A complete construction diagram of the bumper boat water scooter.
I can't speak for anybody else, but there's been many a time when — while fishing in the river near my home — I'd dream of trading in my waders on a tidy little dinghy that'd carry me and my tackle out to where I knew the big ones lurked.
This season, though, I don't have to daydream (well, not about boats, at any rate), because I've recently built — for a grand total of $44.75 — a nifty little craft that suits both my fishing and frolicking needs, and stows away easily in the trunk of my car when the fun's over.
The idea came to me after I'd noticed an amusement park that offered a "bumper boat" attraction using small commercial boats instead of cars. The little craft were made of custom-molded vinyl and sported gasoline-fueled outboard engines — along with, I discovered, big price tags!
My homemade water scooter, on the other hand, consists of a used 16.9-by-28-inch tractor inner tube, three pieces of 1/2-inch exterior (CDX) plywood trimmed to shape, two lengths of electrical conduit, an assortment of threaded hardware, a 1 1/4-inch floor flange, and a 1 1/4-inch E.M.T.-to-junction-box connector. The boat's power source — which I chose to incorporate simply because I couldn't pass up a $15 bargain — is a used electric trolling motor that's hooked to an old car battery. However, for extended jaunts, I'd recommend employing a deep-cycle RV or marine powerpack instead. (Gasoline-driven outboards shouldn't be used with an inflatable boat, as the fuel might melt the inner tube's rubber skin.)
Build It in an Hour or Two
After I'd gathered my materials and tools (screwdriver, adjustable wrench, mallet, C-clamps, saber saw and a drill with an assortment of bits), it didn't take me much more than an hour to trim, assemble and paint my vessel. And, if you're as handy with tools as I am (and Lord knows I'm no workshop wonder), building your own pneumatic cruiser ought to be a snap!
Start by placing a 4-by8-foot sheet of 1/2-inch plywood across a pair of sawhorses and scribing out a circle, close to one corner of the board, that's exactly 33 inches in diameter. (This is easily accomplished by cutting a strip of cardboard about 18 inches long, then punching a hole at each end — making certain the openings are 16 1/2 inches apart. Drive a nail lightly into the plywood to serve as a pivot, slip your corrugated compass over this central stub, place a pencil in the other hole, and rotate the "beam" 360 degrees to mark a ring.) Next, adjust the saber saw to a 45-degree angle and cut out the circle with the blade leaning toward the center of the disk.
With that done, measure and mark two 16" x 43" x 1/2" rectangles, and prepare to outline a cutting guide on each of these bulkheads-to-be — using the grid drawing provided here as a pattern.
Because of space limitations, the illustration has been reduced. Merely redraw the grid, in 1-inch squares, on a 17-by-20-inch scrap of paper, and carefully reproduce the design on this larger "graph." Then cut out your template and position it on the plywood, making sure that its rounded tip butts up against one corner of a scribed rectangle and that its straight lines are parallel with the quadrilateral's long sides.
Trace the pattern on the wooden surface, flip the template over, and repeat the procedure at the oblong's opposite end. Finally, use a straightedge to draw upper and lower "bridge" lines to join the two profiled sections. Go on to lay out the second bulkhead in the same manner, then find the midpoint of the long dimensions of each butterfly shape and draw a connecting line from top to bottom, perpendicular to the two parallel borders.
Now, set your saber saw back to a 90-degree angle and cut out both bulkheads from the plywood blank. Next, measure 6 1/2 inches down from the upper edge of one piece and an equal distance up from the lower edge of the other, and mark a 1/2-inch wide "channel" directly over the previously scribed centerlines, to the 6 1/2-inch limit on both boards. Remove each of these slots with your saber saw, and — using your mallet — pound the two bulkheads together, at right angles, in a tight half-lap joint.
The next step is to center the "cross" on top of the disk, making sure the platform's mitered edge is facing upward. Trace lines on the base by running your pencil along all the bulkhead edges, and take time to code the match so the two components can be repositioned correctly later. Using the marks on the disk as guides, center and drill twelve 3/16-inch holes through this circular floorboard — spacing them three per bulkhead half — then turn the platform over and countersink the openings. Invert the structural wall assembly and place the disk upside down over it so that the two parts mate as before. Drill 1/8-inch pilot holes into the partitions under each of the twelve countersunk bores, then apply a water-resistant glue (such as Weldwood plastic resin or Duro polyurethane glue) to the bottom edges of the bulkheads, and secure the base in position with a dozen No. 10-by-2-inch galvanized flathead wood screws.
