Should the SRCA supply oarlock components?

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Should the SRCA supply oarlock components?

Post by topherdawson on Thu Jan 05, 2017 10:48 am

Don Currie and Robert Graham both suggest stainless steel tubular pins of say 22mm diameter, welded to rectangular base plates. These would be bolted or screwed to level pads on the gunwales, or on inboard blocks if that's what we go for. Don suggests that the SCRA supply them as a way towards a standard design, as some sailing dinghy classes already do in New Zealand and elsewhere.

They could be fitted with wooden plugs at the top if we wanted ball ends or traditional looking ends. The stainless plates could be covered with wooden wear plates which would look more traditional. The plates would need to be unbolted to turn the boat over for painting as they would stress the gunwale of the weight if the boat was rolled over on to them.

This would be a route towards standardisation. I have an alternative suggestion which I'll put in the next post.


Last edited by topherdawson on Thu Jan 05, 2017 12:47 pm; edited 1 time in total

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Re: Should the SRCA supply oarlock components?

Post by topherdawson on Thu Jan 05, 2017 10:52 am

Here is another suggestion about what standard components the SCRA might supply:

I make our (Ullapool) pins on a lathe, and fair enough not all clubs will have access to this. They are tapered at the bottom and so they fit without rattle but can be removed by grabbing vigorously and shaking, or at a pinch by knocking them upwards.

So what if the SRCA supply either timber or black acetal plastic pins, 28 or 30mm diameter. Tapered at the bottom and either flat or hemispherical at the top, mass produced on a batch lathe. Builders fit them by drilling oversize and lining the holes with thick epoxy mix, squaring up the axis with the oversize holes, parcel tape and vaseline as release agent. This is what we do and works well. Nice sealed tapered hard hole. And we can get the cover on.
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Left hand pin is 28mm black acetal with about two years wear on it, still good for more wear.
Middle pin is 28mm oak with a ball end for 2 axis use (no feathering)
Right hand pin is 28mm oak with a 40mm ball for 3 axis use (feathering) although we are leaving that line of development for now as being too complicated.
All three pins have the 2.5 degree taper.

Because the SCRA supply the pins they all fit, and all oars fit them. With either Don's pin and keeper or my ball ended pin, no swivels or oarlocks needed. Acetal wears really well. No screws or bolt holes through the gunwale, which people never seal properly. No shims needed. Politically no need to revisit the metal pin argument. Pins look similar to what we are used to, no big acreages of shiny stainless.

If we go for inriggers (need to decide that soon) they can be drilled before installation or after, and it does not need to be precise.


Last edited by topherdawson on Thu Jan 05, 2017 5:20 pm; edited 2 times in total

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Re: Should the SRCA supply oarlock components?

Post by Robert Graham on Thu Jan 05, 2017 12:10 pm

[quote="topherdawson"]Don Currie and Robert Graham both suggest that the SCRA should source and sell (Correction, Robert Graham suggested a ss pin as a way of overcoming wooden pin breakages but not that SCRA should source and sell them.)stainless steel tubular pins of say 22mm diameter, welded to rectangular base plates. These would be bolted or screwed to level pads on the gunwales, or on inboard blocks if that's what we go for.

Corrected now Robert, i hope the amended text is OK?

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Re: Should the SRCA supply oarlock components?

Post by Ian Mills on Fri Jan 06, 2017 11:04 am

If pins are to be standardised, we prefer the first suggestion.
This is close to our own developed system and allows full adjustment of pitch in all directions with packers if required.
Also allows experimental adjustment of pin position fore and aft - eg if seats are moved.
Very easy to install for the average skiffologist.

Not keen on the second suggestion as pins are fixed.

Regarding concerns about drilling through the gunwales - we drill 8 mm holes through the centre of the gunwale to mount our pin blocks which are held in place with 6 mm stainless steel bolts and wing nuts. The holes are not sealed as Topher points out, (though we do tape over or plug unused holes) but there has not been a problem with timber rot so far as the timber is larch.

Ian


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Re: Should the SRCA supply oarlock components?

