why

[dino123]

i have a glastron mx 2008 4 .3 volvo penta i put a 4 blade 19 pitch i got 25 miles hr at 4700 rpm it really sucked does any ones eles have any ideas on a prop i pull skiers and tubes

 

[orion25]

Re: why

Need more info than that. What did you have before and how did it perform?

 

[dino123]

Re: why

firts time out there was a 23 pitch but people to me is was not good so i changed it

 

[orion25]

Re: why

How did it perform? Speed, WOT, etc. (asking about the 23P prop)

 

[erlindbl]

Re: why

Something doesn't add up there.... a 19P prop at 4700 RPMS with that set up should be higher than 25 MPH. If you could not get over 25 MPH I would think you have either a problem with your tach... a problem with your (speedo or GPS) or a problem with your engine..... You need to figure out which before you can go any further.....

 

[dino123]

Re: why

i dont think the spedo is off we were goin pritty slow come of plain nice but the rpms were to high

 

[a70eliminator]

Re: why

Do you have power trim? Trim makes all the difference in performance. 4700rpm's @ 25 mph sounds like prop was slipping or cavitating from too much trim out.

 

[codertimt]

Re: why

Since it's a new boat and motor and was running fine before change, as long as the prop is the correct size for you outdrive(for example, hub not significantly smaller), I would think you either got a bad prop or it was somehow not installed corrected. Is the thrust washer there and installed correctly, if the new prop has a removeable hub is the correct hub installed? That's all I can really think of.

I guess you could have gotten a prop design that just doesn't work for the boat, but that seems unlikely. What brand/model prop is it? My 21" Solas Amita works great on my 4.3 mercruiser 185 GT. Since the Volvo has a similar gear ratio, I would expect a similar 19" to absolutely rocket on plane and reach speeds in the low to mid 40s...

 

[dino123]

Re: why

its a 19 pitch volvo prop how tight does the nut have to be when i changed it ,it was only hand tight removed it with my fingers. i put the other prop on but put the nut tighter but did not do it to tight

 

[a70eliminator]

Re: why

The prop nut needs torqued, not sure of the spec. but it's pretty tight as in 1/2" breaker bar tight. The prop is on a spline so even if the nut loose it shouldn't slip. Could the prop be the wrong rotation, like a prop for the port engine on a tandem set-up?

 

[cpubud]

Re: why

props tork down to 55foot lbs

 

[dino123]

Re: why

kk i had the 23 pitch prop out today 4800 was like 34 mph at like half throttle i went to 45 mph it was saying 6000rpm at all most full throttle i think the rpm gage in wrong 4800 rpm the enginge was not even working . do you really think the parts guy were i got the 19 pitch would give me the wrong one for the boat

 

[Maclin]

Re: why

Tachs have a switch for 4-6-8 cylinders. I would have the dealer check yours, or you can if that is too far of a trip. This is a brand new boat and I think you need to exercise your "new boat" service window.

 

[alamosaddles]

Re: why

Could the prop be the wrong rotation, like a prop for the port engine on a tandem set-up?

I think if the prop was the wrong rotation, the guys boat won't move much at all..the blades would be angled in the wrong direction to create rearward thrust no?

Also, he says the previous prop was only finger tight? A very loose prop nut like that can't be good for the drivetrain I'd think...

 

[erlindbl]

Re: why

I doubt the 19P is a counter rotation...... Sounds to me like a tach problem. I would get the tach checked out and take out a GPS. Without good information on your tach and speed your never going to figure what prop you need.

 

[codertimt]

Re: why

Okay, now I have a question about the original post. Since the tach is now know to be off, was the observed 4700rpm with the 19" at WOT or was that just as high as you took it?

 

[dino123]

Re: why

as far as i took it did not wanna blow it up still break it in

 

[codertimt]

Re: why

Well, given that information, then I don't think anything is wrong at all with your 19" prop. Playing with the numbers in the calculator, it seems that when your tach is reading is 4700-4800 rpm it's actually running somewhere around 3000-3200. And if you figure 3000rpm with a 19" prop, you get speeds in the mid 20s...

I think if you get the tach issue sorted out, you will find it's performing as intended... You are going to loose about 10mph in top speed from the 23" wheel though, so if that is a problem for you it might not be the prop for you....it should pull like Mack truck though....

 

[dino123]

Re: why

ya i am waiting for the dealer to phone me to day is all was amazes me how long it takes for them to phone back with a problem, but how fast when you buying .but anyways wanna thank every one for there help