Make aka brace sheer bolts stronger.

I have installed a plastic sleeve into the metal hole on the ama brace connection where the plastic sheer bolt fits through. This makes the plastic bolt fit in firmer, reducing the back and forth movement which puts a lot of stress on the sheer bolt. The sheer bolt will still be able to break under pressure, however it will take more force, and the plastic insert will help stop the bolt from wearing out. The yellow plastic sleeve is a cut off section from the end of a plastic wall plug. I found the yellow one to be a perfect fit. Plastic tubing will also work, if you can find the right size. What are your thoughts ??????

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2021 Dune Hobie Lynx

Brilliantly simple idea - I'm going to do the same...

The extra 'padding' provided by the plastic liner should certainly dissipate some of the force exerted on the shear-pin.

Cheers,

Mike.

Interesting idea! Although having safety lines lessens the consequences of a broken pin, making preserving the pin less critical.

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Tony Stott
2012 Tandem Island "SIC EM" with Hobie spinnaker

Good idea. I have not broken a bolt yet, but after three years of hard use I am replacing the bolts in my TI. The old ones will go to the spare parts bin. When I do this a spacer will go in too.

Personally, I don't like Hobie's philosophy of "one size fits all" when it comes to the aka brace shear pin (same pin for original AI, AI 2, and tandem island). Tom Lachner, who designs medical equipment, has suggested nylatron pins as a replacement. You can read about them here. http://www.hobiecat.com/forums/viewtopic.php?f=70&t=7276&start=840

Keith

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2015 AI 2, 2014 Tandem

"Any intelligent fool can make things bigger and more complex ... It takes a touch of genius and a lot of courage to move in the opposite direction." A. Einstein

"Less is more" Anon

Keith:
I'm only chiming in here because what you just suggested can be dangerous.
I'm a design engineer by profession. I have nothing whatsoever to do with Hobie besides being a user of their products however do have a lifetime of experience designing stuff like this.
For my own knowledge and information I tested and calculated the forces required to break the nylon sheer bolts, not just by a single hit or impact but also how many multiple impacts or impact events it takes at lower levels to make the pins shear.
I posted all my results on this forum quite some time ago.

In addition I also calculated how much force is required to destroy the surrounding components (all with un recoverable damage)
If I recall correctly I calculated (by physical testing) it take 150 lbs of abrupt force to sheer the aka pin. However if a steel pin were placed into the same spot (replacing the plastic pin with steel or something stronger), I only takes 200 lbs force to fold the aka bar, and it takes a similar 200 lb force to shear the ball off the kayak hull. Also during my testing I watched the entire hull of my TI flexing way more than I am even comfortable with. As an expert in plastics I can safely state the plastic Hobie uses is pretty much the best available (and uber expensive), however doesn't have a lot of tear resistance strength especially in load bearing application.
The root cause of the problems are not the material selected for the sheer bolt, but the location of it's placement on the AKA bar. Any force applied to the AMA is multiplied 3 fold into the sheer pin joint and also to the AKA crossbar.
In other words it takes 150 lbs of force to break the pin but it only takes 200 lbs force to totally destroy the AKA bar or the hull (random luck of the draw which will break first).
Hobies use of these sacrificial components was a brilliant move on there part to stave off further perminent damage to their boat and hull. Result is you can slam into docks, mooring balls, and 60 ft yachts all you want (lol which I do all the time), and your not going to hurt the boat itself.
Great design, but my pet pieve is if the sheer pin does break unexpectedly while out in rough water, the result is almost always capsizing of the boat and at my age pretty certain death, because there is no way I could right the boat on my own in rough seas.
In other words their design is great for the boat itself, but there is no regard for the safety and well being of it's occupents (probably stated too harshly, but you get my meaning).
There is not enough safety factor left in the original design to change it. If a collision occurs you have to allow the AKA brace to release it's force and transfer that force to the knuckle joints, I'm just guessin here because I didn't physically test the knuckles (just off the top of my head my guess is around 3000psi).
The design is what it is we have to live with it, however we can midigate the results and prevent capsize quite easily just by adding the safety ropes I've outlined too many times over the last 6 yrs.
As you have tested out yourself, you have to allow the aka brace to break (otherwise further catastrophic damage to the hull occurs, resulting in an unsailable craft). With the safety ropes the only thing that happens is you have to briefly stop and replace the broken pin (no capsize).
As far as adding a washer to the AKA brace, that won't hurt a thing (the ultimate sheer/failure forces don't change enough to worry about, and adding the washer will likely increase the number of small hits the pin can take before failure.
Like I described in the last post I takes one big hit (150 lbs) to fail, but it also takes about 15-50 smaller 50 lb. hits to also make the pin fail, (50 lbs being equal to hitting a big boat wake at speed (your guys normal cruise speed)
Didn't mean it to be a lecture on engineering, but I do get concerned about people doing unsafe things.
FE

