How to order a dousing sock: Our spinnaker dousing socks start at 16.5 ft of length and have increments of 2 ft. after the original length. The typical length of the dousing sock equals to the ISP dimension of your boat. ISP stands fro the length of the vertical line coming from the hoisting point of the spinnaker on the mast, down to the lowest part of the deck (not the cabin). Once you know this dimension, just select from the options and add it to your shopping cart and that's all! Feel free to contact us with any questions about ordering your Vela Dousing Sock.