The Evolution of a Lightweight Epoxy/Styrofoam Scow

By David Gray

This project initially began when my son left for the Navy. Single-handedly loading the Cartopper, a Phil Bolger designed sailing/rowing dinghy, into the pickup quickly became a daunting task when I injured a shoulder. I needed a lighter boat for the occasional fishing trips into the shallow backwaters of nearby ponds, rivers, and reservoirs of central Indiana. Wanting a quick and dirty project, I turned to a simple scow design that Dynamite Payson calls the Skimmer. Roughing out the measurements from one of Payson’s books, I quickly built a 4′ x 8′ model of 5mm Lauan Mahogany reinforced on the outsides with 6 oz. fiberglass and epoxy. While the resulting model was light enough for me to wrestle into the back of my pickup, I thought that it might be possible to build an even lighter craft out of polystyrene-type insulation board. After giving the Skimmer to my wife’s family for use on their farm pond, I was able to secure Dixie’s blessing for undertaking “just one more project.”

My primary objective in building Hot Tub was to create a lightweight, multipurpose mini-scow that I could easily load single-handedly into the back of my pickup. I had been impressed with the performance of Skimmer with my 30 lb.-thrust Minn-Kota electric motor, and I expected even better performance from a narrower, lighter version. I even had visions of powering this new craft with a small 5-10 hp. outboard, to see if my experimental scow would throw rooster tails from the skids like Payson’s version of Skimmer. If the project didn’t work well as a boat, I figured, I could always plant it in the back yard as a wading pool, add a set of wheels and have a huge lawn cart, or add a lid and lock for the granddaddy of all truck tool boxes.

I had experimented with Dow Corning Styrofoam insulation board and found that it would take epoxy and fiberglass cloth. A slight yellowing of the epoxy was evident, but the fiberglass and epoxy definitely stiffened the surface of the insulation board. I also found that Elmer’s ProBond glue, advertised as waterproof, could be used to glue the board together easily. Doorskin plies, plywood, Lauan, and other woods can also be laminated to the insulation board using this glue.

The glue reacts with moisture; therefore users are advised to moisten the surfaces that will be mated before they are glued and lightly clamped. When the glue begins to set, it bubbles and expands significantly. I soon learned to use less glue and place duct tape on cracks so that I would not have to try to sand the glue off the insulation board. The insulation board is so soft that the least bit of careless handling or sanding easily damages the surface.

Cutting and shaping the insulation was a simple process using a single hacksaw blade in a plastic holder. After making long cuts, I would sand the edges lightly with 100-grit sandpaper to even out the dips and high places. One piece of sandpaper seemed to last forever on this project. Toothpicks and duct tape were often all the clamping I needed to let the glue set.

I glued a piece of 3/8″ insulation board to 1″ board to form the bottom. The 3/8″ board, I found has a thin film of plastic covering it. If this is not removed, the surface under the fiberglass/ epoxy can bubble when exposed to the hot sun. Unfortunately, that is what happened. Later I speculated that I might not have removed this plastic from the bottom of the hull. I know that I removed the film from the part that is bonded to the 1″ board, but I am uncertain about whether I removed the plastic film from the bottom. The blisters might also be the result of a layer of latex paint blistering beneath the fiberglass and epoxy when I applied spray paint in the hot sun. While the blisters are unsightly and slightly softer than the surrounding areas, they probably don’t affect the integrity of the hull much. I suspect that Hot Tub would float fairly high even if the entire transom were removed. Earlier I found that 1 sq. foot of 1-inch thick insulation (3 oz.) laid flat on the water would support 4 lbs. 4 oz. before sinking below the surface. To support 300 lbs. of motor, battery, and me, I would need only about 70 sq. ft. of 1″ thick insulation. Who even needs displacement?

The hull is covered by 4-oz. fiberglass. I used 6-oz. cloth on the Skimmer, but it didn’t go over the chines and corners as readily as the 4-oz. cloth on “Hot Tub.” I added 2″-high skids to the bottom made from 2″ insulation board laminated to 5mm lauan. The wood provides a little extra measure of protection from cement ramps, stones, etc. that one invariably encounters in boating. The skids also stiffen the bottom significantly. At some point, I expect to epoxy some fiberglass strips to these skids for even more protection. As of now, the skids are only covered with a layer of epoxy and varnish.

