How to Dry or Replace Waterlogged Boat Seat Cushion Foam

Unscrew the cushion from its base or hinge and take it somewhere you can work. Photograph the screw positions and any hinges or brackets first. On many seats the cushion, foam and a plywood base come off as one piece.

Zippered cushions are easy. Stapled seats need the staples pulled from the underside of the base, one at a time, with a staple remover or flat screwdriver and pliers. Pull staples rather than cutting the vinyl, so you can reuse the cover or use it as a pattern. Take photos of how the vinyl folds at the corners.

Squeeze the foam and look inside. Is the barrier film torn or missing? Is the foam wet all the way through, or just on one side? Does it spring back? Then check the plywood base: probe around the screw holes with an awl. Soft or dark wood is rotten and won't hold staples or screws (see folding seat hinges for rebuilding a base).

Don't just leave a soaked block of foam in the sun; it can take days and the sun degrades the foam. BoatUS describes a faster trick: put the foam in a heavy plastic contractor bag, push the hose of a wet/dry shop vac into the opening, duct-tape the bag closed around the hose and run the vac. It pulls a surprising amount of water out. You can also press water out by hand (don't wring or twist the foam; it tears).

After vacuuming, stand the foam on edge in a dry, shaded, airy spot, out of direct sun, and turn it now and then. It needs to be dry all the way to the center before you wrap it, or you'll seal the moisture and mold inside. Squeeze the middle: if it feels cool or damp, give it more time.

If the foam is only lightly spotted, you can sponge it with a mild cleaner, rinse, vacuum out and dry again. Strong mildew smell or black staining inside the foam usually means replace it. Clean the inside of the vinyl cover with a mild boat soap or a vinyl cleaner. BoatUS warns that bleach and high-alcohol cleaners attack vinyl and especially the stitching thread, so seams come apart.

Don't forget the storage space under the seat. A moldy cushion often sits over a damp locker full of damp gear. Mercury's tip for mold in storage compartments: empty it, open it up to air out, test a mix of 3 parts white vinegar to 2 parts distilled water on a hidden spot, then spray and scrub with a soft brush. Use a commercial mold remover only if stains remain, following its label. Clean the stored gear the same way, and let everything dry fully before you close the lid.

The Sailrite guide is clear that no foam is perfect outdoors; each has trade-offs:

• Antimicrobial marine polyurethane foam. Comfortable and the usual choice for upholstered seats. It still soaks up water, so it needs a barrier film and a water-resistant cover. Sailrite rates it at a few years outdoors.
• High-density upholstery foam. Lasts longer and feels better, but only if it's fully sealed: Sailrite suggests it for seats where the foam sits under marine vinyl stapled to a backer board, with no sewn seams on top for water to enter.
• Reticulated ("dry fast") foam. A very open foam with large pores, so water drains straight through instead of being held. It dries quickly, which is why it's used for cushions with mesh bottoms. The trade-offs: it's less durable (Sailrite calls it an occasional-use foam) and sunlight reaching it through mesh fabric breaks it down faster.
• Closed-cell foam. The bubbles are sealed, so it doesn't absorb water and it floats. It's very firm, which is a plus for cockpit cushions you step on. Practical Sailor recommends firm closed-cell foam for sailboat cockpit cushions and says open-cell cushions don't float and shouldn't be counted on in a man-overboard plan.

Use the old foam as your pattern if it kept its shape, or measure the base. Cut slightly larger than the base (a little oversize fills the cover tightly and looks better). An electric carving knife gives clean, square edges. Mark with a marker, keep the knife vertical, and let the blade do the work. Many upholstery suppliers will also cut foam to size if you send dimensions.

• For standard foam: wrap it in barrier film before it goes into the cover, folding the film like a gift and taping it. That's the layer that keeps rain out of the foam.
• For quick-drying cushions: use reticulated foam with no film, a breathable top and a mesh bottom so water runs out. The award-winning flybridge cushions Marine Fabricator featured were built exactly this way. Sailrite suggests wrapping quick-dry foam in polyester batting: it still drains, and it shields the foam from sunlight coming through mesh. If you use film to help slide quick-dry foam into the cover, take the film out afterward or the foam can't drain.
• Sealed vinyl cushions: vinyl doesn't breathe, so Sailrite fits a small vent grommet in film-wrapped vinyl cushions to let air escape when someone sits down.
• Drain holes: if the seat has a plywood base, drill a few small holes in it so water that does get in can drain, and seal the edges of each hole.

Put the wrapped foam back in the cover (Sailrite's trick for a tight cover: wrap the foam loosely in film, put a vacuum hose in the open end and suck the air out so the foam shrinks, slide it in, then let it expand), pull the vinyl tight, and staple it to the base starting in the middle of each side and working toward the corners, folding the corners the way your photos show. Use stainless or Monel staples so they don't rust through the vinyl. If the old cover is cracked, faded or splitting at the seams, this is the time to have a new one made (see the tips).

Screw the seat back onto the boat. From now on: cover the seats when the boat sits, and use a cover that breathes. BoatUS points out that non-breathable covers trap moisture and grow mildew. After washing the boat, leave flip-up bolsters and folding seats open until they're dry.