Ben Sutcliffe-Davies talks through why it is important to both think about and take good care of your keel fastenings

Checking keel fastenings: what to look for

Since the very first fitting of an external keel to a yacht, there have always been risks of failure and in-depth discussions surround what material should be used or how they should be attached.

There are a selection of materials that can be used for fastenings but care has to be excised with the choices made.

I think the first yacht I was involved with was as an apprentice at Whisstock Boatyard, where the surveyor had noticed some weeping along the seam of where the iron keel casting was fitted up to the wooden keelson.

Corrosion streaks were also obvious.

Upon torque testing, it was became clear that the forward keel bolt was slack, so it was pulled.

On removal, we discovered the iron had some seriously wasted sections.

A stainless stud in lead with very obvious crevice corrosion

A stainless stud in lead with very obvious crevice corrosion

It was during this early experience that I first understood how the reactions of iron through oak can cause the iron to be wasted from tannic acid.

While apprenticing, one of the yachts we built used silicon bronze bolts.

I recall they were quite expensive but to my knowledge are still going strong 40 years on.

As with so many things, cost has forced the way craft are put together over the years.

Likewise, when out surveying some of our old classic GRP yacht designs from the 1970s and 1980s some of the builders used iron studs and flow coated the fastenings with gelcoat.

These never caused much of an issue other than some high corrosion to the nuts and washers if exposed to wet bilges over a long period of time, or with some movement or failure of the gelcoat coating.

 A keel bolt and nut displaying stud corrosion

A keel bolt and nut displaying stud corrosion

While most yachts are no longer built from wood, the lesson of what happens with materials in areas that are encapsulated like this are lessons I’ve never forgotten.

With the majority of the modern production yachts these days, the keels are either fitted with studs or bolts that are wound down into the casting using stainless steel.

These, just like iron fittings, are perfectly acceptable as long as moisture can be excluded from the fastenings.

It’s a well- known fact that crevice corrosion happens to stainless steel when oxygen cannot be replenished.

Over the years I’ve seen some spectacular failures in stainless steel fastenings when used under water.

What to look for when examining your keel fastenings

  1. Familiarise yourself with where the fastenings are located. Often there are fastenings aligned with the main areas of the casting, but frequently there will be
    a smaller fastening forward and aft.
  2. Is there any evidence of weeping around the fastenings or under the plate washers? If you have a clean set of bilges and there are areas of tea staining developing from under the fastening washers then there may be an issue. Using a camera to take photos and then magnify them is a very useful way to see problems up close and in detail.
  3. This takes a little time to get used to, but with practice, lightly tapping the tops of the fastenings with a small hammer will reveal issues. Any dull notes may indicate a fastening that isn’t under the same tension.
  4. Are there any reasons for the keel to have loosened? All too often I discover that the craft had a light grounding, then find increasing evidence that the bonding to the framework, bulkhead mastic seams or the GRP internal matrix frame has been overloaded and broken out. If any of these have occurred then it’s time to get her out of the water and talk to your insurance company and a qualified surveyor.
  5. With the craft held in lift strops, check if there are any openings in the hull-to-keel joint that could allow water into any fastenings. Likewise, if you apply some pumping action to the foot
    of her keel does it move or flex the hull? I’ve recorded on a couple of examples of this on my YouTube channel that help illustrate this.
  6. If there is flex, have it professionally checked out. Some cases of keel flexing can indicate the hull softening up as well. In most cases there is only one prudent line of action – replace the fastenings, check the plate washers haven’t been bent, and refit the keel with a new mastic joint. This may seem a bit over the top but having seen so many keel stud failures over the years, to me, for the sake of a few hundred pounds worth of nuts and bolts and the cost of removal and refit, I find it a strange argument to have against the value of life and possession.

Grounding checks for keel fastenings

A yacht grounded. Always check your keel fastenings after a grounding

If there is damage, it is prudent to remove the keel.

Although it is important to check keel fittings over time for signs of stress, for many, the most obvious moment to do so is following one of biggest stress points on keel fastenings (and skippers) during a yacht grounding.

These come in two forms. One is the regular expected grounding and refloating of a boat left on a drying mooring, and the other is a sudden, unexpected grounding.

If you do accidentally find the seabed, there are several things you must do as soon as possible to see whether there has been any significant damage.

It goes without saying that you should have your boat lifted and inspected after any significant grounding.

Sand in particular is extremely hard, and mud can create suction which, should tide or wind conditions cause any twisting motion, can hold tight enough to bend the trailing edge of a lead keel.

With cast iron keels, the impact is not absorbed as efficiently through the keel.

Check for signs of stress crazing around the gelcoat where the keel joins the hull.

Trouble spots at the front and rear of the keel are easiest to find.

On removal of the gelcoat, you’ll find the hull’s reinforcement material is compromised. Due to the nature of gelcoat, hairline cracks take time to become visible to the eye, so periodic checks are vital.

Continues below…

If damage has been found, it is prudent to remove the keel.

With bilge-keelers, even if there is no damage internally, repeated intentional groundings can cause the keels to splay apart, bending the studs.

This sort of damage needs to be assessed out of the water, and should be checked on an annual basis at least.

Lots of boats built in the 1970s and 1980s have encapsulated ballast, where the keel is part of the hull moulding.

The GRP fin contains steel punchings (the pellet of steel that is left after punching out the centre of a washer) and no bolts or studs.

I’ve found these to be very strong and you only need to ensure the GRP casing is not compromised, leaving the punchings open to potential rusting.

After any grounding, remove the sole boards above the keel.

Check keel fastenings

Check if there are any openings in the hull-to-keel joint that could allow water in. Credit: Graham Snook/Yachting Monthly

This may require careful work with a screwdriver, but once the boards are up, check the whole area for stress cracks and any detachment of items bonded in.

On fin-keeled boats built since the mid-1980s, which are more likely to have a hollow-core matrix bonded in to provide support, it’s important to check right back under the engine bed.

If the boat was being sailed with full canvas off the wind when she ran aground, the mast, rig and deck moulding will have been subjected to an enormous load.

On deck-stepped craft, look carefully for crazing in the GRP at the base of the mast step and around the rig’s deck fastenings (either chainplates or D-bolts).

A compression post will also be subject to a heavy load and can become detached. Check at its base and around the underside of the deck, under the headlining.

Bulkheads add rigidity to a hull but can also cause damage in a grounding.

If the bulkhead has been bonded in tightly, it can produce a line of stress on both sides of the craft.

On some boats, this has been known to spread up the side of the hull and across the deck moulding too.

Bulkheads can also become detached.

Most grounding force seems to push the back end of the keel casting upwards, which on traditionally laid-out craft is in line with the chart table and galley.


Ben Sutcliffe- Davies has been in the marine industry for over 40 years as a long- time boat builder, has been surveying craft for over 20 years and is a Full Member of the YDSA.

Look in lockers, cupboards and under the chart table for detachment.

On boats built before the mid-1980s, check for detachment of the floors, where they are bonded into the hull.

I once found a Rival 34 where the floors had completely detached, allowing the hull to twist.

Rudder pintles of transom-hung rudders can become stretched or bent and fittings pulled right through the transom.

However, a less obvious scenario is when they have just been weakened. Again, look for gelcoat crazing around the fittings.

If the rudder stock is housed within a tube, thoroughly check the bonding of the tube into the hull and the gland or method of sealing.

Many new production craft use lip seals.

Normally, lip seals are reliable, but if the rudder blade is forced upwards they can become dislodged and then leak when the stock is turned.