Engines run fine but boat accelerates very slowly

It's confusing. The 2 5.7 gas engines run and accelerate properly. The prop hubs on the Bravo One drives are fine. The boat just doesn't accelerate the way it did just a few outings ago. It was a stretch that both prop hubs might have failed at the same time but that is what it behaves like. No trouble at idling or slow speeds but when I give it some gas it accelerates really really slowly and seems OK once it gets on plane, but it's painful to get there. Sometimes boats will get a big bubble of exhaust around the props so that they don't have any water to bite into but that doesn't seem to be the problem here. I've been wondering if there is some kind of a clutch between the engines and outdrives. Or maybe it's something else.

Anyone have any ideas or want to take a guess?

Sure appreciate your help.

Thanks

Dale

Of course you have ruled out other possibilities like fouled bottom.

Sure sounds like a problem with the boat.-----------Moored where and for how long ?------Antifouling paint used ?

Sorry.
Should have given a bit more detail.
2006 Sea Ray Sun Sport. 200 hours on the engines. Kept on a lift in Florida. Bottom is just the gel coat and it's perfect.
The change from working properly to not working properly happened over maybe just 3 outings.

Thanks, guys, for replying, but I'm sure it's nothing to do with the hull.

Any more ideas?
Thanks again
Dale

If the rpm`s are there but the speed is not like a slipping clutch then suspect the cone clutch or engine coupler

[email protected] said:

It's confusing. The 2 5.7 gas engines run and accelerate properly. The prop hubs on the Bravo One drives are fine. The boat just doesn't accelerate the way it did just a few outings ago. It was a stretch that both prop hubs might have failed at the same time but that is what it behaves like. No trouble at idling or slow speeds but when I give it some gas it accelerates really really slowly and seems OK once it gets on plane, but it's painful to get there. Sometimes boats will get a big bubble of exhaust around the props so that they don't have any water to bite into but that doesn't seem to be the problem here. I've been wondering if there is some kind of a clutch between the engines and outdrives. Or maybe it's something else.

Anyone have any ideas or want to take a guess?

Sure appreciate your help.

Thanks

Dale

Click to expand...

When you put the throttle down do the engines rev up and the boat does not move or do the engines rev up slowly?

A wild guess,Is there a possibility excessive rain water or other water source below deck in your bilge

No issues at all with achieving engine RPM.
I'm leaning toward it being slipping clutches but gosh, what are the odds that two went at the same time? Seems very odd. That's why I wondered about it being a bubble of exhaust around the props such isn't too difficult to create if the drives are not all the way down when you try to accelerate. I've seen that in more than a few boats. Anyone have any thoughts on that? Alternately, what's involved in checking the cone clutch?

Many thanks
Dale

Dale, there isn't any clutch in the sense of what you are thinking. The drive is either in gear or not. The clutch is simply the thing that keeps it in gear, or rather, the thing that allows the vertical shaft to engage the horizontal prop shaft smoothly. These are very robust parts and they either work or they don't. If they don't then you know it in a hurry and there's no doubt.
So what could be "slipping"?
Since the engine is pretty much direct drive to the stern drive, there isn't much can go wrong between them except the drive couplers. They are made of rubber, so that if there is a failure they don't take out the engine...they just spin in place and don't transmit power. Doubtful they are both gone at the same time but it's possible.
So is it something in the drives? Probably not. They were working fine until just a short time ago and again, chances of both failing simultaneously in the same way is slim. The props aren't damaged or fouled since it lives out of the water most of the time.
So where does that leave you?
My suspicion is fueling. When was the last time you checked the filters and pickups? Is this boat pre-ethanol? Was the fuel system updated to handle the new fuels?
I'd also ask when the last tune-up happened. However since both engines are behaving in a similar fashion, the one thing they both have in common is the gas supply. Start there...eliminate the chance that it is contaminated fuel or restriction in the supply.

