Finding the chase and cutting to it

It wasn’t a terrifically warm or sunny Easter, but the week after it was. Time to erect the sail shade I had bought last year.

You waited eight months before putting it up?

When you put it like that, it sounds like a missed opportunity. However, there were reasons, not limited to the fact I couldn’t see how one person could do this on their own. All the shows I’d seen where a sail shade was featured had a team of people doing the task. Was it even possible that two people could install one safely?

1. Sails need anchor points and until the French doors were put it, we didn’t have a good one on the house.
2. Winter is not the time to be erecting a sail – no matter how waterproof it is, leaves, snow, heavy rainfall, and high wind do not make for good weather to be raising a sail.
3. We would not have been able to enjoy the sail, all the while, it is exposed to harsh conditions which would wear it out.

I have been patient and two weekends ago, we started to plan to location and install.

You make it sound like a military installation!

A little bit. Sails need to be secure: being waterproof is not enough to guarantee that once it is up, it won’t collect water, putting enormous strain on the fixings and to what-ever the fixings are attached.

Counter-intuitively, tautness is your friend and that allows water to run off and wind to skip over the fabric. That means the fixings need to be firm and attached to something strong.

Here comes our balcony, which needs to with-stand 1.5kN/m², so a very heavy individual can fall on to it and not break their neck falling to the ground because the rail has failed. The barrier is assured to do that. The sail can exert around 550N in a 60km/h wind. That’s one fixing point.

Of course, the nice shiny barrier is not something we want rubbed by a rope or metal fixing. An Augo Heavy Duty soft loop is our friend here, built to secure goods on ship and on HGVs, they form a strong fixing point for the carabiners that came with the sail.

Next fixing point is one of our fence’s steel reinforced concrete posts. The Augo straps came in handy here, being just long enough to be fixed round the post with a carabiner and a turnbuckle to secure the sail, and give us the chance to tighten everything up once in situ.

Finally, our courtyard has a double layered 1.8m wall on one side, allowing an anchor point to be fixed to the top of it.

The sail came with turnbuckles, rope, and carabiners. With the Augo straps, we were all set to go. Last night, we did the deed.

Only to find that while we did raise the sail, it was a little baggy. Remember how I said tautness was our friend.

Yes, but I really don’t see why some sag in the middle is such a bad thing!

A 5m equilateral triangle (which is what our sail is) has an area of 10.83m². (This is from Pythagorus: a 2m equilateral triangle has a √3m height. A 5cm triangle is two and a half times as big, so it’s height is 5√3/2 – a triangle’s area is a half base time height, so that 5/2 * 5√3/2 = 25*√3/4).

Any chance it has to “billow” makes that a huge area, up to 4,970N for a windspeed of 25m/s, it’s why sails were so effective in powering ships.

The same chance to billow, provides a reservoir for rainwater. A cm of water on the sail is equivalent to 500kg!

The sail being as taut as possible harms no-one.

But with the nylon rope that came with the kit, we just couldn’t get it the materials to work for us. Having seen steel rope used for other sails, I bought a 4m, 4mm 7×19 grade section of rope from our local chandlers. A pair of thimbles and four wire grips, and I set about attaching the steel rope to two turnbuckles.

As we already had the rope up from yesterday’s efforts, I put in the cable.

As I started tightening it, I realised I hadn’t removed the old rope. At which point, I had a problem to solve as I hadn’t done something which would have made the task a hundred times easier. Simply putting the turnbuckle hook outside of the rope would have allowed me to easily remove it. Instead I wasted twenty minutes sorting that out, but it was a much easier job to do on my own that initially putting up the sail.

Because the steel rope is rigid, the turnbuckles give a set tension. It pays, from that point of view, to tighten the rope either first thing in the morning or just before sunset. That allows slack to be built in for when the sun it at its apex. I am now waiting for that moment to come.

Of course, to get it really drum tight, a lever can help me achieve that. From my engineering days, I am going to use a chisel blank I made in 1995 to help me get those ropes as stiff as a tuned guitar.

We’re finishing that tightening this evening, so we can enjoy the sun and shade for the rest of the summer.

You called this article “Dark powers”: not sure this is what I was expecting…

As a child, I was taught you can shade something to keep it cool or try to cool it after it gets hot.

Shading something is always easier.

Having put everything in place and down on paper, I think it could be done by one person next time.