The Reasonable Approach
I've been a canoeist for most of my life. Nothing serious - I wouldn't consider myself an expert. I simply like exploring lakes and rivers and bayous. But a couple of recent life changes have led me to consider the idea of a powerboat. First, my two sons have grown up and moved away from home. Without their horsepower I find it hard to paddle in a breeze, or upstream on a river. I'm also getting older.
But I had no idea if I would enjoy using a powerboat. I had never owned one, or even driven one. I certainly didn't want to spend lots of money to discover that I didn't enjoy it. My paddling canoe, a Wenonah Solo Plus, is too narrow and tippy for a motor mount. The obvious solution, as a canoeist, was to acquire a square stern canoe and put a little outboard on it.
First I looked at Wenonahs. They have a square stern model - in Kevlar it only costs about $4000. Time to look elsewhere. I ended up with a 14 foot Indian River canoe, brand-new for only $550. I also purchased a little Honda BF 2.3 outboard.
This combination was a lot of fun to use - but it had shortcomings. The worst was the weight - at 85 pounds the hull was extremely difficult to lift. My Hyundai has a fragile decorative spoiler above the rear hatch, so I have to lift the whole canoe to place it on the roof rack. I managed to put a dent in the roof on one excursion. My Solo Plus weighs 65 pounds - and that really is my limit.
I experimented with several gadgets for loading the canoe but they were all too inconvenient.
I also wanted to use my boat for overnight camping trips. Around here shore-side campsites are few and far between. That would mean sleeping in the boat - and this canoe has a large ridge straight down the middle of the deck.
Well, why not build my own little powerboat? I started with a list of exactly what I wanted.
Well, why not build my own little powerboat? I started with a list of exactly what I wanted.
A hull I can pick up and carry by myself. I set a limit of 55 lbs. (I'm not getting younger)
Stable enough that I can stand up for casting or poling
A flat deck to allow sleeping on board
Quick and cheap to build
Durable enough to serve for a couple of years, but no need for heirloom quality
500 lb maximum capacity – suitable for carrying two big men on a fishing trip (or, God willing, Grandpa and grandchildren).
I was convinced that I wasn't the first person to desire such a boat. I began searching the web for suitable plans. This did not go as well as I had hoped. In plywood construction, the weight requirement would limit me to something unsuitably small. The other possibility was a skin-on-frame (SOF) boat. I could not find plans for an outboard powered SOF boat. All of the forums that I searched agreed that only electric motors were suitable (less vibration). I rejected that idea because the battery would weigh more than the boat. I didn't find any suitable plans-but instead found ideas.
||Glue it together
||Putty the gaps
||Ready to launch
Dave Lucas, a regular Duckworks contributor, makes kayaks out of foam and fiberglass; how much harder could it be to make a powerboat? I also discovered the foam box boats made by Dave Gray of Polysail fame.
Since all the cool guys are doing it - or have done it - I decided it was my turn to make a complete fool of myself. I'd design a boat made of cheap polystyrene foam. How hard could it be? I'm an experienced engineer who has designed many machine tools that weigh up to a half ton apiece. A 50 pound boat should be a breeze.
With keyboard in hand I began sketching ideas. I came up with some lovely, efficient designs. Fortunately, common sense took hold. A proof of concept vessel should require a minimum investment of time and money. Simplify, simplify!
The final design was a simple jon boat, loosely based on Bolger's Skimmer. It's formed from flat panels of 2 inch thick, 1.0 pound per cubic foot, expanded polystyrene. After careful calculation I decided I could increase the length to 10.5 feet and still bring it in under 50 pounds (plus paint). Actually, my calculations said that it would come in at 42 pounds but I added 20% for "stuff that comes up."
By this time I was quite enthusiastic about the project but, once again, my engineer's sense raised its ugly head. "Run some tests first," it said.
I looked up material properties and calculated the theoretical stresses within foam cored panels. I made sample panels using different foam densities and different weights of glass cloth. (I also made some 1/4" BCX plywood samples for comparison). Then I tested them to destruction. (Hint for materials testing: low-cost scales don't have an instantaneous "maximum weight" function. Use a camera or phone that allows video recording; then you have a record of the reading just before the loud "bang.") I only had a 50 pound digital fishing scale: the sample pieces had to be rather small. The results weren't completely conclusive (problems of scale) but they were encouraging. The foam panels exhibited strength similar to the plywood. As expected, they had much greater stiffness. (Google "stiffness vs strength" if you're unclear about the concept).
However, all of the foam test panels failed by buckling on the compression side. The foam didn't have the strength to fully support the 'glass skin. I questioned the wisdom of continuing the project; I would be sitting on the compression side! Only the onlookers would be amused if my boat folded up. I wouldn't even own the YouTube videos.
I mulled it over until I came up with a possible solution. I could prevent buckling by replacing part of the interior fiberglass with 2.7 mm lauan door skin. There goes my 8 pound "just in case" weight allowance. C'est la vie.
