Thursday 17 June 2010

Sailing Tips: Rounding up and How to Prevent for Sailors

Rounding up is one of the more annoying things to happen when you are sailing into the wind on a gusty day. It slows your boat down and if uncorrected can put your nose right in to the wind and stall the boat. Then you have to bear away and regain boat speed. Not a good look, especially if there are other boats in the vicinity watching!

The following article from explains clearly what to do when it happens and how to avoid by watching your telltales and competent sail trimming:

'Rounding up is caused by many factors. One is too much wind and force aloft which tends to heel the boat over. This reduces the amount of rudder in the water and thus the rudder’s effectiveness. Another factor in rounding up is that the centre of pressure of wind on the sails is too far aft. This then pushes the aft of the boat downwind and thus the front of the boat upwind.

Our SailTrim clinic discussed this topic and so what we wanted to do was test it out for sure. So last weekend we took out a friend’s Beneteau 373 to test out an anti-round up theory. Read on to find out the results of our experiment:

1. First though, we must first understand wind shear.

The phenomenon of wind shear is pretty easy. Wind moves faster at the top of the mast than it does at water level because the stationary water by friction, slows down the wind the closer it gets to the water. So, if you could see wind you can visualise in your minds eye the water at sea level dragging the wind a little at the surface.

2. Secondly, consider the concept of true wind vs apparent wind:

This is best understood by imagining driving your car in a cross wind with your hand out the window of the car. At stand still you would feel the wind coming from the side of the car. The faster you go, the more you feel the wind coming from the front of the car. But when a gust of wind comes (which is just an increase in true wind speed) then you would feel the wind shift back more to the side.

When relating this to a sailboat, if your boat was standing still, the wind at the top of the mast would be the same apparent direction as at the cockpit level albeit, faster (from the wind shear phenomenon). However as your boat picks up in speed the apparent wind moves forward BUT because of wind shear it shifts forward less at the top of the mast, ie., at the top of the mast the wind tends more to the direction of true wind direction because the true wind speed is higher.

Thus at the top of the mast the true wind is more aft than the apparent wind.

So – the fact is: at the top of the mast the wind is higher in speed and more aft than at cockpit level.

Figure A and B show the boat speed, true wind and apparent wind vectors for cockpit level and top of the mast. Obviously in both cases, the boat speed vector must be the same. The true wind vector is obviously the same direction but due to wind shear it is longer (faster) at the top of the mast. This results then in the apparent wind direction being more aft, in this case from 135 deg to 125 deg.

3. Third, there's wind shear and apparent wind phenomenon:

You should understand that if a sail is sheeted in too tight it creates more heel. This then is exactly what is happening at the top of the mast. Even though at the bottom of the sail you may have perfectly trimmed the sail, the top of the sail is sheeted in too tight against higher wind speed. No wonder you’re getting excessive heeling. And excessive heeling creates roundups.

This is now quite a revelation! It means that the top of the main needs to be “out” further than the bottom of the sail for it to operate efficiently. This is usually indicated by the top telltale. Often the leeward telltale will be stalling at the top of the sail. Especially in high wind because of the phenomena above.

So, the top of the mainsail needs to go further out so that the starboard telltale can fly smoothly. Hence the top of the mainsail needs to be let out further so that the leeward telltale can fly smoothly.

This is commonly referred to as twisting the sail out at the top. Except people believe you are just spilling out (wasting) the wind at the top. Not quite so now, as you’ve just learned. Twisting out the top of the sail is letting the top of the sail fly according to the direction of wind it is feeling.

In the illustration, you can see the top telltale on the downwind side is fluttering. If you let out the main at the top, the wind can reattach to the sail on the leeward side and the telltale will fly smoothly reducing the force aloft.

Understanding all the above. How do we stop rounding up?

Option one: Obviously the first and safe option in higher winds is to reef the sail.

Option two: Let out the traveler which is what most people do when hit by a gust. Just so long as you realize what you’ve done is not twisted the top of the sail out – all you’ve done is let out the mainsail from top to bottom and thus depower the mainsail. This reduces the force aloft and thus the heel. It also moves the centre of effort of wind on the sails forward which reduces tendency to round up. The trouble is that you spend all day fighting gusts with still quite a few involuntary round-ups.

Option three: Let out on the mainsheet. Here again you’ve depowered the entire mainsail to handle the gust. Still, it works.

