By William Steiniger and Jack Smith

IF you're a skin diver of any experience you know that an electric-powered sport submarine is great for underwater exploration.

Seated in such a vehicle, you can cover more bottom simply because youdo not expend your energy in swimming and your precious air can bemade to last much longer. Also, Frances Gaar, the underwater swimmingstar who posed for our cover, will attest to the fact that it's great funto operate.

In building the sub, our original intention was to make it of fiberglasswith a Plyfoam core. A wet sub (one that fills with water and is usedwith an aqualung) requires a certain amount of flotation and we feltthe Plyfoam would be ideal. Sold by Plyfoam, Inc., E. Beth page Rd.,Plainview, L.I., N.Y., it is unique in that it is thermoplastic; that is, whenheated to about 180*F, it can be shaped to any mold. Then when it coolsit retains the form of the mold and its strength as well. With a layer offiberglass bonded to each side, it becomes strong indeed.

We planned a wooden mold on which we would lay up a quarter-in,shell of Plyfoam. Then we would cover the Plyfoam with fiberglass,remove it from the mold and apply another layer of fiberglass on theinside. Doing it twice would give us the two halves of our hull.

We still think the foam core construction would be ideal. The onlyhitch was that we missed getting the technical bulletin normally sup-plied with every Plyfoam order. Instead, we had the partial informationthat polyester resin could be used on Plyfoam. The technical bulletinwould have told us that it had to be a special formulation of polyester—one with little of the so-called styrene monomer in it. The styrene mono-mer in our run-of-the-mill polyester made sponge of our first Plyfoamshell.

Yet we figured we had paid for some learning (46 cents per sq. ft.for 24 sq. ft. of Plyfoam plus the cost of one coat of polyester). We agreedthat we would get more Plyfoam and use epoxy, the resin that has noeffect on the foam.

FRAMES (left) are erected at right angles to backbone nailed to buildingplatform. Rib bands (right) are nailed longitudinally, giving hull its form.

BUILD YOUR OWNMechanix Illustrated

BATTEN is bent in smooth curve to make RIBBANDS complete basic mold, could bea template for 3/4-in. pine bow sections. closed up, plastered, then sanded smooth.

BOW of mold is built up with individualPlyfoam sections heat-shaped on the form.

HEATER softens sheet Plyfoam for bend-ing over the ribbands on the basic mold.

It was when we priced epoxy resin($86 for five gallons) that we changed

our construction plans. We decided touse our remaining Plyfoam to make asmooth mold. Then we would cover itwith th in sheet polyethylene plastic toprotect it from polyester resin ($5.50 agallon) and lay up a s t ra ight fiberglasshull without the foam core. If money isno object, you can build the hull withPlyfoam and epoxy resin. Otherwise,follow our lead.

LARGE-SCALE PLANS

are available, complete withtext and photographs. To pur-chase a copy, send $5 toMechanix Illustrated PlansService, Fawcett B u i l d i n g ,G r e e n w i c h . C o n n . 06830.Specify Sport Sub, Plan No.SS4-66.

Mechanix Illustrated

89

STRIPS of plastic under Plyfoam jointsprevent epoxy resin from bonding to wood.

PLYFOAM makes smooth mold, is coveredwith thin sheet plastic for fiberglass lay-up.

TOP hall of hull slips over projecting1/4x2-1/2-in. oak screwed to inside of bottom.

TAIL FIN passes through hull. This in-side view shows cleats and motor shaft.

T h e d r a w i n g s show the simplicity ofthe mold. Each frame is a half-circle—with an ex t r a two inches at the bottom,As is the case with any original project,you often think of a be t t e r way to dosomething after you 've done it. Tha t ex-t ra two inches is the bet ter way wedidn' t use in our construct ion. Thus thephotos differ slightly from the drawingstha t should be followed.

