Thread: Carbon Spars on Storerboats

Hi Michael,
I will be watching this with interest, as someone who is in the midst of spar building I have been thinking about the weight aloft and the pendulum effect of the mast when the boat pitches around in a choppy sea. Of course, having only seen video’s I’m having to use my imagination rather than experience. It’s amazing how the mind wanders as you slowly plane Doug Fir into piles of wood shavings!

Clearly there is a benefit to be had from reducing weight generally, especially in the mast and ends of the boat, but at the same time the GIS is designed be a boat that it economical to build and fun to sail. For the time being I will be sticking with the standard spars but it would be great to have some boat-on-boat testing at some point to see how all these tweaks and changes work in the real world.

Hi MIK,

What about aluminium spars. For my OZRacer what would be the ideal tube thicknesses for the balanced lug rig option?

I pass Capral Aluminium on my way to work everyday and I am considering and off the shelf style solution for the three spars.

It's not like there are racing fleets of Storer boats yet (it would be nice for that to happen one day!) so it's not like going the carbon way affects much. The big advantage is in reducing the weight aloft, and any boat will benefit from that. Each kilogram of weight saved above the deck will be 5 times more important than the same weight saved in your hull and equipment. (Don't ask me how I calculated that, but it's about right, I think!)

If you have a loose footed sail, the mast and boom make no difference to the sail at all. So if you want to sip from the carbon cup, then a stiffish carbon yard will make the biggest difference to your boat's performance without breaking the bank. Paint it a cream colour and nobody will know. Of course it will cost more than one you can make yourself from wood, but this single spar in carbon can spare you from a lot of fiddling around trying to get it to match your sail and make it a lot easier to handle too. Money well spent I suggest.

Howdy,

The big problem with alloy spars it that it can be hard to find ones that are strong enough for the mast and light and right bending for the yard and boom.

The boom is the least critical one.

Problem with masts is that a freestanding mast needs to be (for the PDR) about 62mm with a 2mm wall or thereabouts wall with an internal sleeve fitted at deck level to prevent denting and prevent excessive bending too low.

Most aluminium companies have rationalised their inventories and the right size alloy is just not available as it was 20 years ago.

For example, I know some other designers are specifying 50mm extrusions for similarly sized boats or smaller two person boats (almost double the righting moment) but I KNOW that some will break and some will be too heavy.

The boom is probably not very important.

The yard is quite important.

Building spars is actually one of the most pleasant areas in boatbuilding - and that's from me who is always impatient and in a rush.

The alloy yard would be about the same diameter as the wooden spar, around a 1.3mm wall. It might need a sleeve at the mid point, but we would have to see how it goes to know.

MIK

MIK

I met the young man who developed the Deben Lugger at the Beale Show. His rig is all carbon, so may be the first commercial full carbon tubed lugger on the market.



It turned out he used the same supplier I used. he found them very helpful and they offered to use standard stock tubes with an extra wrap where needed. He was very pleased with how things turned out.

For the smaller rigs it was great that they already had a 40mm to 20mm tapered mandrel which is identical to the Scow yards. The lightness is wonderful and astonishes people who lift them. Also great that when the rig falls down around your head nothing gets hurt or damaged.

Carbon tubes do bend differently to wood though. at first they bend easily, at least my very thin walled ones did. Then they stiffen up. Then bend very sweetly. I found they work better and better as the wind strengthens. Never quite managed a good light wind set though.

Costs were about equivalent to making from wood and very much cheaper than bought alloy tubes as used here.

Brian

Sounds like you can get them a lot cheaper than we can - or from the suppliers I have seen anyhow.

McConaghy's would be the best quality in the world - brilliant builders and on the forefront of technology
http://mcconaghy.com.au/store/defaul...on-fibre-tubes

Carbon Fibre Express
http://www.carbonfiberexpress.com/in...8f6ad0dc4f02d5

And current favourite C-Tec from New Zealand
http://www.carbon-tube.com/round.php

MIK

If you add Carbon Fibre Tubes UK for a UK supplier.

Carbon Fibre Tubes

Prices were about £30/metre 4/5 years ago. Could be higher now I guess.

I think Goat's bigger sail would need a thicker wall tube than I used for the 65 sq ft Scow. I used 50mm x 3.5m for the mast, 50mm x 3.0m for the boom and a tapered 40mm to 20mm x 3.0m for the yard. this one was not listed but they stock as a standard size - possibly for oar shafts.

Brian

We have the numbers for the carbon spars courtesy of Ian in New Zealand.

MIK

Originally Posted by keyhavenpotter

If you add Carbon Fibre Tubes UK for a UK supplier.

Carbon Fibre Tubes

Prices were about £30/metre 4/5 years ago. Could be higher now I guess.

I think Goat's bigger sail would need a thicker wall tube than I used for the 65 sq ft Scow. I used 50mm x 3.5m for the mast, 50mm x 3.0m for the boom and a tapered 40mm to 20mm x 3.0m for the yard. this one was not listed but they stock as a standard size - possibly for oar shafts.

Brian

Off the shelf carbon or aluminium would work for a yard or boom, I think. Woodeneye had success with an alu yard, check his specs on his thread. The yard stiffness has to match the sail cut however, changing wood to alu or carbon yard could cause problems depending on how the sail is cut.

Carbon 40 mm dia by 2 mm dia wall tapered or not would work for the yard of a GIS. A carbon boom would probably want to be a bit heavier - say 2.5 wall and or greater diameter, especially if sail is loose footed. However, there isn't a great deal of 'bang for the buck' in saving a kilo or so at boom height - better to stay with wood, I think Woodeneye's new box boom construction and dimensions are about right.

