Losing speed with RPM increase.

[inrworx]

Hay everyone; I just bought a 1995 Sea Ray that has a Mercuriser 3.0LX from a friend. He took pretty good care of it. I did the engine and stern drive tune up (Plugs, Wires, Cap, Dist, Fluids, Oil, and Drive Oil) and seem to be running great! I took it out over the holiday weekend and our first run full throttle was great, very fast!

Then after about 30min, trying to get back up to plane the Engine?s RPM would jump up to 5000 RPM and the Boat would slow. I did a bit of research on iBoats and found a few threads about Prop hubs and couplers.

I took the prop off and it has a solid core Hub, looks to be in good shape. I didn?t smell any rubber burning from the engine compartment that would suggest a Coupler issue. Is there anything else I could look for? Or could you suggest what I should do next?

Thanks for your help!!!

 

[eavega]

Re: Losing speed with RPM increase.

Still sounds like a spun prop hub. Scribe a line between the prop and hub. Take it back out on the water. When you feel the rev up/slow down behavior, take a look at your prop and see if the scribe mark still lines up. If it doesn't then you know you have a spun hub.

Rgds

Eric

 

[inrworx]

Re: Losing speed with RPM increase.

Still sounds like a spun prop hub. Scribe a line between the prop and hub. Take it back out on the water. When you feel the rev up/slow down behavior, take a look at your prop and see if the scribe mark still lines up. If it doesn't then you know you have a spun hub.

Rgds

Eric

Hi Eric, thanks for your response. It?s a Quicksilver 48-79794 A5 17P Prop. The previous owner told me it?s a welded prop and could not be spun. Is he correct? I tried to look up the prop specs but I cant seem to find anything that it truly is welded?

 

[pevaguy]

Re: Losing speed with RPM increase.

You may have the outdrive trimmed up too high and the prop is cavitating. Try trimming down.

 

[inrworx]

Re: Losing speed with RPM increase.

This weekend I?m going to try the Nail Polish test and trim it all the way down on takeoff... I?ll keep you posted! Thanks...

 

[thumpar]

Re: Losing speed with RPM increase.

Watch the temp. If the coupler is bad the engine will not get water if it is slipping bad.

 

[eavega]

Re: Losing speed with RPM increase.

Hi Eric, thanks for your response. It?s a Quicksilver 48-79794 A5 17P Prop. The previous owner told me it?s a welded prop and could not be spun. Is he correct? I tried to look up the prop specs but I cant seem to find anything that it truly is welded?

I've never heard of a prop that could not be spun, but that might just be a lack of knowledge on my part. What I do know is that the engineers that designed marine propulsion systems figured out a long time ago that props can hit solid objects, and there had to be a way to cause the props to disengage from the prop shaft to avoid damaging shafts, gears, etc. Every motor I have ever run (1960's - 1980's outboards) has always had a way to disengage the prop from the shaft, either a shear pin or a rubber hub that could be spun.

Rgds

Eric

 

[Bondo]

Re: Losing speed with RPM increase.

Hi Eric, thanks for your response. It’s a Quicksilver 48-79794 A5 17P Prop. The previous owner told me it’s a welded prop and could not be spun. Is he correct? I tried to look up the prop specs but I cant seem to find anything that it truly is welded…

Ayuh,... Welcome Aboard,... The P/O don't know what he's talkin' 'bout,...

Have ya got a Spare prop,..?? if so, try It,...
If not, now's the time to buy 1,...

 

[emilsr]

Re: Losing speed with RPM increase.

Mercury does make a "solid" hub that fits in place of the standard delrin flotorq II. It's necessary if you're running upwards of 400hp....so I doubt that's what they put on your boat, but you never know. They also make props with a solid hub, but I don't think this is one of them.

What do you mean by a "solid core hub"? Got any pictures....that would help identify it.

I'd like to go back to the trim for a minute....

When this happened, were you trimming out (up)? No disrespect, but given that you're a new boater we should ascertain that you're trimming properly. I've blown out the prop a time or two by over trimming, and I'm not that new. It happens. :facepalm: You should ALWAYS be trimmed all the way down (in) while you're trying to plane, otherwise the prop will blow out and you go nowhere.

If there's debris in the water you can pick up a stick (or whatnot) which will disrupt the water flow to the prop enough to make this happen as well.

Point being it may not necessarily be a mechanical failure.

 

[thumpar]

Re: Losing speed with RPM increase.

I have a flotorq prop. Those come apart and would be easy to tell if it is the plastic or metal and if it was good or not. My spare prop has a solid hub but there is a layer in between the actual prob and hub and it would spin if it needed to. It would be hard to tell if that type of prop was spun just by looking at it.

 

[inrworx]

Re: Losing speed with RPM increase.

I just bit the bullet and ordered a Silverado 3 SS Blade Prop w/Flo-Torq II Hub. Please tell me that’s a good Prop?....
Going to take her out this weekend, hopefully that solves my issue…

 

[inrworx]

Re: Losing speed with RPM increase.

Confirmed! Spun Hub with a solid hub prop. Installed the new Prop and it ran perfect! Finely was able to get up to top speed! Awesome….