Stanchion bases serve as attachment points for jack lines and deck-stowed dinghy lashings, and even serve as makeshift cleats for spring lines, so they need to be up to the challenge.
A relatively long stanchion magnifies the crowbarlike side loads and focuses them onto the relatively small surface area of the base and the deck under it. An added topping plate as well as a backing plate, spreads the loads and thickens the skin on both sides of fragile core materials. Try the following "heavy-duty" approaches to installing reinforcing plates. It takes more time, but it is much stronger and more waterproof:
Measure And Cut Templates: Using the area of the stanchion base as a guideline, make the topping plate about 150 percent of that area. To better spread the loads imposed and avoid stress risers created by a direct overlap, make the backing plate twice as large as the stanchion base. Cut these patterns out of artist foam board about as thick as the planned reinforcing plates. Use the templates and a stanchion base to double check that there is enough room on deck and below to accommodate the size/shape of the new reinforcing material.
The Topping Plate: Either make or buy a sheet of 1/4- or 3/16-inch-thick fiberglass (FRP). A low-tech layup of mat and resin is acceptable because it is being used to resist crushing. A composite with high-tensile strength isnÕt required. Cut the sheet into the appropriate shapes using templates. Spending some time to shape the edges and fair, epoxy prime and even LPU-coat these plates. This is a good chance to handle these coating materials on a small-scale. Cover up and wear a mask and eye protection when grinding or working with resins/solvents.
Bond Topping Plates: I prefer FRP in lieu of metal or wood for reinforcing plates because you can epoxy them to the deck to create seamless joints that do not require bedding. In addition, FRP and epoxy is similar to the deck material, creating a bulletproof secondary bond between them. You can nicely finish the plates with sculpted edges. I prefer WEST SYSTEM resin thickened with 403 filler or Marintex for the bonding process.
Drill And Fit Backing Plate: After cutting and fitting both topping and backing plates, position the base. Drill appropriate holes, taking deck camber into consideration. Keep holes perpendicular to the surface.
A Trick To Beat The Leaks: Turn sealant into a gasketlike O-ring. First, slightly countersink the holes you drilled for the stanchion base fasteners. Follow John VigorÕs steps on applying sealant. Put a Lifesaver-size bead of sealant around each hole and install the base. After the compound has cured, and you finally tighten each nut, the compression squeezes the gasketlike sealant around the shank of each fastener.