What’s really going on under your deck fittings? Ben Sutcliffe-Davies investigates the hidden weaknesses

When was the last time you checked your deck fittings?

Look on any sailing forum and often there are owners posting issues they have discovered with their cherished yacht.

The majority of the issues are quite common and get spotted at a pre-purchase survey. When it comes to a yacht’s decks and deck fittings, though, any assessment of the deck core is almost always an inspection from the working deck side.

water ingress on a yacht

Water ingress can turn sub-deck structures into a crumbling mess over time

This is because the underside of most working decks cannot be seen thanks to fitted cabin linings or nice cabinets. That’s before we even start to consider fully fitted lockers and side deck voids behind the bunks.

The majority of boat builders for the last 40 years, the likes of Westerly, Moody and Sadler, normally fitted ply blocks in the areas where deck fittings are required and continued with normal balsa core in the non-load carrying areas of decks. This has worked, to a point, but as fittings age and get overloaded, these deck fastenings can start to allow moisture into the sub-deck structures.

Crevice corrosion

Crevice corrosion can cause whole fittings to come away when pulled

With some types of craft, moisture ingress through deck fittings is more of an inconvenience, but for a yacht that has a balsa core to provide the required reinforcement to support you and me lumping around on deck, (trust me on this one – there are a lot out there) it’s much more serious.

Deck fittings

If left untended, cleats and winches could rip away as their fastenings fail

The method of using balsa core isn’t all that detrimental to internal strength, but as soon as someone decides to fit a few extra lines back from the mast to the cockpit or extra spring cleats mid-ships, for example, out comes the drill, holes are made and fastenings fitted.

Roll on a few years and loadings cause some movement and then the core that wasn’t removed and is still a balsa sandwich between the deck and cabin surfaces will start to absorb lots of moisture. Within a few years it’s turned into papier-mâché. All too often it only gets found out when the deck starts the familiar flexing.

Other issues

Before you start to think plywood is any better, let me let you down gently. Generally the plywood used will be marine ply (1088). Over the years I’ve had similar issues with high moisture building up in plywood that’s been used to back deck winches, cleats, genoa tracks and mast steps.

It doesn’t lead to such rapid failure as balsa but an issue with either can be serious if preventative attempts aren’t regularly made to check things out.

Recently I worked on something that was a real surprise to me, where the stanchion bases had the common loops provided to secure life lines. I found one stainless steel loop to be loose – a little wiggle and the whole tting came off in my hand!

Both stainless steel fastenings had completely dissolved with the infamous crevice corrosion, water had found its way in around the fastenings from lack of sealant, and the rest, as they say, is history. (That one is on my YouTube channel too.)

deck fittings

A good-quality sealant is essential when screwing in deck fittings


So, how do we prevent this happening and what do we do to assess the decks? If you are fitting anything through the deck that takes a load, it’s prudent to remove an area of the deck core and replace it with a well-saturated, epoxy- coated plywood packer.

The fastenings require the use of a good sealant and it’s very important to seal the core hole you create for the fastenings. Use good-size backing washers as well. It may sound strange but some craft I’ve surveyed with a balsa core have frequently shown things like boat hook clips, spinnaker snubbers, anchor chocks and wiring plugs around the mast just screwed in without any mastic applied.

In days gone by, my dad loved the old semastic sealant; it came in a container not dissimilar to a toothpaste tube with a massive key to help roll the tube up.

It never really went off, and did a fabulous job of sealing two surfaces while allowing a bit of movement.

Deck fittings

A failed compression pad is evidenced by the damp decking surrounding it

Useful kit

One key piece of useful kit, especially if you cannot visually check moisture levels, is a moisture meter to help locate and identify if there is any moisture ingress from deck fittings and fastenings.

I often use a moisture meter on the underside of cabin linings and around a plywood tout where deck fastenings are located. Sadly, sometimes you can identify that every screw used for the spray hood hooks and blocks is leaking!

Another wonderful bit of kit I use is a thermal imaging camera, as this shows damp very quickly too. I know they’re expensive but they have come down loads from when I had my first unit.

Continues below…

To me they’re worth every penny; if you are a serious cruiser, the thermal imaging camera is also great for checking the engine is running at the right temperature, plus it’s useful at night and in the fog, too.


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.

In an issue of YM some years ago I did demonstrate that if you take a photo with your phone’s camera with the flash on, very often the flash will expose damp and discolouration to the wood finish under the lacquer that wouldn’t have been so obvious when viewed with the naked eye.

Lastly I should stress how important a preventative measure maintaining the integrity of your deck fittings is.

Apart from the issues with the core, get any amount of damp into the decks and when we do have a seriously cold winter you will need some very deep pockets full of coins to put them right.

The basic checks for looking over your deck fittings

Problems every buyer or owner needs to look out for

1 Check pullpit and pushpit feet for any movement. Any wobbles here are usually a sure sign of problems.

2 Check stanchion bases – again various types, but many have the odd crafty screw or bolt that gets too much loading and then allows moisture ingress into the deck sub-structure.

3 Thoroughly check around the baby stay and lifeline harness points on deck

Deck fittings

This balsa core had lots of small screws to fix the teak deck down resulting in this rotting

4 Look at the mast step itself; how is it supported, what is it sat on and how well are the deck sockets sealed around the area of the mast shoe? Is there any downward compression around the mast step developing? Any pooling of water is a serious clue.

5 If you have teak decks fitted it is worth considering or finding out how they’re secured. Recently, I had a 15-year-old production craft that has had terrible issues with the small set screws leaking into the balsa core; the whole deck is a write-off now.

6 Always remember to spend some time walking around the deck. Is it flexing a bit more than you think is normal? There is often some flex, but the feel underfoot of a problem is relatively obvious even for those unfamiliar with the boat. If it doesn’t feel right, it usually isn’t.

Deck fittings

Moisture ingress around keel fastenings can make a real mess

7 The final big area is chain plate fittings.

Cap shrouds and lowers are connected and anchored using a variety of ways.

leaking chainplate

A leaking chainplate showing obvious water ingress. All images credited Ben Sutcliffe-Davies

Some have basic ‘D’ bolts fitted though the outer deck margins, with bolts held internally or hidden away behind side decks or under soft linings that can be pulled back to expose the fastenings.

Unfortunately, where plywood is secured as part of her structure, you have no hope of making a visual check.

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