Apparent Wind and How to Figure It Out ( the answer to the bunny saga)

Ok, so it’s time to review Mr. and Mrs. Bunny’s sailing adventure. If you remember Mr. Bunny wanted to take Mrs. Bunny for a day of sailing. He didn’t want to have to do any work, if you recall. The reality is that he really just wanted to get Mrs. Bunny on the bow of the boat in her new daring naughty bunny bikini. He just had Bunny tail on his mind. He needed our input to see if he could leave the dock, set up for a beam reach in perfect conditions (no current and no leeway), sail for a couple of hours, tack and return back to the dock on another beam reach and not have to sail any other point of sail other than a beam reach.

Apparent wind is more important than you might think

He got tired of waiting for my answer and told Mrs. Bunny that I said that he was correct and the day was going to unfold just as he said. Then he gave her $75.00 for a bunny wax. Well, had he called Tousey, a close friend and sailing buddy of mine, he would have gotten a timely answer to his question and been able to come up with a less risky scheme.

As Tousey figured out, the answer is NO. He cannot sail out on a beam reach, tack, sail back on a beam reach, AND wind up back where he started.

So here’s why. To illustrate the reason for his miserable failure let’s make up a realistic example. Here’s the facts:

  1. They are sailing on a Catalina 350
  2. When they clear the Vinoy Harbor they set sail on a beam reach
  3. They have the auto-pilot steering the boat to avoid any steering errors
  4. They sailed outbound for 1 ½ hours
  5. The apparent wind is 12 knots
  6. The boat is traveling at 6 knots
  7. There is no current
  8. The waves are one foot and not a factor
  9. They were sailing on a course of 090 degrees
  10. The apparent wind was from 000 degrees
  11. They needed to return to the dock on a course of 270 degrees
  12. Bunny was looking really hot

Now, I’m not a mathematician so, my explanations may not be perfect. But, a boat’s speed and direction can be represented by something called a vector. A vector is a line segment that’s length represents the velocity (speed) of an object or force and that’s direction represents the direction of travel of the object or force. An arrowhead is placed on the end of the line segment indicating which direction the travel is in. For example, if the boat is traveling in the direction of 090 or 270 degrees the line segment would be the same. It is the arrowhead that indicates which direction the boat is going.

There is another critical concept we need to understand. We are discussing wind and its impact on the boat. If the boat was moving and there was absolutely no wind, we would still feel wind as the boat moved through the water.   That wind is the apparent wind made by the boat’s movement. We would feel that wind in the exact opposite direction and velocity than the boat is moving. It is that wind force that we are using along with the true wind to make our analysis. So, the vector representing that wind velocity and direction is drawn in the direction that it is felt—180 degrees from the boat’s velocity and direction. In the Bunny’s case we will use a vector to represent the wind created by the boat (BAWD & BAWS), independent of the true wind (TWD & TWS). (see figure 1)

Planning for apparent wind vector

Figure 1:  showing basic vectors
Figure 1: showing basic vectors

It is possible to add vectors together. The sum of which is the combined velocity and direction of the two vectors that were added. So, if we add the boat’s wind vector and the true wind’s vector we can obtain the apparent wind’s vector (AWD & AWS). In fact, as long as any two of the vectors are know the third vector can be determined.

Vectors are added by drawing them with both sharing a common starting point. From that common point each vector is drawn utilizing the information known about the vector (length and direction.) With the two vectors drawn a parallelogram  (a four sided object with opposite side parallel) can be completed by redrawing each vector from the other’s arrowhead.   (see figure 2)  Once the parallelogram is completed the sum of the vectors is determined by drawing a final vector from the initial common starting point to the opposite corner.

Figure 2: Completing the Parallelogram and adding vectors

In the Bunny’s case we already know the apparent wind speed and direction (090 and 12 knots), so the missing link is the true wind speed and direction. To find the true wind vector, draw the two vectors that we know—Apparent wind and Boat’s apparent wind. Next, draw another vector from each of the existing vectors arrowhead, the first of which will connect the two existing arrowheads and the second of which will be parallel to its opposite and extend in the opposite direction.  Finally complete the parallelogram by adding a final vector on the remaining open side.  The final vector is the true wind vector, representing the true wind speed and direction (TWS & TWD.)  (figure 2)

So, back to the problem at hand. Mr. Bunny got his bride, Mrs. Bunny, to go on the trip by telling her that it would be beam reaching the whole way, that she wouldn’t have to do any work, and it would be a great way to spend a frisky bunny hopping day. And, so they set out. All was going as planned. Mr. Bunny got the boat setup on a beam reach and they sailed at six knots for an hour and a half. The apparent wind was a perfect 12 knots.

