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7:30 AM Sun 15 Mar 2009 GMT
 | | 'It is an Orana 44, and she's all yours - now how are you going to fit her out?'
Multihull Solutions
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So, after much research, many discussions and a reasonable amount of anguish, you have bought the new cruising boat.
But that is only the beginning, because now you have to fit it out.
Peter Salisbury here gives the new owner a starting check list of how to decide what to do next.
This is Part One of a multi-part series and considers the issue of navigation.
The main thing to consider when setting up a cruising boat is what you intend to do with it.
A boat used mainly for weekend cruises needs far simpler equipment aboard than one that is to be used for extended live aboard cruising.
A boat that is over specified:
. costs more to set up than it should
. is more complex to operate for both the owner and anyone else who needs to drive it
. represents a greater maintenance commitment
. may be heavier than necessary - particularly a sailing catamaran
A boat that is under specified:
. will not perform to the owners expectations
. will not be as easy to navigate as you would like
. may not be safe or comfortable in the event of a fault
. may suffer from flat batteries, which is a nuisance and will significantly reduce their service life
. might not be as comfortable to live on as the first mate probably expects
Navigation - What you get
The boat will probably come equipped with a basic good quality GPS. It will give a position to within about ten metres anywhere in the world. The difficulty is that the position is displayed as a latitude and longitude, which must then be plotted onto a chart.
What you need to know
The basics of boat navigation are to be able to mark your position on a chart of the local area. This means you need your current latitude and longitude, an appropriate chart and the knowledge to accurately transfer the information from the GPS to the chart.
In addition you need to be able to plan your journey and plot your intended course via waypoints onto the chart. Once the course has been plotted you need to be able to convert the heading read from the chart to a compass heading to steer, adjusting for the earths magnetic variation. These two headings are always different and you need to be able to convert from one to the other wherever you are.
If you do not clearly understand this, go and do a coastal navigation course.
The significant risk with GPS navigation is that it relies on electronic equipment. You therefore need to consider the following risks:
. You could lose electrical power and therefore the GPS
. The GPS itself could fail
. Since the GPS system belongs to the US military, they could degrade or turn off the signal in a war situation. (This is unlikely, but should not be overlooked)
If you are travelling within sight of the coast it is relatively easy to navigate by using prominent coastal features. Away from the coast the options are more limited, though it must be said that most skippers these days do not carry a sextant and current almanac and probably could not use them effectively
anyway.
Options
Many boats are fitted with chart plotters. These have an electronic copy of the appropriate charts, often with a lot of other useful information. Chart plotters use a GPS signal to automatically superimpose your position onto the chart on screen. They are easy to use, both to locate your current position and to plot a future course. The chart plotter can be mounted at the helm station, at the nav. station or in many cases both.
Another option is to use a laptop computer as a chart plotter. There is a wide range of navigation software available, and the laptop can be interfaced with a GPS or have its own GPS receiver. Chart plotters suffer from the same risks as the GPS plus they leave you exposed to the possibility of being left without any charts at all in the event of power or equipment failure.
The best guard against the downsides of electronic navigation is redundancy, examples are:
. Carry paper charts in addition to electronic (and know how to use them)
. Carry more than one GPS. This could be the ships GPS plus a chart plotter with an independent GPS receiver.
. Carry an additional hand held GPS with spare batteries.
. Install two chart plotters with their own mapping cartridges, or a chart plotter and a PC with built
in charts.
. Understand the principals of coastal navigation and carry binoculars and a hand-bearing compass.
Seeing in the dark
Navigating at night, or even entering an anchorage at night presents its own special problems. Ships, small boats, navigation marks and buoys that are obvious during the day can be almost invisible at night.
Even ships can be difficult to pick out among the background shore lights when coastal cruising at night (and that can be scary!)
Radar is the best solution for night-time navigation and is reasonably priced. (Maybe $3,000 - $5,000 if a compatible chart plotter is fitted.)
Radar works by sending out a high frequency beam from a rotating antenna and watching for reflections from distant objects. These reflections appear as blobs on the radar screen. A large or close object makes a big reflection, while a small object produces a small reflection. Radar gives an accurate indication of both the direction and distance of an object, but little information about what it is, thus a ship and a hill could look the same. It takes experience to interpret the radar display but modern sets automate a lot of the technicalities. At least the inexperienced operator can tell that there is something out there and where to look to find it.
Most chart plotters have the ability to plug in a radar scanner thus sharing the screen, rather than the traditional stand alone radar screen. Most can even superimpose the radar reflections over the chart, making it much easier to interpret.
The size of the scanner (also called the antenna) determines the narrowness of the beam it sends out. A small antenna produces a relatively wide beam, which cannot differentiate objects that are close together. It is also only useable over shorter distances. Antennas are classified according to their maximum useable distance. So a 24 Nautical Mile (NM) radar would have an antenna that is about 18 inches mounted inside a 500mm diameter radome and produce a beam about 5? wide. A 72 NM unit will have a 48 inch rotating open antenna and produce a beam of about 1.5?. A small boat is unlikely to require anything more than a 24 or 48 NM antenna.
A new device that can make navigating among large shipping much safer is the AIS (Automatic Identification of Ships). By law all ships over 300 tonnes are required to transmit an AIS signal on a particular VHF band. This signal includes the name and size of the ship plus its position, course, speed
and rate of turn, all in a digital format. Since AIS works in the VHF band it has a range of around 30NM.
An AIS receiver is available which can receive, interpret and display this information. It can be readily overlaid onto a chart plotter display.
It is possible to purchase a 'lite' version of an AIS transmitter for smaller boats. This is called a Class B AIS transmitter. Commercial ships have a class A unit.
The class B transmitter makes all of your details available to any other ships with an AIS receiver, but in the event of heavy traffic a ship's master can remove class B signals from his screen to reduce confusion.
Next week Peter considers power generation.
Sail-World Cruising would like to thank : Multihull Solutionsfor the use of Peter Salisbury's article. For all your multihull needs, click herefor the best solutions.
by Peter Salisbury
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