After going th rough the process oftacking the foam and the fiberglass onthe unders ide of our mold, we decidedit would have been be t t e r to have astraight band a round the bot tom to

which they could have been tacked.F u r t h e r m o r e , if a na r row, 1/8-in. slitwe re left at the top of the band, a sha rpknife could be inser ted and each f iber-glass shell could be cu t from the moldwi th uniform ease. Tha t ' s why the d r a w -ings show a l7/8-in. pine tacking s t r ipa round the bot tom of the mold. The re ' sa solid block unde r the nose.

The way the mold frames a re erectedand braced at r ight angles on the back-bone and the bui lding platform is welli l lustrated. It 's also clear how the 1/4xl-in. r i bbands a r e applied with half-in.brads . The nose is the only thing that

90 Mechanix Illustrated

l - V PINEBLOCK DKBEtBOW FUUtHC

BATTERY CASE will hold two six-volt bat-teries. It is strapped in forward chocks.

STEERING is worked by means of pivot-ing-arm control attached to motor shaft

April, 1966 91

SPORTSUBMARINE

requires extra care. As shown in aphoto, take a thin, flexible batten andbend it from the side around to thecenter point of the nose on the back-bone, establishing a smooth curve byeye. Then tack the batten in place andslip a piece of cardboard under it tomake a template.

The template can be used to make upthe 3/4-in. pine sections that form thebow. Naturally, the bottom edges of allbut the center one will have to be cutand beveled to fit them in flush withthe line of the hull.

At this point you could complete themold entirely of wood, filling in all theopen spaces and closing up small crackswith plaster or patching compound.

You then could sand the entire formsmooth, coat it with a wax releasingagent and lay up your fiberglass. Weproceeded in a different way, using ourPlyfoam to make the smooth mold.

The Plyfoam was easily shaped overthe mold with the aid of an electricheater. We just held the heater closeand formed the foam with our handswhen it got hot Where it tended tobuckle (we used sheets almost half thelength of the hull), we cut narrow tri-angular darts from the bottom up andpulled the edges together smoothly. Alledges of the Plyfoam were bonded to-gether with epoxy resin after pushingstrips of polyethylene plastic under thejoints to keep [Continued on page 124]

92 Mechanix Illustrated

Build Your Submarine[Continued from page 92]

the resin from bonding to the wood.The edges of the Plyfoam required some

care. When two sheets were heat-formedaround a curve and butted the edgestended to curl up. When the sheets wereformed our first cuts were rough. Then, toget the edges to butt perfectly, we madea simple gadget. It consisted of two paral-lel razor blades clamped to a 94-in.-widepiece of wood. By drawing them along oneither side of our rough cut, we got clean,parallel cuts—and also eliminated theslight curl at the edges. Epoxy resin andsome staples into the wooden ribbandssecured the sheets firmly.

On the nose, we formed and cut indi-vidual pie-shape sections of Plyfoam, thenedge-glued them together along the cen-terline of each 3/4-in. pine section. A fewbrads driven in flush kept the foam in placeuntil the resin hardened.

The fiberglass was laid up after we hadcovered the mold with thin sheet plastic.The first layer was heavy woven roving.After it was sanded smooth, a layer of 10-oz. glass cloth was applied. When this hadcured, a complete sanding followed, withclose attention to every imperfection.Where any bad spot was sanded out poly-ester patching compound was used to fillit in smooth.

With the 1/8-in. slit around the bottom,cutting each fiberglass shell from the moldshould be easier than it was for us. But thehull sections at this point are still not stiffenough. A layer of l-1/2-oz. mat on the in-

To get the two halves of the hull to mateperfectly we devised a scheme. A 1/4x2-1/2in. oak strip was screw-fastened to the in-side top of the bottom half of the sub, halfits width projecting above the edge. Theends of the screws, incidentally, wereground off flush on the inside. At the bow,a piece of 4x8-in. fir was shaped and fittedinside to take a bow ring later. Then thetop half of the sub was fitted on and screw-fastened into the oak along the edge. Onthe outside, a three-in. width of glass tapewas bonded over the joint with polyesterand sanded smooth after curing.

