Modifications to the "Allen Screw" sprockets ?

I am considering attempting to modify my "allen screw" sprockets (by this I mean the sprocket assembly which uses a small Allen-Key grub screw to secure the fin mast in the sprocket) to accept a cotter pin as a way of securing the fin mast and am wondering if anyone else has attempted to modify one in this way ?

To my knowledge Hobie has procuced three versions of finmast to sprocket attachment in their drives:
I. Cotter pins - where the fin mast and the (Stainless steel) socket in the drive have a small hole through which a cotter pin is inserted to secure the fin mast.
II. Set screws - in which the fin mast has a flat section at one end and the sprocket has a set screw which is tightened to bear on this flat section and thus hold the fin mast in the socket.
III. Screw-in fin masts - in which the fin mast is threaded and screwed into a threaded brass insert in the sprocket unit.

I have 2 drives: one version I and the other version II.

Version I works perfectly: The attachment of the mast is 100% secure and removal of the stub of a broken mast is dead easy: remove the cotter pin and out it drops.

Version II has problems: the set screws back out and the masts fall out. And if a mast snaps off at the base (as mine are increasingly doing) it is the devil of a job to get the stub of the mast out of the socket. I notice that they always snap where the flats have been machined i.e. where there is least metal. The advice to use loctite to secure the set screw is only partially successful (my screws have continued to work loose) and any loctite which finds its way onto the end of the mast "locs" the mast stub into the socket in the event that the mast snaps at the base - and if you can't get the stub out you have to replace a perfectly good sprocket unit which is wasteful and expensive.

From what I hear I am not convinced by Version III - people have already reported that their screw-in masts back out of the sockets and the perceived wisdom is that they need to be loctited in meaning that the stub of a snapped mast is effectively glued into the threads of the socket meaning that the whole assembly needs to be thrown away to effect a mast replacement. The other issue I have is that I am concerned with turbo fin masts snapping off at the base: cutting the threads into the screw-in masts MUST make the masts weaker at the base i.e. exactly at the point at which mine are snapping off...

So rather than converting my drives to accept screw-in masts I am considering drilling a small and accurately-placed hole through the sockets in my V2 "set-screw" drive to convert it for use with a V1 cotter pin system. Since my V1 "cotter pin" drive has stainless steel finmast sockets whereas the V2 "set screw" drive has plastic sockets I am concerned that drilling these holes may weaken the sockets causing the socket to fail rather than the mast.

• Has anyone else attempted this modification ?
• Are others out there experiencing the same frustration and safety concerns over finmasts snapping?
• Is anyone aware of any reason why a screw-in fin mast should be less likely to snap than a cotter pin or a set screw mast ? (In other words is there a sound justification for upgrading to screw-ins ?)
• I wonder if Hobie has considered/would consider going back to the simple and effective cotter pin system ?

Stobbo,
It's a bit confusing when you refer to V2 as V3 (though I know what you mean others mightn't).
It's accepted that the V1 is actually the first of the plastic sprockets with the allan key grub screw. V2 is the screw in mast ( it's stamped on the sprocket)
I'm not sure if your split pin mod would work. My concern would be the nylon sprocket hole wallowing even more than when the set screw backs out.
You are right about the V2 screw in masts being difficult to replace. I carry a spare sprocket and mast for that reason.
Fortunately I haven't needed to use it yet despite a couple of severe fin strikes and bent masts. The V2 design is much stronger. You can straighten the mast easily on the drive without dismantling it (apart from removing the fin of course).

The original cotter key mast retention system was used on a stainless steel sprocket. That is still available if you wish (81130001 $41.15 USD Fall 2010 Catalog / Page 39). Some like the stainless as the teeth are stronger. Reality is though, it requires a tighter chain to keep the teeth engaged. The plastic sprockets have one tooth that is square which locks the chain on a bit better.

The mast is a bit loose in the stainless fitting, so wobbles and breaks cotter keys. That is one reason we changed. The plastic sprockets allow a tighter fit for the mast.

