R.W. Fernstrum & Company

R.W. Fernstrum & Company is a US manufacturer of closed-circuit cooling systems for marine engines and auxiliary equipment. It is best known for the Fernstrum GRIDCOOLER keel cooler. The company traces its origins to 1943, when Robert W. Fernstrum worked with Gray Marine to solve engine-cooling problems on US Navy landing craft during the Second World War. A patent for the first rectangular-tube keel cooler followed in 1945, and the company was launched that year. Fernstrum describes this as "the basic keel cooler design that is still used today". Some older catalogues and trade articles date keel cooler production from 1949.

The family-owned business is based in Menominee, Michigan, where it runs its manufacturing plant. The fourth generation of the family now works in the company. Paul Fernstrum is Chairman, Sean Fernstrum is President and Todd Fernstrum is Vice President. The company has held ISO 9001:2015 certification since 2018, and its site shows ANAB accreditation. For 2025 it reported 99.8% on-time delivery.

A GRIDCOOLER mounts on the outside of the hull below the waterline. Engine coolant runs through a bank of heavy-walled rectangular tubes and gives up its heat to the surrounding water. This removes the need for an inboard heat exchanger, raw-water pumps, seacocks, strainers and seawater piping. Units come in 90/10 copper-nickel or in TIG-welded 5000-series aluminium for unpainted aluminium hulls. The copper-nickel units have a one-piece rectangular header and are torch-brazed in a single operation with 56% silver braze wire. Critical joints are checked ultrasonically. An enhanced interior tube wall with a truncated-cone pattern, offered since 1998, raises heat transfer by up to 30%, the company says.

The range covers single-pass and multi-pass designs. It also includes the E1, L, HD and Z header and support series, stacked units and angled-tube units, with recessed, external or side mounting. Each cooler is normally custom-sized from a recommendation form covering engine data, coolant flow, hull speed and seawater temperature. Fernstrum also supplies anode kits, gasket sets and compression sealing kits.

Fernstrum has partnered with WEKA since 2001 to build and distribute copper-nickel WEKA Boxcoolers for North and South America. These units mount in the sea chest and need no coating or ICAF system. In 2014 the three Fernstrum brothers bought WEKA Boxcoolers B.V. (now WEKA Marine) in the Netherlands through Dunlap & McCullough Holdings, and the two companies run independently. Fernstrum also offers OMEGA Laser Plate (pillow plate) heat exchangers from Omega Thermo Products. In 2018 it announced a partnership to supply Tranter plate heat exchangers.

GRIDCOOLER units serve tugs and escort tugs, towboats and push boats, ATBs, barges, dredges, commercial fishing vessels, pilot boats, OSVs and PSVs, ferries, patrol boats, landing craft, lifeboats and recreational boats. They also serve stationary uses such as hydroelectric plants, offshore wind generators, pump stations and underwater data centres.