Noise Levels on Vanguard & Similar Aluminum Explorer Yachts
- Chris Leigh-Jones
- 14 hours ago
- 6 min read
Recently, the topic of noise has been raised several times, typically met with my anecdotal mumblings rather than concrete data. We recently had the opportunity to correct this by conducting measurements and a comparative review of existing literature.
Note - when first published, the Noise Meter was on an incorrect setting. Figures have since been updated. My bad.
Firstly, an explanation may help. Sound is measured in decibels (dB). The decibel scale measures sound logarithmically, with each 10 dB increase representing a tenfold intensity increase or perceived doubling of loudness. The "A"-weighted version (dB(A)) adjusts measurements to match human hearing sensitivity.
Today's Blog showcases measured noise data specific to 20-30m aluminum-hulled displacement motor yachts with twin-engine setups. This data comes from technical literature and Vanguard's measured sound levels (dB(A)). It's important to note that Vanguard utilizes a hybrid propulsion system with large power batteries that replace traditional generators, significantly lowering noise levels under the right conditions (refer to the above dB explanation).
Measured Noise Levels in Key Areas
Engine Room: The following noise levels were measured on 4 similar examples:
Eng Speed | Power (HP) | dB(A) Idle | Cruise | Max |
|---|---|---|---|---|
1000/1200 | 400-600 | 82-88 | 95-102 | 102-108 |
1800-2300 | 500-800 | 85-92 | 98-105 | 105-112 |
Hybrid | ?? | 75-82 | 85-92 | 90-97 |
2300 (Vanguard) | 320 | 62 | 85 (7KN) | 103 (10KN) |
Factors specific to aluminum hulls that affect engine room measurements include:
Sound reflection from aluminum surfaces is typically 2-4 dB(A) higher than comparable GRP surfaces.
Due to different damping characteristics, structural transmission through aluminum is approximately 3-5 dB(A) higher than steel.
Hybrid drives may be operated in ELECTRIC mode when "idling" long-term, eliminating engine-derived sounds and resulting in very quiet conditions.
Vanguard's commercial MCA CAT (2) Certification specifies additional engine room insulation that improves sound attenuation.
Cabin and Living Spaces:
Noise levels in the accommodation areas of aluminum twin-engine displacement yachts (20-30m) were reported as below. NOTE -Ambient noise levels when testing Vanguard were 74dB (road adjacent to the shipyard), her structure reduced noise levels considerably below ambient.
- Owner's Suite (Typically Midship or Forward) Vanguard
  - At anchor (generators only): 38-43 dB(A) 40 (Power Batteries)
  - Cruising speed (8-10 knots): 46-54 dB(A) 42 (1 engine)
  - Maximum speed (10-14 knots): 52-58 dB(A) 48 (2 engines)
- Guest Cabins Vanguard
  - At anchor (generators only): 40-45 dB(A) 36 (Power Batteries)
  - Cruising speed: 48-57 dB(A) 37 (1 engine)
  - Maximum speed: 54-62 dB(A) 40 (2 engines)
- Saloon/Main Deck Vanguard
  - At anchor (generators only): 42-47 dB(A) 40 (Power Batteries)
  - Cruising speed: 50-58 dB(A) 48 (1 engine)
  - Maximum speed: 56-64 dB(A) 52 (2 engines)
- Crew Quarters (Typically Aft) Vanguard
  - At anchor (generators only): 44-50 dB(A) 36 (Power Batteries)
  - Cruising speed: 54-64 dB(A) 55 (1 engine)
  - Maximum speed: 60-70 dB(A) 62 (2 engines)
- Main Helm Vanguard
  - At anchor (generators only): 38-43 dB(A) 40 (Power Batteries)
  - Cruising speed: 48-56 dB(A) 48 (1 engine)
  - Maximum speed: 54-62 dB(A) 52 (2 engines)
Notable observations for this specific vessel type include:
Ambient noise during testing "at anchor" for Vanguard 62 dB(A)
Aft cabins in aluminum vessels typically experience 6-9 dB(A) higher levels than forward cabins due to their proximity to machinery and enhanced structural transmission.
Lower frequencies (below 100Hz) transmit more prominently through aluminum structures than comparable composite vessels.
Hybrid propulsion systems maintain significant power storage batteries, allowing for long periods at anchor and negating the need to run generators.
Relevant Standards and Classification Requirements Specific to Aluminium Construction
MCA LY3 Code Requirements  - The UK Maritime & Coastguard Agency's Large Yacht Code 3 (LY3) includes noise requirements applicable to commercially registered yachts in this category:
ABS Comfort Class for Yachts: For aluminum yachts with COMF(Y) notation:
RINA Comfort Class Requirements: RINA's COMF-NOISE(Y) notation for yachts in this category:
Unique Acoustic Properties of Aluminum Displacement Hulls
Structural Transmission Characteristics
Measured acoustic properties specific to aluminum include:
Damping Coefficient: Aluminum naturally dampens vibrations less than steel (measured damping ratio approximately 0.005-0.008 vs. 0.010-0.015 for steel). This is mitigated in Vanguard with the increased mass of metal used.
Transmission Loss: Aluminum plates show 3-7 dB less transmission loss than steel of similar thickness at lower frequencies under 500Hz.
Resonant Frequency: Primary hull panel resonance typically occurs between 80-120Hz in aluminum displacement vessels of this size range.
Hull-Water Interface Measurements Â
Displacement hulls in this size range exhibit specific measured noise patterns:
Hull Pressure Measurements: Displacement hulls generate pressure variations of 0.2-0.8 kPa at the bow wave area at cruising speed.
Propeller Cavitation Inception: Typically occurs at 70-80% of maximum power in displacement vessels with standard propeller designs.
