Still talking about oars!

Above is an image of the recommended hardwood/softwood oar, courtesy of Topher Dawson, complete with the photographer’s shadowy signature.

The oars that we will build are very similar, except that we won’t be having the ball and slot oarlock system devised by Topher, nor his spoon blades.

For that system to work perfectly it’s essential for the pins to be absolutely vertical, something difficult to achieve, given differing crew weights, for example an exceptionally heavy cox brings the skiff down at the stern. Also it’s more difficult to make accurately. Correctly set up, the system works perfectly and smoothly, but we have decided to stick with simplicity.

For those who are interested, here are details of the ball and slot system:

We intend to adopt the pin and gate oarlock system devised by Don Currie, shown here:

Here is Don’s drawing, showing construction details:

You will see from the photograph that Don has made wearing strips from some hardwood. We could use oak, or perhaps source thin strips of polypropylene, which the rules allow. He has provided dowel spacers held by strong woodscrews and the photograph shows plastic bushes round these.

These details are not today’s problem, but will give us something to talk about while getting on with the main work. In the meantime please be thinking about sourcing suitable  polyprop, plastic strips etc that can be recycled for a seagoing future.

We have now sourced sufficient Douglas Fir and Western Red Cedar to make our set of oars.  The first task is to make a cutting schedule, so that the wonderful Mr H in his mountain workshop won’t get annoyed at having his time wasted.

Marking out precisely and very carefully where you are going to cut is far more important that just charging ahead and possibly wasting expensive material. The old adage “measure twice, cut once” applies.

We have more than enough WRC, as I had to buy two pieces – timber yards won’t just cut off the length that you need. We’ve got just enough DF to produce four handles plus strips to go on the front and rear faces of the WRC, to protect the latter from dents and bashes. The strips should be 5mm or probably 6mm thick if we can manage to get that width out of what we have. Each saw cut costs you the width of the blade, about 3mm or 4mm usually, rapidly using up stock.

We will soon run oar building workshops, but for these to be of any benefit it’s important that people understand the problems and help with solutions. As  start please read Topher’s detailed instructions, copied below. We need to modify these somewhat, to take account of the flat blades, and adjust the dimensions to allow for the DF faces on the WRC.  For example I’m inclined to make these faces full length, for strength and ease of building, rather than just the length of the outboard, WRC sections. This means that the handle stock would be machined 78mm x 45mm rather than 90mm x 45mm, allowing for the two 6mm strips.

Here is an image of the handles, per Topher:

 He is suggesting ovoid, 40mm for and aft by 35 deep. I think we should go slightly less depth and also produce a pear-shaped end.

There follow Topher’s Instructions. Please note carefully the suggested dimensions, especially at the outboard end. It makes me think that our current oars are massively over-strength!

Making the Beta test hardwood/softwood oar shaft for the St Ayles oar

The hardwood/softwood shaft has a rectangular cross section with slightly rounded corners for its whole length, tapering down in depth and width towards the tip.

  • The inboard section inside the boat is made of a dense hardwood like oak or ash and the outboard section is made of a light softwood like Western Red Cedar (WRC), spruce or Douglas Fir (Oregon pine). This improves the balance.
  • The number 2 and 3 oars have the thole pin mounted not in the gunwale but in a block screwed and glued to the inside of the gunwale. This moves the pin inboard by about 70mm which allows the oar to be shorter and therefore lighter than current oars. It also allows the bow, 2 and 3 oars to be the same length, 4.3m. The stroke oar is 4.0m. “Short oars” are all 3.5m.
  • The depth and width at each station along the shaft are the same for all lengths of shaft, but the distance between each station varies with the length of the shaft.
  • The spoon blade is a spooned narrow Macon shape made from two blade halves of 4mm plywood. The blade halves are stitched together with cable ties to form a shape which is curved longitudinally and slightly vee shaped in cross section. This is then epoxied and the cable ties removed. The curve allows the light plywood to be stiffer and stronger than a flat blade and more efficient in the water. This light blade contributes to the light balance of the oar.
  • A flat 4mm ply blade can also be made.

Making the hardwood/softwood shaft:

Whatever species of timber is used, it has to be clear of knots and straight grained. In the UK the most likely timbers for the inboard are ash or oak, but elm or beech could also be used. Outside the UK there will be favoured local woods of at least 700kg/m^3 density.