I learned that a builder should only use latex paints on the insulation material. Oil-based paints or varnishes can degrade the insulation if there is any direct contact. If I were building a second version, I would use latex house paint throughout. However, I still am uncertain about the use of any paint beneath the surface of the fiberglass and epoxy. On the interior of the hull, which was painted with latex before fiberglass and epoxy were applied, there is presently no sign of blistering.

Without seat, gunwales, and hardware the hull weighed in at 38lbs. The final product weighs about 45 lbs. with seat, hardware, and substantial gunwales, but without anchor, oars, or motor-still light enough for me to load by myself. Hot Tub fits nicely between the tarp cover and the bed of my short bed pickup and doesn’t extend beyond the tailgate. The boat takes only a moment to load and unload, and I can easily launch it from almost any bank or open spot near the water. Fully loaded with cooler, fishing equipment, battery, motor, accessories, and my 190 lbs., the draught is about 5″.

The seat is moveable so that I can easily adjust the weight distribution and rowing position. The seat top also lifts off to accommodate a deep cycle marine battery when I am using the trolling motor. (Note: the trolling motor moves Hot Tub about as fast as an outboard would power most small fishing boats.) With the seat and oars removed and a few inches of water inside on a hot summer day, Hot Tub could easily become a floating lounge for two.

While I was testing the boat on a nearby river, I was formally warned by a conservation officer that I would need identification numbers on the boat to use it on Indiana lakes and streams with any kind of motor-even a small trolling motor. That warning prompted me to build some outsized oars of wood and 1 1/4″ PVC water pipe, then test the boat again. This time a man and his son hailed me from a nearby canoe to ask, “What is that-a boat or a bathtub?” That question inspired the boat’s name.

Although “Hot Tub” rowed easily upstream in fairly rapid waters, it was no match for the canoes’ speed or ability to work upstream against small rapids. Floating lazily back down the river, I noticed that even the lightest wind was enough to send me coasting upstream again. Might it be possible to sail this tub, too? Stay tuned.

UPDATE 1: Hot Tub’s surface has suffered from delamination. In the heat of the summer, I noticed that bubbles were beginning to form between the epoxy/fiberglass and the Styrofoam. Apparently the heat caused air trapped in the Styrofoam cells to expand and permanently delaminate from the epoxy/fiberglass “skin.” While the appearance has suffered terribly from these effects, there is no evidence that the performance of the boat has suffered. However, it appears total encapsulation is to be avoided.

UPDATE 2: My nephew Andy called with a request for me to build him a boat like Hot Tub so that he and his friends could fish in four or five remote farm ponds. Andy wanted a light boat that could carry two or three persons and could be easily carried into these “back forty” fishing sites. Apparently, he’d told some disbelieving friends about his uncle’s Styrofoam boat; and now he wanted to prove its worth. So that he wouldn’t have to bear the cost of a new boat, I volunteered Hot Tub as the boat to meet his fishing needs. A couple of weeks later, on his wedding day, I delivered the boat to Andy.

About a year later, I got a call from Andy saying that the boat had worked out perfectly. April, his wife and newest fishing partner, also liked the boat and fishing the farm ponds. Andy reported that keeping the boat in the cool recesses of his horse barn had apparently caused the bubbles in the surface to disappear almost without evidence that they were ever there. I told Andy that I had something to report, as well. In the year since he had been married, I had used some pattern boards left over from the very first boat to build Hot Tub III. I had sorely missed my little fishing boat; and, well, I had these pattern boards.

Hot Tub III varies only slightly from Hot Tub. III is narrower, has deeper and longer skids, a different slant to the transom and sides, and is made with 5 mm lauan mahogany plywood with a fiberglass/epoxy bottom and sides. When it became apparent that Hot Tub III was going to weigh about 30 lbs. more than the Styrofoam version, I also added removable wheels. Note the wheels in the picture.

Interestingly, I find Hot Tub III to be less stiff than Hot Tub. I mentioned earlier that I was surprised at how much the fiberglass stiffened the Styrofoam. I have had to add considerable weight in bracing to begin to come close to the stiffness of the earlier version. I believe that the greater width of the fiberglass vs. the width of the lauan mahogany plywood has much to do with this effect. By virtue of its narrower beam, III is also less stable and sits slightly deeper in the water than the last two models. While I can still stand up nearly anywhere in the boat without losing my balance, I feel a little less confident in the stability of a boat that’s only about 40″ wide vs. the 44″ beam of the Styrofoam Hot Tub.

