prop shaft movement

[letterman]

I have NOT looked at this myself yet. Recently I hit a submerged piling with the prop on a 20,000 lb Irwin 37' sailboat. The prop bent, the prop shaft pushed out the side of the hull where the cutlass bearing is, and I have insurance! So, the mechanic says "the shaft moves in and out and it's not supposed to." "Hmm" says I. "How much does it move?" ""A few inches" says he. "Hmmm" says I. Now I cannot imagine the shaft having any play in it at all, or else when you go from forward to reverse, it would tear something up over time. So weigh in! Should I have the tranny repaired too (if possible) as the bearings and who knows what might also have been damaged.

 

[Billbeard]

With damage like that every thing is suspect including any mounting points.

 

[rpwillia]

You need a new mechanic

That one does not have a clue. Run, don't walk away from him.

 

[Don S/V ILLusion]

You need a good surveyor first (before fixing anything).

 

[Tim Huss]

the back lash in a tranny is measuerd in thousands not inches Im thinking you should get another mech.

 

[woodster]

you may also want to check and see if you sheared off the shaft but like has alredy been stated get a good surveyor to inspect the damage ......

regards

woody

 

[letterman]

believe it or not I actually only thought I bent the prop, not damaged the whole area, and so we did motor for days with it in this condition, with no apparent problem except reverse. As for getting a survey, I would assume the mechanic who told me about the problem SHOULD know tranny's, but I will ask the insurance adjuster to send one. The shaft didn't break, but someone suggested that it may have slipped on the coupling. I'll find out more today.

 

[Witzend]

I believe the thrust bearing should not have any play in it.
It is taking the full load of the shaft as it is pushing or pulling the vessel. I would have the tranny checked as will as the strut alignment.
I installed a flexable coupling between the tranny and prop shaft coupling. It is design to sheer off if a significant change in load occurs, (such as hitting a log) protecting the drive train from significant damage.

 

[Maine Sail]

It is design to sheer off if a significant change in load occurs, (such as hitting a log) protecting the drive train from significant damage.

I have seen a number of bent and broken props, bent prop shafts, and a and a mashed gear box all while a "Drivesaver" type device was in use. Just don't go purposely running things over because you think your protected. On bigger, higher HP motors, I can see how they would work I have just not seen them "protect" small gear boxes and drive trains much on smaller engines very well..

I wonder If anyone has actually had a drive saver "fail" on a small diesel sailboat aux engine and actually "save" the gear box??

 

[Roger Long]

On bigger, higher HP motors, I can see how they would work

I suggested them for one of my 1000 hp plus drive trains and the propulsion system specialist who was doing the final design engineering on the shafting system said absolutely, positively, NOT.

I have one on my boat but only because it came that way and the nuts are too frozen and the working conditions too difficult to go through the effort of removing it. Mine was put on without shortening the shaft so I have more prop shaft overhang beyond the stern bearing than I ever would have though could work (from the viewpoint of having designed many shaftlines) but it doesn't seem to be a problem. You can get away with a lot when only dealing with 15 - 20 hp.

 

[Witzend]

Yep, I look for stuff to run over all the time. It may not help much, but I hope to never find out. On my year Catalina, access to the coupling is severely limited due to hoses and wires, the flex coupling I installed also has a rounded bolt head that provides me easier alignment check. This was alone reason enough for me to install it.