QSB6.7 propels interdiction vessel

Somewhere, just over the horizon, an interdiction vessel is apprehending another criminal enterprise at sea. A great chase begins, frequently ending with Coast Guard Cowboys literally jumping from their rigid-hulled inflatable boat (RHIB) onto some partially submerged submarine, forcing open the hatch for takeover.

Built to be fast, versatile and powerful in the harshest sea states, the United States Coast Guard depends upon Cutter-Boats like Over the Horizon (CB-OTH). These missions boil down to time, speed and distance - where they will successfully head off a hostile vessel.

The OTH fleet of rigid-hulled inflatable boats are designed to pursue and intercept fast, non-compliant vessels. Often, they’re pursuing self-propelled narco-submarines and small go-fast boats. Both rely on size and speed to elude detection in international waters around the world, especially in the drug-transit zone of the Eastern Pacific Ocean.

Coast Guardsmen tasked with these interdictions are on-call, waiting aboard their ship which is a carriage for the OTH RHIB. The OTH is stern-launched from fast response cutters (FRC), offshore patrol cutters, polar security cutters and legacy medium endurance cutters. Frequently, OTH RHIBs complement a 38-foot Long Range Interceptor (LRI II) and a helicopter, all working in tandem.

Typically, Coast Guard aircraft sight a suspicious vessel during overhead surveillance. With the target vectored, an OTH vessel is launched, and the interdiction begins.

The world’s most formidable 26 RHIB

Coast Guard cutters, aircraft and boats are standing by 24/7 to respond to safety and security threats in all weather conditions. The Coast Guard is the lead federal agency in the maritime domain for law enforcement, incident response, homeland security, and disaster management. Vessels with specialized capabilities help the Coast Guard save lives, protect the environment, enforce federal laws on the high seas and defend the homeland shores.

Outfitted with a robust onboard navigation and communications system, OTH IV provides high-speed to extend the parent cutter’s capabilities. Where the larger, more robust long range interceptor cannot or should not go, the RHIB deploys supporting multiple Coast Guard missions.

With emphasis on search and rescue, drug and migrant interdiction operations, living marine resources, defense readiness and ports, waterways and coastal security, the OTH IV is the world’s most formidable 26-foot RHIB. The OTH IV is 26-feet long with an 8 1/2 foot beam and a 150 nautical mile range.

With a minimum top speed of 38 knots, this vessel is enabled for quick response by a Cummins QSB6.7L  480HP diesel engine and Hamilton Jet waterjet propulsion. This small boat is seaworthy and stable while moving at a blistering speed in rough seas. Designed with a low profile, crew have a wet ride in the elements at 38 knots.

The next generation

Now in its fifth generation, the updated cutter boat captures technology improvements. With upgraded versions of scalable integrated navigation, automatic identification system, and improved shock monitoring provides the crew with real-time information about wave impacts on the vessel.

Four builders contracted to manufacture the OTH V fleet, including MetalCraft Marine near Niagara Falls. The Falls power 4 million kilowatts of electricity with a watershed rate of 20 miles per hour in the lower whirlpool. Having built tour boats for topsy-turvy conditions encountered with the wildest rapids in the world, MetalCraft’s insight makes OTH IV seaworthy, safer and more comfortable.

Builders choose QSB6.7

“Regarding the engines, we must consider speed requirements with the vessel weight and hull resistance to determine horsepower and force out of a jet pump,” said Bob Clark, contract manager for MetalCraft Marine. “These are great engines to mitigate the vessel weight for a small to medium size patrol boat. The QSB6.7 is easy to work on and proven to be reliable. There’s not another engine in that size from another manufacturer that we’d recommend. It’s truly that good and all four builders chose Cummins QSB6.7. With twin QSB6.7s already on the LRI II, having the single QSB6.7 on the OTH means only needing parts for one engine all carried on the Cutter.”

“The evolution of improvement at Cummins is nonstop,” said Clark. “With the constant pounding and stress on these parts, Cummins made super strong engine mounts. We destructive-tested these boats to 20G’s.”

Additionally, the boat is becoming more comfortable. With seats by SHOX absorbing 8 G’s of force, the vessel soles have almost mattress-like cushioning for crew bounced around in pounding, open seas.

“Can you imagine these guys don’t feel that impact at a hell-raising speed?” mused Clark. "The seats are improved, the electronics are improved for less failures associated with impact. Skydecks are now used as the flooring, with Serta-like mattress coils filled with air, 11/2 inches thick. It all mitigates the shock to the Coast Guardsman in a boat designed to go faster and faster in the most terrible conditions."

Photo courtesy of USCG

Specifications for USCG0CB OTH