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 Post subject: ST fin tear-throughs
PostPosted: Mon Feb 09, 2009 7:38 am 
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Joined: Sat Jul 12, 2008 1:03 pm
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Location: Cocoa, FL
I have seen a thread or two talking about the ST fins flexing to the point where the steel rod pokes through. This happens to me and many of my fellow kayakers on a far too frequent basis. We kayak in the Central Florida area and most places we go have lots of underwater logs and shallows. We try to be diligent and keep are pedals apart when these obstacles arise, but it is only a matter of time before you get the poke through of the rod/fin.
I have read that the newer ST fins are tougher, but they all seem the same to me. I would be willing to spend more money on fins that have some sort of corded construction (similar to belted tires or automotive hoses). The entire fin would not have to be like this, but the lower area towards the bottom of the fin could be. I have resigned myself to knowing that they are likely going to tear on a regular basis, so a ruggedized ST fin would be a God-send.

One idea that I would like to entertain is developing a new style mirage drive that drafts about half of what an existing drive does. I know it would be costlier, more complicated, and maybe not even possible, but imagine having 4 drive fins instead of 2. These 4 fins could be half the length of the existing fins, but the end result would be the same total fin surface area to push water. Shorter fins means shorter rods and shorter rods means stronger rods that would be harder to bend. Shorter fins also means fewer underwater impacts. I am not sure if a 4 fin system would be possible to fit into a single hole in the hull though. Maybe there could be a master and slave drive whereby the prime drive would be mounted forward where the foot pedals are and that could mechanically interface with a secondary drive (a bit further aft in the kayak) via an integrated shaft in the hull of the kayak. Sure - this would make for an expensive, heavier kayak even if it could be done, but at this point I am willing to entertain anything to keep from tearing up fins and bending rods. I am not sure if the efficiency would remain constant using 4 shorter fins rather than 2 though.
Thoughts?


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 Post subject:
PostPosted: Mon Feb 09, 2009 9:34 am 
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Joined: Tue May 27, 2003 12:44 pm
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Try some of the "Tear-Aid" tape around the tips. roadrunner did a thread on this and he was able to repair torn fins.

http://www.hobiecat.com/community/viewt ... light=tear


http://www.hobiecat.com/community/viewt ... light=tear

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 Post subject:
PostPosted: Mon Feb 09, 2009 4:58 pm 
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Location: Cocoa, FL
Thanks for the links Matt. I had seen one of them before, but not the other.
Maybe I am not a good sampling of the average kayaker, but I am an engineer (who by default is solution-oriented), almost 50, and have reached the point in my life where I would rather spend a lot ($$) and have less hassles than to spend a little ($) and have the hassles. While a repair method is great I would rather not have to mess with it in the first place - especially as often as this happens to me. I would pay double the amount per fin if they were for the most part puncture-proof. I just have to believe that a puncture-proof fin can be made (even though it will probably be pricey). If people like me will pay extra for cushy i-comfort seats surely there are those that will pay for ruggedized fins. Just my two cents FWIW.
I have gotten in the habit of taking an extra ST fin with me when kayaking since they are relatively easy to change.


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 Post subject:
PostPosted: Mon Feb 09, 2009 5:49 pm 
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Our challange is to make a fin soft enough to flex, but tough enough too.

As roadrunner mentions... we do have the stronger material these days. You would have to look at the fin to tell. There is a small "TT" on the fin.

The best "rough use" solution may be to use the new fins and add the Tear-Aid on the tip before use.

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 Post subject:
PostPosted: Mon Feb 09, 2009 6:43 pm 
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Location: Cocoa, FL
Fair enough Matt and thanks. I will try the tape as a preemptive strike. Thanks to Roadunner too. (I do not see a TT on my ST fins, but they are very black suggesting they might be the stronger type. It would be nice though to be able to know you are getting the new type when you order them).
On the 4 flipper idea... does that sound like it could even be remotely feasible (even if it is cost prohibitive)?


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 Post subject:
PostPosted: Mon Feb 09, 2009 9:39 pm 
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The Tear-Aid is amazing on rigid surfaces. I had a test strip on the hull and after 4 months had to really work to remove it.

It's a little different story on fins though. As I mentioned in the earlier post, I recommended it for up to about 10 hours of use. Eventually it starts to lose its grip on the corners. Here's what it looked like after about 60,000 flexing cycles:
Image

When I finally removed the tape from the fin, it was again very difficult getting it off where it was undisturbed. So give it a try but you may need to replace it (or trim it) from time to time.

When it comes to fin toughness, standard fins have the best resistance to damage. But as with tires, one can get performance or longevity, but not both. The new fin material is a huge improvement though.

I hit a concealed clay bank in muddy waters over the weekend and came to an instant halt -- had to extract the Drive to free the boat. But after a little de-mudding I was back in operation and on my way again -- straightened the mast later. Frequent mast bends can be annoying, but designating the mast as the sacrificial piece is really a good design alternative to breaking the Drive or boat. Not only is it less expensive for an occasional breakage, but one rarely looses operational function with a bent mast and holey fin as opposed to a broken Drive or cracked hull.

So until Hobie comes up with the extra shallow 4-finned Drive, keeping spare masts and fins is probably a good idea. 8)


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 Post subject:
PostPosted: Tue Feb 10, 2009 4:44 am 
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Thanks Roadrunner. You have provided some invaluable information here and for that I am grateful. I completely agree about the tire scenario (having once had an Audi TT Roadster where the dilemma of performance or longevity was always there). I was hopeful though that the fin could be made such that the area surrounding the bottom end of the steel rod could be made of the corded (belted, toughened) material while the rest of the fin could be made essentially like it is already. In other words only a small area of the fin (maybe even a permanent patch) would have to be ruggedized. Reliably bonding those materials together may be easier said than done though.
I also agree that having the fins and rods as sacrificial lambs is a small price to pay in the grand scheme of things. I could be regularly pouring money into a gas tank of a boat that couldn't even be getting into the areas I go, so overall I am happy.
I also keep these spare parts close by. I bought the new brass threaded insert assemblies and rods and will retrofit when the standard design is in need of replacement.
Hobie has done a great job in being forward thinking and have really come up with some outstanding ideas and products. I am glad that they provide this forum to solicit ideas for future improvements.


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