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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It was a busy 4th of July weekend in my cramped little boat shop. I set out my U.S. Yacht Ensign flag, and got right to work.

After a week of shaping that mahogany shim on the port chine, I finally got it to a point I was satisfied with. So, without any more delays, I epoxied on the forward bottom planking.

The shim on the port chine

3/4 of the bottom planking is now attached.

This time around, I used System Three Silvertip epoxy, thickened with the remainder of my collected mahogany sawdust. I learned a valuable lesson about using thickened epoxy versus Gel Magic.

Although I used the remainder of my mahogany sawdust, the mixture was still not as viscous as Gel Magic. However, it sure seemed thick enough to do the job. In the end, I used perhaps 2/3 as much epoxy for the port side as Id used of GelMagic when I did the starboard. Not only that, but it was easier and faster to apply. This saved me time, stress, and money.... some pretty good selling points. 

I still had plenty... PLENTY... of squeeze-out to fill the gaps I was concerned about, too.

I also used 4” spacing on the screws for this side, compared to the 3” spacing I used on the starboard side. The planking contact seemed just as good, and I used 3/4 as many screws (73 this time, compared to 97 before). Again, this saved me time, stress and money.

And yes, this time I did remember to scrape away excess epoxy from the areas where I’ll need to fit the butt blocks.

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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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Progress is coming along steadily, if slowly on the Utility. The fiberglassing work continues. Its fortunately not difficult. It just takes time... working in sections, feathering edges, sanding, etc.

You know.... "boat building."

At this point, Ive got all of the bottom fiberglassed on the Utility, and Ive begun encapsulating frame # 5-1/2 on the Zip.

Here are a couple of progress photos. Happy New Year to you!

Zip frame #5-1/2, "glued and screwed," and awaiting encapsulation with marine epoxy.

Here are the Zip (L)  and the Utility (R), side-by-side. As you can see, theyre at very different stages of completion.

Zip frame #5-1/2, partially encapsulated.

Hull bottom is fully fiberglassed, but needs to be sanded.

Starboard bottom, forward at the chine transition joint.

Sanding / Feathering the fiberglass cloth at port aft.

Overlapping the fiberglass cloth at the bow.

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I finally put the bulkheads in permanently today. 

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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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Today being an anniversary of sorts, I wanted to do something special to mark the occasion. It seemed like an appropriate time to order the transom decal for my boat. 

The boat’s name will be “Perseverance.” 

In the 3-1/2 years I’ve been building this Glen-L Utility, the project has bridged some pretty major personal events; dark and painful personal storms including divorce, heart surgery, betrayal and loss... things that at times seemed insurmountable. But, by the grace of God, I have made it through, and healed and grown along the way. 

At some point, watching this boat grow from a few pieces of wood, to a graceful framework, to a painted and righted hull, I realized that the project has been a metaphor for my own growth and healing. “Perseverance” seemed like the perfect name. 

I’ll close this post with a beautiful quote from a very eloquent friend of mine: “If the soul had a form, it would be shaped like a boat.”

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In the old days, like back as far as the 60s people used to re-use stuff.  Then along came re-cycling which was not the same as re-use.  Re-cycling meant grinding stuff up and then using it as feed stock for something brand-new.  Old stuff was passe. New stuff was hip.  Recycling was something that hippies did.  Re-use was something your mom or your grandmother did. That is, your mom didnt throw away your old clothes but patched them up or made them last a while longer by maybe altering them or embroidering on them or turning old stuff into quilts, or your dad would take bent nails and pound on them with a hammer till they were straight again and could have another life. 
And then, stuff became so cheap that re-use became too quaint for any reasonable person to countenance.  Re-use became more expensive if you counted your time than simply throwing stuff away and buying new.  That was in the days when people had jobs.
But now that jobs are going extinct, more and more people dont have jobs and all of a sudden, re-use isnt such a stupid proposition.  But re-use isnt a cool name for what we are doing and instead it has been re-branded as up-cycling. Whatever. 
It is what it is and little by little, more and more people are tapping into the recycling and waste stream and extracting materials from it that once upon a time were practically worthless.  Instead of grinding everything down to pulp and then squirting it out of some machine to make new stuff, more and more people are taking the practically worthless stuff and using it as is or modifying it just a little to fit their own use.  Nothing new, really, but as more and more people do this, the stuff that used to be worthless will become more and more precious.  With nobody having jobs and the money to buy the new stuff made from old stuff, the old stuff as is without being recycled will become more expensive.
So this is where the concept of just-in-time upcycling comes in.  You have to grab stuff out of the waste stream and modify it to suit you while you can, before everyone else realizes that this is where its at and makes the stuff that is now being thrown away into an expensive commodity.
Check out Wendy Tremayne and The Good Life in my next post for more on this topic.

