The Utility Trimming the floor battens

Some days you just dont have a lot of time to make any major progress. Still, there are usually some small things you can do to help the project along. Last night was just such an occasion. I took a few minutes to trim the forward tips of the outer floor battens. Now they match the inner battens, which Id trimmed a while back. This will look much better than the squared ends once the bottom is planked.

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Scarfing post mortem

Ok.  I admit defeat on scarfing the panels.  After fairing and filling the first two panels on for the bottom, I have decided to just do the fiberglass scarf joints as outlined on the plans.  I did my Michalak skiff this way, and the seam is not noticeable to the uneducated eye.  I figure that if I need to sand and fair, I might as well make it easy.  Hope to get the foward panels on the bottom this weekend and build the sides as well.  the switch to standard stitch and glue should speed things up.

Also was slowed down by work, weather, and some damage to the transom on the Bolger 18 workskiff.  (nothing serious, just a hairline crack in the glass where it had not adhered well.  No water present!)

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Trimming the sheers

Its a pivotal moment when you get the boat hull flipped over. All at once, you can visualize the completed boat; picture yourself and your family in it, riding across the lake or cruising upriver... It all just seems so close.

The reality, though, is that there is still much work to do. Much.

For me, the wondrous gazing at my righted Utility hull quickly gave way to recognizing the abundance of tasks yet to be done. Theyre so plentiful, I could really just start anywhere. 

So, I started on the sheers.

Out came the planer, quickly knocking down the mounds of cured epoxy, and cutting into the laminations of the sheer to level them somewhat. While a hand planer can be effective on the edges of plywood, you have to be very careful, because you can quickly cause unexpected damage. The planer is fine for roughing through the excess material, but the sander is much safer from that point on.

I found that the vertical joints in the plywood, such as where the sides meet at the bow or at the transom, were particularly susceptible to unwanted damage from the planer. Fortunately, no harm was done that wasnt going to get cut away, anyway.

Its like fairing, all over again. But this time, theres a boat to look at.

The untrimmed sheer at the transom shows just how much work there is to do. This is the starboard side.

The untrimmed sheer at the transom shows just how much work there is to do. This is the starboard side.

On the port side of the transom, things are looking much better.

Mounds of cured epoxy on the untrimmed starboard sheer.

Up forward, the sheer will have to be faired to the crown of the forward frame so that the deck will fit properly. Here, you can see that the laminated sheer has been planed just a little.

The big glob of epoxy needs to be cleaned off of the starboard sheer, where it meets frame #1.

Looking better on the port side.

Here, Ive trimmed off the screw heads, where they were driven through the backing block of the port-side butt joint in the planking. They still need to be sanded flush.

The screws are still untouched on the starboard side.

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Flipping Day pretty easy

We finally had a few days of nice weather, and a day with no other projects on tap.  So, I decided to take the boat out of the garage and flip it.  The process went so quickly, that I did not stop to take a lot of photos.
It was a two person job, but not difficult.  It took longer to clean the boat out than it did to flip it and put it back on the frame.

1. Roll frame out onto driveway, adjacent to a smooth landing spot.
2. Place four strong saw horses that are taller than the building frame left and right, front and back next to the boat. 
3. Lift boat up with a long pry bar and insert 2X4 to receive boat.  The boat is now above the building frame.  remove frame to the front of the boat so it is ready to put back under.  
4. SLOWLY, move one side to the ground level.  I did this 1 at a time.  Boat is now ready to flip. 
5. Get your 22 year old son and have them stand on the low side.  Lift from the high side and SLOWLY roll the boat over.  Son will grab the high side and hold it while you go around to assist. 
6. Choose soft ground to lay it on



Boat has been lowered to ground after flipping,  nice soft grassy spot.  Building frame ready to reinsert.












The 2X4 is slightly wider than the boat, making it easy to lift the frame and kick the pvc pipe rollers under.








ready to go back in the garage.


6. replace the building forms on the frame with stout 2X4s 6-12" wider than the boat. Bolt to frame.  Now the frame can be moved by lifting on the 2X4.  This is very handy.

7. Grab your 22 year old son and lift adjacent to the Centerboard slot and place the boat back on the frame. 


Seriously,  it took longer to write this than flip the boat.  




All seams are now filled with WEST 410 and ready to be faired.  Hope to glass the seams next weekend.  It does take a while.  CB slot needs a bit of trimming out.  thinking that the router with a flush trim bit is the way to go here.  







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Air Subduction in Kayak Paddles and cavitation in lee boards

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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Five Gyres and More

 I saw this photo of kayakers on facebook and the thing that popped into my head unbidden was, Plastic Gyre.  Of course this isnt a plastic gyre, the real plasic gyres are in the worlds oceans and there are five of them and they are huge, and while there may be some plastic kayaks or kayak parts in these gyres, the majority of the plastic is from other sources.  So whenever kayakers decry plastic pollution, I see some irony in their stance.