Post by Ian Mills on Fri Jan 06, 2017 11:09 am

P.S.
Setting up the boat correctly with accurate blade pitch is important and is a part of why our particular boat goes pretty well.
Ian

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Re: Should the SRCA supply oarlock components?

Post by Ian Mills on Fri Jan 06, 2017 4:13 pm

P.P.S:
just wondering about potential wear to the oars due to steel pins - ideally the pins would be of greater diameter than 22mm, but I wonder if they could be made to fit inside an easily/cheaply purchased hard plastic tube which could slip over the pin, reducing wear on oar?
Just an idea...
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Re: Should the SRCA supply oarlock components?

Post by Don Currie on Sat Jan 07, 2017 4:33 am

We used 25mm electro polished SS pins for quite some time - they cause less wear on the oars than wooden pins.

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Re: Should the SRCA supply oarlock components?

Post by Finlay Robertson on Tue Jan 10, 2017 7:41 pm

True, stainless steel is a more appropriate material for a pin than wood, in the same way that carbon composite is a more appropriate material for an oar; however, as Robbie stated in his e-mail, our aim here isn’t simply to make the ‘best’ oar/oarlock system – there’s a much worthier objective at stake here. As such, there are two tests that we should be applying when making decisions:

  • Does this move towards standardisation?
  • Does this level the playing field for disadvantaged clubs?

I’ll come back to this in a moment; first, some feedback on the welded pin/plate suggestion.

Comments on Design
I’ve run the numbers myself and am content that a 22mm pin should have sufficient bending resistance; however, the welds would need to be pretty substantial and the base plate thickness would need to be sized accordingly. Alternatively, the pin diameter could be increased to increase the weld modulus and allow a thinner base plate.
The push-pull loads on the attachment to the gunwale is another important matter; certainly a couple of self-tapping screws would be insufficient, and I think that the plate would probably need to be bolted through the gunwale. A lot would depend on the length of the plate.
Playing with the various options, I reckon we’d be looking at a total weight of around 1kg per unit.

Comments on Cost
By my estimate, materials would be in the £10-20 range depending on batch size, but I really couldn’t hazard a guess as to what a bespoke fabricator would charge for actually putting these things together. We also need to consider delivery costs; assuming a set of 4 of these would weigh 4kg, postage would be around £15, £40, £60 and £80 for UK, European, N American and Antipodean deliveries respectively (unless the SCRA goes down the road of licensing overseas manufacturers). All-told, we’re probably looking at a total of several hundred pounds per set of oarlocks. 75% of survey respondents ranked oar costs in the sub-£50 area as desirable or higher, so we need to justify this.

Comments on Acceptance
This moves away from the ‘traditional’ thole pin. If we were simply looking at replacing a wooden pin with a more hardwearing alternative then we might be able to sell the idea, but this is essentially a brand new component with no precedent in traditional boats (I hesitate to use the word ‘invention’!) and I’m concerned that it would rather jar with the views of the conservative traditionalists in the rowing community!

Test 1: Does this move towards standardisation?
We’re not looking to standardise for the sake of it – we’re doing so to standardise performance. The key variable for pins is the impact they have on the oar’s angle of entry into the water. As Ian notes, this system does not standardise this as the mounting angle can be modified. I’d argue that the system fails this test.

Test 2: Does this level the playing field for disadvantaged clubs?
As discussed in Test 1, the system does not guarantee level performance. Nor, as far as I am aware, is any club disadvantaged by their inability to fit a thole pin – every skiff ever built has functioning tholes or kabes. (Something else to bear in mind: we cannot argue on one hand that a club is capable of building, for example, a hollow oar, and argue on the other that they can’t build a functioning fulcrum!) Why remove the need for knowledge that already exists?

I’m using some pretty hardcore Devil’s advocacy here, so please challenge these points if you disagree!

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Re: Should the SRCA supply oarlock components?

Post by topherdawson on Tue Jan 10, 2017 9:37 pm

Thanks for this Finlay. I agree that for the reasons above and others, a bit of stainless tube welded at right angles to a plate is not all that good a fit with our objectives.

At all four pin positions the gunwale is not level either fore and aft or side to side, so such a plate needs a shaped pad to sit on, plus another pad on top if we are using wooden wear plates.

