A fuel tank on a boat is not just a vessel, an accessory: it is a vital component that must be of the utmost reliability as it involves the safety of boaters, even in extreme conditions.
The petrol fuel tank on a boat must be of utmost reliability because it is housed inside (unlike in the automotive sector where it is placed outside the cockpit), so any leaks will not be released outside but distributed inside the hull.
Potential Risks
The possibilities for failure are many, for example in the event of: a leak at any point in the system consisting of the vessel (tank), sampling connections (drains), vent connections, filler neck, control valves (E.P.A. regulations), level sensor connection, clamping point through hose clamps, connections to the filter, to the feed pump, and so on.
A vast surface area producing vapours in a confined, unventilated space, with the near certainty that when starting engines or operating (even automatically) a bilge pump (just to mention one of the many electrical triggers on board) the condition can only be…. explosive.
The Pressure a Tank is Subjected To
Just to give an idea of the mechanical forces one is subjected to, we can imagine a tank with an upper face of 1 sq.m, i.e. 100 cm x 100 cm corresponding to 10,000 sq.cm. The force applied to a surface is the result of pressure on a more or less extensive part. In this case, F=PxS where F is the force, P the pressure, S the surface. F=0.1 (Kg/sq.cm) 10,000 (sq.cm) = 1000 Kg. Applied precisely to sq.m of surface area. With only 0.1 atmospheres, enormous forces are generated, which will concentrate on some points more than others, generating extremely dangerous situations.
Different Kinds of Tanks
Extreme care must be taken in the choice of the component and its correct installation. In the meantime, a distinction must be made between the different types of tanks: stainless steel, plastic, cross-linked polymer.
Stainless Steel Tanks
Stainless steel tanks have a limited lifespan, which depends on the workmanship of construction, possible galvanic currents, geometry, and conditions of use.
- The workmanship consists of the choice of materials, the quality of the welding, and, above all, the passivation of the materials. The sheet metal should be certified as true 316L (low carbon) stainless steel, the welds tig welded in a workmanlike manner, and their passivation carried out using chemical agents that turn the surface stainless again.
- Possible galvanic currents will be expressed mainly on the most aggressive areas, those where welding has been performed, since the migration of the nickel present in the alloy is responsible for the creation of a very thin, invisible veil of nickel oxide that protects against possible corrosion.
- Geometries with large surfaces tend to generate significant forces, which are even greater when the boat is in strong swell. The breaking points are classically in the weld joints because work hardening of the material occurs and therefore the stress applied by the sheet metal subjected to the swell is concentrated at those points.
Plastic Tanks
Plastic tanks are mainly made of polyethylene, eltex, PVC, etc. These materials have the advantage of costing very little but are only good for small tanks, usually portable ones. Making a plastic fuel tank overcomes all the problems of metal tanks, but involves several challenges:
- Superior mechanical modulus to resist stresses on writings (some tanks reach up to 5 sq.m of surface area on one face).
- Certified chemical barrier to hydrocarbon migration through the molecular mesh of the polymer (hydrocarbon is a very small molecule that easily permeates through polymers).
- An excellent elastic modulus at low temperatures (normal polyethylene becomes brittle at low temperatures).
- Moulding techniques of the inserts that must guarantee an airtight seal when the fuel passes through.
- Proper design of geometries to reduce stresses.
- Proper moulding to guarantee the cross-linking process in the case of special polymers.
- International regulations provide for all this, which is why if a shipyard wants to aspire to export to the United States it MUST have all components on board that comply with these laws.
The Power of Experience
Twenty years ago, SIC Divisione Elettronica chose to focus on the best polymers with peroxide-mediated chemical reaction, in order to obtain a cross-linked mould in its entirety during the process, as the hydrogen bond binds all the high molecular weight chains (base polymer). This not only greatly increases the mechanical modulus but also enhances the elastic modulus at very low temperatures and increases the barrier to fuel permeation through the walls.
SIC Divisione Elettronica has 35 years of experience in the different areas of electronics, mechanics, and chemistry. This has enabled it to:
- Design, patent, and manufacture special brass inserts to its own design to optimise hydraulic and mechanical seals.
- Realise capacitive technology level sensors to guarantee precise and continuous level measurements.
- Design special polymers for different applications; double- or triple-walled tanks with special pure silver fillers for certain drinking water tanks; tanks with nano-filled polymers to achieve special specifications; process modifications to create innovative recipes.
- In-house design and manufacture of moulds to design for the world’s most important construction sites.
