The Choice of Bottoms

by Sherwood Heggen

For the past seventy or eighty years, bottoms on the Chris Craft, Garwood, Hackercraft and similar runabouts and cruisers were built in a common fashion. Bottom framework ran athwartship fastened to stringers, keel, and chines. The inner planking was made up of 3/16″ thick boards of mahogany that were 3-6″ wide and fastened to the frame at a 45 degree angle to the keel. Some laid the inner planking raked forward, but most builders laid it raked back. Canvas was laid over the inner planking and painted in place. Outer planking of about twice the thickness if the inner planking was laid parallel to the keel and fastened with brass screws. All boards were fit with a little gap between each board. This allowed room for the boards to swell when they became soaked with water. The canvas was in place to provide a water barrier to keep the boat afloat while the bottom planking swelled. Once the boards swelled, the bottom became water tight. After a few years, the canvas would rot out and the water barrier was gone. Then, the boat owners would fill there boats with water in the spring before they put the boat in to get a head start on getting the planking to swell up to keep the water out. If the owner was lucky enough to have a lift, putting in was a simple matter of letting the boat sit in the lift for a day to let it swell without the fear of sinking.

Right off the assembly line, this was a pretty good bottom. It was relatively easy to manufacture, durable and was good for at least 10 years. Back in 1940, a 1930 boat was 10 years old and probably out of date or just in need of replacing. It was time to trade it in on a new model. There was not much concern then that the bottom was beginning to leak due to rotted canvas or broken brass screws causing loose planks. The problem went away when the boat was traded for the new one. If the problem was too severe, the boat may have been junked.

Today we are still running the boats from many decades ago with their original bottoms. That bottom may look good, but stories are told of good looking bottoms giving in to one too many jumps over a wake. Now the cost of retrieving the boat from the bottom of the lake is added to the expense of a new bottom. Is it smart to keep the bottom that was designed to last for ten years and risk the investment on the bright work and upholstery? Simple answer. No.

So now it is time to make a decision for replacing the bottom to provide security for that investment. Would you replace the bottom with the method used to provide a 10 year bottom. If you are a purist, you would say “absolutely” if the boat were to be used for an occasional show and in dry dock the rest of the time. Whether the boat is to be trailered or in the water all summer, there are some alternative methods you may want to consider for a new bottom. They have their pros and cons, but for the most part, what ever type of bottom you choose over the traditional, you will gain time before the bottom will need attention again.

There are two basic types of bottoms to replace the traditional. They are called either “hard” or “soft” bottoms. A “hard” bottom is just that. It starts with the typical framework, but the bottom boards can be of three layers of plywood strips glued together on a bias to each other or a layer of plywood with mahogany planking bonded together with epoxy with silicon bronze screws securing everything to the frames. Every square inch of wood, however, must be coated with epoxy, including the screw holes. The “soft” bottom is similar, but there is no epoxy used to bond parts together or coat all surfaces. Instead modern caulking adhesives with brand names of 3M 5200 or Sikaflex bond parts together allowing more flexible construction. An inner planking of 3/16″ plywood is laid in a bed of caulking adhesive. Planking, laid in the traditional style, is bedded in adhesive caulking. Silicon bronze screws hold everything together.

The advantages/disadvantages of these two methods are arguable by the two camps that support each method. The choice for one or the other appears to be a flip of the coin. They both work, but a choice of what pros are to be supported and what cons can be tolerated must be made.

Hard Bottom

Pros – Hard bottoms

  • No need to soak bottom before boat is placed in the water.
  • It is always water tight.
  • With each plank encapsulated with epoxy, the boat will not gain water weight from the planks absorbing water all summer long.
  • Parts can be fit tight for a strong structure with little flex.

Cons – Hard bottoms

  • Scratches and dings need immediate mending to keep water from swelling the wood under the epoxy.
  • Epoxy encapsulation is expensive. w It takes a lot of epoxy to cover all 6 sides of every piece.
  • The cost of quality plywood used for laminating the bottom can get expensive.
  • Working with epoxy is a really messy job.
  • Some say the boat rides a lot harder because the bottom can not flex.
  • Damaged parts are not easily removed without special equipment.

Soft Bottoms

Pros – Soft bottoms

  • Only mating surfaces need to have a bedding of adhesive; not all six sides as with epoxy.
  • Bottom can naturally flex and move without sacrificing longevity
  • Some say the boat rides a lot softer because the bottom can flex much more like the traditional bottom.
  • Scratches and dings are not a major concern because the bottom is allowed to absorb moisture.

Cons – Soft bottoms

  • The adhesive is tacky as all get-out. Don’t be surprised if you end up with it in your hair, your pockets, all over your tools and clothes. It is messy stuff!
  • Like epoxy, it is also expensive, but somewhat less so than epoxy.
  • Damaged parts are not easily removed without special equipment.

There must be other pros and cons, but these are the obvious ones. You would have to make a decision on which one you want.

There is one more method that is a mix of the above two methods if you can’t decide on one or the other. Prior to assembling any parts, each pre-fit piece is coated with a couple of coats of penetrating epoxy. This seals the wood to keep water from saturating the wood. Assembly is done with planks bedded in caulking adhesive. This allows the boat to flex more to allow the more traditional “soft” ride. The world is full of choices and it doesn’t stop with boat restoration. This hopefully will get you thinking of how best to preserve your woodie.

O.K. – what do we keep in mind when we own one of these old wooden boats?

All together now…….. Don’t destroy it; restore it!