According to Frank Bethwaite, at hull speed, the wave crest is exactly on the transom. The crest moves further aft as the speed increases with a massive increase in drag (what Bethwaite calls the "forced mode") until the hull starts planing. In “forced mode” the boat is effectively sailing up-hill until it can get on the plane. It is in this range between hull speed and planing where the wake reaches its greatest with the stern wave resembling a rooster tail (having a corresponding large upward component in the flow).
Before you start adjusting your wings it is important to know what your wing angle is for a given setting. You can then mark off positions so you can readily set the wing to a known angle. A good way to calibrate the wings is to take a photo from the side with the rudder mounted and the wings at different positions. You can then use a photo editor to superimpose lines and see what angle your wings make with the hull (see photo).
Winged rudder on N3530 Very Hungry Caterpillar (DCB design). The upper black line shows the hull angle and the lower black line shows the wing angle with the rudder pulled fully on.
Straight line - Upwind
The wings start to work above about 4 knots of breeze and 2 knots of boat speed. The wing position needs adjusting according to the conditions. The optimum wing position depends on the boat speed and how choppy the water is.
In very light winds the foil doesn’t affect the boat in a straight line much, there is a small amount of drag but the wing sections are pretty efficient at slow speeds. In flat water in medium wings the wings can be pulled hard on. As the wind picks up then the wings can be let off to reduce drag and avoid digging the nose in. As it gets choppier then the wings should be eased further to avoid them trying to push the nose through the waves rather than allowing the boat to ride over them.
The best settings for you will depend on the wing profile, hull design and your crew weight but the general pattern for upwind is:
- Very light; wings slightly off the max position. Your aim is to set them in the lowest drag position
- Light to Moderate; wings hard on for maximum lift
- Windy / Choppy; wings steadily go off to reduce drag (more lift not required).
With the additional lift from the wing the helm and crew can (and should) sit further back in the boat compared to sailing with a non-winged rudder. Boats designed to work with a winged rudder have the thwart positioned further back so the helm and crew are using toe straps in the right place. If your boat has a retro-fit wing and the thwart hasn't been moved then bear in mind that you will need to sit further back than usual - this takes some getting use to as old seating habits are hard to break.
Helm and crew sat slightly back compared to a non-winged 12
When the wings are set there should be little need to adjust them when sailing upwind. It is only if there is a big change in speed or wind strength that you should need to adjust them.
Straight line – Downwind
The T-foil has a stabilising effect; in other words, the faster you go the more stable the boat feels. The generation of 12s before the DCB seemed to have an upper speed ceiling of around 14 knots above which maintaining control became tricky often resulting in a capsize to windward, leeward or bow first (or even transom first on occasion in the Numinous). With the T-Foil there is a much smoother transition from displacement sailing mode to planing mode and there doesn’t appear to be a speed ceiling.
The wing settings follow a similar pattern to upwind, the main difference being that the boat is generally travelling faster downwind so the wings are naturally generating more lift and may therefore need to be backed off more. Also the waves tend to be behind you, so compared with upwind, there is less of a concern about the wings pushing the boat through the waves rather than over them.
Again, the best settings for you will depend on the wing profile, hull design and your crew weight but the general pattern for downwind is;
- Very light; wings slightly off maximum
- Light; wings hard on for maximum lift
- Moderate; slightly off maximum
- Windy; wings go off as required to keep the nose out, sometimes a long way off very quickly in a big gust
In marginal planing conditions, even though you can let the wings off to control the trim, in the first instance it is still worth moving to the back of the boat as you get on the plane and then start to let the wings off. Keep the wings on as long as you can.
Helm and crew sat well back, wing adjusted so the bow is clearing the waves
For downwind sailing more frequent adjustment of the wings is likely, as gusts come the wings may need to be let off and as gusts disappear then the wings may need to be pulled back on. There is balance here: don't get fixated with adjusting the wings to the detriment of sailing tactically, make sure you keep an eye out for gusts, waves and other boats to maintain your speed and position in the fleet.
