Ama safety line advice 2015 AI

I'm putting safety lines on my 2015 AI, and need a bit of placement advice. I will be running the line from the front cross bar. Should I run it to A,B or C.
A

B

C

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2021 Dune Hobie Lynx

Mine goes to B

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

I was thinking that was the strongest place.

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2021 Dune Hobie Lynx

mine goes to C
just tried to reduce the angle between the line and the hull centreline
don't suppose there's much in it.
I wouldn't have capsized and lost a $450 pair of glasses if I'd done this sooner....

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John
2011 Tandem Island
Ocean Kayak Cabo
Ocean Kayak Scrambler XT
Ocean Kayak Scupper Pro

I don't think it's important exactly how and where you connect the safety line. I have only been trying to raise awareness (especially with the offshore crowd) the the plastic shear bolt can become an issue at higher than normal speeds and/or typical offshore conditions. When I first got my first TI it was the original Hobie design (spring 2010 with the 1/4 inch bungys, and the crappy clips (at the time) that held the AKA bars in. Where I had aka sheer bolts breaking too often, AKA bars popping out regularly, and my AMA's flopping around loudly and occationally falling off. Of course Hobie has corrected some of those shortcomings over the years but I'm the type that once I lose confidence in anything I never trust it again. I only shared my safety rope thingy because it solved all my 3 problems with a quick simple 3/16 or 1/4 inch nylon stretchy rope (the same exact rope and clips i'm still using every weekend 5 yrs later. My situation is probably different from everyone elses because I have never had my boat out without the Tramps installed, and have never fished so I have no reason to ever fold my AMA's in (never have in 5yrs). I always rig my TI in the parking lot on the trailer by putting the AMA's out, lacing the tramps, do most of my rigging, then just back to the water and launch. When I come in I pull the boat onto the trailer with the AMA's out, then pull into the parking lot away from the water to batton everything down for transport (it works for me). Exactly how you rig your safety lines needs to work around your particular style and only you can determine that. With the important point being you do something that you have tested and are satisfied with the results. Making sure the problem you are fixing doesn't cause worse and potentially more dangerous and expansive problems than what it solves ( ie.... Ripping the ball off, bending the AKA bars, etc (all of which are not repairable out on the water) unless you don't mind sailing a Proa (lol).
It may not even be a problem if your TI is not massively modified (like mine) or if you don't sail regularly offshore. I'm a firm believer in always hoping for the best but always prepare for the worst, and alway be prepared for the worst (even on a lake you can get hit by a big powerboat wake which will fold your AMA's if you hit it wrong). Keith experienced this first hand recently and hopefully got everyones attention (something I was never able to do).
Bottom do somethin, anythin it may save your life someday.
Bob

I think this is a relatively low probability event but with potentially life-threatening consequences depending on ones environment, physical ability, etc. These are the type of events most of us insure against whether with a policy or an actual risk-reduction strategy.

As I'll be sailing mainly in SF Bay - a challenging environment is an understatement- I've decided to fit ama safety lines.

I agree with fusioneng that the specific rigging of these lines should account for the particular use(s) of the boat. As I need to be able to retract amas while on the water, I've worked out a system to do this conveniently which I'll share with photos when it is done ( hint: waiting for some parts from Hobie).

Regarding the ama attachment point, since maximum load tolerances aren't available for any of these locations, I'll use option B since it will provide the greatest strength. I'm much less confident in the other two locations.


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I'm interested in this subject, and will be fitting my TI with Safety Backup lines. When looking at connections A, B, And C, I'm concerned with these lines running under the trampolines. If someone is on the trampoline wouldn't this add stress to the lines maybe increasing the chance for the plastic bolt to break? If the line runs from the bow to the front ama connection this wouldn't be the case. The negative side to this is the ama can't be retracted while on the water. Still looking at what others have to say, trying to determine which option works best for me.

Sam

You can all check out my "Keep-Out" safety lines at http://www.hobiecat.com/forums/viewtopic.php?f=70&p=255493#p255493 They are described near the bottom of that page. They do not run under tramps, and they have designed shock absorbers.

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

Here is another thought on the nylon shear bolts. I keep all my old broken rudder pins in a jar in my garage (about a dozen of them just lying around), I get tired of ordering so many shear bolts and going thru them, so I figure I can get 3-4 sheer bolts out of each broken rudder pin (product re-cycling LOL). I just saw the rudder pin into as many 1 1/2" inch sections as I can get, then drill a small hole on each end and place one of Hobies split rings on each end (I also have dozens of those split rings laying around, (I usually don't install them because I have fat fingers and can't get them on or off(lol)). Or you can use pull ties like Tony does.

