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Spar gauges

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Spar gauges

Postby Mike G » 18 Oct 2021, 19:55

If you need to plane a square profile piece of wood down to a round shape, then you'll probably need a spar gauge. The name obviously comes from the fact that boat builders and shipwrights need to make spars (masts, yards, booms, bowsprits, gaffs etc) all the time, and they need a way of marking out for the process. Here is a quick sketch showing the principle:

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You don't need a gauge for every size of spar you'll make, because they are used on the diagonal.

Anyway, I'm about to make another set of curtain poles, and thought I would plane these instead of putting them through my dowel making jig. And with a possible boat on the horizon, I thought I'd make one big enough for its mast, This was a quick (1 hour) hand tool project (augmented by the pillar drill).

Firstly, I grabbed a piece of mysterious something or other off a pile. It may be iroko, but I've no idea really. It was part of a snooker table I took apart to scavenge the slate, a couple of years ago:

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I planed those pieces up (funny stuff, with interlocking/ reversing grain, but soft and easy to plane), then instead of using a dowel in the usual way, I thought I would do a pointed shaped leg. Dowels produce an innate inaccuracy as the angle increases, so this might be more accurate:

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Normally, spar gauges are made using a 7:10:7 ratio of gaps between dowel:pencils:dowel, but on drawing it in Draftsight, it turns out the actual ratio should be 7:9.89:7. To save anyone troubling themselves with that I simply drew it out at multiple sizes:

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Transferring the info to wood with a pin and a knife:

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I had to find a drill bit between 7mm and 7.5mm to suit a pencil, so I ended up with an imperial size.

Then a little bit of chiselling:

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......and a bit of glue:

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......and a second or two chamfering:

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I don't think I've made the angle on the faces of the guides steep enough, so I may have to do a bit of shaping tomorrow when the glue is dry.

So, if you ever have need of planing something round, you've now got all the ammunition you need. It works with tapers, too. Most spars were/ are tapered.

Here is a Youtube clip. Go to about 4.00 to see it in action:

https://www.youtube.com/watch?v=QzfdTArTx8c
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Re: Spar gauges

Postby AndyT » 18 Oct 2021, 20:32

Another tool Mike?! ;)

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Re: Spar gauges

Postby Mike G » 18 Oct 2021, 20:56

:lol: :lol: I don't see it as a tool so much as a marking aid.
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Re: Spar gauges

Postby AndyT » 18 Oct 2021, 21:07

Mike G wrote::lol: :lol: I don't see it as a tool so much as a marking aid.


Good point, well made. Carry on!

"It might be useful for the boat" could become quite a powerful justification, I think. :)
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Re: Spar gauges

Postby MattS » 18 Oct 2021, 21:45

I didn’t know Spar sold gauges…. Ours just sells food.

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Re: Spar gauges

Postby Doug » 19 Oct 2021, 07:23

Your angle pieces would be better round like the chap’s in the video, but then I guess you’d need a spar gauge to mark the timber to plane those pieces round :lol:

Or get a lathe :eusa-think: :eusa-whistle:
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Re: Spar gauges

Postby NickM » 19 Oct 2021, 08:06

That’s very clever. It’s obvious when he goes through the maths, but someone was very clever to come up with it. Have they been around for hundreds of years?
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Re: Spar gauges

Postby Mike G » 19 Oct 2021, 08:21

Doug wrote:Your angle pieces would be better round like the chap’s in the video, but then I guess you’d need a spar gauge to mark the timber to plane those pieces round :lol:

Or get a lathe :eusa-think: :eusa-whistle:


There's a built-in error if you use a dowel. The distance between the point of contact on the dowel and the nearest pencil changes as the gauge is angled. On a 6 inch square of wood this error could be over a millimetre if the gauge is at 45 degrees. Using a point eliminates this error, but has problems of its own.......it will wear quickly, and it might catch on any roughness on the surface of the timber.
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Re: Spar gauges

Postby Mike G » 19 Oct 2021, 08:27

NickM wrote:That’s very clever. It’s obvious when he goes through the maths, but someone was very clever to come up with it. Have they been around for hundreds of years?


Yes, they've been found in old shipyards from the 17th century. No doubt they were in use long before that. And actually, I am sure they would have been developed imperically rather than worked out mathmatically. A centre-line marker on the same principal has also been around all-but-forever (and there, incidentally, the error caused by using a dowel doesn't exist.....or at least, they cancel each other out).
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Re: Spar gauges

Postby Andyp » 19 Oct 2021, 09:24

Very interesting video Mike,
Shame about the presenter’s production skills though.
Presumably if you want a tapered spar then the square stock needs to be tapered first?
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Re: Spar gauges

Postby Mike G » 19 Oct 2021, 10:33

Andyp wrote:......Presumably if you want a tapered spar then the square stock needs to be tapered first?


Yes, that's right. Just to complicate matters, they're often curve-tapered, if you like, rather than being a conic section. Entasis is the architectural term.
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Re: Spar gauges

Postby Cabinetman » 19 Oct 2021, 11:06

Interesting Mike, hadn’t come across that type of gauge, but I did do a long spar of the entasis variety as a needle for a large sundial, it was made from a 10 foot length of telephone pole. Just shaped by eye and the gradually curved/tapered effect was a joy to do – lots of standing back to look at it! Ian
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Re: Spar gauges

Postby Andyp » 19 Oct 2021, 12:26

Mike G wrote:
Andyp wrote:......Presumably if you want a tapered spar then the square stock needs to be tapered first?


