Speed under motor

[Torontonian]

Hi Guys,
I have 2005 Mac 26M with 50 HP honda motor. Have tried max speed without water ballast, dogeboard and rudders up. Got only 9 knts with 4000 RPM. What could be a problem?
Thanks,

[beene]

Welcome

50 on an M should get you 15kts or so

9 kts is ridiculous

4000rpm is far too low

what is the spec.... I am guessing 5500 to 6500

So, at the very least over propped

Meaning you need to get a prop with a smaller pitch, like a 9 inch maybe.

What prop do you have now

G

[Tomfoolery]

What prop do you have now

Look on the hub or the blade of the prop. My BF50 has an 11-3/4 x 10 (diameter of the prop tips by pitch). And I agree that it's over-propped, assuming the tach is accurate. The speed range for the BF50 is 5500-6000 rpm.

[Russ]

As mentioned, prop is probably the most likely culprit. Too large and bogging down the motor.

Also, is there a lot of junk on the bottom of your boat? How are you measuring your speed?

[Johnacuda]

How is it running? I popped a plug wire on my 3 cyl. bf50 and couldn't break 10 kts. Turns out Meatloaf was wrong; 2 out of 3 is bad.

[Torontonian]

I do not see any marks on my prop, have a spare one with 11-3/4 X 10, 299x254 marks on it. Will try that one.

[Russ]

I do not see any marks on my prop, have a spare one with 11-3/4 X 10, 299x254 marks on it. Will try that one.

YES. Try that one.

Weird the prop has no markings.

I just switched out my prop. Amazing how simple that was. I was ready with all sorts of tools. Just needed pliers to remove the cotter pin.

[Y.B.Normal]

I just switched out my prop. Amazing how simple that was. I was ready with all sorts of tools. Just needed pliers to remove the cotter pin.

I hope you torqued the prop nut. Not torquing it can cause serious (and expensive) wear to the prop hub and shaft. The torque specs should be in your owner's manual.

[Falcon6086]

I am also curious as to what prop would be the best. The person i bought mine from switched out to a 4 blade prop (C4x11.4x10) and curious if a 4 blade is better than 3?? I have a 98 Honda 50 and i feel like it is struggling. but when i gave it un ballast, i hit 24 km/h i think up around 5500 but it felt like it was to much.

any thoughts or input

[Tomfoolery]

I have a 98 Honda 50 and i feel like it is struggling. but when i gave it un ballast, i hit 24 km/h i think up around 5500 but it felt like it was to much.

That's just under 15 mph. I get 16 mph with the same engine on my '99 . Engine speed range is 5000-6000 rpm, and mine runs around 5800 rpm WOT with no ballast (mast up), so you may be leaving a little on the table. My 4-blade is almost a half in larger diameter, but with one inch less pitch.

But as I said before, I don't know how the 4-blade compares to the 3-blade. I think we're taking a trip to one of the big Finger Lakes in the early fall, so maybe I can do some controlled 2-way speed runs then, to compare the two props. Now that my curiosity is piqued.

Oh, and you should put the boat and engine models in your location bio, as it makes a difference in how people answer, since the and are quite different, including both sailing and motoring performance.

[Russ]

I just switched out my prop. Amazing how simple that was. I was ready with all sorts of tools. Just needed pliers to remove the cotter pin.

I hope you torqued the prop nut. Not torquing it can cause serious (and expensive) wear to the prop hub and shaft. The torque specs should be in your owner's manual.

Nope. The original prop nut that's been on there for 6 years unscrewed by hand so I did the same with the new prop.
Now you have me questioning and I will look in the manual for specs.

[Tomfoolery]

Now you have me questioning and I will look in the manual for specs.

BF50 Installation Manual, to tickle your curiosity.

[paul I]

I just switched out my prop. Amazing how simple that was. I was ready with all sorts of tools. Just needed pliers to remove the cotter pin

I hope you torqued the prop nut. Not torquing it can cause serious (and expensive) wear to the prop hub and shaft. The torque specs should be in your owner's manual.

The procedure I recall is to lightly tighten the prop nut with a wrench, then loosen and tighten hand tight.

[mastreb]

Is your hull clean? Bottom growth will also drag a boat's top speed way down.

[Johnacuda]

I am also curious about how heavy you load your boat. I tend to run pretty light and notice a difference when I try to do a speed run with extra passengers and gear. I should leave the mast at the dock for one when I am wrapping it up this fall.