{"id":148208,"date":"2023-09-20T06:00:05","date_gmt":"2023-09-20T05:00:05","guid":{"rendered":"https:\/\/www.yachtingworld.com\/?p=148208"},"modified":"2023-09-21T09:40:08","modified_gmt":"2023-09-21T08:40:08","slug":"how-to-manoeuvre-a-yacht-under-power","status":"publish","type":"post","link":"https:\/\/www.yachtingworld.com\/expert-sailing-techniques\/how-to-manoeuvre-a-yacht-under-power-148208","title":{"rendered":"How to manoeuvre a yacht under power"},"content":"Wherever we have current (tidal or other) this will always influence the sailing wind and the boat\u2019s course over the ground. At anchor we can accurately measure the wind speed and direction, which we call the ground wind.\r\n\r\nHowever, if we are just drifting the effect of the current will alter the wind speed and direction that we are measuring. This we usually call the sailing wind or apparent wind.\r\n

Navigating in tide<\/h3>\r\nThis relationship between the ground wind and sailing<\/a> wind is not just important for racing around the cans but also when venturing offshore. We can look at the direction of the tide and decide in a general sense where we want to go; for example when beating out of the Solent in a flood tide we will usually choose the north shore, but the routing solution should also take into account sailing wind angle. The simplest example is the tacking and gybing<\/a> angles when with a favourable or adverse tide. We have all looked at our track and been disappointed with the tacking angle when against the tide \u2013 even to the point that we\u2019ve made little or no progress.\r\n\r\nAs boats get lighter and faster, with the ability to plane or even foil<\/a>, wind angle becomes incredibly important. A few degrees one way or another can make a significant difference in boat speed. We see this as we balance speed and angle in a coastal race where competitors are close. However, in longer distance racing we need to take navigating the tide into account, not just on our heading but also for wind angle. The forecast wind direction will be the ground wind, which can be quite a different wind angle to the sailing wind.\r\n\r\nA current from the side will change the true wind angle around 1.5\u00b0 for every tenth of a knot. It doesn\u2019t sound like much \u2013 until we get into a current in excess of 0.6 of a knot when we\u2019re looking at a 10\u00b0 shift in the wind from ground wind to sailing wind; more than enough to change sail settings or the difference between a good layline, or making a tidal gate or not.\r\n

Routing apps<\/h3>\r\nWe can now get racing routing solutions on our mobile phones or tablets. The latest generation of apps<\/a> include cloud routing where, by setting your course and the boat\u2019s polars, a computer ashore will run a number of different models, giving you a series of solutions and routes. By comparing the different model solutions, we can choose our best fit to the actual conditions.\r\n\r\nThe routing solutions also include tidal and ocean currents for navigating in tide. The best known of the companies offering this is PredictWind which (at a cost) provides GRIB file forecasts for weather conditions and current.\r\n\r\n[caption id=\"attachment_138624\" align=\"alignnone\" width=\"630\"]\"Navigating The red route shows the optimum course from the Needles to Cherbourg using the GFS wind model and PredictWind tides (on Expedition). The blue route is just wind without any tidal input<\/span>[\/caption]\r\n\r\nMost racing yachts, however, run onboard weather routing programs and navigators work tirelessly on perfecting their boats\u2019 polar diagrams. These are used to predict the boat\u2019s speed for all wind speeds and wind angles.\r\n\r\nMost computer-generated<\/a> polars are for flat water and, while a top helmsman may be able to sail to the polars, most sailors will find it difficult once waves and the extra weight of equipment on board has been added in. It\u2019s therefore useful to develop our own polars for boat and sails, and most navigation software programmes have datalog facilities to help with this. This information is also used to develop crossover charts for different sails.\r\n\r\nWeather routing depends on accurate information; it\u2019s pointless trying to develop polars if your instruments are not properly calibrated. As true wind direction and speed is calculated from boat speed, heading and apparent wind, all need to be accurate. If they\u2019re not, we\u2019re better off using apparent wind and generic polars for the boat and run them at less than 100%. But calibrating our instruments and generating polars in an area of moderate to strong tidal current is difficult and incorrect polars will give us a poor routing solution.\r\n

