By Joran Gendell (ELIXIR)

Every time I sailed, the scraps of rubber that had been stuffed around the mast would fall out and the situation was getting worse and worse. At the Annapolis Boat Show, I admired the "Spar-Tite" system ( wherein a polyurethane "collar" is poured to chock the mast where it passes through the coachroof (See their web site for extensive instructions)

Diagram of Mast Chocking

Cheapo that I am, I couldn't bring myself to spend $100 for a pint or two of polyurethane rubber/plastic. I found a supplier on the web ( and spent $25.

I don't have pictures of the poured collar, but everything went per plan. I made a boot to make it look pretty and to keep UV off the plastic.

Mast Boot

In the rain, it doesn't leak whatsoever, but the real test will be my next nasty beat to weather.

First, get your mast where you want it: Check the rake, check the step, etc. Follow the Spar-Tite web site instructions to build the dam at the bottom of the mast opening. I used some old carpet padding for the foam layer (Yellow in attached illustration). Denser foam would have been better, perhaps pipe insulation. Ordinary modeling clay worked fine for the next layer (White in attached illustration). After the pour is cured, it will be hard to remove 100% of the clay, so consider this when selecting a color. Be thorough, this step is critical. Don't forget to Vaseline coat all fiberglass surfaces so that the mast can be pulled in the future.

Next, use a spirit level to check the deck flange (cabin top). Since the liquid polyurethane will seek it's own level, the deck flange must be level to achieve a uniform depth all around the mast. If you are in the water, shift temporary ballast fore/aft as required. I didn't think of this in advance and my collar is about " thicker (vertically) at one end, compared to the other. To help make a rain-tight installation, I wanted the polyurethane to actually "roll-over" the flange by 1/8 - 3/16". To do this, I built up a spacer layer using double-faced foam tape (Black in attached illustration). This was followed by the exterior dam, formed with wide masking tape (Gray in attached illustration).

From "Smooth-On", I chose "Smooth-Cast 45D". This has a Shore Hardness value of 45D, which is slightly softer than the polyurethane that Spar-Tite supplies. A Shore Hardness of 45D is comparable to the hard plastic used to mold the plugs and receptacles on the end of electrical extension cords.

"Smooth-On" does not specify this product to be UV resistant. I added black pigment to enhance UV resistance, but in the end I made a Sunbrella boot anyway. I could have skipped the pigment.

While looking at that receipt, I see that the product I ordered from "Smooth-On, Inc" was "Smooth-Cast 45D" in the pint size (which was more than enough).

Double-double check all dams and then mix and pour. I used about two-thirds of the two pint "Trial Size" kit. I poured on a cool day and it took over an hour to gel and a day to finish curing. Advertised pot life is only 5 minutes. There will be some very slight shrinkage.

Remove the masking tape, remove the foam tape, remove the foam, and remove the putty/clay.

The lip created by rolling the polyurethane over the deck flange serves another purpose. When I made the Sunbrella boot, I encased shock cord in the lower hem. This grips the flange under the lip. I put brass grommets in the boot where the bolt passes through the mast to secure the boom vang bail. The boot wraps around the mast and secures with Velcro. I made mine quite high just to hide badly scratched paint on the mast.

Admire your work!!.