EC PDRacer Design Idea 2By Scott Widmier #104 "Half and Half" (2es 1eo 7ea 2ad 23ar)
There has been some good discussions happening on the ECpuddleduck website and I wanted to catch you up to date on the resulting design modifications. I want to start the build this week if at all possible.
The boat should look fairly similar to the drawings I sent you before but with a few notable changes. First, the sides are 16" tall giving more room down below and more room for the leeboards discussed next. Second, despite my personal (irrational?) reservations, I am switching from daggerboard to pivoting leeboards. Their ability to kick up in shallow water is a plus on the Everglades Challenge route and the ability to change angle will allow adjustment as the sail is reefed all of which can be controlled from inside the cabin. I am planning on two leeboards both for backup, more area when sailing in shoal waters, and ability to use the leeward board on long tacks reducing the stress on the pivot bolt. Third, I have increased the size of the side airboxes from 6" to 8" to both provide more floatation and provide more support for the 1/4" plywood bottom.
We have also had a lot of discussion regarding human propulsion. Ideally, we want a system that can be used motorsailing. In other words, a system that can be used from inside the cockpit while facing forward and still sailing. We discussed a Mirage drive but I am not a big fan of the required well in the middle of the boat. I searched the web and classified propulsion system into propeller, fin, and traditional. The mirage drive is a fin based system but is not the only system out there. I found a 1939 article (attached), from popular science about an early fin system called the fishtail drive. I also read some lengthy discussions including some tests of different systems. Using all the information provided, I came up with two different possible drive systems I could build for the EC duck both of which do not require holes in the hull and are fairly robust.
The first system I called the Duck Feet system primarily because it has two flexible fins (like ducks feet) on either side of the boat. The fins are made from scuba fins and attached securely to a vertical shaft. The vertical shaft goes through bearing blocks that fit into oarlocks making them easy to remove. At the top of the shafts you have two handles attached which can either be rotated by hands or, through the use of rods attached to pedals, rotated by feet. You would pump both handles forward at the same time to move the fins in opposite directions to counter spinning the boat. The shafts can be raised to raise the fins above the water alongside the boat and locked into position. Oars can be brought as backup.
The second system is similar to the fin on a shark. A fin is attached to a long flexible shaft poking out over the transom attached to the boat by a pivot. At this pivot, there is a cross bar to which the ropes from pedals are attached. When you pump the pedals it pulls the rope moving the crossbar on top of the flexible shaft. This sweeps the fin back and forth through the water.