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Help me pick a prop...

Discussion in 'Members Zone: Props and Power' started by kaydano, Jun 21, 2013.

  1. kaydano

    kaydano Well-Known Member

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    I have a 24SSL, Express Tube, 6 strakes, Mercury 115 (4-stroke), current prop is a Mercury Black Max 13.75 x 15P. I get 35 MPH at 6400 rpm. WOT rpm range is 5800-6400, so I’m at the very top end.

    The problem I hope to fix with a new prop is when we run a full boat (6 kids and 6 adults that think they are kids), I can barely hold 20 mph in a straight line pulling a tube. There’s no way to whip the tube out in a turn, as the boat drops to around 15 mph in a turn. The kids intentionally slip off the back of the tube and starting kicking to help push, it's that bad. Had I known last summer what I know now (thanks to some of you guys), I would have taken note of the max engine rpm in those conditions, but I’ll just have to guess it’s ~4500 rmps. Maybe. Give or take 500. That’s a wide range, but I really don’t know. I also know now that I was probably lugging the engine in those conditions and that’s not good either.

    I’m willing to sacrifice all the top end speed I can to be able to pull a tube with a full load and get a few more mph and the rpms back up. I’ll still have the other prop if I ever want to get the speed back, so I’m willing to trade as much top end as needed for more torque, hoping it will squeak out a few more critical MPH under heavy load, which could make a huge difference since I’m right on the bubble between suck and fun.

    I’m wanting to try Merc’s new Spitfire 4-blade pontoon prop. I don’t know what size to buy, as there’s very little info online to help me. They only make 6 sizes that would work with my size motor.

    The “pontoon” sizes are:

    13.8 x 10P

    13.8 x 11P

    13.8 x 13P

    They have three “regular” sizes (I don’t know if there’s much special about the pontoon props or if it’s mostly marketing):

    13.4 x 15P

    13.0 x 17P

    12.5 x 19P

    I’ll eliminate the 10P, 11P, 17P and 19P props as bad ideas (unless someone thinks otherwise), so I’m left with two choices:

    13.8 x 13P or 13.4 x 15P.

    Which one should I get? Pretty sure this will be non-returnable, so I hope to get it right the first time.

    Thanks in advance for any comments anyone has.
     
  2. Bamaman

    Bamaman Well-Known Member

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    Kaydano: Your prop dilemma is a real world example of how a boat properly prop'd for top performance doesn't necessarily meet your needs. Your 35 mph @ 6400 rpm's is about as good as it gets. But you're already at the top rpm's you need to run your motor.

    I would say try the Spitfire Pontoon prop 13.8 x 13P. You need more pulling power, but going down much in pitch might make you hit the rev limiter too easily.

    Maybe the 4th blade and a prop designed specifically for pontoons will give you the pulling power you need for tubing. I see my local dealer selling that prop for $149, so it's not too much of an investment.
     
    kaydano likes this.
  3. cwag911

    cwag911 Moderator

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    I vote for 13p.
     
  4. BigKahuna

    BigKahuna Well-Known Member

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    Wow! 12/13 on the boat????? Might have to start running the tubing in shifts, Kay.............
     
  5. Bigtop

    Bigtop Well-Known Member

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    Kaydano,

    I to went thru the same issue. I have a 150 instead of the 115 but needed more pull with a load. If your going with the spitfire, I would try the 13 pitch in the 4 blade. Keep in mind that when going to a 4 blade, you will automatically lose RPM's. they say going to the 4 blade from a 3 is a difference of 2 pitch sizes but does give more torque and bite. I had a larger diameter 4 blade 15 pitch prop and would run 41mph at 5800 rpm, but loaded was another story like yours. With a load and pulling a tube or skier, I could only get 29 to 30 I changed to a little bit larger diameter 4 blade 13 pitch prop and only lost 3 mph on the top end, but now with a load and skier I can still run 35. The prop company I used was Power Tech. You can call them and give them your info such as speed, rpm, engine and boat and motor specs, then tell them what kind of performance your wanting from your boat. They will then suggest a prop for your needs. The best part is, if your not satisfied, they will let you exchange for another prop with only paying for a small restocking fee. They are very good and customer friendly. The tech that I talk with is Marcus. If you do go with them, be sure you ask for their "Cushion Lock" hub. It is great at taking out most of the backlash and rattle of the stainless prop.

    Good luck. I am sure there's not one guy on here who hasn't gone through the same issues.
     
  6. RiverBill

    RiverBill Well-Known Member

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    Kaydano,

    We have a 2012 22SSI 3 tube Bennington (XL performance package) with the Mercury 150 4 stroke. I highly recommend the Mercury SS Enertia 15X15 3 blade prop. Our top speed is 42 mph (gps) 5600 rpms with 6 adults on-board with clean tubes. The boat comes out of the water fast & pulls tubers, skiers & wake boards fine. I have tried a few other props , but I always go back to the Enertia!

