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Big Twin R/C Outboard Motorboat
May 1957 American Modeler

May 1957 American Modeler

May 1957 American Modeler Table of Contents

These pages from vintage modeling magazines like Flying Aces, Air Trails, American Modeler, American Aircraft Modeler, Young Men, Flying Models, Model Airplane News, R/C Modeler, captured the era. All copyrights acknowledged.

Airplanes and Rockets visitor Kevin B. requested that I scan and post this article on the "Big Twin" R/C outboard motorboat model. It appeared in the May 1957 edition of American Modeler magazine. American Modeler was one of the forerunners of today's Model Aviation (the official AMA publication), and was more all-encompassing in regards to modeling as it included model boats, cars, rockets, and trains. It also was known to occasionally have articles on full-size aircraft. Anyway, the Big Twin is 32" long and is built of traditional model boating materials like mahogany plywood and spruce. This model's claim to fame is the use of balsa planking on the hull - which is much easier to form than spruce - and then a layer of fiberglass is laid over it for strength and waterproofing. An Allyn Twin outboard motor is specified for power.

Big Twin R/C Outboard Motorboat

Bill Baughman

"A.M.'s" West Coast Boating Whiz Gives You an Honest-to-Goodness Man-Sized R/C for K&B-Allyn's Outboard Twin; Overall Length, 32"

Big Twin R/C Outboard Motorboat, May 1957 American Modeler - Airplanes and RocketsWith the advent of large displacement motors and remote controls there has been an increase in the number and types of full-size outboard-cruisers, This new form of safe, economical family boating has proven very popular in recent years.

Now that the Allyn Twin miniature outboard motors are on the model market, it is only natural that model builders try their hand at this type craft; the ease of power installation and the running cleanliness make it ideal for model use.

Ours is a composite model in that it uses features found in many different full-size cruisers adapted to model operation. If you will take a closer look at the plans, you will note Big Twin" is designed primarily for radio-controlled operation. However, if you are not an R/C bug yet, don't let this throw you, "Big Twin" can be built as is and operated as a free-running craft very nicely. Too, if you would rather have inboard power, the simple matter of closing in the outboard motor rear deck and transom cut-outs and the installation of motor mounts at Frame #4 will make for an easy conversion.

With the preliminaries out of the way, let's get to building. To assure a true hull of this size when completed, the removable jig shown in plans is used; take care in its construction and adhere absolutely to the measurements given as the jig will determine the final result of your building.

After cutting out all ribs, transom and stem from the designated plywood, these are screw-fastened to jib-board blocks, blocks in turn screw-fastened to jig-board (see photo #1). Now spring in all sheer and chine stringers, bottom and side battens, fastening with Weldwood, Elmer's, or similar hardwood glue. It is good practice to fasten to chine and sheer pieces to stem with a miniature screw at each stringer if these fastenings are available locally (photo #2 shows construction at this stage).

Big Twin underway - Airplanes and Rockets

Big Twin underway.

With all ribs, transom and stem piece cut out and set in place on jib-board - Airplanes and Rockets

Photo #1 - With all ribs, transom and stem piece cut out and set in place on jib-board, actual hull construction gets started.

Horizontal stringers in place, hull frame sanded and faired, ready for planking - Airplanes and Rockets

Photo #2 - Horizontal stringers in place, hull frame sanded and faired, ready for planking. Keep careful check on rib spacing.

Ease of applying sheet balsa planking obvious here - Airplanes and Rockets

Photo #3 - Ease of applying sheet balsa planking obvious here. Although Bill applied both sides and bottom at same time, better practice is to follow article and apply sides, true up, then the bottom. Pins and Scotch Tape hold everything while glue dries.

Finishing final bottom planking "course," note penciled marking - Airplanes and Rockets

Photo #4 - Finishing final bottom planking "course," note penciled marking along forward part of chine. As you apply bottom planking at this point, change from over-lap to butt joint between bottom and side planking due to increasing "V."

one last covering board and monkey rail for port side - Airplanes and Rockets

Photo #5 - Other than one last covering board and monkey rail for port side, hull is complete. Monkey rail is placed flush with outside edge of planking, sheer rub rail extends beyond.

removable cabin unit is built in completed boat hull - Airplanes and Rockets

Photo #6 - Using rough-cut parts, removable cabin unit is built in completed boat hull to assure accurate fit. Cord keeps lines correct as roof beams are glued in place.

