Recovery
Craft Recovery
CraftI know I'm not the only one to ever have a ship go dead out in the middle of the pond. I even had one sink once, on a practice day, just because it had a small leak and no power! Usually, though, all that's needed is to wait for the wind and/or current to drive the stricken vessel ashore somewhere (usually not where it's convenient) or mount a rescue with one or more other ships. I've managed to become reasonably adept at recovering dead ships using one of my Liberty Ships - I maneuver into a "T-bone" configuration and push the dead ship sideways. This maneuver doesn't always work perfectly, though - you've got to get centered just right, and still the effects of wind, current, the dead ship's hull form and rudder position all can conspire to send you in an arc when you want to go straight. Sometimes, the best you can do is get to any shore in a half-way reasonable time.
Enter the specialized recovery craft!
The idea is to build a fork-shaped craft (or, Greek-letter "pi", if you prefer) that can be maneuvered into position surrounding a cripple, then drive it back to safety. Also, I wanted it to float lightly and have no propellers or rudders protruding below so that it could rescue ships from moss banks as well. The result was the craft shown above, constructed out of 3" schedule 20 PVC pipe and fittings. It's wide enough to accomodate a Yamato (should we ever get one) with about an inch to spare. Length is about half the longest ship we should ever see. A pair of "T"s connect straight pipe sections to create an elongated "horseshoe". Connected to the outside of the "T"s are a pair of "L"s, angled at 90 degrees to the plane of the "U". Pipe caps close off the long ends.
Here's where it gets fun: To achieve the goal of being able to traverse moss, propulsion is via fans - that's right, the thing is an air boat! Mounted atop the upturned "L"s are a pair of fans of the type found at an auto parts store. Originally intended to be run at 12V from a cigarette lighter, with a clip and an oscillating gear, the fans have been modified to rotate on tube shafts. The original motors were removed, to be replaced with Mabuchi 550s - that just happened to be a direct form-factor fit! At half the voltage, they crank out about 4-6 times the velocity of air as the originals! Oscillating gear and clips were scrapped, the fan assemblies were mounted onto 1/4" ID styrene tubes.
Power wires are passed through the tubes to a pair of standard servo-operated forward/reverse switches located in the center of the "U". Another pair of standard servos, hacked for continuous rotation use small ServoLink chain and sprockets to allow each fan to be rotated 360 degrees for steering. A 4-channel radio controls the thing - one stick controlling each fan for forward/reverse and rotation left/right.
You might think that allowing continuous rotation of the fans would eventually cause the power wires to bind up. This would normally be correct, and was a problem that the craft needed to address. The solution was to use slip rings made from phono plugs and jacks! A 2.5 mm phone plug was mounted into the bottom of each fan tube. A corresponding jack was mounted in the "L"s, centered on the hole at the top. Wires from the motors are connected to the plugs, and wires from the jacks are connected to the switches. When the jacks are inserted into the plugs, electrical contact is made and the whole assembly is free to rotate 360 degrees with no bind-up! The plug and jack also serve as a bearing, supporting the weight of the fan assembly.
Figure 2.
Fan Power Slip-Rings.
A flange at the top of each "L" provides a perfect mount for a circular plate that the steering servos are mounted to. A flanged nylon bearing is also inserted into a hole to keep each fan upright and able to rotate around its pole.
A pair of CSB 6V 3.3 AH gel cell batteries provide main power. A rectangular hole was cut out in each "leg", close to the "base" and the batteries inserted there. Covers for these holes were made by cutting a length of the PVC pipe just a bit longer than the hole, and making a lengthwise cut through it. The resulting covers snap firmly over the "hull" of the craft and can be slid out of the way to access batteries. Another similar cover provides access to the radio receiver, fan forward/direction servos & switches, and the receiver battery at the base of the "U".
The resulting craft floats nicely, with the tips of its "legs" just barely below the water's surface. It moves along at a pretty good clip, too. It's a real challenge to operate - the first time out it was barely controllable, but subsequent practice runs have revealed some operating tips. In particular, since the fans' orientation does not self-center, it takes a little practice to keep it from going into an uncontrollable spin!
The following photos show a sequence where the craft successfully rescued
a crippled Richelieu. Click on each thumbnail for a larger photo.
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This has got to be about the strangest craft around, and gets lots of attention wherever it goes - but it works!
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