4.3m 90x45 hollow cedar/ply outboard oar

View previous topic View next topic Go down

4.3m 90x45 hollow cedar/ply outboard oar

Post by topherdawson on Sat Mar 04, 2017 2:00 pm

This oar is being made by Topher Dawson in Ullapool.

topherdawson
Admin

Posts : 211
Join date : 2016-11-24

http://sasoo.forumotion.co.uk

Back to top Go down

Re: 4.3m 90x45 hollow cedar/ply outboard oar

Post by topherdawson on Sun Mar 05, 2017 1:46 pm

4.3m oars suit the bow position and also positions 2 and 3 if the pins are fitted to blocks on the inside of the gunwale.

This oar has a rectangular section 90x45 solid ash inboard and a hollow outboard with Western Red Cedar flanges (front and rear strips) and 4mm okoume plywood (Robbins Elite like the skiff kit) webs on the top and bottom. Adaptations of this design are available for Spruce and Douglas fir. This oar was made to correct the lack of stiffness in the previous hollow oar. It has the best combination of UHF and stiffness of any of our prototypes yet.

The WRC strips are 8mm thick at the pin, tapering to 3mm at the tip which is alarmingly thin, but it works. Deflection is 70mm which is stiff.

The total weight is 5.12kg and the UHF at gears of 3.0, 2.8, 2,6 are 1.64kg, 1.29kg and 1.00kg.

The shaft is bulkier than the solid oar and so has more windage, and may be entraining more water at the neck of the blade.

The build needs a jig of 10 stations accurately cut out of plywood and mounted on a straight base. Adding this to the build time means I'd estimate 50 hours to build 4 oars.

The material cost comes to £75 per oar, compared to the £100 for solid oars, reflecting the reduced amount of wood.

I will post photos and rower accounts when I have them.

topherdawson
Admin

Posts : 211
Join date : 2016-11-24

http://sasoo.forumotion.co.uk

Back to top Go down

Re: 4.3m 90x45 hollow cedar/ply outboard oar

Post by topherdawson on Sun Mar 26, 2017 9:37 pm

Design 4B 4.3m 90x45 Hollow outboard ash/cedar/plywood oar

This follows the Design 4 hollow oar and was designed to be stiffer and still well balanced.

The Unbalanced Handle Force (UHF) @ gearing of 3.0 = 1.64kg. @ 2.8 = 1.29kg @ 2.6 = 1.00kg.(very light)

Total weight = 5.12kg and deflection at 10kg at 2.5m =70mm which is stiff.

Build time 25 skilled hours. Cost of timber about £75.

This oar is stiff and light to row with. It is technically the lightest and stiffest oar but harder to make. One bigger rower found it too light to handle well in a strong headwind.

topherdawson
Admin

Posts : 211
Join date : 2016-11-24

http://sasoo.forumotion.co.uk

Back to top Go down

Re: 4.3m 90x45 hollow cedar/ply outboard oar

Post by Sponsored content


Sponsored content


Back to top Go down

View previous topic View next topic Back to top


 
Permissions in this forum:
You cannot reply to topics in this forum