2019 G23 Shaft breaking?

[seachicken27]

Marine propulsion shaft failures are nothing new. Do a Google search on that term and you will find over 800,000 hits. In large yachts such as the Hatteras shown in the video, the propellers are mounted as close to parallel with the water flow as possible to reduce the angle of attack of the blades and therefore reduce prop shaft bending forces. Large Yachts clearly don't have surf systems that yaw the boat and introduce bending forces on the shaft either. Shaft failures on large yachts occur primarily because of the very high torsional forces required to turn and reverse the large diameter props.

Failure analysis for prop shaft fractures is a VERY well established science. Failures are easily classified using the diagram below.



If you look at the shaft failure in the Hatteras video you will see that the fracture plane of the crack is not 90 degrees but rather angular along the length of the shaft, similar to the Torsion failure plane example in the diagram above. This confirms excessive torsional loads.

The failures on all of the G23 shafts that I have posted and the others pictured in the numerous images in these forums are 90 degree fractures. This is indicative of BENDING forces on the shaft. These bending forces occur because of Yaw and Shaft Angle of the propeller, not torsional overload.

Finally, the new G shafts are cut with a rounded key way to reduce this stress point. However, I have not seen a round key yet. I suspect that might be coming soon.

Well, this may be the most informative post I've ever seen on this topic. Thanks for posting.

[scottb7]

Be reminded of the story...When i purchased the boat it came with the trolling motor. The previous owner had the shaft break and lost a prop. The previous owner was an army medic having completed 2 or 3 tours in Afghanistan and similar places just after 911, and an author. I don't know if he came up with idea of putting the trolling motor in the boat or if someone else suggested. But given a read of his book and his resourcefulness I wouldn't be surprised it was his idea.

Yes, as other have said this is not gonna help you in a storm. So you need an anchor. And while me and a couple friends were putting in place for the pictures I realized that if lost prop, first step would obviously be anchoring. It moves the boat pretty easily but not at a great speed. No, I don't know what speed we got up to. We put it on, the 3 of agreed it is a nice thing to have just in case, and then we put it away. We had a 4th guy waiting on the dock to be picked up.

The point seems to be lost on quite a few on this forum. I live on a lake with no service you can call. At the beginning and end of season we are only boat dock/lift and we obviously are not going out on stormy or windy days. So if we lost a prop we could get home. That is all.

[GMLIII]

Where is the skipper ?