Boat Electrics & Instrumentation

Battery size
Anyone who has a Garmin GPSMAP fishfinder, which was (and still may be) a standard option on BR20’s and other Swallow Boats, will know that the 7ah Yuasa NP7-12 battery that came with that unit barely lasts a day of constant use.  This is not a huge problem as this 12 volt battery is quite small (it weighs 2kg) and a spare only costs about £15.
However, it is possible to fit a larger 18ah battery (the Yuasa NP18-12, costing around £40) in the space in front of the BR20 centreboard without it getting in the way, because the battery is tall and narrow. This should be good for nearly three days of constant use.
Even further upscale, large capacity lithium-ion batteries of various flavours have been around for a while but are now becoming more common in everyday use.  LiFePO4 batteries seem to be the favoured version as they are more stable, less toxic and less prone to bursting into flames than other types. LiFePO4’s are still around 4-5x more expensive than the Yuasa-style sealed lead-acid batteries but they claim to be better in the following ways:
* They charge more quickly and hold each charge for longer when not in use
* In use, their discharge rate is consistently flat rather than slowly petering out like a Pb battery, so that more of the battery’s power is available.  When a Yuasa battery is only half-discharged, the voltage is nearly too low to power a fishfinder. An equivalent lithium battery would keep pumping out 12v until nearly fully discharged and would therefore give greater autonomy between charges – say five days instead of three.
* They are much lighter than Pb
* They last a lot longer in terms of the number of times that they can be recharged before giving up the ghost
The extra capacity gives the possibility of fitting a 12 volt cigar lighter-type socket which, with a suitable plug, can be used to charge a mobile phone, drive a small electric pump (to empty the ballast tank) or power a dusk-to-dawn LED anchor/steaming light on a long flex that can be hoisted up the mast on the spinnaker halyard.
Battery charging
If your boat is on a trailer, the battery can be charged from a suitable nearby outdoor socket once the boat has been towed home.  If this is not possible, then the alternatives are removing the battery from the boat to take it home for charging, or using a solar panel to charge the battery in situ. The 18ah battery is heavy (6kg), so if the boat is on a mooring, solar charging is probably to be preferred to removal.  It is not however cheap – a good quality long and narrow solar panel that can be secured along the top of the boom, plus a waterproof controller to prevent the panel from overcharging the battery, can cost over £300.  This system has been good enough to charge the battery adequately during a less than perfect summer in North Wales and is very effective in sunnier climes.

A battery box enclosing a Yuasa 18ah lead battery, installed forward of a BR20 centreboard case. From left to right a solar controller, a 12v socket and (just visible behind) an LED that changes colour depending on the state of the battery

An alternative electrical installation ahead of the centreboard case. A Tracer LiFePO4 24Ah battery is on the right of the picture and waterproof enclosure protected by a hinged acrylic plate on the left. On top of the enclosure are two waterproof output sockets, a solar panel charging socket, a battery state LED indicator and battery isolation switch. Inside are a non-waterproof solar charge controller and combined busbar/fusebox.

On the odd occasion when port/starboard navigation lights need to be used (even though they are not compulsory),  so called ’emergency navlights’ (powered by their own AA or D sized batteries) and tied to the shrouds are probably good enough for an open boat like the BR20.  This is particularly so if the lights are bright and efficient LED versions. However, make sure that they are certified as waterproof – some are not and they can fail after one dunking.
Wind measurement and beyond
There is an excellent but expensive (£700 or more) wire-free solution to electronic measurement of wind speed and direction.  Tacktick make the T101 system with a wind transducer that can be mounted on top of the mast, powered by a small integral solar panel.  This communicates wirelessly with a wind speed and direction analogue display that is also solar powered and can be mounted anywhere convenient, such as on the aft end of the centreboard case or (for better visibility) on the forward bulkhead, just behind the mast.  The units need little daylight to charge and can run on reserve rechargeable batteries for several days. A much cheaper solution is a long coloured streamer flown from the top of the mainsail!

Garmin GPSMAP 556s, compass and Tacktick T112 analogue wind display mounted at the aft end of the centreboard case.

In theory the Tacktick system can be linked to the Garmin GPS and a water speed transducer to give all sorts of other readings, such as true wind speed and direction and VMG upwind or towards a waypoint (useful for racing).  In practice the Garmin and Tacktick systems use different NMEA communication protocols.  The translation from one to the other is not an insurmountable problem but is probably a sophistication too far for a small boat.
Handheld navigation
Another breed of wireless instrument that can be used onboard for navigation is the iPad/iPhone family and its Android competitors, many of which have an accurate GPS built in.  There are excellent Navionics and NavX charting apps available for some or all of these instruments which allow you to navigate at least as accurately as larger chart plotters like the Garmin.  Unlike, say, Garmin chart updates, app chart updates are usually free and frequent. There is an increasing range of waterproof and shockproof cases available which means that these instruments can be taken on board with greater confidence. Battery life is not too much of an issue (particularly if your boat’s 12v battery powers a charger socket) although screen visibility can be a problem in bright sunlight.

iPhone 4 in waterproof case and floating “Lifejacket”, showing chart of Pwllheli Harbour in the Navionics UK & Holland app

Outboard alternator
There is the possibility of using the outboard to help run the electrics.  Some 6hp outboards (such as the 4 stroke Mariner/Mercury/Tohatsu) come with the option of an alternator that can be used to charge the battery or run wired navlights.  Some small boat owners even use the alternator to power an automatic tiller pilot. If you are going to do this, specify the alternator with the outboard from new – it is much more expensive to retrofit it.
If you want wire-free music on board and have a player with Bluetooth (such as the iPhone), waterproof Bluetooth speakers with rechargeable batteries are beginning to come on to the market in the US, and should be available in Europe soon.  They also double as handsfree phone microphones and speakers, although speech quality is reported as a bit fuzzy-sounding.  Reviewers recommend the Turtle Box and Ecoxbt and no doubt others will appear soon.
Finally, whatever electrics you fit, make sure that your circuits are adequately protected with waterproof fuses.  A short circuit on a boat can cause a fire, which is unhelpful at the best of times but is really dangerous out at sea.
Graham W     November ’12