pokey engine/transmission?

[anaisdog]

i have hull 99, 1986 and last night was the first time i took her out, from the dock, this year. in forward, she was really slow and the engine was pegged at 3200 rpm, for going really slowly.  i put her in reverse, in case there were weeds, didn't see anything coming off, went back into forward and for probably 3-5 minutes, the engine remained pegged then it slowly backed off the rpm, with the same amount of throttle.  turned off the boat, sailed for a few hours, turned her back on, and it was sluggish again with high rpm, going forward.  if the weather holds, I'm going to dive the prop tonight but what else could this be?

thanks

becki kain

[Noah]

Caveat: I am NOT a mechanic but...Did you notice whether the shaft was spinning faster when you accelerated? If your prop is clean...tie boat to the dock and run engine in gear and look at the shaft to see if it is spinning faster as you give it more throttle under load, or perhaps the transmission is slipping...

[anaisdog]

um, forgive me for being confused but how would i?  she's in the water?  like dive behind while someone else is driving?

thanks!

[Noah]

NO!
1. Tie the boat to the dock with to a good secure cleat with strong spring lines fore and aft.
2. Go below and remove aft bunk cushions and open compartment bunk board so you can see transmission and coupling and stuffing box
3. Run engine in gear(forward and reverse) at different RPMs and see if shaft turns at different speeds or slips.

[anaisdog]

DUH!  completely forgot we can see the shaft from the aft cabin. thanks!

[Craig Illman]

and, if you can't count the revolutions, optical tachs are pretty inexpensive. 

[mark_53]

Make sure your not wearing a necklace when counting revolutions.  Also, keep long hair away!

[anaisdog]

owowowowow!

[KWKloeber]

becki

You're getting the RPMs, so by elimination it has to be something past the flywheel.

Check in this order:

Dirty hull/prop
Loose prop
Slipping tranny/plate.

kk

[anaisdog]

remember she's in the water.  how do i check the last?

[KWKloeber]

becki

Well, as others said, check it running under load (shaft vs engine RPM -- though you should use a hand tach for both since you can't rely on the panel tach being accurate.)  Or with the transmission locked, try turning the prop in the water (if you've verified it's not slipping) or turning the shaft itself.  Probably safer than getting hair or clothing caught up!   

Applying Occam's Razor to this situation, go for the obvious/easy first (hull and prop.)

ken

[Bobg]

hope you can come up with the answer, my boat has been slowing down for the last 2 years, started after I re pitched the prop to 10", after re-pitching the prop, I got 6 knots at 2500 rpm, witch was about a half knot improvement, now I get around 5 knots, calm seas, bottom clean, boat empty, comparing it to a phone or gps and my speedometer is right on,
can't turn the prop by hand while in gear with engine off, hand held lazor on shaft gives me about 50 to 70 revs less than half of engine speed with a 2-1 reduction, i.e. at 2200 rpm on engine, the shaft turns about 1050.  can't figure it out, I can get 3200 rpm out of engine, one dock mate says I may have taken on water thru the gel coat as I don't have bottom paint on any more, that sort of seems far fectched tho to me.  So If you come up with anything, let me know

[Noah]

No bottom paint & no barrier coat?

[Jim Hardesty]

if the weather holds, I'm going to dive the prop tonight but what else could this be?

Becki,
Did you dive?  What did you find?   You didn't say what you have for a prop.  If you have a folding or feathering prop you may have one of those pesky zebra muscles not allowing the prop to fully function.
Hope you find the problem.
Jim

[anaisdog]

is there a engine schematic for the m25 diesel, which came on the c34 1986?  we're going to try to change the transmission oil.  thanks