I have a 2004 27 hp MBLT with a kohler motor. Its on a 16x54 boat (actually an old bass tracker that I gutted). I bought it used a couple years ago, and its the first mud motor I've had.

Anyway, I was finally able to get some GPS speeds with it a couple weeks ago and was hitting a whopping 10 mph. That got me looking at the prop. It was a mud buddy prop (anyone know when mud buddy's parts dept. became BPS . . .that may help determine the age of the prop), and it was worn quite a bit. It was on the motor when I bought it. It was less than 8 inches in diameter.

I ordered a new 9x7 from BPS and swapped it out this weekend. We took it out last night, and it seemed to have alot more grab, but my RPMs dropped significantly. No GPS this time so not sure about speed, but it didn't feel like a significant difference. With the old worn prop, I was getting ~3550 rpm WOT in clean water. With the new prop, I was getting ~3050.

Do I need to adjust the throttle to get back up over 3500 rpms? It was pretty surprising to see that big of a change in RPMs. I would prefer to be conservative with the motor to prevent a kaboom, but I don't want to leave safe performance on the table.

Would the wrong transom height affect RPMs at all? Or just speed performance?

Thanks for you help!!!

Scott

Thanks for the reply.

If i remember right, the transom is about 17". I used to have a long shaft outboard with a jack plate on it and I was able to jack it up above the "normal" height, but I couldn't get a short shaft outboard to work.

It (transom) also has quite a bit of angle/overhang to it. In other words, the top of the transom is further back than the bottom. As I think about it, that might cause a little more downward force on the bow than a normal straight transom would have, causing worse performance.

The load was 2 guys, a dog and about 4 dozen decoys, as well as a medium size fold down blind and 2 batteries.

I'm not hugely concerned about speed as I typically don't make long runs, but if I can go faster I'd like to be able to have that capability.

Thanks again.

Scott

I have the same motor, I get near 20 mph by myself on a 1648 grizzly. I do get better performance with a 9x6 prop versus a 9x7. This might help you but I believe that transom aft angle is probably the reason you are not getting optimum performance. If the transom is higher than 17" then that is also a negative factor.

Dosent sound like you have a tall transom, try to measure it on a right angle to get the true height of it though (not how tall the piece of aluminum is). Id try to get your RPMs back to normal and see where it's at. The angle of the transom (for LTs) can usually be compensated for with cavitation plate adjustments, is your cav plate running right under the water as it should?

My experience with longtails has been better with narrow boats, that 54 is a tall order. I think if you could tweak your RPMs and get 15 it would be a success on that boat.