RYA Chief Instructor, Sail Cruising, Vaughan Marsh shares a few ideas for moving on to the next level of sail trim.
When we are out on the water enjoying our sailing we strive to sail the yacht efficiently. Many of us look at the yacht beside us and “tweak” to try to keep up or even overtake, which will normally involve looking at the tell tales to determine that the sail is sheeted correctly.
Once the principals of tell tales and over or under sheeting are understood there are other areas to look at that should make the yacht sail more efficiently, and help arrive at your next destination earlier. Here, Vaughan Marsh, RYA Chief Instructor, Sail Cruising highlights a few ideas from the book RYA Sail Trim Handbook for Cruisers to move your sail trim onto the next level...
A good starting point is to understand the bigger picture by introducing ‘twist’ and ‘camber’. This will help you think in terms of the sail shape that you want rather than simply learning a list of controls and actions.
When teaching this, I personally like to start with twist, introducing it as the changing angle of the sail in relation to the wind as you move higher up the sail. The more the top of the sail is ‘sheeted out’ compared to the bottom of the sail, the more twist you have. To see this in action place the yacht on a reach, then adjust the kicker, as seen in the diagrams.
Because in most cruising boats the kicker will have limited effect on twist in stronger winds or when going upwind, the next step is to move swiftly on to the effect of mainsheet and traveller position on twist. To understand this, sail upwind and monitor the effect on boat speed and pointing ability as you adjust the mainsheet and traveller to change the sail shape.
Camber can seem a little more complicated, particularly if an aerodynamicist tries to explain it, but we’ll simply say it is the curve of the sail.
We are interested in two parameters:
the draft, or fullness of the sail (how curved is it)
where the maximum curve is (i.e. the maximum draft position)
If we talk about reducing camber we mean less curve, or flattening the sail. If we talk about moving it forward, we are moving the maximum draft position closer to the luff of the sail.
Easing the clew outhaul is the easiest way to see increasing the draft but the effect of this adjustment on the position of maximum draft is less obvious.
To understand the position more effectively and see it moving forward, try tensioning the luff using the halyard or Cunningham. As the diagram indicates, the optimum position is about 40% along the sail.
If you understand the bigger picture of sail shape you should now be able to work out, how to change the twist and camber of the headsails on your own. After all there are very limited options in terms of controls.
To really understand this, you need to be thinking sail shape whenever you are sailing, take the opportunity whenever possible to experiment. Monitor the effects of various controls on the boat’s performance, then you will begin to develop an idea of what shape you are looking for in certain wind strengths or sea states.
Sail trim is a huge subject. In fact you could write a book about it, which we did!
Read more about Sail Trim in the RYA Sail Trim Handbook for Cruisers available from the RYA Shop
The RYA Sail Trim Handbook for Cruisers, written by Rob Gibson, illustrated by Andrew Simpson, focuses on the needs of the cruising sailor and is crammed full of useful tips and pointers on one of the fundamentals of good seamanship.
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