Hints and Tips



Vetus COMFL1230 shaft coupler

Doug Bostrom upgrades the OEM coupling with a Vetus unit


Chapter 1


Background: in 2017 the dripless seal on our SO39ip needed to be replaced. Without going into too many details, the cost-optimized OEM coupler supplied with the prop shaft was not removable. The situation strongly indicated an upgrade, time was of the essence, and a replacement part would have to address loss of shaft length due to slicing off the old coupler.


Product: The "Vetus COMFL1230" addressed the preface above. Thanks to a little serendipity in dimensions, this part allows the old coupler to be cut off and due to its construction "adds back" the lost length, with a short bit to spare for fitting purposes (there's a bit of extra length to play with, which makes cutting the shaft less of a frightful proposition).



As well, and this is key, this is a split coupler which means "stuck" is a thing of the past. There is absolutely no sense in retaining a one-piece coupler after the first time it's necessary to get it off the shaft. "Stuck" is nearly inevitable, and life is too short to spend on removing fused couplers. I'm not sure how many if any Jeanneaus are made with shafts at this point, but if I were the owner of a fresh boat, I'd swap couplers immediately, before seizure happens.


A side benefit of this coupler is that it absorbs up to 2 degrees of misalignment. I suppose this should not be taken as an invitation to stop paying attention to alignment. For our boat there is a rumor that overdoing the backstays can throw the shaft out of alignment. I don't believe that's significantly true, but still the backstop is a comfort.


Measurement: the new Vetus coupler absorbs a certain amount of length within the clamping portion. Ahead of that are several centimeters of additional coupler structure. The length of the shaft needs to end up with the prop in the right position and with the coupler flanges ready to mate, after pulling the shaft forward to its normal position. Measure carefully, do the arithmetic carefully, then do it all over again. There needs to be absolute certainty on where to cut.


Cutting: On advice from an old hand, I did not use a power tool with a carbide blade to cut off the old coupler, as apparently the nitrides in a typical cutting disk will rapidly alloy with the stainless, causing cutting to become extremely slow.


As well, using a disk cutter in this situation (shaft in "alley") is an invitation to a nasty injury and will certainly make a hell of a mess.


Instead, I used a quality nitride-free blade in a hacksaw to accomplish the cut. Given the location, the stroke on the saw is short. Even so, the actual time spent cutting the shaft proved to be only ~25 minutes, with total time including resting tired arm about 40'.


Even though it's not a critical matter, the cut should be as close to perpendicular to the shaft as possible, a weakness of a hack saw. More by luck than skill, my cut ended up with a degree or so of true. For the picky, I think it would be possible to fashion a guide out of a semicircle of other material placed over the shaft.


After making the cut, use a file to thoroughly dress the freshly cut edge of the shaft, so that burrs don't become annoying when sliding on the new coupler.


Fitting: A piece of cake but see chapter 2. Simply follow the Vetus instructions. Vetus called for a torque and I was lucky; my torque wrench happened to fit in this space.


Results: Excellent. It wasn't an objective for me, but the coupler does (as promised) reduce noise and (especially the higher frequency) vibration from the shaft. This was never obnoxious, but it's still noticeable when gone.


More importantly, the coupler paid off exactly as anticipated the very next year, when I had to fly in to where the boat was located on a light aircraft with a scanty subset of tools and a spare transmission, to swap out the failed unit. "Failure was not an option" on this mission, and knowing and then confirming that the coupler was the least of worries as opposed to the main worry was a huge benefit, hard to describe short of living the experience.


Chapter 1 is a solid win; chapter 2 should not dissuade somebody from doing this modification, with one important caveat which will be addressed shortly.


Photos: cut shaft (as a ray of hope for those thinking about cutting), shaft with project complete.




Chapter 2


Early in summer of last year (the infamous 2020) I got an advisory call from our charter firm to the effect that propulsion on our boat had failed. Happily the crew on board were calm and able to use the scanty wind available to keep the boat off a reef it was being set onto due to tide, for long enough to allow a tow to arrive. The situation depicted via AIS confirmed that we were fortunate in our crew.


