I dont know if subduction is the right word to describe the phenomenon of air getting sucked down along the back side of a kayak paddle, but there I am using it.  Dictionaries indicate that common usage of subduction only applies to the geologic phenomenon of one piece of the earths crust getting shoved under another but here I am with no one to stop me and so I am expanding the usage of subduction.
I mention subduction because it is a phenomenon that impacts paddle efficiency adversely but looks so normal when it happens that its easy to miss entirely.  Subduction happens because pulling the blade of a paddle through the water creates a low pressure region on the back side of the paddle.  If the pressure is low enough, air will get sucked down along the blade of the paddle in response to the lower than atmospheric pressure there.  The result is reduced efficiency of the paddle.  Why? Because the amount of thrust you get from the paddle depends on the pressure difference between the front and the back of the blade.
Furthermore, this phenomenon seems to happen only with paddles that have long narrow blades.  At the start of the stroke with a long bladed paddle, only part of the blade is in the water and part of it is still out of the water, as you pull on the paddle, low pressure is created on the back side of the blade and the relatively flat surface of the blade that is sticking out of the water directs air down the back of the blade.  I suspect that water coming off both edges of the blade creates stable vorteces on both sides of the blade with a low pressure area in the middle that becomes the pathway for air subduction.
Commercial paddles with short, wide blades dont generate this phenomenon because the blade is fully immersed in the water before power is applied to it and the only thing sticking out of the water is the circular loom which does not produce any pathway for air to travel down to the low pressure area behind the blade.
But the phenomenon of air subduction with a long skinny blade is not unavoidable.  Depending on how the paddle is held and moved through the water the phenomenon can be avoided.  If the paddle blade is moved sideways as well as straight back, water moving across the face of the blade will not form the vortices that allow air to travel down the face of the paddle.
Since air subduction is dependent on low pressure on the back of the paddle blade, the lower the pressure, the higher the likelihood of subduction. Pressure is force divided by area so the same amount of force on a smaller area will create a greater pressure differential. And since on paddles with long narrow blades, only part of the full blade area is submersed at the start of the stroke, much more of a pressure differential is created across the face of the blade than in a paddle with a short wide blade where the whole blade is already fully submersed at the start of the stroke.

Lee board on a shallow draft Dutch craft.

The lee board deployed.  The angle at which the board is deployed controls the amount of lateral resistance that the board supplies.  The backward rake also allows the board to kick back and out of the way harmlessly should it hit bottom.

Not surprisingly the phenomenon of air subduction can appear anywhere that you move a  fin shaped object through the water like for instance a lee board on a sail boat.  The purpose of the lee board is to provide lateral resistance to a sail boat when it is sailing at an angle to the wind.  Some sail boats use keels to achieve the same results but lee boards are more handy in places where the water is shallow.  And they dont take up space in the cargo area of the boat like a centerboard does.  Lee boards are generally used on relatively slow moving boats which cargo boats generally are. And the triangular shape of the lee boards on Dutch craft puts most of the surface area of the board toward the bottom of the board, keeping the top of the board relatively narrow to minimize air subduction.
A slightly related phenomenon to air subduction is cavitation.  Unlike air subduction which happens when a foil pierces the surface of the water, cavitation generally happens when a foil is moving rapidly while fully submerged. If the speed of the foil is sufficient, it can create pressures low enough to cause water to vaporize. If you remember your high school physics, the temperature at which water turns from a liquid to a gas gets lower and lower as pressure drops.  The net effect of water turning to vapor is the same as air getting sucked into the water, it reduces the efficiency of the moving foil.  Generally, cavitation occurs in high speed propellers, but it can also happen in vertical fins on fast moving water craft like the one I posted about a few days ago.  Read more about it on the Vestas sail rocket site.