Mast dimensions given by keyhavenpotter above are for the stayed rig of a smaller boat (66 sq ft sail, single handed), and would no way work for the unstayed rig of the GIS. I don't think you could find an 'off the shelf' carbon tube solution to the GIS mast, it's unstayed so forces change dramatically as you go up the mast so it needs to be engineered for that. Best to go to a dedicated spar maker if you're looking for an unstayed mast of this size.

Also be aware that carbon comes in a wide range of specs - from 50-50 carbon glass up to the highest end of 'high modulus' carbon. Stiffness variation of perhaps 100% across this range. Prices vary accordingly of course. My spars are standard modulus, which is about 90 Gpa, so if you're getting a quote, make sure you understand what you're getting.

More details are available on my thread and Mik's wiki.

Ian

CST Carbon Fibre Express - Online store for purchasing carbon fibre tubes, rods, profiles, spars and accessories, express shipping worldwide got back to me in relation to my enquiry about a suitable tapered tube for my yard.

I asked for a 3600mm, stiff tube tapering from 38-40mm down to 20mm.

They don't have any stock tapered mandrels close to what I'm after.
The only mandrel they have in stock is a straight one that is 32mm which can be used to manufacture a tube with a 3mm wall to give me a 38mm OD.

Cost is about $550 + GST for a 3.6m length, so about $600 plus freight.

Lead time is roughly three weeks from time of order.

Will keep looking...

You would look like a genius if you made one using the specs that are becoming clear. Have a look at the UK Cherub website for info on DIY.

Originally Posted by Boatmik

You would look like a genius if you made one using the specs that are becoming clear. Have a look at the UK Cherub website for info on DIY.

I'm hearing you! I just have to brush off the memory of a big disappointment when I went down this path in 1971/2.

Production plastic Windsurfers were just starting to appear in South Africa and I had a sail on one of the very first of them (or at least I tried!). I think they were copies of an American design. When I saw the glass fibre mast, I thought it would be cool to have one for my Dabchick. I borrowed the mast and took it to a friend of my Dad's who had a business making all kinds of glass fibre products to see what could be done. His first reaction was that the windsurfer mast had way too much resin in it and it was too heavy. Wow, I started to get excited, because I thought it was quite light as it was. It was certainly much lighter than my aluminium mast.

Don thought that we could easily make one that would be plenty strong enough and it would weigh 1/4 less by squeezing out most of the resin. The catch was I had to make the mandrel.

My Dad and I went to a lot of trouble making the wooden mandrel to Don's specs. The sad part was that the mandrel would not release and when desperate measures were taken to separate the mast, it got smashed along with the mandrel.

However, Don didn't use the hot wax method that that the Cherub guys use, so I'm a little encouraged!

Originally Posted by IanHowick

it's unstayed so forces change dramatically as you go up the mast so it needs to be engineered for that. Best to go to a dedicated spar maker if you're looking for an unstayed mast of this size.Ian

I have to admit to being slightly confused with the attitude to using stays. Mine are simple thin dyneema string. Both shrouds stay attached to mast head and gunnel and the forstay just clips on. Lift mast and clip forestay, takes but a minute.

And what benefits do I get.

Better upwind pointing
stable masthead
able to use a lighter section mast
use an off the shelf 50/50 glass carbon low cost standard tube
hugely better strong wind performance
concave mast bend on port tack creating perfect sail shape

It's a no brainer. The hull has to be very strong in the mast area anyway and it has to be better to spread the loads around this area rather than all at the short support structure for an unstayed mast.

When my son ordered his new lug sail from Sanders he asked whether he should stay or unstay the mast. Pete sanders insisted it had to be stayed.

Think about it. Think about how the lug rig works. It need a stable vertical mast. It needs a stable boom and it needs a matching sail and yard combination.

Think about what is happening to sail shape on a lug when the mast tip bends off to leeward. It's not like a bermudan sail which open the leach and lots can be achieved. The yard does all this in a lug. But it needs a stable masthead.

Can all our Scows, the most people racing lugsails anywhere in the world, be wrong?

Sorry to rant but saying you cannot buy an off the shelf tube and you have to buy a really expensive engineered tube just because you cannot see that adding some dyneema string gives a better solution in every way is doing my head in.

Brian
Brian

Originally Posted by keyhavenpotter

Sorry to rant but saying you cannot buy an off the shelf tube and you have to buy a really expensive engineered tube just because you cannot see that adding some dyneema string gives a better solution in every way is doing my head in.

Brian

Hi Brian, yes I very much agree that there is great potential to follow the direction of the Key Haven Scows and do these Lug rigs with lightweight, un-tapered alu or carbon/glass masts with stays. I think it's a great solution, and something I have in mind for a possible later project.

As far as the GIS goes, I thought of going this way at the time I was looking at the carbon spar route, but decided to stick to the unstayed mast and engineer it to be strong enough in carbon.

My point wasn't that you have to buy a really expensive custom engineered solution, just that if you do stick to the unstayed set-up of the GIS, you had better make sure any substitute mast is engineered accordingly.

The main things that steered me away from the stayed route (apart from not wanting to mess with Mik's design too much), was the risk of the whole rig coming down if one of those stays breaks, and the need to feed forces from the stays into the hull which hasn't been designed specifically to handle them. I guess they are issues that could be overcome, but it seemed easier to stick closer to the original GIS concept, and just make sure the mast was strong enough, which is much easier engineering to understand.

By the way, I'd been meaning to ask you the specs on the dyneema stays you used on your scow - what diameter, and was it strong enough?

Ian