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Silencing Canada's frigates
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| 16 April 2000 |
Silencing Canada's frigates
Canada's
navy has completed a three-year evaluation of different approaches to
reducing the noise levels in the Halifax-class frigates and has opted
for a low-cost, compromise solution.
The ships, although quiet, did not meet the navy's specifications when deliveries began in 1991. According to Joe Muller, Canadian Patrol Frigate (CPF) Project Manager, "We knew with the first ship (delivered in 1991) that we had a noise issue." The prime contractor for the shipbuilding project, Saint John Shipbuilding Limited (SJSL) of New Brunswick, made some adjustments but the noise problem persisted. In February 1997, an evaluation team was tasked with determining what was causing the noise and what could be done about it.
The heavily censored evaluation team's report, released through an Access to Information Act application, noted that "the current noise signature reduces the effectiveness of sensors and increases vulnerability to acoustically activated weapons." The evaluation team studied the effects of propeller modifications, mufflers, the Air Emission System (AES) and acoustic decoupling tiles.
Approximately
12,500 anechoic tiles were applied to the hull of HMCS Montreal (see JDU,
Vol II, No.1 p2) at a cost of about C$3 million (US$2m). The synthetic
rubber tiles have a honeycomb interior designed to reduce machinery tonal
vibration levels transmitted via the ship's hull.
Muller says: "What we found was for the hull noise and the radiated noise, the tiling worked very well." The team recommended that acoustic decoupling tiles be applied to the other 11 ships in the class at a cost of approximately C$30 million (US$20m). The Chief of Maritime Staff (CMS), Vice Adm Greg Maddison, however, decided "it was not high enough priority at this time to spend that kind of money on it." Muller told JDU that if "more money becomes available, then we'll go ahead and do it. We know how to do it, we know what it will accomplish for us." The navy is leaving the tiles on HMCS Montreal.
The original system
The evaluation team also looked at the effect of the frigate's AES. This system was designed into the Halifax-class frigates because "that technology was state-of-the-art back when we specified the noise requirements for the patrol frigate, back in the seventies", says Muller.
The system, which consists of belts of thousands of tiny holes around the ship through which air is pumped, requires an extremely high maintenance effort (the small holes foul up easily) and does not make the ship any quieter. Muller explains: "AES was designed for noisier ships of the sixties and seventies and, for those, it worked. For a ship as quiet as the CPF is to start with, in its present configuration, it just didn't improve it."
The navy has, therefore, decided not to maintain or operate the system, although it will not (yet) be taken off the ships, despite the prospective savings in space and weight. "It's a fairly integrated system in the ship's machinery plant. It's not like just going on board and taking one piece of equipment off," says Muller. "There's piping, there's plumbing, there's a fair bit of work involved in doing that, so it's not going to be that inexpensive." So for now, the system stays on board.
What the navy will do to reduce the noise levels is spend C$3 million (to make some minor modifications to the propellers and fit certain pieces of onboard machinery with hydro-acoustic mufflers.
Opting for these inexpensive solutions however, will not bring the ship up to the original noise specification. Muller notes that "It will not meet the spec, but at the same time, even in its present configuration, without these other modifications that we're putting in, the CPF is a world leader in quietness among warships."
He says the noise is not interfering with the ship's sensors or capabilities. "This is primarily an anti-detection issue. We're quieting the ship to make it less detectable by other ships."
The manufacturer, SJSL, is not being held responsible for the noise problem. In 1994, the Department of National Defence and the contractor negotiated an Omnibus Amending Agreement, which covered all outstanding work and contract disputes related to the frigate project. As part of that agreement, the navy took responsibility for fixing the noise problem.
This is because "we had all the noise experts in house anyway", says Muller, and the navy believed it could do it for less money than SJSL would charge. "As it turns out, we were proven right. For in the neighbourhood of C$3 million, we're going to basically fix the noise problem. Except for the tiling, of course."