1980C, it's not trying to get more speed so much as gettng to motor closer to its rated wot rpm.
for the health of the motor.The motor will use about the same gph(gallons per hour) at wot wheather its turning 4800 or 6000 the key is running within it's wot rpm while producing a good speed.Speed at a given rpm determines mpg gph devided into miles per hour.
I understand you don't want to lug the motor......but with the improvement from moving the motor, the rpm is now in the low end of the WOT range. Which I understand to mean that the motor isn't lugging. My point was that with a displacement type hull there is a point at which more rpm doesn't equate to more speed due to the hull limitations. Which means that the increase in rpm is just burning more gas for no gain in speed. So, even if you have the motor operating at a higher rpm, you aren't connecting that hp to the water. I don't know that this is the case here.....was just postulating.
What do you think about the idea to move to a 3-blade, same dia. and pitch? It's a 25% reduction in blade area, so it should increase the rpm without sacrificing speed like a pitch reduction would.
I was hoping Steelespike might chime in on the 3-blade vs 4-blade idea. I know the rpm would increase, the amount is up for debate. I think you'll have to try a different prop to get more rpm out of it...if you want to get to the 5000 mark. There are only three ways to do it....decrease diameter, decrease pitch, or decrease the number of blades. You might try a local marina to see if they would let you try before you buy. If you bought it from a dealer maybe they will work with you?
The 4 blade should do better overall than your typical 3 blade.Should resist venting and have better slip numbers.The 4 should give better control around the dock.
A 3 blade same pitch could increase rpm but will likely have higher slip numbers.
could improve speed probably a toss up.
Pontoons do produce higher slip numbers.
Decreasing diameter on a pontoon risks venting problems and increased slip.
1980C, increasing wide open throttle rpm doesn't burn more fuel wot gph remain relatively constant if you lose wot speed mpg goes down if you increase wot speed mpg goes up. but gph remains relatively constant.
my only thing between the 4 blade and the 3 blade is a 4 blade will usually cause slightly lower WOT RPMs...if it was my motor I would be hoping for over 5K, so I would vote for a 3 blade in your instance. but you would probably be ok to go with the 4 blade, you should be in the high 4K RPMs since you are dropping a pitch.
The 4 blade should do better overall than your typical 3 blade.Should resist venting and have better slip numbers.The 4 should give better control around the dock.
A 3 blade same pitch could increase rpm but will likely have higher slip numbers.
could improve speed probably a toss up.
Pontoons do produce higher slip numbers.
Decreasing diameter on a pontoon risks venting problems and increased slip.
1980C, increasing wide open throttle rpm doesn't burn more fuel wot gph remain relatively constant if you lose wot speed mpg goes down if you increase wot speed mpg goes up. but gph remains relatively constant.
No....it has to do with the difference between the theoretical distance traveled per revolution and the actual. A 10" pitch prop should move you through the water 10"/rev theoretically. It is actually less than that due to slip. The higher the slip the more the difference between theoretical and actual.
new prop showing no change on the RPM gauge. the only way I can get the RPM's to increase is by trimming the motor up which sometimes causes cavitation.
that sounds exactly like what I predicted..you dropped 1 pitch but went to a 4 blade hence you should have the same WOT RPMs as the 10P 3 blade. which is why I suggested going with the 3 blade 9P prop. If you are around 4800 RPMs you should be ok though, that is kinda on the low end but should not harm your motor.
that sounds exactly like what I predicted..you dropped 1 pitch but went to a 4 blade hence you should have the same WOT RPMs as the 10P 3 blade. which is why I suggested going with the 3 blade 9P prop. If you are around 4800 RPMs you should be ok though, that is kinda on the low end but should not harm your motor.
so you did..i thought you had a 3 blade for some reason.... 1 pitch will not make much difference depending on manufacturer and style of the prop, if you purchased the exact same make and model prop as your old one you should have picked up 100-200 RPMs..which is not a lot. you have the boat slightly under powered in my opinion so you are really working that 40, a 50 would be a better choice probably. but if you are in the high 4K RPMs, I would say you are ok.
the specs on the boat call for 40HP max. I plan on having the motor serviced this winter to make sure lubed, cleaned, tuned, tweaked, etc. im now having a shifting problem, but thats another thread that I probably should not get wrapped up into this one.
