Fitting out a new cruising boat - Part 4

4:15 AM Sun 12 Apr 2009 GMT

'Salina 48 - you’re almost finished. Now to think about communications...' Multihull Solutions

Peter Salisbury continues with his series on fitting out a new cruising boat.

This is Part 4, the final part of the four part series. This week Peter considers the issues of communications and lightning protection.

To find earlier parts, click below:

Part 1 Navigational Requirements

Part 2 Power Generation

Part 3 Water Supply and Heating

Communications
What you get
The boat will be equipped with a VHF radio at the nav. station. This will communicate up to 20 - 30
miles.

Options
The main thing to consider with communications is the distance you intend to be from civilisation. Radio used to be the only option, but now mobile phones and satellite services are viable alternatives.

For coastal cruising VHF radio is sufficient for communicating with other boats, rescue organisations and coastguard stations. Mobile phones will work close to the coast, with some limitations. Also reasonable internet service can be achieved through the mobile network.

HF radio - vital communication on scheds for long range cruisers - .. .

Radio
Traditionally boats have used VHF radio for coastal work and an HF radio (sometimes called Single Side Band or SSB) for long distance work.

Possible improvements to the standard VHF include:
. An external speaker at the helm station
. A remote control head with speaker, microphone and basic controls at the helm station
. A Digital Selective Calling (DSC) radio interfaced with the GPS. This has a number of advantages, but the main one is probably the ability to send a digital distress signal at the press of a button. The signal includes the ship's identification and location and will transmit further than normal voice communications. (This feature is also handy for communicating directly with other boats to help keep calling channels clear.
. A handheld VHF can be carried in order to provide backup and portability. This can be protected against lightning strike and is independent of the ships batteries.

HF radio can achieve worldwide coverage but is more complex to operate and voice quality can be quite variable. The main advantage may be the ability to receive weather updates anywhere in the world, but long range cruisers use HF for daily scheds, either formal or informal, with other boats and/or shore stations.

Marine HF can be received over very long distances, but relies on someone listening on the selected frequency at the time of the transmission. It should be noted that many cruisers, in an effort to conserve power only turn their HF radio on when they want to use it. Additionally some coast stations do not continuously monitor the HF bands any more. DSC is available on HF sets.

It is quite complex to set up an HF radio properly so that good broadcast and reception is achieved and this is one job that should be left to an expert. Think in terms of several thousand dollars. On a catamaran it will probably include a 6 metre whip antenna, though other options are available.

Email is also possible over HF using services such as Sailmail. This is a bit complex to set up, with a specialised modem required to interface between the HF radio and computer. Sailmail is an annual subscription service, and is an extremely cost effective way of receiving specialist weather services as well as providing a no-attachment email service.

Mobile Phone
Mobile phones will operate out to sea for about the same range as they reach on land. Close to main towns and cities any service should be adequate. If there is no coverage ashore there will obviously be no coverage at sea.
Wireless internet is available from a number of carriers. This can prov ide quite reasonable internet speeds within the range of the network.

Satellite phone - complementary and easier to use than HF - .. .

Satellite
There are a number of satellite providers providing varying levels of service. They use one of two forms of service. One needs a satellite in a position that can 'see' both the phone and a land based station. This type of provider will publish a map showing coverage footprints.

The second type (more expensive) uses a network of satellites that can talk to each other, so service will be available when the user can be seen by any satellite. Depending on the network chosen, this will be over most or all of the world.
Some of the services do not give coverage in remote ocean areas, and others do. Check carefully when investing.

Satellite will provide voice communication and some form of data. Different providers offer different data speed capability, with greater speed definitely costing more money. Speeds available vary between email only, to moderate internet speed. Satellite services cost between about $2,000 and $12,000 to set up.

From a safety viewpoint, satellite has a number of pros and cons:
. A satellite phone is portable and has its own batteries, so it can be taken ashore or into a liferaft if necessary. It can also be protected from lightning strike.
. A satellite phone is as easy as a normal mobile phone to use with full phone book capabilities etc. HF on the other hand needs some experience to use effectively. Someone who has never used an HF set before may have difficulty establishing communications.
. Satellite is a point to point service and so relies on knowing the number to call and having someone competent answer it. HF on the other hand transmits over a wide area so anyone can respond.
. HF is relatively cheap to use, while any satellite service will represent a significant ongoing cost.

Nothing can be guaranteed to prevent electronic destruction from a lightning strike - .. .

Lightning protection

Why is lightning a risk?
Lightning is a very high voltage, high current discharge between the clouds and earth. The forces involved are so great that it is not possible to produce insulation strong enough to withstand it. As a result when an object is struck by lightning, very large currents will pass through it and the associated voltage will permanently damage its insulation. In addition large voltages can be induced into adjacent wiring, damaging equipment that is not even attached to the object struck.
The charge in storm clouds will discharge to earth whenever it finds a path that it can spark across. When a boat is at sea, it often represents the highest point in the vicinity, thus representing the shortest path to earth. For the sake of the following discussion the sea is taken as the electrical earth.

Lightning strike is potentially catastrophic, but on the other hand is very rare. Consequently most boat owners do not do much to reduce the potential for damage. This is more due to the difficulty and expense, with no guarantee of success, rather than lack of concern.

