Mini-Trawler Conversion -- Part 1

In terms of production volume and innovative design, fiberglass-based small boat construction probably reached its apex during the years before the oil crisis of the 1970s, when shortages and rising prices put a permanent crimp in demand. Fifty years later, the incredible stability and resistance to rot of fiberglass -- considered a big advantage over wood construction -- has become a huge problem [1]: How to get rid of unwanted, outdated fiberglass boats. Good old fiberglass boats now frequently show up on Craigslist for “free” -- just haul them away. Sounds like an opportunity to me, if -- and this is important -- if you choose the right boat.


Some years ago I acquired a 1960 Cutter runabout. It’s a classic fiberglass boat, 14 feet long, about 5 feet wide, and designed with those iconic tail fins so common in the 1950s and ‘60s. A boat this size was rated for a load of 1,200 pounds (four adults plus) and would typically be powered by a 40-hp outboard (www.fiberglassics.com/library/index.php?title=Cutter). In an earlier era, my Cutter runabout might have looked like this nicely restored beauty...

(photo: https://weberautogroup.com/Inventory/Details/1839)

Today, a ‘60 Cutter is so rare that, if it were restored to original condition, it could win a ribbon at a “classic” power boat show. But most of the original interior on my boat was missing. And after years of neglect, the metal parts that still remained were in bad shape and would need to be replaced; the original red gelcoat was mostly burned up; and the plywood in the transom was mush. But other than those issues -- and the trees growing out of the flotation chambers -- the hull was still in great shape! How can that be? The first generation of post-war fiberglass boats were constructed with hand-laid layers of mat and fiberglass, held together with polyester resins [2]. Although wood might be used, mainly for transoms, stringers, and hardware attachment points, compared to traditionally-built boats there was not much wood to rot or decay.

These boats have frequently been characterized as “overdesigned and overbuilt,” but their solid fiberglass hulls, built without cores, were stiff and strong. And since the equipment on board was fairly basic and the interiors tended to be rather spartan, they are not very heavy and are easy to trailer. As petroleum-based resins became more expensive, and production experience increased, boat manufacturers removed material where they could to save cost and weight, and began to use vulnerable wood cores more extensively. And as more accessories and fancier interiors were added, bigger (and heavier 4-cycle) motors were needed to push ever heavier boats. Now a full-size pick-up with a V-8 engine is necessary just to haul a bass boat.

Since I already have boats with sails, and a collection of good old outboards, I figured the solid Cutter bones could be reused to build a small motorboat with a cabin and a hard dodger, which would provide shade and some protection from the elements for overnight cruising. And since I have more time than money and far too much boat “stuff” that has accumulated over the years, building a little “trawler” from a solid, used hull -- for gunkholing around the Chesapeake Bay or cruising the Erie Canal -- would be an interesting challenge. And it would also be a low-cost way to experiment with materials and techniques that I might use for my next boat build project.

Hull Clean-up

My first task was to gut the Cutter’s interior, removing faded and broken seats and cable-pulley steering gear, and cleaning out accumulated debris from the cockpit. I cut open the flotation chambers, which doubled as seat supports, that were never sealed. The brown urea-formaldehyde foam used to fill those spaces was saturated with water -- you could squeeze it out of each handful of foam. There was also plenty of “organic debris” inside. This open-cell buoyancy foam was widely used for a couple of decades of fiberglass boat construction and is one of the biggest hazards of old fiberglass boats. And unless the flotation chambers have both a drain and a means to dry out the foam in the off-season, it will slowly saturate with water. The weight of the boat then increases year by year as the amount of water held in the foam increases. And, of course, the emergency buoyancy of the boat is severely compromised. While open-cell urea-formaldehyde foam, which was also used for house insulation, was eventually banned in the 1980s, nearly every boat built before that date is at risk, and the dryness of the buoyancy foam should be verified, not assumed. For newer boats, the polyurethane foam now used for positive flotation is closed-cell foam, and theoretically it does not absorb water (at least, not much). But you should still verify that the flotation chambers are not filled with water because there is a possibility that the foam could disguise a leak into the hull. Even though the mini-trawler’s closed cabin will add buoyancy, I will still look for opportunities to add more positive buoyancy. In addition to the two-part foams, many boat builders are now using closed-cell foam, commonly called XPS (expanded polystyrene) for hull cores, insulation, and providing positive buoyancy.

The transom was one place where the builders of the first generation of fiberglass boats continued to use wood to add strength. Typically a thick plywood stiffener was bonded to the molded fiberglass transom and tabbed to the sides of the hull. On the Cutter runabout, the plywood transom was not encapsulated in glass and the exposed wood had never been repainted. Exposure to weather, as well as dozens of holes though the transom to mount several different outboard motors over the years, had taken its toll and reduced most of the plywood in the transom to wet mush. Using a sawzall I removed the slop well and extracted anything organic, trying to salvage as much of the fiberglass transom laminate as possible. I hosed out the debris, removed all of the damaged trim pieces, and then cut off a few non-structural panels that were not going to be used, such as the dash panel.

To learn more about the history of the early years of fiberglass boats, you can read Dan Spurr’s article in Good Old Boat magazine (“The birth of fiberglass boatbuilding”, vol. 13 (July/August 2000), pg. 24) or his definitive book, “Heart of Glass” (International Marine, 2004). 

References

1. Eric Sponberg, “Recycling Dead Boats”, Professional Boat Boatbuilder, Aug/Sept 1999, Issue No. 60. Link: www.ericwsponberg.com/wp-content/uploads/recycling-dead-boats.pdf).

2. Jamil Mehdi, “Fiberglassic Guide to Boat Construction and Repair”. Link: www.fiberglassics.com/research-sp-59834616/80-fiberglass-history-part-one.html