No. 21 - March 1976

SPEED AND DIRECTION

Mike Nicoll-Griffith

 

1. INTRODUCTION

At the Tanzer 22 Class Association Seminar on December 3, 1975, I presented some ideas on a Research Project I have been tackling to do with boat speed. As I explained, the project is unfinished, but it remains an ambition of mine to bring it to a satisfactory level of accuracy some time during my life.

 

John Charters asked me to translate these ideas into writing for the Newsletter. Inevitably, I will have to use less pictures and more numbers than I did at the Seminar, but some study on your part can result in the ideas getting across.

 

In our fleet, competition is tough, measured against the background of traditional technology, i.e., hull shape, sail shape, tactics and the things one always reads about in yachting magazines. To win required some new investigations.

 

This report is to outline the present stage of my investigations into Boat Speed and Direction.

 

2. WHAT STARTED THIS PROJECT?

Initially, I became curious about Tornados tacking downwind at 450 . (Let’s measure this from up wind and call this 1350). Prior experience in Y-flyers at the 1965 Nationals also made me realize there were some unqualified factors in moving downwind. I decided to determine the "Optimum Downwind Tacking Angle" for a Tanzer 22.

 

The project became enlarged from this initial goal when Phil Whitting­stall and I had an insight about spinnaker flying during the Coupe du Lieutenant-Gouverneur (Rimouski) in 1972. Later on, upwind angles became of interest. This work was mostly done two years ago.

 

3. WHAT IS IT ALL ABOUT?

Earlier on, I mentioned the traditional technology in the yachting magazines. This technology concerns:

- the skipper -- what he knows and his physical health;

- the hull  -- its shape, length and surface roughness;

- the sails  -- their area, curvature and twist.

 

What I propose to concentrate on are:

- the wind -- its strength and variability;

- the angle sailed to the wind -- a choice of the skipper;

- the sail plan -- again the skipper's choice.

 

The investigations concern the speed that a boat will go at various angles to the wind. As a convention, let us call upwind 00, beating 450, a broad reach is 1200 and a dead run becomes 1800.

 

For those of you who have a copy of Marchaj's book, take a look at fig. 193 on page 311, and fig. 180 on page 295. Consider that this type of picture can be elaborated and extended.

 

In a certain wind, we should expect a Tanzer 22 to go at a certain speed, if we point it in a certain direction. We should be able to measure speeds achieved at all angles to the wind, under all wind speeds normally encountered, and using a reasonable choice of sail plans (i.e. what sails are hung up there).

 

There is a key issue here. The angle a skipper chooses to sail to the wind can be an important variable in racing IF the fastest route between two marks is not a straight line. (Forget about current differences over the course area.) Ha! you may say - the fastest route is obviously a straight line. But we already know it is not a straight line when the mark is to windward. Why should it be a straight line when it is else where? Let me suggest that we delude ourselves into thinking that upwind is "special" because we observe that a boat pointed at 00 (dead upwind) moves backwards. What about the boat that flies a spinnaker too close on a reach? The spinnaker may be full, yet the boat moves backwards relative to the rest of the fleet.

 

If we could show that the fastest route is not necessarily a straight line off the wind, all sorts of useful manoeuvres would become available to us at no cost in distance covered.

 

Inputs we will need are Wind Direction and Speed, Boat Direction (rela­tive to the wind) and Boat Speed. We can set as our objective the plotting of performance curves under various sail plans, and hopefully learn something in the process.

 

We took approximately 250 readings on Mindemoya but this proved to be an inadequate number.

 

4. WHAT HAS THE PROJECT YIELDED?

I think I have gained:

 

a) Better understanding of speed under different sail plans.

b) Some very specific facts about speed achieved in a particular direction in a particular wind (although I know these facts are not all that accurate).

 

c) The effect of wind speed on optimum tacking angles upwind, on optimum tacking ("gybing") angles downwind, and on the angle at which a spinnaker can be usefully flown.

 

d) The knotmeter can be a useful instrument.

 

5. HOW ARE READINGS OBTAINED?

 

We have to take measurements of the angle of the boat to the wind, the wind speed and resulting boat speed.

 

On any day, you first point upwind and take a compass reading. You allow the boat to stop and measure wind speed (we used a Dwyer windmeter of doubtful accuracy). You then sail a compass course, set the sails on your best intuition and read the steady speed achieved (we used a water pressure tube for speed which is hard to handle).

 

You need to reread wind speed and direction now and again to check for changes.

 

Having got the readings, you must correct for compass deviation and adjust for instrument errors if you can determine them. Then plot the results on graph paper.

 

You then develop smooth curves through the points obtained and plot the curves on polar graph paper (more on this later).

