Sailboat Keel Bolts and the Keel-Hull Joint: Signs of Trouble and What to Do

Find out from the owner's manual, the builder or an owners' association what keel your boat has (fin, bulb, wing, full or encapsulated), how many bolts it uses and what they are made of. Owners' groups often know about common keel problems on your model and sister ships. Write the bolt count and layout in BoatMend so you can check that every nut is accounted for.

Look along the keel-hull joint on both sides and at the front and back. A fine hairline crack in the bottom paint at the joint is common. Things to note and photograph:

• A "smile": a crack or gap at the front of the joint that curves like a smile. It often means the keel is flexing.
• A gap you can slide a thin plastic blade into, especially if it is wider than last season
• Rust stains weeping from the joint, which suggest water is reaching the bolts
• A joint that stays wet long after the rest of the bottom has dried
• Cracks in the hull itself, forward or behind the keel

Then step back. In its buyer's self-survey article, BoatUS suggests standing directly in line with the bow and the rudder and sighting along the keel from both sides: the rudder should line up perfectly with the keel. A keel or rudder that looks canted to one side can point to a bad repair, a hard grounding or a building defect.

SAIL Magazine points out that a separation can close up once the keel carries the boat's weight on the blocks, and Yachting World says gaps and movement are easier to see with the boat hanging in the slings. Ask the yard if you can look at the joint during the lift.

Look for gouges, flattened spots or missing chunks on the leading edge and the bottom of the keel, which tell you it has hit something. On iron keels, look for rust blisters. Note the location and size of any damage with a photo and a ruler in the frame.

Inside the boat, lift the floorboards over the keel and pump and sponge the bilge dry. You need a dry bilge to see new water coming in. Find every keel nut and backing plate. Some boats have the nuts covered with resin or filler; leave those caps alone unless a surveyor asks to see under them, but note any that look discolored or cracked.

With a bright light and a mirror, look at each bolt end:

• Heavy rust, flaking or crumbling bolt ends
• Rust stains or weeping around a nut or backing plate
• Backing plates that are bent, cracked or sinking into the fiberglass
• Cracked or crushed laminate under the plates (on cored or light hulls, the core can crush and let the nut loosen)
• More thread showing above a nut than last year, which can mean a bolt is slowly pulling out of the keel

Do not put a wrench on the nuts to "check if they're tight." Tightening a corroded or pulled bolt can hide a problem or make it worse, and SAIL warns against re-torquing bolts that show signs of water getting in.

The keel's load is spread through the hull by floors, frames or a molded "grid" bonded into the bottom. Look closely for:

• Cracks in the floors or grid, especially across the top or at the corners
• White stress lines or cracks in the paint or gelcoat inside the bilge
• Places where the grid has peeled away from the hull (a gap or a hollow sound when tapped)
• Cracks around the mast step, which often sits right above the keel

On many production boats the grid is hard to see. Do what you can safely reach and note the rest for a surveyor.

If the bilge fills with seawater over a few days or weeks and you cannot find another source (stuffing box, through-hulls, deck leaks, the water tank), the keel bolts or joint may be leaking. SAIL Magazine describes a simple check for when the boat is hauled: put some fresh water in the keel sump, stand a straight-sided jar of water in it, and mark both water levels. Over a day or two the jar only loses water to evaporation. If the sump level drops more than the jar, water is escaping into the joint or bolt holes, which means seawater can get in the same way when the boat is afloat.

Salty water in the bilge of a saltwater boat, with no other source found, is another strong hint. Report either finding to a surveyor.

BoatUS's accident investigator explains that when a deep fin keel hits something hard, the back of the keel tends to be shoved up into the hull while the front pulls down, which can damage the hull, the keel sump, the grid and even the mast step and rigging. Damage may not show on the outside. After any grounding beyond a light touch in soft mud:

• Check the bilge for new water immediately, and keep checking every hour on the way in.
• Lift the floorboards over the keel and look for cracked floors, grid bonds that have let go, and cracks around the bolts and mast step.
• Check the rudder, steering and engine mounts too.
• Watch the bilge closely for the next few days. Boats have sunk at the dock hours after what felt like a bump.

While you're still stuck, BoatUS's advice on getting a sailboat off a shoal includes a warning that matters here: spinning the boat hard to point back toward deep water can damage the rudder, especially a deep spade rudder. If keel bolts were loosened or the hull was holed and water is coming in fast, man the pumps and call for help right away.

Yachting World's insurance experts advise hauling the boat and inspecting it out of the water after any grounding, however minor, and say a diver's look is not a substitute. BoatUS's investigator says a sailboat that has taken more than a bump needs a professional inspection. Call your insurer early: many policies, including BoatUS's, cover a preventive haul-out and inspection after a grounding, and waiting can complicate a claim.

Depending on what they find, options may include:

• Monitoring only: a cosmetic hairline crack with no water, rust or structural damage
• Fairing and resealing the joint: cleaning out the gap and filling and sealing it, after the cause of movement is understood
• Re-torquing: only after the bolts and structure are judged sound, using the builder's spec and procedure
• Pulling a bolt for inspection, often possible on iron keels with through-bolts, or other non-destructive checks
• Dropping the keel to inspect, reseal and rebed it, or to repair the hull and grid
• New or "sister" bolts added beside old ones, or full bolt replacement

BoatUS's investigator notes that if the hull and sump around the joint are badly damaged or delaminated, the keel has to come off, but if there is no sign of damage in the keel bolt areas, dropping it is often unnecessary. Yachting World also advises not to draw the bolts and lower the keel without evidence of damage, corrosion or loosening. Practical Sailor describes keel-drop work as potentially dangerous and best done with a travel lift or crane.

Photograph the joint and every keel nut each haul-out, from the same angles. Note the date, the boat's condition and anything that changed. Store survey reports and repair invoices in BoatMend. Good records make the next survey faster, help your insurer, and add value when you sell.