Curious about you guys who write that they’ve trialed 3-4 props before they chose which one to stick with. They aren’t cheap so are you all buying the props and selling the once’s you don’t want to keep, just keeping them on the shelve or are you able to get loaners from prop stores that as long as you buy from them they will let you try out a few options?
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Great topic, just a quick FYI, moved to the proper section. Cheers!
Thanks iMacattack, sorry about that. I quickly scanned the topics and missed that topic section. Cheers for moving
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I am also curious on this topic. Propping can be more of an Art than a science at times.
I think a lot of people are un aware about how much you can really dial in a prop with a reputable Prob Shop. If you have the luxury of having a local Prop Shop that you can bring or call in and give all of the information (hull, length, motor, prop, wide open throttle rpm, and load) they will be able to get you a prop that will be at least good enough, then really dial it in to how you want the boat to run. I personally like having an old or cheap spare prop on board just in case. I think the best approach is getting up with a SME so you aren’t running the trial and error alone with buying and trying out props. I do know some places let you try and return props if it’s not your fit.
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No prop shop locally to speak of. I just need a stainless prop for a Yamaha 25. Is there even going to be a noticeable difference between props on a boat that runs 25mph? Do t necessarily need hole shot- just want efficiency. Agree with OP- I can see how testing pros gets pricey quick!
Snap, also looking for a prop for a 25hp 2-stroke Yammy. Only managed to run the boat once before it quit on me. That’s a whole different story but once I figure that out I plan on getting some RPM numbers and was hoping to get a prop that could maybe get me a slightly higher top end speed. Also hole shot is not important to me and I was around the 26mph mark. Figured once I got a better prop I could get a Permatrim, which I believe is an anti ventilation plate rather than a foil.
A prop that matches your boat and needs makes a huge difference over a stock prop unless you got real lucky. You might get a lot of improvement calling the tech guys at Powertech. I believe they will swap props out as long as it stays in new condition. I don’t know the details.
Chip
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Well that’s a rabbit hole… And long dark deep one.
You can basically go off the shelf or custom. And not all off the shelf props are created equally either.
The main thing to consider is budget and needs.
For me, I don’t want or need a full blown custom prop, not that the boat couldn’t benefit from it, it just doesn’t fit my needs or budget.
That being said, you can be money ahead having someone knowledgeable (ie: baumann/foreman/prop gods) ect.. build you a prop, because like you said, “trying” 3/4/5 props generally means buying 3/4/5 props.
However some shops, such as Ken at prop gods does offer test props at a small fee if he has one that fits your needs.
If you’re just after a general use prop, Amazon and their return policy can be your friend.
For a 25hp 2s your going to likely be in the 11-13 pitch neighborhood, so start there.
If budget is a concern, get an alum Solas 12p from somewhere with a return policy and giver a try, assuming you don’t have a baseline to start from.
Personally I’m running a 4b Stainless Solas (12p) with a pretty heavy cup, that I did myself, on my 25hp 2s Merc tunnel boat.
Wot sees 30mph solo. It’s taken a lot of trial and error to get it there, but I’m happy with it.
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@ MikeCockman Cheers for the info fella. Curious how many props you trialed before you kept that one? What was your main reason for cupping the prop so much?..to lower rpm’s?
My skiff is a tunnel skiff, so I have to have a cupped prop for it operate properly. But yes adding cup will reduce the RPM.
Usually what I do is establish a base line. So get a tach, and run the boat to see where you are at. If you need more RPMs get a lower pitch, if you need less RPMs get a higher pitch.
If you’re experiencing blow out or cavitation you need to either add cup or adjust engine height, both of which can affect RPMs.
There’s a lot that goes into prop tuning which is why most will recommend a prop shop.
The 2s 25hp Merc standard prop was 13p. So that’s generally the baseline for that engine. The Yamaha you’re running id imagine is in that area as well.
As to how many props I tried, not many. I’ve had several of these motors and several similar skiffs, so Ive learned what works on them.
It’s usually a 12p 4b alum, or a 3b alum 13p, but this tunnel boat liked a 13p 4b alum with added cup to get it right.
I ran that prop for about a year or so, and recently changed to a Stainless 4b 12p. The 12p does everything the 13p alum prop did, but better, same top speed, but better holeshot and lower planning speed.
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100% agree have to have a tach to even begin to establish a baseline to build on (wot max rpms),…then a ton of other variables (fuel amount, people on board or solo, gear, etc.) Ive always found where I have to just pick whats the best all around compromise, go fish, be happy.
The other thing is im not putting my PowerTech on in Crystal River / Homosassa 
(cheap aluminum is used), but I will in 10k / Estero / Pine Island
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@ MikeCockman and @ Kirc, thanks fellas. Have a small throw on RPM readout although sometimes those things give goofy numbers but I’l see if it works when I can get the engine back up and running.
