Propping a 22' Pontoon: 3 or 4 Blade?

[Dennybot]

Hello all! Believe me when I say I browsed this forum for hours before posting this. There's just a lot of variation to the opinions, so I thought I'd post this with my specific situation to see if I can narrow down my options.

Issue: We just purchased a used Four Stroke outboard to replace our Two-Stroke on our pontoon. We're looking to for the BEST GUESS for a first prop to try.

Details on the boat/motor:

Boat: 2007 Sun Tracker Regency Party Barge 22
Motor: 2005 Mercury Saltwater FourStroke 90 (EFI, WOT: 5000-6000, Gear Ratio: 2.33:1)

We'd like to prop the boat for average cruising with around 6-8 people on board. We're willing to give up (a little) top speed for good all around performance and fuel economy.

After lots of research, it would seem a good starting point for a 3-blade aluminum prop would be a 13.5 x 15.

Any differing opinions on that?

Also... We are very intrigued by a 4-blade prop, for its low-speed maneuvering and hole shot qualities.

So, bottom line is, we are looking for recs on starting points for both 3 and 4 blade props for this boat/motor combo.

Thanks in advance!

 

[Dennybot]

Re: Propping a 22' Pontoon: 3 or 4 Blade?

By the way, this is the 4-blade prop I was curious about:

Mercury Spitfire
Boating Gear Center - Mercury Spitfire 4-Blade Aluminum 13.4 x 15 Propeller

 

[jestor68]

Re: Propping a 22' Pontoon: 3 or 4 Blade?

The Mercury prop selector comes up with a 15 pitch in either 3 or 4 blade.

I would consider a Solas Rubex prop in a 15 pitch to save about $50 over the Merc prop. It will perform as well(maybe better).

For what it's worth, I had a 24 ft Tracker toon with a 2 stroke Merc 90 and ran a 15 pitch prop with good results.

 

[Dennybot]

Re: Propping a 22' Pontoon: 3 or 4 Blade?

Thanks, jestor68.

For diameter, does 13.5 sound right?

Using various prop selector apps and reading up a bit, I got 13.5 as the right place to start diameter-wise.

 

[Dennybot]

Re: Propping a 22' Pontoon: 3 or 4 Blade?

Something else to add, we have a brand new Solas 15 x 15 prop that we had on hand as a backup prop. I don't suppose that would be usable in any situation on this boat/motor combo?

 

[steelespike]

Re: Propping a 22' Pontoon: 3 or 4 Blade?

Put her on and see what it does, might make a reference point.

 

[Bamaman1]

Re: Propping a 22' Pontoon: 3 or 4 Blade?

You don't commonly see 4 blade props on pontoons. Your 15 pitch prop sounds about right on your boat.

I don't know what size 2 stroke motor you had on your boat. If it was a 90, you may experience less acceleration out of the new 4 stroke. The four strokes are quiet, smooth and more efficient than 2 strokes and better suited for how most people use pontoons. Top speeds are usually close, however. You'll be very satisfied with the 4 stroke. (I've had both.)

 

[WaterDR]

Re: Propping a 22' Pontoon: 3 or 4 Blade?

Thanks, jestor68.

For diameter, does 13.5 sound right?

Using various prop selector apps and reading up a bit, I got 13.5 as the right place to start diameter-wise.

The diameter is sort of meaningless. 13.5 is fine.

 

[jestor68]

Re: Propping a 22' Pontoon: 3 or 4 Blade?

Something else to add, we have a brand new Solas 15 x 15 prop that we had on hand as a backup prop. I don't suppose that would be usable in any situation on this boat/motor combo?

That won't fit on his motor's intermediate size gear case. Largest diameter is 14".

 

[jestor68]

Re: Propping a 22' Pontoon: 3 or 4 Blade?

deleted-duplicate post

 

[WaterDR]

Re: Propping a 22' Pontoon: 3 or 4 Blade?

The diameter is sort of meaningless. 13.5 is fine.

Just to clarify this earlier point I made, it is my understanding that prop manufacturers when making props, within a particular series, will adjust the prop diameter as you move through the pitches so that rpm changes will be more conistent.

 

[Dennybot]

Re: Propping a 22' Pontoon: 3 or 4 Blade?

Thanks, all.

I've gone ahead and ordered two aluminum 15 pitch props:

1. A 13.75 x 15 3-blade
2. A 13.4 x 15 4-blade

I'll post speed and RPM results when I can!

 

[blackhawk180]

Re: Propping a 22' Pontoon: 3 or 4 Blade?

Very interested to hear your results. I have a merc 115 4 stroke that was WAY over prop'd when I bought the boat (used) Started with a 19 pitch aluminum and took about a week to get on plane. Went to a 14 pitch aluminum (I run heavy, usually 3 big guys, cooler, beverages etc) and was much happier but felt the hole shot was still slow and since I never run WOT, I was mostly looking for better economy and hole shot. I ended up with a SS 4 blade 13 pitch and for my boat it's perfect. Quick hole shot and I burn .46 GPH LESS at the same cruising speed. It feels like it's lifting the stern some so the boat rides flatter, even trimmed out. For whatever reason, it even steers better. Obviously, individual results with vary but I'm looking forward to your comparison results between the 3&4 blades with same pitch.

