A trunnions is a bearing with two orthogonal bearing axes. (two axes at right angles) In short so far as oars are concerned, one bearing axis is the fore and aft movement of the blade of the oar, and the second is the blade up and down movement to put the blade into the water at the catch and take it out at the finish. That’s all we need to do with a St Ayles Skiff oar – there’s no feathering.
I felt that the pin and plate system could be improved upon. I’d noticed wooden replications of rowlocks, suspended domes on pins and all sorts of things. I was looking at a leaving present I’d been given – a Portland Canon – which was made in the workshops and given to all engineers when leaving RNAS Portland – the Naval Air Station in Dorset where I’d been the Maintenance Test Pilot. The barrel of the cannon rests on a trunnion and at right angles to that is the vertical axis, a bit like a Hardy Spicer joint you see in motor car drive shafts – why not make one in wood? So I decided to take a bit of Sycamore, bore it in the appropriate directions and make a box to carry it in. And so the rowing trunnion bearing came into being.
After that I wanted to make it a little more robust so took closer note of grain direction, timber type and used sheets of PTFE to prevent too much wear. The trunnion box was made from purpleheart, the pivot pin from purpleheart and the trunnion itself finally was made from ekki. Ekki is somewhat tough on boring tools so I needed to sharpen frequently but it all worked and now we have the Mark 3 trunnion bearing (the first picture) which seems to be a reasonable solution.
I did make a set of light oars from Western Red Cedar for the shaft, Oak for the loom and with the trunnion set in a slot cut in the centre of the oar. Oak is quite acid, does not glue well and when put to the test at a friendly set of races, the crew managed to break 3 of the 5 oars I had made. Not the trunnion’s fault, just that the oak did not glue well and the epoxy joints failed. I have repaired them using meranti instead of oak, but whilst the oars are very nice and light, they do not have the ‘heft’ crews seek – they don’t necessarily know it but the seek it!!
Disappointing as it may be to have oars broken, at least it is a go, no go test and you know exactly where you are. AND it wasn’t in a race. It does have the added advantage that people feel sorry for you as well!!