|
The Compass – A New Concept by Steve Cockerill
If every time we go out on the race track, the wind direction was stable and the course configuration was perfect, there would be no need for a compass. However, this is far from the truth. The black art of reading shifts using boats around you and the angle of the waves can get very confusing in the height of the race – but can be solved with the use of a compass. It can be a very useful tool for pre start line bias, using it as a transit, beat strategy and an indication of changes in the wind pattern, but more importantly the wind-shifts upwind and downwind. I am not saying that I stare at mine hoping that it tells me the secret shift for the next beat, but it tells me valuable information all the way around the course: - Off the start line – I am on the headed tack, I must tack now.
- Around the leeward mark – I am on the lifted tack – wait, be patient.
- The whole fleet is in my window – we have a 30 degree lift – I had better foot off and get in front of the rest of the fleet before the next shift back.
- It has occurred to me that there are many ways of considering the speed of a boat in a race:
- There is the basic boat speed, knots through the water
- There is the VMG towards the wind speed – velocity made good speed considered on all legs which monitors your ability up wind and downwind to appreciate how high/low you can sail your boat before the increased height/depth in the course compromises the speed through the water.
- There is the ‘round the course speed’ which is the ability to use the VMG speed you are able to create and make it count towards the next mark in the race, by sailing all the lifts and not the headers. It’s a numbers game!
I like to tell the story of the first practice race at the Torbay Laser Nationals in 93. I started 30 seconds late uncertain of my speed through the water and needing a confidence boost. I ignored the other boats and tacked when my compass told me, taking the 7 shifts to the first mark. Half of the fleet were on the right tack on the first shift, then a quarter on the next, then an eighth on the next and so on, I found myself in 8th at the top mark, very satisfied that Laser sailing was just like any class sailing, sail the right shifts all the time and you will be ready to count the result at the end of the regatta. At no time had I compared my speed to anyone, I had not even thought who I was sailing against, it was just a matter of mathematics. I was not yet a very fast Laser Sailor, but I could point the boat in the right direction. The best way to see the racing line or lane markings in our sport is with a compass. Fundamentally it should provide you with the information that tells you if you are on a lift (sailing higher than you were previously) or a header (sailing lower than you were previously). Before we start looking at the ways this information can be displayed – perhaps we should consider the importance of wind-shifts on boats in a race.
The diagram 1 below shows how boat A has sailed less distance than boat B.
A more mathematical explanation of shifts shows, if a 10 degree shift on 2 boats 100m apart – see diagram 2 above.
Assuming L and R tack through 90 degrees, and have identical boat speeds and are 100m apart. The solid triangle shows that, if L were to tack (and loose no distance tacking), she would sail distance x, R would sail distance y, which shows that they would meet. In the dotted triangle, the wind has backed 10 degrees. The distance x’ is much smaller than distance y’, and by subtracting one from the other, we can determine the amount by which L has gained. Diagram 2 shows the ‘mathematics’ of the situation.
In a 10 degree header, boat L gains 25% of the distance of separation. Which means a 25 meters gain. Consider the time it would take to make the distance back in a race! Imagine if the boats were half a mile apart, then the gain made by L would be 200m. No wonder corners look so juicy, but are sometimes so very bad!Let us look at the types of compass on the market that are meant to help us see this racing line. The original compass provided the sailor with a heading in degrees that needed you to remember two 3 figure numbers (the heading on each tack) and keep an idea of how the lifts and headers effected the number, i.e. for starboard, header = number gets smaller and lift is number gets bigger – opposite for port tack.
The ‘compucourse’ is a very useful aid for these types of compass. You can set the wind direction and it tells you the bearings of starboard and port tacks and some help with the line bias. It was however, always difficult to see the heading of the boat when hanging out of the side. The more small course racing style compasses have ingeniously used tactical scales to provide the information in a more palatable style to the sailor. The tactical scale is visible from each side of the boat in a normal position. Most of these types of compass do give the bearing of the boat, but it is often not very clear and often involves a straight look at the top of the compass from behind to see the magnetic scale. Not a ‘normal’ sailing position. Silva have long been the accepted ‘classic’ Laser compass using a tactical scale that divides conventional scale into 20 units, marked 0 to 19, each corresponding to 18 degrees. 5 units is 90 degrees - nice number. The viewing lubber lines give the sailor an easy pair of numbers to remember. For a northerly wind (at 0 degrees) the helmsman reads 0 on the tactical scale on the starboard lubber line and given a tacking angle of 80 degrees the viewer sees 10 in the port lubber line. For every starboard number the port number is ten difference. So 1 on starboard is 11 on port. This would have been an 18 degree shift to port. It makes me think "take the 11 shift quick before it goes back to the 10". I can remember races by the numbers all the way around and I can exchange "I got a 13 on the port tack approach to the top mark!" banter back in the club.