Option four: Permanently reduce the force aloft by letting out further on the mainsail and tightening up on the traveler. The trick here is to bring the mainsail bottom back in again using the traveler. Yes, bring the traveler to windward up past the center point. Most sailors are reluctant to do this because they’ve been taught that it detaches the wind on the leeward side. But not when you’ve let out the mainsheet. In effect, by letting out on the mainsheet, you’ve allowed the boom to rise up and the leech of the sail to slacken. This creates the desired twist at the top and allows the top of the sail to fly according to its apparent direction. At the same time, the bottom of the sail can fly according to its apparent direction.

By trimming the traveler and mainsheet together you can manage the twist at the top of the sail as desired yet still keep power on the bottom of the mainsail. Keeping power on the bottom of the mainsail keeps your speed up which also increases the effectiveness of the rudder. Increasing the effectiveness of the rudder means it can hold more against any turning effect created by the shifting of center of pressure backwards. Wow – see how it is all connected?

What happened on our 15 knot gusty sailing day? Well, not one round up.

So to summarize, the sailing lesson here is when in higher winds bring the traveler up and sheet out the main. You’ll also need to release the boom vang a little. Letting the boom vang out allows the boom to rise which loosens the leech (trailing edge) of the sail and allows the top part to “twist out”. '

Article courtesy Sail-World and Grant Headifen, images courtesy Sail-World

You can read much more about sail trimming and techniques in my ebook 'Voyage of the Little Ship Tere Moana' downloadable to your PC, iphone or ebook reader, from my website

Thursday 10 June 2010

World Oceans Day 2010 Recognised by Sailors

For cruising sailors pollution of our oceans is a major concern. There is nothing more objectionable when sailing in pristine waters to then come across some discarded flotsam disposed of irrresponsibly - as humans we leave a trail wherever we go! I would trust that these days all yachties keep all trash on board to dispose of correctly at the next port. This way we can collectively make our contribution toward keeping our oceans clean.

The more worrying occurences are the major pollution events such as the current Deepwater oil spillage off the Louisiana coast - this is ocean pollution on a massive scale and even after it is finally plugged the ongoing effects from it will be long term.

World Oceans Day is now officially recognised by the UN and celebrated annually on June o8.

The following is an extract from cruising blog:

'World Oceans Day' .
June 8th is World Oceans Day, and never were our oceans more in need of a friend.

With discarded plastic bags killing thousands of precious sea animals, with the world's fish stocks at record lows and the oil well damage on the shorelines of the Indian Ocean, Canada's Pacific coastline and now the Gulf of Mexico, the world that the sailor loves to inhabit is under threat like never before.

Go to the World Oceans Day website to see how you can be involved!

About World Oceans Day:

As a result of a United Nations General Assembly resolution passed in December 2008, World Oceans Day is now officially recognized by the UN as June 8th each year.

The concept for a “World Ocean Day” was first proposed in 1992 by the Government of Canada at the Earth Summit in Rio de Janeiro, and it had been unofficially celebrated every year since then. Since 2002, The Ocean Project and the World Ocean Network have helped to promote and coordinate World Oceans Day events worldwide. We help coordinate events and activities with aquariums, zoos, museums, conservation organizations, universities, schools, and businesses. Each year an increasing number of countries and organizations have been marking June 8th as an opportunity to celebrate our world ocean and our personal connection to the sea.

Together, we also developed and widely circulated a petition to the United Nations urging them to officially recognize World Oceans Day. With help from our Partner organizations, tens of thousands of people from all parts of the world signed online or paper copies of the petition. Congratulations to all for helping to make this happen!

Designation of World Oceans Day provides an important boost to those organizations and individuals who have been deeply committed to ocean conservation. Official UN designation is another important step toward improving the health of our world's ocean.

Now we need to capitalize on this fresh momentum! We hope you will be involved in planning or participating in a World Oceans Day celebration near you!

Extract courtesy Sail-world, images courtesy google.

We can all do our bit by acting responsibly when at sea and getting involved with various anti pollution programmes when on land. The long term survival of the marine environment is in the interest of us all as humans. Remember, the oceans will survive without us but we will not survive without the oceans.

You can read more about responsible habits at sea in my ebook 'Voyage of the Little Ship Tere Moana' downloadable from my website