SOLAS IV/13 • 1 h / 6 h Reserve • Radio Load • C1 / C6 Capacity • 40% Life-Cycle Allowance • Charger 10 h Recovery • Voltage Drop • Emergency Endurance

GMDSS Reserve Battery Tool Radio Load, Capacity, Charger & Emergency Endurance

Size and screen the GMDSS reserve battery from the actual radio load instead of relying only on nameplate amp-hours. Simple mode converts receive/transmit duty into reserve current, applies the 1-hour or 6-hour SOLAS basis, rapid-discharge capacity effects, battery condition and charger recovery. Advanced builds a full reserve-bus load register, handles simultaneous versus alternative radio paths, checks current-condition endurance, life-cycle sizing, charger recovery, peak-current cable voltage drop and multiple reserve scenarios.

Figures represent
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Need individual radios, duplicated/alternative paths and voltage-drop checks? Click Advanced above.Simple uses the SOLAS/IMO reserve-load concept with a user-entered transmit duty factor and a 40% life-cycle sizing allowance.
Reserve1 h or 6 h endurance
CapacityUsable vs nameplate Ah
Recovery10 h charger screen

Reserve Load & Battery

“Adequate” means the applicable emergency source can operate radiocommunications for the required 18 h cargo / 36 h passenger period.
V DC.
A for radios/inputs that remain connected.
A maximum transmit-current basis.
% of transmit current added to receive current. 50% is the IMO general reserve-load formula.
A, e.g. required emergency light / navigation-data inputs.
Ah at the selected nameplate rating basis.
% remaining after state-of-charge, ageing and temperature effects.
A available for battery recharge.

SOLAS Reserve Duration & Battery Bank

h available from the ship’s emergency source to radiocommunications.
V DC.
Ah.
% of nameplate capacity available at the required discharge period when custom is selected.
%.
% of new-battery capacity retained.
% from manufacturer data / engineering basis.
% added to the bare minimum calculated capacity.
IMO guidance: capacity check interval should not exceed 12 months.

Reserve-Bus Radio / Essential Load Register

Average reserve current per row = quantity × (receive/standby current + transmit duty factor × transmit current). “Alternative” rows with the same group are treated as mutually exclusive and only the largest group load is counted. Use “Simultaneous” for loads connected at the same time. The default 50% transmit factor follows the IMO general reserve-load formula; change it only where the applicable equipment/flag calculation basis supports another duty factor.

UseLoad typeQtyRx / standby ATx max ATx duty %Demand modeAlt group

Automatic Charger & DC Distribution

A.
% used for recharge-time screen.
h; IMO guidance uses 10 h.
m for voltage-drop formula.
mm².
V, user/manufacturer limit.

Survey / Installation Checks

Engineering / regulatory limitation: this tool screens a GMDSS reserve-battery installation from entered electrical data. Actual compliance depends on the ship’s SOLAS applicability, flag-State interpretation, approved equipment, manufacturer C1/C6 performance, battery chemistry, temperature, battery condition, charger configuration and verified radio load. Use approved battery-capacity calculations and survey documentation as controlling.
Regulatory basis: IMO COMSAR.1/Circ.32/Rev.2 guidance for SOLAS IV/13 uses a reserve-radio load of ½ transmit current + receive current + additional loads, requires at least 1 h reserve when the ship has an adequate emergency radio supply and 6 h otherwise, recommends an extra 40% capacity to maintain the requirement through the battery life cycle, gives approximate rapid-discharge factors for C20 lead-acid and C10 non-lead batteries, and calls for a charger capable of restoring the completely discharged battery to the minimum required capacity within 10 h.
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