Help - Lost RPMs

[Nimrod]

1983 46 Hatteras with the 8V92s. We are down 200-300 rpms and are having a a hard time figuring out why. He had all of the running gear and bottom checked and cleaned. Then had our diesel guy check out the engines and transmissions. Drivetrain got a clean bill of health from the trannies forward.

He discovered that the starboard shaft was hard to turn by hand and impossible to turn without the use of a wrench after we ran the boat and the shaft heated up. Stuffing box did not get hot and seems to be adjusted properly. His thoughts are that the cutlass bearings may need to be replaced. They have not been replaced in about 14 seasons.

There is no vibration and props seem to be true. Any thoughts on what elese to check? Do you think the cutlass bearings could be the culprit?

Thanks in advance for your input.

[clt_capt]

Have you run over any line recently (I only ask, cuz I seem to do it regularly) that could have wedged into the cutless bearings?

[perfectscore]

there is probabally an alignment problem somewhere, is the tranny oil burnt????

[JD5652]

Paul-

Need a little more info.....

When you say you're down 200-300 RPM's....is that based upon full load WOT??...or what is it based upon??

Did your mechanic check your no load WOT RPM?? If so, does it meet spec??

When cutlass bearings normally fail, the shaft gets loose in the cutlass bearing not tight.

You might want to check the TIR (Total indicated Runout) on the shaft to determine if the shaft is bent.

Disconnect the shaft from the tranny and see if shaft rotates freely when not connected ....this will determine if the binding is dependent or independent of tranny. That way you can eliminate one thing or the other.

Good luck!

[LuckyLady]

Sucks get her fixed its almost wmo time!

Cutless bearing or maybe something happened to the props. I bit of cupping should fix it and a prop scan would tell all but it could just mask another problem.

If you need anything just call. There is quite a few places that I deal with in Jeresy that have been life savers when it comes to the underwater running gear! I think I still can cash in a favor if need be!

Good luck!

ps.
Stop breaking boats j/j

[rarhomes]

Maybe a dumb question, but did you check the fuel supply?
Lines and filters.

[jawz12]

need some more info...but one thing is for sure,adding cup too a prop is gonna drop the rpm even more,so...that may not be the best approach
as far as the shaft being tight,personally,i would check the alignment,be sure the shaft isn't contacting the shaft log...you may have a mount that failed,this threw off the alignment...

no rpm problem before ??? those guys turned up fully???

[marc2061]

Sucks get her fixed its almost wmo time!

Cutless bearing or maybe something happened to the props. I bit of cupping should fix it and a prop scan would tell all but it could just mask another problem.

If you need anything just call. There is quite a few places that I deal with in Jeresy that have been life savers when it comes to the underwater running gear! I think I still can cash in a favor if need be!

Good luck!

ps.
Stop breaking boats j/j

adding cup would make the problem worse. He is lacking rpm so adding resistance at the prop would bring the rpm down further. Cutless bearings cause vibrations ect not rpm loss. This isnt an outboat boat with twins or trips,this is a real boat.

[Deep C]

I'll tossin a simple one that happened to me... Probably not but could be? I reported losing speed over a couple days then rpm started sliding too. I had just checked running gear before launch and all was good. Finally pulled her out expecting a tranny gone bad... There was a small tuft of rope cinched down tight between wheel and bearing. Tight as a drum (Rpm) and enough disturbance to cut water flow to the blades (speed)...

[jawz12]

I'll tossin a simple one that happened to me... Probably not but could be? I reported losing speed over a couple days then rpm started sliding too. I had just checked running gear before launch and all was good. Finally pulled her out expecting a tranny gone bad... There was a small tuft of rope cinched down tight between wheel and bearing. Tight as a drum (Rpm) and enough disturbance to cut water flow to the blades (speed)...

braid line does the same thing...it will get between the shaft and the cutlass as well as the shft log....the braid will tear up the shaft too...