The abseil shackle I use for the boom preventer is rigged on a Bav 38 as follows:-From port side cleat up through the abseil shackle down to the star side cleat back to winch or aft cleat. you need to keep it tight so the winch is better.I have been useing this for 8 years and it works, I sail in the Biscay so lots of swell, it's a no brainer.It's on my web site in year 2011 and about year 2007www.scanmar-odysseus.co.uk