Hot Tub III retains the versatility of the original with its wide open interior, light weight, adjustable seat, and ease of transport. With her deeper skids and narrower beam, she seems to row more easily than either of the earlier versions. Hot Tub III is also scary fast with just a 5–7 hp outboard driving her. With that much power, she planes easily, riding up on her skids more and more as she reaches top speed. One of the younger, more adventurous participants at a recent messabout in Michigan tested her for me with both a 3 hp and a 7 hp outboard. The 3 hp motor wouldn’t quite push her up on a plane, but after an initial try with the 7 hp, my test pilot came in for his helmet. He reported that Hot Tub III was faster and more maneuverable than his homemade tunnel hull with the same motor onboard. Note, however, that he was testing in very calm waters. While I’ve rowed Hot Tub III in some pretty stiff breezes with good success, I don’t know how much porpoising might be caused by chop and waves when she’s under power.

Experiments with this boat have led me to believe that encapsulating Styrofoam with a layer of 1/8″ lauan plywood and a layer of fiberglass would create a thick, stiff, structural material that could find many uses in lightweight skiff building. I’m currently building a 20′ mast of this laminated material that I intend to mount on one of my boats for testing. I wonder what would happen if I rigged up Hot Tub III for sailing.

UPDATE 3: Hot Tub III now has a sail rig. I had created a pattern for a 35 sq. ft. D-4 sprit rig to be used by a school class in constructing PolySails for the nine D-4’s they were building. That sail seemed to be about the right size for the 8’ long Hot Tub, so I set about creating the little sprit sail and rigging it up to try it out. At first I thought that I might get by without making a board and rudder—I would just use the oars and the skids for resistance and steering. But a test in light winds quickly altered that view as I went skidding sideways whenever I tried tacking.

A couple of days later, I had my board and rudder ready to go, thanks to some scrap plywood that happened to be lying about the garage. I decided to make a simple lee board rather than going to all the effort of creating a centerboard trunk. Besides, the Midwest Messabout was looming, and I wanted to try Hot Tub III out on Lake Rend.

But before I showed up on a bigger lake with this little boat, I decided to give the rig a few more tests on our little 12-acre lake. With a good stiff breeze blowing, I took Hot Tub III out for another test. It was good that I did, because a hard jibe exploded my lightweight mast step and left me rowing for home.

The June 8, 2002 weekend found Hot Tub III in the back of my pickup headed for Lake Rend, Illinois, a four-hour trip from my home in Fishers, Indiana. As I neared my destination, I began to notice the absence of movement in the treetops along the roadside. “Where’s the wind?” I asked myself.

By 10:00 a.m., Saturday, Hot Tub III was unloaded and in the water. With almost no wind, though, it didn’t make sense to rig up the sail. A fellow messabouter, lingering nearby with his daughters, admired the boat and recounted the sad fact that he didn’t get his boat finished in time for the event. Consequently, I invited Mike Z? to take Hot Tub III out for a row and he gladly accepted. On Sunday, with a little wind in the channel near the boat ramp, Mike had the opportunity for a sailing lesson in Hot Tub III, and I got to shoot some pictures.

Learning to tack.

By late Sunday morning a nice breeze had kicked up out in the main lake and the speed boats were starting to kick up a 1’- 2’ chop. Deciding to give Hot Tub III a real test, I removed the wheels, and headed out from the safety of the channel.

Reaching downwind was a cinch. I just sat in the back of the boat and skipped over the chop. With a little bigger sail, I might even have been able to get up on a plane. Heading back was a different matter. In order to tack, I had to move forward almost to the lee board so that the boat would pivot around the board. This placed my weight forward and made headway difficult into a chop that was now threatening to break over the lowered bow. After several attempts to make headway with the wind and speedboat traffic picking up and the danger of swamping imminent, I decided to jibe for the relative safety of the shoreline where a small group of fellow boaters had gathered to witness my battles with the wind and waves. Luffing the sail and getting out the oars, I conceded to the onlookers that Hot Tub III wouldn’t tack well enough to get me back to the boat ramp. Rowing back into a stiff breeze also proved slow going.

