Saturday, May 24, 2014

Ama for a kayak

May 24, 2014
I’ve been poking around the internet looking for information on amas, aka outrigger (usually 1 on one side.)
Here’s what I understand so far:
1. Amas on one side of an outrigger have two basic functions. 1. to provide supportive buoyancy when the ama enters the water. When  the canoe leans on that side, the ama keeps it from tipping or rolling over. 2. The second function of an ama is to provide a counterbalance to tipping on the side that doesn’t have an ama. A theoretical ama that has no mass would work in one direction only.
I’ve seen some discussion of adding weight to amas but nothing conclusive.

An ama in the water should be designed so as not to create significant drag that would slow down the canoe or cause it to turn. Outrigger canoes with amas can be longer and narrower even longer and narrower than surf skis. Outrigger canoes are usually about 25% faster than kayaks.

The outrigger ‘arms’ that hold the ama are usually one fore and one aft of the paddler. I’ve seen mention of single arm amas, but none that seem practical. There’s a lot of leverage on an ama.
My concern about placement of the arms is I still want to use a double bladed kayak paddle which is used differently than are the single blade outrigger paddle.

A typical kayak paddle float is 3” x 18” x 8” (NRS), displaces about .25 cubic feet, or more useful: 7.07 liters so it has a buoyancy of 7.07 liters (minus the weight of the float...which is minimal).
This is a special temporary outrigger device. If you remember practicing with a paddle float you should remember doing it a bit wrong, submerging the float. Once a float is submerged, the upward force does not increase, so a firmly attached float that is submerged can travel 180 degrees.
This is the submarine problem. Inventors would add more and more ballast until they reach neutral buoyancy, once neutral buoyancy is reached, the submerged object could sink or rise to just about any level in the water. Water being incompressible makes a submarine different from a lighter than air balloon which does reach a level based on buoyancy, pressure, etc.. and then will tend to stay there.
What used to happen to early submarine experimenters is that once submerged the vessel would just sink right to the bottom. Modern subs tweak buoyancy and have dive planes. If a sub reaches  particular depth, if it levels off, it looses its up and down momentum and so is better able to keep a particular depth.  I don’t claim expertise on this. My point is that once an outrigger or paddle float is submerged its usefulness is severely diminished.

Where we get this wrong (usually when we are about 15 years old and male) is when we try to push a ball down into the water. It seems to get harder and harder so we gain a false understanding that pushing it deeper will be even harder. It isn’t. Before we find this out, the ball has slipped through our hands popped out of the water and smashed us in the face. We are then reluctant to repeat the experiment.

All of this is why many discussions of amas say that an ama should be able to support the displacement of the whole craft (the weight)
Do not design and paddle an ama based on this article, it is far from complete. Frankly, I’m surprised how all the information on this subject seems so disconnected. This is a result of three factors. 1. An ama means many different things, I get sites that discuss 60 foot trimarans, and 23 foot outriggers and hollowed out traditional Polynesian craft. 2. The web seems to be fragmenting, where the challenge used to be finding the right terms to query, increasingly what comes up in google is uniformed discussion, chitchat, a discussion among experts or one that started a long time ago. (More and more problems I have with my Apple computer that I search for solutions instead brings up complete and utter nonsense. Apparently fewer and fewer people who actually know anything post in Apple’s Support blogs. (I can’t figure which Apple password to use, so I stopped bothering. See my comments about wireless Magic Mouse batteries above).

Why am I posting this? First of all, why I’ve been thinking about amas: I have a 20’ kayak that is 18” wide that I’ve found to be a bit too tippy. I like paddling solo, miles off the coast, so this vessel seems too dangerous. (No complaints) If I can add an ama, I get to tinker (which I enjoy) and I should wind up with a hybrid (bastard) kayak that is even more stable than my wider 23” kayak. It’s worth giving it a go.
The reason I’m posting this is that I considered making a very small ama that would keep me from rolling. This would work but not in the range of situations it should or I might assume it would.
I am still not sure of how much buoyancy I need. I do intend to make one, make it using foam (if there’s a breach a foam filled ama will still float, a waterlogged one won’t).

Amas also work another way. The design and the angle of the keel make their first effect like that of a kayak paddle brace. They skim the water providing enough upward force to stop the roll.
Another facet of this idea is that amas become increasingly buoyant the deeper they are submerged. This doesn’t contradict what I’ve written above. As more volume of the ama is submerged more water is displaced, so more buoyancy is achieved.
A well designed ama should provide enough ‘skim’ to minimize the drag of a hull moving through the water. It should be long, often 3/4 the length of the outrigger canoe. Hull speed applies here--long and narrow is a more efficient hull than short and wide. Finally they are tall so they progressively submerge only to the depth needed to proved the amount of buoyant force needed for the particular situation.
Finally, if submerged or nearly submerged,  they should be able to buoyantly support the entire weight of the craft and the paddler. This keeps the canoe from rolling completely over. In catamarans, especially racing boats, this allows them to ride up on one hull without it sinking in and rolling over.

I’ll add updates when I have some results.

Note: I apologize for not posting more photographs, videos, drawings, etc…. This is inexcusable for a professional photographer. My only excuse is that no one seems to be reading, or even to have noticed, this blog. So, I guess it doesn’t matter.

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