The design of a lifeboat starting system is a redundancy and cold-availability problem with a two-minute deadline. This paper develops a sealed nickel-metal hydride implementation of the LSA Code requirement that a power-started lifeboat or rescue boat engine carry two independent rechargeable energy sources capable of starting it at -15 degrees C within two minutes. It sizes each source from the engine's cold cranking demand - the starter current over the cranking sequence plus any glow-plug or controller load - derated at the minimum temperature and at the end of the service interval so that either pack alone completes the start with margin, and it checks terminal voltage against the starter and engine-controller cut-out throughout the procedure. It then separates the starting function from the house loads (searchlight, navigation and interior lighting, instruments, alarms and release-system indications) so these cannot drain the cranking source, and it designs the charging architecture: the engine alternator during the mandatory weekly run and the davit or on-board charging connection while stowed, with a sealed-NiMH-appropriate profile that keeps both independent sources full without overcharging through years of mostly-idle, thermally hostile stowage. The paper addresses the mechanical realities - salt-mist corrosion at charging contacts, vibration and shock in free-fall and davit-launched boats, sealed enclosures and crew safety in an enclosed survival space - and compares sealed NiMH candidly with the flooded or valve-regulated lead-acid that dominates today's lifeboats and with nickel-cadmium, showing why a sealed, cadmium-free, cold-capable, low-maintenance dual-source pack reduces the most frequent cause of failed lifeboat weekly tests while staying within the LSA Code and MED approval framework.
The redundancy rule means each source must independently start the engine, not merely contribute in parallel. Sizing begins with the starter motor's cold cranking current at -15 C, the voltage required by the starter and any electronic engine controller, and the maximum cranking time within the two-minute procedure including starting aids; the pack is chosen to hold above cut-out through repeated cranking cycles at that temperature.
Capacity is then derated for the cold condition (electrochemical power falls sharply below freezing), end-of-service fade and the self-discharge accumulated since the last charge, with a survey-friendly margin. The first animated figure builds the cranking energy and power budget. Two physically and electrically independent packs, each with its own protection and switching, satisfy the LSA requirement and let the crew select the healthy source if one is degraded.
The -15 C/two-minute test is the design driver. Sealed NiMH delivers substantially better low-temperature current relative to its rating than lead-acid and does not freeze and crack, but the design still verifies cold cranking by chamber test, accounts for the voltage depression under load at low state of charge, and integrates any approved starting aids (glow plugs, decompression devices, pilot pumps) into the energy budget.
Cell selection favours low-internal-resistance industrial cells and robust interconnections capable of the starter's peak current, with conductors and fuses sized for cold high-current flow. The starter duty is short and high-power - fundamentally different from the long low house load - which is why separating the two functions and using pulse-capable cells gives more reliable starts than one oversized general-purpose lead-acid bank.
Best practice isolates the cranking sources from the house bus so that leaving the searchlight or interior lights on cannot flatten the battery needed to start the engine - a documented cause of lifeboat launch failures. A sealed NiMH service pack handles the searchlight, navigation and interior lights, instruments, alarms and release indications for the required survival period, while the two starting packs remain dedicated to cranking.
The house pack is sized to the LSA runtime of the searchlight and lights, recharged by the alternator once the engine runs and by the stowage charger when aboard ship. This split also lets each chemistry be matched to its duty: ultra-low-resistance cells for cranking, capacity-oriented cells for the house load, rather than compromising both in one bank.
While stowed, the lifeboat batteries are maintained through the ship's supply via the davit-mounted or on-board charging arrangement, with weatherproof connectors that are themselves a frequent corrosion failure point; while launched, the engine alternator recharges them during the weekly three-minute run and in actual use. The charger uses a current-limited, temperature-compensated profile suited to sealed NiMH, avoiding the continuous overcharge that would age or dry sealed cells during years of standby.
Low-self-discharge cells keep each source ready across gaps between weekly runs and even after a charging-contact failure, providing a graceful safety margin; charge and fault indication at the lifeboat station and, where fitted, remote annunciation help the crew spot a degraded source before it matters. Isolation diodes or intelligent switching keep the two independent sources from discharging into each other while allowing either to start the engine.
Lifeboat batteries must survive long-term salt atmosphere and humidity, ship vibration, and the substantial shock of a free-fall launch or wave impact. Construction uses sealed cells with welded interconnections, positive retention and anti-vibration mounting, corrosion-resistant terminals and sealed or vented enclosures appropriate to the enclosed crew space, with no free acid to spill or gas to accumulate - a direct safety improvement over flooded lead-acid in a sealed lifeboat.
Charging contacts and connectors are marine-grade, sealed and corrosion-resistant, and the pack is located away from direct spray and extreme engine heat while remaining accessible for the certified servicing regime. The packs are designed so a lifeboat technician can swap a unit without altering the approved two-source architecture, preserving type-approval integrity.
Flooded and VRLA lead-acid dominate current lifeboats through familiarity and low first cost, but they are cold-weak, heavy, contain acid, can gas, and - flooded - need electrolyte attention; failed or weak lifeboat batteries from corrosion, sulphation and charge loss are among the most frequent PSC and classification findings. Flooded NiCd is rugged and cold-capable but needs watering and carries cadmium.
The second animated figure scores the options on cold cranking, sealed/no-service operation, charge retention for long stowage, crew-space safety and environmental compliance. Sealed NiMH offers NiCd-like cold and reserve tolerance in a sealed, cadmium-free, acid-free, low-maintenance package, directly reducing failed weekly tests and survey deficiencies; the qualification paper sets out the MSC.81(70), MED and battery evidence required to convert that engineering advantage into an approved installation.
Weijiang Power designs and manufactures sealed nickel-metal hydride cells and matched industrial packs for remote, off-grid and safety-related equipment, and supports OEM partners with IEC 61951-2 performance files, IEC 62133-1 safety evidence, pulse-load characterisation, wide-temperature testing and charger/pack co-validation. Tell us your duty cycle, peak current, temperature envelope, autonomy target and the standards your product must meet, and our engineers will specify a cell-and-pack combination that protects runtime, reliability and service life. Review the range on the products page.