No such thing as total protection
It is not possible to protect anything completely from the effects of lightning. Because of the immense amount of energy involved the consequences of a strike cannot be predicted, therefore cannot be protected against. It is however possible to reduce the risk of damage in the event of a strike.

What are the problems?
When an object becomes part of the path for the electricity to flow to earth, a large current will flow through it. If the object is metallic and large enough (like an aluminium mast), the current will flow through it without damage. The problems arise if the conductor does not go all the way to earth or is too small. In such cases the current will flow through it and then jump to earth, or to another conductor on its path to earth.

In a traditional monohull with the mast stepped onto a metallic keel, most of the current will flow straight down the mast and out the keel to the sea. This will reduce but not eliminate the risk. If you consider, as an analogy, a garden hose with water freely flowing out the end and you prick a hole part way along the hose. Although water still flows out the end of the hose, some will also come out the hole. Similarly, with the current flowing down the mast, some will leak out down the shrouds. Because of the large amount of energy involved, this leakage may still be catastrophic.

Similar parallel paths towards earth include the mast top radio antenna and cable and the wires to the masthead lights. The only insulator between these wires and the ship's earth is a transistor in the case of the radio and a switch in the case of the lighting wires. These may either fry or explode in the event of a strike.

Another problem for electronic equipment is the fact that a large current spike through a conductor induces voltage into other conductors. This is the principal that allows electric motors to work, but in the case of a lightning strike the very large current flow will induce large voltages in the wires leading to electronic equipment, which may lead to equipment failure.

Catamarans have the potential for much greater damage than a monohull because the mast is stepped on the deck and there is no direct path to earth. The current will therefore flow down the mast and then jump to any or all nearby objects that lead toward earth. These will include the wires inside the mast and the ships wiring that passes in the vicinity of the mast in the saloon and the anchor locker. There are large cables from the anchor winch at the base of the mast leading to the engine bay and earth via the motors with the saildrives immersed in the sea. Thus all the paths to earth on a catamaran involve current passing through something else, potentially destroying all of them.

Reducing the risks
The primary concern in a thunderstorm is the protection of people. Try to avoid touching, or getting in between two metal objects, particularly if one of them is earthed. Also avoid as far as possible being in the water, or being on the boat and touching the water. Lightning striking the water nearby can easily electrocute a person in the water, even if they are not touching anything. The best place to be is inside the boat, away from the mast and the nav. station.

Protecting equipment involves trying to create alternate paths to earth that are easier for the energy to get through than going through your important equipment.

Some things to consider are:
. Any alternative paths must be constructed with heavy wiring that is capable of carrying the heavy current involved. 13mm2 being the minimum.
. The huge energy involved does not like to go around corners, so the wiring paths must be as straight as possible.
. If possible avoid using the saildrive as the connection between the boat's wiring and the seawater.
(This is the only connection on most catamarans!)
. Care must be taken with grounding cables run inside the boat below the waterline, because lightning could blow through the hull to the seawater.
. Electronic equipment wiring should be run without loops or coils. (To reduce the size of induced voltages)
. Earthed surge suppressors should be connected to electronic equipment.
. Disconnect (rather than turn off) electronic equipment during thunderstorms. Do not do this when lightning is likely in the immediate vicinity, or you risk becoming part of the path to ground yourself if you are touching the wiring at the time of a strike.
. If the mast is well earthed, a lightning rod extending above everything else at the masthead may help to protect the fittings and wiring. Such a rod should be 15 - 20 mm round copper or aluminium securely bonded to the mast.
. Bottle brush type lightning protectors which claim to dissipate the charge buildup that precedes a strike are available to attach to the top of the mast. There is some controversy about whether they are any better than a plain lightning rod, but in any event they will not do anything if the mast is not well earthed.

In practice if you do plan to undertake some form of lightning protection on a sailing catamaran, I would consider, in order of importance:
. Arrange to earth the mast to the sea. Perhaps a heavy cable or bar clamped to the mast and extended down through the bridgedeck, with some method of lowering it or an attached cable and ground plate of 0.2m2 or so, into the water at the first sign of storm activity.
. A reasonably heavy cable around the perimeter of the boat at about deck level, forming a loop, connected to the mast and chaiplates and bonded to all main metal components. 6-8 heavy down conductors should then be spaced around the boat from this loop, terminating with metallic through hull 'air terminals' just above the water line.
. Connecting surge suppressors or lightning arrestors to the leads of electronic equipment.
. Remove spare cable coiled behind electronic equipment. Installers often leave spare wire coiled to avoid having to cut it off and reterminate.

All of these things will help, but as I said at the beginning of this section: There are no guarantees when it
comes to lightning.

Protecting specific items
After all of the doom and gloom of the preceding, there is one piece of good news. A device called a Faraday cage will protect anything inside of it from the effect of a high voltage surge. A Faraday cage is simply an enclosure of metallic conductive material. Regardless of the electric field outside the enclosure, the inside will remain at a constant voltage.

A cake tin or a cooking pot with a well fitting lid makes an ideal Faraday cage. Wrapping an electronic device in uminium foil would probably even work. I normally keep a handheld VHF and GPS in such a tin.

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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