My first thought was the water issue also. Have you had alot of rain lately. If both engines respond the same my guess is fuel supply or the hull is water logged. Check the deck all over for dryrot, if you find dryrot open it up and see whats inside. Old foam can soak up alot of water and never dry out it must be removed.

Hey, thanks very much for what I'm pretty sure is good news. Makes sense about the clutch. I agree that if it was something serious wrong then I'd know it. As in noise or grinding or something very obviously not right. That's not the case here. This now points to the drive couplers, and although it's unlikely they both fail at the same time, I guess it's possible. That's probably what I'll investigate now since I really don't think it's a fuel issue as evidenced by the fact that I have no issues achieving engine RPM. Just a few hours ago I had the boat over 50 MPH. Obviously no issues there.
I suppose drive couplers are difficult to get at, right?
Thanks again.
Dale

[email protected] said:

Hey, thanks very much for what I'm pretty sure is good news. Makes sense about the clutch. I agree that if it was something serious wrong then I'd know it. As in noise or grinding or something very obviously not right. That's not the case here. This now points to the drive couplers, and although it's unlikely they both fail at the same time, I guess it's possible. That's probably what I'll investigate now since I really don't think it's a fuel issue as evidenced by the fact that I have no issues achieving engine RPM. Just a few hours ago I had the boat over 50 MPH. Obviously no issues there.
I suppose drive couplers are difficult to get at, right?
Thanks again.
Dale

Click to expand...

It's not your cone clutch or your drive couplers. Your props are cavitating or ventilating air from the surface.

Your props may need to be serviced. They can cavitate when the leading edge gets little tiny pits in them. (They may look good to you)

Are your drives trimming all the way in?

And this I have only seen happen on an Alpha, Being that you have Bravo one drives(same dimensions as an Alpha) you have an exhaust bellows, there is a chance your bellows is off the bell and blowing exhaust right into the prop.


Now, Everyone blasting out suggestions to this boat owner with out asking more questions is not helpful. He is ready to put in drive couplers.

Time to have a shop test run one or both motors on a dynomometer or a test prop.

What is the WOT rpms for both engines once it is up to speed? Get someone to scrub the hull and see if it makes a difference in performance it dont take much to effect performance.

""What is the WOT rpms for both engines once it is up to speed? Get someone to scrub the hull and see if it makes a difference in performance it dont take much to effect performance.""

BOAT IS STORED IN A RACK, PERFECTLY CLEAN

[email protected]


You have yet to answer some questions SPECIFICALLY, You were asked ""do the engines rev up slowly""???? your answer was not correct! please re-answer this question correctly.

You were not asked if they rev up you were asked HOW THEY REV UP.

When you throttle up what happens exactly? be as descriptive as possible.

What if any parts have been replaced?

Any couplers? Any props? anything?

Anything added to the boat? thru hull fittings? anything?

Did you hit anything three outings ago or maybe run thru a sand bar?


both Couplers being bad would not allow for 50 mph, possible one being bad may, but not sure what top speed was before so what was top speed before this issue occurred? Specific answer please!!!

What are your wide open throttle RPM readings for each engine???

As Chris said not the cone clutches

There is no mention of new couplers unless I missed it????

you say hull is clean. Got it!

did you fill up with gas just before this started to occur?

Are these EFI or carbureted engines?

Also how long is your boat. You dont say....................................


More F'n questions then then there should be about your boat and its history...............Get it?

Do both engines rev at the same time and rpm? I think if one prop hub is slipping you would see this type of acceleration...however, I would think one engine would rev higher and faster than the other.

Oh and one other question...have you done anything to the boat that would affect trim? That is did you add any new equipment, or install anything heavy or have a big group aboard, or fill the fuel tanks (that you normally have 1/4 full or something)? Just ruling out the obvious...(like oh yeah, I installed a tower!)

Owner says ----" engines run fine "--------------So I think no further help is required.

The only time I was on a boat that the drive coupler failed, it smelled really bad...like when you burn out your clutch on a car. A burning rubber smell.