Does it make sense to use a radio controlled backstay and/or vang?

I can't speak for "most top skippers" but would totally agree that "Good starts, staying in phase, and a clean race are way more important than adjusting a vang or jib flipper".

The IOM class strictly limits the number of channels and functions controlled by radio, to 2.

On the other hand, you will see many 2 channel boat skippers making changes to the tune of their boats between races. This is particularly true at events using heats where the off-the-water time can be extended and changes in wind and water conditions are easily seen, can be significant and are responded to through adjusting tune prior to launching for the next heat.

The rise in popularity of “swing rigs” was due, in some small but significant part, to the need to quickly change rigs prior to the start of a race, often within the last minute. Lots of thought has been given to developing an ability to get the right rig onto the boat in the very shottest time possible. You can see this intent in the design of some of the systems for attaching sheets and shrouds etc.

So it would appear that most skippers, top or otherwise, understand the need to get the right rig on the boat and get the right shore-side tune prior to the start of the next race.

But what about once the boats are on the water?

An important factor to consider is the average duration of a heat or race. Most people would accept that an average duration of a heat or race would be between 10 to 15 minutes. (e.g. with 5 heats per race at a world championship regatta with 84 boats competing, an average heat time exceeding 15 minutes would result in fewer than optimum races being sailed).

Very important factors to consider are

1) the extent and frequency of changes in wind and water conditions that you may experience once you have launched your boat 2) tactical performance considerations during the final countdown, the start, the sailing of the course and the finish of the race.

So, On to the Vang and Backstay…

Let’s look an example and make some assumptions…

 Assumption 1: The average duration of the race is 15 minutes  Assumption 2: we have 3 top skippers (and the rest of the fleet) and the top skippers are all at the same skill level and capable of “Good starts, staying in phase, and sailing a clean” and do so regularly.  Assumption 3: Each of the 3 top skippers are sailing nearly identical boats... the same hull (let’s say a hull016) with from the same maker, same foils and lead bulb. The only differences are: o Skipper 1 has RC control of rudder and winch only (the lightest boat – just 2 channels) o Skipper 2 controls rudder, winch and backstay (and additional 0.84 ounces) o Skipper 3 controls rudder, winch, backstay and vang (an additional 1/68 ounces) o There was a skipper 4 but he is hung over)  Assumption 4: let’s assume that the average wind is 8 knots and the frequency of lulls is twice that of gusts and the cycle between the average wind speed and a gust OR a lull is 3 minutes. So there will be 5 cycles in a 15 minute race.  Assumption 5: All three boats a nicely tuned to the average wind speed of 8 knots.

So, on to the race! Handling Gusts and Lulls…

We start the race with the average wind speed, 8 knots. True to form, our heroes, the top skippers, get off to a great start, ahead of the fleet and separated enough that all are in clear air and essentially on an equal footing. And all else being equal, they have had a “good start, stayed in phase, and have sailed cleanly”.

1. Now, at +1 minute into the race each of our top 3 boats experience a gust, the same gust, the wind increases from 8 knots to 10 knots.

QUESTION: How much has the force of the wind increased? The force increases by 10/8 squared, or 1.56 more force available to power or heel or propel the boat. More than 1 ½ times the force available just seconds ago.

So how will each Skipper handle the gust?

Skipper 1 has RC control of rudder and winch only so he:

a. luffs up a bit to counter the increased healing forces b. or he eases the sheets to align the forces on the rig in a more forward direction c. or he carries on with increased heel.

The first 2 options have their own reasons for being good under the circumstances but the increased heel is probably accompanied with increased leeway and that is not good

But there are other potential problems too. Along with the increase in side-force, there are a number of nasty things that could still happen, including:

 Increased jib stay sag which definitely affects pointing  An initial “stagger” when the gust hit, with increased leeway, as the boat may not have been headed up early enough ahead of the gust because to do so in advance would be pinching and the boat would slow down. When the boat staggers it sends a boat sideways a little more and increases leeway  , with the boat rounding up quite violently (the CE and Lateral Resistance couple definitely shift when we sail in varying winds – you know that because most of us use the common practice of shifting the center of effort of the sail plan forward or aft (repositioning the rig ahead or at least raking the mast forward (or aft if lighter winds)) to counter weather helm in heavier winds and in light winds)  Additional drag in countering weather helm - we have all, at one time or another had to fight weather helm by increasing the deflection of the rudder… this increase drag a lot. There are other challenges our two channel skipper has but the above is enough to make the point.

Skipper 2 controls rudder, winch AND backstay.

Skipper 2 is a bit better off because:

 backstay control can be used, in response to the gust, to tighten the jib stay to limit sag  with a fractional rig, the back stay can be used to bend the mast, flatten the main and twist off the top of the main leech.  the preceding will help to reduce heeling, reduce the resultant leeway and in fact reduce weather helm because of the flatter twisted main.  the flatter twisted main leech also has the effect of moving the effective CE forward.

Other than what the backstay offers, this skipper can also luff up a bit to counter the increased healing force available and ease the sheets to align the forces on the rig in a more forward direction, just like Skipper 1 did.

Skipper 3 controls rudder, winch, backstay and vang.

Note: We have been talking about an average wind speed of 8 knots. Generally, a boat with more ballast will be able to carry the #1 or A rig a little longer than a more lightly ballasted boat. Perhaps most would agree, 8 knots is probably the top end of a #1/A rig. Boats like the Venom are intended to be sailed with their B rig in all but the lightest winds.