The crew reported that the shaft coupler was detached from the transmission, the flanges having separated with what appeared to be fractured bolts. Our thought was that a strike with a deadhead had happened, or maybe a solid contact with an errant net. The crew were repeats and quite trustworthy, said that nothing obvious in that way had occurred. Even so, some form of jam in the prop seemed most likely given the failure mode and that the engine was running at speed when propulsion stopped.


This past year 2020 - despite the whole virus hassle or maybe because of it thanks to isolation needs - we had an extremely busy charter year. The boat was towed home but had to dispatch again with 36 hours of arriving at her slip because the company was fresh out of boats and it's just not acceptable to refuse a crew a boat. So, my challenge was to get her turned around very quickly, but safely.


First inspection showed that the coupler had come detached at the transmission flange. However, no strike had happened. Instead, examination revealed that three bolts for the flange-coupler adapter had separated from the receivers in the coupler, and the last had failed under fatigue (visible "beaching").


Wow, what a lousy coupler, eh? Well, not quite. What happened was that the kit of parts supplied by Vetus included incorrect fasteners, a fraction of the length intended. At the time I installed the coupler I'd noted this but thought, "who am I to question?"


Total threads engaged: ~ 4 per fastener. Enough to handle torque setting, but not to live for long.


Given that the parent metal of the drilled and tapped receivers in the coupler is cast aluminum, the stress imposed on the scanty threads was too much. The aluminum worked under this abuse, the tapped threads eroded, and eventually the foregone conclusion happened. 3:4 fasteners fell out and the last which somehow hung on was not intended to handle all of the propulsion torque alone. It fatigued and snapped.


Repair: With the peculiar length requirements of this coupler, there was simply not enough time to either source a direct replacement or a potentially superior alternative. However, the parent metal of the coupler casting offered plenty of depth for additional drilling and tapping. The key then would be to arrange that the unsupported portion of fastener passing through the area of former threads would be supported.


That drilling and tapping happened in the dead of night, lubricated by cutting oil and beer, after driving south again 80 miles to my shop plus some mad scrambling to obtain a generous supply of metric taps and drills of correct size, extractors just in case something popped up. With that complete, up at dawn the next day to drive N again, get the part put back on the boat before the next GC showed up.


Mitigation of loss of material, and a tip: These couplers are supplied with a flange adapter that only needs to be installed once. It's not plausible to say that a flange will be moved to a different coupler-- they are bought as pairs and married for life. Therefore, an additional backstop for reliability is to fix or seize the fasteners after this marriage has been made.


Support of "flying" portion of flange-coupler fasteners where coupler receiver threads were gone and seizure of fasteners was done with epoxy.


Tip #2 In retrospect, for monitoring purposes it seems a good idea to make alignment marks across the entire kit of coupler, flange adapter, transmission flange, so that movement can be assessed at a glance in routine inspection.


Vetus response: I contacted Vetus about this. After my first getting and replying to a request for more information with all the info and photos, Vetus clammed up, maybe because even though I emphasized I wasn't looking for financial recovery I did fully paint the picture of where short fasteners can lead (tow was covered under insurance in any case). Presumably and hopefully they're now doing a better job of kitting. I feel as though this particular coupler that I modified is now better than original, trustworthy, but I might choose another brand/model assuming I had time and dimensional freedom for that.


It remains the case an easily removable coupler is still a solid win.


Photos: Supplied fastener vs correct length (no, the correct one is not the right style), upshot in receiver portion, "laking" to fixate fastener heads.





Oh yeah: one more thing. The extraordinary luck of finding four and only four 10mm "cheese head" metric fasteners to replace the failed/destroyed ones, in a dusty bin and after the fellow helping registered my desperation and ransacked shelves. Metric here is still along the lines of rocket science. It's the United States. Otherwise it would have taken at least 24 hours to obtain these. Without that key bit of luck, the boat would not have dispatched


Doug Bostrom


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