Using sandpaper fastened to a flat board approximately 12" long, carefully fair up hull framework by sanding each side and bottom section full width at one time. Working in this manner will give you the necessary bevels on the frames, at the chine and other necessary fitting spots, will take out all humps and hollows and allow the planking to lie flat on the framework.

Having a large quantity of pins and Scotch Tape handy and using the 1/16" sheet balsa, start the planking procedure by gluing random lengths with grain running vertical along each side, working both sides simultaneously. You will find this will go very quickly and when completed and with glue dry it is a simple matter to sand the side planking to conform to the bottom contour.

After gluing exterior keel in place, the first course of bottom planking can now be fastened down, working both halves at same time as with the sides (see photo #3). Sand off random bottom lengths to side contour and give entire hull a solid sanding with a medium paper to secure a good, true base for the final course. This is applied in the same manner as the first, laying the balsa strips with grain running lengthwise with the hull, however (see photo #4). As all ribs have a straight bottom configuration rather than a developable curve, it will be necessary to use fairly narrow strips to plank the forward one-quarter of the hull bottom. Now a final dressing down of the planking, sanding the exterior keel piece flush with planking, and hardwood false stem piece installation completes this portion of construction.

When placing the false stem, you may find it necessary to steam the wood or make numerous small saw-cuts on inside edge to obtain required bend. If you will take the time and effort at this point to fibre-glass your hull from chine to chine with Berkeley "Fib-Res" and model weight glass cloth supplied by this concern, applying same according to their directions, you will have a boat that should be as strong as any hardwood job and many times lighter.

The hull may now be removed from the jig by the simple process of loosening all screws. This is a good time to build a supporting cradle to hold boat while completing construction and later when running and storing it. Anything will do, the one shown in the photos was made from scrap ply and an old round handle; supporting surfaces well padded with heavy wool material.

With hull right side up in the cradle, it is apparent that sheer line is automatically determined by designed rib tops and sheer stringers; a careful trim sanding down to the sheer stringer line will bring the extended edges of side planking down to a nice straight sheer. Before applying the front deck and covering boards, it will be necessary to fashion and glue the front deck beams to Frames #1 and #2. The outlines for these two parts are shown at top of these two frame patterns in plan.

Cut out the two half sections of front deck and glue into position; these will be slightly oversize to allow trimming to your hull when in place. Small clamps, nails or miniature screws will undoubtedly be needed in this fastening operation. As the monkey rails will cover the section of the deck at sheer edge where application of temporary fastenings will be necessary, the removal of these fastenings after glue has dried will not mar the final result.

The side covering boards come next and cardboard patterns can be taken roughly from the plans. As all hulls will vary slightly in construction, check pattern thus made to your hull before cutting the wood. Glue on covering boards, sand outside edges of these and front deck to angle of side planking and then apply the mahogany sheer rub rail at this point flush with top edge of deck and covering boards. The center rub rails can now be installed where shown and the chine splash rails along the chine line.

If you have fibre-glassed the hull, use the resin as glue in this operation, otherwise regular glues are okay. The making and installation of the two monkey rails on forward deck completes actual hull construction (photo # 5 shows this stage).

So that the R/C hound will have room enough to work with both hands on the control gear, the entire rear deck, cockpit area and cabin are built into one removable unit. While patterns are given for the parts of this unit, to assure a perfect fit it is best to build the unit in your hull. Cut out the cabin sides, rear deck, seat and seat back, removable section of cockpit flooring and rear cabin bulkhead as a start. Test fit these main parts and the reinforcing pieces of hardwood used at bulkhead, rear of front deck section, and rear seat area. Glue up these parts, being careful not to glue to hull. You will undoubtedly find use of light cord necessary to hold side sections in position while drying (see photo #6).

The two cabin roof beams come next and before gluing in permanently, lay a straight edge across the bulkhead top and the two roof beams to check proper height. The cabin front supporting brace is glued to reinforcing hardwood piece at rear of front deck, after which the two cabin front sections can be fitted and glued. You will find it necessary to bevel all four edges of these two parts if a proper fit is to be secured - the patterns provide enough extra material to do this.

The cabin front patterns show the front ports per the pilot model; should you not want ports at this location, or perhaps something different, now is the time to decide and make your cut-outs before gluing these parts in place. The 1/8" balsa roof can be applied by gluing on strips approximately 3/4" wide. Use sandpaper to trim the front, side and rear bulkhead contours.

From mahogany scrap pieces, make up the flying bridge windshield brace and cross pieces and glue in place. If desired, plastic or light-weight glass can be attached to rear side of windshield frame as well as all cabin port openings later. Use of blue-tinged material helps create large-boat illusion and hide radio gear placed in cabin.

