Building Shesha, a Hunter Valley GIS, Australia

[Boatmik]

Howdy - thanks for explaining that.

I think the commercial carbon spars you are using are worthwhile - on the assumption the person can pay for them.

But they start getting less worthwhile as the building gets less high tech.

Sleeving the lower part is a valid recourse - it's still used with lots of aluminium masts when one section is too small and another is too large for a specific boat.

I did at one point have a link to the UK Cherub website which has about the best explanation of setting up making a homebuilt carbon mast - for a stayed rig.

Problem is with most one-off carbon masts is that there is no real attempt to find a reasonably optimum solution - that's the function of the WIKI for the GIS (the acronyms sound rather military-industrial). Most give it a shot and think it's great with little or no real comparison - rather than see the weight savings over a wooden mast are not as great as they think.

Here we have some data on a range of wooden spars and their carbon alternatives. I would still go for the timber mast personally - but at least I can put some numbers to the decision.

Thanks hugely for your part of it!

MIK

MIK

[IanHowick]

Yes, great to get such direct comparisons on the same design of boat. I would expect that a reasonably optimised carbon section should come in at 60-67% lighter than a reasonably optimised wooden section just from the fact it's specific modulus is about three times wood (10 times the stiffness but three and a bit times the density)

I would think that your wooden and my carbon spars are optimised about as much as is reasonable - going any further would be doubling the effort and or cost for the last 10% of possible weight savings.

Further weight reduction on the wooden ones would involve being brave dropping the wall thickness below 15%, and or planing the staves so the wall thickness reduces with height. You might get away with reducing the wall % by using a longer base infill/more spacers, all of Paulownia to save weight. Bruce's (Woodeneye) mast got down to about 16 lb with 10mm thick staves, I assume it is standing up well?

Anyone up for trying a 50mm dia/10mm wall hollow birdsmouth yard from hoop pine or spar oregon?

I'm going to stick with a hollow wooden box section for my boom - the benefits of saving a kilo are much less at deck level than they are at mast top height. Also, if the forces are more in one direction than the other, and you're free to increase the overall section size/reduce side wall thickness, a hollow wooden box section can get a lot closer to the stiffness/weight of carbon. Interesting to see in any case.

Ian

[woodeneye]

Bruce's (Woodeneye) mast got down to about 16 lb with 10mm thick staves, I assume it is standing up well?
Ian

Hi Ian, yes the mast is fine. My brother and I gave it a real work-out in some strong wind, which if it was borderline, should have broken it. I think it's a testament to a flexible rig when you think about it. There are so many components that are flexing that there is very little stress concentrated anywhere to cause a problem.

I've just acquired a 38mm aluminium tube (3mm wall thickness). It's not ideal due to the weight of it, which comes in at 3.2kg. That's a whole 1kg more than my wooden one. However, it is 2.5 times stiffer, so it's an experiment more than anything. (Flex is 20mm with 10kg mass attached).

I wouldn't mind having a go at the birdsmouth yard. However, instead of a birdsmouth I was thinking of making it in two pieces, and routing the two halves with a half round bit so that the core is a round hollow when they are mated together. I have different size bits, so I could even step the core, but am unsure if that would be necessary. Being a smallish section there is probably no real benefit in doing that at all. What do you think?

[Boatmik]

I would think that your wooden and my carbon spars are optimised about as much as is reasonable - going any further would be doubling the effort and or cost for the last 10% of possible weight savings.

You could work on the assumption that the mast was going to be loaded less than I did when designing the boat. I assumed three people hiking hard as the maximum likely load. There is very little bend in that mast in normal situations, so for single and doublehanded use the diameter could come down.

Further weight reduction on the wooden ones would involve being brave dropping the wall thickness below 15%, and or planing the staves so the wall thickness reduces with height. You might get away with reducing the wall % by using a longer base infill/more spacers, all of Paulownia to save weight. Bruce's (Woodeneye) mast got down to about 16 lb with 10mm thick staves, I assume it is standing up well?

Anyone up for trying a 50mm dia/10mm wall hollow birdsmouth yard from hoop pine or spar oregon?