After about fifteen minutes Mrs. Bunny came up from below exhibiting her new naught bunny bikini and Mr. Bunny thought the 75 bucks he spent for the bunny wax job was the best money he ever spent. The naughty bunny bikini certainly showed it off and there was no question that there was going to be a nearly all bunny tan hopping around the den later that night. In what seemed like no time they were at the shallow water off Apollo Beach, due East of the Pier in St Pete. Mr. Bunny called to the bow for Mrs. Bunny to lay flat while he gybed around to head back to the Vinoy. Mrs. Bunny asked if she should come back to the cockpit to which Mr. Bunny replied, “No, baby it will be a smooth beam reach back, just stay put.”

And, so she did. When the gybe was complete Mr. Bunny was a little rattled when he had to trim in the sails so much. Before he could say “Holy carrots” the boat was heeled and starting to pound in the waves now striking the bow. He watched in horror as Mrs. Bunny started sliding off the bow toward the leeward lifelines. Thank goodness for the stanchions, her tail had just caught on one and it saved her from falling off the boat.

Acting quickly and trying to save the day he fell off the wind and back onto a beam reach. He quickly realized that he was now heading, at six knots, directly at the shoals of Ruskin Inlet. That wouldn’t work and so he turned back to the original plan of 270 degrees. Once there he found he was schlepping along at 5.2 knots and on a very close reach into 16.4 knots of wind. Mrs. Bunny had made her way back to the cockpit, put on a cover-up, and was visibly bunny hopping mad! Nearly two hours later they pulled back into the Vinoy where Mrs. Bunny hopped off the boat and caught a cab.

Apparent wind can get any-bunny hopping mad

So, what happened and why? Well by taking what we know from figure 2 we can complete a new parallelogram showing the return trip (see figure 3).

Figure 3:  Showing the Bunny's return trip problems
Figure 3: Showing the Bunny’s return trip problems

We can see that Mr. Bunny was doomed from the start. Looking at figure 4 we see that if there had been a clear sailing path to sail the course that figure 4

Figure 4:  Showing the required course to return west on beam reach.  Doesn't really work, does it?
Figure 4: Showing the required course to return west on beam reach. Doesn’t really work, does it?

prescribes they would have been heading to the Manatee River and may never have gotten back.

By the way, I heard that Mrs. Bunny has since divorced Mr. Bunny and has been hanging out with some guy named Bugs. I hear that this guy, Bugs, has a big powerboat and is always playing hippty-hoppity music onboard. And, that Mrs. Bunny’s near all bunny tan is now an all bunny tan.  Can you say high maintenance?

I created these drawings using a CAD program, that’s why this article took so long to get printed; I had to learn the damn program. But, you can work these problems out just as well with about $20.00 worth of tools. It doesn’t have to fancy, it just has to work.

The basic tools necessary to manipulate vectors
The basic tools necessary to manipulate vectors

Planning is everything and planning takes understanding. Understanding requires knowledge and knowledge takes learning. Come learn with me, On the Water With Captain Frank.

Elements of Close Quarters Maneuvering, Part two

In this, the second article in the series on close quarters maneuvering, we will look at the shifter and its role in maneuvering the boat.

Neutral is the preferred gear

As mentioned in article one, 99 percent of the time our primary transmission position is always neutral. How we use the transmission depends on what kind of propulsion system our boat has and the adequacy of the rudder’s size, if there is a rudder at all.

There are two primary propulsion systems used in boats today, fixed and directed. Fixed thrust systems have the propeller in a fixed position. That is, the propeller is rotated on a shaft that is in a fixed position parallel to the centerline of the boat.

The boat relies on a rudder, usually mounted directly behind the propeller, which is turned via the helm. As the rudder passes through the water the water is deflected in the direction of the trailing edge of the rudder. If the rudder is straight (parallel to the boat’s centerline) the boat goes straight. If the rudder is turned to port then the water is deflected to port moving the stern of the boat to starboard.

When the stern pushes to starboard it rotates the bow to port and the boat turns in that direction. Rudder size is critical to how effective the rudder turns the boat. The boat only turns when water flows past the rudder. More water flow…more turn. Single or twin inboard boats including sailboats use this system.

In the other propulsion system, directed thrust, the propeller is rotated from the center-line toward one side or the other. Using this system, the boat is turned by the thrust of the water being directed in a certain direction. That thrust pushes the stern in the opposite direction from which the thrust is directed and that force rotates the bow opposite and the boat turns in the direction of the bow. Single and twin outboard, single or twin stern-drive, and jet drive boats use this type of propulsion system.

The practical difference between these two systems can be summed up as follows:

Directed thrust: The boat can only be turned when the transmission is in forward or reverse. With this system the turn is accomplished by water being trust in the direction the prop is facing. If the transmission is in neutral there is no steerage. Some outboards will have a slight amount of steerage from the water flowing past the lower-unit (the part of the motor that is submerged) but this steerage is minimal. In close quarters the helm must be turn in the desired direction BEFORE the transmission is engaged.

