Need to fit extra tanks to carry more fuel (or more fresh water) for an extended cruise? Our marine engineer explains how to safely increase tankage aboard any boat.
Carrying more fuel tanks on a boat is easy - as long as you do it properly.
Adding fuel increases the range of any boat, or does it? More fuel means more weight, which in turn means more fuel-burn to go the same distance. Is this cycle of "diminishing returns" a problem? Not really in practice but its worth considering particularly on high-speed vessels working well-planned runs. Keep the hull clean and well trimmed and only carry enough fuel for the run (with a small safety margin) and you will keep your accountant happy. Extended voyages are another issue altogether and they need careful planning indeed.
CARRYING MORE FUEL TANKS
New tankage is the permanent solution, but also the most costly. Often it’s not just the expense of the tanks, but the cost of losing internal space that needs to be considered. Try to keep the tanks low and on centreline both athwartships and fore and aft. Search for voids that can have speciality tanks built to fit. Empty keels can often be used as spare fuel tanks, or consider custom building a tank to conform to the hull.
To save money as a DIYer try building a model of the tank with thin timber strips glued together to form the shape of the tank. Removing the model from the space gives a clear indication if the purposed built tank will fit through the hatch, on its way to its final resting place. Take the model to a tank builder for a bid. Tanks can be made from plastic, stainless steel, or even fibreglass.
Pro tip: Look for locations that are hard to reach thus utilising unused space
Hints for building a fuel tank on your boat
* Have a sump where water or other contaminants can be drained off.
* Slightly elevate the filler access from the deck to minimise water intrusion.
* Install the tank-vent as high as practical above the deck level.
* Be sure to use a wide diameter vent hose; 13mm is a good starting point.
* Install the pickup about an inch off the bottom of the tank.
* Tanks more than 500mm long will need baffles to reduce the very real danger of "free surface" effect.
Carrying plenty of water is both essential for survival and an excellent moral booster on more testing voyages. Nothing goes down better with a tired crew than a hot shower at the end of the day. For a small dayboat, adding a couple jerry cans of water is pretty simple, but if a large supply is needed it might pay to install a watermaker and a bit of extra fuel. Diesel can be converted to freshwater at a rate of about 10 to one. In other words a litre of diesel provides enough energy to produce 10lt of freshwater via a watermaker.
However watermakers do breakdown so those who undertake journeys that do not allow for a quick trip back to port in emergencies should consider installing tankage.
Water tanks are considered easy to build. If anything goes wrong the water just spills into the bilge where it won’t burn, or cause much damage. However, it is important to remember that any chemicals leeching into the water will find their way into our bodies. The "plastic" taste found in some boat’s water may be more than just an annoyance. The taste is our body’s way of warning us of an unwanted chemical in the water.
Gougeon Brothers, who sell West System epoxy have written extensively about this subject and came to the conclusion it’s safer and cheaper to buy readymade tanks, or have plastic tanks built. Epoxy water tanks need to be coated with a non-toxic FDA-approved paint. If the paint inside the tank begins to peal, unwanted chemicals can leach into the drinking water. For these reasons the use of epoxy tanks specifically for water has been minimised.
Pro tip: Long known for building tanks for superyachts Hercules Tanks in NZ builds plastic tanks that meet the European CE Survey Certification.
Petrol tanks are not allowed to have any holes in the sides or the bottom. This means no sight tubes and no bottom drains. The ABYC (American Boat and Yacht Council) states petrol tanks are not to be integral parts of the hull.
Petrol tote tanks have to be specifically built to withstand the pressure that builds inside. Be sure the chosen container is specifically "petrol approved".
Flexible bladders are a semi-permanent solution to storing more fuel. The bladder can be rolled-up, inserted into a void, and then filled. Inflatable bladders can also be custom made to fit speciality spaces, or even be used inside a leaking tank. Flexible tanks have the advantage that when left empty the space can be used for other storage.
Intuitively, wear and tear would seem to be an issue but most boat owners report years of trouble-free service after taking basic chafe precautions. Remember, the space where the tank is to be placed should be structurally sufficient for holding the weight of the full tank and able to withstand some sloshing. Some tanks have tiedowns on the corners that help secure the tank in place minimising the need for extra structural support.
Pro tip: Flexible bladders used for blackwater often last more than 15 years till they begin to pick-up an odour. Keeping the flexible holding tank empty and rinsing with vinegar will help extend its life.
Fuel Tank Deck Storage
The most common method of temporarily increasing fuel or water storage is the use of deck-loaded storage tanks. Large boats often carry a barrel or two on deck. The main advantage is the simplicity of buying some fuel cans and setting them in place on deck. The main disadvantage is the reduced stability due to the amount of weight added above the centre of buoyancy.
Diesel is pretty straightforward and safe but petrol is another story. A container of petrol is at its safest when it’s either full or completely empty. A half-full petrol barrel in the sun is literally a bomb waiting to explode.
Transferring Fuel From A Tank
Transferring fuel can be a smelly and messy operation. With a good plan, fuel transfer can be as simple as running a hose and pushing a button. Sometimes the use of a simple funnel is all that is needed. Many boats carry oil absorbent mats that are laid out during the fuel-transfer process. Small containers may be poured or siphoned successfully but always use the largest funnel you can find. Some funnels come with a small filter built into them that can help prevent dirt and algae from entering the fuel tank during the transfer.
It pays to experiment with your container of choice as some pour better with the spout up allowing air to enter the can, preventing any "burps" and the accompanying splash. A good supply of containers is especially handy if the boat can’t come alongside the fuel or water dock. Simply pile the containers into a tender and fill them where possible.
Pro tip: Everyone who has ever tried to start a siphon by sucking fuel through a hose knows the taste of a mouthful of diesel. This unpleasantness can be a thing of the past by using a simple check-valve device. Sold under many names, and usually for less than 10 dollars, a siphon starter fits on the end of a 13mm hose. Drop the hose into a tank, pump the hose a few times to start the siphon and stand back amazed. The EZ siphon starter is sold at many home brewery shops.
More Hints And Tricks
If the boat has wooden decks, start by spraying a solution of soap and water over the working area. In the unlikely event of a small spill the fuel will not soak in leaving a stain. Sealing up the boat’s scuppers will help contain a spill, and be aware than in many cases fuel spills must be reported to the authorities.
Plastic fuel tanks
Plastic tanks can be purchased pre-built right out of a catalogue, or they can be specially made to almost any size or shape. Mass-produced tanks are usually made of Polyethylene and are often rated for fuel only. Freshwater tanks need to be custom ordered in order to ensure they are up to food-grade standard. The rugged plastic tanks last for years and are relatively inexpensive to purchase.
Metal fuel tanks
Tanks are normally built from steel, stainless steel or aluminium. Steel is initially cheaper to build, but often the savings in material is lost when the cost of coatings are considered. Steel needs to be sandblasted before painting, while aluminium is often simply put into service. Stainless steel can be tricky to weld and work. All metal tanks need to be baffled in order to reduce the stresses of free-surface effects and to help strengthen the construction.
Tip: It is said that baffles and vents are never big enough. Consider making them larger than originally planned.
News atricle written by:
Scott Fratcher and published on: www.TradeBoats.com.au