Be interesting to see. And get some measurements.

I'm going to stick with a hollow wooden box section for my boom - the benefits of saving a kilo are much less at deck level than they are at mast top height. Also, if the forces are more in one direction than the other, and you're free to increase the overall section size/reduce side wall thickness, a hollow wooden box section can get a lot closer to the stiffness/weight of carbon. Interesting to see in any case.

Ian

Yes .... particularly if the boom doesn't tend to wrap itself around the shroud in a gybe.

MIK

[Boatmik]

Hi Ian, yes the mast is fine. My brother and I gave it a real work-out in some strong wind, which if it was borderline, should have broken it. I think it's a testament to a flexible rig when you think about it. There are so many components that are flexing that there is very little stress concentrated anywhere to cause a problem.

I've just acquired a 38mm aluminium tube (3mm wall thickness). It's not ideal due to the weight of it, which comes in at 3.2kg. That's a whole 1kg more than my wooden one. However, it is 2.5 times stiffer, so it's an experiment more than anything. (Flex is 20mm with 10kg mass attached).

I wouldn't mind having a go at the birdsmouth yard. However, instead of a birdsmouth I was thinking of making it in two pieces, and routing the two halves with a half round bit so that the core is a round hollow when they are mated together. I have different size bits, so I could even step the core, but am unsure if that would be necessary. Being a smallish section there is probably no real benefit in doing that at all. What do you think?

I would say try the alloy spar first and see how the boat behaves in terms of gust response. Particularly one up, where it might count for quite a bit.

If it is more powerful you will probably note it in extra speed close reaching (the extra weight will be less important) or possibly higher pointing if the extra sail depth is more important that the increase in weight aloft.

MIK

[IanHowick]

Hi Ian, yes the mast is fine. My brother and I gave it a real work-out in some strong wind, which if it was borderline, should have broken it. I think it's a testament to a flexible rig when you think about it. There are so many components that are flexing that there is very little stress concentrated anywhere to cause a problem.

I've just acquired a 38mm aluminium tube (3mm wall thickness). It's not ideal due to the weight of it, which comes in at 3.2kg. That's a whole 1kg more than my wooden one. However, it is 2.5 times stiffer, so it's an experiment more than anything. (Flex is 20mm with 10kg mass attached).

I wouldn't mind having a go at the birdsmouth yard. However, instead of a birdsmouth I was thinking of making it in two pieces, and routing the two halves with a half round bit so that the core is a round hollow when they are mated together. I have different size bits, so I could even step the core, but am unsure if that would be necessary. Being a smallish section there is probably no real benefit in doing that at all. What do you think?

Hi Bruce, I agree with Mik it's worth trying the stiffer alu yard first to see how it goes before making another wooden one.

The stiffness you report for the alu tube is the same as my carbon yard, I'm keen to see how you find it. My yard is tapered to nearly half the diameter toward the peak end, so that last metre should flex more. Other issues - my sailmaker will have data for my yard when he cuts the edge round on the head of the sail, your sail is presumably cut for the bendier wooden yard, not sure how that will go with the stiffer one.

Regarding making a stiffer wooden yard - timber such as hoop pine could be better. Numbers off the net seem to show up hoop pine is up to 40% stiffer than radiata, but only 10% heavier. 12-13 GPa for Hoop pine versus 8-9 GPa for Radiata pine.

Assuming the original yard is 40mm dia, made from 9 GPa radiata pine, weighs 2.2 kg, and bends 50mm with 10kg hung off it, some options could be:

Same timber, go to solid 50mm dia: Weight now 3.4 kg, bend now 20mm with 10kg.

Go to 12 GPa Hoop pine solid 45mm dia: Weight now 3.1 kg, bend now 23 mm with 10kg.

Hollow Yard:

If you could do a good job with a 50mm OD hoop pine section with 10mm wall thickness (Hole diameter 30 mm from birdsmouth or router), you might be able to get a yard that weighed about 2.6 kg and bends about 18 mm with 10kg on it.

Hard to be sure exactly how much you'd save by going hollow at this diameter, I've tried to make a bit of an allowance for the ends being plugged and possibly leaving it solid/putting in an infill where the halyard attaches.

