Build A Hard Dodger, Cabin Extension, Pilothouse - Getting Started With The Cabin Extension

As part of this project to convert an older Cal 25 as a dedicated (outboard only, no sailing gear) power boat, I wanted to build a cabin extension and then add a hard dodger as a separate piece to yield a completely weather tight living space and enclosed cockpit.

As background, the Cal 25 was made with a hard pop-top which provided a weather shield when lowered and standing headroom in the main saloon when raised.  As such, it really wasn't very practical since it offered no forward visibility when raised and made its use usually restricted to in-slip or on a mooring.

I wanted it to be long enough to go to the forward edge of the large cabin top opening and, since I was not going to ever use the mast on this boat, possibly go all the way to the aft edge of the hatch.  This would offer some additional cabin storage.  I wanted it to be wide enough to still allow easy access forward but some additional dry space along the sides as well.

I decided that about 62 inches long on deck and 48" wide would cover the opening and bring it back to about the forward cockpit bulkhead where it could be joined with a dodger/aft pilothouse structure.  The steering station would be mounted (tentatively) on this bulkhead.

Without the formality of making a CAD drawing of the boat and proposed structure (s), I decided to make this first section slope back from the front and slope in from the sides.  Along with ensuring drainage around (to be added later) fixed or opening windows, it avoided this enclosure simply being a big fiberglass box perched on the deck.

I made a quick test structure using 1/2" PVC structural foam, but judged that it would be too flimsy and hard to work with.  So, I layed out the dimensions and began to construct using 21mm Core Cell foam.  This was the new M80 Marine Grade and was a great choice. This thickness is just shy of 13/16" and would provide both the strength I needed and relatively light weight.

This foam was very nice to work and cut.  After drawing a line to represent the cut area, three or four passes with a razor knife was adequate for it to be snapped cleanly with no need for doing any cleanup to the edges.

To give me the required slope, I cut the foam for the front to 44" at the top and left 48" at the bottom.  This gave me a side with about a 7 degree from vertical slope.  Since the sides would only be about 20" tall, this amounted to an almost 1" per 1' cant in for the sides.  I cut the sides in from vertical 4" at the top which made the forward section lay back about 15 degrees.

Front is canted in 4" from vertical over the 20" height.  Sides are canted in 2" from vertical over the same height.

From the experience with the test panels, I decided to glass this foam and make construction boards to be assembled when all surfaces of the front and sides were rigid composite structures.

Using West System Epoxy, I layed up the Saertex stitched cloth which consisted of 3 layers:  One of CSM (chopped strand mat) and two layers of cloth.  This is a heavy material which weighs about 37 oz. per yard.  One well wetted layer of this on both sides yielded a very strong (and mostly board rigid) panel that was very light weight.

Since this was doing to be the permanent interior of the cabin top in the center, I decided to build "roof ribs" to add strength and allow wiring to be inserted.  A removable panel of headliner material will be secured to the flat underside of the ribs.

The Roof Ribs were made the inside width and then cut on the ends to match the slope of the sides.  With an overall height of 3 1/2" and height at the sides of 2" this gave a slope 3/4" per foot for adequate draining on the roof. The foam was encased in fiberglass cloth on three sides with the top section left open for attaching the roof panel with epoxy at a later step.

Construction was amazingly easy as the fiberglass "boards" were set up on a lofting jib on the top of a 4'x8' sheet of OSB.  I screwed cleats in four locations so that the sides could be supported.  This was necessary because the bottom width would be exactly the same width as the "table" making it very easy for the side to slip off while panels were being assembled.

The front was attached (without any epoxy) using 2 1/2" deck screws.  Each Roof Rib (note screw heads shown) was attached with West System 610 Epoxy.  This made the initial assembly very easy:  Each Roof Rib was laid on side side and the end got a heavy coating of 610 squeezed out with a caulking gun.  Once the epoxy was added, the rib was secured with one screw - to be removed after everything was dry and cured.

When the epoxy was cured from the attachment of the Roof Ribs, the front was attached using a thickened West System epoxy.