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Here is the winter update.  I finally had a couple of days off to make some progress.  I cant glue in this weather, but can fabricate parts and dry fit.  Centerboard trunk is under construction and being fitted.  will screw it all together then glue up on a warmer day.

Made a list of a pile of things that can be done in the cold or indoors.  Rudder, mizzen step, fit cross beams, and then wait for a warm day. 

Dec. 28, 2013
Not quite as cold in the garage today, and found my 5/4 dimensional mahogany at the local lumber yard that will serve as the inboard rail for the CB trunk.  I have notched the riser at the bulkhead using the multi-tool and a Japanese hand saw, and temporarily screwed it even with the seat tops with a temporary cleat aft.

notch at forward bulkhead

temporary cleat to hold in vertical space.  

Rail from above.  

Rather than ripping into a $100 sheet of marine ply, I purchased a sheet of Masonite to do a template from.  This worked quite well and the curve of the trunk matched the hull perfectly.  Next is to transfer the lines to the original sheet of ply. I will cut a little tall, just in case.  

Masonite template from above.

Homosote template a tad shy at the top,  will transfer this to the real panel.

Bottom fits the curvature perfectly.

December 29th - All parts fabricated.

Finally got all the parts for the centerboard trunk fabricated and fitted.  Will glue up on a warm day.  

But first,  a stupid idea that saves a lot of time.  I had been sharpening my pencils with a knife, rasp, or whatever i happened to have in my pocket.  It finally dawned on me several boats later that the pencil sharpener in the basement had not been used in many, many, years so I removed it and put it in the garage.  No excuses for poor lines now.  

The next time saver was to place the essential tools close at hand in the boat storage lockers. Obvious, but not at the time I needed to recognize this fact.  

Step 1 - fit the port side of the trunk, cut a little tall and long.  

The board on top is from my Michalak rowing skiff, I know it is relatively flat and spans the gap from side to side nicely.  The port panel was marked, trimmed, then planed with a block plane until level.  

Next was the king posts.  the forward post has multiple bevels, but easy to mark in three directions prior to sawing.  The fit was pretty good, but I sanded it a little to get as much in contact with the bottom as possible. Epoxy grout will hold it in place along with fiberglass tabbing.  Panels will be screwed and glued to it.  

Sheet rock screws have taken the place of the clamp for now.  

Add caption

The aft king post is now installed.  There is a compound bevel, but it is not extreme.  

Starting to look like a centerboard trunk.

Starboard panel was fitted:

• use masonite template to set curve on bottom.
• transfer to plywood
• mark from plans, note discrepancies.
• cut curve, but leave panel long and tall.  
• fit curve to boat via scribing with a pencil riding on a block of wood. 
• recut to be exact.  
• fit to boat.  

• Starboard rail is fit. It has been left long on purpose to aid in setting the top of the rails and panels level with the seats. 
• port panel is scribed to rail to be level.
• case is removed from boat for trimming, sanding, and final shaping. 
• 
  

Final photo.  Ready to fiberglass the inside of the board and cut the slot.

The seat is actually in the correct approximate location and it is level!

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I finally realized that with the temporary center  bulkhead in place, aligning the seat bulkheads was very easy.  Shape them, then temporarily screw to the bulkhead while the glass and tape set up on one side.  I will remove the temp bulkhead this week and finish the seat framing.  

In preparation for setting the centreboard case, I decided to put the seat framing in to help line things up.  Interesting problem in that striking a line 16.25" off the centerline from the forward bulkhead to the stern bulkhead was more difficult than I thought. It actually took me three tries to get a line that measured correctly from stem to stern.  

This got easier when I cut access slots through the temporary bulkhead, then ran the lines through the slots and up to the bow.  I made a wooden measuring device 32" wide and marked the center.  Then I ran the lines up both sides keeping the tool centered over the C/L.  This looks good to me.  

Next, I made a template from some cardboard and transferred the lines from the plans onto the cardboard, then cut and fit the boat with a little trimming and filling to make it all look good.  I have now glassed in one side of the bulkheads and will remove the temporary bulkhead after the epoxy has set.  

Hope to get the framing in place next weekend, and perhaps the seat chambers constructed.  This will help me get the Centreboard case level and positioned correctly.  

the thing sticking up from the bulkhead top is a spring clamp that I use to hold the roll of glass tape for easy access.  

I realized that the lines I put on, were actually 16" off the centerline, that would be to the outside face of the plywood.  The framing needs to be at 16.25" off the centerline. Easy to fix. 

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