Then the need for bolts (2 bolts? 4 bolts?) means drilling the gunwale at some funny angle in order to get the nuts on, never mind washers. The bolts will not be vertical so the heads will be awkwardly lying out of plane, and nobody ever paints or resins the hole so water gets into the timber.

The tube will need a drain hole in the weld or else forever be full of water.

I think the SCRA should supply 28mm (or whatever) black acetal (Delrin) pins already machined to a 2.5 degree taper, get people to drill oversize vertical holes and line them with epoxy as suggested above. No fecking great bits of stainless with bolts, easy to put in and out, easy to post, estimated cost about £5 each, weighs 135grams.

Both Don's pin and keeper and my 2 axis ball ended pin and dimple would work with existing pins, it's just that many are not 28mm or whatever we decide, and many are not vertical. But neither are life threatening.

Perhaps we need to declare an official pin diameter, sell tapered acetal ones for those who want, and encourage vertical holes. Certainly stainless tube welded at right angles to a bit of plate is not going to encourage vertical pins, because the easiest and neatest way to install them would be to bolt them straight to the gunwales leaning out.

Welding the tube on at the correct angle would be an improvement but then you'd need 4 different designs.

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Re: Should the SRCA supply oarlock components?

Post by john mcintyre on Thu Jan 12, 2017 6:16 pm

All

The wooden or delrin pins Ullapool use are a nice solution for the following reasons:

1. They are easy and cheap to make and could easily be mass produced and supplied with the kits. The tool to cut the tapered hole in the gunwhale is easy to make, (from scrap wood and an old saw blade - instructions in wooden boat magazine.) or could be lent / supplied with the kit.

2. They are low friction and have a very long, indefinite life?

3. We take them out which is easy with the taper when we put the boats away so the cover is not damaged by the pins and does not need to have holes for the pins or covers for the pins incorporated in it.

4. If the skiff is tied up or in a raft of boats the pins or other boats are not damaged by the pin if the boat is moving in a swell.

5. They have low friction so are silent and support the oarlock and oar off the gunwhale.

John


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Re: Should the SRCA supply oarlock components?

Post by topherdawson on Thu Jan 12, 2017 6:57 pm

Just to clarify, there is no need to make tapered holes as we did at first. The idea is to make an oversized hole with one or more drill bits and then line the hole with thickened epoxy and insert the greased pin.

Final alignment of the pin and then allow the epoxy to set. Hole is the right shape, hard, and the wood is sealed.

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Re: Should the SRCA supply oarlock components?

Post by Don Currie on Thu Jan 12, 2017 7:55 pm

I wonder Finlay whether you did the numbers with a solid pin - our SS pins were more like 250 grams each. Anyrate, the main thing is to make it easy for clubs to have a standard system, and the main point, as in the subject line, is whether SCRA wants to step into the supply chain and provide the pins. This will be especially important if you are going to have a system of practice pins (delrin) and racing pins (wood) - it will be important to have accurate and consistent tapers cut on both, otherwise the advantages of the "liquid engineering" of the tapered hole are lost. A single supplier could be a significant advantage.

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Re: Should the SRCA supply oarlock components?

Post by topherdawson on Thu Jan 12, 2017 9:14 pm

Accurate tapers don't seem too difficult to make on a lathe and several generations of pins still seem to fit the holes. Probably Delrin/acetal pins would be better than wood as wet wooden pins swell about 1mm in diameter, so they need to be 1mm undersize dry to fit swivels etc when wet. The acetal pins don't swell so they don't jam immovably if put in dry and allowed to get wet. The wooden ones are not a problem if you take them out each time, they only jam if you leave them in the hole.

The taper we use is 2.5 degrees on each side and as John says would be highly reproducible on a CNC lathe. Material cost is less than £2 each. The pin does need accurate machining and the SCRA would need to find a supplier and get a big batch made.

John suggests that whatever oar design we decide on, we should also supply or arrange the supply of oar kits with the correct timbers machined to the correct sizes, plus strips of ply if we use ply webs and also bits of ply for blades.

In other news the solid oar shaft is in our living room for warmth as it's snowing and blowing hard outside and the big scarph joint needs to set well.

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