Cutting out the cockpit opening was[Continued on page 126]

April. 1966

On each side, 6-1/2 in. above the cen-line, we cut straight lines, curving themby eye into the back of the cockpit. Thecross the front is a straight one fromto side. A curved 1-1/2-in.-wide cleatglued and screwed across the forwardof the cockpit on the inside to providefastening of the dash and 3/4-in.-sq.

were glued to the undersides aroundeither edges. Then all cleats were cov-with fiberglass tape which was latersanded smooth.Rather than fasten a weak tail fin onthe side, we made a one-piece tail to passthrough the hull . To accommodate it,

1x10-in. slot was cut in the lower halfthe sub from the centerline down onthe side. The part of the tail which passesthrough the hull extends 10 in. forward ofstern and provides great rigidity whereneeded. As illustrated, cleats brace theinside and the thickness is doubledwith another layer of 3/8-in. plywood on

outside. It 's all faired off nicely, sealedthe joints with fiberglass tape andsanded. It is not necessary to fiberglass

The watershield is necessary to keepface mask from being torn off becausesub can move up to 4 mph underpower. Cut the quarter-in. Plexiglas to thesize shown. Then hold the sheet in frontof open oven with the heat turned upbending it gradually to the hull form,

work can be simplified by making afrom a sheet aluminum template

wich is bent to shape on the hull. Thenplexigias can be formed over the moldor you can send the mold to a plasticsshop to have the job done.YOUR dash, a quarter-in, plywood panel,fitted with a decompression gauge and

instruments: thermometer, depthgauge, timer and pressure gauge to keep awatch on the air tanks. A compass, whichhelps keep the sub level, is mountedup behind the watershield.Little could be said about the steeringcontrol and the diving planes that isn't de-tailed in our drawings. Use an exterior-

-construction-grade aluminum andcover the planes with epoxy after prim-Chocks for the battery case can beglued to the inside of the hull with epoxy

The power in our sub is a pressure-

the wood.

sealed 1/4-hp, 12-volt motor developed bythe Davee Co. of New York City and soldthrough Richard's Aqua Lung Center, 233W. 42nd St., New York, N. Y. 10036. Themotor and battery case have been testedto a depth of 100 ft. and this is the recom-mended safe limit for our sub.

With wiring harness and a safety shroudover the propeller, the motor sells for S112.The battery case, complete with wiring,switch and O-ring seals, costs $101. Thecase will hold two AC-78,12-volt, aircraft-type, Exide batteries. They list at $48.35each. One battery may be used for slowspeed; two batteries hooked in series toput 24 volts on the motor will give speedsup to 4 mph.

The sub must be buoyed in the samemanner as a diver. This is accomplished bytrial and error, using Styrofoam flotationand weights as necessary. P u t the flotationin the top half of the sub fore and aft andsecure it firmly when you have it right.Any weight should be in the bottom to keepthe sub upright. Be sure it trims level foreand aft. Jus t the slightest amount of posi-tive buoyancy so the sub floats withthe top just awash at the surface is de-sirable.

In handling the sub the tendency of be-ginners is to over-control, depressing orelevating the diving planes too much andturning the motor too far. Only slightmovement is required and it even wouldbe advisable to put limit stops on the con-trols. Rolls should be avoided The bat-teries won't spill in a quick roll but theywill if kept upside down too long. One cau-tion: the sub is not for novice divers. Be-come proficient as a free diver before youattempt to handle an underwater vehicle.

There you have it. In construction of themold and the basic hull we used seven gal-lons of polyester resin ($38.50); six yardsof 10-oz. glass cloth ($7.92); six yards ofwoven roving ($8.40); six yards of 1-1/2-oz.mat ($6.60); two 4x8-ft sheets of %-in.plywood ($14); 224 ft of 1/4xl-in. pinestrips ($11.20); 16 ft of 1/4xl-in. oak($1.12); and the Plyfoam ($16.50)—atotal of $107. Hardware and Plexiglasbrought our full cost to near $150. Com-plete, the sub can be put in the water forabout $476, which is less than half what acommercial equivalent was selling forwhen we set that mold up. •

Mechanix Illustrated