Cooking with diesel

For many years the humble LPG cooker’s been a popular cooking option for small and medium-sized boats, caravans and RVs. Economical and simple to use, it’s regarded as the best option when mains-powered appliances aren’t an option. But is it?

One of the main causes of explosions on boats is LPG gas. The highly volatile gas is heavier than air and any leakage will sink to the bilge, where just a tiny spark can have catastrophic consequences. In the past year gas leaks have caused explosions on at least three boats in New Zealand, resulting in some serious injuries.

LPG cookers and hot water heaters have two further disadvantages: they produce colourless and odourless (but toxic) carbon monoxide gas, and combusting LPG produces water vapour as a by-product. So, cooking on a gas hob can result in a damp galley, even if good ventilation takes care of the carbon monoxide issue.

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Regulations for on board LPG installations have tightened up considerably. It’s no longer such a simple/cheap installation since a licenced gas fitter now has to install and sign off all gas fittings. Most marinas now require a gas fitter certification for a boat as well as proof that gas detectors are installed and may even prohibit LPG-powered appliances altogether.

So, what other heating solution uses a non-volatile and cheap fuel source?

As it turns out, diesel is an excellent option. Disregard any thoughts of smelly diesel fumes filling your cabin – modern diesel-fired cookers and heaters are smell-free, cost just a few cents per hour to run and use the same fuel that most yachts or medium-sized boats already have on board. They provide dry, toasty-warm air, and multi-function units can be a water heater, a cooking hob/oven while also serving as a space heater.

The key to modern diesel water heaters, space heaters and cookers is in the burner unit. Since diesel is relatively non-volatile (it does not readily evaporate) it is hard to ignite normally. This of course is what makes it a safe fuel, but it does create some challenges when used as a fuel source.

Modern diesel-burning units have a system which uses a small pressure pump to atomise the fuel, creating a fine mist which is then introduced into the combustion chamber where it is ignited.

The heat then passes through a heat exchanger to warm up either water or air, and this is circulated through the boat. Note that the air used during the combustion of the diesel is never used for heating directly – it’s vented safely out of the boat through an insulated exhaust system.

The stainless-steel exhaust is a surprisingly small, flush mount, a through-hull unit of around 25mm in diameter, and options are available for wooden, fibreglass and aluminium boats.

This circulation system is the second important component of a heating system. It can be fan-fed air vents in the case of a space heater, where ducted warm air is directed around the boat.

A second option is to heat water directly, then pipe the hot water to radiators and cabin fans at points where warmth is required. And the third option is where a hybrid system is used, such as a diesel cooker where for cooking purposes the hotplate is heated directly.

When the unit is not being used for cooking, a lid and ducted fan uses the hotplate to heat up and circulate warm air around the cabin instead.

The final component of the diesel burner is the control unit. Since these heaters and cookers rely on a combination of fans, pressure pumps and electric ignitors, they are all electronically-controlled.

These allow push-button ignition, and thermostat-controlled heat distribution through a simple control panel and dial. Some models even have touch-screen controllers, allowing effortless control of heat through the vessel.

Diesel space heaters have been on the market for some time and, naturally enough, the best models come from the colder northern hemisphere. It’s important to check you have a marine-rated unit, not one of the slightly cheaper RV units which are not corrosion-resistant.

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I looked at units from Eberspacher in Germany, International Thermal Research (ITR) in Canada, and Wallas in Finland. All three brands have local agencies and are highly regarded, with somewhat different capabilities.

SPACE HEATERS

Both the Eberspacher Airtronic and Wallas range are fully self-contained units, including a circulating pump, which are easily installed together with insulated ducting that feeds the hot air to where it’s required.

Apart from the circulating air, they also require a smaller fresh air inlet and heat-insulated exhaust outlet for the combustion process, and of course a diesel source. Blair Geldard, Director of Advanced Trident (the Wallas agent) says in the South Island a common location for the hot-air outlet is on the inside of the windscreen. Just like the defogging option on a car, a few minutes of warm air blowing up the window takes

COOKERS

New to New Zealand, and likely to make a much bigger impact in coming years, is the Wallas range of diesel cookers and ovens. These provide a practical cooking facility as well as cabin heating.

By building the combustion chamber under a single or dual hotplate, the Wallas unit provides a hot surface for cooking, similar to a domestic ceramic hob. And, just like a ceramic cooker, its smooth surface is easy to clean – it just needs a wipe down.

A circulating fan and an insulated hood over the hot plate also provides an air heating capability. With the hood down and the fan on, air is passed under the insulated cover and out the front, becoming an efficient space heater. Despite the cook top being hot enough to fry on, the insulated hood never gets beyond finger-warm and is safe from accidental contact.

Wallas also provides a range of marine ovens, in the usual compact marine sizes, and these have options of an all-in-one unit with a cooktop (with conventional round hob or smooth ceramic surface type) or with separate cooktop units.

All have the option of the space-heater hood and come in single- and dual-hob sizes. The clever Finnish have even designed a kettle holder to prevent a pot or a kettle sliding off the hob when the boat is moving around – a great safety feature.

Diesel’s energy efficiency as a heating source is amazing. Space heaters vary from 1,400W to 4,500W, and even the biggest size at full burn consumes just over 400ml of diesel per hour, or around 65c per hour at current diesel prices.

The Wallas 85Dt dual-hob cooker uses less than 150ml of diesel with both cookers running, producing 1,900W of heating. Compare that to the couple of litres per hour of fuel required to run even a modest 2,000-watt genset, and you can see how efficient it is to convert the diesel directly to heat rather than first into electricity and then to heat.

Note, though, that diesel heaters also require some electrical power, since they contain fans, pressure pumps and an ignition source. This is not a huge load, but that same 85Dt, for example, also consumes up to 350 milliamps at 12V while operating. This current drain needs to be considered when sizing up a house battery if the heater’s left running all night.

Also consider that both diesel cookers and the water heater configurations do not produce instant heat – the unit needs some time to get the appropriate elements up to the correct temperature and boiling a kettle may take slightly longer than on an LPG cooker. Space heaters on the other hand do give almost instant-on heated air through the heat exchanger.

So, is diesel cooking and heating a viable option?

Definitely. Many high-end launches and yachts are now standardising on these units, and together with an electric outboard for the tender (see story page 84) boats are tending towards a single fuel source for everything.

Several notable New Zealand boatbuilders, including Stabicraft, are now installing the Wallas cookers in large trailer boats. This enables them to provide a cooktop and a space heater in the same compact space that previously would have held a dual-burner LPG hob.

FOR MORE DETAILS CONTACT:

Advance Trident on 09-845-5347 or www.advancetrident.com or www.wallas.fi Sopac Marine on 0800-489-8800 or www.sopac.co.nz Absolute Marine on 09-273-9273 or www.absolutemarine.co.nz

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