I think I would still do the safety line, but the stronger delrin 100 rudder pins would be working on shear strength of a 1/4" diameter rather than depending on the 3/16 dia minor diameter of a 1/4" threaded piece of nylon 101 with sharp grooves( DAH as weak as it gets). I have no idea whatsoever it it would be too strong, but it would be definitely less strong than a stainless steel bolt..

I also have several of the old white rudder pins laying around, I could try them as well.

FE

From what KB has said and you, Bob, breaking shear pins is not a rare event. It seems Hobie ought to rethink and strengthen the shear pin. It would probably have saved me a lot of grief avoiding my recent capsize.

Keith

_________________
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

Oops spoke too soon.

The Nylon sheer bolts are .240" diameter, and the rudder pin is .300" diameter, the rudder pin fits into the AKA bar but not into brace holes (you would have to drill them out to a larger diameter).

Since I have a strict policy to never modify the boat itself (never have on any of my TI's, everything I have simply bolts on, whenever I get a new boat I just transfer all the junk to the next boat)) I won't be drilling the holes out.

However I did test how much force it actually takes to break a sheer bolt with a fish scale (another broken bolt in the big pile (lol)).
I maxxed out the fish scale at around 70 lbs, and the bolt sheared shortly afterward, so if I had to guess the bolts sheer off at around 85 lbs of steady force ( I think substantially lower if it's a fast jerking motion (because of momentum)). ( I also noted quite a bit of hull flex during the test, near the ball)
I did a bench test with a rudder pin in a test piece in my vise on my work bench and the force appeared to be at least quadruple.

Bottom line the rudder pin is way too strong and defeats the purpose of the shear bolt, you would definitely fold (elbow) an AKA bar or sheer off the ball long before the stronger shear bolt (ie....rudder pin material) broke. I'm now beginning to question even if a solid 1/4" pin (no threads) might be too strong as well, and definitely a 1/4" stainless bolt would be even stronger than the rudder pin material.

It's back to the plastic shear bolts for me and my handy dandy little safety line.

Just like on Myth Busters "BUSTED".

Keith:
I just tested all the forces involved and I don't think the shear bolt can be made any stronger than currently (just tried all that stuff out in my garage, just out of curiosity for my own knowledge (remember I'm an Engineer and think thru all the crap, keeps me awake at night actually)).
Both you and I know for a fact that the current design can break just by speed and water force from waves and chop (you found out in a little harder way than me (lol)). And I'm sure like me you no longer trust the design......(with me once trust in anything is lost, it's gone forever)
I'm going to keep the current sheer bolts and make sure I always have plenty of extras, and continue to use my handy dandy safety rope thingy to prevent the AMA from folding in (in the event of a shear pin break), but purposely not strong enough to allow other damage like folding the AKA brace (elbowing), or knocking that ball off the hull (both of which I think would be a sailing termination events (not repairable on the water, (unless you like Proa's)), and parts would have to be ordered (which can at times take a long time), or you could die out there ( I only think of safety based on my own experiences, and there are many occasions I could have died out there offshore (it's not a forgiving place the sea)).

FE

Thanks for your good work, Bob. I was convinced a 1/4" Delrin pin was the way to go. It does seem to me that Hobie should replace the threads on their current pin with solid material, i.e., making a 1/4" solid pin with threads on the last 3/8" or so.

Keith

_________________
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:
As an Engineer I have all the coolest software you can possibly imagine to figure all this junk out (this is what I do for a living).

Just for my own information I just ran all the calculations thru my FEA software (it's like a 20k program lol) with interesting results.

According to the FEA simulation the Nylon bolt exceeds the yield strength of the nylon, at a little over 125 lbs of direct force ( my rough test with the fish scale verified that test). I was pulling on the AMA and damage to the bolt begins at around 60 lbs of force (because of the leverage (aprox 2x force)).
However I made a significant discovery while doing my tests that Tom Kirkman has been telling us all along (he is very clever). After the 75+ to 85 lb test I removed the shear bolt and put in a new one (did the same test twice just to make sure). The first sheer bolt (because it is threaded) showed deformation on the threads (the threads were crushed a little because we exceeded the 125 lbs of direct force on the sheer bolt (because of leverage, we are pulling on the AMA further out, but the sheer bolt is about halfway inboard (basically doubling the direct force on the shear bolt))). This is one of the unique things about plastics (they have very little memory). What this means is each time the AMA takes a 65lb or greater shock there is some damage and deformation to the sheer bolt. So in other words if you tug on the AMA 4-6 times with 65 lbs of force it may break eventually (via material fatigue and creep), I'm just guessing here but maybe a dozen hits at 50 lbs force, and it may break, and just guessing 30-40 or so 40lb hits and it may break. Basically the threaded shear bolts are ticking time bombs ( lol)

Tom was exactly correct in his observations and statements (he replaces his pins on a regular basis with new ones ( quite probably the root cause of your problem). Going to a pin without the threads would lessen the creep factor in the plastic, because it is a cut thread the plastic creeps each time it is hit with a smaller than ultimate (125 lb) blow. According to my FEA anything over about 85-90 lbs tugging force on the AMA can possibly take the pin out on the first try.
In other words if your AMA takes an 85 lb hit, even if it didn't break the first time, once it has begun deforming the next time it may only take 75 lbs to break it, (as per Tom's own observations).

