WOT Issue

Hello, I have new MFS40A and from the very beginning the maximum rpm at wot were 4200. After adding trolling motor, trolling battery etc the maximum now is at 3900 with me alone.
I very rarely used WOT since it only increases the speed only by a couple of miles from lets say 3400 -24 mph at 3400 and 26 at WOT.
I am trying to understand if my prop is simply way too high in pitch or something else is wrong. The main concern is that I am overworking the engine.
The prop is 11.4x12 for moderate loads.
The boat is aluminum RIB 14 ft , pretty deep V -about 170 kg according to specs, plus motor 95kg or close, trolling motor with batter about 50kg, console - about 20 kg maybe, and all the other stuff is probably extra 20 kg plus me about 80kg. oh fuel tank 24 litres. So about 440 kg. I feel like it is not a "moderate" load at all.
The lowest pitch prop I found is 12.2x7 from Solas 3 blade, or Tohatsu 4 blade 11.4x7 (which is described as " high thrust for very heavy loads like pantoon boats". Which one should I get if it seems as a prop issue? Or is it something else?
Any advise is much appreciated, thank you.

Is the Tohatsu HT prop a 4-blade?

pvanv said:

Is the Tohatsu HT prop a 4-blade?

Click to expand...

Yes, it is 4 blade

OK, those are usually for barges, etc. Yes, you'll get full RPMs, but maybe not much speed increase.

Thank you, would not 4 blade prop produce less rpm compared to the same pitch 3 blade prop? I saw something like "switching to 4 blade will reduce rmp by 300-500 so it should be compensated by reducing the pitch", not sure though.

Correct, but it's a low pitch prop.

All right, thank you, makes sense.
I think I will try Solas 3 blade prop with 7 pitch first. It is basically half the price of Tohatsu 4 blade prop.
If it fails to get me to at least 5000 rpm at WOT 4 blades we go or I am going on a diet.

Hi everybody,
got the new prop with much lower pitch, put it on and gave it a go today. It does everything it is supposed to (like was able to troll with proper speed) and then at around 4100 RMP the control box starts beeping short beeps (not continuous one but a non stop series of short beeps). The beeps go away once you lower rpms. Can anyone suggest what might be causing it?
I can not find anything in the manual. Thank you in advance.

Do you get any flashing lights? How many poles is your tach set to?

No warning lights at all, I will check the oil level one more time (replaced it recently) and tach but it seems to be showing correct numbers at idle. Can it be the issue with cooling water going out? I put T fitting into pissing tube recently for water pressure gauge and it seemed pretty narrow to me. Maybe it is obstructing the water flow out and causes overheating at higher rpms? Water pressure gauge was showing around 8 psi at 4000rpm, that seems to be too high? Thank you.

and an update: was checking oil and it smells of gasoline, now draining it and replacing an oil filter as well. Looks like even before the recent oil change there was also a bit of gas in the oil but I did not pay attention at the time. Can it be something stupid like not disconnecting fuel hose when the engine is tilted all the way up for several days? Or should I look for the nearest Tohatsu dealer number at this point? The engine is new but raising my blood pressure way too much lately.

Changed the oil and filter and took her out for short test. Same story, beeps at 4100. Checked the tach, it was set to 6P, switched to 4P and now it is beeping at about 6300 rpm, which seems to be consistent with rev limiter. So I guess back to the old prop we go. Checked the oil after half ah hour driving around, did not smell any gas this time

4P is correct. Yes, you should disconnect the fuel hose at the motor overnight.

I got out today and with the correct tach setting and old prop rmp at wot are 5900. I am going to stop tinkering with the motor ( for now) and just enjoy fishing.
Paul, I can not thank you enough for your help, thank you very very much.