prop question

[jmarsh223]

Sorry, I'm sure this question has been answered but I haven't found the answer I need. I have a glastron SSV 175 with a volvo penta 230a 4.3. Engine runs super smooth, bogs a little, im sure a carb rebuild is on its way. My question is at WOT why am I over revving with the standard prop? I've called around and talked to number of boat gurus and I've yet to have my answer.

 

[alldodge]

If your prop is not damaged and your over revving there only a few things which can cause this. The prop does not have enough pitch and/or diameter, the trim is to high, or the drive has been installed to high

The one other thing could be either the prop hub or engine coupler has spun.

What are you seeing?

 

[Maclin]

As AllDodge asked for, we need the MPH and RPM from a WOT run, I think we can infer the gear ratio. With those numbers plugged into to a prop calculator we can see if the numbers make sense as stated. Should be able to tell if the Tach is accurate or not, slip factor, all that is related and a prop calculator can tell us what may be out or "range" or if you just need a higher pitch prop.

What year are we talking about? And is it a Single or DuoProp. A 4.3 could have either type.

 

[jmarsh223]

As AllDodge asked for, we need the MPH and RPM from a WOT run, I think we can infer the gear ratio. With those numbers plugged into to a prop calculator we can see if the numbers make sense as stated. Should be able to tell if the Tach is accurate or not, slip factor, all that is related and a prop calculator can tell us what may be out or "range" or if you just need a higher pitch prop.

What year are we talking about? And is it a Single or DuoProp. A 4.3 could have wither type.

Top speed is 30mph, that takes a minute to get that high. Thats with 3 to 4 ppl and maybe an ice chest. Any higher than 30 mph is over 5000 rpm. WOT is around 5400 55000 and the mph I don't really know. It was an accident and I panicked and brought her below red line.

 

[jmarsh223]

As AllDodge asked for, we need the MPH and RPM from a WOT run, I think we can infer the gear ratio. With those numbers plugged into to a prop calculator we can see if the numbers make sense as stated. Should be able to tell if the Tach is accurate or not, slip factor, all that is related and a prop calculator can tell us what may be out or "range" or if you just need a higher pitch prop.

What year are we talking about? And is it a Single or DuoProp. A 4.3 could have wither type.

It's a 95 volvo penta 230a sp, single drive. The stock prop from what I've read and been told is a 14.25x21 and that's what is on her

 

[alldodge]

Top speed is 30mph, that takes a minute to get that high. Thats with 3 to 4 ppl and maybe an ice chest. Any higher than 30 mph is over 5000 rpm. WOT is around 5400 55000 and the mph I don't really know. It was an accident and I panicked and brought her below red line.

Going from 30 mph and try to increase just a bit more and it goes to 5K rpms, sounds like a spun prop hub or engine coupler. If your not smelling burnt rubber then it's probably the prop hub

 

[Maclin]

Taking a minute to get to 30mph seems like it is lugging, but there must be something else going on if the RPM's are really at 5000.

When you say it takes a minute, do you mean you move the throttle wide open and it takes that long? Does the engine rpm climb slowly? Or does it rev to 5000 and stay there and it is like you are waiting for whatever is slipping to finally grab?

As for the 5000+ rpms, Are you sure the Tach is accurate?

For example, if prop is ok then at 30mph you should be at around 3000 assuming a prop slip of 10-12% and gear ratio of ~1.75.

A 17 footer with a 4.3 and 21p prop should hit 50mph and still have good holeshot. Time to look at averything incluidng a tuneup.

 

[jmarsh223]

Taking a minute to get to 30mph seems like it is lugging, but there must be something else going on if the RPM's are really at 5000.

When you say it takes a minute, do you mean you move the throttle wide open and it takes that long? Does the engine rpm climb slowly? Or does it rev to 5000 and stay there and it is like you are waiting for whatever is slipping to finally grab?

As for the 5000+ rpms, Are you sure the Tach is accurate?

For example, if prop is ok then at 30mph you should be at around 3000 assuming a prop slip of 10-12% and gear ratio of ~1.75.

A 17 footer with a 4.3 and 21p prop should hit 50mph and still have good holeshot. Time to look at averything incluidng a tuneup.

Takes a minute to get up to 30mph, at WOT it's opens up past 5000rpms. I mean the engine runs smooth, and has no problem getting the rpms up. The issue is the more on the speed pick up. If you slam it to wot it bogs just a bit but picks up quick. The speed how ever just kinda lags. You almost have to hold your tongue just right to get 32mph, thats even on a gps read. I mean I've pulled a tube like this and it doesn't get above 20mph.

 

[bruceb58]

or engine coupler. If your not smelling burnt rubber then it's probably the prop hub

Those drives don't have rubber couplers. They have dampers and if they ever go south, there will be no drive at all.

Sounds like a prop hub to me.