Is your tidal information accurate?<\/h3>\r\nWhen inputting information into cloud routing or onboard navigation software<\/a>, we will get a weather routing solution that takes into account all the variables. However, the times of high water will vary between different sources of data. There are also other variables to take into account; atmospheric pressure will alter tide heights \u2013 not much as a 1mb change in pressure computes to 1cm. We rarely get changes of more than around 30cm due to changes in atmospheric pressure, but 30cm can be a lot if you\u2019re trying to keep out of the tide!\r\n\r\nAdditionally, the direction of the wind will add or subtract to water depths and also the timing of high and low tides. An onshore wind will increase water depth and will tend to induce a stand at high water. This will delay the start of the ebb tide, which is then likely to be stronger. When the wind blows parallel to the coast the wind tends to set up long waves and storm surges. These waves have a period of hours and a wavelength of hundreds of kilometres. All of these factors become increasingly important when navigating tides.\r\n\r\nWhile it\u2019s difficult to take into account all these variables when sailing, it helps explain why the tide information that you have may not be the same as what you are experiencing, either in time or magnitude. Inshore, it\u2019s always worth verifying the rate of tide when passing navigation or racing marks.\r\n\r\nOffshore paper tide atlases have been used for many years, but we now tend to use electronic versions. These tend to be a mixture of theoretical and observational data and can vary between sources for accuracy for navigating tides. With well calibrated instruments we\u2019ll see a difference between COG and SOG compared with the boat speed and heading. By continually monitoring the actual effect and comparing it with the theoretical we will get a very good idea on the accuracy of the data.\r\n\r\n[collection]\r\n

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When handling under power is done well, it\u2019s like a black art. It wasn\u2019t until I became an instructor that I realised it could be broken down into a few key concepts. I called them \u2018The 10 Golden Rules of Boat Handling\u2019. However, when I wrote them it was largely from the perspective of a heavy displacement yacht with fine ends, using a shaft drive. Most of the large yachts I\u2019ve sailed in the past 10 years, such as the Clipper and Challenge yachts, matched this profile. Recently, I\u2019ve realised that the rules need updating. Yacht design has moved on considerably, and sail drives, long waterlines, bow thrusters and high topsides are now the norm, and twin rudders are increasingly commonplace. Flexisail, which operates a fleet of modern cruisers, kindly lent me the keys to Varvassi, a Hanse 418, for a day last winter to refine these Golden Rules, and in this two-part series I\u2019ll explain how to make manoeuvring under engine so much easier. There are two elements to good boat handling: understanding the boat\u2019s handling characteristics; and understanding the external factors which impact a manoeuvre. In the first of this series we\u2019re going to look at how a boat behaves, and next month we\u2019ll consider the real-world scenarios we find ourselves in. Rule 1: Slow is pro The number one rule of boat handling, especially on large yachts, is that if it\u2019s all going wrong, go wrong slowly. You\u2019re unlikely to do much damage at 1 knot. At 3 knots things become expensive. There are times when a burst of power is necessary and, carefully applied, this is an important tool. However, panic revs can cause more problems than they solve. If in doubt, step away from the throttle and pick up a fender \u2013 just use the throttle to maintain slow control. Minimum speed is essential on a heavy boat which carries its way. Once moving, many manoeuvres can be done in neutral. However, the Hanse 418 didn\u2019t hold her way as much as I expected so I had to be more assertive on the throttle, both to keep her moving and to stop her. Rule 2: Maintain steerage The counterpoint to Rule 1 is that you always need steerage. Steerage is created when water flows over the rudder. There are two ways of achieving it which I call Type 1 and Type 2 steerage. Type 1 is what you experience when you\u2019re actively propelled through the water, either by the engine or the wind. It\u2019s easy to forget that the wind can still be used for propulsion, even without sails up. If you\u2019re doing a downwind park (perhaps into the tide), or have some way on, you might not even need the engine in gear to achieve Type 1 steerage. Type 2 steerage is what is generated when a burst of prop wash flows over the rudder while the boat is stationary. This is an effective technique for tight turns when you need to control the …Continue reading »<\/a><\/p>\n","protected":false},"author":4392,"featured_media":148214,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[975,977],"tags":[2447,2361,1633],"review_manufacturer":[],"acf":[],"introduction":null,"_links":{"self":[{"href":"https:\/\/www.yachtingworld.com\/wp-json\/wp\/v2\/posts\/148208"}],"collection":[{"href":"https:\/\/www.yachtingworld.com\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.yachtingworld.com\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.yachtingworld.com\/wp-json\/wp\/v2\/users\/4392"}],"replies":[{"embeddable":true,"href":"https:\/\/www.yachtingworld.com\/wp-json\/wp\/v2\/comments?post=148208"}],"version-history":[{"count":3,"href":"https:\/\/www.yachtingworld.com\/wp-json\/wp\/v2\/posts\/148208\/revisions"}],"predecessor-version":[{"id":148224,"href":"https:\/\/www.yachtingworld.com\/wp-json\/wp\/v2\/posts\/148208\/revisions\/148224"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.yachtingworld.com\/wp-json\/wp\/v2\/media\/148214"}],"wp:attachment":[{"href":"https:\/\/www.yachtingworld.com\/wp-json\/wp\/v2\/media?parent=148208"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.yachtingworld.com\/wp-json\/wp\/v2\/categories?post=148208"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.yachtingworld.com\/wp-json\/wp\/v2\/tags?post=148208"},{"taxonomy":"review_manufacturer","embeddable":true,"href":"https:\/\/www.yachtingworld.com\/wp-json\/wp\/v2\/review_manufacturer?post=148208"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}