ROADHOG

Stevesxm, Your right the boat is a 2006 42 Ex with 525's, My last boat was a 2005 42 Ex with 525's. The reason I'm asking this question is because the 2005 would run 30' props to 5000-5200 rpms. The 2006 will not go past 4000 rpms. I know the dealer switched the lower ends on the Bravo's with another boat and I'm hoping they did not put 1.36 on by mistake.

The 30" props that are on the boat are the ones they issued with the boat at time of purchase. I'm just thinking that the drive ratio's are incorrect,because my 2005 Ex would turn 30" props 5000 rpms all day long.

stevesxm

sounds to me like your logic is impeccable

ROADHOG

If you knew me, you would be giving me TOOOO MUCH CREDIT!!!!

Griff

1000-1200 rpms ?????? They might even be 1.25's.

PatriYacht

Did you buy ANOTHER boat?

ROADHOG

YES!

I hope I did not make a mistake.

PatriYacht

Mistakes can always be fixed. Just takes $$$$ Would you like to borrow a pair of 26 pitch Bravo's to see how they run? I won't be in the water for another week or two.

stevesxm

forgive my ignorance as i am not a prop expert or even knowledgeable but wouldn't just putting on shorter props to bring up the revs be the same as just putting on shorter tires on a car ? i.e ... yes the revs would come back but the top speed wouldn't be there ? for example... for the sake of discussion if the motor spins 4000 w/ 1.36 gears he is getting 2950 prop revs w/ a 30.

now a 28 is roughly 6 % less prop which would require only 6 % more revs for a "break even" or roughly 4250 ... lets say it actually does that... but what he really needs is 25 % more revs so that would imply an impossibly small prop... and no top speed at all....

now.. i understand that this whole thing is not precisely linear like it is w/ tires but it is substanatially so.... and you have the added unassailable fact that this combination worked flawlessly in what are essentially identical circumstances on the first boat...

i think something else is fundementally wrong. this seems like way too much " problem" for an incremental prop change...

i don't have any meaningful suggestion or solution but it just doesn't add up for me somehow.

ROADHOG

Your right, not trying to fix the problem with the props. The drive train is the first place to start. The boat is in the shop as we speak and one way or another they will find out is going on.

Maybe it's something in the engine managment system that's not letting the engines come up to full RPM'S.

PatriYacht

It would be like a car with taller gears and smaller dia. tires. In the end they would travel the same distance and speed. However, common wisdom seems to be that 1.5 ratio is more efficient in our speed range. Just suggesting. To me it seems like more is wrong than just gears. If the former rpm was 5000-5200, with the new ratio, the new rpm would be 4500-4700. 1.50-1.35 is not a very big change.