FE!!! I'm not suggesting a steel pin! I've never suggested a steel pin, just the opposite. No where in your lecture do you point out why my (and Tom Lachner's) suggestion (Nylatron pins) are dangerous. Tom has estimated the Nylatron pins are much more resistant to wear than the Hobie pins and 25% more resistant to breaking. I use safety lines like you. My safety lines are designed to allow the pin to break, but prevent the ama/aka from folding in, at least initially. You can read about them here (way down at the bottom of the page.) http://www.hobiecat.com/forums/viewtopic.php?f=70&t=7276&start=720 I've tested my safety lines in preventing an unbraced ama/aka from folding in at 8 mph. see http://www.hobiecat.com/forums/viewtopic.php?f=70&t=7276&start=735 I have even posted your comments about shear pins and breaking forces on my "expedition" thread. That discussion is also on this lengthy page. http://www.hobiecat.com/forums/viewtopic.php?f=70&t=7276&start=720

Now, regarding capsizing and dying--of course, that can happen, although I have not heard of it. I am probably one of the real senior members of this forum. I don't like to talk about my age, but it is 81. I capsized my boat due to an aka pin failure last year, and it was totally unexpected. It was fully loaded for camping. I righted the boat without trouble, although it took some time because I was not prepared for it. Because of that capsize, I made numerous modifications to my AI 2. You can read about them here (top of the page) http://www.hobiecat.com/forums/viewtopic.php?f=70&t=7276&start=750 A friend of mine, Royd Whedon, capsized his Tandem, and righted it in minutes. Did it twice. Royd is 68.

The real question is "Do you want to chance unexpected breaking aka/ama brace shear pins with insta-capsize, or do you want to use a stronger pin on AI 2 and Tandems." I've chosen to use the somewhat stronger, more wear-resistant Nylatron pins.

BTW, you can read about my capsize and recovery here http://www.hobiecat.com/forums/viewtopic.php?f=70&t=54465

Keith

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2015 AI 2, 2014 Tandem

"Any intelligent fool can make things bigger and more complex ... It takes a touch of genius and a lot of courage to move in the opposite direction." A. Einstein

"Less is more" Anon

Keith:
Of course I'm sure you are correct, I've just become a little oversensative on this subject, and probably should just shut up.
FE

Keith, looking at FE's numbers, the aka or the ball on the deck the brace fits onto, have a break point of 200 pounds, which is about 33% more than the force required to break the aka brace bolt.

You said that the nylatron pins have a breaking point 25% greater than the standard Hobie items.. That puts them mighty close to the breaking point of the aka or brace mounting ball, at around 187 pounds.

I would certainly not like the idea of increasing the break point of the pins so perilously close to the far more serious alternatives. The keep out lines are the perfect alternative, IMO.

PS. Never shut up Keith, your contributions to the forum are way too valuable (and interesting!)

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Tony Stott
2012 Tandem Island "SIC EM" with Hobie spinnaker

Thanks, Tony. Having been one of the few who have broken a Hobie brace shear pin, AND INSTA-CAPSIZED, I'm sticking with the Nylatron pin until further notice!

We all enjoy your posts, FE (well, almost all your posts.)