Tricky bit with the router would be getting the hole/wall thickness nice and accurate. It would possibly be worth reducing the hole diameter a bit at the tapered end of the yard so wall thickness doesn't reduce too much. I don't have any experience of making a hollow spar of this diameter either with the router or with birdsmouth, but I've been thinking of hollow wood shaft oars which are about the same dia so I'm keen to find out what works/doesn't work at this size. Clint/Compass Project would be worth talking to, he's made a few birdsmouth spars and makes lots of oars as well.

Looking at the above, going to 45 -46 mm dia solid hoop pine might be the easiest/best solution if you decide to go stiffer but stay with wood.

Ian

[woodeneye]

Wow, thanks for that number crunching Ian! Gives me something to work on when the time comes I have some really hoop pine planks that I could use for it.

Another thing I could try later to reduce some weight from the alu yard is to taper it by slicing a long V out and then closing it up. This would help reduce windage as well as weight up top. This would create a slight tear drop profile which would still be quite stiff in the fore/aft direction wouldn't it?

I would then just braze the join with Durafix. I've used this stuff to repair car parts, and it's very good. Durafix Easyweld - making aluminium welding easy

[IanHowick]

Hmmm, not sure about the idea for tapering the alu spar, it would probably save only about 5% or so weight, and make that end vulnerable to buckling, both because you cut and bend it, but also because you're heating it.

A lot of the strength of these alu alloys comes from the heat treatment, heat it up again and it goes really soft. I think there are ways to heat harden it again, (24 hours in a hot oven?), but times I've had alu welded, the joint area has been really soft.

Things in your favor are this kind of welding might not make the alu quite so hot, and the 3 mm wall alu tube you have is probably way over strong to start with.

It might work, but then again it might not - be interesting to see!

Thanks for the link to the Durafix Easyweld, looks like a useful product.

The biggest problem with alu is it only comes in manufactured sizes. If you could call up a manufacturer and say you wanted for example, a 42mm OD tube tapering to 25 mm OD at one end, 2.5 mm wall in the middle tapering to 1.5mm wall at the ends, it would be much more useful stuff, performance would come up much closer to carbon (where you can specify exactly what you want in this regard).

Ian

[Boatmik]

Howdy - with cutting and shutting a spar to make it tapered - only very experienced welders were able to save much weight - the smaller the spar the harder it is to save weight too. Also the additional thickness of the weld material can mean you end up with similar bend characteristics that you had before.

The classic way is to get a spar with a too small wall thickness for the middle and sleave it in that area - just gluing or rivetting the sleeve in place inside or outside.

I would go sailing first just to see how the boat performed with the untapered spar.

MIK

[woodeneye]

I would go sailing first just to see how the boat performed with the untapered spar.
MIK

Yes, that's the plan. I was just getting way too far ahead of myself...

[woodeneye]

I tried out my new aluminium pole in the driveway today, and it's made an enormous difference to the way my sail looks. It's now setting beautifully and looks every bit as good as as the McNamara. So for my sail the yard needs to be as stiff as possible.

Naturally I want to get sailing with it as soon as I can now to compare how it performs with the new yard, but I just know from looking at the sail it will be a no contest. I just wish it was lighter than it's 3.2kg that's all.

The first pic shows the new yard under very high down haul tension and the sail sheeted in quite hard. By comparison my original yard would have looked like a banana.

As per Keyhavenpotter's suggestion, the sail is attached via a carbineer to a saddle riveted to the pole. It works well so the tension along the yard is adjusted only at the peak. This is definitely the way to go. I just need to replace the carbineer with a small shackle as the carbineer is just a tad long. This will be better and that crease where it attaches will then disappear.

I have removed the ring that attached the yard to the halyard at the mid-point, and this has allowed the yard to be hauled up further, right up to the block. Remember, you are hauling the halyard which is attached to the base of the yard, so a block isn't required on the yard either. Not having the ring at the attachment point hasn't made any difference to the effort required to hoist the sail.

