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Chips Howarth answers a couple of tricky dinghy sailing questions

Chips is currently the Performance Product Manager of Selden Masts, managing all aspects of the design, development and supply of the Proctor spar range. Chips is also the personal coach of the top GBR 470 team, Nick Rogers & Jo Glanfield, coaching them to a 1st in Hyeres in 2001, this following his role as 29er National Coach where his boys dominated with a 1st & 2nd in the 2001 World Championships. As a sailor, Chips has campaigned a 470 on the Olympic circuit and been a National Champion in no less than 9 dinghy and sports boat classes, as well a European and World Champion and Endeavour Trophy winner. He most recenty notched up a win at the Fireball Worlds.

Paul Lewis asks:
I race dinghies and wish to understand if there is a way of setting the mast prebend on a fractional rig by examining the shape of the mainsail. Having set the prebend, is there a preferred sequence of other sail and rig adjustments to tune the rig to the conditions on race day?

Paul,
This is a good question and probably needs input from your sail maker too. The (what I would consider very basic) method I use would be to hoist the mainsail on the settings you currently use, pull a 'heavy weather' amount of kicker and cunningham on the sail under very light wind load (in the dinghy park). I sometimes like to do this with the boat lying on its side to allow the sail to 'shape' under its own load.

If this sail load generates a 'bubble' against the mast, this suggests the mast is too straight for the luff curve built into the sail. If this bubble is behind the spreaders, I would cure this by either winding the spreaders back (or increasing the rig tension, although this has other affects including jib shaping). If the bubble is lower down, look at easing the deck level control (strut, chocks etc..).

If the mast under these loads creates creases and/or a 'fold' from the spreaders to the clew of the mainsail, this suggests the mast is over bending for the luff curve and should be straightened by angling the spreaders further forward.

There are other factors to take into consideration, such as, are you using the correct mast section? And is the ratio of luff curve to broad seam correct to create the shaping. I would always recommend consulting the sailmaker's guide to determine the recommended pre-bend and the mast section inertia it is cut for.

Chips


Charlie Muir asks:
Given the high speeds and thus large induced wind component in downwind dinghy asymmetric sailing, how do you tell the difference between a shift and a straight gust? Which initially causes apparent wind to shift aft, and then forward again as the boat accelerates. Maybe I've just answered my own question, but for a gust you obviously want to take advantage of the extra speed, whilst on a lift you probably want to gybe relatively quickly to take advantage of a better angle to the leeward mark.

Charlie,
I have always struggled with this, and in basic terms, I would always say that with a high performance, asymmetric boat, the crucial speed and apparent wind advantage gain would be to stay in the pressure (gust) as long as possible as this will give you the most advantage (i.e. wind angle is less important than the wind speed). In reality, this theory works well as to stay in a 'cats paw' gust like you often see in a lake and offshore wind will result in you having to sail the gust at the best true wind angle for the majority of the time to sat in the gust for the longest.

This may be a more subtle thing than in an instrumented yacht, but you can calculate the optimum 'apparent wind angle' for a given wind speed for your boat and determine from the calculated true wind whether you are on a lift or header and gybe or stay-on accordingly. This can be achieved in a dinghy but is a more 'seat of the pants' calculation based on how much pressure you are feeling on the sheets, although I have seen it used to great affect in 470 regatta where the fleet spread over a mile wide down a run with the leader doubling his lead by running down bearing numbers and gybing in a lifted gust.

Chips

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