Speed under power - Merc 50hp 4 stroke - what is your speed?

[bscott]

You should always prop you engine to the WFO range as per the manufacturer--if you cannot meet the range with an average load then you are overpropped and will lug your engine even at 1/2 throttle. Lugging can cause detonation, over heating and poor gas mileage. Find a prop shop and have them repitch your prop with the understanding that they will repitch it again until you can find the pitch that works--they will usually do this at a discount OR buy a new prop with the understanding that they will exchange it for a different prop provided you do not damage it. Go to iboats.com for prop info.

Bob

[dive4it]

I agree with the last two posts. I would love to send my prop back since you can't tell it's not brand new (I only have ten minutes on it). I think I'll just order the new one and keep this as a spare in case of damage on the water. The tach on my X is from the orig. Nissan motor I believe, not sure of it's accuracy. I have a tinyTach left over from an airplane project that I'll see if I can dig up....that's should give me a good reading when I set it up for testing. After all, what's a couple hundred bucks right?

JT

[dlandersson]

I have a 50HP Merc and I get 16 with the ballast out and the rudders up.

Finally got my 26X all fixed enough to go out. The engine has just been gone over at the Mercury dealer as the carbs were all gummed up. It tests well on the dyno.

The person I bought the boat from said the previous owner had changed the props, but I didn't think much of it at the time. Now I know what he was talking about.

The WOT (Wide Open Throttle) will go to about 4500 RPM. I understand the engine should go to 5500. The prop currently is a 12.5 x 8. The old prop (in a box) is a 12.5 x 10 which I think is the original.

The boat does 9 knots according to the GPS. The Merc dealer says that the engine is ok like it is and I shouldn't be concerned. But one of the the reasons I got the 26X was the under power speed. I was expecting at least 12 knots or more.

Is this a concern? The ballast tanks were full at the time. After reading here, not sure if they are supposed to be full or not for under power? Does anyone know?

What speed do you power at?

[DaveB]

I have the Solas 4 blade 11.8 x 9 pitch on my Honda 50. Does 16.4 mph in waves under 1 ft. @5800 rpms. It sings between 2200 rpms up to 2800 rpms.
I cruise at 3000 rpms and at 2000 rpms 5+ mph so singing is not a concern.No paint on bottom.
I have 425 lbs persons, 3 batteries,refig. coolers that total 200 lbs. 3 anchors with rode and chain and bunch of other gear that weighs in around 600 lbs including water tank.
Dave

No bottom paint? Tach not reading correctly? Tailwind? What's your secret?

The Suzuki DF50 is rated at 5500-6500 rpm, if I'm not mistaken. Whatever it is you're doing right, let us know, as I want to do it, too.

I'm getting 16 mph with small waves, 3 POB, mast up, no ballast, and a Honda BF50 with 11-3/4" x 10" 3-blade prop. Maybe this weekend I'll be able to take my new Solas 11.8" x 9" pitch 4-blade prop for a spin at speed.

Oh, and I have old bottom paint, and a bit of slime, all the time.

[vitger]

I just tested my 2000 26 with a 50HP Nissan TDLI ( I think) yesterday and with one person, empty ballast, one full tank and two full water tubes plus some gear I could not get above 12.5 knots. Seems like the engine does not really do much after 2/3rd of the throttle on mine either. Gas mileage is not great. I was wondering about being overpropped as well. Next time 'll check my prop (but I think it is original manufacturer recommended, slightly chipped) and also check my RPM. Will also try to see what my GPS reads, although I noticed some difference between the tach and the GPS last year.

[vitger]

Has anyone tried to play with the trim at WOT or would that be counterproductive?

[Catigale]

Playing with trim a back room topic obviously....

You aren't going to get 500 -1000 rpm changes T WOT with trim adjustments....IMHO

[DaveB]

Maybe he will but will only cause cavitation, reduction of speed and bring the Bow up. Causes RPMS to go up but less performance.
Dave

Playing with trim a back room topic obviously....

You aren't going to get 500 -1000 rpm changes T WOT with trim adjustments....IMHO

[mmason_az99]

'96 50 HP Mercury, recently only running approximately near 9 . This after a carb kit and lookover from the marine mechanic. Unfortunately, I have to take it back in. Grrrr. But such is life with a 2 stroke .

[Russ]

Interesting comments about lugging the engine.

My Suzi DF70 came propped from BWY with what I believe is the correct size wheel according to what others have. However, I don't get over 4600 RPMs out of this thing. The boat seems plenty fast and maybe the tach is wrong.

I'm also at 5,000 feet altitude and engines don't breathe well up here. I always figured it was the lack of O2 that was keeping it down. Maybe I should try a smaller prop.

Lugging huh? I didn't realize this was such a problem.

[bscott]

Interesting comments about lugging the engine.

My Suzi DF70 came propped from BWY with what I believe is the correct size wheel according to what others have. However, I don't get over 4600 RPMs out of this thing. The boat seems plenty fast and maybe the tach is wrong.

I'm also at 5,000 feet altitude and engines don't breathe well up here. I always figured it was the lack of O2 that was keeping it down. Maybe I should try a smaller prop.

Lugging huh? I didn't realize this was such a problem.

5,000' above sea level = 15% power loss. You need to drop at least 2" of pitch. When I run my E-tec 60 at 5,300 in Denver I am running a 14 X 9 and manage 5,500 rpm, 16 knts. My home lake is at 8,200' and using the same prop can only get 5,000 rpm My prop guy cannot repitch the 9" any lower.

Bob