How to Tell if Your Boat's Flotation Foam Is Waterlogged

Look at the boat on the water, empty and with the usual gear. Signs of heavy, wet foam:

• The waterline or bottom paint line is under water when it used to show.
• The boat lists to one side or sits stern-down more than before.
• Water reaches the scuppers or splash well more easily. Photos from previous seasons, or the same model at the dock, help you compare.

Waterlogged foam can add hundreds of pounds; water weighs a little over 8 pounds per gallon. Owners notice the boat is slower, harder to get on plane, uses more fuel or will not reach its old top speed with the same engine and prop. These signs have other causes too (see the loss-of-power guide), so treat them as clues, not proof.

Take the boat on its trailer across a certified truck scale, then weigh the trailer alone (or use the trailer's published weight). Compare the boat's weight with the builder's dry weight plus engine, battery, fuel and gear. A big difference you cannot explain points to water in the hull or foam. Ask the builder or a dealer for the original weight if it is not on a spec sheet.

With the boat on the trailer and the bow raised, pull the drain plug and see how much comes out. Water that keeps trickling out for hours or days after a rain, or comes out of rivet heads, screw holes or seams, suggests water trapped under the floor or in the foam. Note whether it smells of fuel; if it does, stop and see the fuel tank guide or a pro.

Walk the floor and press on the seats. Soft spots, a floor that flexes, screws that spin, or a squishing sound are warning signs. On fiberglass boats, tap the floor and sides with a small mallet and listen for dull, dead areas compared with crisp, solid ones.

Open inspection ports, seat hatches, the bilge and any storage under the floor. Look for foam that is dark, crumbly, swollen, or wet when pressed through a gap. Do not cut new holes just to look; every new hole is a new leak path.

A meter made for fiberglass can show wet areas in the floor and liner of a fiberglass boat. Readings are relative: compare suspect spots with areas you know are dry, such as the topsides above the waterline. Moisture meters do not read through aluminum, so on aluminum boats rely on the other signs. A marine surveyor has better tools and experience reading them.

Wet foam pressed against an aluminum hull keeps the metal damp, and that can lead to pitting and corrosion along the bottom, ribs and rivets, especially if salt water got in. Look for white powder, pitting or weeping rivets in the bilge and along the outside of the bottom (see the aluminum guides).

A boat that is getting heavier may simply be leaking: a missing drain plug, a cracked fitting, a loose rivet or a bad livewell or bilge hose. Fix and find those first (see the boat-taking-on-water and aluminum rivet guides). Foam can only stay wet if water keeps getting in or cannot drain out.

Foam trapped under a sealed floor has almost no way to dry. Leaving the boat in the sun with the plug out helps the bilge, not the foam. Some owners drill drain holes or leave the boat tilted for months with little change. Waterlogged foam usually has to be cut out and replaced.

Replacing foam generally means:

• Removing seats, consoles and often the whole floor or deck (on aluminum boats, drilling out rivets; on fiberglass boats, cutting the deck).
• Digging out the wet foam and drying and inspecting the hull, stringers and transom underneath.
• Fixing the cause of the water (leaks, drainage).
• Installing new marine-rated foam, either cut blocks or two-part pour foam, in the right amount and places so the boat floats level again.
• Rebuilding the floor and reinstalling everything. Shops often find rotten stringers or transom wood while they are in there (see the transom and stringer guide). Get a written estimate; on older small boats the cost can approach the value of the boat.

Write down what you found, with photos, and note it in BoatMend. Options are: get a surveyor or shop to confirm, budget for a restoration, or, if the boat is worth less than the repair, use it cautiously in calm water near shore with everyone in life jackets until you decide. If you are buying a used boat, a heavy, wet hull is a strong reason to walk away or to negotiate hard.