Prototype oarlocks for the Standard Design

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Prototype oarlocks for the Standard Design

Post by topherdawson on Thu Feb 16, 2017 5:56 pm

Possible designs for the oarlock we eventually choose are currently:
1 Don Currie's pin and keeper
2 Robert and Don's stainless steel tube welded to a base plus keeper or other fitting
3 Some kind of swivel like North Berwick's plywood one or Ullapool's Permali one
4 My ball ended pin and slot, either cut into the oar itself or formed between the oar and a keeper.

I think each of the systems needs a post in this topic with as much detail as possible. I will transfer Don's photos and description to this topic. Anyone who has a system they would like us to consider please post here.
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Re: Prototype oarlocks for the Standard Design

Post by topherdawson on Thu Feb 16, 2017 6:09 pm

Ball ended pin and slot:

This system is based on thole pins we in Ullapool have used for over 2 seasons. Although we race with timber pins, for all other rowing we use pins made from an engineering plastic called acetal, black in colour.

Currently our pins have flat tops and carry the Permali swivels which on turn carry the oar. We are still using the original pins after two years. The new ball ended pin and slot system uses the oar itself as the swivel, which eliminates the need for a swivel.

Acetal is easy to machine, costs about £2 per pin in materials, has low friction and wear, and is stronger than timber. It also does not swell when wet. If we proceed with this design the SCRA would need to source a supplier of standard pins, and I estimate they would cost £5 each in a bulk order.
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This picture above shows the new gunwale block needed at 2 and 3 to move the pin inboard about 70mm, which allows a 4.3m oar to be used at Bow, 2 and 3.

The bottom end of the pin has a 2.5 degree taper and a matching hole in the gunwale is achieved with an oversized hole lined with epoxy mix allowed to set around a pin coated with Vaseline. This matching hole is an exact fit which does not rattle, and yet allows the pin to be removed easily to get the boat cover on. The epoxy strengthens and waterproofs the hole surfaces.
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The top end of the pin is hemispherical which allows the weight of the oar to rest and rotate on the top of the pin, which lies in one of three dimples formed in a plywood top plate, defining three gears at 2.6, 2.8 and 3.0 true gearing.

The pin lies in a slot either formed between the front face of the oar and a keeper spaced forward of the oar, or in a slot cut into the oar itself. 3mm polypropylene sheet lines the slot to make low friction wear surfaces.
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The oar does not touch the gunwale in any way. The top of the pin carries the oar weight via the dimple and the slot faces locate the oar in pitch. The aft slot face takes the oar thrust. So far there has been no detectable play or wear, but this is a new system. To prevent the oar jumping out of gear into the next dimple, two separators of hard wood or plastic are held in place by stainless screws passing right through the oar, wear plates and spacers.
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The system is quiet, simple, very easy to mount, unmount and change gear. It is low friction and low wear. The components are cheap unlike the Permali swivel, and easy to make. The pin removes easily to replace or get the cover on, and the wear plates are also easy to replace. There is no shiny metal visible (except the screw heads) and very little black plastic when the oar is mounted.

I can think of three objections:

1   Will the oar split or the pin bend under max load?

I don't think so because the sides of the slot are bound together by the ply top plate and the screws. But I will undertake a full load test at 1000N handle force as this is an untried system.

2   Will the oar jump gears or come off altogether in big waves?

Our current system will change gear if the oar is lifted 18mm but it seldom does even if the tie-down is not cleated. Much has been made of the need for the oar to be easily and quickly hauled into the boat when going into narrow harbours. I think the oar will be easy to lift off the pin in this situation.

To keep it in place when out at sea there needs to be a light rope across the top to hold it down, cleated to a small cleat on the inside face of the gunwale. This would be released when returning to harbour, as we already do.

3   Does it look traditional?

No, but neither does it look high tech. Here is a photo of two oars, one with integral slot and the other with the slot formed between the oar and a keeper:

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