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A week or so back I paddled halfway round Alameda, an island off the coast of Oakland.  People paddle all the way around the island occasionally, a trip of about 15 miles.  A complete circumnavigation is something that can be done in about four of five hours and is a good way to kill a Saturday when you figure in drive time to get to the launch point and a stop at a restaurant afterwards. 
I dont often do these kinds of paddles because they take up too much time.  Usually I drive the half mile to the boat ramp closest to my house and put the boat in the water for a short, less than an hour paddle.  The truth is that I dont much care for paddling any amount of distance.  Distance paddling is quite frankly boring.  It is like driving on the interstate across Nebraska.  Lovely, but unvarying views.  It can be done if one works oneself into a trance.  I much prefer playing around in waves, a little surfing, some rolling and just enough paddling to get warm.  Then back to the car.  But the bay has no surf, just short waves and when there are waves, there is also an unpleasant amount of wind.  Tribulation exceeds excitation.
The trick when trying to paddle somewhere solo is to get oneself locked into some sort of no-return situation where one has to finish the trip or might as well finish the trip when the temptation is to turn back after half an hour and go somewhere for a beer or a cup of coffee. 
This is how it was on this paddle.  My plan was to endure paddling for an hour and then turning back for a total time on the water of about two hours rather than doing the usual turn around after 20 minutes which would have me back at the boat ramp in under an hour. 

The view at the Grand Avenue boat ramp in Alameda.  The nose of my kayak is visible in the foreground. Beyond that, the estuary which in this region goes by the name of Oakland inner harbor. The white ship in the background is one of the coastguard cutters tied up to the pier on Coastguard Island.  To the left lies Oakland Middle Harbor and the Bay.

As it turned out, I was ready to turn back after half an hour of paddling but hung on and kept going down the estuary and in the general direction of San Francisco bay.

A nice purple boat house about two miles down the estuary.

Some more boat houses.  Jack London used to tie up the Snark somewhere around here before he took off for Hawaii.

The Snark on the estuary.

 Having paddled two miles, I would normally turn back without having wasted too much time and gotten some exercise and taken in some of the sights.  Unlike the scenery on land, the scenery on the water is always changing due to the mobile nature of the nautical bricabrac that floats in the water.

A tug tied up to a barge.  The big white thing behind it is one of the floating dry docks at Bay Ship.  Off to the right, the iconic cranes of Oaklands container port, images of which turn up on tee shirts.

The SF to Oakland ferry passing by a scrap metal carrier.  The soundtrack here is of big chunks of metal being dropped into the metal hold of the ship, creating much clanking.

 And here, in case you never read the country of origin labels on the stuff you buy is a picture of where your stuff comes from (China) and how it gets here (in containers) on top of a big ship.  Most of the ships are black (American President Lines) but sometimes also blue (Maersk). 
Returning to the journey, at this point I was about 45 minutes into the trip.  This would have been a good time to turn back.  I could have been back at the boat ramp in another 45 minutes and would not have done too much damage to the day.  Instead I kept going forward since I could see the channel marker at the end of the estuary, just another mile or so off.  Also, at this point I considered the option of paddling around the tip of the island over to where my shop is, taking the kayak out there and riding my bike home.  More paddling but I wouldnt have to look at all the same stuff I looked at going out.  And so I went.

I did it.  I paddled out into the bay and rounded the corner of the island.  Off to the left, newly installed steel pilings to prevent toxic trash from decades past from washing into the bay.  The VA intends to build a hospital here on top of the toxic soil so the deal is to bulldoze about six feet of untoxic soil over the top of the toxic soil and thats that.  When it rains, water moves in a downward direction so the toxins move down or sideways, but not up.  Anyway, thats what they claim and their lawyers approve.

The view west across the bay, about two miles distant the bay bridge and beyond that, the red lead primer painted Golden Gate Bridge. At water level, decommissioned warehouses where cargo used to be unloaded the old-fashioned way by longshoremen. Now the warehouses are home to restaurants and circus troupes.

