Line in prop shaft

[copaco]

Can the turns around the shaft pull out the shaft from the coupling? The shaft comes out about an inch from the stern post.Is this normal? I'm reticent to unbolt the coupling along the saying :''don't fix it if it ain't broke''.Is there a torque to these bolts?Thanks.

[sailormed]

Are you sure that this is a new situation? Maybe it has always been like this but you never looked at it.

[copaco]

I will look at other boats when I get back to the boatyard, in the spring.In any case ,I guess, I would just have to pull the shaft back in.Would not loose anything.

[jkishel]

Not sure I understand the question. If you are worried that the shaft has slipped aft, there should be a set screw or two on the coupler engaging with a dimple or flat in the shaft. The set screws should be wired to prevent them from backing out of the coupler. If the set screws are tight in place the shaft can't move aft unless the set screws shear at the tip (unlikely). You could remove the set screws to make sure they're OK. Often you can see the dimple with the set screw removed using a flashlight.

[skipperpete]

Originally Posted by copaco

Can the turns around the shaft pull out the shaft from the coupling? The shaft comes out about an inch from the stern post.Is this normal? I'm reticent to unbolt the coupling along the saying :''don't fix it if it ain't broke''.Is there a torque to these bolts?Thanks.

The answer is definitely YES!!! and even worse things can happen. This gearbox was on the back of an idling in gear 75hp engine when the boat overshot the buoy and picked up the top line. There was no rapid approach or crash stop, just the half inch line winding between propeller and deadwood...... then no ahead or astern.
In a vaguely related event, a marine mechanic created a slide hammer tool that was held by the prop nut on the outboard end of the shaft....... theory was to release the coupling setscrews inside and with a few quick hits on the slide hammer the shaft would pop out of the coupling but he got a really tight one and pulled the end out of a similar Hurth gearbox.

[copaco]

Interesting.Thanks all.

[Boatyarddog]

Originally Posted by skipperpete

The answer is definitely YES!!! and even worse things can happen. This gearbox was on the back of an idling in gear 75hp engine when the boat overshot the buoy and picked up the top line. There was no rapid approach or crash stop, just the half inch line winding between propeller and deadwood...... then no ahead or astern.
In a vaguely related event, a marine mechanic created a slide hammer tool that was held by the prop nut on the outboard end of the shaft....... theory was to release the coupling setscrews inside and with a few quick hits on the slide hammer the shaft would pop out of the coupling but he got a really tight one and pulled the end out of a similar Hurth gearbox. Attachment 208043

Yes, this can and does happen, never slide hammer a shaft out of a coupler.
Remove the Bolts holding the coupler faces, separate them and use a properly sized nut to insert between the gear end shaft and the prop shaft end the use the Coupler bolts to pinch them together, this will push the prop shaft out of the coupler.
Properly service the shaft and check for a press fit of the coupler and shaft, when installing. Never will a loose shaft Retighten.
It's a press fit. Then Dimpled and set screws or thrubolted.
SV Cloud Duster

[Dsanduril]

If the line looks like the shaft coming out of the coupling then it needs attention as described above. But if the line is back by the “stern post” check that the transmission doesn’t move the shaft. Some transmissions move the shaft forward/aft by 1/2” (12mm) or so when shifting. This causes a line at the strut and at the stuffing box when in neutral and the shaft is not at the “forward” location (the forward gets the most wear). An easy thing to check, just shift the transmission and see if the shaft moves.

A picture of your area of concern would go a long way to helping make sure we’re answering the right question.

[jmschmidt]

Does you coupling have set screws and does the shaft have provisions for the use of set screws? If so the set screws should be safety wired together to prevent loosening. If the set screws are loose the shaft can back out of the coupling, if not completely out of the boat, when in reverse. Without a keyway with a key properly in place the shaft will slip in forward and reverse so check that too. Property torqued and safety wired set screws and a keyway with key in place should cover all possibilities.

[AKA-None]

I had set screws come loose once while reversing into a slip. Only thing I noticed as I was leaving the boat was the sound of the bilge pump. The prop pulled the shaft right out of the boat. Luckily it could not fall out but I now had a hole where water was coming in as fast as the pump was taking it out. A quick plug with a rag and a call to the dock manager got me on a travel lift where I pushed the shaft back in and revolted it. Fixed the problem but I still check those safety wires very regularly

[copaco]

I appreciate this good advise.Will check all this in the spring, back at the boatyard.