new prop?

[lncoop]

I couldn't decide whether to post this here or in the prop section, so I flipped a coin. Here goes. I have a 21' Suntracker with a 90 horse Merc propped with an aluminum three blade Solas 13.75x15. I'm very happy with the rig, but I've started pondering whether I should consider a different prop. Right now at WOT with no one else aboard I can attain 23-24 MPH according to GPS. I think that's probably all I can ask for, but I'm maxing out at 5K RPMs, and the top end is supposed to be 5500. I don't want to fix it if it ain't broke, but I can't help but wonder whether 1) I should be concerned about lugging and 2) whether I could get a little more speed for my daughter's tubing. I'm realistic about the capabilities of my rig. I just want to make sure I'm doing everything I can to get the best out of her.

 

[EGlideRider]

Re: new prop?

Yes, you are lugging. Sorta like having a heavy trailer permanently connected to your vehicle. For maximum engine life, you should drop to a 13 pitch.

I doubt if you'll gain any more speed and in fact it may drop 1 or 2 mph, but your engine will thank you.

 

[kentuckyguy]

Re: new prop?

I have a 21 foot triton with a 90 merc on it.. My prop is a 13.75x17.. With me and the wife, I get 5200 rpm and a gps speed of 27-28 mph.. Now last weekend we had 10 people on the boat and I could only get 4800 rpm.. I changed the prop to a 13 and would turn 5500 with everyone and also done some tubeing with everyone...

 

[lncoop]

Re: new prop?

Thanks guys. Any brand recommendations? Kentuckyguy, how was the tubing with the 13 pitch?

 

[lncoop]

Re: new prop?

Looks like the Solas Amita 13.75x13 is a good bet. Great price and free shipping on good ol' iboats. Thoughts anyone?

 

[Silvertip]

Re: new prop?

5000 RPM would be considered lugging by many but as far as the engine manufacturer is concerned, WOT range is generally in a 500 RPM band so 5000 is within that range. However, it is also known that engines operating at or very near the top of the band are a tad more efficient and perform slightly better. So dropping pitch to 13 would theoretically bring rpm up to about 5400 with speed staying the same. The advantage of less pitch is that the boat can now handle a heavier load (towing or carrying people) because you essentially "downshifted" a bit. Before, a heavy load would indeed pull RPM below 5000 which would cause lugging. When you look for props for pontoons, look for pontoon-specific props which have large blade area with rounded blades (hence the term "elephant ear prop"). Running the numbers for the prop you have shows a 21% slip factor which is not terrible by any means on a pontoon so you are close to optimum. A good 13P run through the calculator showing the same speed results in a 16% slip. Remember -- when switching props a change of manufacturers can impact performance results even if the props have identical pitch and diameter. Prop designs vary between manufacturers and pitch/diameter are not the only performance affecting characteristics. Cup, no cup, high rake, low rake, blade shape, etc., all affect performance.

 

[lncoop]

Re: new prop?

13 pitch it is. Thanks everyone. I'll let you know how it goes.

 

[kentuckyguy]

Re: new prop?

Thanks guys. Any brand recommendations? Kentuckyguy, how was the tubing with the 13 pitch?

It was awsome.. Everyone couldnt believe the hole shot the boat had..

 

[JEdA]

Re: new prop?

I have a recently acquired 20' with an 88hp 2 stroke. When I bought it it had a 19 pitch prop on it. It would max out at 4200ish RMP at 17ish mph (GPS). I went to a 15 pitch and it is now running 23-24mph at 4500ish RPM. These were with just me and my wife and a little stuff. Suggested RPM range for this motor is 4500-5500. I've got a 13 pitch prop that should be here tomorrow that I am hoping to try out this weekend. Both new props are Hustler Turning Point props. They have much broader blades than whatever was on there before.

I'm fairly happy with the performance, I just want to be able to have similar performace with a few more people on the boat.

I ordered both props from iboats (which is how I found this forum) and have been really impressed with their shipping speed. I put the order in late Tuesday night and UPS says it'll be here tomorrow.