 

6. PLOTTING RESULTS

 

The initial plot is done on ordinary graph paper. You use the x axis for degrees from 00 to 1800, and the"y"axis for boat speed in the direction of "x". I intermixed port and starboard tack headings. Most of my discrepancies seemed to be in wind speed measured on different days.

 

Normal graph paper is good for smoothing the results, but polar paper is needed to get at the directional meanings.

 

Polar graph paper consists of concentric circles and radii fanning out through them. The wind is taken to blow from the top. The speed. achieved is plotted as a distance along the radial line at the proper angle to the up and down direction. i.e. Instead of using x horizontal and y vertical, we use 9 around from the top and r out from the centre.

 

When I showed a sample curve at the Seminar, I said that it looked like an apple, but the audience found it significantly pornographic. (Spin­offs can be many and varied.)

 

On the next page you will find a reproduction of the polar plot results. We will discuss mostly Genoa and spinnaker curves on the right hand side. The different curved lines are for values of wind speed, and, the shape of the curves defines the boat speed achieved in the appropriate direction.

 

7. LEARNING FROM THE CURVES

 

There are three important areas of the plot: Upwind, Downwind and at 80 degrees. These are where "cusps" (indentations) occur. The 80 degree cusp occurs because of the option to fly a spinnaker and go faster (or a Genoa and go faster). A cusp means that, if a mark lies within the direction of the indentation, the fastest way to it is NOT a straight line. To put it another way, while you may be able to move towards a heading in an indented direction, it is faster to head some­what to the left for awhile, and then somewhat to the right; and thus arrive at the place you were going sooner.

 


 

Let's get scientific and tabulate these three cusps:

 

 

In a

4

Cusp 1

 

Cusp 2

Cusp 3

knot

wind

Up wind

 

Close reach

Running

Angle to wind

00

 

800

1800

of cusp centre

 

Optional

Port/starboard

Genoa/

Port/starboard

courses

tacks

 

spinnaker

gybes

Optimal

500

 

750,

870

1550

angles

 

Range of

350-600

 

(see

later)

1400-1800

Optimal angles

 

 

Cusp 1 we are all familiar with. We know we can point too high and actually go backwards. We may also know that in stronger winds we can (should) point higher.

 

Cusp 2 is the great dilemma of whether to fly a chute for the course we are sailing. -- Better expressed as: what course to sail while the spinnaker is up and what course while the spinnaker is down.

 

Cusp 3 is tacking downwind, well known to Tornado catamarans that never sail below 1350 (although there may be occasions when they should). Be aware that what you are trying to do, T22ers, is to get downwind as fast as possible. Just simply that: GET DOWNWIND. When the mark lies within your downwind lay lines, the across-the-wind element takes care of it-self. Like it does up wind.

 

8. THE EFFECT OF WIND SPEED

 

By looking at the polar curves, and using a ruler for a tangent, we can pick off information about the best angles to sail as the wind picks up. Tabulation herewith:

WIND SPEED

 

 

FASTEST SAIL

ING ANGLE NEAR

CUSP

(knots)

1.

Upwind

2.

Genoa

2.

Spinnaker

3.

Running

 

 

 

 

Reach

 

Reach

 

 

3

 

550

 

710

 

810

 

1410

4

 

490

 

750

 

87°

 

1540

5

 

470

 

850

 

930

 

1580

6

 

460

 

960

 

1050

 

1630

Estimated:

 

 

 

 

 

 

 

 

10

 

450

 

1000

 

1080

 

1700

20

 

350

 

1050

 

1100

 

1800

 

Please note that the best angle to sail is what will determine our lay lines, not vice versa. e.g. You may tend to overstand a weather mark when it's blowing, and tack too soon when it is light.

 

Going downwind (Cusp 3. Running), the lay lines get closer together with increasing wind velocity and this means a reduction in our down­wind manoeuvrability. i.e. in stronger winds, we have to go straighter and lose some tactical advantages.

 

9. WHAT CAN WE DO?

 

More readings and more accuracy are needed. If in the Tanzer 22 Class there is someone who will volunteer to collect readings and publish revised curves, then those who wish to develop this idea further can add their information to mine.

 

When we have got some better accuracy, we will be able to go further with confidence.

 

10. GOING FURTHER WITHOUT CONFIDENCE

We have been using true wind speed and direction. When we are racing, we have to use apparent wind. Let me therefore return to my original objective by translating "Optimum Downwind Tacking Angle" into terms of boat speed and apparent wind angle.

Geometry tells us that we have a defined triangle when we have two sides and an included angle, or two angles and the side between them. The vector triangle is therefore defined by wind speed, angle of boat to true wind, boat speed: or by: angle of boat to true wind, boat speed, angle of boat to apparent wind.

Some sketching of triangles would produce a table showing related boat speed experienced during a race with the optimum angle to sail to the apparent wind. This can make us responsive to variations in wind strength (and maybe direction) and enable us to reach the leeward mark in the shortest time.

