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Eclipse Sailing 1
What? Or do I mean "What!"

This section of the website documents what is being built. Swing Cat is an Eclipse, a Richard Woods' catamaran design. Here, though, all the other design decisions made are chronicled such as what variant of the Eclipse, what electrical system, what navigation equipment, what safety equipment and, most importantly, what is being done to limit its impact on the environment.
What Variant of Eclipse?

What Design Philosophy?

What Construction Materials?

What Refrigeration System?

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What Variant of Eclipse?

The Eclipse is available in either cruising or performance cruising variants.

The cruising version has twin inboard diesel engines, low-aspect-ratio keels and fixed rudders. The fixed keels give it a draft of 0.9m and protect the props and rudders when beaching or drying out.

The performance-cruising Eclipse has an outboard motor, daggerboards and kick-up rudders. With one or both daggerboards down, and acting as high-aspect-ratio keels, the draft is 1.7m. With the daggerboards up, the draft is only 0.5m, so when beaching or drying out, the rudders and outboard motor must be raised. The hulls of the Eclipse are protected by a shallow beaching keel.

Compared to the cruising Eclipse, the performance-cruising Eclipse has the following advantages:
  • it is lighter because it is not weighed down by twin diesel engines;
  • it points higher because high-aspect-ratio keels are more efficient than low-aspect-ratio keels;
  • it is faster because high-aspect-ratio keels have less wetted surface area than low-aspect-ratio keels - particularly when off the wind when the daggerboards are partially raised;
  • it has a shallower draft for better creek crawling;
  • it is simpler to build since the diesel engines are more complex to install than an outboard motor.
For these reasons Swing Cat is going to be a performance cruising Eclipse.

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What Design Philosophy?

For me sailing is about getting away from the ugliness of our urban environment, with its noise, pollution and over-crowding. What is the point of motor cruising or motor sailing? Why transfer our terrestrial addiction with the internal combustion to the ocean? Although an engine is a valuable safety feature, putting it on at sea should be the last resort. Swing Cat has an outboard motor for itself - not for its tender. The tender is wooden, rather than a rubber inflatable, for ease of rowing (and it looks better).

Three adults and a dog

A concerted attempt is made to minimise our impact on the environment:
  • battery charging is done by solar panels;
  • a wind generator provides back-up;
  • fridge and freezer have 125mm and 150mm of high-quality insulation;
  • space heating is from a wood-burning stove fired by drift wood;
  • water heating is from LPG, the cleanest off-mains fossil fuel;
  • human waste is composted;
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What Construction Materials?

On the Eclipse the hull below the knuckle is a compound curve which, according to the plans, is built using strip plank construction, in our case Western Red Cedar. Above the knuckle, the topsides are simple curves and can be built from either 12mm thick strip planks or 9mm plywood sheets. Since both plywood and Western Red Cedar have the same density (approx 350 kg/cu m), a hull built from the former should be lighter as well as quicker to build.

As an alternative to the plywood and/or strip plank building materials mentioned in the plans, an Eclipse can be built using foam sandwich. There are arguments for both as far as I can see and I have no particular insight into their relative merits. For a novice boat builder like me, going for wood seems a more straightforward process to get to grips with, which is why I have gone down that route.

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Cool Box

What Sort of Power Generation Capability?

Many yachts use DC power only and rely on an engine with a high output alternator to charge the batteries. Battery charging is done when the engine is being used to leave and enter marinas with additional charging being done on the pontoons using shore power and a battery charger. "Blue water" cruisers, which spend a lot of time between harbours and cruise in areas where shore power may be rare, need supplementary charging capabilities.

Swing Cat has an outboard motor with a small alternator, sufficient to charge up a starter battery but not much else. We could use a generator, or shore power, but will try and generate enough renewable energy to supply an energy habit of about 100Ah per day; how this figure is arrived at and the research behind the choices made of the number, type and mix of solar panels and wind generators is presented in this document.

The heart of the electrical system is the Mastervolt combination chager/inverter 12/1200-60 shown here. This can operate as a battery charger, with input from either shore power or a generator, or an inverter, providing AC from either the battery bank or shore power.

The combi is hown here with a battery isolation switch, a distribution panel, a battery monitor and 2 digital thermostats - one of which is controlling the refrigerator and showing an internal temperature of 2.4 degC.

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What About Heating?

Here we talk about space heating, water heating and cooking. To minimise the impact on the environment we are using a wood burning stove for space heating; provided the wood is from sustainable woodland, it is carbon neutral. One can use the stove to warm food or water but, for meaningful quantities of hot water and for cooking, the choice is between LPG, diesel or spirit burners.

Environmentally, LPG is the best choice. Neither propane or butane (LPG can be either) are greenhouse gasses. When burned they generate about the same C02 as diesel and 20% less than petrol. It is a very clean fuel, generating very much fewer nitrous oxides and particulates than diesel. The photograph shows a Morco D61B LPG water heater - more details of the installation are given here.

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What Sort of Power Generation Capability?

What About Human Waste?

What About Heating?

What About Paints?

Eclipse Sailing 2

A Scenic Anchorage

  • lights are light-emitting diodes throughout;
  • autopilot power drain is very low - this is a feature of catamarans which are very light to steer;
  • computer, navigation and media equipment chosen on the basis of low power consumption;
  • no chart plotter, electric winches, electric windlasses, washing machines etc;
  • wide use of non-toxic paints without the off-gassing of Volatile Organig Compounds.

Smoothed Strip Plank

What Refrigeration System?

For a small boat there are two obvious answers to this question: a system consisting of a DC compressor, an evaporator and a condenser; a very well insulated cool box. The new breed of efficient DC compressors have seen off the alternative of a holding plate based system. If your aim is to charge your batteries from solar panels and/or a wind generator, rather than running an engine once a day, then this reinforces the case for a DC Compressor system.

However, how big can a fridge or freezer be and still be run off solar panels and/or a wind generator? How well insulated should the cool box be? How will your cool box, refrigeration system and power generation capabilities perform in the tropics and in more temperate climes? In this section and the one below I attempt some answers.

This document on the cool box designassumes that a small boat wants to run both a refrigerator and a freezer and has worst case a power budget, (i.e. in the tropics), of about 50 amp-hours a day. The document links to a spreadsheet which can be downloaded and tweaked for your own use. If you enter details such as volume of box, thickness and conductivity of the insulation, the required internal temperature and the ambient temperature, the spreadsheet will calculate how many amp-hours/day will be required to run it. If you find any mistakes, please let me know.

The picture on the left shows a cool box being constructed - more photographs and construction details are given here..

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What About Human Waste?

It has always amazed me that us yachties can shit freely into the sea anywhere along our lovely coast. We rely on the tides to clear up after us. Even in the Mediterranean we can empty our holding tanks once 3 miles from the coast even if we have to hold onto our effluent closer inshore.

There is an alternative to the conventional marine heads of 2 below-the-waterline through-hulls, a "poop soup tank" sloshing around under someone's bunk, metres of hose, levers, vented loops, pumps and valves: it is the composting lavatory.

What makes shit particularly smelly is the addition of urine, lack of oxygen and anaerobic bacteria. A composting heads separates out the liquids from the solids and mixes the latter with a peat-like compost in a steady supply of air - thus encouraging aerobic bacteria. This treatment transforms the shit into something which can be easily managed onboard until such time as you can take it ashore.

After about 4-6 months (in the UK), depending upon the season, the composting process has gone far enough for you to be able to dig it into your rose bed; in hotter climes the composting happens more quickly.

Here are details of how a composting heads works, here is a link to the manufacturer of this composting heads and here is a link to the UK supplier.

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water heating