Another Dia vs Pitch Prop question

[KevinWI]

Surprising when you look online at what prop is recommended for your motor.....nothing in the manual, nothing online.
Right now I have 10 1/4 x 13. When I first got the boat I was running 33 top end....now I'm down to 29-31 just depending on wind.
After the initial break in period it dropped to 31.....after I beat up my prop a bit, it's around 29-31.....
Looking to get a bit more top end. There really is nothing to rely on as every boat is different and every boat is loaded different.
I'm considering an 11x15 Stainless. Found a good deal on an off brand with decent reviews. I have to determine clearance first to see if an 11 will even fit. I'm assuming a 15 will get me a little more top end and the extra diameter will keep RPM's down to give a bit more power for a heavier jon boat.

 

[Zum]

Do you know what your Rpm is? (You mention keeping it down)
Rpm is the key when chosing a prop....without it we can get you close but a motor runs best at a certain rpm.
They make little induction tach's that work pretty good,easy to install
What do you have for a motor and boat?
Edit...a 15 pitch will get you more speed if your motor can spin it

 

[KevinWI]

I don't have a clue what the rpm is, and it'll be 4 months before I can find out due to the frozen water out there. I don't have a tachometer and even with one, I wouldn't know what the target would be or what prop would be too much RPM without buying said prop and trying it out.
Right now it's a 40hp Merc 4 stroke with a 1654 Tracker Grizzly with lots of toys installed.

 

[airshot]

Without running your engine at proper peak rpm you could be causing damage or excess wear on your motor. If that 15" ends up lugging your motor, you will loose speed and use more fuel and cause more wear on your motor. Purchasing a tach would be a wise investment, and much cheaper than buying another engine !!

 

[Still Afloat]

Kevin, an 11 x 15 sounds like too much prop. Get the tiny tach and check your max rpm with the existing prop. At least this will allow you to make a reasonable guess.

It could be that the 2 mph drop is just from a worn prop and all that Humminbird gear that you have recently added.

 

[MrGiggles]

I don't have a clue what the rpm is, and it'll be 4 months before I can find out due to the frozen water out there. I don't have a tachometer and even with one, I wouldn't know what the target would be or what prop would be too much RPM without buying said prop and trying it out.
Right now it's a 40hp Merc 4 stroke with a 1654 Tracker Grizzly with lots of toys installed.

Seems to me that it would be very unwise to buy a prop (an expensive stainless one, no less) four months in advance, without knowing your baseline. If it turns out to be wrong, which it very well could be, you'll be well past the return window and have an expensive doorstop.

I'd spend the winter rigging a tach first.

I'll jump on the bandwagon of a 15 being way too much for a 40. In addition, diameter typically decreases with an increase in pitch, which makes me wonder if you are looking at a prop that is not designed for that motor. Pitch and diameter aren't everything, there are a myriad of hub diameters as well.

 

[FuzzyGrub]

As everyone has mentioned, you need your current wot rpms. If you are in the high end or above for your motor, than you can consider a prop with more pitch, but would not recommend going larger diameter. Larger diameter is for more "bite" at the sacrifice of more high speed drag / loss. I also wouldn't recommend jumping to an SS prop until you have/know current performance.

 

[Zum]

Those induction tachs are easy to hook up...tiny tach is a well known brand but others out there do the same thing.
Its as easy as a few wraps of wire around a spark wire and attach a ground.
Im pretty sure your rpm range is 5500 -6000 rpm and I agtee with others 15 pitch plus stainless is probably to big. Theres lots of varibles(llts of reading),when you really want to dial in props...Id concentrate on getting your motor running in the proper range, Id bet a 13 in good shape is going to be close to the right prop.

 

[KevinWI]

C'mon man....I've got a $250 Amazon gift card burning a hole in my pocket and I need a new prop!

 

[Zum]

C'mon man....I've got a $250 Amazon gift card burning a hole in my pocket and I need a new prop!

Was going to put a link for a tiny tach from Amazon but they look to be atleast twice the price of what they should be. There like 50 bucks non Amazon.
There are cheap chinese knock offs for like $20, ive had one in the past, worked okay for me.

 

[MrGiggles]

Was going to put a link for a tiny tach from Amazon but they look to be atleast twice the price of what they should be. There like 50 bucks non Amazon.
There are cheap chinese knock offs for like $20, ive had one in the past, worked okay for me.

A Sierra tach is only about $80. Not hard at all to hook up, a little more involved on a tiller outboard but still not bad.

 

[Crazyboat]

What size/type of boat, what RPM, weight of boat that you usually run, get those answers and reach out to
https://propgods.com/
Ken will be able to tell you exactly what you need.

 

[thill]

I recommend that you first try a 10-1/4" x 13P stainless, or whatever diameter comes in 13P. Typically, stainless will have better cup and higher performance, despite having the same numbers.

IF you go stainless and jump to 15P, you will probably lug your engine, which can damage it.

Be careful when testing props and buy from somewhere you can return, and try others if you don't like it. I have a local marina that I know, and they will give me several, knowing I'll take care of them, but I've also done at West Marine and Amazon, due to the easy returns.

Once you find the right one, you will instantly know it.

 

[Crazyboat]

Bear in mind a SS prop won't flex like an aluminum one and the same dia/pitch prop will turn slower.