Optimum Propeller 26X - 50 hp Yamaha

[Late2sail]

I'm sure this topic has been covered, but have struggled to find info particular to my question through search.
I'm wondering if anyone has experimented with prop sizes/pitch/# of blades to find the optimum "all around' best prop for a 50 hp 4-stroke set-up. I need to take my boat out to collect more data - i.e. max speed and rpm at WOT with ballast empty / full. I recently took it out an achieved max speed 14 mph (I believe my guage is mph rather than kph)? Our boat is kept at a lake and has minimal gear on board. Passengers are typically my wife and I (285# total) and 2 kids (160# total). Usually smooth to light chop. current propeller is Solas YC 25 14 3311-121-09 Any help would be much appreciated.

[Snowdancer]

I would like to know your propeller recommendation for the 26x 50 hp yamaha. Retired my 50MD tohatsu 2 stroke for a vibrating undersized Yamaha t25c .

[Herschel]

Sorry to take so long to notice this thread. When I replaced my '98 50 h.p Merc and had my new Yamaha 50 h.p. installed on my 26X back in 2013, I had been experimenting on the Merc. with 14 in diameter props with three different pitches (10, 11, and 13), finally settling on the 10 to help get the Merc engine RPM's up close to the prescribed range at WOT. Frankly, I was a little tired of constantly wondering if I had the right pitch going. When I asked the Yamaha dealer about the pitch of the new prop for the Yamaha 50, he said he had a perfect prop for the boat. He was a dealer in Trader pontoon boats, and he seemed to be really knowledgeable, so I went with his recommendation. He put on a 14 inch, aluminum, 11 pitch prop, and I have been totally happy with it. I top off at 15.3 mph with my wife and copious gear aboard. It runs in the mid 5000 revs at WOT, so I am happy on all counts. And my Yamaha has never failed to start in the past 7 years except one time in the first year when I got some bad gas. And that is my story and I am sticking to it.

[Tomfoolery]

When I asked the Yamaha dealer about the pitch of the new prop for the Yamaha 50, he said he had a perfect prop for the boat. He was a dealer in Trader pontoon boats, and he seemed to be really knowledgeable, so I went with his recommendation.

This comes up every so often - pontoon boats seem to be the best model for plugging into online prop selector programs for our hybrid boats.

[Herschel]

When I asked the Yamaha dealer about the pitch of the new prop for the Yamaha 50, he said he had a perfect prop for the boat. He was a dealer in Trader pontoon boats, and he seemed to be really knowledgeable, so I went with his recommendation.

This comes up every so often - pontoon boats seem to be the best model for plugging into online prop selector programs for our hybrid boats.

typo: Tracker boats not Trader. sorry. Herschel

[wakataka]

There are two versions of the 50hp Yamaha, the F50 and the T50. The T50 has a lower gear ratio and can turn bigger props. It's the better engine for a 26x, but for some reason many 26x boats (including mine) had the F50 installed. So the discussion below is only relevant to the F50 version.

I've recently been trying different Solas Amita 3 blade props on my F50 trying to find the best option. The previous owner had a 11.6 x 11 prop mounted. The engine was over-propped and would only turn up about 4,400 rpm. I switched to a 11.8 x 10 which put the full throttle RPM up to about 4,900, just below the Yamaha recommended minimum of 5,000. I then tried a 12.2 x 7, which allowed the engine to turn up to 5,400 rpm but the top speed was decreased just a bit from 14.5 to 14.1 knots. The bigger problem was at low speed cruising (~2,500 rpm) I lost half a knot. Also it seemed that the prop wasn't loading the gears enough. At rpm below about 1,500 there was a loud and annoying whine coming from the gearbox. I rarely run the boat at full throttle, so this noise and inefficiency at low speed was a deal killer. I switched to a 12.2 x 8, which I'm happy with. The speeds and RPMs are almost identical to the 11.8 x 10, there seems to be slightly more thrust at idle, particularly in reverse, with the larger diameter prop. I'm keeping the 11.8 x 10 as a spare. With either prop, I get full throttle speeds just a little over 12 knots with ballast and about 14.5 knots without ballast. This is with one person aboard and the boat loaded with several hundred pounds of cruising gear and fresh water.

Hope this helps.

