Bend in the Mast

[Jonno Snell]

Hi all, probably a stupid question but I notice in photos around the web there is a lot of bend in the masts.
I would like to know how that comes about, is something that 'just happens' in stronger winds as the end of the boom gets lower towards the stern? Photos of me on the water show my mast straight, but was 8 knot day.....
Sorry if stupid question, new to sailing and want to learn with my kids.

 

[torrid]

The mast is specifically engineered to flex under a load. It helps de-power the rig when the wind comes up.

The boom may flex where the vang attaches. This isn't particularly desirable, so there is an inner sleeve to help stiffen it. Older boats may not have this sleeve, though.

 

[Wavedancer]

In addition to what torrid wrote,
Even in light winds, racers put on some vang which will bend the mast.

 

[Voodoo 158546]

It's all about sail shape.
With no tension on any of the control lines and your mast dead straight vertical, the laser sail has a 'saggy' chord.
Right behind the mast in its central two quarters you would see it looking very un aerodynamic.
The laser sail is cut with this extra cloth built in.

See the fold where the sail can't lay flat.
Also look at the curve built in to the luff.
The sail only becomes an aero foil once the kicker is banged on which pulls the centre of the boom down and the forward end of the boom forward also bending the mast ( by design ).
Part of the art of laser sailing is using your judgement to constantly assess and adjust the shape using the five control lines.

 

[Jonno Snell]

Thank you everyone, I must lay the sail out and have a look at the shape. I'm brand new to this.
Here's a pic of us on my first ever sail in light winds, was about a whopping 7 knots so don't laugh.
I can see the lines in my sail, should I have let some outhaul out to get rid of the creases and fill the sail more? ... give it more 'belly'
That was the rig was set for me for the day. Sorry if this seems dumb. I appreciate any guidance.
J

 

[steveo1]

Jonno, you need a tiedown on the end of the boom to sail clew, this will help when you sheet in the sails.

Just a rope, bout the thickness of the kicker rope and around 18 inches long will do it.

Run this rope through the clew( metal hole in the sail where it attaches to the boom end) then under the boom back through the clew, under the boom again and tie ends with a reef knot, leaving a gap between sail and boom of a finger thickness.
Make sure your traveller rope is tight.

Good luck Steve

 

[andyatos]

Hi Jonno,

Here's a few more tips about setting your sail shape. The first photo below is Lasers sitting on the beach.

Several things to notice here. First, all the masts are straight, somewhat similar to your photo. And the stern end of the booms are high. That's because there's no, or very little, vang tension. Also, because they are on the beach, the main sheets are completely loose. So again, there's no tension on the mast and no bend. The red arrow shows vertical creases on the sail at the luff. This is from a lot of cunningham tension, where the sailor likely just left the cunningham tensioned between sailing sessions.

You'll also notice that the 3 boats on the left have loose outhauls which give those 3 sails "belly" as you say. The boat on the far right however has quite a lot of outhaul so the sail is flatter. The sailor probably did this to flatten the sail so it wouldn't flap as much while on the beach.

The next photo below is a couple of guys racing in close proximity while beating up wind.

Notice the difference in the bend of the mast of the boat on the right in comparison to the boats on the beach. Also notice that the water is showing quite light winds but this is the mast shape you want in those conditions when going upwind. Also notice how low the end of the boom is.

The sailor is creating most of this mast bend with the main sheet by pulling the main sheet in almost all the way and pulling the end of the boom towards the deck. You can see this by how close the end of the boom is to the deck. But if he were to ease the main sheet to let the sail out a bit, he could maintain this shape by having a tensioned vang. When going upwind in light winds, this is the mast and sail shape you want.

A trick for tensioning your vang without having to pull really hard on it is to point high, pull in the main sheet so the boom end is very close to the deck (referred to as "block to block") and then tension the vang. You can then let the sail out and the mast will still have the bend in it.

In this photo you'll also notice that the leach of the sail is very straight and has a lot of tension where it runs from the top of the mast to the end of the boom, a result of pulling the end of the boom towards the deck. This helps for going upwind. But look at the bottom of the sails where the red arrows are pointing. Look at how full, or how much "belly" the sails have. This is because the sailors have the outhaul set to a loose setting. So, even in light winds, you want a bent mast to match the cut of the sail but a loose outhaul with a full sail shape for power.

Finally, notice the creases running diagonally across the sail where the cyan arrows are pointing. You would think that the sailors would want to remove those but they don't. That's because they want the point of maximum camber in the sail a bit further back for going upwind. Pulling on some cunningham would remove most of those wrinkles but doing so would move the location of maximum camber further forward.

If you go on YouTube, you can find a number of Laser rigging videos. There's also a ton of sail rigging info at "Improper Course" Here's the link to that web site.

Cheers,

- Andy

 

[Jonno Snell]

Thats superb, thank you so much for taking the time, we appreciate it.
Bring on the wind! We can't sail on a wind with any North in it as our lagoon is on the southern side of our tiny island and is surrounded by Norfolk Pines, and guess what we have forecasted for the next tens days!

 

[andyatos]

Where is that lovely spot?

- Andy

 

[Jonno Snell]

Thats our lagoon on Norfolk Island. We're a small 5 x 7km island about an hour flying time south of New Caledonia and 3 hours east of Brisbane, Australia. An absolute gem of a place, don't lock our cars or house etc, know most people. Lots of water sports and as well world class facilities in a lot of other common sports such as tennis, pistol, clay, golf etc. At the moment about 2,000 people on the island at any given time. Sailing used to be big with lots of lasers, its just starting to come back with us being a group of mates with 4 boats, hence the questions.
It is the homeland of the descendants of the Mutiny on the Bounty - Bligh and Christian.
Here are a couple more pics
The lagoon is tucked behind the ring of pines. Thats our golf course. Some do sail out to the back island, about 7 ks. We go out there for fishing weekends to a fishermans cabin. The island is an uninhabited bird sanctuary.

This is how we get our freight...

I think we do it right... a sail with the kids, bbq and couple of beers....

The lagoon from anther angle at low tide (same table). There is another bay in the same lagoon just round the corner, probably same length. At high tide waves cover the reef to the left, and on certain swell direction waves run along that point in the bay you can see. Its where the kids learn to surf and where our school hold the swimming carnival. Its Norfolk's pool.