Small Boat Flotation and Howard Hughes' Flying Boat

Some boats, like Boston Whaler skiffs and MacGregor powersailers, are built with flotation foam between the inner and outer laminations. Roger MacGregor was quite willing to flood any of his boats just to prove that they would not sink and would keep you safe, even though they were water-ballasted. And if you check out his old sales videos on YouTube, he even did it a few times. 

When the boat is not built with integral flotation, you might have to really look for it. For example, the “built-in” flotation on a stock Potter 15 consists of three parts. The easiest-to-see, assuming it's still there, will be two large blocks of styrofoam, one located beneath each of the cockpit seats. They keep the aft end of the boat afloat in the event of cockpit and cabin flooding. Each block provides about 3 cubic feet (1 foot x 1 foot x 3 feet long) or 192 pounds (3 cu-ft x 64 pounds of seawater per cubic foot) of flotation. Since the empty weight of a Potter 15 is about 500 pounds, the foam blocks in the stern are not enough to keep the boat afloat if it floods. 

The rest of the flotation is much harder to find -- because it is underneath the cabin floor. On the forward end of the boat there is a bulkhead that crosses the hull under the mast support. If you open up the cabin floor panels and look forward, you will see it. Foam fills the space ahead of this bulkhead to support the cabin floor and to keep the forward end of the boat from sinking. Unfortunately, without removing the floor or cutting an inspection port, there is no easy way to inspect the forward flotation. Fortunately, Potter's builder did provide a way for any water that gets into the boat to drain back to the cabin, where you can get at it. I estimate the volume of under-floor foam is 6 to 8 cubic feet, or 300 to 400 pounds of flotation. 

Add the three parts together and you come up with 700 to 800 pounds of built-in foam flotation. This is enough to keep even a loaded Potter from sinking, and there are old sales photos showing a young woman standing in a scuttled Potter full of holes in the hull. If you find that photo, note that there are no waves, it is nice calm water. Sufficient flotation is necessary, but not sufficient to keep you safe. Placement of the flotation -- where it is located -- is the other aspect that needs to be addressed. How many runabouts have we seen where the occupants end up clinging to a capsized hull? Because most of the flotation is under the floor, a big enough wave could roll a flooded hull and it will "turtle" -- the flotation in the floor now up high. So, the best flotation is up high -- near the gunnels -- to reduce the tendency to roll over. Since much of the flotation of a Potter (and many other small sailboats) is also low in the hull, they have the same predilection to turtle when flooded, especially if the centerboard is not locked down or is lost, and the mast fills with water. Steve Potter described capsizing his Potter 15, and explains why it happened (“Capsize at Clipper Cove,” Small Craft Advisor, No. 56, March/April 2009, page 22). His experience is applicable to a lot of production and home-brew small craft.

If you find that the styrofoam blocks in your Potter (or other boat) are still under the cockpit seats, be aware that they can work themselves loose, which is not a good situation. And if they got loose before you bought the boat, they might even be gone. Some Potters have been "customized" with hatches cut into the seats, and the foam was removed to increase storage for anchors or fenders. Yikes! Hope the hatch covers stay secured. So it is important to make sure that enough flotation is still in the boat, and that it is secure and not rattling around. If the blocks are loose, then you can try to re-secure them using a good polyurethane construction adhesive such as PL Premium (test to make sure that it doesn't dissolve the foam). If necessary, fabricate a suitable “wedge” (using polystyrene foam sheet) to force the foam block up against the bottom of the cockpit seat. 

If the styrofoam blocks are saturated with water (it's an "open cell" foam) or if they are missing, you might want to replace them. Extruded polystyrene foam sheet, which is closed-cell and won't absorb water, is available up to 2 inches thick. The 2-foot wide sheets are especially useful and each piece, 2.8 cubic feet of foam, is good for about 170 pounds of buoyancy. Build up a “block” and secure it using PL Premium adhesive. It is also possible to add even more flotation by sticking polystyrene foam to the bottom of the underside deck surfaces. And if you are planning some cool weather sailing, more foam can be used to line the inside of the cabin walls. In the Potter, it is possible to insert additional sheet foam between the cockpit seat back and the hull -- the best place for more flotation.