The end is in sight.  The structure ahead is in line with one of the disused runways of the former Alameda Naval Airstation.  Runway lights were mounted atop this structure.  Now it is used mostly by aquatic birds.  Gulls, cormorants and on this day, one great blue heron. Visible in back and to the left, the Shop, where the aquatic portion of my journey ends.

So that was it.  For he last part of the journey I had the wind in my back, wind out of the north with me heading south, then for the last mile, the wind off my left flank as I headed east. 
Total mileage according to google maps, 7.6.  Elapsed time, roughly 2 hours.  After that, four miles home on my bicycle.
Since I dont get out in the kayak all that much, I was pleasantly exhausted, with my mind empty of thought, a wonderful state to be in, but came at the cost of spending two hours in a kayak. 

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In my previous post, I described how one of my kayaks spontaneously changed shape in response to a shrinking skin.  While this type of response would generally have been regarded as mechanical failure, researchers are now trying to steer this kind of phenomenon to make it perform useful tasks, that is by creating a variable shape that can adapt to conditions.

Buckliball changing from large to small (left to right) in response to external stress

Paraphrasing here - One stress makes you larger, one stress makes you small, and the stress that mother gives you dont do anything at all. Never mind.  Pause for groans to subside.

geodesic dome assembly

By the way, if you didnt grow up in the sixties, which is likely, you probably missed Buckminster Fuller and his geodesic domes and also buckyballs which he invented and which I suppose buckliballs is a pun on.

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I have started the construction of an Eastern Arctic Kayak based more or less on the information provided by Dr. David Zimmerly in various articles.  Zimmerlys own reconstruction is, as he states in his article in Sea Kayaker Magazine, a composite of various designs.
My own construction is in turn a variation on Zimmerlys interpretation. 
Major deviation for me is that I did not want a 22 foot kayak and so shot for something more like 17 feet long and lighter in weight,  hoping to keep is under 50 pounds rather than ending up with a 65 pounder.
Step one is the fabrication of the gunwales which for the Eastern Arctic Kayak are a good deal more complex than two straight boards I normally use for building Unangan style kayaks.

Whereas Zimmerly built his gunwales from two lengths of 3/4 by 5-1/2 boards scarfed together, I started with a 16 foot two by four that I ripped down the middle giving me something like two 5/8 x 3-1/2 x 16 boards which I then built up to approximate the Zimmerly design.  Lots of clamps and Gorilla glue in use. I used Gorilla glue rather than epoxy because Gorilla sets up faster and is easier to clean up than epoxy and less hard on tools.

Here the nose piece goes on.  The design I am copying has the gunwales more or less flat up to the front of the cockpit, then rising from there forward.

After the glue has dried, I faired the lumps out of the top of the gunwales resulting in something like the above.

Here I am using a spline to draw the part of the bottom of the gunwales that I intend to remove.

And heres the whole thing with the top faired and the bottom scooped out.  The gunwales are made to rise amidships because normally, when you bend them, the middle drops down.  The rise counteracts that drop to give you a more or less flat deck.

And some additional rise at the bow to help the bow stay out of the waves.

And thats how it looks faired and trimmed.

And finally, the long view.

I am thinking I probably overdid the midship rise in the gunwales by at least an inch, but Ill stay with it since it doesnt affect the bottom of the hull at all.  Sometimes it is good to go with ones mistakes just to see how much harm they do to the proper functioning of the boat.  After that you can speak with authority on why the way you did it was not a good idea.  Still, you have to admit that what I ended up with looks pretty cool.  And by the way, when you do gunwales that are 3-1/2 inches deep, you dont need fancy lumber since small knots dont affect the structural integrity of the end product by much.

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I have some historical photos of Eastern Arctic kayak construction.  I have no idea where I got them.  But here they are.  Mostly what I want to comment on is the fact that while these photos dont reveal all that much, they do reveal some general specifics about Arctic kayak construction methodology.
The most important revelation to me is that these boats were built without the benefit of any sort of building platform other than what looks like pretty bumpy ground.  What this means is that in order to get a symmetrical boat, the builders had to rely on the parts of the boat itself to achieve symmetry.  The deck, once built became the building platform for the rest of the boat.

