High RPM but no speed

[Marineduster]

I have a Carver Santego with twin 5.7 Mercruisers. The engines seem to run fine, but at times, I can't seem to get the boat on plane. The boat should comfortably cruise at between 20 - 25 mph, and I've had it up to about 25. However, there are times when I've got both engines spinning at 4,000 RPM but can't do more than 10 mph. So far I haven't found any answers via "Google." I'm not sure why this could be happening. Trim tabs not functioning? Props not biting? can anyone help?

 

[Barnacle_Bill]

Re: High RPM but no speed

You may have a spun prop. Put a mark on the inner and outer part of the hubs then try it again. The marks shoudl still be lined up as you marks them. If not have the prop(s) rebuilt.

 

[Marineduster]

Re: High RPM but no speed

Thanks, I take it that I'll have to do this "in water." Is there any way to check this while it's in storage?

 

[Silvertip]

Re: High RPM but no speed

Very closely examine the rubber between the hub and the outer shell of the prop. If the prop has spun, there will likely be some bits of rubber dust or at least signs of burned rubber due to the slippage. It's not always obvious so look very carefully. It's unlikely that both drives spun the hubs so compare the two.

 

[stevens]

Re: High RPM but no speed

Spun props, or perhaps engines trimmed/tilted way too high up?

 

[oops!]

Re: High RPM but no speed

welcome to i boats.....


im not a prop guy...

but i would have to guess one is spun.......
doubtful both would have the same prob......

did you lift the anchor


this is a great place for everything boats

cheers
oops

 

[tashasdaddy]

Re: High RPM but no speed

how old and what size is the boat, you sure it is not holding unwanted water in floatation. here's how to mark the props.

 

[Bondo]

Re: High RPM but no speed

Ayuh,....... Does the Time of Year make any difference,.......

I gotta believe this is a Dock Boat,+ Not a trailer boat........

Marine Growth will do Exactly as you explain.......

 

[Chinewalker]

Re: High RPM but no speed

Being that it only happens sometimes (spun hubs are usually not intermittent.), I would guess it's as simple as having some seaweed on your props. A short burst of throttle in reverse is usually all that's needed to shake them loose...
- Scott

 

[QC]

Re: High RPM but no speed

I was thinking the same as Bondo and Luke (Chinewalker) These are IBs so we don't have spun props, especially not intermittent ones. Some stuff on da bottom could cause ventilation issues. When was the last time anybody got a peek at the bottom?

Edit: I did some quick research and it looks like the under 30 foot Santegos are I/Os and the over are IBs . . . Need some more info.

Edit 2: the 34s are V-drives

Edit 3: Now I've found a 38 with Volvo I/Os . . . (still looking for a jet)

 

[seven up]

Re: High RPM but no speed

yea,

Checking the v-drives for dark or burnt fluid as well as the cooler for blockages and rust-through might help.

A worst case scenario would be waterlogged hull coring.

Best

 

[Marineduster]

Re: High RPM but no speed

Thanks for all the great tips. I'll look at the props for traces of rubber (spun). It could be that something clogged them though as this problem is somewhat intermitent. The 5.7s are I/O with Alpha 1 drives. I didn't check the props prior to the powerwashing when the boat was hauled out last October so I'm not sure if there was something there. They are free of stuff now.

One thing that I also noticed was that the boat never seemed to want to get on trim and as I manuvered the tabs, there seemed to be no difference in bow angle. It's a slug when not trimmed-out and runs nicely on plane. If my trim tabs were not functioning, could this cause the same type of problem where I'm not able to get past 10 mph?

 

[Marineduster]

Re: High RPM but no speed

Bond-o. You are correct. This is a dock boat on Lake Michigan and the boat went out about once every 10 days to two weeks or so last summer (hoping for more time this year). While it's not weedy by the docks, there is a heavy algae content.

 

[Marineduster]

Re: High RPM but no speed

Tashasdaddy - Thanks for the photo on marking the props, I'll do that.

 

[QC]

Re: High RPM but no speed

It's a slug when not trimmed-out and runs nicely on plane. If my trim tabs were not functioning, could this cause the same type of problem where I'm not able to get past 10 mph?

Probably not, but your drive trim being too high absolutely could. Your drives (tabs too) should be all of the way down when you are trying to plane her off.

If your trim tab switches are wired correctly, they kinda work opposite of your drive trim switches. You press up or forward on the trim tab buttons to move them further down. This is confusing, but the idea is to think of what you want the bow to do. Pushing the top of the tab switch pushes the bow down on the side you push. So actually the opposite tab is also affected by the opposite switch. Left switch, operates starboard tab . . .

 

[180shabah]

Re: High RPM but no speed

Bond-o. You are correct. This is a dock boat on Lake Michigan and the boat went out about once every 10 days to two weeks or so last summer (hoping for more time this year). While it's not weedy by the docks, there is a heavy algae content.

That is definately enough time to get significant growth.