An option to sheet foam is to add flotation or buoyancy bags, which have become common on small boats, kayaks, and canoes (e.g., www.nrs.com/category/3049/kayak-touring/float-bags). In addition to adding buoyancy, these devices also reduce the amount of water that might fill the cabin or compartment. Buoyancy bags are not cheap, and the selection seems fairly limited -- there's just not that much demand. In contrast, dry bags, used for rafting and camping, are readily available from many sources and come in volumes of up to around 90 liters (seatosummitusa.com/collections/outdoor-gear-dry-bags/products/ultra-sil-pack-liner). And the prices are very reasonable. To replace a Potter 15's styrofoam block (displacing 3 cubic feet) you would need a flotation bag with a volume of at least 85 liters (1 cubic foot is equal to 28.3 liters), and a quality dry bag would run about $50. You can fill them with inflated play balls or beach balls -- they are very cheap (find them on sale in the spring), tough, and can be inflated using any pump with a needle. If you are old enough to remember Howard Hughes, you might have heard of his gigantic flying boat, the "Spruce Goose," so called because it was built toward the end of WWII using laminated plywood -- steel and aluminum was in short supply due to the war effort. 

After it's single test flight in 1947 -- for about a mile at a maximum altitude that was under a 100 feet -- the plane was stored in an air-conditioned hangar Long Beach, CA until 1993. It's now at the Evergreen Museum (www.evergreenmuseum.org/the-spruce-goose). Hughes had already survived several airplane crashes during test flights of his planes. So he filled the plane's cargo compartments with beach balls secured with nets to provide removable positive flotation -- just in case.

Unlike the "Spruce Goose," the most effective position for these flotation bags in small boats is probably at the level where the flooded boat will settle, around the gunnels. And they should also be secured so that they'll stay put in a capsize (unlike in the above photo).

How about attaching flotation to the outer gunnels of a trailer-sailer, like on the hard-bottom RIBs? A string of fenders can add a lot of flotation, but they are expensive. A 22-inch fender gives about 1/2 cubic foot of buoyancy and costs around $30, although you can frequently find them on sale. And if you can figure out how to lash it to your gunnels, Duckworks sells a 9 x 60-inch beach roller ($70) that can double up by providing about 2 cubic-feet of additional flotation (duckworks.com/beach-rollers/). Wakeboats use "ballast bags" that are rated by pounds of water. A 375-pound bag has dimensions of 14 x 65 inches, or 6 cubic-feet, for $100 (www.evo.com/fat-sacks/straight-line-big-bag-375-ballast). That's a lot of flotation if it is pumped up with air instead of water. Two 350-pound ballast bags (5 cubic-feet per bag, $135, at www.wakemakers.com/launch-pad-350-twins.html) would make ideal replacements for the styrofoam blocks in the Potter's stern.

For lots of reasons it's important to load the boat so that the heaviest items, such as water bottles, anchors, and chain rodes, are secured as low as possible, ideally between the cabin floor and the hull bottom. In addition, it is useful to store lighter items, such as clothes and sleeping bags, in sealed “dry bags” that are secured as far forward and as close to the deck as possible. This puts flotation up high and, together with a couple of flotation bags up high under the cockpit seats, should help keep the boat from turtling if it is flooded. If heavy weather is expected, right-side-up buoyancy can be further enhanced by securing dock bumpers to the gunwales using the deck cleats and railings.

And it’s worth repeating the obvious: the Potter -- and any small cabin boat -- has it's maximum amount of flotation in its cabin. If the cabin hatch boards are in place and the sliding hatch is closed during a knockdown, much of the green water will be kept out of the cabin, the boat will stay afloat, and it cannot turtle. Water inside the cockpit should drain out (make sure the plug is out, or is easy to pull out). I sail my Potter with the hatch boards in but the sliding hatch open, for ventilation and so that I can get to stuff in the cabin, and the odds are still excellent that a knockdown will not cause cabin flooding. And whenever the wind pipes up, the best insurance is to "batten down the hatches" and I close up the cabin.

The Potter 15, like many small boats, has a hollow aluminum mast and boom, which can help resist the tendency of the boat to capsize if it fills with water if the ends of the mast (and boom) are plugged. The spars don’t have to be “watertight,” even a wad of soft foam is better than nothing. If the mast is plugged it may slowly fill with water from all the little holes at the fittings, but until it does you have about a half cubic foot of buoyancy (30 pounds, or more than an typical inshore life vest), which should help keep the mast up off the bottom. If you sail where “turtling” into mud is a distinct possibility, then adding a masthead float (a la Hobie cat) might actually be the best solution, at the cost of windage and weight at the top of the mast.

In Roger MacGregor's sales video for the powersailer, was the ballast tank flooded, or empty Answer: flooded.