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Old 12-06-2009, 17:03   #1
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How Does a Sailboat Work?

I have recently taken up windsurfing. I generally I have sailed a Laser II before that. While doing my very best to go anywhere on the wind surfer the thought donned on me that i have absolutely no idea how the sailboat works. I immediately fell headlong in the water narrowly missing getting hit in the head by the mast.

I know what parts are needed for a sailboat to work, centerboard, rudder, sail etc. Can someone please help an ignorant young man and explain to me in three year old detail how the sail boat ends up going forward?

I appreciate any help anyone can give me.
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Old 12-06-2009, 17:22   #2
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bebalu its a bit like electricity.You can find lots of explanations about how it works but the truth is nobody actually knows and anyone who says they know is probably full of c**p.
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Old 12-06-2009, 17:30   #3
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This is the best explanation I have seen: The physics of sailing
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Old 12-06-2009, 18:30   #4
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RainDog nailed it.

That is also the best example of why excessive weight on a boat is deleterious to performance.

Do the math.

Steve B.
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Old 12-06-2009, 18:44   #5
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Excellent Rain Dog...now if I can find more of those Rivers
flowing in my direction at 10 knots!
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Old 12-06-2009, 21:08   #6
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Nope, Raindog's link doesn't address the original question (sorry Raindog) - I believe the request was: "Can someone please help an ignorant young man and explain to me in three year old detail how the sail boat ends up going forward?". For God's sake, that site has vectors and equations! Try again, guys. Are you up to it?
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Old 12-06-2009, 21:17   #7
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Ha

ha Dragonfly, you are right. Although after spending the better part of an hour looking at that site I do have a much better understanding of what is going on while I am sailing.

if anyone has better laymen lingo please feel free to post it up. I am however somewhat satisfied after looking at the diagrams.

Thank you too all.
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Old 12-06-2009, 21:18   #8
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Let's see if I can make it simple and still get it right.

Going downwind it is easy. The wind blows against the sail and pushes you.

Going upwind is a little more complicated. In short you are pulled upwind by the wind on the sail.

The wind blows across the sail like the wind across an airplane wing. Due to the curved shape of the sail and the angle of the wind blowing across the sail the wind makes a force (lift like lift on a wing) that pulls on the sail which pulls on the boat. You add some help from the centerboard or keel that moves you closer upwind.
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Old 12-06-2009, 21:26   #9
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Quote:
Originally Posted by BeBalu View Post
I have recently taken up windsurfing. I generally I have sailed a Laser II before that. While doing my very best to go anywhere on the wind surfer the thought donned on me that i have absolutely no idea how the sailboat works. I immediately fell headlong in the water narrowly missing getting hit in the head by the mast.

I know what parts are needed for a sailboat to work, centerboard, rudder, sail etc. Can someone please help an ignorant young man and explain to me in three year old detail how the sail boat ends up going forward?

I appreciate any help anyone can give me.
Bebalu, you already feel the resistance when you push your windsurfer sideways. See HERE for the rest. Sailing upwind was once considered to be magic. The church condemned those who would practice it. Sailors wishing to escape the flames of perdition waited until they were over the horizon before hardening up and getting on the wind.
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Old 12-06-2009, 22:17   #10
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it's not that complicated

the wind wants to push the boat sideways. the boat provides lateral resistance to that sideways force in the form of a keel (or centerboard/dagger board/whatever). the lateral resistance transforms the sideways push into forward thrust because it's so much easier to push a boat forward than sideward.

a simple experiment will illustrate the point, one that doesn't require the sails to be up. Go out on a windless day, and lock the rudder of the sailboat. Now, take the tender (this experiment works best with an inflatable) and line it up abeam to the boats center of lateral resistance. Now using the tender's outboard, attempt to push the sailboat sideways. Note that how the sailboat quickly transitions from moving sideways to moving forward.
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Old 12-06-2009, 22:59   #11
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Perhaps an understanding of physics and energy:
Nothing that is not now on the earth will ever be created,,,just changed from one form of energy to another. Light given off creates heat ,,an equal amount of heat ,minus the effort to do so. motion created by a gas motor,,motion equals the energy created ,then changed into forward motion and the motor driven object moves the appropriate distance/speed that the initial energy caused,but then when we humans get involved ,with our intelect,we have to screw things up
Motion: the wind hits your sail and instead of your boat moving in the direction the wind is going ,you change the geometry a bit ,,,you make the boat move a little differently than the wind intended ,using a few different tools at our disposal: a keel , the movement of the sail in realtionship to that very same wind and then the rudder.all the same tools you use on a windsurfer
We simply use the power of the wind ,whcih can be measured , and store it up in our sails for a mili second and then use it to propel us in the direction we want to go. Sometimes, we are willing to give up a large amount of energy to make small forward progress. That is just about the time when everyone else on the boat begins to question the captains sanity..." What the $%#@ is he doing ???? "
But the whole point is that we harness the winds energy and then spend it as we see fit,,sometimes wisely[ we won the race ] and somtimes foolishly [ what went wrong? we were doing so well ????? ]
Same as you on your windsurfer. we just do it on a larger scale and things happen more slowly..
So many people ask me how can i control a huge sailboat of 50,000 pounds ,either alone or with one person helping me...the answer is that the larger the boat ,the slower things happen. There are some who will argue with me on this point, but after years and years of observation,i have concluded that the larger the vessel,the more the captain understands that things NEED to happen slower,even when the boat is moving faster through the water,the reaction time MUST be slower,needs to be slower and that is the sign of a good captain...one who can see things happening before they do and adjusts ...just like you do .You simply do it so much faster; your reaction time is quicker,your movement time is quicker and your time for adjustments is so much faster or perhaps we should say that your reaction time is a "MUCH SMALLER WINDOW " THE "GOOD CAPTAIN" sees things happening ,,before they happen and is ready for them when they do occur,,,,,just like you do ! Remember: A large sailboat will run about 35,000-65,000 pounds ..your windsurfer weighs as much the pillows on my queen sized bed ...perspective !
W
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Old 13-06-2009, 03:12   #12
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Quote:
Originally Posted by BeBalu View Post
I know what parts are needed for a sailboat to work, centerboard, rudder, sail etc. Can someone please help an ignorant young man and explain to me in three year old detail how the sail boat ends up going forward?

