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A Tender for Swing Cat

Building a tender is a great way to get some experience with some boat building methods required for the bigger project. A wooden tender is so much easier to row than a rubber dinghy, and a lot more beautiful!

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Moulds & jig from plans by Selway-Fisher of an 8' dinghy called Aerial. Moulds made out of 12mm plywood. Cedar strip (20mm * 6mm bead & cove) from Fourposters, Sussex www.cedarstrip.co.uk

. Electrical insulation tape was used to stop the planks sticking to the mould. There was a lot of curvature on the hog, so getting it to bend to fit the moulds took a lot of force. I was therefore glad that I had used plywood for the moulds rather than a composite board; the screws holding the hog in place would have pulled out of chipboard or MDF.

stern mould

Planking started from the gunnels and worked up towards the hog. At some point the curvature on the strip planks was too much to get them easily to lie flat against the moulds. When this happened, planking had to start using a different orientation.

almost smoothed stern

This shows some interesting detail. Firstly one ends up with a couple of gaps between planking of different orientations - they can easily be filled with an epoxy resin filler paste later. Secondly, one can see the holes left by screw holes and staples - the latter will almost disappear after sanding and will easily be covered by the sheathing process, without further filling. The lower half shows how the hull looks after scraping off the excess Gorilla Glue.

smoothed bow

With the belt sander you have to be very careful not to sand a flat on a nice curve so I used it on flat areas, or areas with simple curves, and I kept it moving.

filled and sanded

Half the hull and stern sheathed with 200g/sq m woven glass cloth, from Marineware, Southampton, and many coats of West System 105 epoxy resin with their 205 fast hardner. Notice that the finish is a little cloudy, perhaps due to high humidity when applying the resin.


A big moment. The hull is lifted off the mould, and came off easily - the electrical insulation tape did a good job.

inside 2

Ready for sheathing. It looks a bit patchy because it is drying out after being sponged down. Note the epoxy fillets along the hog and the filling of screw holes to cover fastenings applied from the inside into the skeg and runners to re-enforce the epoxy bonding. Sheathing used the same glass cloth but a special clear hardener - West System 207. This hardener required a higher temperature for curing, so the dinghy was moved inside to an enclosed space where the temperature could be maintained at 20 deg C day & night.

inside glassed

All elbows, inwales, centre thwart supports, thwarts and rowlock positions added. All have been coated with epoxy (ie 105 resin, 207 hardener mix).

finished - view from bow

Another view. Note the rubber 'D' fender.

dinghy in floods

The tender was originally carried on the davits by a cradle made out of webbing. This meant it was easy to add a dinghy cover to keep the tender from filling up with water and to prevent UV damage to the varnish. However, the height of the dinghy above the sea was insufficient and, in rough weather, the plunging stern meant the tender would be buffeted by waves surging between the hulls.

dinghy without cradle

To avoid the UV damage, I constructed another cover. This was more complicated since it had to fit over the davits and could not be as watertight as the first cover. However, any water ingress could easily drain out through the bung hole. The bottom photograph shows some wear in the cover after the first season so some reinforcing patches are required. At least the varnish is still looking good.

Finally, here is an atmospheric picture of the tender on the beach by Burgh Island, with Swing Cat at anchor in the distance.

Glue used is a polyurethane type called Gorilla Glue. It foams when applied so fill gaps. When dry the excess is easy to scrape off. Note the chamfer on the hog which (approximately!) matched the chamfer on the moulds. The chamfers were cut by eye, using a plane, to follow the curves of the hull so that the planking makes maximum contact with the moulds and hog. The hog is mahogany as is all other wood used in its construction. All of the mahogany was also supplied by Fourposters.


Planking was fixed to the mould with either screws or staples. Each staple has a length of wire underneath so it can easily be removed.

close up detail

Almost ready for filling & fairing. A lot was done by hand using the sanding board which can be bent over the curves, particularly compound curves. The flatter areas can be done with a belt sander.

smooth stern

Ready for glassing. I tried various filler powders to thicken the resin for filling: West System filleting blend (405); West System micro-balloons and sawdust from the sanding operations. None of them really blended-in. It didn't really matter on the outside as the final finish would be a paint, but it did matter on the inside.

half glassed

All the hull is sheathed. The skeg and runners have been attached using epoxy adhesive, epoxy fillets and a few screws.

inside 1

The clean-up inside is well underway. It is difficult to use a belt sander, or the sanding board, on the inside, so most sanding was by hand, using small blocks of wood to give a lot of pressure.

inside filled & sanded

A much clearer coating than the outside! The stem elbow and thwart supports have been epoxied into position during the application of epoxy layers to fill in the weave of the glass cloth.

inside furnished

The inside has now been varnished and the outside given an extra 4 coats of epoxy containing a dark green pigment paste.

finished - view from stern

The tender came in useful in an unexpected way - in the floods of November 2012, we used it to cross the road to have a cup of coffee with our neighbours, Debbie and Andrew. I also used it to row into town and get the newspaper! On the way back I was filmed by a Sky News camaraman - have a look.

tender in cradle

The solution was to dispense with the cradle and haul the tender to the davits from eye bolts fixed to the keel. This meant that the dinghy could be raised by another couple of feet which was enough to significantly ameliorate the problem. Of course, the tender could now fill up with water and the inside is exposed to sunlight all the time. The answer to the former problem was to have a bung in the bottom of the tender - of course one has to remember to remove the bung after raising the tender and put it in before lowering!.

tender without cradle 1

tender without cradle 2

dinghy on beach