How to Handle Wind Gusts and Rounding Up

Posted by Director of Education on February 17, 2014 under Bareboat Charter, Crew, Rules of Right of Way, Skipper, weather | Comments are off for this article

Rounding up is so – so – so dangerous. Last weekend we were out sailing and a speed boat came ripping by at about 20 knots to the windward of us and only about 60 ft away. Yes they are stupid – yes they should know better and yes they should be shot – but that is not going to save your life. You have to take responsibility for yourself out there. Think about what could happen if a last minute gust hit you and you rounded up into that speed boat. You’re dead – and actually by maritime law it would be your fault.

So you’ve got to know how to handle a wind bullet and you’ve got to be at the ready. A last minute gust can kill you and your crew.

… and btw if you are a speed boater please pass to the leeward side of a sailboat …  (leeward is the downwind side btw)

First a definition and explanation of Weather Helm:

weather helm on a dinghy

Forces from the wind aft of the keel are balanced by the rudder.

Weather helm is when the boat wants to turn towards the wind and you have to hold the helm in a leeward turning position to maintain a straight course. i.e. if you let the helm go the boat would automatically turn towards the wind.

Usually a boat is trimmed so that you purposefully have a little weather helm. Why? Well if you are turning the rudder so that you are fighting the weather helm it means that the leading edge of the rudder is pointing upwind. i.e. the boat wants to turn upwind but you are counteracting this by turning the boat downwind. Turning the boat downwind means by definition the leading edge is pointing upwind. See the graphic.

All this means that as the water hits the rudder there is a component of the water force that pushes the rudder (and thus boat) in a windward direction i.e. it actually makes your boat  climb upwind from  the water force on the rudder. This is a desired outcome when sailing towards a windward destination. Few sailors know this.

I say all that to say this – your boat should naturally have a little weather helm.

Here is what a wind gust does:

First, it immediately heels your boat over. Because of the heeling angle, less and less of the rudder area  is effective in providing turning force to counter act the weather helm. See the animation below.

Second, in a gust, the wind force on the sails increases with the square of the velocity but the counteracting force from velocity of water over the rudder does not increase because in that instant the boat speed has not increased.

So you’re trying to dip twice to use the rudder – eventually there is none left. The helm will be all the way over and the wind force has completely overpowered the rudder = round up.

Third, by definition an increase in true wind speed across the water shifts the apparent wind angle on your boat so that it comes more from an aft angle. i.e. if you are on a close haul, the wind now more feels like a beam reach. This exacerbates the heeling force because your sails are now in too tight. The wind gust is pushing sideways on the sails rather than flowing smoothly around both sides of the sails. This is now a triple whammy on the rudder. Poor Rudder!

Why does an increase in wind increase weather helm?

A boat is trimmed with weather helm by raking the mast backwards. This shifts the force on the sails backwards. To see the effect now, push sideways on a pencil on your desk. If you push in the center, the pencil moves laterally sideways. If you push towards the eraser end the tip moves “upwind”. Increase the force, the tip mores upwind more. i.e. the more force towards the back of the boat, the more the boat wants to turn up into the wind = weather helm.

But remember – a small amount of weather helm actually helps you “climb” upwind using water force from the rudder.

Why does an increase in wind speed move the apparent wind angle more aft?

Best you take a look at our free sailing course on sail trim. There is an excellent explanation there.

Wind Gust Directions

Offshore the wind gust is more likely to be in a consistent direction as the existing wind. Close in to cliffs, the gust can be heading in many different directions.

Back to dealing with gusts.

First off – you can see them coming. They are a change in perceived water color because the light reflects different off the small ripples generated by the extra wind. Seriously – they are easy to spot. Haa haa during the daylight.

Here is an animation that we did for our iBook “Your First weekend in Dinghy Sailing” showing how a gust is handled on a dinghy but also note how the animated rudder effectiveness changes with the heel angle.

As the wind gust approaches you should be prepared in your mind and with your crew for the outcome. Don’t leave it until the gust hits to start battle stations. Remember, gusts can be dangerous. Unprepared crew members can be thrown around. Boiling water in the galley can be splashed. People tossed out of bunks. Gear can be thrown around into someone. Someone can be thrown against a bulk head. Someone can loose footing and go overboard and finally as we started, you can be rounded up into another boat.

