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Say Goodbye to Ama Bungees
http://www.hobie.com/forums/viewtopic.php?f=71&t=46906		 Page 3 of 3
Author:  augaug [ Wed Mar 20, 2013 7:33 pm ]
Post subject:  Re: Say Goodbye to Ama Bungees
Tom Kirkman wrote:
What I'm trying to convey, is that it's not the weak link in the chain. Not even close.
This is what I'm seeing. You seem to have taken the weakest link in a decent system, and replaced it with a stronger link. I think that's the key to this whole discussion.
Author:  yaknrugger [ Thu Mar 21, 2013 11:21 am ]
Post subject:  Re: Say Goodbye to Ama Bungees
Tom, I'm going to implement. I found a couple of places that sell hdpe uv treated. I don't really want to do aluminum because of galvanic corrosion. Can you tell me the thickness you're using? I found a 24x48" sheet at .0625 or so for $20. I was going to cut up the bottom of a 5 gallon bucket but those aren't uv treated from my understanding.

One more thing. I read a few posts about your eyebolt washer solution for bow anchoring. Couldn't find a video or pics. Want to semi permanently fix my Cooper anchor to the bow with a lightweight simple pulpit of sorts. Have you got a solution before I get crazy with it?
Author:  Tom Kirkman [ Thu Mar 21, 2013 11:31 am ]
Post subject:  Re: Say Goodbye to Ama Bungees
The plastic these boats are made from is tough, Very tough, Particularly in the bow area. Just bore a hole as high and far forward as you can (look inside to make sure you can back it with a washer and get the lock nut on).

You can lift the entire boat with an eyebolt mounted like this. You'll never pull it out.
Author:  Tom Kirkman [ Thu Mar 21, 2013 11:32 am ]
Post subject:  Re: Say Goodbye to Ama Bungees
I'll refine this a bit more as I go along, but am stopping here for now while I look at a lower retention system as I had originally planned.

http://www.youtube.com/watch?v=C6f5GUUSFg0

By the way, if you're worried about losing the hitch pin, attach it to the retention clip via a small hole and a plastic wire tie.
Author:  tonystott [ Thu Mar 21, 2013 12:50 pm ]
Post subject:  Re: Say Goodbye to Ama Bungees
Getting better all the time Tom!
Author:  Hobienutter [ Thu Mar 21, 2013 2:14 pm ]
Post subject:  Re: Say Goodbye to Ama Bungees
Just a note on the oft mentioned "only force downward on the Ama is gravity".
This is not true at all! To this you can add acceleration (as the boat heels the other way) and more importantly, resistance to a change in heel when the Ama is buried, and this can be massive. I think this is definitely where breakages would be occurring, out in strong winds, change of boat direction, sudden gust from a different direction etc, hey presto - a huge force suddenly applied to the ama and hence the bungie! :o It comes down to doing a thorough check of the boat components after each sail and sailing withing the boat's designed parameters. If I fly my plane outside it's parameters I risk it coming apart in the air. Not very forgiving :oops: Food for thought.

Cheers, Peter
Author:  Tom Kirkman [ Thu Mar 21, 2013 2:57 pm ]
Post subject:  Re: Say Goodbye to Ama Bungees
The forces you're talking about are absolutely minimal compared to the force applied by the Ama trying to stay on top of the water, not to mention those forces are not brought to bear upon the items I've added. If they were, the simple bungee system already in place would be failing left and right, and we know that isn't the case.

As far as "change in heel" when an Ama is buried - the only real force to contend with is still upwards. The Ama doesn't have to be "pulled" upwards towards the surface if heel is reduced. The Ama is already trying to come back up to the surface and is, in fact, pushing against the heeling effect all the time that it's either on or submerged in the water.

In fact, if the Ama was never lifted out of the water - i.e., it was either in contact with the water's surface or submerged 100% of the time, you could take the bungees off and the Ama would stay solidly put on the Aka. The only thing the bungee, or my retention clip is for, is to keep the Ama on the Aka when the Ama is lifted out of the water.

Those that don't believe this really need to get 2 or 3 guys and go out and submerge an Ama (it's not easy to do). Then let go and see what happens. Just make sure to get out of the way - the thing is hell bent on getting back on top of the water. You can lose your teeth if it hits you in the face.
Author:  Tom Kirkman [ Thu Mar 21, 2013 3:19 pm ]
Post subject:  Re: Say Goodbye to Ama Bungees
Here’s a better analogy to describe what’s going on the instant the Ama touches the water and is forced down upon or into it.

Picture a large, heavy coil spring. A really big one, similar to what you might find in the suspension of a large automobile. Now put downward pressure on the spring, enough to severely compress it. What happens when you remove or reduce that downward pressure? Is there any instance where you would be “pulling” the spring back to full extension, or would it quickly, even violently, do so of its own accord?

As long as the Ama is either on the water, or submerged in the water (and in practical use, never more than a few inches submerged), the overriding force is upwards, towards the Akas. In practical use, neither the bungee nor my retention device will ever be called upon to lift or pull the Ama upwards through the water.
Author:  stringy [ Thu Mar 21, 2013 8:52 pm ]
Post subject:  Re: Say Goodbye to Ama Bungees
Great innovation. Outstanding! 8)
Author:  Crazy Yak [ Mon Nov 04, 2013 10:31 pm ]
Post subject:  Re: Say Goodbye to Ama Bungees
Tom, thank you for your in depth contributions to the Adventure Island and TI sailing kayaks. Many thanks!
Author:  mkrawats [ Tue Nov 05, 2013 10:25 am ]
Post subject:  Re: Say Goodbye to Ama Bungees
Hi Tom,

I really appreciate this thread. Ever since my TI was upgraded last year to the double bungee system, the amas are secure and no longer bounce. But one day in the future, due to UV damage and wear and tear, the elastic in my double bungees will probably fail. With your system, we may be able to eliminate the bungees all together.

In your "Ama Retention Part 2" video, there is a thin metal clip that holds the plastic collar. The clip is now supporting a portion of the ama's weight. When sailing in the ocean, the windward amas hover up in the air and the double bungees absorb all the shock of the boat hitting the water's chop and waves. This pressure will place even more strain on the clip. Is this correct?
Author:  Tom Kirkman [ Tue Nov 05, 2013 11:29 am ]
Post subject:  Re: Say Goodbye to Ama Bungees
Probably, but it can easily take it. It's a very solid piece. Probably overbuilt.

However, I have been using the double bungee/yoke system this past summer and have been extremely pleased with it. Everybody that has been out has remarked how the windward ama no longer bounces in heavy seas and high winds. I suppose I may have to replace the bungees every few seasons due to normal wear and tear, but it won't be a big deal. It's a more simple fix than the plastic retainer and seems to be just as effective.
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