Before finishing the detail on the cabin unit, it is best to install the two permanent cockpit flooring pieces and the two permanent rear bulkhead pieces. These must be fitted to the hull and removable unit while in place and then glued to hull. Small scrap gluing pieces may be utilized where necessary in this step. Build the pilot seat, cut out steering wheel or rustle one up, make kick strips, but do not install until boat is painted.

You should now be able to separate the cabin unit and hull and be ready for the painting. A boat of this size, type and use is best treated as a full-size craft when finishing.

Stain and fill all parts to have a natural wood finish with a good grade of mahogany filler-stain and follow the directions on the can explicitly. If you have used the woods designated, the complete decking, cabin sides and front, seat back, windshield framework, and covering boards can receive this treatment. Using a good spar varnish, give this stained wood at least five thinned coats, sanding with fine paper or cutting with fine steel wool between coats.

When the varnish has reached a glass-like finish and has set up - and be sure this is the case - mask it all off with masking tape and newspaper and start with the paint. If a little of the stain and varnish has run over onto the area to be painted, don't worry as the paint will cover. Now if the hull has been fibre-glassed, get the special fibre-glass primer-sander available at all boat shops; if you are using the wood hull only, regular auto primer-sander for auto synthetic enamel is fine. Use a spray gun if at all possible.

On hull exterior, with the first application of the primer-sander, it is sanded with wet-or-dry sandpaper of fine grade and the alternating painting - sanding process continued until a perfectly smooth base is obtained. The finish glossy auto synthetic enamel coats are next applied, two with very light sanding between should do fine. Please note that the paint referred to is auto synthetic enamel, not ordinary house enamels. The hull interior does not need the sanding but be sure enough material is applied to protect against fuel, oil, etc. Painted portions of the cabin unit receive same treatment as hull exterior, giving a glossy finish when completed.

Allyn Twin Outboard Motor

This Allyn Twin outboard motor recently sold on eBay for $405 - Airplanes and Rockets

This Allyn Twin outboard motor recently sold on eBay for $405.


MATERIALS LIST FOR HULL - Airplanes and Rockets

Miscellaneous small fastenings called for in plan, Weldwood or Elmer's Glue, etc. If hull is double-planked with sheet balsa, some 1590 square inches of 1/16" material will be needed, single planking would call for approximately 1/2 that amount. To fibre-glass this hull, secure the regular Berkeley Model. glassing kit consisting of 1 square yard of glass cloth and sealed can of enough resin and hardener to process that quantity of cloth.

As to color scheme, let your conscience be your guide; the pilot model has white hull inside and out, red bottom to chine line, buff cockpit flooring, blue seats and cabin roof, red steering wheel. Naturally masking tape should be utilized for any color change.

To complete the model, the mahogany kick strips, pilot seat, and steering wheel are glued in position. Commercial fittings such as bow lite, flag pole socket, bits and cleats as well as numbering decals can be obtained from your hobby dealer, if desired.

MATERIALS LIST FOR REMOVABLE CABIN UNIT  - Airplanes and RocketsOther than providing for the radio installation in the design, it is futile to attempt to cover that in detail here. The R/C builder will have his own ideas anyway! It should be pointed out, though, that the arrangement of this boat contemplates the placement of radio gear and batteries inside cabin area of hull, with either a servo unit or escapement placed in rear deck area to turn rudders or motor itself. With the rib cut-outs, the servo can be installed up with receiver, operating a torsion bar arrangement leading under cockpit flooring to motor area under rear deck, turning motor itself.

Materials List for Removable Cabin Unit

Material for Jig board, together with screw-fastenings for same, usual pins, Scotch Tape, glue, knife, finishing materials (preferably auto synthetic enamel paint), mahogany wood filler-stain, spar varnish, decals, trim hardware, race car steering wheel approximately 2" in diameter, material for boat stand.


Big Twin R/C Outboard Motorboat Plans Sheet #1 - Airplanes and Rockets

Big Twin R/C Outboard Motorboat Plans Sheet #1

Big Twin R/C Outboard Motorboat Plans Sheet #2 - Airplanes and Rockets

Big Twin R/C Outboard Motorboat Plans Sheet #2

Full size plans for "Big Twin" are on Group Plan #557 from Hobby Helpers, 770 Hunts Pt. Ave., New York 59, N. Y. ($1).   {Note: These are no longer available}



Posted January 19, 2022
(updated from original post on 1/23/2013)

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