Prop Shaft Backing Out of Coupler

[Terra Nova]

SM--lock-wiring is the correct solution.

[a64pilot]

Originally Posted by Cadence

I would be more prone to us grade eight bolts for a coupling JMHO

I don’t think they are necessary, in fact I’d say go with SS for corrosion resistance, and I’d rather those bolts be the weak link anyway.
Look at the tiny bolts holding a V8 rear wheel drive automobiles drive shaft in, and one assumes the torque seen by that is way more than I’ll ever send down my shaft with my mighty 44 HP.
Don’t remember the size of the bolts, but a 7/16” wrench fit them.

[Terra Nova]

Originally Posted by a64pilot

...Look at the tiny bolts holding a V8 rear wheel drive automobiles drive shaft in...

The automobile drive shaft torque is usually transferred by a spline.

[a64pilot]

Originally Posted by Terra Nova

The automobile drive shaft torque is usually transferred by a spline.

Not on the end that hooks to the rear end, the U joint sits in a yoke.
Now these bolts are not subjected to direct shear like the ones on a coupler are, so it’s not a direct comparison, but if memory serves my old coupler had four .25” SS bolts, and even if you disregard the friction between the two halves, the shearing Force required to shear four .25” bolts is rather a lot.
My Sigma drive connects to the shaft only by friction, and it seems to hold very well.
Unless you hit something, Then I’d rather something easily replaceable break as opposed to a prop or a bend the shaft. Assumption is the Sigma drive will just slip. I guess I ought to slippage mark it.

[Cadence]

Originally Posted by Terra Nova

The automobile drive shaft torque is usually transferred by a spline.

Spines and universals. not sure about the relevance. I love SS for corrosion properties, it sucks for tensile strength.

[Suijin]

Bolt heads on the coupler should be drilled and seized with wire. That’s standard best practice.

[jkishel]

To close the loop on this - I was able to move the shaft forward by running in forward with the boat tied to a dock. However the dimples in the shaft went past the set screw holes. I did engage a pro, Andy Kimble, Stock Island, who unbolted the coupler and pulled it aft by hand. BTW, the prop and shaft were stopped by the rudder long before the shaft cleared the stuffing box, so no danger of sinking...anyway, we were able to tap the coupler forward with a hammer and align the set screw holes with the dimples. Reinstalled the set screws and checked engine alignment. Unfortunately the coupler was rounded way out of spec. Rather than haul and remove the shaft, I found a split coupler (Buck Algonquin - short version so that installed it doesn’t prevent unscrewing the stuffing box) that looked like it could be installed in the boat. It was a tight fit, but progressively driving wedges in the slots and applying propulsion, the shaft eventually made it home. Andy drilled a new dimple for the single set screw, wired it in place, adjusted the engine alignment and we were back in business or so I thought. However, the cutlass bearing which was only 300 hours old, sounded pretty bad, so in the end we hauled out at 3D Boat Yard, Stock Island, and replaced the cutlass bearing. My theory is that the old, rusty coupler (rounded out) and/or engine misalignment prematurely destroyed the cutlass bearing and the whole vibrating mess (alignment/coupler/bearing spit out the unwired set screws. Lesson learned: check engine alignment and coupler runout annually (not hard) and correct as required.

[Suijin]

The whole running gear needs to be aligned or you'll end up with further problems down the line. If it were my boat and it was hauled I would:

1. Pull the shaft and have it checked for runout. If it's not straight nothing else you do will matter.

2. Put a new solid coupler on it, ideally having it faced on the shaft by a machine shop. Split couplers are asking for trouble...your boat is right at the limit of where they are even viable imo.

2. Put in a new cutless bearing.

3. Align it all after the boat has sat back in the water for a few days.