On a final point, you'll know if the wings are too hard on because either the nose will be pushed down or there will be air-pockets / ventilation on the wings, look for the water flow separating and air-bubbles coming off the wings. If either of these happen then ease off the wings until they stop, when the ventilation stops you'll feel the boat pick up speed again.
Tacking is the manoeuvre where you really notice the wings and if not careful they can slow you down significantly. The trick to this manoeuvre is smooth and gentle movements to maintain the speed whilst tacking. This may take some practice to get right.
Points to note:
- Rocking & rolling is slow. If you tip the boat from side to side wildly, or wiggle the rudder madly then you’ll very quickly find that the boat stops as the wings create a lot of drag.
- You have three rudders now! As the boat heels through the tack then the near side wing ends up more vertical. Essentially the wing becomes a rudder, it stops creating vertical lift and becomes a steering foil.
- Watch for the pop-out. With most winged rudders the wing is mounted around 200mm to 250mm below the waterline. At this height the leeward wing will pop out of the water on the tack and then dip back in when the boat is pulled up on the new tack.The pop-out isn't detrimental and in fact reduces the wing drag thereby helping the boat turn.
When tacking use as little rudder as possible; and avoid rolling the boat too vigorously as this affects the flow over the foil causing drag. Try and steer a path so the wings follow a gentle curve through the water rather than a 90 degree turn.
With the boat heeled coming out of the tack, try and bring the boat up slowly so the boat accelerates forwards as the wing goes gently into the water. This helps the flow re-attach quickly onto the wing. Avoid slamming the wing down into the water as that causes drag.
In most cases the wings help you get around the gybe, particularly as they can prevent nose diving, but with all that foil surface area at the back of the boat when you go into the gybe the wings can start steering you (they become part of the vertical foil) and they can also “catch”, stall out and send you in the drink.
If it is honking then consider easing off the wings another 10mm or so just for the gybe to give you some tolerance to nose diving.
To get through the gybe, the principle is similar to tacking, try to use as little rudder as you can, avoid rolling or righting the boat too vigorously as this affects the flow over the foil and try and let the wings follow a gentle curve through the water.
Most of the winged rudders in use are rotational lifting rudders. This is great for handling on the shore and also means the rudder can be in a raised position for launching thereby avoiding the need to wade into freezing cold water up to your waist/neck to fit the rudder (as has to be done in many foiling classes).
The trick when sailing off the beach is that the rudder either needs to be fully up or fully down, there is no good half way house. Control of the boat is tricky with the rudder fully up so it is best to keep the speed low and the boat flat to avoid the wings digging in. Speed can be kept low by keeping the crew weight in the middle of the boat. Wait until you have enough depth, slow the boat and pull the rudder fully down in one move.
The T-foil has a couple of effects on coming ashore. The first is that as soon as the wing comes up there is a lot of drag so the boat slows rapidly, at this point the rudder needs to be fully raised so that the wings poke out of the water allowing you to maintain forward movement, there is no good half way house. Having lifted the rudder it is tricky to steer, more so than with a normal rudder. As soon as you heel the boat over, one of the wings goes back in the water slowing you further. The best plan is to;
- Leave raising the rudder to the last possible moment
- Sail slowly once the rudder is up
- Avoid aiming for tight gaps on the shoreline and
- Wait until there is plenty of space on the shore.
The second effect is the change in balance of steering, you’ll notice this if you drop the main whilst sailing. With a non-winged (a.k.a. normal) rudder you can drop the main and sail around on the jib ok making headway upwind and downwind in all directions. This is not the case with a winged rudder.Instead when the main is dropped the boat wants to turn around the rudder, making going upwind under the jib alone difficult. Keep in mind that if you plan to drop the main to come ashore it is best to do this when you are upwind of your final destination, so you can sail downwind under jib alone to the shore.
Enjoying the ride