  1. A crew member should be stationed and attentive to the traveler. You should warn the crew member of the approach. As the boat begins to heel, the traveler crew member should begin to ease the traveler. With a big gust, the traveler may need to be dumped all the way to leeward. This spills the wind out of the mainsail.
  2. The mainsheet crew member should be made aware that if the traveler dump does not work that the mainsheet should be eased. But make sure that both sails are not being dumped at the same time. Traveler first then mainsheet if needed.
  3. Tune the crew into whether an ease will work or a complete dump is needed. A good crew member will be able to anticipate and adjust. Training is good!
  4. As the helmsperson, you can turn up into the wind gust a little assuming it is a lift. A quick look at the masthead wind indicator can tell you that answer. The gust will hit the top of the mast before it hits the boat. Turning into the gust will alleviate the heeling a little and allow you to take instant advantage of a lift. But make sure that you don’t overturn.
  5. The headsail (jib or genoa) is to be left alone in a gust. Since the force on the headsail is positioned forward of the keel, the headsail does not contribute to rounding the boat up into the wind. In fact it acts opposite it helps prevent rounding up because the force on that sail is far forward of the keel. i.e. push on that pencil on your desk again. The head sail does however contribute to heeling. But again, the heeling in a gust can be controlled by the mainsail traveler and sheet.

If you’re getting hit by a lot of gusts and the crew is working hard to control – consider reefing the mainsail. This has three effects:

  1. It shifts the center of pressure of the sail forward so that the rounding up effect from aft pressure is reduced
  2. It reduces sail area aloft which reduces the heeling moment
  3. It reduces the sail area in total which reduces the heeling moment

Heeling will be reduced by reefing the headsail, from the above arguments then this helps the rudder effectiveness.

Don’t try to tough out a windy situation by not reefing. Your boat will actually sail faster if you’re not weaving all over the place each time you round up and your crew will have a better time.

A professional delivery Captain told me once that his motto when crossing the Atlantic was “if you are thinking about reefing you should have done it yesterday. If you are thinking about shaking out the reef, wait until tomorrow”.

 

 

Reef un reef reef unreef

Posted by Grant Headifen on January 3, 2009 under Skipper | Be the First to Comment

When you’re racing you need to get the most out of your rig and that’s exactly what we had to do in the Austin Yacht Club Red Eye January 1st Race event. While one weather channel was predicting 6-8 knots another was saying 15-20. In the last sailing blog I’d mentioned that we were going light wind sailing – not true. Biggest gust was to 25 knots and mostly the wind was around 17 knots. That’s reefing time. Ahh that’s for the weak at heart might say some – but reefing increases your performance.

Reefing reduces the size of the sail. When reefing a roller furling sail the sail is rolled up a little. The first reefing point for a roller furler is about 15%. Thus is the foot of your sail is 12 ft long then roll the sail up about 18 inches.

They way that the sails performance is increased is it helps the wind stay attached to the lee side of the sail. Slow moving air can bend around the curve of the sail and stay attached. Fast moving air has more momentum and can not stay attached. Thus it swirls off creating turbulence in its wake which vastly upsets the balance of low pressure on the lee side of the sail and high pressure on the windward side. The art of sailing is all about the even flow of wind over the sail and allowing this turbulence to happen is one way to loose a race.
The image below is taken from Module 7 of the Skipper course and from the Sail Trim Clinic. It shows wind swirling inefficiently off the sails.

The other part to reefing is that the height of the center of force acting on the sail is reduced. This reduces the heeling force. IE the boat tips over less. Most boat hulls operate with the least amount of drag either flat or slightly tilted. Tilting over too far will increase the hull drag in the water. With high winds and an unreefed rig, you’re certainly going to be tipped over beyond the most efficient point.

So reef that sail.

Downwind is a slightly different story. As long as it is safe – ie the winds aren’t too high – you can let the reef out to capture more wind against the sail area. Remember the apparent wind against the sail going downwind is reduced because your speed subtracts from the true wind speed when going down wind. However you have to be a wee bit cautious with this. At one point we needed to steer up wind a little to miss a shoal, a gust came through at the exact same time and also a boat flying a spinnaker came past us. Our boat began to round up into the wind but also into the other boat. To save the day we let all the sails fly so that the rudder could overpower any turning effect the sails had against us. This allowed us to turn back down wind with out loosing much of our speed or heading.

About 2 hundred yards short of the mark on the down wind leg I had the crew re-reef the main sail so that we were prepared to come back up onto a close haul for the next upwind leg. Always make sure you do this is plenty of time. Being 50 yards early is better than being past the mark and still messing with the reefing where you’ll loose valuable time.

We had two downwind legs and 3 upwind legs so we had to reef – unreef – reef – unreef – then reef again. Good practise for the crew and the barking captain – right? Wrong Captains never bark!

In our sailboat race on new years day, we elected to reef the main sail about 25% (2 reefing points) to reduce the rounding up effect. See last blog on rounding up. But we left the head sail fully out. The reason for not reefing the head sail was because a reefed roller furling head sail never really behaves efficiently due to the disturbance on the sail created by a bunched luff. IE the rolled sail on the leading edge doesn’t allow for smooth wind flow over the sail. Also the sail shape is always not quite how you want it. Even tho you move the cars forward, the shape is never how you’d want it. But if the wind conditions had gotten any worse then we’d be forced to reef the head sail as well.

Admittedly we didn’t do too well in the race but at least we all did our best and had a great start to the new year.