5600 WOT 17p ok?

[countvlad]

motor is a 120 Johnson J120TLCEM 1989 boat is a 19' 1976 Renken CC deep V... at 5600 WOT i do about 41MPH on the GPS... the prop is a 17 pitch SS prop but no idea the make....

i looked in the repair manual and couldnt find anywhere the recommended WOT....

so does anyone have any idea for that motor what is a good WOT?

should i go with a lower pitch would my fuel and top speed increase or decrease?

right now i cruise around @4500 with the motor half way trimmed on the gauge,doing about 32MPH.. is 4500 hard on the motor or should i increase the rpms ?

thank you

 

[junior1113]

Re: 5600 WOT 17p ok?

yea your pretty good now. id run it at 5800. where is cavitation plate in relation to bottom of transom? or do you have a jack plate? doel fin? raising the motor always seems to pick up a coulpe rpms and mph. does this prop have cup to it? great motors i had a 93 140 (samething) loved that motor.

 

[crb478]

Re: 5600 WOT 17p ok?

It sounds like you are dialed in pretty good right now. You might get Hwsii to run a prop slip calculation for you for piece of mind, and you could raise it a hole to see if it got better or worse, but I suspect you are nearly maxed out on efficiency. You can run it up to WOT and then back off just enough that the timing is still advanced and you will get better mileage at nearly the same speed.

 

[steelespike]

Re: 5600 WOT 17p ok?

Yes sounds pretty close.You need to experiment to get the best cruising speed.Best can be anywhere from just on plane to 2000 rpm higher.
Fill up, do a timed run at a selected rpm then fill up.Make the time easy to devide into an hour. So you simply multiply Gallons by the time devided into an hour.Usually mileage is rated by GPH (gallons per hour) Of course aq flow meter greatly simplifys the procedure.
If you simply like a certain speed this all doesn't matter.

 

[hwsiii]

Re: 5600 WOT 17p ok?

Vlad, my calculations show you should be running a 19" pitch prop and that appears to be what you have at this time. If I run the prop slip on your prop as a 17" prop I find it is running negative prop slip and that doesn't happen, but as a 19" prop it shows the normal prop slip it should. It could be you read it wrong or it could be the prop has been reworked to a 19" but either way that is what it is acting like theoretically. Her are my numbers and that is a good matchup between the prop and the boat in my opinion.

Prop Slip

H

 

[Tacklewasher]

Re: 5600 WOT 17p ok?

I'm pretty sure the gear ratio is 2:1.

That would put the slip at around 9%.

Could probably improve a bit it you can raise the motor.

You'd like to be around 5800 but you can likely get there with setup and the current prop.

Take a picture of the stern of you boat with the motor down and post it. We are looking for where the anti-ventilation plate is in comparison to the bottom of the boat. If you are even or below the bottom of the boat, you can probably raise your motor up a hole or two and pick up the little bit of rpm before you prop loses bite.

 

[countvlad]

Re: 5600 WOT 17p ok?

Vlad, my calculations show you should be running a 19" pitch prop and that appears to be what you have at this time. If I run the prop slip on your prop as a 17" prop I find it is running negative prop slip and that doesn't happen, but as a 19" prop it shows the normal prop slip it should. It could be you read it wrong or it could be the prop has been reworked to a 19" but either way that is what it is acting like theoretically. Her are my numbers and that is a good matchup between the prop and the boat in my opinion.

Prop Slip

H

thank you for the input on this...

i actually have an aluminum 19p and brings my rpms down to 4800... but it is also a 14 diam.... the prop that i have on the boat right now i cant really tell the size because i cant read any numbers anywhere.... so i assumed its a 17p...

i dont have a plate and i dont intend to install one.... i dont think its worth spending money on a plate.... if the boat was newer it would be diffrent....

ohh yeah if im not mistaken gear ratio is 2:1.... does anyone know whats the redline ,6100,6200???

thank you

 

[hwsiii]

Re: 5600 WOT 17p ok?

Vlad, I showed your RPM should be 4,500 to 5,500 but I also showed your gear ratio at 2.25:1 , so don't believe what I say. Tackle you are right it is 9% prop slip and Vlad you should be using a 17" Pitch prop with a 2:1 gear ratio.

H

 

[countvlad]

Re: 5600 WOT 17p ok?

yea your pretty good now. id run it at 5800. where is cavitation plate in relation to bottom of transom? or do you have a jack plate? doel fin? raising the motor always seems to pick up a coulpe rpms and mph. does this prop have cup to it? great motors i had a 93 140 (samething) loved that motor.

no idea ow far up is the plate in relation to the bottom... i will measure tonight... i just looked for about $200 i can buy a jack plate so i think thats not out of the question if its going to help me any.....

yes i do have a doel fin its a sting ray hydrofoil if im not mistaken....

no cup on the propeller...

 

[Dhadley]

Re: 5600 WOT 17p ok?

You have room to go up before adding a plate. You probably won't be able to go very high with that prop anyway.

The rev limiter is at either 6200 or 6700, depends on which pack you have. You can safely target 6000 with an average load. Todays fuel may not let you get quite that high, maybe 5800 like Jr mentioned.

 

[countvlad]

Re: 5600 WOT 17p ok?

You have room to go up before adding a plate. You probably won't be able to go very high with that prop anyway.

The rev limiter is at either 6200 or 6700, depends on which pack you have. You can safely target 6000 with an average load. Todays fuel may not let you get quite that high, maybe 5800 like Jr mentioned.

so should i give 15,16p prop a try???

raise the motor? plate or do nothing?

 

[junior1113]

Re: 5600 WOT 17p ok?

#'s really are'nt bad. if it was mine id go up 1 set of holes on transom and see. bet theres an improvement. jack plate is a good idea. stingrays suck they stress the tansom more than needed . id also look for a 4 blade and get the fin off. we really need to know what size that prop is. if a 19 gave you 4800 then this prop must be a 15 to get you to 5600.

 

[countvlad]

Re: 5600 WOT 17p ok?

#'s really are'nt bad. if it was mine id go up 1 set of holes on transom and see. bet theres an improvement. jack plate is a good idea. stingrays suck they stress the tansom more than needed . id also look for a 4 blade and get the fin off. we really need to know what size that prop is. if a 19 gave you 4800 then this prop must be a 15 to get you to 5600.

thats weird.. cant believe its a 15 on a 19 foot boat with a 120 johnson... i have the same prop that i used to have with the old original motor which was a 1976 75Hp johnson.....

what im probably going to do is put the 14*19 prop back and take it for a drive and see again what are the rpms... just to make sure im not wrong....

adding a plate i think is out of the question because it will put the motor back and my steering cable is probably going to be out of reach... i definetly dont have the money for a hydraulic steering....