I also measured the ball on the hull, according to the charts the bolt should be able to withstand 1400 lbs of sheer force, However because it is a thread, the factor of safety is exceeded at around 600 lbs direct side force. In other words that ball may be able to take a 500 lb hit, but that's not saying the brass insert won't be ripped from the hull. Because the force is amplified via leverage, I'm guessing about 200 lbs against the end of the AMA will snap that ball right off.

I'm just guessing off the top of my head here (based on experience with such things) but I would think it would take around 500 lbs of direct force to elbow the AKA bar material (just a guess on my part). Because of leverage and the mounting point to the brace, if you apply around 200 lbs force to the AMA if the ball doesn't break off, the AKA bar will likely fold and elbow.

Bottom line summary of my results:

The worst thing you can possibly do to your AMA's structural integrity is to put a stainless bolt into the brace replacing the Nylon sheer bolt. The reason for this is the direct force pushing back on the AMA is concentrated and amplified at that small point 1/2 way down the bar, the result is the AKA bar will elbow and fold with as little as 200 lbs force (this is just simple physics and leverage). If you want to prevent the AKA bar from elbowing, allow the nylon bolt to go ahead and sheer off. This allows the entire length of the AKA bar to obsorb and distribute the force and hinge on the hinges (can't possibly elbow). By adding a safety line lets say to the bow, then tied to the center of the AMA, all the forces are direct (no amplification or leverage), so if you have a 250 pound test line tied to the bow (I have 1/4" nylon 250 lbs test line tied from my bow to the center of the AMA), it will take 250 lbs of direct force against that AMA to break that line (if you hit something), but once the line is broken, the AMA and AKA bars just fold out of the way harmlessly (no damage to the AKA bars or the AMA's, or the ball (simply not possible)).
If you have a stainless bolt in the brace, either the ball will pop off (200 lbs force against the AMA), or the AKA bar will elbow (200 lbs force) more likely both, or the ball will be ripped from the hull. Personally I would much prefer to replace a small nylon bolt, and maybe a small piece of rope (all of which can be replaced on the water) than have to replace either my hull, or the AKA bar, or the brace ball, likely all three.

Now here is the reason for using the nylon stretchy line. When you hit something your boat is moving, right away the shear bolt breaks, The nylon rope completely obsorbs your forward motion energy as it stretches and bring the boat to a halt. You will never in a million years break that 250 lb test rope if the collision is being created by your forward motion, because just the act of stretching that rope stops your boat (like a big rubber band stretching). Once your forward motion is stopped, the stored energy in the rope pushes you boat backwards in the water ( like a giant shock obsorber). Resulting in no damage of any kind to your TI ever..... (besides have to replace a shear bolt once in a while). Hobies design is brilliant, the only thing they didn't count on is eventually boats being modded, and going faster, or being taken out into open ocean, and big waves. But by adding the simple safety line I have been trying get everyone to understand very frustratingly now for over 5 yrs now, that totally compliments Hobies original design and intent, the only additional thing the line does is if you do happen to break a shear bolt while out on the water, the lines only purpose is to prevent the AMA from folding in completely so you can make repairs and then get back underway.
My little line thingy totally compliments Hobies incredibly good design and collision damage prevention system that they so cleverly designed into every Island boat.
Hopefully everyone now gets it.

Bob

So the main complaint about the lines seems to be folding in amas on the water. What about adding a cleat on either side to run those lines through? Make the lines long enough that you uncleat and fold in the ama and it's still threaded through the cleat. When you're ready to sail extend amas, set tension and cleat the lines, store excess in the side pockets. (Granted, my side pockets are already stuffed full...)

I suppose for really smooth operation you might need turning blocks out front of the cleats but since the lines don't actually need to move freely for the most part it might be sufficient to wrap under/around the aka brace mounts then through the cleats?

Alternately, some have talked about putting a sort of jackline down the sides. Have a clip at the aka brace mount that lets you move the safety line to the jackline where it can slide backward as the ama folds in?

So many doggone lines to think about... I thought the Island was supposed to be SIMPLE?

Bob, that was a thoroughly interesting technical discourse. After that, it is difficult to imagine anybody not understanding ther benefits of the safety line.

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