72 402 merc, prop size confusion

[dkonrai]

1972 402
the motor has a bent prop housing, and if i spend 50 bucks to true it up, should i just get a new prop?
now this is where im confused.
boat is a 14 foot bayliner i 1986 (i think the dry weight is 600?)
me 200
motor 150
gas 12 gallons 80 pounds, so around lets round it out and call it 1200 pounds.
to go 40mph @ 5500 rpm i would need a 10-19 prop? but would this thing ever plane?
11" prop ok? like 11x15?

i fish/troll but like to have some wind in my eyes (no hair so, its the face/eyes)
dino

 

[Maxz695]

Re: 72 402 merc, prop size confusion

Is the LU bent at the prop or is the prop is bent? give more info to get some help what size prop do you have now? have you driven this boat to see what RPM you have with a normal load.14 ft bayliner with a 402 2 cyl 2 stroke.. I have a 79 40 hp 2 cyl 2 stroke (ther year they dropped the 402 identification and classified as a 40 hp) I have it on a 17 1/2 foot bass boat/ my prop is 11 X 12. I get about 4900 rpm max and did some asking around here and was told it should be more like 5200 - 5500 RPM so after i made a decision from all the posts I decieded to go to a lower pitch to gain RPM and lighten the stress on the engine. I,m waiting on my new prop it,s 12x11. I,ll see where i,m at there hopefully dropping 1 degree in pitch will help alot if not I have to go to a 10 Pitch

 

[Moody Blue]

Re: 72 402 merc, prop size confusion

1972 402
the motor has a bent prop housing, and if i spend 50 bucks to true it up, should i just get a new prop?
now this is where im confused.
boat is a 14 foot bayliner i 1986 (i think the dry weight is 600?)
me 200
motor 150
gas 12 gallons 80 pounds, so around lets round it out and call it 1200 pounds.
to go 40mph @ 5500 rpm i would need a 10-19 prop? but would this thing ever plane?
11" prop ok? like 11x15?

i fish/troll but like to have some wind in my eyes (no hair so, its the face/eyes)
dino

You'd get more attention and better response if you posted this in the PROPS section. I think you would be hard pressed to see 40mph with a 40hp on a 14ft Bayliner though. Without a tach, you really have no idea what prop you need. You could run a 23" pitch for the speed but would take you all day to get up to speed and you would kill the motor. The motor needs to be propped for the spec'd max RPM under typical load.

Maxz695, prop pitch is specified in inches, not degrees. That is, for every revolution of the prop, it theoretically will travel 15" (as an example) forward thru the water. In reality that is not achievable because of a number of factors. As a general rule of thumb, RPM's will increase/decrease about 200rpm for each 1" change in pitch.

 

[Maxz695]

Re: 72 402 merc, prop size confusion

TY for the info, and as you stated in your reply a 17 P as opposed to the 12 P i,m running now would make a slug out of it and stress the motor dramaticly, but give me more top end whenever I ever got there. So thanks for the correction on it being in inches rather than degrees. Some people learn something new everyday. I learn more and more everyday on here. This is a good thing. Thank you again and iBoats for this site

 

[dkonrai]

Re: 72 402 merc, prop size confusion

sorry for the delay. here is some pictures of the 402, showing the bent housing (probably dropped?) as well as the prop. i wanted to get the prop rebuilt, but wasnt sure if i was wasting time and money.
the boat is a 86 bayliner, 14 foot
motor is a 72 402. and it runs pretty good considering it was on the side of a house since june.
dino

my old motor was a force 50hp/2 cylinder. i figured the merc should have the same performance, but a little more reliable?
dino

 

[donzi gt230]

Re: 72 402 merc, prop size confusion

A bent blade would be an issue, that little ding in the diffuser is of little consequence. Take it off and straighten it with a hammer or pliers or whatever. It doesn't have to be perfect. If you can make it look good, it's good. On some props you can actually remove that diffuser ring, but there shouldn't be a need to.

 

[dkonrai]

Re: 72 402 merc, prop size confusion

donzi,
thanks. will update you all when i get this thing mounted and in the water. the cool thing is it was sitting
in a side yard since june. and it fired up so cool.