5000 rpm’s
23 mph

14 x 13 6300 rpm’s 24 mph add 3 people 21 mph Eats Gas.

I’d like to stay with aluminum because I don’t have any thing to compare one too

My thinking is to take the 13.75 x 15 and change the diameter to 13.25 or 13. Should Bring rpms up 300-500 or roughly 5600 rpm. I could lower the pitch to 14 but probably loose mph but not sure

The 14 x 13 if I change it to 14x14 and be 5900-6000 rpm’s.

I know the boat has two toons I know but I feel like I could get more.

If I have to I’ll go to a ss but I’d be starting over.

I’ve looked through all the Yamaha Bullintens but can’t get one close enough to compare.

I know this is long. Maybe I’m chasing a rainbow. And No I can’t go buy a 150. Lol

Really hoping someone can use there math skills and help out.
Click to expand...
Call Protech. Give them your stats. They will get you the right prop.
 
Rssuttle said:
The slip calculator. How does it work without putting the weight of pontoon or any boat.

first off it not lol.
How does a slip calculator work with out knowing the weight or if it’s a pontoon or bass boat etc.
Click to expand...

It inherently takes those factors into account because it's a ratio of theoretical distance travelled vs actual travelled.

In the case of your data, your boat with the K prop moved roughly 10.2 inches per revolution when the theoretical distance is 15. 10.2/15 = 68% efficiency, 32% slip.

The weight of the boat, hull type, other forces causing drag etc. all will serve to reduce your efficiency. If the boat was lighter or had a planing hull like a bass boat, your top speed would be higher and therefore an improved slip %.

If you want to do the hand math on slip here it is:

5800 engine RPM / gear ratio (2.15) = 2698 prop RPM

2698 RPM x 60 = 161,880 RPH

161,880 RPH x 15 inches = 2,428,200 inches travelled per hour

2,428,200 / 12 inches = 202,350 feet per hour

202,350 / 5,280 feet per mile = 38.3 theoretical miles per hour

Your top speed was 26mph so 26/38.3 = 68%
 
Poto: correct! The misunderstanding stems from a desire for some input of parameters to identify a "perfect" prop. No such math-based determination, or otherwise, exist. And, that's before trying to factor in personal preferences and wide-ranging operational factors. The point of a slip calculation goes beyond any selection protocol. Slip is a great clue on how well a given prop is doing it's job under actual operation for specific conditions.

A classic example is Rssutle's Yamaha 15p. That prop taxed the motor the same (5800 RPM) with two significantly different load conditions. The difference was a loss of 4 MPH, meaning slip jumped an additional ~15%. That's also a clue that prop ain't exactly great at low load either. No surprise even that slip calculation is over 30%! Props that are oriented to the speed/drag regime of a modestly powered pontoon won't do that. Increasing load will show up as not only loss of speed, but also increasing engine load (loss of some RPM). High HP applications frequently don't show that relationship because they can overwhelm a mismatch with more power and more than enough satisfying speed.

On another point: focusing on either prop diameter and/or pitch is a mistake. Manufactures balance many design features to produce best performance targeted to expected application. A better approach is to find a prop with the best combination of features for the desired use. The best way to do that is from actual user results of VERY similar boats/conditions (good empirical data). Tampering with prop design is a quick way to unknown territory and expensive frustration. Anyway, prop variability (especially SS props) right off the production line is enough of a problem.
 
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Potomacbassin’ said:
Given the 115 HP, two tubes and no lifting strakes I don't think you'll be getting more than high 20's. As PartyBarge noted you already have the data you need to indicate what improvements can be made.

You need more diameter to overcome the plowing of your tubes that are sitting deeper in the water without strakes. 14+ is what I would recommend or else you could be losing efficiency and grip. Yes more diameter hurts top speed but these are the tradeoffs in any prop selection. Go too small on the diameter and you're just wasting gas especially under load (more people, towing tube).

Better prop design is also key - trialing a Talon SS or Turbo would be the first step for me as these are made to handle heavier boats while considering top speed as a goal.
Click to expand...
Thank you for
Potomacbassin’ said:
Given the 115 HP, two tubes and no lifting strakes I don't think you'll be getting more than high 20's. As PartyBarge noted you already have the data you need to indicate what improvements can be made.

You need more diameter to overcome the plowing of your tubes that are sitting deeper in the water without strakes. 14+ is what I would recommend or else you could be losing efficiency and grip. Yes more diameter hurts top speed but these are the tradeoffs in any prop selection. Go too small on the diameter and you're just wasting gas especially under load (more people, towing tube).

Better prop design is also key - trialing a Talon SS or Turbo would be the first step for me as these are made to handle heavier boats while considering top speed as a goal
Click to expand...
Potomacbassin’ said:
Given the 115 HP, two tubes and no lifting strakes I don't think you'll be getting more than high 20's. As PartyBarge noted you already have the data you need to indicate what improvements can be made.

You need more diameter to overcome the plowing of your tubes that are sitting deeper in the water without strakes. 14+ is what I would recommend or else you could be losing efficiency and grip. Yes more diameter hurts top speed but these are the tradeoffs in any prop selection. Go too small on the diameter and you're just wasting gas especially under load (more people, towing tube).

Better prop design is also key - trialing a Talon SS or Turbo would be the first step for me as these are made to handle heavier boats while considering top speed as a
Click to expand...
Potomacbassin’ said:
It inherently takes those factors into account because it's a ratio of theoretical distance travelled vs actual travelled.

In the case of your data, your boat with the K prop moved roughly 10.2 inches per revolution when the theoretical distance is 15. 10.2/15 = 68% efficiency, 32% slip.

The weight of the boat, hull type, other forces causing drag etc. all will serve to reduce your efficiency. If the boat was lighter or had a planing hull like a bass boat, your top speed would be higher and therefore an improved slip %.

If you want to do the hand math on slip here it is:

5800 engine RPM / gear ratio (2.15) = 2698 prop RPM

2698 RPM x 60 = 161,880 RPH

161,880 RPH x 15 inches = 2,428,200 inches travelled per hour

2,428,200 / 12 inches = 202,350 feet per hour

202,350 / 5,280 feet per mile = 38.3 theoretical miles per hour

Your top speed was 26mph so 26/38.3 = 68%
Click to expand...
Thank you for this info.
 
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