Mechanical properties.

6^th May 2024

Taiohae, Nuku Hiva, Marquises, French Polynesia – Anaho, Nuku Hiva, Marquises, French Polynesia

UTS, creep, yield strength, Young’s modulus, stress vs strain. These are all terms that ring in the ears of mechanical engineering students*. These terms have also been ringing in our ears as we have tuned our new rigging and sailed with the confidence that our mast isn’t going to come crashing down.

One of the great properties of Dyneema is that it is stronger than steel (UTS), but one of its problems is that it creeps and all the splices need ‘setting’. As we left the sheltered waters of Nuku Hiva and our sails started to put load onto our new lowers ,we watched them creep, and felt the splices becoming harder and harder settling into their new high stress life.

As the lowers crept, and they became looser and looser, the mast started to resemble one of the bananas that hung on the gantry, and something had to be done. We slipped over onto the other tack and armed with no more than a couple of screwdrivers we undid the lashing and attached the bitter end to the jib sheet. Undoing the frapping knot we felt the jib sheet take the tension of the mast, and we tightened and tightened the Dyneema lashing. With everything retied the mast was once again looking like a banana, but on the other tack. The starboard lowers had now crept.

Once again we tacked and repeated the process, pulling more and more line through (on the other side). We built more and more tension in the lowers as the creep exited the rope and the splices became tighter and tighter. This was nearly as scary as sailing with broken lowers, but we knew that the UTS of the Dyneema was high, the creep was now low and with every tack the mast became straighter and our confidence grew.

Now ensconced in a bay that was straight out of the book ‘landfalls in paradise’, the waves broke on the reef around of us while the palm trees swayed the trade wind that cooled us, our rigging work was still not finished**. Once again we undid the knots and worked more and more tension into the Dyneema, and with each mm we pulled on we checked that the mast was in straight and in column. As the Dyneema lashing became as tight as a guitar string it’s UTS wasn’t being tested and neither was the knowledge that had been given to us by Nic on “Mindelo” in getting Ruffian rigged and happy.

With Ruffian finally back in working order we could now have fun in the form of hiking the hills that protected us from the elevated trade winds. As soon as we stepped ashore and Brock’s wheels sunk into the white sand we were enchanted by the bay.

Along the shoreline not a leaf was out of place, and the local wildlife welcomed us. Dogs tentatively approached us, all they wanted was a quick sniff. The kittens, which had been frolicking in the dappled palm shade, had other ideas as they spied new playmates (us) approaching. They bounded towards us without fear and instantly adopted us on what was going to turn into their walk.

Skipping between our feet with their out of proportion paws and looking up at us with their oversize eyes they accompanied us along the beach, over the hills, through dense jungle and into a local farm. Still not spent they continued with us across sand dunes and along another endless beach while the sun baked down on them. Their little bodies held seemingly endless energy and their enthusiasm was infectious.

Worrying about their their longevity and well-being Fiona took a very charitable approach giving them shade under her wide brimmed hat and tried to get them to drink chilled water from her cupped hands. Sensing a easy way out of their walk home they them seemed to loose all energy, and Fiona succumbed to carrying these friendly little furballs home in her t-shirt. This was all while Iain looked on thinking that Young’s modulus wasn’t a measure of stress vs strain but something to do with the pulling power of young kitties.

Thankfully the kitties never made it on board Ruffian*** and we once again sighed with relief as our rigging is able to take the strain having delivered us to a picture perfect protected bay.

* Which Iain was one a very very long time ago.

** It’ll be a while until our rigging is finished as we will be constantly tuning the mast as everything settles and we put more and more load through the boat.

*** If one ever did it, would be called Frank, as Frank is such a cool name for a ships cat on Ruffian.