The latest version sprockets using a threaded mast have been the least problematic. The threads are "rolled" not cut. The mast materials may have been a little weaker on earlier versions. Does require loc-tite.

Safety concern? You can pedal with a single fin... and you can always resort to the dreaded paddle.

_________________
Matt Miller
Former - Director of Parts and Accessory Sales
Warranty and Technical Support
Hobie Cat USA
(Retired 11/7/2022)

Stobbo, I would rate the current threaded sprocket (V-2) best (most trouble free), followed by the stainless (V-0? cotter pin version), and the Allenhead version (V-1) weakest.

I agree with Stringy that the cotter pin in the plastic sprocket will probably not hold up. The most trouble free solution for the V-1s is to epoxy the whole assembly together including the "grub" screw. Even that will eventually work loose, at which point it's time to change over to the the V-2s IMO. I converted all my Drives to the V-2s and find them to be much more trouble free.

I've never had a V-2 un-thread when using thread locker, but it will un-thread in short order if you use nothing, no matter how tight you assemble it. You MAY find that Teflon tape could be used as a substitute, but it's not really necessary. If you break a mast flush with the sprocket using Loctite blue, you should be able to extract the broken piece using a screw extractor. If you break a mast having used a "permanent" thread locker like Loctite Red however, you will likely have to replace the sprocket as well as the mast. That's probably why it's not recommended.

All Turbofin masts are subject to metal fatigue with frequent bends and/or aggressive use -- they can take a lot of flexing but not an infinite amount. Apparently Hobie uses the strongest stainless alloy available so you just have to consider it as a wearing part.

Great advice, insights & corrections Fellas !

it sounds like what I describe as Version 1 should in fact be referred to as Version 0 - the stainless steel with cotter pin version.

The problem for me is that here in NZ Hobie parts are very expensive and often not available off the shelf. Things are getting better due to a stronger NZ dollar and an increasing community of Hobie owners, but still the costs are probably 2x the USA and shipping delays are weeks and can be months if items have to be ordered.

While I accept that it would appear that the masts are a wearing part I would like to minimise the cost and inconvenience associated with a breakage. It's a bit of a Hobson's choice having to decide between discarding sprockets or investing in a thread extractor to make them re-usable and in any case replacement of a whole sprocket while out on the water would be a dicey proposition if practicable at all.

Matt's right in that the masts definitely do slop more in the stainless steel drive but that has never really bothered me and it might be possible to shim them in with e.g. a matchstick (I have never felt it worth trying). Personally, I have never had a cotter pin wear fail out on the water, though I have replaced them. If one did fail at sea it would be an easy fix and it is not a large or expensive part to have to carry in the toolkit.

I have experienced cog skipping on both stainless and plastic sprockets but this goes away if the cables (and particularly the idler cable) are properly adjusted.

So rather than upgrade to the screw-in version I rather like the sound of a downgrade to the stainless steel version... unless anyone can give me a more compelling reason why not to ?! Another benefit, if I were to do that, would be that I have a stock of perfectly usable cotter-pin-ready masts minus the last 1.5 cm from all the broken set-screw masts that are lying about in my garage

Very interesting, have now discovered why the V1 masts I bought for the second hand Sport didn't have a hole for the cotter pin, they were what Stobbo calls V0

Stobbo when I took the V1 masts down to the local engineer to get a hole drilled in and the older masts straightened he said he could make me some new masts, if required way cheaper than the genuine parts. He is also replacng the pedal shafts for me as they were quite badly corroded.

My wife loves her Sport heaps more than any of the paddle yaks we owned.

Yo Charlie,

I have thought about the possibility of doing that myself on several occasions. Where were you going to get them made & have you been able to verify that the same (or a better) grade of metal would be used ?

Hi Stobbo, I live in Te Awamutu so just go to the local engineers, Stewart and Cavalier. They are really helpful and quite happy to do small jobs. As a matter of interest the masts aren't stainless steel, the engineer ran a magnet over them and it was attracted to the metal. But I guess you wouldn't want too hard metal as you do want the mast to bend on impact!