Need a new prop for 50hp yamaha 2 stroke on Aluminacraft c165

[tnq5546]

I need a new prop for a C165 with a 50 hp Yamaha 2 stroke. Should I just replace it with the same Yamaha prop which is a 10 5/8 x 12, or do other brands offer better performance. Boats is mostly used for cruising and fishing.

 

[alldodge]

I need a new prop for a C165 with a 50 hp Yamaha 2 stroke. Should I just replace it with the same Yamaha prop which is a 10 5/8 x 12, or do other brands offer better performance. Boats is mostly used for cruising and fishing.

Props are real tricky things and slight variations can change for the good as well as bad. You need to first determine if you like the way your boat performs. If the response is "well kind of. sort of, maybe, then just maybe you want to tinker with it. Changing props can give you better hole shot, higher speed at WOT, and good midrange. There is not one prop that provides all the previous if weight (load out) is changed. So if you always load the boat the same way, and you want something a bit different, then let us know what that is and we can provide an opinion

 

[steelespike]

Read the stickys at the top of the prop forum.
get us your present prop size and lightly loaded wot rpm and gps speed .
Drescribe your present performance Hole Shot etc.
If you get us that information we can tell better if your setup works and what may be needed.
Your prop size is right on but we need to have your performance numbers to tell if the setup works for you.

 

[tnq5546]

Boat is a 16' 6" Aluminacraft c165 with a two stroke Yamaha 50 hp outboard. As a fishing boat the current prop works just fine. On occasions we use it to two a tube or wakeboard. The boat with its current 10 5/8 x 12 prop will do 30.2 mph by GPS filled with fuel and with one driver. Rpms running 4400. I was thinking of possibly a 4 blade prop for better hole shot and towing of toys, or maybe investing in a three blade stainless prop. Any suggestions. All help welcomed.

 

[alldodge]

Don't fall into the hype of a 4 blade props, while they have their place most 4 and 5 blade props provide more lift. Lift is good to a point and only if you have enough power to pick the boat out of the water. Motors without sufficient power will have the stern come up more and then the bow goes down. The more blades you have the more friction.

As a non-Yam expert I don't know if 4400 is in your sweet spot or not. I need to go look it up

 

[tnq5546]

4400 is at wot.

 

[steelespike]

I suspect the tach is not accurate.The boat can't go 30 at 4400 rpm. Going by your numbers it appears the rpm is about 5500.
You need to verify your tach.Perhaps borrow a shop tach. or use an induction tach to check the rpm.

 

[Sea Rider]

Get the factory wot parameters for that engine, as suggested barrrow a tach and check current wot rpm with actual prop, if being a standard delivered prop with engine, should be a medium pitched prop, which works quite well on light to medium applications. Induction tachs don't read accurate on 3 + cylinder engines, are limited to 1-2 stroke engines.

Happy Boating

 

[tnq5546]

Okay I will try to locate a tachometer. Thanks

 

[alldodge]

Never mentioned what year your motor is but the WOT for the 1997 to 2003 is 4500-5500 rom. If your hitting 4400 your close, but as others mentioned this could be an issue

I just used BBlades prop slip calculator, and I don't know you drive ratio so I used 1.5. Using this ratio 30MPH works for 4400 rpm which allows for a 10% prop slip
http://bblades.com/propeller-slip-calculator/

 

[Sea Rider]

At 4400 wot rpm you're lugging the engine if factory parameters happen to be 4500-5500 rpm, worst if riding solo and light loaded. Before venturing with a new prop check your tach is reading well, if so, go for a prop maximization to suit your boating needs.

Happy Boating

 

[tnq5546]

Ok, motor is a 2008 yamaha 50 hp 2 stroke. Per owners manual, full throttle range is 4500-5500 rpm and gear ratio is 1.85. The prop is a 10 5/8 x 12 and my rpm at wot are at 4600 with a GPS speed of 30.2 mph. Would like to switch to a stainless three blade prop, what would you recommend. Your input is appreciated.

 

[Sea Rider]

With 4600 still at the lugging side. Yam has lots of alum props to play with, anyway will need to drop several pitches down to be at least middle to ideal max wot numbers stated for that engine. A SS prop Guru should chime in for an appropriate tech answer.

Happy Boating

 

[Maclin]

Something is amiss in your numbers. A 1.85 ratio with 12" pitch prop at 4400 can only calculate to 25mph at 10% assumed slip. The 1.85 ratio sounds off to me, just seems like a 2.0-2.3 range is more appropriate for a 50hp, but that is just me. Even so the actual rpm reading is probably off

Since your mph is from GPS we can use that as the constant for some comparison calculations

Here is an example using 12" pitch prop and assumed 10% slip (which is low, 15% is more likely what you have)...:

4400rpm at 30 mph would have to be from a 1.5 ratio,
the rpm would have to be more like 5427rpm with a 1.85 ratio to get to 30mph with the 12 pitch.

 

[tnq5546]

I will have to have the tachometer (rpm) gauge checked. I know the gear ratio is right because it came straight out of the owners manual. Should I consider replacing the analog tachometer with a digital one

 

[Sea Rider]

Digital tachs are more accurate reading small rpm numbers, go for any one of them.

Happy Boating