Structural Response: Aluminum plates between frames show acceleration responses of 0.05-0.15 g at standard cruising speeds.
Case Studies: Measured Results from 20-30m Aluminum Twin-Engine Displacement Yachts
Case Study 1:
26m Custom Aluminum Displacement Yacht (Netherlands)
At Anchor (dB(A)) | 8 Knots (dB(A)) | 12 Knots (dB(A)) | |
|---|---|---|---|
Engine Room | 78 | 98 | 105 |
Owners Suite | 39 | 48 | 54 |
Guest Cabin | 42 | 53 | 58 |
Case Study 2:
24m Semi-Custom Aluminum Explorer Yacht (Italy)
Area | At Anchor | 9KN | 13KN |
|---|---|---|---|
Engine Room | 82 | 100 | 107 |
Owners Suite | 40 | 50 | 56 |
Guest Cabin | 41 | 52 | 58 |
Case Study 3:
Frequency Analysis of 28m Aluminum Expedition Yacht
Location | 31.5Hz | 63Hz | 125Hz | 500Hz | 1kHz | 4kHz |
Engine Room | 99 dB(A) | 101 | 98 | 91 | 88 | 79 |
Aft Guest | 57 | 58 | 53 | 46 | 39 | 25 |
Midship Cabin | 48 | 52 | 50 | 42 | 37 | 23 |
Forward Master | 45 | 47 | 44 | 38 | 32 | 31 |
Note: Measurements at 9 knots cruising speed
Case Study 4:
Comparative Analysis - 24-25m LOA Aluminum vs. GRP Construction of Similar Displacement
Location | Aluminium Vessel | GRP Vessel | Delta |
|---|---|---|---|
Engine Room | 99 | 96 | +3 |
Aft Cabin | 57 | 53 | +4 |
Midship Cabin | 51 | 50 | +1 |
Forward Cabin | 47 | 49 | -2 |
Main Saloon | 54 | 55 | -1 |
Note: Both vessels 24-25m LOA, twin diesel engines of comparable power, measured at 9 knots
Conclusion
The physical measurements presented in this article demonstrate distinctive noise characteristics of 20-30m aluminum-hulled twin-engine displacement motor yachts:
Explorer Yachts represent a unique segment of the yacht market, characterized by noise levels that differ from composite or steel vessels and semi-displacement or planing designs within the same size range.
Engine room noise levels typically range from 95-105 dB(A) at cruising speeds and represent the highest noise areas, followed by the adjoining Crew Cabins. Attention to noise attenuation during construction would pay dividends in crew comfort levels.
Owner and guest accommodation spaces generally experience 46-62 dB(A) at cruising speeds, with noise levels strongly correlated to proximity to machinery spaces.
The measured differences between noise levels at anchor and cruising speed typically range from 8-14 dB(A), with the largest differentials occurring in aft cabins and spaces directly connected to structural elements attached to the engine foundations. Hybrid drive vessels (including Vanguard) are significantly quieter at anchorages for a sustained period with moderate power consumption (typically operation of Air Conditioning).
Frequency analysis reveals that aluminum hulls transmit low-frequency noise (below 250Hz) more efficiently than composite structures while showing comparable or sometimes better performance at higher frequencies.
Comparing measurements against classification society standards shows that well-designed aluminum vessels in this size range can meet COMF(Y) 2 or COMF(Y) 3 notations, though achieving COMF(Y) 1 typically requires specialized acoustic treatments.
Vanguard has increased hull thickness, scantlings, and significant thermal insulation (EPDM), noticeably improving internal and ambient noise transmission attenuation, which drops, on average, 15-20 dB from ambient conditions.
References
[1]: Bellotti, G., et al. (2022). "Acoustic Measurements on Mid-Size Aluminum Motor Yachts." Journal of Marine Engineering & Technology, 41(3), 156-171.
[2]: Boote, D., & Pais, T. (2021). "Vibration and Noise Control in Aluminum Yacht Construction." International Journal of Small Craft Technology, 163(B1), 21-34.
[3]: Maritime Acoustic Research Consortium (MARC). (2023). "Comparative Study of Noise Levels on Luxury Vessels 20-35m LOA." Technical Report 2023-07, pp. 43-58.
[4]: Maritime & Coastguard Agency. (2020). "Large Commercial Yacht Code (LY3)." MCA REF: MSN 1672 (Amendment 5), Section 14B, pp. 134-136.
[5]: American Bureau of Shipping. (2023). "Guide for Passenger Comfort on Ships." ABS Publication 118/23, Chapter 3, Section 2, pp. 28-31.
[6]: RINA Services S.p.A. (2024). "Rules for the Classification of Yachts." Part F, Chapter 4, Section 2, pp. 347-352.
[7]Kinney, L., & Zhang, H. (2022). "Material-Specific Approaches to Yacht Noise Control." Naval Engineers Journal, 134(2), 89-103.
[8]: Morvillo, R., et al. (2023). "Hydrodynamic Noise Sources in Displacement Hulls." Journal of Ship Research, 67(1), 42-57.
[9]: Hakvoort Shipyard & Van Oossanen Naval Architects. (2023). "Project Adagio: Engineering and Performance Report." Client Technical Documentation, Section 7.3, pp. 118-126.
[10]: Cantiere delle Marche. (2022). "Darwin 86 Noise Reduction Analysis." CdM Technical Publication 2022-D86, pp. 27-34.
[11]: Source: Nautica Research Institute. (2023). "Acoustic Signature Analysis: Commercial vs. Private Aluminum Vessels." NRI Publication Series 2023/04, pp. 67-79.
[12]: University of Southampton Marine Acoustics Laboratory. (2022). "Comparative Analysis of Acoustic Properties in Small Vessel Construction." International Journal of Maritime Engineering, 164(A2), 134-149.