USCG Guidance on Inspection, Repair, and Maintenance of Wooden Hulls (NVIC 7-95)
A Partial Wooden Hull Checklist
Check for fairness; for hard points where butt- blocks (mechanical connections between short planks) may have failed. How many butt blocks are there in the hull? Are there signs of rust on the exterior planking? Rust stains are usually indicative or iron or steel
fastenings which are to be avoided in a wooden hull. A boat constructed with iron or steel
fastenings will have a much shorter life than a copper or bronze fastened hull.
Is there evidence of hogging in a motor
cruiser’s hull; that is the centre appearing to be pushed up while the fore and aft ends droop down? Hogging is a possible pointer to light construction, advanced age, and/or deterioration in fastenings.
Hogging is not a good sign.
Timber will always move to some extent in response to changes in temperature and moisture content. This is one reason why wooden hulls tend to do poorly in hot climates.
Hull colour can accentuate this. A dark painted hull while it might look spectacular will attract the heat and depending upon the boats location may go so far as to destroy the hull.
Visible indications that the planks are moving may be due to the influence of tropical heat or it may be due to fatigue and fastening sickness. This can be an indication to the need for re-fastening.
If the hull leaks
, it can be important to know where.
The obvious starting point is the garboard plank (the first plank set into the rabbet joint into the keel/stem). In a wooden yacht the mast
is forcing the keel
down and the chainplates are pulling up, which has the effect over time of pulling the stem up from the keel
and opening up the garboard seam. This is usually why a traditional carvel built yacht may tend to leak when close hauled in a sea way.
A sure sign of owner ignorance is a (traditional construction) wooden yacht set up for racing
with a high tensioned rig. High rig tension will quickly destroy a traditional wooden yacht. If the boat has too much tension in the rig and it’s not yet leaking… give it time. It will leak!
The floor components of a wooden boat are transverse members holding both sides of the hull together (somewhat analogous to “joists” in a building). They can be constructed of heavy timber or constructed in metal.
Cast bronze floors are possibly the strongest and most durable solution, affording the most flexibility in the placement of the cabin sole
in relation to head-room. They are also far and away the most expensive solution.
Metal floors constructed from galvanized steel are absolutely to be avoided. The most obvious problem is rust and corrosion
of the metal and loss of strength in this vital area of the hull. Less obvious but possibly more insidious is the degradation of the timber around the floor fastenings caused by the galvanic action of dissimilar metals in a wet bilge
Yachts having galvanized floors need to have these members replaced. It’s a major job.
While in the area of boat floors check the limber holes. These allow bilge
water to move from high points in the centre of the bilge to the low point. Inadequate limber holes or limber holes that are blocked will cause problems.
Dry and wet rot
are the most common problems to be found on timber hulls.
, being a fungus that attacks lignum, needs moisture to grow. Take away the moisture and you eliminate most of the potential for rot to establish. Accordingly the biggest problems with a wooden hull are usually associated with the ingress of fresh water.
In your pre-survey inspection
of the hull, try to identify areas where leaks
are in evidence and follow the leaks, testing for mushy wood in any areas that look suspect.
Solid wood that has been properly dried (which eliminates much of the lumber
available today) is generally less prone to dry rot than is ply wood.
The worst kind of deck
, from the viewpoint of leaks, is a traditional sprung deck
, which is sad because nothing looks quite so good on a traditional boat as a beautifully bleached sprung timber deck. This form of deck construction is increasingly rare, being mainly found on classic boats of the pre-war era.
The most common deck is constructed from plywood
fastened over deck beams, and usually sealed with a light glass cloth or Dynel. Plywood
provided it is of first quality, marine
grade, will give satisfactory service
for many years, provided fresh water is kept out of the hull. Once dry rot takes hold in a ply deck, it tends to wick through the end grain quite quickly. Plywood cannot be resurrected form the dead once dry rot takes hold. The only solution is to remove the deck and start again. This is going to be an expensive yard job.
Frequently, a teak deck
will be laid upon a ply substrate. On the face of it, this solution offers the best of both worlds, combining the waterproof qualities of plywood with the look and aesthetic appeal of timber. The problem, however, is that when water ingress starts to rot the ply, the remedial solution becomes quite complex, and even more expensive.
Problems with leaks occurring, via stanchions, tend to be less prevalent on timber boats compared to GRP boats, probably because a timber boat typically offers greater deck rigidity, and less tendency to flex in that area under load.
Nevertheless, stanchions are a common source of deck leaks. As such, the areas beneath stanchions are more likely to be prone to dry rot.
leaks are difficult to eliminate on a timber boat, at least where chain plates are fastened inside the hull, thus penetrating the deck. Obviously long term ingress of water, in these areas, can cause rot. Often the presence of plank movement in the vicinity of the chain plate
can provide a clue.