Wednesday, 20 August 2014

The Minehead Currach

From time to time we do divert ourselves with other boating types and this week we were in Minehead, Somerset, for the annual raft race supervised by and raising money for the Royal National Lifeboat Institute (RNLI).

Some of the rafts were more speedy canoes-cum-catamarans, while others were ramshackle frames lashed to barrels (and this one made up as a tank!)
But what caught my eye in particular was this traditional boat, a currach,  a type of Irish boat with a wooden frame, over which animal skins or hides were once stretched, though now canvas is more usual and this particular boat uses "ballistic nylon" sewn by the Leather Workshop at Withycombe.  The construction and design of a currach are unique to the west coasts of Ireland and Scotland, and what is astonishing to me is that this boat was made in one week using local materials (Exmoor spruce, green oak and hazel) and local volunteers.
For more information go to The Minehead Currach on Facebook or UTube "Minehead Currach Build".

Friday, 8 August 2014

Welford to Foxton

Now that Welford Marina is Patience's new home (and very pleased she is with it!), we have planned several trips to explore our new patch. So Duncan and Jenny set out to head north up the Leicester Arm for the short but delightful 9 miles up to Foxton. It was from Foxton that we set off on our very first family narrow boat holiday in 1994.
With only one lock (that on the Welford arm) between the marina and Foxton Top Lock we had an easy time of it with only the Husband's Bosworth tunnel to negotiate and the rest beautiful calm green countryside and harvested fields, the sun beaming down on us all the way to Foxton for about 4 hours.

We approached the Foxton top lock, turned in the side arm that once lead to the inclined plane and came back under Bridge 60 to moor.

Moorings directly above the Top Lock are best kept for those waiting to go down the locks, or filling up with water.
Above Bridge 60 there were ample moorings, including one Candy Boat supplying sweets.

On arrival we explored the locks and ended up in the Foxton Locks Inn - good grub, good selection of beers, delightful sitting out in sunshine by the waterfront.

Next day we returned to the locks as gongoozlers and admired the way the locks are planned with side ponds to hold the water and direct it to the next lock in the staircase.
The trick, as a boater, is to open the red paddle followed by the white paddle. This fills one lock and empties the next, while directing the water into the pond for re-use. Much more detail here.
Looking up from just below the central pound which divides the two lock staircases so boats can pass each other half way through the flight.
Again looking up the flight, from a vantage point on top of the museum which was the engine house for the inclined plane. The lock keeper's house is the white building at the top.
Looking down from near the top of the flight. This is gongoozler heaven! The museum is the red brick building on the right
The museum is excellent and well worth seeing. It explains the working of locks and this system in particular, the history and significance of Foxton locks and would be of interest to all ages.
The mechanism for the Inclined Plane, which from 1900 to 1911 moved boats speedily up a steep gradient, avoiding the slow and tiring locks and saving water, was sold off for scrap in the 1920's but enough remains to visualise the engineering achievement and envy the system.
 The Inclined Plane in 1900
One of the pulley wheels around which the cables turned, holding the caissons in which the boats sat for their journey up or down the plane.
See The Anderton Lift and The Falkirk Wheel amongst other remarkable boat lifts for ways of moving a boat up or down between water levels.

How wonderful it is that people come from far and wide to be awestruck by engineering ingenuity!

Our return trip (another 9 miles with the Welford lock and the Husbands Bosworth tunnel, was equally attractive and enjoyable. Welford to Foxton - a good trip of two short days with overnight stay. And our new fridge worked brilliantly!

Thursday, 7 August 2014

Boat Fridge Installation

Although it had been previously successfully repaired (see earlier blog, 24 June 2013),  the 20 year old Electrolux gas fridge was always temperamental and finally gave up the ghost during our trip from Oundle to Welford. This time its decline looked terminal so we investigated our options.  Here it is when we bought Patience in 2009.  Note the shelf space below the fridge, which was not much used.

The latest boat safety regs make it almost impossible to fit a new gas fridge (see, for example, Waterways World) and, as electric fridges using the new Danfoss DC compressors are very efficient, we took the opportunity to go to electric power.  We carefully removed the old fridge and capped off and leak tested the gas supply pipe.  We discovered some thermal insulation panels, which looked as if they might contain asbestos, see photo below.
These were sprayed with a fine water mist and very carefully unscrewed, wearing an approved disposable face mask and disposable overalls.  The panels were immediately double bagged and sealed, prior to disposal at an approved local authority asbestos disposal site. The cavity was carefully wiped down with water to remove any residual dust.