So Skipper 3 is confronted with the same gust, increasing from 8 to 10 knots. Skipper 3 has the largest scope of options. Skipper 3 can head up and/or ease the sheets like skipper 1 or additionally tighten the backstay like Skipper 2 would but then:  Skipper 3 can use an even larger range of backstay adjustment because, even if the amount of backstay required to flatten the main was such that the main leech had too much twist, the leech can be tightened to remove the excessive twist with the radio controlled vang.  Some would argue that you can tighten the mainsail leach with mainsheet. The problem with that is you are bringing the main boom back to the centerline and increasing the side force and heeling of the boat. The Vang allows the leech to be controlled independently, no matter what the sheeting angle is.

So, Back to the Race! This is where it really counts!

2. At +4 minutes, the gust dissipates and we head into a lull at say 6 knots. The force available at 6 knots, as compared to 8 knots, is 0.562 or roughly ½ the force that was available at 8 knots. The winds further drop to 3 knots (it happens – that is about 15% of the force that was available at 8 knots)

 Skipper 1 can’t really adjust the sails from what was accomplished during the shore-tune for the average wind of 8 knots. Some skippers have excellent skills in developing flexible rigs that, in some ways, automatically adjust in gusts, it most often not the optimum but works with reasonable effectiveness. Nothing can be done about the lulls however if you don’t have radio control functions to deal with the lulls. (Above design wind requires flexibility and below design wind things are a bit stiffer)  Skipper 2 is in a little better shape. Moving back to 8 knots, he can power up the main a little by easing the backstay. This also eases tension on the jib stay and creates a little more shape. He may be able to get back and somewhat beyond the tune for the average wind of 8 knots BUT as he progressively eases the backstay to accomplish the former, the mainsail leech gets harder and harder and hooks to weather, generally much more than desired. This creates unneeded drag even at 6 knots wind speed and is absolutely hopeless at 3 knots or less.  Here is where it really hurts both Skipper 1 and 2… As the wind drops even further both skipper 1 and 2’s boats are hopelessly out of tune for the lighter air and often will cut their speed in half or even stop  Skipper 3 (you can always recognize who he is by the great big smile on his face) now says very quietly, muttering even, now they’ll be sorry they didn’t put that extra servo weighing 0.84 ounces in the boat… as he eases the backstay inducing not only jib stay sag but additional twist in the leech of the jib! In these (very light) winds now, the wind gradient is even more greatly marked and while easing the backstay hooked the main leech, the VANG COMES TO THE RESCUE! The main boom is on the quarter, the jib is drawing and the mainsail leech has been twisted and is open. Comments are heard at pond side, somewhat muted, “yeah right, well every knows he is a light wind specialist!”

Here is a photo of the vang arrangement for the B rig on Connection

CONCLUSION:

The vang and the backstay take no more consideration or skill in operation that the rudder or the winch. They just require a bit of study and a little practice.

So, at this point, we should probably do the old Benjamin Franklin thing and take a piece of paper, draw a line down the middle, from top to bottom, and label the left with “Advantages of RC controlled backstay and vang” and on the right side, “Disadvantages of the Backstay and Vang”. It is really important, if you do this, to check over the list and ask your self have you listed facts or assumptions in either column. Is what you have written really true?

Unchallenged assumptions become facts for many people and, of course, influence decision making. Don’t deprive yourself of the opportunity to gain a competitive advantage simply based on the hearsay of, otherwise well intentioned people, who have never actually tried it out for themselves.

I can't speak for "most top skippers" but would totally agree that "Good starts, staying in phase, and sailing a clean race are way more important than adjusting a vang or jib flipper". And, as long as no one else has the advantage of adjusting their sails to suit the wind (and wave) conditions then you are all on a level playing field. But, all else being equal, he who can control his sails, can own the gold.

Hi John and all,

A PDF has been added to the files section of the US 1 Meter Yahoo group.

The file include 2 items that may be of interest: 1) a photo of the vang arrangement on the B rig of Connections 2) a table I created in MS Excel showing the relationship between the changes in the force of the wind ad wind speed changes.

The second item, the table, supports the notion that if you don't change the trim of the sails, twist etc as conditions change the boat will be tuned at much less than the optimum. It supports that notion because no one or very few people would disagree that with such huge changes in force being produced by such relatively small changes in wind speed you must be able to dynamically change the tune of your rig to suit the new condition. The radio controlled vang and backstay enable tuning to the moment to a great extent.

Here is a link to the TASAR Manual. http://www.tasar.org/index.php?option=com_content&view=article&id=12&Itemid=22

The TASAR was designed by Frank Bethwaite. His treatment of what, how, when and why to tune may be of interest to those who are considering going down the RC backstay and vang route. The last 3 sections hold the gold.

His son Julian designed the now Olympic class 49’er.

Franks “best” (IMHO) book is High Performance Sailing – Adlard Coles Nautical. So much more than you will ever want to know. It’s like the “new testament” to Marchaj’s old testament of the sailing bible “Aero-hydrodynamics of Sailing”

I have never worked so hard to give away what I know is a competitive advantage. But the task is done. And you only asked a simple question John.

Introduction and Contents (137.27 kB)

Section I (8.2 MB)- Assembly and rigging instructions

Section II (1.78 MB) - Basics of handling, sailing and maintenance

Section III (787 kB) - Principles of design and aerodynamics

Section IV (1.2 MB) - Sailing upwind Section V (623.51 kB) - Sailing off the wind