This is another Learn to Sail Artical is a series on the sails. The articels are written by Grant Headifen, Educational Director for NauticEd Sailing School. NauticEd is the World’s Most Advanced Online Sailing Education and Sailing Certification Company.
Reefing the sails is such and important safety aspect of sailing that it’s one of the first things you should understand as you begin to learn to sail.
Now is a good time to discuss something a tiny bit technical – force from the wind. Force imparted onto the sailboat is multiplied by four every time the wind speed doubles.
So if you go from 5 knots to 10 knots the forces quadruple. Then if you again go up to 20 knots, the forces are 16 times higher than at 5 knots. And 40 knots? 64 times. To put that in more perspective if it takes about ½ your strength to pull a line at 5 knots, at 20 knots you would feel 8 hefty guys pulling against you in a tug of war. You’ve got no chance. Now also think of the stress on the rigging and how 16 times more force aloft is heeling your boat over. Sixteen times!!!!
I hope you’re getting the point. The quadrupling effect comes from the well established Bernoulli’s equation which says the pressure applied is proportional to the square of the velocity. And by definition, force is equal to pressure multiplied by area.
So if we halve the area we halve the forces. Makes sense right? And that is what we are doing by reefing. We’re reducing the area while the velocity is increasing in our best attempt to manage the forces.
And one more thing – when you’re heading up wind, your boat speed is somewhat additive to the wind speed and so the forces increase even further.
The mast on your sailboat is probably supported by shroud lines attached to the sides of your sailboat and by a forestay and aftstay. They are designed to hold certain forces aloft. Should the forces become higher than design or the connections deteriorate which on a boat they are guaranteed to do over time, then you’re going to have some serious problems with a dismasting.
In reality and practice, you should start to think about reefing the sails at about 12 knots of wind. At 15 knots, you should definitely be reefing and at 20 knots, you’re crazy if you don’t have 1 or 2 reefs in. The boat will be uncontrollable if you haven’t reefed and you’ll be probably breaking items on your boat due to high forces from the wind. At 30 knots, the boat will probably explode. Well, not quite, but I’m making a point to reef reef reef and get comfortable with the process especially when you are starting out in your learn to sail quest. And get a sailing school instructor or practiced sailing friend to teach you how to reef your sails.
The process should not be intimidating. What can be intimidating however is if you leave it too late. A good professional captain of mine who would sail across the Atlantic had a saying. If you think you should be reefing – you should have reefed yesterday and if you are thinking about “shaking out the reef” (unreefing (if that is a word)) wait until tomorrow.
Leaving the reefing until it is too late means that there are excess forces already on all of the lines you’re going to want to be handling which is a safety issue for you and your crew. So reef early. An additional incentive to reefing is that actually, you can make your boat go faster anyway. So if you’re trying to be mucho and waiting to reef, you will be going slower and loosing the race (there is always a race).
Not reefing causes rounding up. One of the best things to see in a race is when the boat that is ahead of you has too much sail aloft and they get over powered and round up into the wind. This is so awesome because in doing so they will have lost 50 meters of lead on you.
Rounding up is a wee bit technical but essentially it is when the wind force takes over your boat with out your ability to counter act using the rudder. The boat just turns up into the wind. It’s dangerous because you can be turned right into other traffic. And it’s just a pure waste of good sailing.
When you begin to learn to sail, you’ll find that the boat is trimmed so that the rudder balances the turning force of the sails. The force from sails want to turn the boat up into the wind and the force from the rudder wants to turn the boat down wind. This is done for two reasons. (1) For safety: if the tiller or wheel is released the boat will round up into the wind and loose power. And (2) if the rudder is pointing slightly up wind the boat gets a lift to windward from the force of the water on the rudder. However this balance is lost as the boat heels over too much. If you imagine that the boat has heeled over 30 degrees then according to Pythagoras, you are down to 70.7% of your rudder counteracting forces. So too much heeling is bad.
On top of all that, as you begin to learn to sail and understand the forces, you’ll learn that the sail relies on efficiency of the wind over the sail to create lift. This requires that the wind on the back side of the sail flow evenly across the sail (stays attached to the sail) to create the low pressure and thus lift. When the wind speed is too high and as the boat heels over, the wind has great difficulty in staying attached to the sail. Thus the wind peels off and you loose efficiency. A smaller sail requires the wind to stay attached for a shorter distance and thus increases the efficiency.
We sum all this up to say when you reef in high wind conditions your boat can go faster with less heeling and less likelihood of doing serious damage to your sailboat. That’s good.
In the next learn to sail series we’ll cover how to reef the sails.
This article was written by Grant Headifen, Educational Director of NauticEd. NauticEd is an online sailing school providing sailing courses and sailing certifications for beginner to advanced sailors.