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HR SOLUTIONS-POLYSAILS
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NOTES ON HOT TUB: THE ORIGINAL THROUGH HOT TUB III
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
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
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
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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
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
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.
This
page last updated 7/31/04