Question about the proper prop. Paul, you out there?

Hey Paul. Hope all is well in 2013. This post is in reply to a previous post titled "M40C wont accelerate past 1/2 throttle". Yeah we went over the usual rigamarole about carb being clean and troubleshooting with the manual and all that. Then it occurred to me....the previous owner of my boat had an aftermarket prop on the boat. So here's what I've got. It's a 14ft. aluminum flat bottom jon boat with a tohatsu m40c on the back. With 2 grown men in the boat and mostly calm water, it will only get up to 15mph. I need a little bit more than that to run to duck blinds and fishing holes. So I looked at the prop and here's what I've got. It's a stainless, 3 blade with about a 10.5in diameter. Stamped on it is as follows "Quicksilver 48 79792 A5 12P". Then spin it over and the next blade has stamped on it in a larger font "Y1P942". With my boat in the water, the motor sits straight up and down. The bottom of the foot extends 13in below the bottom of the boat. So what im looking for is the proper prop to where I can atleast hit 25mph. I mean a 14 footer with a 40 should definitely haul some ass. Please help. Thank you in advance. Jarrid

Jarrid,

You will want to see whether the antiventilation plate is even with the bottom of the boat. Sounds like you have a 12 pitch prop. Toss a shop tach on it to see if you are hitting the correct WOT RPM. Feel free to drop me an email at the office: [email protected] and we should be able to help you out.

pvanv said:

Jarrid,

You will want to see whether the antiventilation plate is even with the bottom of the boat. It should be parallel and even with the bottom of the transom (within an inch). Sounds like you have a 12 pitch prop, which was marketed for the Merc 50 hp motors. Toss a shop tach on it to see if you are hitting the correct WOT RPM. Feel free to drop me an email at the office: [email protected] and we should be able to help you out.

Click to expand...

You may be over-propped. Remember that SS props behave like a steeper pitch, because they flex less... so your 12P SS prop may be behaving like a 13 or 14P. Currently, Tohatsu America offers 3 different props for that motor: a 7.1 pitch 4-blade, and the 8.7 and 9.9 pitch 3-blade props. Tohatsu Japan used to also have 11.3, 11.7, 12.7 and 13.9 pitches, but they were so unpopular in the US that they are NLA.