"Russian Noise Test"
By Dan Spurr

June/July 2003
Professional BoatBuilder No. 83

Noise reduction is an important issue in boat design, one that sometimes doesn't get the attention it deserves. Not only is excessive noise annoying, it also can cause fatigue, an in extreme cases, damage one's hearing. Riding shotgun aboard an offshore powerboat is roughly equivalent to standing in front of a subwoofer at an Ozzie Osbourne concert. Bring earplugs.

Recently we heard from Kvartet Ltd., a yacht design firm and Volvo Penta dealer in St. Petersburg, Russia, announcing noise tests it conducted last year with the North-West state Transport Sanitary inspection authority. "Here in Russia", wrote Kavartet chief designer Vasili Alexeev, there is a paradox. According to standard tests [made, however, at different times and under different conditions], the noise levels of Russians engines supposedly do not exceed the noise levels generated by the world's best engines. Nevertheless, when people cruise aboard boats first with Russian engines and then with imported engines, thereby having the opportunity to compare, they say - with one voice - that imported engines are much quieter."

The Russian-made engine Alexeev specifically refers to is the model 3D6, made by Barnaultransmash, in Barnaul, Siberia. Alexeev says Barnaultransmash is the largest manufacturer of diesel engines in Russia, with about 30% of the domestic market. The 3D6 has undergone small modifications for more than 40 years, and, he adds, "It still works on thousands of Russian boats."

Last summer Kvartet and North-West State Transport performed noise-control tests on four 371U-type motorboats (former deck-service boats for naval ships, now in widespread use as inexpensive motoryachts). "Results of these tests," wrote Alexeev, "help us better understand the effect of the propulsion unit on noise in a boat's compartments." The boats tested:

· Police boat "1. Retains it original propulsion unit, a Russian diesel engine 3D6 (150 hp at 1,500 rpm), rigidly mounted on its beds. The boats original wooden deck and superstructure were replaced with steel and aluminum.

· Police boat #10. The original 3D6 engine was replaced with a Volvo Penta TAMD 41, rigidly mounted on beds.

· Motoryacht Brabus-2. The original 3D6 engine was replaced with a Volvo penta TAMD 41. Engine is connected to the propeller shaft via a CV (constant velocity) Aquadrive and thrust bearing.

· Motoryacht Solnyshko. The original 3D6 engine was replaced with a Volvo Penta TAMD 41. Propeller shaft is connected to a water-cooled thrust bearing and flexible coupling. This boat's engine is covered by a soundproof box, and the saloon is separated from the wheelhouse by a fiberglass wall.

Noise measurements were made for three regimes: idle, medium and full throttle, in three compartments - wheelhouse, engine room, and the saloon at a bulkhead nearest to the engine room. Test results appear in the table below.

By way of comparison, here are permitted noise levels in Russian waters, according to domestic standards:

Engine compartments -120 dBA
Service compartments - 75 dBA
Living compartments - 75 dBA

And here are various examples of everyday noise levels:

Quiet music - 40 dBA
Loud radio - 60 dBA
Truck motor - 70 dBA
Loud horn - 90 dBA
Turbojet at 5m - 120 dBA
Painful noise - 130-140 dBA

"Noise measurements in an engine compartment," wrote Alexeev, "confirm that the Volvo Penta TAMD 41 engine really is quieter than the Russian-made 3D6. At full throttle the difference is 2 dBA; at idle - 16 dBA! The reason for such a tremendous difference is that in the Volvo Penta's sound spectrum, there is a large share of high-frequency noise from the turbocharger that is not a factor at idle. As a result, total noise level greatly decreases.

"In other compartments, much of the noise is caused by vibration of the boat's structure. As can be seen from the table, the use of flexible mounts and flexible propeller-shaft coupling, which disconnects the engine from the hull structure and propeller shaft, decreases noise about 12 to 15 dBA - that is, sound pressure decreases 12-15 times.

"Unfortunately, the test setup did not allow us to test the influence of flexible mounts and flexible couplings separately. But the total effect of all taken measurements is about 20-25 dBA in the engine compartment and wheelhouse, and 7-15 dBA in the saloon."