One of the beauties of the Flat Earth Kayak Sails rig is its simplicity. Apart from the stays (the forestay act as the uphaul) and the sheet there are no other lines such as kicking strap (vang) between mast and boom or Cunningham (tack) downhaul line which are found in more complex rigs. However, this does mean that there is not a lot holding the sail and boom down on the mast. The boom gooseneck is not fixed to the mast but slides over and is free to rotate round it.
Many people are worried that launching in surf with a furled sail on deck will result in a wave washing the sail and boom clean off the top of the mast. There are various solutions on the internet. Some advocate a large quick release cable tie round the boom just above the gooseneck. Well I tried that and there is not enough friction it just slides up.
Others have devised a number of complex ties that hold the boom down but these can get tangled up and interfere with boom rotation.
My solution is very simple. Once the sail is furled I just tighten the sheet and cleat it. This prevents the sail from sliding up the mast. In this photo the bow is at the right and the sheet is the thick red line which is tight and leads back to the cockpit cleat on the left. Just remember to let the sheet off before launching the sail.
If the wind is off or cross off shore, there is an even better solution. Keep the sail up in the wind and out of the surf and use it to power out, great fun!