The building process was fairly simple. All the cuts were straight lines. The panels were glued together with PL Premium and "clamped" with old paving blocks and scrap 2x4s.
The most complex part was the transom. I designed it on the fly and made a mistake or two. The top six inches is a 3/4" foam core skinned with 1/4" plywood. There is plywood blocking in the center to take the force of the motor clamps. The lower section is the same two-inch foam as the rest of the hull. This assembly was glued together and then bonded to the sides and bottom of the hull.
The exterior, and part of the interior, were skinned with 6 oz. fiberglass cloth. The last step before launching was to cover the deck with the door skin. You read that right. I didn't sand or paint it until after the test launch! The fiberglass work was so rough that I cut myself more than once.
I've been recording the start and stop times whenever I work on the boat. These times include finding misplaced tools, making and fixing mistakes, setup, cleanup, and head scratching. To date I have put in less than 30 hours. This includes sanding the whole boat and all of the improvements I've made so far. It does not include shopping or final painting (I don't have time to let the paint dry!).
I expect the second prototype to take quite a bit less time, now that the designer has finally figured out the correct assembly procedure.
I bought all of the materials locally at Home Depot and Fiberglass Coatings, Inc. FGCI has a resin mixing plant and showroom less than two miles from my office. How lucky can a man be? My total cost was about $330. This includes consumables such as sandpaper, mixing cups, and roller covers. It also includes the paint that I haven't used yet. It doesn't include the materials I used for testing or the 7% sales tax.
The list of necessary tools is pretty short. Foam is easy to work with.
The boat, as launched, weighed 46.8 pounds. The fit and finish can charitably be described as "farm boat." I decided to name her "Toad." She's a friendly, useful little lass. It isn't her fault she's so rough and ugly.
Launch day was November 14, 2015. My eldest son and I drove a couple extra miles to Boca Ciega Bay because Toad wasn't registered yet. Lake Seminole Park has too many government officials hanging about. Yes, I know there's a 30-day grace period, but who needs the hassle?
The weather was pleasant and typical for this time of year. The NOAA said the wind was 7 knots, gusting 12. Moderate chop; about 6-9 inches in very confused seas. Plus powerboat wakes.
Toad performed nicely with the little Honda. I took her out alone for the first run. She appeared to be semi-planing at full throttle. With both Rich and me aboard, she handled the confused seas and powerboat wakes with aplomb. I needed about half throttle to reach hull speed. It turns out that square, flat-bottom Jon boats are more capable than I imagined.
I did manage to run her across an oyster-encrusted rock and crash into a mangrove tree; fortunately the damage was slight. I might need to add bottom runners or a skeg. Directional control in the wind was a little loose.
We only went a quarter-mile offshore, staying out of the main boat channels where the 30-40 footers were running on plane. I wasn't as comfortable as I might have been; I forgot to bring something to sit on (Toad has no seats. Too heavy). I also forgot my tiller extension.
It wasn't until I saw Rich's photo of Toad zooming past the launch point that I realized I had forgotten to cut the notch in the transom. She might work better with the prop all the way down in the water. Good thing it's an air- cooled motor.
Toad is now registered (but I haven't ordered the numbers). I've taken her out on Tampa Bay with my other son, Simon. We plowed through powerboat wakes up to 18". We also (deliberately) took them on the beam. "We're going surfing," said Simon. And we did-but didn't ship any water. Toad has been dragged across boat ramps and stumps and is holding up well. She never takes offense at the puzzled looks she gets.
Testing showed that a few modifications were in order. I've added anchor points for tie-down ropes. I put some rope handles on the inside to make carrying easier-four feet is an awkward width. Yes, I remembered to notch the transom. I may add a couple of pounds of reinforcement-for car topping. Currently I must load it transom-forward or it flexes too much at speed. Two areas are overbuilt; it could be slightly lighter.
I'm very pleased so far. Only time will tell how durable she is.
I have some ideas in mind that I have to test-different skin treatments. To that end I bought an inexpensive chain hoist and a 500 pound digital scale. Now I can test BIG samples. I believe I can make the design less expensive and/or more durable without increasing the weight.
The next level of performance testing will include a 5.5 hp Johnson 2-stroke (if I can find one, cheap). That should go fast enough to be interesting!
LOA 10' 6”
Beam 4' 0” (no flare)
Hull depth 17”
Draft maximum 4.1” (calculated)
Displacement: Maximum 620 lbs (U.S. Coast Guard Guidelines, COMDTPUB P16761.3B, smooth water)
As tested 510 to 570 lbs
Empty weight: 46.8 lbs (no paint)
Engine weight: 33 lbs (full fuel)
Passengers: 4 / 485 lbs (U.S.C.G. Guidelines)
Foam flotation: 840 lbs (to the gunwales)
Horsepower: Maximum 5.0 (U.S.C.G. Guidelines). As tested 2.3