The outboard timber needs to be light, straight grained, clear and available in lengths of 3.5m, although they can be scarphed. Western Red Cedar, spruce, and Douglas Fir all fit this bill. WRC is the lightest, spruce is the most expensive, and Douglas is the heaviest. Slight variations of the width and depth of the tapered outboard are in the design to take account of the different density, strength and stiffness of the three timbers. If you are using other timbers, measure the density and stiffness of a sample of your timber and pick the design for the timber which most resembles yours.

The procedure depends on what dimension of timber you start with. If you use 100×50 thicknessed down to 90×45 then make one 45mm face straight, flat and at right angles to the 90mm face. Use this face for the aft face (nearest to the cox). Mark the stations on it and draw the widths at each station. Cut this taper leaving enough timber to plane to a smooth curve. You may want to use this blank to draw around on the other shafts.

If you are using Western Red Cedar in the commonly available 150×25 sawn finish house cladding plank size, you will need to thickness it to clean up the sawn surfaces and then glue two layers together to make a blank. Your blank will likely be a bit under the 45mm thickness needed near the gunwale, but only short padding pieces 150mm long are needed because it thins rapidly.

Then on the fore and aft faces, mark a centre line and set off the depth equally on both sides of the centreline. You want to take wood off both sides, perhaps with a hand held power planer to begin with, and then a hand plane as you get near the line. Finally you knock off the sharp edges with a hand plane and some sandpaper, aiming for a 5mm radius or whatever seems right. This is to make the oar shaft more robust against knocks, and kinder to rowers.

The oar needs a big scarph joint just outside the gunwale where the hardwood meets the softwood. This is just like the scarphs in the skiff planking but bigger. Make sure the final oar is straight!

It is easiest to make a hardwood blank 90x45x1500 and work the end down to the handle size, make the slot and line it with 3mm plastic, and make the scarph, before gluing it to the outboard.

Dimensions:

This table shows the width (fore and aft) of the shaft at each station, in mm. Station 0 is at the gunwale, and the ten stations are equally spaced going out from the gunwale to the tip of the oar. The cross section of the oar is everywhere rectangular, with  slightly rounded corners, about 5mm radius.

The depth of the shaft (top to bottom) is exactly half of the width at every station.

The inboard part of the oar, from the handle end to the gunwale, is hardwood of a constant 90×45 rectangular section.

 

The dimensions vary a little for different timbers, to take account of the different density, stiffness and strength of each timber. It is important to avoid knots, especially near the forward and aft faces of the shaft.

pastedGraphic.png

 

If making this oar out of Western Red Cedar, the lightest of all three timbers, the shaft can be made of two layers of 150×25 plank which is the most commonly available size, used for house cladding. It needs to be thicknessed down to clean up the surface, but taking off as little wood as possible. Depending on the plank, you may end up with 19-22mm thickness. A small section on each side may be needed to thicken up the 150mm nearest to the gunwale to make 45mm.

The oars come in three lengths. The shortest, 3.5m, is for short oar clubs, and all four oars are 3.5m long.

For long oar clubs the stroke is 4.0m long, and oars 1, 2 and 3 are 4.3m long. To allow oars 2 and 3 to be this short, the pins need to be mounted on blocks glued to the inside of the gunwale.

The dimensions at each station are the same, but the distance between each station is less for the shorter oars.

pastedGraphic.png

The inboard and outboard are joined with a 6:1 scarph, 270mm long. The scarph joint is cut so that the feather end of the outboard is at the top of the oar, and the feather end of the inboard is at the bottom of the oar.

The handle needs to be 400mm long, and around 40mm in diameter according to taste. A good section is oval 35mm deep and 40mm fore and aft, which allows smaller hands to grip but keeps more strength. It is sensible to make a gradual transition to the rectangular section for rowers’ comfort and to reduce stress concentrations.

Varnish or paint the oar well, as the additional weight is less than the weight of moisture soaked up by an inadequate paint job.

This entry was posted in Building the boat, Getting Involved, Job lists, Uncategorized and tagged , , . Bookmark the permalink.

Leave a Reply