 

TABULATION:

 

 

 

Stick this on your Boat

 

Boat Speed

Wind

Optimum Angle

Boat

Optimum Downwind

Off

(knots)

Speed

to True Wind

Speed

Angle to Apparent

Down

 

 

from Graph

 

Wind

Wind

2

3.4

1480

2

1120

680

3

4.6

1560

3

1240

560

4

6.6

1700

4

1500

300

5

?

l750?

5

1680

120

6

?

l790?

6

1760

40

 

So read your knot meter and sail all over the lake like Nicoll-Griffith used to. You may find yourself in: a) a more favourable current, b) a better wind, c) not blanketed or d) sewered.

 

CONCLUSION

Of course, it is a competitive Class and only in exceptional circum­stances will we wish to give our secrets away.

 

 

 

JIFFY REEFING - TRY IT, YOU'LL LIKE IT

John Charters

 

Although there are 2 or 3 variations, the principles of jiffy reefing are the same. Basically, jiffy reefing is the same as the old reef point system, except that it is faster, more effective - and 100% better than the roller reefing that was standard on the T22 until 1976.

 

The following diagram shows the factory jiffy reefing installation. Before you drill holes in the boom, make very sure that the various fittings are in the right place for YOUR sail. To do this, put the sail on the boom but don't hoist it. Hook the luff cringle onto the reefing hook. Then pass a line through the leech cringle, pulling this cringle down to the boom and as far aft as you can. Mark the boom directly below the cringle. Fasten the lacing eye two to four inches aft of this mark; and on the other side of the boom fasten the offset block at a 45 angle opposite the lacing eye. If you are only instal­ling one row of jiffy reefing your lacing eye should be on the port side of the boom, the offset block on the starboard side and also the cleat. Because the halyard is on the starboard side of the mast it is easier to handle the reefing lines if they are also on the starboard side.

 

The standard reefing hook, no. 4 on the diagram, as supplied by the factory, has a hook on both sides of the boom. For two rows of jiffy reefing you need this fitting; however, if you want only one row you might prefer to use the hook as supplied by Custom Fittings, Ltd. (near Cascades if you are a local). This hook replaces the gooseneck pin. To install, drill out the gooseneck pin and replace with the hook - one end of which is threaded to take a self-locking nut. This is the type of hook I use, and it has the advantage of being more or less tucked out of the way.

 


 

 

This drawing shows the position on the boom of the fittings required for two rows of Jiffy Reefing. The long dimension, namely 8' 1-5/8" is for the first row and. the short dimension for the second. The cringles in the sail should be installed at 4 ft. vertically above the boom for the first reef and 8 ft •. for the second. Additional tabling is also required on the sail around these cringles. If reefing cringles are installed at heights other than 4 ft. (or 8 ft.) then the location of the fittings will differ from that shown here. When reefed, the reefing line should exert a 450 pull on the clew cringle, in order to flatten the foot of the main, as well as the leech.




Ideally, the fittings should be installed with 3/16" rivets.


When possible, you should reef while on starboard tack and have, there­fore, right-of-way. It is most disconcerting to have to alter course suddenly in the middle of reefing.

 

In addition to the fittings listed on the diagram, you will also need a length of line. This should be the length of the boom plus 2 times the reef depth. For our boats, use 5/16" Dacron - nylon stretches too much. Lead the line from the lacing eye on the port side of the boom, up through the leech cringle, down the starboard side through the block, then forward to the cleat.

 

There are 2 ways to jiffy reef:

1) If you have a topping lift permanently attached to the end of the boom and 2) for those who tie off the topping lift to the back stay when under sail. FIRST METHOD: (possible with one person; easier with 2). Crew eases the main halyard while you pull down the luff of the sail until hook can be attached to luff cringle. Tighten up halyard. Then one of you hauls on the leech reefing line until leech cringle is as close and tight to the boom as possible. Cleat it. The main sheet must be eased during this last operation in order to get the line tight enough. If you have inter­mediate reef holes in your main you can gather up the loose sail at the foot and tie the foot down to the boom.

SECOND METHOD: (Topping lift not attached to boom under sail). When helmsman is ready to reef he eases the main sheet while one crew tightens the leech reefing line. This raises the boom to a 20 - 30 degree angle. At this point, haul in the main sheet. Then ease main halyard, bring the luff cringle down to the hook. Tighten the main halyard and the intermediate reef holes can be tied to the boom if you desire. 

 

I haven't mentioned sail modifications, as this is for your sailmaker. If you are having only one row of reef points, it is probably best to tell him to put the cringles just below the first batten. Sailmakers are busy just before the season. The time to take your main in is now, if you want jiffy reefing this summer.

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