This boat frame appears to be almost done.  The builder appears to be doing some trimming with a hand saw, or maybe he is just using the deck of the kayak for a saw horse to cut a piece of wood.

Meanwhile, a little earlier in the building process, this builder has inserted some rib blanks into their mortises.  Bending and trimming the ribs remains to be done. 

Women are covering a finished frame in canvas.  It looks as though they will have some canvas left over.  The fact that they are using canvas indicates that this photo was taken very near the end of the era of kayak construction.  And the building site is remarkable for its ruggedness.  No nicely swept floor, strictly open air.

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Time to bring the EA kayak building project back to life, on this blog anyway.  Time to make some comments on the building experience, a time when the building is done but the boat hasnt been in the water yet and provided feedback on its suitability as a water craft.  I could have waited another few days to comment on the completion, but Im thinking that once I try the boat out, I will become preoccupied with how the boat handles and forget all about what I learned from building it.
Part of what building an actual boat is all about is internalizing its structure in three dimensions.  Plans are flat representations of a boat and typically dont show any more than a top and a side view and some cross sections.  But the flow of the form of a boat in three dimensions is a lot more complex than the plans show and to get a feel for the form, you actually have to build the boat.  Once you have the feel, you gain the understanding of how that form interacts with the water and determines performance.
In any case, if you did some careful reading of the title of this posting, you may have noticed that called it Eastern Arctic-like Kayak.  What I mean by that is that when I laid out the shape of the kayak in the horizontal and vertical planes I improvised, that is, I didnt follow a particular plan but rather adapted length and beam to fit the wood that I had available.  I came close to building something that could be called Eastern Arctic, but not quite dead on.  Lets look at some photos.

Heres a picture of the frame just before the skin went on.  If you let your eye follow the right gunwale line you will notice that it has some bumps in it.  I think in general EA kayaks had a smoother sheer line.

Heres a shot of the boat frame. Bow down.  As you can see, the plan view is more like a Greenland hull than an Eastern Arctic.  Part of the problem with working by eye in a tight space.  Should have dragged the frame outside at deck setup time for a better view and probably would have noticed that the back end should have been wider.  I suspect the boat will behave ok, just with a narrower stern wont have as much carrying capacity.  And anybody who knows anything will feel compelled to tell me that I didnt make the back wide enough.  Yeah, I know.

View from the side with the skin on.  The nose is unorthodox, a little taller than traditional.  Looks more like a northwest pacific canoe bow.  Also the sheer line is a tad extreme.  Well see how that works out.

Meanwhile, the cockpit turned out more or less standard, maybe a few inches longer than traditional.  Soon this boat will have some paint and then hit the water.  Till then Im holding off on any predictions re performance.  I am most curious to see how the flat bottom will feel and how much stability vs. speed tradeoff there is in such a flat bottom.  Stay tuned.

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Yesterday I blocked in the keelson on  the inverted deck of the kayak in preparation for installing the ribs.  I am now at a crossroads where there are a number of ways to construct the ribs.  Not knowing exactly what the shape of the bottom of the kayak should be since I have never built this type of kayak before, I have to come up with a way to do this.  I can think of any number of ways to proceed but would like to go with the aboriginal scheme of shaping the ribs, whatever that is. 
Zimmerly is of no help here. His article in Sea Kayaker gives you the exact dimensions to cut the ribs to.  This only works if you also shaped the deck exactly like he instructed.  Since my deck is not shaped like his, his dimensions will do me no good.
I could do the ribs the way I normally do them, that is, steam bend them which would produce rounded chines and a slightly rounded bottom, but I want to go for the flat bottom and hard bends in the ribs approach that is more common for the EA kayak.  I guess I will just have to experiment and see what happens.

