Thwart Reinforcement

In this instance, there has been a difficulty keeping water out of the hull of the Yellow Trio, and many attempts have been made to fix it, and also strengthen the thwarts. The thwarts appear to be a design weakness in this era of build, and while the green one has been back to the manufacturer for strengthening, the thwarts on the yellow one have been stregthened and repaired by ourselves.

In this instance, the screws holding the thwart to the bulkheads were pulling out and it has been looked at by dinghy experts who recommended that we abandon the manufacturers original design and install a stronger structure.

Getting the boat where we have home comforts was the first task – mains electricity, cups of tea and so on… very civilised.

The night before the day to repair the boat there was rain in the forecast, and it was important that the boat was completely dry, so it was stored upside down overnight.

The best way to work epoxy is with gravity helping, so we got the boat in the correct orientation to allow gravity to assist.

The first job was to make the struts from a softwood, and I chose pine. Each pair of struts is subtly different in profile.

Then the pine struts were offered up to the underside of the thwarts.

There was a little fettling to do, and then the screws and the grey wedges removed.

And this is the root cause of the problem. The orange light through the screwhole shows that the bulkhead was not padded to accept a screw. Good practice is to glass a pad of ply in place behind anywhere where a screw will be later fitted, so that the screw has wood to bite into. There is no pad behind the bulkhead. Either we needed to install the pads (which is a very big job after the boat has been built) or do something different – hence the installation of support struts.

This picture shows the strut against the inside of the hull.

 

 

Epoxy is very sticky, but needs roughness to create a mechanical bond. This was achieved by using a dremel with a diamond bit to cut into the existing gelcoat and make a very rough surface.

f

 

 

 

 

In order to maximise the strength of the bond between the wood and the gelcoat, the wood was first impregnated with unmodified epoxy. This soaks into the wood and forms a tremendously strong bond. Then the epoxy was thickened with Cabosil to the consistency of mayonnaise. This both fills the gaps and stays put until the epoxy hardens. It also allows a rounded fillet where the wood meets the hull to help the glass fabric shape effectively.

This is allowed to set enough to stay in place while the glass is laminated.

All were set in place.

Next coloured epoxy was stippled over 200gsm woven glass fabric and the pine is now completely sealed.

All were completed on both sides.

 

This structural improvement supports the thwarts, and further structure was required to bond the thwart at the stern. The missing support caused the thwart to break from the side, and this has now been supported with 300gsm chopped strand – which is incredibly strong.

All this was let to set.

The next day the boat was upright on the trailer and it was time to plug the holes in the buoyancy tanks, done by sliding mayonnaise thickened coloured epoxy between the thwart and the hull to give a generous covering to the holes.

This should provide both additional structural integrity to the thwarts, and also permanently fix the leaking into the buoyancy tanks through the thwart wedge screw holes.