Fixed thrust: The boat can be turned anytime there is water passing by the rudder. Therefore, the transmission position is irrelevant to steerage; however forward or reverse momentum is necessary for the boat to turn. The propeller, when rotating in forward gear throws a constant stream of water directly at the rudder. So, even when the boat is stopped, if the transmission is engaged in forward, there will be immediate steerage. We will use this to our advantage especially on single engine inboard boats. The faster the water passes by the rudder the more steering control the boat will have.

A special note about inboard sailboats

While it is true with all boats that the primary transmission position is neutral, sailboats may require the use of some throttle when maneuvering in close quarters. Sailboats by design have a lot of lateral resistance (it keeps them from blowing sideways as they move forward). For more on this see my article ‘Blowin in the wind, how the wind impacts your boat’.

They are also equipped with relatively small engines, to reduce the weight and because it takes only a little power to move a sailboat, and small propellers to reduce the drag and because they have small engines. All of these things are admirable and desirable traits of sailboats.

They enhance the sailing performance. But they SUCK for close quarters maneuvering. Therefore, it may be necessary to add a little bit of throttle to get the same results as with other boats.

 States of momentum

Boats are always in one of three states of momentum. They are building momentum, exhausting momentum, or have no momentum. Furthermore, we can exhaust the boat’s momentum in two ways, actively or passively.

When done actively, a manipulation of the boat’s controls is done, such as moving the shifter from forward to reverse, or turning the helm from starboard to port, or a combination of both. Passively exhausting the momentum is accomplished by using natural means.

For example, if the boat is in forward gear and then shifted to neutral, the drag of the hull in the water will dissipate the forward momentum. Like wise, if the boat is yawing (twisting) to starboard in forward, and the transmission is shifted to neutral the twisting momentum will be exhausted by the required force to move the boat through the water. Got it?

In close quarters maneuvering we really like to passively exhaust the boat’s momentum. The best way to assure that is to always keep the boat needing more momentum, never less. When maneuvering in close quarters, we accomplish that by keeping the boat in neutral most of the time and when in gear, at idle speed. Yes I know that’s not what you’ve witnessed when on the docks or observed when on boats, but it should be.

The slower the approach the better

When approaching a slip the boat should be in neutral, only adding forward or reverse to maintain steerage. For directed thrust boats that means shift into gear to steer and then shift back to neutral. At the slip, as the back and fill turn is made, between each step, pause in neutral and let the momentum nearly exhaust itself before shifting to the other gear. Make sure the helm is turned prior to engaging the transmission to minimize unwanted forward or reverse momentum and maximize the yaw (twisting, for the last time.)

When approaching a dock, side-to (like coming along side a fuel dock), the boat should be under steady power only while a considerable distance from the dock. As the boat approaches from either a thirty-degree angle shallow approach or ninety degree angle steep approach the boat should be in neutral. The goal is to be able to add forward as needed to keep control when close to the dock. If the boat is moving at idle speed the whole way we will build far too much forward momentum and have to exhaust it actively, and that can have unpredictable results.

For example, we are approaching the dock on a shallow approach for a port side-to tie up. All is great except that we are moving to fast because we stayed in idle forward on the approach. We are going to overshoot our target spot. So, what do we do? We add reverse as necessary to stop the boat. YEAH! But the prop walk that we forgot about now slams the stern of the boat into the dock pilings and bends the stern pulpit or breaks the rub-rail. BOO! Had we been in the proper mode of always needing to add more momentum we would not have overshot, would not have needed to add reverse with power, and been able to charter from the company again. Golf anyone?

When executing a steep angle approach to the dock minimal momentum is critical. I have two things to say here. One, never approach the dock faster than you are willing to hit it, and two, you don’t look like an a*&hole until you hit the dock. Slow and steady wins the race. When we are about five feet from the dock we want to shift into reverse and start our rotation. How we rotate is fodder for another article and will be coming soon, but for now we need to rotate. This will be accomplished by forward motion nearly stopping and sideways momentum (yaw) starting. Again, neutral is the gear to be in on this approach. Start the rotation by aiming the gun to which ever side you want to be next to the dock and clutching into reverse idle speed, FOR THREE SECONDS. Now, back to neutral and let the boat’s yawing momentum carry the boat to the dock. Drop the lines onto the pilings, hand out business cards, and make some beer money teaching others to do the same.

There are times in life that you want momentum. Close quarter on a boat isn’t one of them. Go practice, or better yet give me a call and we can work on it together. But for now, I’ve got to run; I hear there’s a boat for sale with only some broken rub-rail and scratches. Maybe I can get it cheap.

See you soon, On the Water…With Captain Frank