 

I posted this picture before under the heading, how many kayaks are there? and this massive assembly of kayaks really does come close to being a genuine plastic gyre. And before you accuse me of being holier than thou with my wood frame skin on frame kayaks, I confess that yes,  there are plastic resins used in its construction, mostly in the skin and the lashings and the coatings used to seal the skin.  And I also wear some plastic garments when paddling and the small fibers that theyre composed of break off during washing and end up in the ocean where they displace plankton in the bodies of animals that eat plankton.

Lets let the issue of whether I am a hypocrite or not rest for a moment and look at the obvious problem of plastic pollution in the worlds oceans.  The organization Five Gyres has devoted itself to the problem. Click on THIS LINK to find out more about them.

Policy director Stiv Wilson of Five Gyres explains in an ARTICLE that plastic pollution on the worlds beaches is not the main problem but could be a big part of the solution. While the five gyres collect plastic that has made it into the oceans, they also spit out a certain percentage of plastic each year.  Some of the plastic moves on to different gyres, but some of it also gets spit out and ends up on beaches.
If we were to stop making plastics tomorrow, and did annual beach cleanups, plastic would be gone from the worlds oceans in a matter of decades.
The problem with the plastic in the oceans is not that the plastic ends up on our beaches and assaults our esthetics but rather that when in the ocean it harms the animals that live there. Inundating the world in plastic products and then expecting none of them to end up in the oceans is not realistic.  Maybe stopping the production of plastic is not realistic either but it sure would fix the problem.  What we have to decide is whether not having plastics in our lives is a bigger inconvenience than having it in our oceans. Weve lived without plastics before and we can do it again.

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Paddle Dynamics

Three Greenland style paddles on display at the boat ramp where I just got done testing them. The breakdown paddle on the left had the tips thinned. The one in the middle had the varnish touched up. Note that the paddle in the middle has a more curved face than the one on the left which has a flatter, thinner face. The one on the right, the long one, is one I just finished carving.

I recently did some maintenance on two paddles for a client of mine.  One of the paddles was just worn and needed a little sanding and a coat or three of fresh varnish.  The other one was making noises in use because the tips were too blunt so I made the tips sharper.  Before returning the paddles, I took them out to test because that is the right thing to do when you make a repair and charge someone for it.
Oh yes, there was also a third paddle, one that was supposed to be a blank for a paddle making class that a prospective students wife had given him as a Christmas present.  Three years or more passed and the student still hadnt managed to arrange a class date to finish the paddle, so I finished it just get the thing out of my shop.  And so while I was testing the other two paddles, I thought I would test this one as well.
Things got off to a slow start.  The boat I used for a test vehicle belonged to someone else and had very slack deck lines that made it hard to keep spare paddles on deck but after some experimentation, I managed to figure out a way to carry the spare paddles while testing.
Paddle testing for me is usually comparative.  Given my testing tools which consist of myself as motor and test evaluator, a gps as speed indicator, a kayak and some suitable body of water to float the boat and offer resistance to forward progress, the tests tend to be subjective and relative.  That is, I dont have absolute numbers at the end of the test.  I take several paddles, paddle back and forth and compare the performance of the paddles under more or less identical conditions.  The two things I can measure are speed and the amount of effort I put into paddling.  Effort is hard to measure so it usually means that I try to make the boat go as fast as I can with a given paddle.  And when I am going as fast as I can, I measure the speed with the GPS.
Usually what happens is that one paddle feels better than another or one paddle gives me a higher top speed than another.  And in general, results tend to be vague impressions more than anything rigidly scientific.  But some good can come out of even an unscientific test, as happened in this case.
Let me share my observations.
As expected with the three paddles pictured above, the long paddle gave me the best top speed. This paddle was 98 inches long.  The two shorter paddles were both 84 inches long.  Normally I like a paddle that is somewhere between 88 and 92 inches long so I expected the 84 inch paddles to be slightly underpowered.  As it turned out, they produced top speeds not that much slower than the long paddle.  Acceleration with the short paddles was lower than with the long paddle, but by and large, once I got the boat going, the short paddles did pretty well.
What was happening was that the hull speed of the boat was the limiting factor in the test and not the paddles.  That is,  the short paddles were adequate for getting the boat up to hull speed but couldnt push the boat much beyond that.  And thats probably adequate for most situations.  The long paddle with its greater blade surface could push the boat beyond its hull speed but at the expense of greater effort.
So the problem with testing paddles using a GPS and a slow boat is that just about any paddle can push the boat up to hull speed and further effort even with a larger paddle produces little extra speed so that measurement of top speed are more an indication of the boats limitations than any measure of the paddles effectiveness.
It would be nice to have a meter that could measure the speed of the boat, the resistance offered by the boat and the power needed by the paddler to keep the boat at that speed.  If such a thing were available, it would be able to offer a good comparative test of different paddles effectiveness.  Even if two paddles were able to bring a given boat up to the same speed, the one that requires less effort by the paddler would be the better paddle.  However, since there is no good way to measure that effort, it is hard to make meaningful claims about the effectiveness of one paddle vs. another and the question of which of two paddles is the better one remains largely subjective.

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