    RiverBill
     
    Last edited by a moderator: Jun 21, 2013
  7. Bamaman

    Bamaman Well-Known Member

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    I agree about the Enertia prop being a great one for pontoons. If you look at all the Mercury factory boat tests, they're with Enertias--available in every 1" of pitch. Yamaha's Reliance props are comparable, and that's what I've got in 15 pitch.

    But Enertias are stainless steel, and Kaydano is trying to get the job done with a less expensive aluminum prop.
     
  8. kaydano

    kaydano Well-Known Member

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    With a 115 HP, seems like SS is all wrong for me. I don't think I'll get any of the benefits of rigidity because the motor is small (making SS a waste of money), and I WILL have greater impact on the gears if I hit something. Both say go aluminum. Correct me if needed.

    I talked with Power Tech. Wow. Lots said. Like a fire hydrant in my ear.

    Bottom line is they didn't recommend a 4 blade, but thought I should definitely drop down from 15P to 13P. Here's why.

    When you have a loaded boat, there are generally two ends of the spectrum regarding motor rpm vs prop. At one end, if the motor rpm stays high (at or near WOT range) but you're running slow (with a loaded boat) the prop is slipping badly. The motor is winding up, and the prop's not biting into the water. At the other end of the spectrum, the prop is biting in, and the motor RPMs come way down. As far as I recall from last season, the second is my problem.

    So, they didn't recommend a 4-blade because it would just add more surface area, and probably actually make things worse. What they said I really need is less pitch. But, had the motor been running at near WOT, even with a full load and running half speed, then more blade surface area would be in order because the prop would be slipping too much, so they would have recommended the 4-blade in that situation. I don't think I misunderstood anything they said, but that's possible in a fire hydrant situation! Let me know if something I wrote doesn't make sense.

    They recommended one of their 15x13P SS models (3 blade). I asked about aluminum, and they said the options at small pitches are too flat in the blade (no cup).

    I wonder what effect dropping down to 11P would have if I went up to 4-blade. The Spitfire comes in a 13.8 x 11P. Any thoughts???
     
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  9. kaydano

    kaydano Well-Known Member

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    One other thing they said. You know that rule of thumb where if you drop 1 inch of pitch, it increases rpm by xxx rpms? That doesn't hold as true at the low pitch sizes as it does at the high pitch end. At the low pitch end, it goes more by ratio (it's non-linear). The example given was dropping from 15P to 13P is a 15% change in pitch, so the rpms would change by 15%. Now that I think about it, that's a very big difference, and maybe I didn't hear right. The "fire hydrant" of info didn't give me time to run things through the "does that really make sense" hopper in my head. Now that I think about it, 15% of 6000 rpm is 900 rpm. So I must have heard the details wrong. But, I'm certain I heard correctly that the "rule of thumb" don't work so much at the low pitch end. For what that's worth.

    The more I learn, the more I realize I don't know. But that's true about most things in general.
     
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  10. Bigtop

    Bigtop Well-Known Member

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    Yea I know what you mean about learning more but knowing less. The other thing you have to keep in mind is that different brands of props are also different in their pitch, rake and cup. It's kind of like golf clubs, a 7 iron in a Taylor Made may be a different degree of loft vs a Calloway 7 iron. That being said, I wouldn't expect the same performance from one prop brand or another in the same diameter and pitch. Rake and cupping also change speed and rpm's. another way of putting is you have to compare apples to apples instad of apples to oranges. There IS NO science to selecting a prop, it's 90% trial and error.

    Good luck.
     
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  11. Bigtop

    Bigtop Well-Known Member

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    Dang it !!! Sorry for the double post
     
  12. kaydano

    kaydano Well-Known Member

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    Okay, one more thing they said, which is more of a "word to the wise" comment I thought I'd pass along to potential first-time buyers here, is most dealers are selling boats/motors/hulls based on top speed. Everyone asks what the top speed is. I admit, I did that too. Dealers hear it so much, it's easier to just prop it, gps it, and sell it, than it is to teach it. Hope that makes sense.

    But now I get it. Real world is not top speed. How you use the boat is FAR more important. But, that's not a simple question to ask like "What's the top speed?" is. I am learning I don't really give a crap anymore about top speed, and it's more about that mid-range performance. Water sports performance, in my case.

    Bamaman said it EXACTLY above when he mentioned my dilemma is a real world example of how a boat propped for top performance doesn't necessarily meet your needs. I finally get it. For those thinking about purchasing a boat, I really have no idea what question you would ask a dealer in this regard. You'd just have to tell him you want it propped for water sports I guess (if that's what you really want, but take a minute and be serious with yourself about how you'll really use your boat). For an aluminum prop, a change out is only $100. Stainless steel is 4-5x that, and a mistake there sets your retirement date back a bit more!
     
  13. Bamaman

    Bamaman Well-Known Member

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    Let me say something about aluminum vs. stainless. I used to have a couple of I/O's. With the first one, I'd destroy an aluminum propeller per year. When I got my second boat with a stainless prop, I used it 10+ years without the first scratch on the stainless prop. Despite the extra performance, the stainless prop was actually a good value in that I wasn't visiting my local prop shop often--and cheaper per year to run.