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My last post on the EA kayak, probably should be called EC kayak for Eastern Canadian kayak, mentioned that I blocked in the keelson.  But I didnt have any photos yet.  Now I do. 

This view shows the pieces of two by four that hold the keelson at the desired distance from the deck. Pieces of rope hold the chunks of wood in place.

Heres an overview of the entire assembly.  I installed a block of wood at each deck beam.  I usually do this since when I install steam bent ribs; they push up on the keelson and distort its shape unless I lash the keelson down very securely. But in this case, the ribs will be flat and exert no pressure on the keelson and so would not need all this blocking. I kept the keelson pretty straight.  Regular EA kayaks have some upsweep near the stern to let the kayak turn into the wind when the hunter is approaching game.  But for recreational kayak, turning into the wind is an annoyance and not an asset and so I have chosen to keep the keelson straight.

Heres a view of the setup for an EA kayak. The rib blanks have been inserted into their mortises and await bending.  The height of the ribs will be judged by eye and the keelson wont be added until all the ribs are in place.  This is probably more efficient than what I am doing if you know what the bottom profile of the boat should look like.  I imagine they bent a few key ribs and filled in the rest for a smooth transition between them.

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Unangan kayak terminology has been set down in an article written by Knut Bergsland, Norwegian linguist, now dead, in Contributions to Kayak Studies, Eugene Arima, editor. I think thats the most commas Ive ever put in a sentence.
Ive been wanting to do an illustrated version of that article for some time, but what has discouraged me is the messy nature of the information in Bergslands article.  The information is messy because there was never just one official way of naming kayak parts in the Aleutians.  For one thing, Unangam Tunuu, the Aleut language had multiple dialects, at one time, probably as many dialects as there were tribal groups, something like nine, possibly more.  Along came the Russians, consolidated settlements and moved people around and a number of dialects disappeared.  The documented dialects remaining were the Eastern Aleut, the Atkan and the Attuan dialects. Then during WWII, the Japanese invaded Attu and moved the Aleut community there to Japan while the US moved the remaining Aleut population to the Alaskan mainland.  After WWII, Aleuts were repatriated, Attuans moved to Atka and so the only two dialects that were still alive were the Atkan and the Eastern Aleut. 
So when Bergsland collected his list of kayak terminology, he had some historical sources available that documented Attuan terms and speakers of both the Atkan and Eastern Aleut dialects. Not surprisingly, documented Attuan terms are fewer in number than for the other two remaining dialects at the time that Bergsland did his compilation. 
And terminology varied over time so that some kayak part may have been called one thing in the 19th century and then something else in the 20th.  Keeping all of this straight is not an easy thing. 
On top of that, we have to deal with Bergslands dense and sometimes cryptic writing style.  I give one example here.
"On top of the taamx^aax^, on the right side in front of the hatch, there was a hook for holding the paddle when not used, made of wood or baleen, or sometimes ivory (Atka 1952), possibly in the shape of a sea otter (Jochelson 1952:131), called in western EA (1909, 1950) x^aach(a)g^iilux^, in AA (1840, 1952) haachachag^iilux^, derived with the suffixes -g^i- + -alug^- place for having - from the above-mentioned term for paddle, EA (1778-) x^aasi-x, AA Au hassi-x."  inhale.  and so on he goes.  So you rub your eyes, go back to the start of the paragraph, try to match up the English with the Aleut term the two of which are invariably separated by a string of parenthetical phrases and hope you dont miss the period that lets you know that you have finally arrived at the end of the sentence.  By the way, the AA, Au and EA sprinkeled liberally around the sentence are abbreviations for the dialects respectively, Atkan Aleut, Attuan Aleut and Eastern Aleut. 
You get the idea.  I thought it might be nice to have a version of this that puts the Aleut term right with a picture of what it is referring to. 
I might put the pictures and words in this blog if I can make that work, the problem being that the blog software controls the size of the pictures, (small) and the layout of the text. Stay tuned.

