Replacement Prop - Suggestions

[cigar_stub]

I have a 2002 Yamaha 115hp outboard on a 19' center console. The current prop is a 13x19 K (that's what I can read from the prop itself). My Seloc manual states the test prop for this motor was a Kent Moore Part #YB1624. I assume that means a 16" 24 degree pitch and I also assume the current prop is 13" with a 19 degree pitch. I have very slow takeoff from dead stop and with just me in the boat, once I'm up on plane which also takes longer than I think it should, I run about 33 mph at 5500 rpm which is the recommended top end.

I want to order a second prop to both see if I can improve the performance and to have a spare. Any thoughts about the current prop vs the factory test size? Also, any suggestions on what I should purchase to improve the hole shot? I was thinking of getting the smart tabs to improve the time needed to get on plane, but thought a different prop might help as well

Thanks in advance for any help/suggestions.

 

[Silvertip]

Re: Replacement Prop - Suggestions

Just for the record, pitch is measured in inches, not degrees. Pitch is the theoretical distance a prop pushes the boat forward with each revolution. 19P means "theoretically" that the boat would move forward 19 inches with one revolution. A test prop is not a propulsion prop but rather a "test" prop used in a test tank (it keeps the motor from blowing all the water out of the tank if one were to use a standard prop but it loads the motor like a standard prop). You don't need one of those. All of this said, you might step back to a 17P prop to get the wide open throttle RPM closer to 6000 RPM which I think is where that engine needs to run. That would help hole shot and possibly give you the same or slightly faster top end.

 

[cigar_stub]

Re: Replacement Prop - Suggestions

That's interesting since I've always thought of pitch in degrees. I live and work the HVAC world and all of our fan blades are rated (and purchased) based on diameter in inches and pitch in degrees. Of course, they are designed to move a specific amount of air, not push an object forward.

As for the current prop, I can throttle up to 6000 rpms and get a couple more MPH, but since the manual shows WOT as 5500 I generally try to stay in that range. But I'll take a look at some 13" diameter, 17" props during my search.

What are your thoughts on aluminum verse stainless steel? In my bass boat, I stayed aluminum as I fished lakes with submerged stumps. The intent was, if hitting the submerged stump, the prop would be bent or broken, but the motor would not (hopefully) be damaged. Stainless steel may hold up better, but at a greater risk of engine damage.

Mine current prop is also a 3 blade, something I failed to list earlier. Is there any value in going to a 4 blade? From posts I've read in the past my hole shot problem, which is taking so long to get up on plane, may be better solved with smart tabs than making any drastic prop changes.

Thanks for the input.

 

[Silvertip]

Re: Replacement Prop - Suggestions

Whoa back big fella! If you are already "under propped" with a 19P (meaning the engine over revs by 500 rpm) you do not want to look at 15 and 17P props. That will make the engine rev even higher. You want at least a 21P which will DROP rpm about 200/inch of pitch. That will also increase top speed somewaht. Why? Because more pitch takes a bigger bite of water, hence more forward motion within the power limits of the engine. A 21P from one manufacturer may not perform the same as a 21P from another so prop selection is somewhat a trial and error process. You are close to the proper setup though. Before you buy that prop however, check the position of the AV plate on the engine in releation to the bottom of the boat. The engine should be mounted so the AV plate is at flush with, but typically and inch ro two above the bottom of the boat. Then test WOT, note rpm and select the new prop based on those numbers. The theory here is the less leg you have in the water, the less drag there is. Less drag = higher speed and higher RPM. You need to prop accordingly to keep RPM in check.

 

[Frank Acampora]

Re: Replacement Prop - Suggestions

As far as your hole shot, if the boat is slow to get up on plane now, the higher pitch prop is going to adversly affect your ability to dig out of the hole. Do you tuck your trim all the way in when powering up from a stop? Try a set of trim tabs and if you have a lot of crap in the stern, move some of the weight forward to help drop the bow.

 

[cigar_stub]

Re: Replacement Prop - Suggestions

I always have the motor lowered when starting out. As for crap in the stern, my wife comes along from time to time. (God help me if she ever reads this......)

But seriously, I think the smart tabs are my next move. Silvertip suggests checking AV plate position, something I've not thought of in the past. The boat is used (2002). I just assumed that was correct, but I'll give a look anyway. The person I bought the boat from didn't strike me as someone prone to making engineering changes on a boat (he used it rarely), but I could be wrong.