TOPIC: Broken drive shaft at propeller

Hi everyone,

Took the '67 Arena Craft out for it's first spin with me yesterday. Pretty nice hole-shot and an overall fun boat Unfortunately, the fun lasted for about ten minutes.

The solid brass drive shaft sheared somewhere in the propeller hub (I assume this because there is a good inch of key way still there at the broke end). How does one go about even finding something like this? And what should I do about sourcing a propeller? Best guess at pitch?

Really my largest concern is WHY this happened as I don't recall hitting anything. And, after a looksy under the hull, I'm a little concerned with how the drive shaft exits the hull. The packing-housing-thing (sorry, not up to snuff on my boat terms) appears to have been removed, holes plugged, and relocated. And the drive shaft seems to be riding on the fiberglass.

Any input would be great. I'm going to continue researching how to determine the shaft size, but I can't help but wonder if there is an underlying issue here.

Looks like the shaft was indeed broken because of fatigue, possibly from imbalance or prop strikes in the past. From the picture it looks like it has been twisted off and there are some signs of fretting indicating some old cracks. Anyway that is the least of your issues. The shaft is indeed running out of true, you must check the engine mounts for collapse and the strut for being bent, pulling the shaft all over the map. The stuffing box mount is cracking the hull from the strain of misalignment and this will require repair and the whole works aligned on assembly. There is a lot to fix here and you may need the help of a pro who knows what the Hell he is doing.

Thanks for the feedback! The misalignment issue definitely became more apparent as I went through the process of removing the drive shaft. I'm pretty sure the Cutlass bearings are gone... once the shaft was free of binding the play became noticeable.

As much as I enjoy entertaining the idea of just taking it to someone, that simply isn't an option. Aside from qualified repair shops being open only while I'm at work, there's the budget issue. Guess I picked the wrong hobby haha.

I definitely have the mechanical dexterity to do the work myself, it's really just a matter of understanding alignment. And, I understand the theory behind alignment, and the factors that come into play (just as you have mentioned), I just need to figure out which feature "rules all" in choosing the reference to determining alignment. I thought it would be the strut, but now I'm thinking it may be a combination of the strut and shaft log as a partnership. Supposing the shaft log was in the wrong spot, AND the strut was bent, how would you go about determining alignment at that point? Shoot a laser down the center of the hull?

Also, the original shaft was only tapered at the prop end... making the coupling a real pain in the ass to remove (it may have involved a cut off wheel). Couldn't I purchase a double-tapered A.R.E shaft through Skidim, so long as the diameter, length, and coupling features are correct? I don't see a reason as to why I couldn't "upgrade" the driveshaft profile instead of looking for another single taper shaft that's going to make me sweat putting the new coupling on.

As for the fiberglass? I figured the shaft log's mounting flange-to-hull was large enough to alleviate leak issues with the worn fiberglass. I was just going to fill the cracks with a recommended, off-the-shelf item. I know there is a definitive "right way" and "wrong way", but certainly there must be a gray area on this.

gfgarland wrote: Looks like the shaft was indeed broken because of fatigue, possibly from imbalance or prop strikes in the past. From the picture it looks like it has been twisted off and there are some signs of fretting indicating some old cracks. Anyway that is the least of your issues. The shaft is indeed running out of true, you must check the engine mounts for collapse and the strut for being bent, pulling the shaft all over the map. The stuffing box mount is cracking the hull from the strain of misalignment and this will require repair and the whole works aligned on assembly. There is a lot to fix here and you may need the help of a pro who knows what the Hell he is doing.

No magic involved in alignment, just slow careful work. A laser will work to sight down the log to see if it is square with the hull, but the strut is the real bugaboo as it has to be straight and true with the engine coupler on the flywheel. Once all the roughing in has been done you can take it to a a shop for the final alignment, or just take your time and do it yourself. The shaft and engine coupler are an interference fit by a thou or so, but you can get split couplers that slide tight on and you just snug the bolts up after. The coupler faces should align to within .003" when all is good, and remember to check the alignment in the water after the boat has been launched for a few days, never on a trailer or cradle as this will alter the readings significantly. Take your time, double check everything and you should be alright.

There is a great video on alignment on youtube. you can find it if you search under correct craft and shaft alignment. I still have that to do with my ski nautique.