Piranha prop vs OEM AL

[Mirus]

Just picked up a Glastron GT 185 a month ago. Second time on the lake I nicked a rock and bent 2 blades on the factory prop so I was still able to idle it back.

It's a 135hp Volvo which came with a 14x21 aluminum prop. Having barely broken it in I really don't know the performance of that prop too well (max. speed I got was about 44 on dash, GPS speed is about 4mph less so somewhere around 40mph fully loaded with 2 adults and 2 kids and a dog).

I ordered and installed a Piranha 3 blade with 14x21 blades expecting similar results as the AL. I was quite disappointed at the performance. I could barely get it to plane and WOT was only 3800RPMs with an indicated speed of 25mph. It would just bog down at 2800RPM during hole shot and I had to keep max trim to keep the bow down. I kept it at about 2500RPMs/15MPH and only stayed on the lake about an hour to keep from damaging anything.

I have a set of 19" blades which I put on yesterday and haven't had a chance to test those yet.

Is there that much difference between the Volvo prop and the Piranha? Personally, I thought the 14x21 AL was a little high but it seemed to do okay.

 

[rndn]

Re: Piranha prop vs OEM AL

I had the same results with the compsite props. You get what you pay for these days.

 

[marcus.adelman]

Re: Piranha prop vs OEM AL

I am/was looking into getting this prop setup. Now I am a little worried and just ordered a stock replacement. They say this prop is stronger than aluminum. I basically use the boat for tubing and other watersports so a stronger prop would be better and the ability to change pitch in five minutes would be great. Please let me know how the 19" pitch does for you. I have a 4.3l with 185 horse so it might be able to spin the prop up a little better. I also don't know if I want the three or four bladed ones. Man so many options...

 

[atthelastminute]

Re: Piranha prop vs OEM AL

I went from an old banged up Michigan 14x19 3 blade to a piranha 3 blade. I have tried two sets of blades so far, 14x19 and 15x17. The 14x19 got me to just under 4000 rpm, and the 15x17 got to 4600rpm. This weekend I will be trying a 14x17 and a 15x19 to try and get into my sweet spot. I guess my point is going from one companies 14x19 to another changed my revs enough to get me out of my ideal WOT range which is 42-4600. Running piranha's prop selector led me to trying these other two sizes.

 

[Mirus]

Re: Piranha prop vs OEM AL

I sent an email to Piranha and their suggestion was to make sure the prop nut wasn't on too tight causing the prop to bind. That was my first thought on the water with what was going on. Unfortunately, I forgot my prop wrench in the garage so didn't get a chance to loosen the nut. Last night I picked up a cheap torque wrench and will try it at the recommended 30ft/lb (I did crank it down pretty hard). Didn't get to the lake last night since it was crappy weather. Hopefully I can get this sorted out before the weekend.

As far as the prop, it is an impressive use of plastics. Seems durable enough and should work well if I can get these kinks worked out. Initial observations as to possible reasons why performance isn't better than it is:
1) blades are not polished/smooth like a freshly painted AL or mirror like finish of SS. Like dirt on a car this probably has unnoticeable effects on performance.
2) blades are thicker than AL and not sharp. This is also a minor performance issue.
3) blades are not perfectly flush against hub. Since the pieces are fit together there are gaps and ridges around the hub.

 

[hal2814]

Re: Piranha prop vs OEM AL

I had the Piranha's lesser-known sibling the ProPulse. It was never a particularly bad propeller but it didn't have the top speed or the hole shot of my aluminum 3 blade and it vibrated more than I would've liked. The ProPulse could adjust pitch without changing blades so I tried a wide variety of pitches. I finally gave up on it when 3 of the 4 blades would break both times I hit something. At $30 per blade, I might as well repair an aluminum prop. Especially since the composite blades had a tendency to completely shatter on things that would at most ding aluminum.

 

[atthelastminute]

Re: Piranha prop vs OEM AL

I would agree with all three of your observations. I figured I could sand down the mold lines once I have the set of blades that works best with my boat, including on the hub and the base of the blades. Another idea that I just had that might help is waxing the blades to reduce friction from the less than perfectly smooth surface.

 

[Mirus]

Re: Piranha prop vs OEM AL

Got out late last night and tried the 19p blades. Ran much better. Me and a tank of gas resulted in these numbers:
Plane @ ~4seconds
WOT @ 4500RPM
GPS @ 39MPH

Stock tests online with 1/2 tank of gas:
Plane @ 3.4seconds
WOT @ 4500RPM
Radar @ 42.2MPH

I know I had it above 40MPH with the stock prop w/ 2 adults 2kids a dog and half a tank of gas (46 indicated). So, it's not a horrible prop, will make a usable backup and great for unknown waters. Should be okay cruising too, but I suspect it'll run a little higher Rs increasing fuel consumption.

I swapped the 21P blades back to test as well. Not quite as doggy with only 1 person but plane was a good 8+ seconds and WOT was only around 4K @ ~35MPH GPS after half the lake at max throttle.

I think my best cruising setup would be a 3 blade AL or SS 14x21. Next year I'll probably pick up a 4 blade 14x19 SS for max hole shot.

Hoping I can get another month on the lake before winterizing in MN.

 

[ktmrider]

Re: Piranha prop vs OEM AL

I love my propulse composit props. Easy to get back to enjoying the day if you damage your prop while on the water.

Since you can adjust pitch, it's easy to match the prop to the wot setting.
Personally, it's smoother with a hydrofoil installed.