Let's build a towboat

Radio Control Boat Modeler, Oct 2005 by Fryant, John

The towboat is a workhorse that can be found on inland rivers, harbors and coastal waters in all parts of the world. They push, not pull, their "tows" of multiple barges lashed together. The most familiar ones are those that work the Mississippi River and its tributaries. In this and the next installment of "Scale Views," I'm going to tell you how I built a small twin-screw RC towboat using a fiberglass hull. The first half of the series deals with the hull construction; the second will cover the superstructure and detailing. Complete plans will be available.

My little towboat is typical of those found on many navigable rivers of the U.S. The model is fictional but closely resembles the "Capt. Merdie," one of Merdie Boggs' fleet that works on the Ohio River. Thanks to Joe Brown, who runs Towboat Joe's website, for furnishing the plans from which this model was adapted.

HULLWORK

I'm using a fiberglass hull from Microglass. It's 16 inches long with a beam of 6 inches and a depth of 2 ½ inches. The hull comes with the raised aft section. The forward portions of the deck need to slant downward about ¼ inch from the bow, so I measured 3 ¾ inches back from the bow and down ¼ inch. I drew lines from this point to the top of the bow and then all the way around the sides and stem to the opposite corner of the bow. I then cut the top edge down to these lines using a Dremel tool and a cutoff wheel. This should be done over a large trash can to catch the dust and debris, and a dust mask should be worn. The next step is to locate the openings for the prop shafts. There is about 1 1/8 inch of vertical space under the stern for the props, which should not extend below the hull bottom. I had two small, a little more than 1-inch-diameter Rivabo 3-blade props; the stock number is 524-30. The size as listed on the package is L-M4-30 for the left-hand and R-M4-30 for the right-hand prop. Being of European origin, they were bored and tapped for 4mm threaded shafts. Their size was perfect for the available space. The shaft openings must be positioned in the middle of the slanted portion of the hull's stern. Their size will be determined by the size of the stuffing box tubes. Mine were ¼-inch diameter. I started the holes with a smaller drill and enlarged them with a rotary burr.

All towboats have a pair of "tow knees" mounted on the bow. These are what make contact with the multiple barges that they shove around. Mine are made from pieces of 3/8-inch-thick pine. I cut the steps into them with a scroll saw. I faced the steps with 0.020 styrene and covered the top surfaces with pieces of Plastruct diamond-tread plate styrene. I covered the front faces with pieces of neoprene cut from an old computer mouse pad.

The raised stern deck is a combination of wood and plastic. The hull sides around this deck slant inward, which would normally be rather difficult to model. However, the job is made simple by using tapered trailing-edge balsa strips made for model aircraft wings. I used ½-inch-wide strips positioned with the tapered side facing outward. I glued these in place on the plywood deck and sanded the comers round. Then I glued 1/8x3/8-inch-wide basswood strips to their inner surfaces, forming a lip for the plastic deck to set on. I gave the wood three coats of sanding sealer, sanding between each coat. The stern deck is a piece of Plastruct 0.030-inch diamond-tread plate held in place with two tiny RadioShack rare earth magnets. I expoxied these in holes drilled into each side of the deck piece and placed a small steel strip on each side. The rear cabin bulkhead will also help hold this deck piece in place. The rub strip around the top of the hull is a piece of 1/8-inch half-round styrene strip from Evergreen, CA'd to the fiberglass hull. This strip can be carefully bent with the fingers to go around the corners. Evergreen styrene is available at most hobby shops.

My deck fittings are mostly scratchbuilt. The bitts on the foredeck, however, are from Robbe. The cleats (called kevels by river men) are scratch-built, but these are widely available from ship model suppliers. I recommend Loyalhanna Dockyard; check their catalog for 1-inch to 1 ¼-inch-long cleats. You need seven. The two gray objects on the foredeck are electric winches, used to tighten the steel cables that hold the barges to the towboat. These are not available commercially, but the plans will show drawings for typical winches. I scratch-built mine from bits of scrap plastic. Towboat hulls do not have water lines. My entire hull and the tow knees are painted semi-flat black, while the deck is painted red. I used Krylon spray semi-flat Black for the hull and Humbrol #100 Red Brown for all the deck surfaces. Humbrol is a British-made enamel paint that comes in small, one-ounce cans. It is often available in hobby shops that sell plastic model kits.

STEERING DUTY

Towboats have lots of rudders so they can maneuver large groups of barges around the many bends in the rivers and in and out of lock chambers. This one has six: two for steering ahead and four for steering ' in reverse, or "flanking," as it is called by river men. I made my rudders from 0.020-inch Styrene by edge-gluing two halves together around 3/32-inch brass rods, which then became the rudder shafts. I bonded the edges of the plastic together with Testors styrene cement, clamped them and left them overnight to set. Then I epoxied the rudders to the shafts and filled the voids with Sig Epoxolite putty. Drilling the locating holes for the rudder shaft tubes is easy if you have a drill press. You must position the flanking rudders about 3/8 inch from each side of the prop shafts. Once the rudder shaft locations are determined, you can place the hull upright on a drill press table and drill all six holes clear through the deck and hull bottom. Because of this model's small size, it was impossible to find ready-made steering arms for the tops of the rudder shafts. Searching through the airplane fittings at the local hobby shop, I found some nickel-plated steel straps (Du-Bro catalog no. 202) that I cut down into perfect arms. The bellcranks are nylon servo arms mounted to the deck with screws, and the connecting rods are ¼-inch-wide brass strips. All of the rudder hardware must be close to the deck so that nothing will rub against the raised deck to be installed above it.