After reflecting on the pictures above, I think that I will have to provide Hot Tub III with a larger sail and a center of effort that is positioned further aft if I want to sail her into a stiff breeze. The larger sail and repositioned center of effort will allow me to move the lee board further aft, and perhaps get up on a chine more for tacking. However, if I do get up on a chine, that flat scow bottom is an invitation to a gust to pick the boat up and flip it over. I fear that this particular scow shape, with its straight chine, will never allow me to tack very close into the wind.

For all her faults, Hot Tub III has proved to be a good learning platform. After three versions, I more fully understand the compromises involved in rowing, motoring, and sailing a box boat—or any boat, for that matter. Her stability, transportability, and low waterline make her ideal for fishing the shorelines of Indiana lakes; and she’ll work well enough to teach the neighbor girls the principles of sailing this summer. For a small boat and for me, those are pretty good compromises. I don’t think I’ll need a Hot Tub IV.
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UPDATE 4, April 2009

Ha! Looking into the future was never one of my strong points. Over six years have passed since I wrote that lame prophesy. It is now 2009 and I am living in Florida. In the meantime, the neighbor girl, who was about to enter a local Indiana middle school when this was written, is now about to graduate from high school with no interest whatsoever in sailing. I have a grandson who is now six, whom I am still hoping to interest in boating; a granddaughter six months old here in Florida, and I have built or helped to build eight more 4’ x 8’ scow-type boats, beginning with Hot Tub IV, a NASCAR-themed race boat built as a tribute to Tony Stewart back when he was still with the orange #20 Home Depot car. An interested reader can learn all about this project by clicking on the study plan at the left. This was a great little boat, complete with windshield, lights, an adjustable seat, and even a steering wheel. And, it was the only boat in my fleet that my grandson seemed to enjoy out on the water. Even under electric trolling motor power, Hot Tub IV moved quickly around the lake. My one regret is that I never tested the boat with the 5 hp Briggs engine that she was designed to carry. Both engine and boat were sold recently before I moved to Florida.

After retirement in 2006, my interest was captured by another 4’ x 8’ scow that was the brainchild of David “Shorty” Routh–the PDRacer. The PDRacer (PD stands for Puddle Duck, by the way) was perfectly suited to our small lake in Indiana; and Shorty had actually had the basic design approved by the US Sailing Association as a racing class sailboat. I was hooked as surely as the many bass and bluegill that were caught off our pier on Lake Vista. Seven boats later, I am still dreaming of the improvements I will make to the next design.

Why do I like this little boat so much? There’s a raft of reasons, but listed below are the main points:
· Simplicity. Few boats are easier to build. More than a few of the nearly 300 PDR hulls have been assembled from scratch in two days or less.
· Cost. In this ailing economy getting out on the water in a new boat for under $350.00 is nearly unheard of. A PDRacer can be built for even less.
· Stability. With its deep rocker and flat sides, the PDRacer is difficult to upset in even the stiffest breeze. It’s a great trainer for novice sailors, but sophisticated enough to challenge experts.
· Flotation. One class requirement is that enough flotation is required to make the PDRacer self-rescuing.
· Weight. While most PDRacers weigh around 100 lbs., they can be built to weigh around 70 lbs. That’s a boat that I can still move around readily without help.
· Challenge. These boats can be purpose-designed to be raced, set world records, attract youngsters to sailing, or even to look good.on the water. Because only the bottom 10” of the defined hull shape must be the same for all class boats, the rest of the design is up to the imagination of the the builder. The opportunity to experiment will continue to draw boatbuilders to this class.
· Fun. Shorty’s motto for the PDRacer is cheap, creative, and fun on the water; his genius is that he’s achieved all three of these objectives with the PDRacer.

I have built three PDRacers for myself and helped build the hulls for four others. Most of these boats participated in a race and regatta we sponsored on our lake in the summer of 2008. The variety of sail plans included a lateen, a balanced lug, two leg o’ mutton sails, and a biplane rig. A youngster, who had just completed his boat the evening before, was the eventual winner. What a blast! Details about the PDRacers and the race and regatta can be found by clicking on the picture of Lame Duck, hull #100,.below. This picture was taken at the 2008 Midwest Messabout at Rend Lake, Illinois, on a day when the wind and whitecaps kept most of the boats off the water. Four PDRacers braved the wind, however; and one set an American record for speed of over 9 mph on that day. Sadly, I had to part with both Lame Duck and Webfoot, hull #199, when I moved. I did keep Wild Duck, hull # 143, in the hopes of inspiring some new builders in South Florida where I now live.

What next?