Rot in a Wooden Hull — Signs, Teredo Worm, Termites and Where It Hides

By Wooden Yacht For Sale Editorial Desk

Rot in wooden hull signs: a dull thud under the hammer where sound timber rings, a spike sinking into soft wood, and trapped moisture behind leaking deck fittings, ceiling boards and the turn of the bilge. Teredo and gribble can attack unprotected planking within one warm-water season if antifouling fails. Look first, then haul out.

This guide is for your first viewing, before you commit to the cost of a survey. It will help you spot a boat worth walking away from. It cannot prove that a boat is free of rot, because rot usually starts where nobody can see.

How does the sounding test separate sound timber from rot?

Boatmere puts it simply: sound timber rings when tapped, and rot gives a dull sound. Surveyors use a soft-faced mallet or small hammer and work methodically, comparing each spot with the ones around it. You can do a small version during a viewing if the owner allows.

1. Ask permission, and use something that will not mark the finish.
2. Tap along a plank run, then frames and floors you can reach.
3. Listen for changes from one tap to the next rather than for any one absolute sound.
4. Mark doubtful spots and photograph them for the surveyor.
5. Press a fine spike only with consent, and only where it will do no harm.

A dull note does not diagnose rot by itself. IIMS links a dull sound or a bouncing plank to rot or corroded fastenings, and only further inspection will separate them.

Where does rot start?

Rot needs moisture and stale air. Cali Coast Marine Services names the usual places: around leaking deck fittings, behind ceiling boards, and in the bilge or at the turn of the bilge. Look for the water source as well as the damage, since the leak is what keeps it going.

Be wary of new paint in old places. A freshly painted bilge can be good housekeeping, or it can be a way to hide a problem. IIMS also warns that a sister frame added to a weak member can hide decay in the gap between the two.

What do teredo and gribble do in warm salt water?

These marine borers eat timber from the outside in. Cali Coast Marine Services says they can damage unprotected wood in warm salt water, even within a single season if bottom paint fails. That matters for any wooden hull lying in Indonesian waters.

They leave different evidence. NOAA's leaflet on marine borers describes shipworm larvae boring in through a pinhole, then tunnelling inside the timber, so a plank can look fine while it hollows out. The Maritime Archaeology Trust describes gribble cutting shallow, branching galleries just under the surface, usually more visible as erosion.

What to check at haul-out:

• Any area of failed or missing antifouling, including rudder, keel and deadwood.
• Small holes in clusters, particularly around scrapes and at plank seams.
• Planks that sound hollow although the paint looks fine.
• The date and product of the last bottom job, backed by a yard invoice.

A boat that has been ashore for days may show no live borers. That proves nothing about the timber, so search for exit holes and galleries instead.

Are termites a risk during shore storage?

Yes, in the tropics. Caribbean Compass documents termites attacking boats kept ashore there, and we found no equivalent data for Indonesia, so treat this as caution rather than a measured local risk. The USDA describes teak heartwood as very durable against termites, while sapwood is much less so.

If a boat has been laid up ashore or in a yard for a long time, widen your search. Look for frass, discarded wings, mud tubes and hollow timber in joinery, deck structure and stored spares, and ask how she was supported and covered. Ask your surveyor to record what was inspected and what could not be reached.

What should you look for in caulking, seams and garboards?

Seams tell a story about movement. Weeping along the same seam after repeated caulking can point to a loose fastening or a working structure, and not merely to tired caulking. Boatmere includes seams and deck joints in the survey scope.

The garboards deserve special attention. These are the planks next to the keel, and they carry both water pressure and loads from the keel joint. Ask to see them with the boat out of the water, along with the fastenings holding them.

Remember that dried-out hulls look worse. A hull left ashore in sun and wind will show open seams that may close again once it is back afloat. Timing matters when you read this sign.

What can a moisture meter tell you, and what can't it?

Very little by itself. Boatmere says an ordinary moisture meter is not enough to judge a timber hull, because hull timber can legitimately hold a high moisture content. A high reading is no proof of rot, and an acceptable one is no proof of health.

A meter is useful for comparing one area with another, or for tracking change, when used by someone who knows the boat's construction. If a report leans on meter readings without any sounding, spiking or opening up, ask for more work. Our wooden yacht survey checklist sets out what a complete scope includes.

When should a finding stop the deal?

Not every soft patch ends a purchase. A plank can be replaced. What should stop you, or at least pause you until you have a written repair scope and a price from a yard, is the following:

• Rot or wasting in the keel, floors, stem, sternpost or engine beds.
• Wasted keel bolts, or no record of them and no permission to check.
• A seller who refuses a haul-out, a sea trial or the opening of panels.
• Decay whose limits nobody can define until much of the boat is opened.
• Pressure to accept without a report, or to pay a deposit without escrow.

Boatmere treats refusals of haul-out and sea trial as warning signs. Keep the timber in mind when you decide, too: our note on teak, ulin and bitti explains why species alone will not protect a neglected boat. If you are comparing several boats, our used wooden yacht guide shows how to rank them on evidence.

What do buyers ask about rot and borers?

Plain answers to common first-viewing questions. None of them replaces a surveyor with experience of wooden hulls.

What does rot look like on a wooden boat?

It may not look like much. Soft or spongy timber, dark staining, flaking paint, weeping around fastenings and swollen plank edges are all clues, yet paint can hide it completely. Sound the area and test it with a spike before drawing any conclusion.

How can I detect rot in a wooden yacht without a survey?

You can find warning signs, but you cannot rule rot out. Tap planks and frames and listen, press suspect wood, and inspect around deck fittings, the bilge and behind any panel you are allowed to open. Then hire a surveyor before any acceptance.

Can teredo damage be seen from outside?

Often only small entry holes show, and galleries run inside the plank. A boat that has been ashore for some time may show no live borers, so look for holes and tunnels where paint has failed. Sound the planks during the haul-out too.

How do I check a wooden boat for termites?

Check timber that sits above the waterline or spent time ashore. Look for tunnelled wood and soft spots in joinery, deck structure and stored spares, and ask how long the boat was laid up. Sources on this are thin, so have your surveyor note what was examined.

Is some rot acceptable when buying?

Local rot that can be cut out and replaced may be a matter of price and scope, if the surveyor can define its limits. Rot at the keel, floors, stem, sternpost or engine beds, or findings no one can bound, should make you stop and take advice.

Which sources support this page?

Checked by the desk in October and November 2026. A source being listed does not mean the source agrees with us or has reviewed this page, and limited-verification items deserve a second look before you rely on them.

• Boatmere, Surveying a wooden hull
• IIMS, How to survey wooden boats
• Cali Coast Marine Services, wooden boat maintenance guide
• USDA Forest Products Laboratory, Tectona grandis
• NOAA Fishery Leaflet 505, marine borers
• Maritime Archaeology Trust, gribble
• Caribbean Compass, termites of the Caribbean

Written and checked by the Wooden Yacht For Sale Editorial Desk.

Where can I get help with a boat that shows these signs?

Send what you have found, with photographs, along with your buyer brief. Reach the desk on WhatsApp 6281139414563 or at bd@juaraholding.com.