[Herschel]

There are two versions of the 50hp Yamaha, the F50 and the T50. The T50 has a lower gear ratio and can turn bigger props. It's the better engine for a 26x, but for some reason many 26x boats

Went to my paperwork and confirmed that my Yamaha 50 h.p. is a T50 TLR. I think the TLR is similar to the Mercury High Thrust designation, but I am not sure.

[wakataka]

Yes. The T50 is a 2.33 gear ratio vs 1.85 on the F50. So the T50 turns a bigger prop and produces more low-end thrust. Same idea as the Merc Bigfoot. The T50 should be very good motor for the Mac IMHO.

[Drifter]

Would I be hijacking the thread to ask the best prop for the Honda BF50?

I'm inches away from importing a tatty old 26X. The boat dealer says this:

"We have talked to the owner once again and get more information about the condition of the boat.
Regarding the engine, the boat has an original 3 blade propeller and runs without any problems with it. The owner tried to replace the propeller with a 4-blade propeller which makes the boat go faster but sets an overheating alarm off if you run the engine higher than 3,000 rpm.
Since the owner is running it below 3,000 rpm, he still prefers a 4 blade propeller and has been using it like this for several years. Original 3-blade propeller is included in the sale as well.
The owner hired a mechanic and tried to figure out if there are any other problems that might cause the alarm go off, mechanic dismantled the engine, checked everthing and confirmed that it works fine. He assumed that the 4 blade propeller might be inhaling some air with water when running higher than 3,000 rpm.
Anyway, the owner is using it on low rpm with a 4 blade propeller without any problems and says the engine can run for a long time without any problem."

Does the above make sense to you guys?

Thanks

[Tomfoolery]

Would I be hijacking the thread to ask the best prop for the Honda BF50?

The original 3-blade was an 11-3/4" x 10" pitch. My engine runs just shy of max speed with no ballast.

I've also used a 4-blade Solas, 11.8" x 9" pitch, with similar results, but it howls between 2000-3000 rpm. Better hole shot for pulling a wakeboard, but not much fun for slow speed noodling.

Here's a thread on the topic, with pictures of my two props somewhere in there.

viewtopic.php?f=9&t=26625&p=330868

Oh, and if it's overheating with the 4-blade, it's possible it's too much prop for the boat/engine combo. Lugging the engine will result in high heat generation coupled with low water flow. Not a good combo, which is why it's recommended that the prop should load the engine to the recommended speed range at WOT. Running at lower engine speed with a properly sized prop will put substantially lower load on the engine, while an oversized/over-pitched prop will put high torque load on it at low engine speed, and won't allow it to get into the recommended max speed zone.

[Drifter]

Cheers! That's an interesting read, despite the numbers not really meaning anything to me yet.

Wonder if the whine mentioned is some cavitation or something? It does seem to make sense that the current owner is happily poodling around with his 4 blade, though for me I think I'll return it to the original. My plan is to sail for fun but motor home on plane, as there are thunderstorms frequently in the late afternoon here, so WOT is probably more likely to occur than below 3000

[Tomfoolery]

Cheers! That's an interesting read, despite the numbers not really meaning anything to me yet.

First number is outside diameter.

Second number is the theoretical distance it would travel in one revolution if there was no slippage. Like a screw.

Larger diameter contacts more water due to larger blade surface area and higher tip speed at the same rotational speed. Higher pitch moves more water per revolution due to, well, higher pitch. So it's a balance between diameter and pitch, but you can't simply adjust one without considering the other. A small prop with high pitch will likely cavitate and overspeed the engine. A big prop with shallow pitch will likely not go very fast and overspeed the engine. It's actually pretty complicated. Look at some prop web sites for more (lots more) detail.

The howl is not cavitation because the boat and prop are moving too slow, nor is it ventilation, which is the prop sucking air from the surface, as the anti-ventilation plate is well below the surface. It's just a something resonating within about a 500 rpm range. Others with the same prop have reported the same thing.

I use the 3-blade most of the time.

[Drifter]

Well I trust old man MacGregor to know his own boat and if it came with a 3 blade then that's good enough for me

My impression the important bit is to keep the weight low, only carry what you need and keep it all lightweight stuff?

So i best work on my lock-down belly then....

[Catigale]

Don’t let your props cavitate, the the Russians can hear and track you.

Especially in Red October...