I can still remember the number 7 all the way in from the right of the course to lead at the first mark of the first race on Sunday at the Plymouth Qualifier by 40 seconds. I had sailed the port tack on an ‘18’ off the start line and just waited for it to go back. It had been swinging between 18 and 17 in my previous practice beats, so I waited for the ‘17’ and tacked and sailed into the center of the course near the top mark on a ‘7’!Those who play the numbers game understand.
Tactical compasses give much more than just the wind-shifts – I use mine for the line bias. The 5 unit difference giving the 90 degrees on the Silva gives a simple measure of the bias, and also an idea of current wind pattern. Lets get back to that Sunday. Starboard tack had been 8 to 7. At head to wind the compass read 3 to 4 on the middle lubber line (5 numbers bigger). When the gun was about to go the wind was in the 4 region on the middle lubber line (i.e. 8 on starboard). So tack immediately was on the cards. However, the port end of the line had been 7 ½ so the port end would be biased at the start. Remember the pin end of the line and the middle lubber should tell me the same number as I could sail on starboard tack for an even start line. If I have to point below the pin end to get the same number, then the port end is the favored end, if I point above it, then the starboard end is the favored end.
The 10-minute warm-up told me that the port end was favored only in the left shifts and that the average wind made it even. I was conscious that I wanted to go right to get to the favored current so a starboard end start was OK and a quick tack to port was OK until we got the ‘17’ wind-shift back when I should take the shift back to the center of the course. The clear drawback for all analogue compasses is that they are all set up for a specific tacking angle. The tacking angle in the Laser does vary from light to windy conditions – so sometimes the numbers are not quite as sweet as they should be i.e. ‘17’ & ’7.5’. I have seen some people add extra lubber lines in different colours that they can use in different conditions, but it always seems messy.
The latest development in compasses has been the electronic compass such as the 'Tacktick'.
The 'TACKTICK' race compass
With ever more efficient circuitry and solar power supply together with the development of the accurate flux gate measurement of the magnetic field, programmable electronic compasses just make the numbers game a little easier and in some ways cheaper. I imagine I hear you say – thank God for that – having got lost in my explanation above! With help from the sailor prior to the start of the race, it logs the wind direction and the tacking angle. This is done internally by measuring the angle of both port and starboard tacks and from them it works out the wind direction. All shifts from then on are relative to this pre - programmed wind direction and are shown as a lift or header depending on the tack. This little programming bit takes a minute before the start by pressing one button. The sailor has to then sail for 20 seconds or so where it measures perhaps the last 5 seconds of angle, then asks the sailor to tack before measuring the angle again . If the wind later goes right and the info looks a little silly, the sailor can alter the internal wind direction with a push of another button, the tack angle remains constant. The game is still the same however, do I take this little header now or wait for a bigger one and risk a lift? But the info is clearer, the devise is lighter and it also has a handy built in racing timer for the start thrown in for the price of a normal analogue compass!
The display of the shift is presented as number of degrees header or lift relative to the pre set wind direction. The main display shows magnetic direction, on the more advanced ones it also shows wind direction. However, currently these compasses are not legal on the Laser – so why am I telling you about them? Well there may come a time when you are asked to vote on accepting this style of compass and you now have some information on them. Most classes have accepted the electronic compass with open arms, where as others have resisted it as they see it as making the sport a little easier.I think this standpoint might be that held by the Laser Class - who have so far resisted the electronic compass. Perhaps it is the possible programmable aspect that offends the true 'at one with nature' part of Laser Racing. With this in mind - Tacktick have recently hit back with a new development that simplifies the setting up and removes the 'programmable' nature of the device. Steve Cockerill worked closely with Tactick to come up with a non programmable electronic compass that offers the same info as that available via the analogue compass with its lubber lines - yet gives the sailor a better overall picture. With a split screen display - the new T060 Micro Compass is not only light, but also displays the approximate wind direction whilst sailing. It does this by showing direction minus 45 degrees in the left screen (as seen on Port) and the direction plus 45 degrees in the right screen. This effectively gives the sailor the wind direction at all times (assuming the boat tacks through 90 degrees). This perceived tacking angle can be changed to become class specific by a pre-set on the compass - so if you point higher than 45 degrees to the wind - then there will be a pre-set just for you. There is also a setting just to show the direction you are pointing - just in case you want to do the sums in your head! So ideally - once you have set up the tacking angle for the Class you are sailing - the compass gives you a clear idea of the wind direction - bigger the number - the more right it has gone - the smaller the number - the more left it has gone - - how cool is that. Even more of a bonus - if you know where the forecast direction is moving to - at least you can see if it has got there! No longer do you have to ponder - does 8 mean 240 degrees??
View our on-line shop compass selection
View our on-line shop compass selection
Personally, I do not care how easy it is to see the shift – I just wish there were a device that could help me predict the next one! I am sure that many would find the investment in a compass a cost effective way of adding round the course speed for many seasons to come. It is a way to dial into the risk management numbers game!
 |