Posts for a sun sail

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Benoire

2798 posts

Uber Geek

#205217 3-Nov-2016 15:01

Hello

We're considering installing a Sun Sail over our raised deck. The sail will be attached to the house and then to steel poles that are attached to the outside of the deck in such a way that it considered to be pin-jointed and the bending moments induced by wind will be dealt with by the poles themselves. I believe that a 100mm bore with a 6mm wall should be sufficient for each pole.

I'm now looking at trying to find suppliers, does any body know of reputable suppliers that could do 2 poles near west Auckland? Does anybody have an opinion on the above as well as I'm open to suggestions.

Cheers,

Chris

Disrespective

1926 posts

Uber Geek

#1663369 3-Nov-2016 15:33

Don't know about suppliers i'm afraid (call around met suppliers from the yellow pages?) but I would recommend you look at capping the posts or they'll fill up with water and be prone to rusting out.

Fred99

13684 posts

Uber Geek

#1663374 3-Nov-2016 15:45

Those sound like very heavy poles - but I don't know how long they'll be or how large the sail.

Steel and Tube or another steel supplier should be able to sort you out with galv steel RHS as well as end caps to hammer on the top of the poles.

Steel will come in standard lengths - you'll need to check as it'll be something like 8m lengths - too long to load on a trailer. I've bought steel for that purpose etc from S&T in Chch, they'll cut it to length no charge.

You'll need to think carefully about how they'll attach to the deck as well as to the house. I've fitted a sun shade over one of our first floor decks. Fitting to soffits, I used some heavy galv angle back to back - about 40x40 x 5mm, fixed with tech screws into joists and spanning across joists so I could get the corners of the shade in the right place. A bit more complex than a shade sail as it's a canopy which retracts back under the eaves on a system of pulleys etc, but there's a lot of force on fixings either way.

Benoire

2798 posts

Uber Geek

#1663377 3-Nov-2016 15:53

Fred99:

Those sound like very heavy poles - but I don't know how long they'll be or how large the sail.

Steel and Tube or another steel supplier should be able to sort you out with galv steel RHS as well as end caps to hammer on the top of the poles.

Steel will come in standard lengths - you'll need to check as it'll be something like 8m lengths - too long to load on a trailer. I've bought steel for that purpose etc from S&T in Chch, they'll cut it to length no charge.

Sail is 15m2 plan area, anchored at the edges. Length of pole will be around 2.5m at the most so happy to have other suggestions for pole diameter and wall thickness.

I'm looking at Steel & Tube at the moment, will contact and ask for some prices. Yes end caps are necessary for aesthetics and water control!

Fred99

13684 posts

Uber Geek

#1663383 3-Nov-2016 16:14

That's quite large, perhaps the kind of size you mention is about right. I've used RHS, but I assume you want round poles. I'm not entirely convinced that the idea of deliberately having a lot of flex in the poles is a good one - experience sailing tells me that if you want to "depower" a sail in strong wind, you flatten the thing out as much as you can by tightening everything up, and the last thing you want is stretchy lines etc allowing it to "bellow out" and catch the wind.

Benoire

2798 posts

Uber Geek

#1663384 3-Nov-2016 16:21

Ah no, the poles are not designed to flex per se, but instead of transmitting the forces by a completely fixed moment in to the deck (like a mast of a boat is setup generally) I would want the poles to have a slight movement; rigid moment transfer would require excessive 'bonding' of the poles to the timber... pin jointed moment transfer relies on the vertical elements to absorb some of the movement before transferring the remaining forces through the fixings. I'm only thinking of a few mms of moment, maybe 5 at the most hence the size of pole.

SepticSceptic

2195 posts

Uber Geek

Trusted

#1663391 3-Nov-2016 17:17

I think you're on the right track - I used a 75mm gal tube, with 5mm walls for a sun shade, 3m x 3m.

However, that was only for two sides, the other two were 150mm sq rough sawn pillars.

I had the gal tube cut to 2x 3.5m lengths, plus 1m left over.

I think it was around the $100.00 mark.

Purchased and cut from a supplier of gal tubes in Warkworth - via TradeMe.

One metal post was bolted to a 300mm dia fence post, and the other, well, I kinda stuffed it. I used the remaining 1 meter length, and sunk that into the ground, and then bolted teh other 3.5m post to that.

I didn't sink the 1m post deep enough, and now the top of the whole corner is bent inward by about 6" - the post I had sunk and concreted into the ground has moved somewhat over the course of winter - it was sitting in a very boggy clay mixture. Rock hard when dry, and elastic when wet.

There is another supplier that will supply cut tube and bar - Steel North Shore, in Diana Drive, Wairau valley. I had a boat trailer drawbar supplied and cut by them.

gasgob

44 posts

Geek

ID Verified

#1663392 3-Nov-2016 17:18

Used to work in the shade sail industry A LONG TIME AGO.

The material of the shade cloth has a bearing on Pole specs. 90, 95% shade mesh loads differ with a significant jump when looking at PVC waterproof material, which I don't think you are - remember also, a wet sail also adds to loads. A well built quality sail has SS wire running along edges to the corners, reinforced corners just like a yacht sail. This all helps you to tension the sail with SS rigging screws to prevent to much flogging in higher winds. If the sail sags too much in the middle it will flog itself to death over time. Make sure the anchor points house-side are in securely, D plates with SS screws screwing into studs. You can rest in peace even when the wind blows 20-25 knots. Take down winter and clean, store for the next summer. Coolaroo mesh is good quality back in the day.

Instead of one rectangle shape 2 triangles overlapping can be quite nice - I reckon they look great ... all location dependent and triangles a little less effective to shade a big area. If you keep 4 sided try and get some twist in it if possible, 1 pole and anchor point (house - if possible) higher than the other 2. Keep the sunny side or corner with the most sun as low as possible to shade the area. Keep in mind, if both poles are higher that the points on the house it will simply run the rain but towards the house!

I would probably look at 5" poles but its really a best guess recommendation. Poles can get powdercoated or left galv. Angled poles (top half 45deg outwards) is a good option to get the sail and shade further out. Rigging screw and shackles all reduce the size of the sail by about approx. 200mm or more from pole to sail (going off memory).

Good luck.

Sharesies

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icekayak

50 posts

Geek

#1663959 4-Nov-2016 19:56

Could try this place, he has more than is listed on the website and will cut to length.

http://www.steelcuts.co.nz/

SepticSceptic

2195 posts

Uber Geek

Trusted

#1670830 14-Nov-2016 15:27

Watch out for cheap galv fixtures - I removed a shade sail that has been up one year. The smaller fixtures were nearly rusted up, the big coach bolts etc were all fine.

Obviously different standards in galvanising quality. Stainless steel next time.

k14

629 posts

Ultimate Geek

#1670839 14-Nov-2016 15:44

I'll be interested to see how you get on. We recently had a quote to get one installed at our place (Central Otago). For a 6m by 8m sail installed the quote was $6600!!! We were a bit taken back by the cost (and thus it has been put on the back burner). We could save $1k by installing the posts ourselves, which I probably would do. We were expecting around $4k but at $6600 I don't know how anyone can afford one!

Where did you source your sail from?