I got to borrow an MD-180 for several days and been having a blast with it. It's amazing how well Hobie managed pull off this seemingly impossible accomplishment! Here are some answers to a few hypothetical questions that explain what they did and how it works. A second post will take a look at how the Drive performs on the water (see link at bottom).
How do the fins rotate?The entire fin assembly sits on a rotating drum that is mounted on a highly modified sprocket assembly:
The rotation is accomplished by retracting an internal latch, rotating the drum assembly 180 degrees and re-latching. Here is a pic showing mid-rotation:
Activation is accomplished by pulling one of these loop handles -- each handle is dedicated -- one for forward and one for reverse. Pulling the appropriate handle retracts latches for both fins, rotates the drums and re-locks the fins in the opposite direction. Cord is used because of it's compact nature and it's ability to operate in 2 dimensions simultaneously (left and right and forward and reverse).
The entire underwater assembly has been streamlined for drag efficiency.
What's up with the fins?Here's a view comparing the old and new Turbofins. As you can see, there are a lot of differences.
1. fins are mounted vertically. This is more efficient aerodynamically, allows the new Turbos to sweep the same area underwater and minimizes the space needed to swing 180 degrees.
2. The foot or root of the fins had been severely shortened but some area had been added on the opposite end -- as you can see, it is wider at the tip. Construction has changed resulting in a stiffer, slightly thicker and more rugged fin; the old "clew-outhaul" had been replaced by a "traveler" (traveler adjustment and settings are discussed in part 2).
3. The short footed fin can be reversed with the Drive in limited motion instead of straight up and down (hull clearance).
See part 2 for performance on the water.
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