You can further strengthen the assembly by cutting four 1 1/2" x 1 1/2" x 13" blocks from scrap lumber, and fastening a pair of them — using glue and 2 1/2" flathead No.10 wood screws — across from each other at a vertical joint of the bulkheads, and securing the other two horizontally along both sides of the junction of the facing wall and disk.
I made my seat mount from two pieces of electrical metallic tubing. To build a similar base, just clamp one section of 1 1/2 x 9 1/4-inch E.M.T. to the right side of a bulkhead — immediately above one horizontal brace and about 4 inches back from the half-lap joint — with two 1/4" x 1 3/4" x 3" U-bolts (you may have to slip a plywood shim between the pipe and the wall to get a tight fit). Then take a second piece of conduit, this one 1 1/4" x 8" in size; fasten one end of it to your junction-box connector; and thread this, in turn, to the floor flange. The completed assembly serves as a seat base and can be easily slipped into and out of the "mount" pole.
Your "captain's throne" could be either a fancy store-bought boat seat like mine, or a salvaged fiberglass or plastic "lunchroom" chair. You might also consider building a seat, out of conduit and plywood, to save money. In any case, you can secure your saddle to the floor flange with four 1/4-inch stove bolts of the necessary length (the required size may vary, since you might want to support the seat on a 1/2-inch plywood "plate" for added strength).
For safety's sake, you'll want to be able to lash the inner tube to its plywood frame. I've found that the easiest way to prepare to do so is to drill 1/4-inch holes at the top of each bulkhead through the "wings," and make complementary bores in the floorboard, near the outer end of each wall. Fit the four upper holes with 1/4 x 1-inch eyebolts, then cut four 48-inch lengths of 3/16-inch polypropylene rope, knot one end of each strand, and pass the lines through the holes in the disk from the top side, so the knots hold them in place. At the opposite ends, you can temporarily tie dogleash-type snap fasteners, which — once their position is adjusted to match the bulge of the inner tube — will allow quick attachment to and release from the bulkhead-mounted eyebolts.
Additionally, if you plan to use a trolling motor — as I did — you'll have to remove an approximately 4-by-9-inch section of floorboard from one of the quadrants in front of your seat, to accommodate the unit's propeller housing and shaft. (Of course, although I haven't tried doing so, it would probably be easy to mount a pair of oarlocks to the plywood walls, on either side of the seat, and rely on elbow grease to propel your craft!)
As the final step, paint the wooden components of the water scooter, to protect them from the rigors of marine life. Choose a good oil-based waterproof paint in your favorite bright (again, for safety) color, and give the wood several coats. It's important that you take extra care to thoroughly seal any exposed ends of the sheathing (using silicone if necessary), since cut plywood is particularly susceptible to moisture separation.
Roll the Boat to Shore
Once the paint's dry, simply pull the tube over the bulkhead "wings" and inflate it until the valve stem area begins to swell and the pneumatic doughnut is tight against its frame. For security, pass the four girth lines around the rubber ring, snap them to the metal eyes, and tighten the lines as necessary.
I find it easiest to roll my boat to the water's edge, then clamp on the motor and place the battery in the adjoining front compartment before shoving off. (I usually carry along a small hand pump and a life preserver, just in case the inner tube "lets me down" en route.) Naturally, common sense dictates that a simple craft such as mine should be used only in calm bodies of water, but don't believe for a minute that my little aqua-scooter isn't stable. The nearly five-foot "stance" of the gigantic tube just about guarantees that you'll always sail along on an even keel, and the craft's built-in buoyancy allows it to carry a total load of — I'd guess — well over 200 pounds.
In any event, you'd be hard-pressed to find a boat of any sort that's as inexpensive, easy to build, and just plain fun to use as the one I've made here. And, if you do decide to knock your own scooter together, I think you'll agree with me that I haven't "blown" its capabilities out of proportion!
(And, before you take to the water, be sure to check the boat-licensing and water access regulations in your area.)