Its been a windy winter series at Hamble this autumn, with winds consistently in the 20 knot range, and often more. After 7 years away, coming back to sail Impalas has been great fun, and an opportunity to apply experience learned in other craft to help understand the fascinating business of getting to windward in a breeze .
The Impala’s light weight, easy sections and relative lack of beam contribute to the slippery performance that we all find so appealing , but upwind in a breeze these same attributes make it very easy for her to be knocked over in the gusts . So how should we set the boats up to perform best in these conditions? As ever with sailing , we still have as many questions as answers , but there are a few principles that will at least point us in the right direction.
Weight on the rail helps ! Its a great excuse to eat more bacon sarnies , but even lighter crews can help by making sure that as much sail handling as possible is done from the windward rail , and of course a full crew will be faster than a shorthanded boat in these conditions.
Sail shapes should be low drag (flat ) and wave tolerant( draft forward). The most important thing is to keep the forestay sag to a minimum as the greater the sag , the fuller the headsail becomes , and up goes the drag and heeling effect. Tighten up the rig until you cannot shut the loo door , and then some. You need to get hold of a rig tensioner to put some science and repeatability into this but the shrouds and lowers need to be very tight indeed to keep that forestay standing. Monitor halyard tension. In flat water the maximum draft can be as far back as 50% of chord , but in waves you will need to grind on your halyard to pull the max depth forward towards 30%. Any increase in wind will force the fullness aft again requiring yet more halyard tension . Halyards need to be marked and calibrated and records kept of fast settings for each wind strength. Fairlead positions will vary . At the top of the wind range of any particular sail you may be sheeting a long way aft of the mean position in order to depower the top of the sail and open the slot.
The amount of prebend required will depend on your mainsail. A full sail will need a lot , whereas a flat sail will allow you to keep a fairly straight mast. Loads of prebend will give you a nice flat main , but make it very difficult to control forestay sag, the mast comes out of column and essentially reduces forestay hoist. Luckily we have other ways to get a nice flat low drag shape. Max outhaul and halyard are the starting positions for these conditions. Lots of vang induces mast bend low down as well as popping the mast to windward and opening the slot. It is however not good for the boom and indeed Polly’s boom gave up the ghost 2 weeks ago after 20 years of abuse! The backstay flattens the upper 1/3 rd of the sail and should be played continuously so that in the gusts there is almost no shape up there , but let off in the lulls to recover the drive from high up. If you do let off the backstay , consider easing the vang in case you stall the leach. The Cunningham pulls mainsail draft forward , helps flatten the sail and perhaps most importantly , twists off the top 1/3 of the sail so that it contributes less heeling moment . Ideally this should be playable by the crew without coming off the rail.
Sail handling has to be much more dynamic than is required by more powerful , stable craft. The time honoured technique is to depower the main when the helmsman starts squeeking – but of course then its usually too late and you end up head to wind. Much better is the crew on the rail giving plenty of warning of a gust coming through so that the main is depowered , the backstay comes on and the helm gains a fraction of height just before the gust hits so the boat powers on through the gust at speed , rather than rounding up and stopping . All that needs a constant dialogue between helm , mainsheet and side deck so that the boat stays at the ideal angle of heel.
So far so good , but now we come to the questions. Which headsail should you carry in which wind strengths? To be honest I don’t know but the following might help . I think of the main and overlapping genoas as a combined aerofoil, with the top bit of the main sticking up and working on its own in a different way. The most important bit of this combined aerofoil is the slot. This is where the genoa increases the acceleration of air over the lee side of the main and allows the boom to work on the centre line .With this rig , the nearer the boom to the centreline , the better you will point. Contrast this with the single aerofoil of a Finn or Laser where the boats go upwind with the boom over the quarter. The top of your main needs to adopt this angle to the wind as it has no genoa in its lee, which explains the twist that may be present in a ¾ rig compared with the ( less complex) masthead rig which has a genoa feeding air over its lee side over the full hoist.
How wide should the slot be? I don’t know, except that for any given wind strength too tight a genoa sheet chokes the slot and you go very slow , whereas too loose a sheet drops the speed just a bit. Around 16 knots true there is a sweet spot where the main backwinds but the slot is obviously working efficiently and the boat gets up to astonishing speeds , but achieving this is a bit like finding the Holy Grail ; you get occasional glimpses of it but achieving it consistently seems impossible. Work at getting 5.8 knots , and you wont be far off the pace.
When that gust comes through it would be nice just to depower the sails and keep the boom in the centre to maintain height – but all too often the traveller has to go to lee as well , and I believe that with everything else depowered , if you cannot keep her on her feet with the traveller fairly high up , then its time to change headsails to the No 2 . This sail is flatter and more tolerant of the traveller down to lee and potentially closing the slot.
In flat water , changing early to the close sheeting 3 may allow you to keep the traveller in the midline and thus sail considerably higher , but in waves , the No 2 might allow you to punch through and maintain your speed better (albeit heading lower ). You can hang on to the No 1 in loadsa wind by hauling the draft forward on the halyard and sheeting further aft but you will probably be stretching it horribly and ragging the main a lot , so its an option for rich crews only! When its howling , the No 3 allows you to keep the traveller low , but if you have to twist off the main to stay on your feet , don’t forget to ease a bit of genny sheet to allow a similar twist in the high aspect 3.
When should you reef? Again I don’t know , but would do it earlier in big seas offshore where you might have to be sailing lower to get through the waves. Equally , if the main is ragging then its kinder to reef , and of course short handed it is astonishing how fast you can go with small sails. Nevertheless , you should be able to blade out the full main and perhaps twist off the top of the No 3 til the wind is consistently 25 knots or more if you have a full crew.
Well thats my theory anyway!