About Boat

contributed by Adam Bowers, RellingOne Design Sails in November 2004
(note Relling are now part of North Sails)

There are lots of words here but at least they're all short!

You never know you may learn something! One of the great things about Osprey sailing is the flexibility and diversity of the rig. The direct upshot of this is the marvellous mix of people involved in sailing the boat. This short article is an attempt to explain some of the fundamental objectives in rig tuning to allow you and your Osprey to maximise your potential.

Let us take for example two fictitious crews ( for crews read helm and crew), one combination weigh in at 27 stone and the other weigh in at 21 stone. The obvious conclusion here is that the big boys will perform spectacularly in a breeze, while the lighties will sniddle to great effect in a drifter. Wouldn't life be dull if this were the case, and the fact is we've all seen fat blokes win races in the light and many is the time a heavy weather race has been taken by weight challenged teams. OK so how can this be?

At this point I would like to introduce you to a hypothetical cut off point, and we'll call it "20 units". This is the point where any boat is at maximum power, on an Osprey this is when the crew is fully extended on the trapeze with the mainsheet just about to be released from it's average upwind position. Now it goes without saying that 20 units for the big boys comes in more wind than it does for the lightweights, but the thing to remember is that it comes to all of us at some stage , the game is to achieve 20 units before your opponent and control the release of extra units once you've got there.

Now here's the rub. 20 units is the maximum we can deal with, less than 20 units and we're sailing below our potential , more than 20 units and we're struggling to maintain control against increasing drag and heel.

Time to go out for a sail on the perfect day.

The morning is bright and beautiful , but sadly there is very little wind as we push off from the dock. Aha we say to ourselves light airs what do we need to do here.

Fundamental: The wind must come into the rig , flow over the rig , and exhaust from the rig.

Stage two: power is generated by turning the wind away from it's original course by the rig.

Stage three: power is released by not turning the wind away from it's original course by the rig.

Now here we are faced with a very weak wind, which doesn't have sufficient strength to get over big curves and would stall before reaching the leech. We can't make the wind any stronger, but we can reduce the curve in the sail dramatically by pre-bending the mast, pulling on the out haul to the max, and opening up the sheeting angle on the Genoa. Mast rake has a powerful influence in all conditions and if it is too far upright it will create very big curves in the sails which we don't want in this light zephyr, so rake back to your moderate wind settings for now. Use your deck level mast control, be it a strut mighty screw chocks or whatever to bend your mast forward (pre-bend). By flattening the sails we have made it easier for the sluggish wind to travel across the sails and with careful trimming will be able to satisfy the fundamental.

Tell tales give us a very accurate guide to wind flow over the rig, if their not flying wind isn't going passed them, if they are flying wind is, yes it's as simple as that, and in these very light airs we need to see as much activity as possible in the upper mainsail and Genoa leech telltales. Sails must be trimmed very gently in these conditions so as not to disturb the incredibly sensitive and delicate breeze which is timidly blowing around your rig.

As the sun heats up this perfect day a slight wind develops increasing the hypothetical power available to 10 units. The tell tales stream merrily in the maturing breeze, and as the breeze builds it forces both main and Genoa leeches to open under increasing pressure. Now here's where we get to be a little sneaky,

Stage two of the fundamental states :- power is generated by turning the wind away from it's original course by the rig, and now that the wind is strong enough to push the leeches open we can straighten the mast, go to our upright position, sheet both sails in a little harder and create a slightly deeper curve hence turning the breeze even further.

How do we know when we've overcooked it, simple we look at the upper leech tell tales and keep loading the main or jib sheet until the relevant tell tale starts to dance. A dancing tell tale shows us that the air flow is getting to the back of the rig (by flying the tell tale ) but is on the verge of a stall (thereby collapsing the tell tale), correspondingly this amount of activity shows that the wind flow is just about accepting the amount of curve that we're asking it to follow. Any more sheet tension will result in the tell tale hanging down showing us that the wind is no longer passing it and subsequently the sail is stalled, if the tell tales are flowing consistently they are indicating that we can pull the sheets on a little stronger.

