Fernstrum® GRIDCOOLER® Keel Cooler

The Fernstrum® GRIDCOOLER® Keel Cooler is a custom-engineered, closed-circuit cooling system mounted externally on the hull below the waterline. Engine coolant circulates through the cooler's rectangular copper-nickel tubes and rejects heat directly to the surrounding seawater before returning to the engine — no raw water ever enters the hull. Fernstrum, the pioneer of the rectangular-tube keel cooler, has built GRIDCOOLER units in Menominee, Michigan since 1949.

Why keel cooling

• Eliminates the inboard heat exchanger, raw-water pumps, strainers, seacock and seawater piping
• No sand or silt build-up in the cooling circuit and no saltwater corrosion inside the vessel
• Zero-discharge solution — no contaminants released into the water
• Low maintenance; effective even at 0 knots

Design features

• One-piece rectangular header — minimal joints for maximum durability and design flexibility
• 56% silver braze (BAg-7) throughout, brazed in a single operation; critical joints ultrasonically inspected
• Heavy-walled 90/10 copper-nickel tubing — corrosion resistant and naturally anti-fouling (when isolated from the hull)
• Enhanced interior tubing (Fernstrum exclusive, since 1998) — truncated-cone pattern inside the tube raises heat transfer by up to 30%, especially with glycol coolants, often reducing cooler size or count
• Factory assembled and pressure tested; available in three tube sizes

Configurations

• Single-pass (nozzles at opposite ends) or multi-pass (nozzles at the same end) for compact designs
• E1 — anodes and drain plugs on the end to reduce hull projection (fishing vessels, high-speed craft)
• L — extended support plates that minimise hull penetrations; ideal for retrofits
• HD — stiffener plates for heavy seas, strong currents or bow-area installations
• Z — external flanges replace through-hull nozzles, eliminating hull penetrations and often the need for cofferdams
• Stacked and Angled Tube versions for high heat loads and zero-knot/stationary duty
• Options: bending/twisting, extended nozzles, mounting foot pads, side venting, vented studs

What it cools

Propulsion and auxiliary engines, generator sets, reduction gears, bow thrusters, hydraulics, HVAC, compressors, winches, pumps, electrical equipment and battery systems. Fernstrum keeps current data on all major engine makes, including Caterpillar, Cummins, MTU, Volvo Penta, John Deere, Scania, MAN, Wärtsilä, Mitsubishi and Yanmar.

Typical vessels

Tugs and push boats, ATBs, barges, inland river boats, ferries and passenger vessels, OSVs and PSVs, commercial fishing vessels, dredges, patrol and pilot boats, landing craft, lifeboats, recreational craft and repowers — plus stationary uses such as buoys, wave and tidal generators, pump stations and underwater data centres.

Service parts

Zinc and aluminium anode kits, gasket sets and compression sealing kits (for cofferdam installations) are available for every unit.