I hijacked your thread to say all that for two reasons. One I'll let you know how going from a 15 to a 13 works for me. Two I'm in Sherwood so right down the road from you. Maybe I'll see you on the lake someday.

 

[lncoop]

Re: new prop?

Cool! Several Arkies on here, but what are the odds? I started to get the Hustler, but the Solas is so much cheaper by the time you throw in the free shipping I just went with that one. That's the brand I have on there now and it's been fine. I was tempted though. Where are you in Sherwood? I live on Seminole Trail. If you've ever driven down my street you've probably seen the barge.

 

[JEdA]

Re: new prop?

I live on Devon between Country Club and Wildwood.

 

[lncoop]

Re: new prop?

My folks live on Alanbrook. What lake do you typically frequent?

 

[JEdA]

Re: new prop?

I don't typically do anything when it comes to lakes. This is my first boat that wasn't used for duck hunting or maybe a little trout fishing on the Little Red. We went to Greers Ferry two weeks ago and that is the first time out other that a trip on the river. I think we are going to go to Greers again this Saturday, but may try one of the lakes in the Hot Springs area instead (Hamilton or Ouachita).

 

[lncoop]

Re: new prop?

We had a great time on Greers over the 4th, but we're usually on Catherine. My wife and daughter like it because it's quiet and very kid friendly. It's a nice little lake, but frankly I'm getting a little tired of it. They don't want to go out Saturday so I'll probably take the flatbottom up to Heber.

 

[lncoop]

Re: new prop?

Okay, the new prop arrived yesterday and I stuck it on there but I'm starting to second guess myself. I went with this one, http://boatpropellers.iboats.com/Me.../7285/?**********=308625093&*******=739949967, which I think will work fine, but now I'm wondering whether I should go with the same one in the four blade configuration http://boatpropellers.iboats.com/Me.../7278/?**********=308625093&*******=739949967 for only $15 more. I'd love to experiment, but iboats won't take one back once it's been tried. I guess for that price I could just keep one as a spare. Or, am I just completely off the reservation with the Amita? The Solas model (Myth) that came on it doesn't appear to be available any more or I would have just gone with that one in the 13 pitch. What say ye?

 

[JEdA]

Re: new prop?

I don't know anything about 4 blade vs 3 blade, but I said I'd share the results of my switching (3 blades). I switched while on the lake so it's as fair a comparison as I could get. The 15 pitch I was getting 24 mph at about 4600 RPM. The 13 pitch I was getting 23 mph at about 5200 RPM. The 13 pitch was noticably quicker to get up to speed and would be good with a more loaded boat.

 

[lakegeorge]

Re: new prop?

We have a 22ft Sweetwater with a 60hp Yamaha and I get 21 mph on GPS, With a 90hp I would think that you should be in the higher 20's

 

[lncoop]

Re: new prop?

I ran her with the 13 pitch this weekend and was not happy with the performance at all. It did get me up to 5500 RPMs and hole shot was a little better, but at WOT I could actually feel the boat surging forward a little with the rotation and see the tach needle move with the surging. It was really strange. We were at the lake for the entire weekend and I had the good sense to throw in the old prop and prop wrench, so when I reached the dock I threw the old prop back on. Believe it or not, the next day I started getting 5500 RPMs at WOT with the old 15 pitch, so I guess I've found my prop. Now I have to decide what to do with the 13 pitch. I know Iboats doesn't take back used props, but it still looks brand new, so if I were the dishonest type I could tell them I never used it. If they don't take pity on me I guess I'll just try and sell it or keep it as a spare.

 

[jasperpso2]

Re: new prop?

hmmm.. were you hitting the rev limiter? does your motor have a rev limiter? that could of been the surging.. i wonder why the 15p didnt do 5500 before?


i recently learned that i have been running on 3 cylinders, probably since i bought the boat in june, from changing props. the 13p it had on it was lugging so bad, i didnt catch on.. after going to a 11p, i hear a noticeable miss on midrange to high rpm.. so i changed the plugs, and one was obviously not firing.. not to hijack the thread, but i ordered a coil an plug wires, and anyways - just a comment on how props can certainly change things..