 

[Dennybot]

Re: Propping a 22' Pontoon: 3 or 4 Blade?

Very interested to hear your results. I have a merc 115 4 stroke that was WAY over prop'd when I bought the boat (used) Started with a 19 pitch aluminum and took about a week to get on plane. Went to a 14 pitch aluminum (I run heavy, usually 3 big guys, cooler, beverages etc) and was much happier but felt the hole shot was still slow and since I never run WOT, I was mostly looking for better economy and hole shot. I ended up with a SS 4 blade 13 pitch and for my boat it's perfect. Quick hole shot and I burn .46 GPH LESS at the same cruising speed. It feels like it's lifting the stern some so the boat rides flatter, even trimmed out. For whatever reason, it even steers better. Obviously, individual results with vary but I'm looking forward to your comparison results between the 3&4 blades with same pitch.

UPDATE! We got the 13.4x15 Mercury Spitfire four-blader installed and took her on a test run.

So far so good: We got a WOT RPM of 5800 with a speed of 36MPH. This is much faster than I thought we'd be. I hope the speed was accurate; we used an iPhone speedometer app.

We were a bit underloaded with just two people on board.

Next test will be with the 13.75x15 Mercury Black Max.

 

[Silvertip]

Re: Propping a 22' Pontoon: 3 or 4 Blade?

Here's the deal. You cannot have top speed, economy, hole shot, and cruising comfort with one prop. In fact there is only ONE correct prop for any boat. That's the one that lets the engine rev at or near the upper end of the manufacturers rpm band. Speed will be what that prop provides, as will economy and hole shot. You can obviously go with more pitch and lug the engine which really hurts hole shot and causes fuel economy to go into the toilet because you need to run with more throttle opening than normal. Or you can decrease pitch and over rev the engine at WOT but hole shot will be better. Fuel economy again goes out the window because the engine is running faster than it needs to. For pontoons, some manufacturers make "pontoon specific" props and those are by far the best bet for all around use. The big rounded blades provide the push needed and work very well in reverse. You will not likely see any economy difference in props that are reasonably close to proper on any boat. It is when you reach the extremes that you hurt performance and economy.

 

[steelespike]

Re: Propping a 22' Pontoon: 3 or 4 Blade?

Your speed isn't accurate. prop calculator says you can't go that fast with the information supplied.
You can't have negative slip. Using 20% slip I get 28.3.mph a more treasonable figure.
Slip could be higher, not likely to be lower.

 

[Dennybot]

Re: Propping a 22' Pontoon: 3 or 4 Blade?

Your speed isn't accurate. prop calculator says you can't go that fast with the information supplied.
You can't have negative slip. Using 20% slip I get 28.3.mph a more treasonable figure.
Slip could be higher, not likely to be lower.

I was using the application 'SpeedBox' on my iPhone. It sounded too high to me as well, but that what it read, multiple times. We were out on the SF Bay, it was calm, but we may have had a tail wind.

Any suggestions for a more reliable speed indicator?

But, bottom line is, we don't care about top speed. We're looking for as the previous poster suggests, the right prop overall. And so long as our tach is accurate, we have found it in the Spitfire, topping out at 5800 RPM at WOT.

Sound right?

 

[jestor68]

Re: Propping a 22' Pontoon: 3 or 4 Blade?

Mercury Marine quote: " The Spitfire pontoon is the best pontoon prop in the Mercury prop line up". It should produce considerably better slip numbers than a 3 blade prop.

Your theoretical speed is 35 mph @ 5800 rpm with no slip. Like size pontoons achieve 29 mph with a 13" Spitfire in tests; therefore I see no reason to think your 15" Spitfire isn't doing 32-33 mph.

Your WOT rpm is right on. That's 90 hp @ 5500 rpm. So your rpm range is effectively 5500-6000 rpm. Go below 5500 rpm at WOT, and you're not producing full power.

You are, as they say, dialed in.

 

[steelespike]

Re: Propping a 22' Pontoon: 3 or 4 Blade?

Speed is an indicator. Generally the prop best suited to your motor will produce the best/higher speed.
As suggested you are "dialed in"
As far as the speed discrepancy perhaps you were running with the tide or reading kilometers.
A gps would probably be most accurate

 

[blackhawk180]

Re: Propping a 22' Pontoon: 3 or 4 Blade?

I suspect the 4 blade will perform better than 3 in your situation but will await your next test. If budget allows, try a stainless 4 in the same pitch. I'm still amazed at the difference on my boat.
I agree, a good GPS will give more accurate MPH. Too bad you don't have a digital fuel monitor like I have (Merc Monitor). It really allows you to dial in trim/RPM for max economy. Like I said, I was able to reduce my GPH by .46 with the 4 blade SS prop and still maintain the same speed. Shoot, in 50 years, I could pay for the monitor and prop but at the rate they keep raising gas prices, maybe 5 years!