    But fortunately, Jim's Prop Shop in Florence, Alabama is owned by a cousin, and he always cut me a deal.

    But if you're running 115 hp or less, I can certainly understand why you don't want to make such an investment.
     
  14. TomS

    TomS Well-Known Member

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    The other thing about some of the Merc stainless props is they use a Delrin type of hub kit that is designed to break first if there is a hard hit of some type. $40 or so and you're back in business. Just carry a spare hub not an entire prop.
     
  15. kaydano

    kaydano Well-Known Member

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    Yeah, at one time I thought about just getting a spare hub, but I'd have to spend $400 to get a SS prop first. Then the spare hub makes more sense. But, since I only have an aluminum prop, I figured if I hit something hard enough to rip the hub in half (I already have a Delrin hub on my current prop), I can only imagine what the aluminum prop would look like. I'm thinking it would be bent up so badly I wouldn't want to expose a brand new engine to that kind of vibration as I limped back to the marina. And I'd still have to go buy a new prop.

    My current mission isn't so much having a spare prop/hub (but that's certainly part of it) as it is my hoping a new prop would help my full-load performance. Which really would be great as it's not fun to take two couples and their kids out on the boat and then have to drop half of them off at the beach to tube.
     
  16. Ben & Suzy

    Ben & Suzy Well-Known Member

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    Kaydano,

    You have a 115 with the smaller diameter gearcase. You can't run an Enertia or the 15 x 13p that PowerTech recommended because 14" diameter is the largest prop that your gearcase will accept in that hub size.
     
    Last edited by a moderator: Jun 22, 2013
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  17. kaydano

    kaydano Well-Known Member

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    Really? Wow. You'd think Power Tech would have known. Thanks for the heads up. Never heard or thought about that before.

    Is that just a simple clearance issue between the edge of the prop and the plate just above it, or is it some other kind of mechanical issue (like too high of an angular moment or something strange like that)?

    Any thoughts on me getting an 11P? Too small?
     
    Last edited by a moderator: Jun 22, 2013
  18. kaydano

    kaydano Well-Known Member

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    Mercury's prop selector says:

    If current prop is 15P, with 4800 rpm and 22 mph (which are close to my full-boat numbers), it recommends the Spitfire 13.8 x 11P.

    If current prop is 15P, with 6400 rpm and 35 mph (which are my light-load numbers), it recommends 13.4 x 15P.

    They also sell the 13.8 x 13P, which is between the two above. That size just starts to show up in the recommended list when I slowly bump the numbers from 4800 up to 5200 rpm and 22 mph up to 26 mph. Since my "real-world" situation I'm trying to improve is much closer to the 4800 rpm at 22 mph numbers, I'm thinking I should try the 11P. I originally thought this would be too small, but I'm having second thoughts.

    Does this trigger any thoughts from anyone???
     
    Last edited by a moderator: Jun 22, 2013
  19. Bigtop

    Bigtop Well-Known Member

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    Ben & Suzy is correct on the 14" being the max diameter for the 115. My first boat was a 2250gcw with the twin elliptical tubes and A yamaha 115. I remember that the max diameter was a 14". This is due to the clearance between the prop and the plate. I ran a Yamaha potoon series 3 blade 14x13. My top speed was 28 mph with a light load and 24 with a good load. Still not enough for good tubeing so i traded up to a boat with esp and a 150. I personally think the 11 pitch is to low. I would try the 13 or 12. Again though, that's just my opinion, I'm no prop expert.
     
  20. kaydano

    kaydano Well-Known Member

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    Sounds like Power Tech really missed the target big time on the max diameter. Sounds like a pretty novice mistake. I would have been ticked to buy a prop and with of all the complexities surrounding props, to not have it fit??? Even with all the problems Keithkz is having trying to dial his prop in, getting a prop that don't fit would have to take the cake.

    Thanks for the catch guys.

    On the 11 vs 13, I'll probably just have to pick one and see what happens. 11P does seem low, but I would be adding a 4th blade, so that removes some of the gut feel that it's wrong. They don't make a 12P in the Spitfire, so I'd have to go to a different model. If I went to a different model, I would always be wondering how a Spitfire would have worked, so I might as well just stick with it and avoid ending up with 3 props down the road!

    I can't believe I seem to be the only one that wants to tube with a heavy pontoon load and a 115 HP, but I can't find much info online at all. I seem to be the only idiot that didn't pony up for the 150. The Spitfire is new, so maybe that's part of it. I haven't read anything bad about them, everyone seems to like them, I just can't find the info I'm looking for.

    The Merc prop selector seems to point to the 11P. I may buy them both, and sell the slightly used one that doesn't work out.

    If anyone is interested, Mercury has a $20 rebate until the end of June (2013). Only for aluminum props though.
     
    Last edited by a moderator: Jun 22, 2013

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