Attachment 149791Attachment 149792Attachment 149793Attachment 149794Attachment 149795

I've also been busy building my new trailer. The hull sits on longitudinal bunks at the rear, and a horizontal one at the front. Loading is easy as the tipping rear bunks locate on the outside of the GIS's two skids, and she tracks nice and strait as she's hauled up. The small winch will help when the boat ramp is steep. I just need to find or make a small jockey wheel.

It's an Easy Trailer kit imported from Taiwan by Carlex in Australia. I have been quite impressed with the quality, and doing it this way gets you a good hot-dipped galvanised trailer at far less than a custom made one. I saved at least $1000. All the bolt holes lined up and there were no missing parts. I bought the version rated for high speed, and it comes with bearing buddies as well. It should cope easily with its load which is less than 15% of of it's rated capacity! The Easy Trailer folks are very helpful and friendly and even included some freebie parts and some promotional items.

Here's Hakuna Matata sitting on her new bed. I like too that it's low enough to rig on the trailer, so I won't need a dolly for launching and retrieval any more.
Attachment 149815

[IanHowick]

Hi Bruce,

Good to see pictures of your sail with the stiffer yard, hear that it sets much better with it. I posted a long time ago that I thought the yards needed to be two to three times stiffer than the existing spec so good to see that is starting to be confirmed.

(Especially as I have already committed about $800 on the basis of this opinion!)

Be interesting to see how it goes on the water, how it manages gusts when you're powered up for the lulls.

My theory was more or less as follows, I'm curious to hear what you think having seen your sail with a yard from both ends of the stiffness range:

If the yard is bending 50mm with only 10kg, then with the downhaul tensions that we are using, the yard is already bent to the extent of the edge round of the sail before full downhaul tension is on. More tension will not bend the yard more, but the increased tension will become concentrated in the line between the yard attachment point and the downhaul attachment point on the boom. At this point, the luff will not be as tight as it can/should be.

With the stiffer boom, it is reaching it's full bend at about the maximum downhaul tension we can apply, at this point the higher tension is distributed better across the full front half (luff) of the sail, which should give better control of its shape.


Do you have an approximate figure for the amount of bend in your new yard under sailing conditions, i.e. rigged and with full downhaul tension on?

Great to see so much development of these rigs going on!

Regarding weight, you might be able to get a piece of un-tapered carbon tube of the right size for a better price than my tapered one. After sorting out the quote for my mast plus yard, I changed the yard to a cheaper/easier to make single taper, but added some extra to the mast spec, overall quote price stayed the same. Looking at 76mm ID/1.8mm wall carbon tube, I'm guessing about $140-$150 per metre, so about $500 for 3.6 metres, at a weight of about one third of the alu one.

Ian

[woodeneye]

Hi Bruce, Good to see pictures of your sail with the stiffer yard, hear that it sets much better with it. I posted a long time ago that I thought the yards needed to be two to three times stiffer than the existing spec so good to see that is starting to be confirmed. Be interesting to see how it goes on the water, how it manages gusts when you're powered up for the lulls.

My theory was more or less as follows, I'm curious to hear what you think having seen your sail with a yard from both ends of the stiffness range:

If the yard is bending 50mm with only 10kg, then with the downhaul tensions that we are using, the yard is already bent to the extent of the edge round of the sail before full downhaul tension is on. More tension will not bend the yard more, but the increased tension will become concentrated in the line between the yard attachment point and the downhaul attachment point on the boom. At this point, the luff will not be as tight as it can/should be.

With the stiffer boom, it is reaching it's full bend at about the maximum downhaul tension we can apply, at this point the higher tension is distributed better across the full front half (luff) of the sail, which should give better control of its shape.

Great to see so much development of these rigs going on!

Ian

Hi Ian

Basically, one’s set ups for cruising and racing are the opposite from one another. When adjusting for racing, you generally power up for the lulls, but for cruising you power up for the gusts.

