Bang, Thump, and Thwack: Sailing Theory

Just a head's up: this is going to get pretty technical.

WW figures he has sussed out the problem Django has been having. At first we thought it was the ka-bangs and the ka-thumps that were the problem. To refresh your memory:

• Your ka-bang occurs when a wave hits Django's belly (between the two hulls), which also happens to be the salon floor. It produces a sound like a small detonation and has the effect of pitching you an inch off the floor, should you be standing on it.
• Your ka-thump occurs when your bow is heading into the seas and meets a cresting wave head on. Water is hard when you meet it at speed. The interesting thing in a cat is that you can have sequential ka-thumps separated by very little time. That's because each hull can produce it's own personal ka-thumps.

Well, WW believes the ka-bangs, apart from being annoying, are reasonably innocuous. The ka-thump is also not a terrible thing, unless it contributes to your ka-thwack.

• Your ka-thwack happens when the sails back and then snap into place (I told you this would be technical). If you are sailing close to the wind (pointing as close as possible to straight into it and still able to sail), from time to time, the boat will head into the wind, the sails will go aback (oh nevermind...they flutter) and then, because you have an autopilot forcing the boat back on course, the sail will snap back into action with considerable force. A wind shift or your ka-thump can contribute to the start of a ka-thwack, whereas your ka-bang doesn't. Both your mainsail and your genoa can ka-thwack and affect their supports (mast and forestay) as they do so.

WW thinks our problem has been ka-thwacks of which there have been many as we've beein sailing almost constantly into the wind. Each of them results in a cracking fexion of the mast. Carrying on in this fashion for three days at a run will ensure you fulfill the maxim: While you're sleeping, your boat is breaking.

Here endeth the lesson.