I appreciate any help anyone can give me.
What the hell, I’ll take a shot at it.

When you have your sails up (and no rudder or centerboard in) you are being pushed along by the wind just like a piece of trash blown along. The real change to make sailing is being able to harness the wind rather than just go where the wind wills. So now you drop in the rudder and start to steer where you want to go. At this point you notice two things. The first is you immediately notice how hard it is to steer as the whole things seems super sensitive and hard to maintain course. The second is that you are being pushed by the wind in a direction you usually don’t want to go. For example you want to go straight but end up getting pushed mostly to the right with only a little headway. So you then drop in the centerboard and have a complete set up – rig, rudder and centerboard. The centerboard helps resist that pushing motion of the wind causing you to go leeward. You now can harness the wind.

Now, we haven’t said anything about how the sails work and you might think you are still being pushed along, but that isn’t the case. In actuality, you’re being pulled along. And the way it works is like this: Sails as you notice aren’t exactly flat. As you sail in a direction other than exactly downwind the speed of the wind is different on one side is just a little bit faster that the other, just like with an airplane wing or (slightly differently) like a pitcher who throws a baseball so that it curves. In other words, the distance the wind travels is a bit further than on the other due to that curve. The wind starts off at the leading edge together and ends together (you can test this with smoke). So if the wind starts in the same place and ends in the same place but has further to go on one side, the wind on one side has to travel faster. It does and you can test this with a wind gauge by measuring both sides. The difference in speed creates a difference in pressure. You are being sucked into the low pressure side which is the leeward side.

A couple of things you may notice: When you have both the main and the jib up and trimmed correctly, the effect is more than just the area of the sails. That is, the effect isn’t 1 + 1 = 2 but rather 2 plus a little bit more. The second is the description I gave of being pulled along accounts for what you feel on the boat. You may know by the gauges the wind is coming from the side, yet it feels like it’s blowing more in the front that on the side of your face.

So, a skeptical inquirer might ask. “Ok, how does a sailboard work? There isn’t a rudder.” I’ll leave that for a bit later, if you’re interested.

Hope that helps...
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Old 13-06-2009, 10:55   #13
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I think Maren makes the single greatest point for someone who is just starting on the road to garnering an understanding of "How a sailboat works". If you get yourself first wrapped around the concept of being pulled, as opposed to pushed - then as you learn more about the dynamics at play, that perspective will make it all make more sense.
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Old 23-06-2009, 19:40   #14
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OK, I've got a simpler expanation and its one my dad used to use to explain to people how a yacht sails forward. It may not be technically correct and certainly isn't detailed, but it generally gives folks an inkling.

The wind exerts force on the yachts sails in one direction. The water exerts an opposite force on the keel (or centreboard) of the yacht. The direction of movement that results from these two forces depends on the balance of them relative to each other.

A practical example: Take an apple seed (looks a little like a yacht hull). Get the seed wet (to make it slippery) and pinch it between thumb and forefinger. This represents the opposing forces of wind and water. The apple seed will shoot forward as a result of the two forces. The greater the forces, the further the apple seed will shoot.

Even if folks still don't understand you can watch them spit on apple seeds and fire them at each other.
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Old 23-06-2009, 20:43   #15
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If you can take the time to go to the public library you can find all kinds of books with explanations. The best I've seen for easy to understand language is "Start Sailing Right!"
A simple answer is that you can sail to windward for the same reason that an airplane can fly. All you need to do is control the wing (your sail) efficiently.
These are all things we should be learning in a basic sailing course.
kind regards,
JohnL
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