Building a Comet/Part 2
By Dick Robertson

The Plans are in the Mail —

Jan 26, 2002

I just got an e-mail from Dick Harmon that my plans and specs are in the mail. It’s time to start thinking about a set of goals to strive for in building my Comet .Any builder would like to build the most beautiful and fastest boat ever. I’m no exception. Unfortunately I’m not a good enough builder to build the most beautiful boat or a good enough sailor to even know if the boat is fast.

There are some activities that seem to illustrate the lessons of life, either by contrast or similarity. To me boat building is one of these. By contrast neither chance nor divine intervention plays a part, what you get is a pure product of your own effort and skill. Like life however, it is subject to the only law of economics I remember from college — the law of diminishing returns. As any racing sailor knows, small increases in boat speed often require great expense in terms of practice, complexity, or cash. Building is the same, you have to decide on a threshold that once met, signals that additional effort is probably not worth it. Here is my straw man, in no particular order.

  1. Have the boat in the water in the May/June timeframe.
  2. Follow the specs closely enough so the boat can be officially a Comet.
  3. For ease of maintenance have a painted hull.
  4. For beauty, have a natural wood deck.
  5. Keep cost low (I’m on a fixed income)
  6. Use modern construction techniques (plywood/epoxy, glassed seams)
  7. Keep the rig as simple as possible
  8. Keep construction quality high enough that someone would buy the boat, if not for a racer at least for fun.
  9. Rig for single handed sailing
  10. Use wooden spars

This list may change or be prioritized as I get further along.

A few notes on different boat building materials (subjective to be sure).

  • Fiberglass

    • Relatively maintenance free

    • Well suited to mass production

    • Strong but heavy

    • Not bio degradable

    • Poor sound/temperature insulator

    • Good resale

  • Wood

    • Light

    • Beautiful

    • High maintenance

    • Requires high degree of skill to build

    • Good wood hard to find

    • Leaks

    • Wood bends in 3 dimensions

  • Plywood / epoxy

    • Many choices of wood available — from AC exterior at your local Home Depot/Lowe’s to exotic veneered marine plywood. Note — AC fir plywood uses the same glues as more expensive marine but may have more voids in the cores. Fir AC is also more difficult to finish since it is not smooth and it "checks" (top layer cracks) when exposed to the sun / weather even if painted.

    • Epoxy is an unpleasant material to work with

    • Must be painted or varnished (Epoxy requires UV protection)

    • Very strong, water tight and light hull

    • Lower skill level required

    • Easy to repair

    • Plywood bends in 2 dimensions

 

The Plans at Last —

Thursday, February 07, 2002

I’ve had the plans for a couple of weeks now.

Reviewing the plans, forming a list of questions and developing a building strategy is one of the best parts of building a boat, like solving a complex puzzle.

My initial impressions are:

  • I’m glad I picked a Comet. Remember I’ve only ever seen Comet # 1 and that for only for a few minutes. It was unrigged.

  • Its size is almost perfect for 4 x 8 sheets of plywood

  • There are many decisions to be made (e.g. cockpit size, rigging, rudder)

  • Double curve on the bottom will be a challenge for plywood.

  • How the hell did the original builders get a boltrope groove in a wooden mast?

Initial Questions: I’m also posting these to the Comet Messages so I can get some help.

    1. The cockpit size is variable within certain limits — Any suggestions or opinions? My guess is that the original small cockpit was so the boat would not flood when capsized.

    2. I live in a shallow bay so the shallow draft rudder looks good—Any experience with this?

    3. The specs suggest foam flotation. I’ve read on other class web sites that sailors are going to flotation bags (as used commonly in kayaks). What have people done on their wooden Comets?

    4. The rigging shows a 3 or 7/8 stay options. Opinions? I’m going to use a wooden mast/boom.

    5. The plans show the stays/shrouds running through the deck. This seems inordinately complex as well as making it difficult to remove the mast for trailering. What are your suggestions?

    6. Anything else I should know in way of tips / modifications from the original plans?

The First Steps —

I won’t bore you with the arcane details of boat building. There are many good books on the subject. Suffice it to say that that the trick is to translate a table of measurements (offsets) into a three dimensional object (the boat).

The first step in this process is called "lofting". Lofting seems to be approached with trepidation by tyro boat builders; I avoided it like the plague on my first couple of boats. It consists of drawing the boat full size on a flat surface and then using that drawing as a pattern for the pieces that will be used in constructing the boat. Much of the information that the builder needs is not specified in most boat plans and can be gotten only from the lofting process. Examples are the true shape of the transom, the angles where frames and sides meet, effects of the thickness of sides / deck / bottom, etc. This is especially critical when you need to diverge from the plans for any reason. For example, in my case the plans are for a conventional wooden boat and show 16 frames, twice as many as needed for a plywood boat. Lofting is also something of a Zen experience for those of you into such things. I used two 4x8 sheets of Luan plywood (9 bucks each at Lowe’s) painted flat white and drew the lines with colored magic markers; red for the side view, blue for the top view. The result was almost good enough to frame (bad boat building pun).

I also used Microsoft Excel to do all the frame size calculations so I could check my lofting work. At 40 dollars a sheet for even the cheapest marine plywood, mistakes are costly. Excel also allowed me to accurately calculate the radius of the deck and bottom for each frame.

The lofting also helped me to design the building jig, which holds the frames in correct alignment until the longitudinal bracing is in place, and the sides and bottom put on.

Making Chips

Making the first cut for the first real part of the boat is something of a milestone. I decided to build the stem piece first. No part of a boat better shows the difference between traditional boat building and building with plywood epoxy. In a traditional wooden boat the stem is a work of sculpture requiring good woodworking skills. In the Comet it requires rabbit that tapers in all three dimensions to be cut in a curved piece of wood about 18 inches long. This operation needs to be done by hand with a chisel and needs to be fairly precise since the ends of the boards that plank the sides are fastened there and leaks would result if the fit were not good. For my plywood boat, all I have to do is to make an appropriately curved piece of wood with chamfers on the front edge, which the plywood sides overlap. Any inaccuracies are automatically filled with the thickened epoxy adhesive. The result is very strong and forever watertight.

One last word before I go back out and finish the stem piece. Some of the cardinal rules of epoxy boat building:

    • Never permanently install a piece in the boat until it is completely finished, ready to paint or varnish.

    • Smooth all epoxy as much as possible while it is still wet.

    • Wear rubber gloves.

End of entry 2/8/2002 5:33 PM

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