You are partly right in that yard bend is limited by the curve of the sail. However, I’ve found that luff tension isn’t affected by a bendy or stiff yard at all, or at least it shouldn’t be if it’s set up correctly! This is because downhaul tension from the luff should only be between the two attachment points, ie. between the boom and bottom of the yard. If downhaul tension is affecting the tension along the yard as well, then things are not right. In my last post I mentioned attaching the lower yard to the sail by means of a shackle. When Keyhavenpotter first mentioned this it was like a light went on, and the way this sail works all became clear to me. Tensions between the boom and bottom of the yard, and between the peak and bottom of the yard must be independent in order to set up the lug rig properly.

The other thing is that downhaul tension is one thing, but the tension from the mainsheet has a far greater effect on the leach. Now I come back to what I said about you being partly right that the yard bend is limited by the curve of the sail along the yard. What was happening with my bendy yard, was that the tip was bending more than the curve of the sail once hard mainsheet tension came and then it bent some more! This resulted in a horrible thing happening to about 2/3 of the leach from peak down. The leach just became floppy and flapped around. I have never seen this in a Bermuda rig which maintains its leach tension so it was quite perplexing.

What I’ve discovered through my problems is that the balanced lug requires a stiff peak to support enough tension between the peak and the clew. There is already plenty of twist at the top afforded by the way that the yard attaches at the mast to not worry at all about the yard needing to flex at the tip. It will depower in a gust anyway, so any additional flexing at the tip of the yard isn’t required.

Well, that’s my take on how this rig works, for the moment anyway! What I’ve learned iso far is that I had to stop thinking how a 3 sided Bermuda rig works and then work out what is happening with a 4-sided one. Keyhavenpotter really started me on the right track with the attachment of the luff to the lower yard, and then things just went from there. The key really is getting all sides worked out so that they are independently adjustable.

[Boatmik]

Great comments - look forward to building up some sailing time in different conditions.

If it clearly improves performance of the basic rig setup without making the boat harder to sail in stronger winds I will edit the wooden spar drawings as much as I dare without it all getting too heavy.

MIK

[woodeneye]

Do you have an approximate figure for the amount of bend in your new yard under sailing conditions, i.e. rigged and with full downhaul tension on?

Great to see so much development of these rigs going on!

Regarding weight, you might be able to get a piece of un-tapered carbon tube of the right size for a better price than my tapered one. After sorting out the quote for my mast plus yard, I changed the yard to a cheaper/easier to make single taper, but added some extra to the mast spec, overall quote price stayed the same. Looking at 76mm ID/1.8mm wall carbon tube, I'm guessing about $140-$150 per metre, so about $500 for 3.6 metres, at a weight of about one third of the alu one.
Ian

Ian, I ran out of time this morning to comment on the rest.

That first pic above is pretty much at maximum bend for the alu yard under full downhaul and some mainsheet tension. Full mainsheet will add a bit more, however but I’m not really concerned about that at this stage, as long as the tip for the top half of the yard is stiff. I took that pick to show you how much bend can still be induced in a stiff pole, so what would that amount be do you think? Maybe 20-30mm perhaps? It will be interesting to see how your carbon ones go.
https://www.woodworkforums.com/attachments/f169/149791d1286699743-building-shesha-hunter-valley-gis-australia-dscf0386.jpg

I’d love to get my hands on a straight carbon tube. For now, I just want to see how she sails with this alu one and go from there. If it all works out I will fork out for one as a 2kg weight saving at the top of the mast is very worthwhile I think as I won’t have to go on a special all-beer diet to look like a Finn sailor. Carbon spars are at the crossroads right now where I think we should start seeing prices start to fall fairly soon.

MIK,
On the trailer I can see much more power up there with the new spar, so I’m sure that sailing with it will show up a nice gain, but of course things are likely to be livelier to handle as well. If so, there are still sail settings to adjust, so that if things are too lively, I can take some of that extra power away by tensioning the peak and clew some more. I think I’m going to add a small clam cleat to the peak to make adjustments up there quick and easy. They are cheap and it means I can work to some marks for different anticipated conditions.

Later on I have other things to add such as a kicker and a tube style mainsheet traveller, but will hold off adding those things until I’ve had a few sails with the set up as it is so I can compare any differences to what was before without wondering what amounts, if any, are attributable to the other stuff. Small steps… J