Safe coupling uses double springs

Tom Shelley reports on a mooring system for boats whose philosophy offers benefits to most kinds of coupling and mechanical connection A mooring system for boats avoids damage to hulls from fenders by adopting a unique philosophy. Restraint is still by mooring ropes but the boat is pushed away from the pontoon at the same time by a system using strong and weaker springs, universal joints and break away couplings. Invented by a retired petrochemical instrument engineer, it manages to achieve its goal while avoiding the effects of any kind of mishap, whether caused by man, tide or weather. Despite its sophistication, it is not excessively expensive, and its underlying ideas are applicable to any kind of mechanical attachment, whether fixed, linear or rotating. Richard Meredith, who lives in Crowborough, calls his inventions, Epor, which is rope spelled backwards. He has named his company, Silverpin. He came up with the idea as a means of holding a boat away from the edge of a mooring pontoon without totally relying on fenders. While fenders do a superb job in protecting a boat hull from the worst effects of banging and grinding against the side of a mooring pontoon, they do mark the gel coat on the hull. This is unacceptable to somebody who has just spent a small fortune on purchasing their shiny new toy for big boys. His idea comes in two forms for boats. A "Low Power" type for craft up to 30 feet in length, and a "High Power" type for craft from 30 to 40 feet. For larger types, he suggests two High Power types could be used. The Low Power type, shown in our diagram, has a heavily constructed spring housing permanently attached to the pontoon. Into the shaft in the centre of this slots a torque arm. This ends in a universal joint to which is attached a male member, fitting into a female element on a connecting arm, permanently attached to the boat by a second universal joint. A foot pedal which clamps onto the torque arm assists partial compression of the main spring during mooring. Although not in the original design, the arrangement now includes a weak spring element to keep the end of the connecting arm pressed against the male member element under all circumstances. These include situations, where, perhaps the boat is not tied up tightly enough, and it is able to move beyond the point where the torque arm reaches its extreme outward position. When the weak spring decompresses, it exposes fluorescent bright red painted on its normally covered shaft. In the High Power version, there are also two spring elements but in reversed positions. The pontoon spring is the weaker spring, but the main spring force is exerted by a gas spring forming part of the connecting arm. We were told that it requires 600kN to even start compressing the gas spring. Mooring involves using a screw or block and tackle gas spring compressor. The weak spring enables the compressed gas spring to be connected to the torque arm, freeing two hands to gradually disconnect the compressor. As the gas spring expands, it gradually pushed the boat away until its is constrained by its mooring lines. When this happens, the compressor can be completely removed. During surges in gale conditions, the maximum spring force is designed to be momentarily overcome, allowing the craft to kiss its conventional fenders. Meredith claims that, "For 99.99% of the time, the craft's conventional fenders do not come into play." The sliding male-female connection, it is said, "Allows easy, safe connection and disconnection even in gale conditions." In the event that the craft loses all its mooring lines, either because of extreme weather or incompetence by the crew, the connection just pulls apart, without causing anything to be pulled off the side of the hull. The connecting arm then drops down, a rubber doughnut ensuring that the falling end of the connecting arm does not mark the hull when it hits it. The incorporation of two universal joints in the system ensures that the craft can range horizontally by about plus or minus one foot (300mm) and rise and fall vertically by about the same amount relative to the pontoon. The torque arm is adjustable in length in order to cope with a range of gunwhale heights above the pontoon, and incorporates an adjustable mechanical stop, which allows it to overhang while in the 'parked' position, before attaching to the connecting arm. This stop can be adjusted to suit different craft and fender diameters. The length of the connecting arm may be adjusted by means of an incorporated screwed rod. Custom clamps fit different pontoons and custom gunwhale and toe-rail attachments fit different craft. Hooks on the connecting arm allow fenders to be positioned amid-ships, away from the hull. The prototype equipment was manufactured by ER Edwards and Sons in Horsham, and looks solid and dependable. Meredith describes it as being, "Fully marinised with sealed for life lubricated springs, self lubricating bushes and a hard anodised finish. Richard Paine, the managing director of agents Inventorlink Products estimates production scale manufacturing cost to be around £1,000, which he considers to be quite trivial to the sorts of end customers he intends it to be sold to. But more than a product, it represents a philosophy. It is often desirable that mechanical couplings should at the same time couple securely, yet be able to break away in a worst case scenario. Using springs to absorb force and hold in place is quite a common approach but usually, the spring force only takes performance into account, and not possible problems that might be encountered when coupling up or which might result from excessive movement. Two springs is the solution in the design of the Epor, but it is also possible to consider variable rate springs, which exert a weak force when they start to compress, and a strong force when further compressed, although it would be hard to design one for the Epor application. All aspects of the designs are covered by patents either granted or applied for. Inventorlink Products Richard Meredith Email Inventorlink Products Eureka says: It is not often that somebody comes up with a new idea in mechanical couplings. Leisure activities have given rise to more than a few inventions that we have featured in Eureka over the years Pointers * Coupling is designed to work in conjunction with rope moorings, but keep a boat hull at a sufficient distance from a mooring pontoon to avoid the fenders marking the gel coat * A weak spring keeps the system in engagement, and in the case of the system with a gas spring, also assists in the engagement process, while a strong spring absorbs the main forces. * The system copes with vertical and horizontal movement and breaks away without causing damage should the rope moorings fail