E-Mobility Engineering | January/February 2024 53 passengers and crew, particularly during boarding, or while fishing, or other ondeck activities when the boat is at rest. Several factors influence initial stability, including general hull shape, with broad-beamed boats, offering good high resistance to tipping, which is also helped by high freeboard (the distance between the waterline and the deck), and high buoyancy. Weight distribution is also an important factor here, and placing heavy components such as, in the case of the Pulse 63, the battery pack lower in the hull contributes to a lower centre of gravity, again contributing to greater initial stability. Secondary stability applies when the boat is in motion or encounters dynamic conditions, such as waves or turns; this determines its ability to resist further heeling once it has started to heel. Good secondary stability is crucial for maintaining control and comfort in varying sea conditions. There is often a trade-off between initial stability and secondary stability in that high initial stability might make the boat more prone to tipping in dynamic conditions, and that some design decisions conflict to a certain extent. For example, a higher centre of gravity can increase secondary stability while reducing initial stability. The ideal combination depends on how the boat is intended to be used. Displacement and planing efficiency The engineering team stresses that the main requirements for the Pulse 63’s hull included high efficiency both at displacement speeds and at planing speeds. Also to have space for the batteries inside the hull with weight in the right place in the boat for optimum trim. It is also designed to maximise displacement while minimising the amount of hull below the waterline. The term ‘displacement’ refers to the weight of the water that the hull pushes aside when afloat. The displacement speed is the speed at which the length of the bow wave equals the length of the hull’s waterline, and is effectively the maximum speed that the hull can achieve without planing. The cathedral hull form is a good way of maximising displacement while minimising the amount of hull below the waterline; boats with higher displacement-to-length ratios often exhibit better efficiency at lower speeds. Relatively high displacement can also result in better load-carrying capacity and stability than comparable boats that displace less. “With a cathedral hull, the boat is pushing a lot less water at displacement speeds and also gets up on the plane really nicely at a speed as low as 8 knots where a more conventional hull would do so at about 12 knots,” NewtonSouthon says. The rigid part of the hull is constructed of laminated composite materials including carbon fibre and glass fibre, which reinforce an epoxy resin matrix. The construction method that RS Electric Boats chose is resin infusion moulding, in this case using reusable silicone vacuum bagging, according to the company’s engineering team. Infusion moulding Resin infusion moulding starts with the construction of a mould, which is polished and coated with a release agent to ease extraction of the final part. Dry fibre reinforcement cloth is then laid out in the mould in precise orientations and thicknesses to yield the required strength and stiffness in the final part, often with foam cores for spacing and extra stiffness/strength. Next, a vacuum bag and a network of resin distribution tubes are placed over the dry fibres in the mould, creating a sealed environment with a means of getting the resin everywhere it needs to go. Then a liquid resin, usually a two-part resin and hardener, is drawn into the fibres and air is expelled using vacuum pumping. The part is then left to cure for a predetermined time at water and reduce steering workload. Cathedral hulls are known for good combination of speed, manoeuvrability and ride quality, as well as energy efficiency, with the V-shaped central hull portion reducing drag at higher speeds. Cathedral hulls also offer high initial stability as well as good secondary stability. Initial stability refers to the vessel’s ability to resist tipping or rolling when it is in a static, level position on calm water; effectively when it is not subjected to external forces, such as waves or wind. This is important because it affects the comfort and safety of RS Electric Boats Pulse 63 | Digest
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