Roger that on the info Mike, appreciate the tips and explanation. I’ll be honest I’ve only just got into owning a skiff and working on outboards, in the last few years so the prop/anti-ventilation plate/cavitation/engine height is a giant aqua Soduku puzzle for me and I can see how it gets expensive if trying to learn all this stuff by trial and error. Happy to do a little of that, just don’t need to fall down every pit hole.
I do have a jack plate (manual), I do have hydraulic tilt and trim and I do have electrical trim tabs so I guess I have a few variables I can play with but sounds like I need some RPM numbers before I do any spending.
Here is the prop thats on the motor now and what you’re all telling me, this might not be the original prop. What would be the 'general characteristics of a 9-7/8 x 11-1/4 prop? I have no idea what the F means…maybe it’s just the series of prop?
So where would you start on a 25hp Yamaha 4 stroke tiller. No tach. Just match what’s already on there?
You should be able to throw out some of the goofy numbers because of what the engine sounds like and what the rpm range for the motor is. If you are hitting the rev limiter, you rpm shouldn’t be 3000. You probably won’t go over 6500. A lot of the time the goofy number is half of what it should be. Check the settings. Make sure the pigtail is wrapped around the plug wire well.
Get some good rpm numbers, get a gps speed from your phone app or chart plotter and maybe time how long before it planes?? Call PT or one of the other contacts and let them guide you. They may want to know how long the boat is, what type hull, the existing prop and maybe the weight of the boat. A ss prop will affect the pitch needed and a 4 blade will affect the pitch needed. Don’t just go buy a prop when we have experts that will give you lots of information for free that can save you bundles.
You can definitely do better than that prop if the goal is to get the motor higher.
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As already mentioned, get your max rpm’s at WOT & top speed. Then you’ll have an idea of where you need to go.
Unfortunately the “tiny tachs” can be erratic, but you can get a good idea and weed out most of the crazy numbers. I’ve also got a multimeter with RPM input I’ll use for confirmation.
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OK, so I played a little work hooky this morning, if you can call it that being self employed and seeing a weather window (flat calm) for a few hours of engine testing. I did start a post on MS and I’ll probably start another one here just to thanks to the few folks who steered me in the right direction in getting the engine up and running again. It’s purring pretty.
Just for the record, this is my second day on the newly built boat and I’m in the steep learning class on all of this…so for numbers wise this is what I was getting…
The best I got was at WOT with some trim and some down tabs with the wind perfect and the rainbow shining, the max I could get was 29mph at 5955 rpm. I would say that was short lived and 90% of the time I could easily get 28mph at 5850 rpm. If I slightly tapped, even just one on tabs or the engine trim or wind direction changed etc it would alter the numbers 100 rpm and/or 1 mph. Sometimes it was 27 mph at 5850rom and sometimes it was 28 mph at the same rpm. Time taken to get on plane is around 3-4 seconds.
So there you have it, please start educating me, I’m all ears…
@ TXJM Thanks for the input fella, truly. I’m just holding off on contacting a prop shop for now, simply because I just don’t want to waist someone time when it will probably be a $100 aluminum prop sale. Maybe in the future I’ll splash out on a SS but I’m sure anyone doing all that work to figure out a prop for someone would rather not for such a small sale…maybe I’m overthinking it.
28/29mph is perfect at that RPM for a 25hp. I believe 6k is max for that engine so 5950 is right on the dollar.
Keep in mind, that You’re always going to have fluctuations in speed and rpm because of winds,tides ect.. If you wanted a little more Rpm you can drop one pitch, which will give you a tad quicker holeshot, and roughly 1-200 rpm more.
@ MikeCockman. Thanks Mike, yea doing a bunch of reading, trying to educate myself. I think on these small engines you can be splitting hairs trying to squeeze everything out of such a small engine. I have a permatrim on the way as it was almost the same price for me to buy one as it was to buy the metal and get it bent. I’ll test it out with that on, and also test it with another person in the boat before and after I install it. Get some numbers and I think if anything I’ll be doing what you suggested and add a little extra pitch, keeping the same diameter and maybe tweek the height of the engine. I know you guys need everything you can get for hole shots down there on the lowest of tides but the hole shot thing just isn’t a thing up here. I’d be stoked if I could get 1 more MPH top end solo and slightly lower the rpms or barely drop current speed with one extra person in the skiff. That would be my sweet spot I’d say. Found this in the owners manual for the engine. Looks like any rpm’s over 5500rpm doesn’t give you anymore power output, just burns more gas and gives you a little more wiggle room for changing conditions but I definitely need to be able to hit that mark or a little higher, like you said with those conditions changes if I make any adjustments. I’ll post back when I’ve figured it all out and installed everything but for now I thank everyone for their input and I’ll call it a wrap…in the mean time, better go fishing!
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