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Sand Point, Alaska is home to one of the larger fishing fleets in the Aleutians.  The pictures below show the boats which have replaced the kayaks of the Unangan (Aleut) hunters.

Good bye, kayaks.

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Construction progresses.  After I set up the deck, I started adding deck beams.  They are temporarily nailed in place 3/4 inches below the top of the gunwales. 

Before starting to add deck beams, it is a good idea to stabilize the deck by lashing the ends together and also doweling the two sides together so they dont shift with respect with each other which would cause asymmetry in the deck.

The deck prior to pegging the ends and dropping in deck beams.

And here, at the end of the day, all the flat deck beams are trial nailed in place.  You could of course dowel all the deck beams in place as you go but trial nailing them lets you do some last minute adjustments in deck shape before committing to more permanent joinery.

The last two deck beams to be added are the two curved ones just fore of the cockpit.  Shaping them is more time consuming than shaping the flat ones.  Unlike the flat deck beams which are mounted 3/4 inches below the top of the gunwales, the curved beams are mounted flush with the tops of the gunwales.  A batten is temporary clamped in place to show the curve that the deck stringer will take.  The beam just in front of the cockpit will elevate the front of the coaming 4 inches above the deck.

And here is a view down the length of the boat with all the deck beams in place.  The number of beams, coincidentally is less than in a traditional boat to keep down the overall weight of the finished boat.

And just before I started adding in the two curved deck beams, I had a crisis of faith about where the widest part of the boat should be.  Seemed like it wasnt far back enough.  But then I checked back with the drawing in Arimas book on EA kayaks and it appears that my placement was OK.  Seems that the original for this adaptation was a demo boat done for a Canadian museum and was shorter than the type usually is because available lumber was only 16 feet long.  So a shorter version with a slightly more forward beam was built.  In any case, the first boat of a type is never just right and gets modified when the second one is built.

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While looking for something which I did not end up finding, I ran across these pictures taken several years ago at SSTIKS, the South Sound Traditional Inuit Kayak Symposium which takes place every year in the vicinity of Tacoma, Washington.  Its time to dust off these pictures and share them with the world.
(Side note 1 - Dusting off is a metaphorical term from the age of printed photos.  Since these photos have never left their digital format, the dust they may have gathered is strictly figurative.  Digital of course is forever or at least as long as the storage medium lasts and as long as you have some display technology and so they do not gather dust, not even figurative dust.  In real life, they just seem to disappear never to be found again.)
I have no particular agenda to this posting other than pointing out that when you make your own stuff, you get to have it your way, within the limits of your ability, of course.

 This is a molded seat which you can just stick into your kayak or if ambitious, you can glue it in place with contact cement. Note the coaming attachment.  (side note 2 - the white stuff on the ground is oyster shells, hard on bare feet.)

 This boat may be one of the Tom Yost model kayaks.  Coaming rim looks to be plywood. Back rest is a block of foam and the seat cushion is of uncertain origin, possibly foam inside a cloth sleeve or maybe one of those inflatable seats.

 Heres another back strap version, adjustable, possibly home made.  Seating is foam pads.

 Yet another foam solution.  The seating mat seams to have a sculpted seat under it.

 The frame of this boat is made out of bamboo and the mouth has a fanciful dragon design painted on it. 

 Cushions of the dragon boat have a tie dye fabric cover on them.  Note the hull stringers of bamboo.  If you click on this photo, you can see the innovative joining of stringer parts with the skinny end of the tapering bamboo pole overlapping.

 And yet another seat cushion.  This one looks like the level of complexity that I usually aspire to.  One reason my boats have no fancy seats is that it never occurred to me to put fancy seats in my kayaks since a simple mat on the floor seems to work.  However, if you come to DIY kayaks from the commercial realm, you are more likely to feel like you should put a fancy seat in your boat like the commercial kayaks have.

One last seat.  Looks like commercial back band with foam seat.

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