Yes, that's right. Just to complicate matters, they're often curve-tapered, if you like, rather than being a conic section. Entasis is the architectural term.


Thanks for a new word for the day. Just have to think of a way to drop entasis into the dinner table conversation now :)
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Re: Spar gauges

Postby Squib » 13 Nov 2021, 11:42

The traditional pattern guage eliminates some of the dowel errors....this one was made on the job,I can't find my posh one..... it's somewhere safe!
Panel pins instead of pencils ....
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Re: Spar gauges

Postby Mike G » 13 Nov 2021, 14:25

Squib, we're going to need some photos of some of the boats you've worked on. It's compulsory, you know. ;)
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Re: Spar gauges

Postby Squib » 15 Nov 2021, 20:27

We new built small craft, carvel, clinker,cold molded and ply and did restoration of bigger yachts.
I will try and find some pics and scan them, I don't have any digital ones.
We actually built a cat boat, I think from memory it was about 19' long and about 8' wide! Very fat with a single gaff sail set right up in the bow. Interesting beast.
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Re: Spar gauges

Postby Mike G » 15 Nov 2021, 20:33

I thought cat boats existed only across the pond.

Have you ever done a glued ply clinker boat?
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Re: Spar gauges

Postby jimmy s » 15 Nov 2021, 20:57

The traditional shetland model boats were what I presume you would call clinker built Mike. They use a copper clink - like a nail that gets driven through the boards and is clinked in situ?. The smaller boats (fourareens - or 4 oared boats) are used for sailing in regattas up there still - they are based on old Viking boats I think. Traditionally they were built from larch or oregon pine but a lot of the new built ones are (or certainaly were when I still lived in Shetland) made of fairly thin marine ply boards, clinked up and were often coated in west systems epoxy from memory.

Always wanted to build a boat, but my Wife is not keen on the sea at all.
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Re: Spar gauges

Postby Mike G » 15 Nov 2021, 21:21

Yes, that's the idea Jim. Clinker is where the boards lap over each other by a little. The traditional alternative being carvel planking where the boards butt up against each other with packing between to keep the water out. Traditional clinker boats were riveted together, but I am planning on building the modern type where the joints are epoxied, and the strakes (planks) are made of marine ply.
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Re: Spar gauges

Postby heimlaga » 16 Nov 2021, 21:24

jimmy s wrote:The traditional shetland model boats were what I presume you would call clinker built Mike. They use a copper clink - like a nail that gets driven through the boards and is clinked in situ?. The smaller boats (fourareens - or 4 oared boats) are used for sailing in regattas up there still - they are based on old Viking boats I think. Traditionally they were built from larch or oregon pine but a lot of the new built ones are (or certainaly were when I still lived in Shetland) made of fairly thin marine ply boards, clinked up and were often coated in west systems epoxy from memory.

Always wanted to build a boat, but my Wife is not keen on the sea at all.


The shetland boats, sixareens, fourareens, yoals and whilly boats and so on are all based on what the Norwegians call "hjaltbåter", that is boats builts for export to Hjaltland which was the old Norse word for Shetland. All the way from the Viking age up to the early 19th century boatbuilders in western Norway built boats which were shipped over to Shetland as well as boats for local use in a tradition with roots even before the viking age. Those boats were either taken apart and shipped over to Shetland as bundles of ready made parts or stacked inside one another for transport. That is probably the reason why Shetland boats to this day have fastibands which could be nailed in after unloading where a Norwegian boat for the home market would have a beite which was an integral part of the frame.
In those days all boats built for Shetland were rivited using wrought iron rivets with very low carbon content. Like Norwegians do to this day.
When the old boat export came to an end shetlanders started building their own varieties with narrower planks and copper rivets but otherwise quite similar. Even the old Norse names of the parts of the boats were kept. To my great surprise I found that I understand most of the old Shetland boat terminology as the same words can be found both in my own very oldfashioned dialect of Swedish and in west Norwegian dialects which are pretty much mutually understanable with my dialect. Had the Shetlanders kept their Norn language I would probably be able to chat with them too without having to speak any foreign language.
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Re: Spar gauges

Postby heimlaga » 16 Nov 2021, 21:29

By the way....I would like to some spar gauges too. I need to make a new pair of oars and I rekon they would be useful.

Would you mind if I copy the dimensional pattern?
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Re: Spar gauges

Postby Mike G » 16 Nov 2021, 21:33

For anyone interested in these sort of topics, both heimlaga and I are members of The Wooden Boat Forum, which is a fascinating place for those with any interest in the subject.
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Re: Spar gauges

Postby jimmy s » 17 Nov 2021, 00:59

Most if not all of the words used in Shetland model boats are Old Norse I think - Tilfurs, keabes, humlibaands and suchlike. I'm from one of the isles and a lot of the old norse words are still about. Most of my family were involved with the sea. There are still a lot of the fourareens about not so many sixareens. They were used for the Haaf fishing more.
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Re: Spar gauges

Postby Squib » 18 Nov 2021, 08:28

Very interesting, I was aware of the close Norwegian connection but had no idea is the disassembly before shipping. The origin of boat kits....
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