Mirage drive mast torture

I’ve had my AI for about a year now, absolutely love it.

I’ve bent the drive masts now a few times in shallow water groundings. For the most part, I just bend them back and keep on using them. It would seem that after being bent back - good as new.. Last time I bent them, I just popped the drive out and bent the mast back by hand out on the water.

It seems to me that I can probably keep doing this many more times.. Should I be more worried about this? Anyone actually wore a mast out so that it won’t hold it shape during normal peddling?

I think most people wear out fins first! I haven't heard of too many masts being replaced, but it does happen.

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IMO the mast begins to crystallize at the bend and become brittle at that spot -- each bend weakens it a little bit and it can eventually break without warning. It looks like this:


Your safest option is to replace the mast(s) at this time. Or you can keep one spare mast and sprocket on hand as replacements when an existing one fails. The sprocket is advisable in case there is no mast nub left to spin the mast base out (your Easy-Out option will not necessarily work in this situation). In that event you would need to replace the sprocket as well.

If you decide to go with option #2, be sure you are current on your one-fin operational procedures.

One fin operational procedures? Please explain. Apologies to all Australians for whom that phrase is traumatic

This should cover it: viewtopic.php?f=11&t=8240&hilit

Here's a confirming opinion:


This is a GPS printout of a one-Turbofin cruise on an Adventure -- not as bad as one might expect. Note the relatively weak acceleration. Obviously the AI would be a bit slower and more subject to wind and chop.

Note: An overly tightened fin clew gives more rock and roll, less thrust.

Please explain.

I have found that the sprockets are the weak spot. How is it that the fin mast is bent and not shear the teeth on the plastic sprockets?

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One fin and apoligies to us aussies would be DarDap DarDap DaDaDaDa Jaws


Probably because of forward motion and the collision bends just the mast where as a side impact would put pressure on the sprocket.

Wouldn't it be easier to just be more careful and protect your drive. In my first twelve months of owning one, I constantly bent fin masts and destroyed a set of fins. Then I just got smart about how and when to use the mirage and have not bent a mast in many years, it's a far better way to go.

How many sprockets have you had fail?

Third sprocket in nine months. It is always the front one on the turbo drive. I don't hit bottom and pull the drive before the boat ramp and beaching. The cable and chain tension are correct.
Have two other standard drives one almost two years old and never a failure.
The only modification to the turbo drive is the bolt through replacement of the adjustment pins and the other holes are filled with epoxy. The plastic there failed also.
The scary part about the last sprocket failure was the when of the failure. I was taking my sister in law out for a quick sail and it did the pop and slip. But that was just after a 26 mile off shore solo trip and the one thing I didn't have was a spare drive. Think that was my free warning.

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Fly, three failures, one location -- I don't think you have a sprocket problem, but rather a chain problem. One or more links may be too narrow, causing the chain to ride over one or more cogs and ultimately chewing the cogs up. Visually, it would look something like this:


If you cycle the Drive by hand, you would feel a little "lumpiness" where that link jumps on and off the first cog, as opposed to a smooth cycle throughout the normal (180 degrees) operational range.

I have bent several masts, broken a few and even straightened them side to side where the sprocket takes the full force of the bend -- never had a sprocket cog break, chip or wear out. Hopefully, a chain replacement will solve your problem.