Keith

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2015 AI 2, 2014 Tandem

"Any intelligent fool can make things bigger and more complex ... It takes a touch of genius and a lot of courage to move in the opposite direction." A. Einstein

"Less is more" Anon

As I have mentioned elsewhere on the forum having 1, survived five or six years often bold sailing in my AI1 and now my AI2, thinking I was smart to push the envelope and Hobie's design parameters, 2. seen a Ti turn turtle after breaking a brace bar sheer bolt in conditions that kept the old sphincter water-tight and 3, reading your various reports about the hazards of instant capsize, I have finally lost my nerve and taken FE and Tom's precautions and fitted keep-out safety lines... to bow AND just to cover all contingencies, from the stern also. So simple and easily removed to be stowed in the net pockets. I have never had to right my AI's and I sure as hell don't want to have to, BUT I admire any-one who can, especially in the conditions our very fit 81 year old Chekita has done.
I will release the brace bar and try them out in tomorrow's expected mild conditions.

Cheers vintagereplica...If it works ok, modify it anyway!

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Like I mentioned earlier in this thread, I really like the plastic sleeve idea. I'm pretty sure Hobies original engineering design for the bracing included a plastic sleeve, but that sleeve was likely removed by manufacturing (cost savings) without consulting with the designer (this is pretty typical in industry).
Anybody can measure the load bearing capabilities on these components themselves with a fish scale,( that's what I did). I've broken many many nylon sheer bolts over the years, and wanted to determine for my own safety what was going on, and in particular what the limits are of each component, as well as finding some means to make the design safe for offshore use at much higher speeds than most owners experience, (ie.. 15 mph cruise speed in rough offshore conditions).
As previously outlined the sheer force for the pin is around 150 lbs pull on the AMA. However because of the location of the brace, all forces are multiplied 3x because of leverage. So the sheer force on the actual pin itself is around 500 lbs force.
All this is well and fine, however this leaves out one minor detail that Tom Kirkman pointed out. Because of the slop in the joint each time the joint takes a smaller hit there is some deformation in the pin. You can test this yourself by simply putting in a shiny new pin, the jerk on the AMA. With 75 lbs jerk (2-3 times), remove the pin and look at it, you will see the threads crushed slightly, keep on jerking the AMA repeatedly with the same 75lbs force (using a fish scale measuring the force appled). The pin may fail in 10 hits or it may fail in 20 hits, the point being failure occurs eventually even in normal sailing conditions over time,(Tom pointed this out to us, and regularly replaces his pins (a smart thing to do).
Adding the sleeve as described, should lessen the need to have to replace the pins so often. In otherwords the accumulated effect/damage of many smaller hits will be greatly deminish.
Of course I still highly recommend adding the safety lines. Adding the sleeve shouldn't affect the ultimate sheer force too much which is determined by the sheer force of the plastic itself.
Just tryin to keep everyone safe out there.
FE

Here are a couple nylatron aka-brace pins I took out yesterday. The one looks fine, and I re-inserted it. The other looks ready to go, and I replaced it. The marks at the top of the pins are due to the pliers I used to pull them out. If you have broken a brace pin, you know it is much easier to pull a broken brace pin out than to pull out a whole, unbroken pin. Both of these pins had been in a little over a year.



Keith

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2015 AI 2, 2014 Tandem

"Any intelligent fool can make things bigger and more complex ... It takes a touch of genius and a lot of courage to move in the opposite direction." A. Einstein

"Less is more" Anon

Gents,

Thanks for revisiting this topic. I had meant to change out my bolts for this season, forgot to, but have now placed my order with McMaster (thanks for the reference, Chekika!).

Sail away!!

How many of you are familiar with the original "Rock Shox" mountain bike front suspension? It was a very simple yet effective system of two tubes sliding along each other with a slug of rubber inside. Although it would add a bit to the cost of a boat (not too much I wouldn't think) I have been thinking that this type of "shock absorber" would be a better method for protecting the boat from ama collisions while remaining intact so as not to allow a capsize. I mention the original Rock Shox model because it didn't require the fittings, oil, etc., that the later, more sophisticated versions have, and therefore was a lot less expensive to build. Just something to think about...