This intermittent period of light medium up to medium wind strength is the most difficult to get right, it takes constant attention and continuous adjustment to keep the sails working at their full potential and get as near to 20 units as they can.

As the day continues to warm the breeze continues to build, until we get to a stage where the wind is approaching 20 units The crew is now comfortably out on the wire the boat feels good, all the tell tales on main and jib are flowing and as the gusts increase we may well have to ease the mainsail to relieve the power. This is good, we have achieved the 20 unit level and hopefully we have achieved it before our competitors giving us the edge we need to win races, moving fast and pointing high.

Now we must consider how to get rid of any unwanted power, remember we can only deal with 20 units, and this is where the kicking strap starts to play it's part. We have just spent great effort getting the mainsail to perform correctly through mainsheet tension, now what happens if a gust comes and we have to release the mainsheet? All that effort will be wasted as the boom travels skyward and the mainsail leech opens dramatically, losing lots of power and dumping an unsuspecting crew in the water. The natural reaction now is to sheet in again ,this closes the leech, bringing the power back on and the crew is catapulted back up through the air again.

You can break this cycle of events by pulling the kicking strap on enough to take up any slack so that when the mainsheet is eased the boom travels horizontally and retains the leech profile you have spent so long achieving. This gives us far greater control of the power available to us, and now when a gust comes and we wish to ease just a tiny bit of power, we can do. A point to remember when using excessive mainsheet loads and or kicker loads, the mast will be forced to bend fore and aft unless controlled by spreader and deck controls, so make sure that these systems work properly.

All of a sudden God decides to chuck 25 units at us and the boat gets knocked all over the place. With the mainsail backing the jib flogging and the boat over on it's ear progress to windward is slow noisy and uncomfortable. Are we down hearted? No, we know that we can only deal with 20 units and all we have to do is release 5 units from the rig and all will be well. So what do we do? If we had a raking rig now would be a good time to drop it back a little by releasing a bit of jib halyard and pulling on the shrouds to maintain rig tension.

Be careful here, raking is great at de-powering but it also opens up the leech of the Genoa and increases the mast bend, unless it's really windy this will stop you pointing so as you rake you need to move the jib cars forward ( or down depending on your system ) to regain control of the Genoa leech.

If we have a fixed rig ease the deck control to let the mast bend a little more and move the jib cars back to open the Genoa leech.

Whichever rig system you have the kicker is becoming more and more important and must be heaved on at this stage. Remember the loads in the sail are enormous now and we must counter these loads by pulling harder! As a consequence of our pulling hard the sail will be being stretched to pooh (a technical term much used in sail making) and here the cunningham comes into play.

This is without doubt the most dangerous control on the boat and has two major functions. In light to medium airs pull it on to remove the creases only in the presence of a photographer. Crews will know when a photographer is around because the helmsman starts sitting out !!!

In big breeze lots of cunningham will pull the flow forward and open the leech, significantly reducing the amount of curve in the mainsail and satisfying stage three of the fundamentals.

As the breeze increases and we need to dump more power keep these basic properties in mind.

1. We need rig tension to hold the Genoa luff straight and keep the mast in control.
2. We need Genoa sheet tension to keep the Genoa shape constant and under control and to do this we move the jib cars further and further back as the wind increases. I hear of people sailing boats with the jib sheets permanently eased to create the desired sail shape and this is bad Karma , for although it is acceptable to be easing sheets temporarily on a gusty day , slack sheets offer no control of the design shape of the sail.
3. A bit of mast bend is fine but don't over do it , you'll know when you have because a crease will appear running from the clew to the spreaders.
4. Use lots of kicker ( much more than you think ) to keep the mainsail flat and driving.
5. Use lots of cunningham to keep the low forward and the leech open.
6. Keep the boat driving by easing the mainsail over the quarter in gusts, don't try to point by stuffing the boat in the gusts, you'll just stall and stop, try to keep the boat free and fast by playing the mainsheet and steering smoothly, it's hard work but very rewarding.
7. In big breeze try pulling the plate up a little this will take some weather helm off and make steering a bit easier.

As a final thought remember that in big breeze you'll end up sailing with just the tack of both sails pulling and that's why sailmakers put their logos there so you know who's getting you home.