The next task was to choose a new fridge.  Three manufacturers were investigated: Isotherm (made in the US), Waeco (made in Germany) and Shoreline (made in the UK).  All use the same Danfoss BD35F compressor, so there isn't much to choose between them on the basis of power consumption.  We did realise that by removing the bottom shelf in the cavity, we could fit a larger fridge than the old 60 litre Electrolux fridge that we were replacing.  In fact our friends at the Oundle marina chandlery had a Shoreline RR102W in stock that would just fit the space and give us an increased capacity of 98 litres.  It was also about £100 cheaper than the smaller Isotherm and Waeco 65 litre fridges.

Before finally committing to this, we did some sums to check that we had adequate domestic battery capacity to run the fridge while moored.  The Shoreline fridge is claimed to have an average energy consumption of 0.95 Ah/h. We rarely moor up for more than an overnight stay, so if we assume a period of 18 hours, the fridge would consume a nominal 17 Ah of battery charge.  We have 2 x 110 Ah domestic batteries and no other large current consuming appliances, so this seems well within their capacity, even allowing for only accessing 50% of the nominal energy from the batteries.

The next task was to check the routing of the cable back to the main switch board, where fortunately we had a spare 15 A switch and circuit breaker. It was not easy to find a route for the cable and we discovered that we would need a 10 m run each way.

All the fridge manufacturers recommend cables whose cross sectional area must be increased in proportion to their length.  Shoreline recommend 10 sq mm cable if the fridge is 10 m from the supply and Isotherm and Waeco specify even larger cables than this. 10 sq mm cables are not only very expensive, but also more difficult to route through the boat.  At this point we went back to the theory.

It seemed that the objective is to reduce the voltage drop along the cables to acceptable limits rather than keep the resistance of the cables constant, which is implied by the manufacturers' recommendations that their cross sectional area should increase in proportion to their length.  There is a very useful formula for the voltage drop along copper cables on the SmartGauge website, which gives the required copper cable size in sq mm as: (18 x length of cable in m x current in amps)/(voltage drop x 1000).  Our installation has 20 m (allowing for both live and neutral).  The current draw of the Danfoss compressor was measured at 4.2 A. In fact their data sheet gives a range of 4 A (at 0 deg C evaporator temperature) to 4.45 A (at 5 deg C evaporator temperature) when running at 2000 rpm.  The current is likely to be lower as the freezer compartment (which determines the evaporator temperature rather than the chiller compartment) will be below zero once the fridge has reached its normal operating condition. If we take a cable length of 20 m, a current of 4.25 A and a voltage drop of 0.34 V, the formula gives us a cable cross section of 4.5 sq mm, which is a commercially available option.  Quite independently of this, Nick Billingham's book on Narrow Boat Care and Maintenance (1995, The Crowood Press) suggests a 4 sq mm cable for a 4 A current draw with up to 10 m between the device and the battery, which fits in with the theory of limiting the voltage drop to about a third of a volt.  The 10 sq mm cable recommended by Shoreline would only reduce the voltage drop from 0.34 V to 0.15 V, a reduction of just 0.19 V.  In the context of the significant variation in supply voltage from a battery depending on its state of charge and the fact that the fridge cut-out is set as low as 10.4 V, it seemed a reasonable risk to go with 4.5 sq mm cables and monitor the situation. Of course, we may be proved wrong and find that the fridge cuts out when moored up for a few hours.  If this proves to be the case, we will simply double up the supply cables.

After installation we measured a voltage drop at the fridge of about 0.7V going from no load (12.5V) to when the compressor cut in (11.8V). However, in addition to the voltage drop in the cables between the switchboard to the fridge, estimated at about 0.34V, the balance is presumably due to the voltage drop between the battery and the switchboard, as well as the voltage drop in the battery itself when current is drawn from it.

A second requirement when sizing cables is to ensure that they are capable of carrying the current without overheating, although in low voltage DC systems, this is not likely to be a problem if they are correctly sized to manage the voltage drop, as described above.  The total heat generated (in Watts) in 20 m of cable is the current (4.25 A) x the voltage drop (0.34 V), which is about 1.5 W along the whole length, or 0.075 W/m of cable, which is negligible. For example, a smaller cable (2.5 sq mm) than we are using here is typically rated as being safe for up to 20 A, see for example the SmartGauge website.

Anyway, after all this theory and practice, the new fridge looks good and, at the time of writing, seems to be working fine, see the photo below.  The final task was to reverse the door hinge so that it opens more conveniently towards the galley area. This was achieved by removing the top panel of the fridge and swapping the upper hinge from the right to the left hand side and similarly switching the lower hinge plate on the base of the fridge.

We will of course have to be even more careful that we remember to switch over to the domestic batteries when we moor up to protect the charge in the starter motor battery.  

Finally, don't attempt any of these tasks unless you are competent to do so!