I have a GTR 37 EFI hanging on a 1852 CC, bone stock right now, factory 3 blade ( 10.5 P prop is what the folks at GTR told me it was anyway). Boat is a flat bottom with a hunt deck and is setup with a tall transom to run a MM on it

With me 235 LBS a 45 quart cooler w/ ice / beer 50-ish LBS (rear deck ) 6 gal gas tank ( under front deck ) and your typical crap that stays in the boat 50ish lbs ( life jackets, tie out lines, brush clamp, boat gun, box of shells, paddle ect ) Cranking bat, trolling bat and trolling mtr. I am getting about 25 @ 3650 RPMS. 22, ticking 23 once in a while when I put my buddy in it he is about 250, still right at 3600 RPMS. I guess my question is does this seem about right or does it seem low, speed and RPM wise. Trimming it to right at 3600-3700 gets me my best speeds, trim up anymore and RPM will increase but prop blows out and it slows down, trim down any and the motor starts to bog and slows down. I am not hugely concerned about having the fastest boat or breaking any speed records but it also seems to lack on the bottom end, just dont have any balls. I have heard / read that GTR had some issues with their wiring harnesses and they were effecting the motors performance. Is this a true statement, has anyone else experienced this or benefited from having the harness replaced? Motor has right at 10 hours on it. Just not broke in, need to put more time on it before I have anything done?? This is my first dance with a MM, I have always had OB's so that is why I am asking you guys here that have more experience / knowledge than me in this dept.

I looked at those SeaArk mud runners when they first came out. The reviews from those that purchased one was that they where slow as fuck.

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I'm not a fan of that 10.5p prop. It's a lot for a stock motor to turn. Would also explain your low rpms. That's assuming the transom is setup correctly for a gtr.

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Great job on presenting your problem and asking the question. Hopefully you'll get some useful information and advice out of that!

Sea arks are suppose to be slow so 25-26 seems maybe a little low for a stock 37 with that prop. Your RPMs seem a little low, what does it do when you run 4000-4100 RPM's? Have you ever ran a different prop?

You have an older prop. You have either a 10P or 11P. It almost sounds like an 11P with the low RPMs, But you should at least get to spin 4k or close to that. Some setups turn more or less depending on the hull. I would suggest getting it looked over at a service center.

Having similiar issues with my new EFI PD, been at shop for weeks now. Only getting 3800 rpms at best trim. Motor doesn't have near as much balls as my last 37EFI. It is a new model Briggs motor. Does your have the little red light on the tack? Like a check engine light?

Gator Tai does not install a CEL

@Roostertail, I can trim it up to where it will get 4k + on the tach, but when I do it is trimmed up so high that the prop blows out and the MPH starts dropping. EDIT: I have not tried any other props other than the scenario below. I really dont know what to try without just taking a shot in the dark.
V V -------- V V
@Maxxis The prop that came on it was an 11p, it had bad vibration and best speed I got out of it was about 23 solo at about 3450-3500 RPMs. I called GTR and asked them about it and they said that they had a bad batch of props come thru and the vibration was actually causing blades to shear. They asked that I take mine off and send it back and they would send me a new one, I thought he said that it was a 10.5P, but may well have not heard him correctly, could have said 10, I am not 100% on that.

@JPHIII at least in regards to my motor Maxxis is correct, mine does not have the CEL.

I see now. Your pic is the old prop, The newer ones are the 10.5 Yes. If you want it to work well Send it to Chris Courville, he makes them perform better.

I have a mud runner too mine is a 1748 though but ive always had my best speeds with a 2 blade every three blade prop I have ran has been a POS. Try a big blade on it. I have on if you wanna run it.

Hotsauce, I may take you up on that I am only about 1.5-2 hours from Blackshear, depending on where exactly you are. I am back and forth thru there a good bit I go to Seminole pretty often to see family / fish and whatnot.

Thanks everyone for the responses, and to everyone for future responses as well.

Well I ordered a Big-Blade today, we are going to see how it does with that prop on it.

I will reply back end of week and see if it helped any.

Not sure if anyone on here is from Mid-GA but if you find yourself up near Sinclair in Milledgeville Saturday they are blowing up the smokestack at Plant Branch sometime between 8 and 2. Would be pretty cool to see a several hundred foot structure brought down.

Got my BB in Thursday, and was able to go the river to fish for a while today. Big improvement It was me and 2 buddies and our somewhat conservative fishing loads. I would guess between 650 & 700 LBS of people in the boat, cooler 50-ish, normal boat BS ( paddle life jackets anchor ect) 75-100 total of fishing gear, cranking batt and trolling batt, 6 gal of fuel.

It stepped all 3 of us pretty decent and down river we were steady 23, and hitting and holding 24 for a few secs at a time.

I dumped Blake and T off on the sandbar and took a run at it with all things being the same except the fishing poles they were using at the time and them not in the boat. It stepped quick as hell, probably 2-3 boat lengths and topped out at 28.

I was not able to get any real good data as far as RPM's and all because our river is extremely low so I had to have my eyes to the front to keep from hitting anything crazy.

River level was reported at .61' this a.m. full pool is somewhere near 10' and flood stage is 21'. In bad need of some rain. Long story short, a factory BB did alot for my boat.

Thanks for the suggestion Hotsauce.

Just got a 17' mudruuner by sea ark
With a 37 gtr
With me 220 brother in law 280 we ran 26 bumping 27
Me by myself i run 30 turning 4200 rpm