Ericson 25, Companionway Hatch, Construction, S/V 10X

The Finished Hatch, Teak with Black Polysulfide Sealant, for S/V 10X
Terry Steller, an Ericson 25 owner from Michigan, recently sent me this article on the construction techniques he used to create a new hatch for his boat, 10X. His account is as follows:

The original companionway hatch on my Ericson 25 was shot, as are most, so it was necessary for me to create an entirely new one.  I used many conventional construction techniques to create my new teak hatch, but I also used many modern materials and methods in this construction. Below is an outline of the steps I took in the construction of this new hatch.
A Set of Sweeps of Varying Sizes, Stored in a Rack
Step 1: Discovering the Sweep of the Cabin Top of the Ericson 25

First, I scribed a cardboard template to get the shape of the cabin. I discovered it to be a #34 sweep (108+" radius).

For those who may be unfamiliar with the terminology associated with sweeps, I am providing the following background information:  Sweeps are used in automotive, aircraft, and other industries as a logistically easier way to draw large diameter circles. The numbering system is not arbitrary, but is relative to the rise at center of a 60" cord line through a circle. If you don't have access to a full-sized (60 inch) draftsman's sweep, you can point off points of a sweep at 2.5"increments using sweep charts available online.
The #34 Sweep, as seen from the Side
Step 2: Constructing the Form

I drew up and milled the form from urethane foam board, commonly called Renboard. I made the form slightly oversized, so that the laminated skins that I would create on this form would themselves be slightly oversized and thus capable of being trimmed down to size.
The Finished Hatch placed beside the Form for the Sake of Comparison
Step 3: Laminating the Skins out of Fiberglass Cloth and Epoxy

My plan was to use the form to create two separate epoxy skins. These skins would then be used to cover both the top side and the bottom side of 5/8 inch Kevlar honeycomb material.  These skins, together with the honeycomb material, would result in a ¾ inch structural core.

First, I created the top skin by laminating several layers of fiberglass cloth with epoxy. I allowed the epoxy to cure. Then, I removed this top skin from the form. Next, I turned to the creation of the bottom skin. For this I followed the same procedure – several layers of fiberglass cloth laminated with epoxy.
The Aramid Honeycomb Core
Step 4: Creating the Honeycomb Sandwich

The honeycomb sandwich is typical of the construction on some airplanes these days or an Americas Cup boat. For those applications, you are more likely to see carbon fiber and epoxy rather than glass cloth and epoxy used for the creation of the skins. At any rate, as far as the honeycomb sandwich that I created for my hatch, this is how I did it: After the two separate skins had fully cured, it was time to epoxy them to either side of the Kevlar Aramid honeycomb core. I placed the bottom skin on the form and then wetted it out again with epoxy. I then placed the honeycomb material on top of this bottom skin. Next, I wetted out the underside of the top skin with epoxy and placed it on top of the honeycomb. At this point, I had essentially created a honeycomb sandwich, with the top skin and bottom skin serving as pieces of bread, if you will. I then covered this sandwich with a vacuum-bagging film, and I vacuumed the whole thing down to the form.
The Honeycomb Sandwich with the Top and Bottom Skins Attached
Step 5: Laminating the Veneer to the Bottom Side of the Honeycomb Sandwich

After the honeycomb sandwich assembly had cured and I had removed it from the form, my next task was to laminate a veneer to the bottom side of the honeycomb sandwich. To accomplish this, I used spray adhesive to cover the form with plastic shopping bags. I then cut pieces of wood veneer and tapped them together. Next, I placed them on the plastic-bag covered form. Then I epoxy coated the bottom side of the sandwich. With this bottom side well-coated, I placed it on the veneer and then I vacuumed bagged it once again to press the veneer onto this still-oversized sandwich.
The Veneer, as Seen from Underside of Hatch
Step 6: Fitting the Honeycomb Sandwich to the Teak Hatch Frame

After I had laminated the veneer to the bottom side of the honeycomb sandwich, I cut the completed sandwich to size and fit to the hatch frame. Prior to permanently affixing the honeycomb sandwich to the frame, I filled all the edges of the honeycomb with an epoxy that had been mixed with microballoons to a consistency of paste. I allowed the edges of the honeycomb to fully cure. Then, I sanded all the edges.  At this point, the honeycomb sandwich was ready for assembly to the hatch frame. For this, I used G/flex and microballoon paste. 
Wedge-Shaped Block of West System G/flex with Nails and Screws
Here are the reasons why I used G/flex instead of other epoxy. West System has a promotional sheet showing the tolerance that this product has for screws and nails. You can drive screws and nails through it without cracking or shattering the epoxy. In my experience, if you tried this with other resins formulated specifically for laminating, you better have on your safety glasses. West System claims that G/flex has very good bond strength to teak and other "oily" woods.

Step 7: Bonding the Teak Slats to the Honeycomb Sandwich

On top of the honeycomb sandwich I bonded teak slats with West system G/flex for its resilience. Then, I vacuum bagged them, sealing the vacuum film to the hatch frame. I should note that I used 1/4" spacers to keep the slats from moving during the vacuum-bagging process.

Step 8: Paying the Seams with Black Polysulfide

The final step I made involved the paying of the seams with black polysulfide. I used Life-Caulk Two-Part Sealant. I waited three days before sanding, but now I know that I should have waited about two weeks to minimize shrinkage.

If anyone of you would like to have the foam sweep form, you may have it. It’s of no use to me
anymore. I'm sure you know that it could be used in many different ways to make a hatch.

Terry Steller

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