# Battling Barnacles (DD-705)

> Barnacles are crustaceans that cement themselves to hard surfaces, including ship hulls, as part of 'biofouling' along with slime, algae and other organisms. A 2007 study by Michael Schultz of the US Naval Academy, modeling a mid-sized naval frigate, predicted that heavy calcareous fouling such as barnacles and tubeworms raises the shaft power needed at cruising speed by up to 86%. Even slime films brought significant penalties. Hulls are protected with antifouling coatings and cleaned in dry dock or in the water by divers and robots. In-water cleaning has its own risks. The IMO's 2023 Biofouling Guidelines warn it can damage coatings and release invasive species and toxic coating debris. They say heavier fouling should be removed with systems that capture the debris.

- Department: Tech (also Nature)
- First published: 2026-03-18
- Last updated: 2026-03-18
- Permalink: https://detailenjoyer.com/case/battling-barnacles/
- Author: Marcus Easterling (DetailEnjoyer), The Detail Department

## On the timeline

- **July 2023**: IMO adopts revised Biofouling Guidelines

Full timeline: https://detailenjoyer.com/timeline/?case=battling-barnacles

## Quick facts

- **DD-705-F01**: Heavy calcareous fouling can raise required shaft power by up to 86% (Schultz, 2007). _(Write-up · Exhibit B (The drag penalty))_
- **DD-705-F02**: The IMO revised its Biofouling Guidelines in July 2023. _(Write-up · Exhibit D (Cleaning risks))_

## Write-up

Hitchhikers that burn fuel. Heavy hull fouling can raise power needs by up to 86%.

1. **What fouls a hull**: Biofouling starts with a slime film of microbes and builds to 'macrofouling' such as barnacles, tubeworms and weed. Barnacles glue themselves on with a protein cement.
2. **The drag penalty**: Schultz's 2007 model of a frigate predicted that heavy calcareous fouling raises required shaft power by up to 86% at cruising speed. Light slime alone carried a smaller but significant penalty.
3. **Prevention**: Antifouling coatings slow growth. 'Proactive' cleaning removes slime before barnacles settle, and 'reactive' cleaning strips heavier fouling.
4. **Cleaning risks**: The IMO warns that cleaning can damage coatings and release harmful waste and invasive species. Its 2023 guidelines limit uncaptured cleaning to light fouling, below rating 2, in approved areas.
5. **Capture tech**: Newer robotic in-water cleaners use suction and filtration to capture debris, and researchers are developing tests of how much they capture, including with artificial barnacles.

## Related case files

- [Offshore Oil (DD-033)](https://detailenjoyer.com/case/offshore-oil/): Another case about structures that spend their lives in seawater
- [USS Gerald R. Ford (DD-710)](https://detailenjoyer.com/case/uss-gerald-r-ford/): Another case about naval ship operations
- [Sandy Scaridae (DD-591)](https://detailenjoyer.com/case/sandy-scaridae/): I linked more life that lives on hard ocean surfaces
- [Concrete Reefs (DD-632)](https://detailenjoyer.com/case/concrete-reefs/): Another case about marine life growing on hard surfaces

## Reel vs. record

- **Scale**: the penalty depends on how heavy the fouling is. Schultz (2007) modeled up to 86% more shaft power for heavy calcareous fouling, so a 'thin layer' and '20%' aren't fixed figures.
- **Missing culprit**: slime films alone, before any barnacles, already add significant drag.
- **Note**: Missing environmental context: in-water cleaning can release invasive species and toxic coating debris, which is why the IMO's 2023 guidelines call for capturing debris when removing heavier fouling.
- **Missing prevention**: antifouling coatings and regular 'proactive' cleaning are the main defenses, along with dry-dock cleaning.
- **Precision**: robots and divers don't only work in port. Cleaning location is controlled, and many authorities restrict where uncaptured cleaning is allowed.

## Video: Battling Barnacles: Hitchhikers That Burn Fuel

- Duration: 26.8 s · Published: 2026-03-18
- File: https://detailenjoyer.com/assets/videos/DWCoZoakUO4.mp4

### Transcript

DID YOU KNOW? Cleaning barnacles off ships is an important maintenance process because these hard-shelled marine organisms attach firmly to hulls and dramatically increase drag as a vessel moves through water. Even a thin layer of barnacles can raise fuel consumption by 20% or more by disrupting smooth water flow along the hull. Increasingly, specialized underwater cleaning robots and divers perform the work while the ship remains in port, using rotating brushes or high-pressure jets to strip away barnacles, algae, and other fouling organisms. NOW YOU KNOW!

## Questions & answers

**Q: What kind of animal is a barnacle?**  
A: Barnacles are crustaceans. _(Source: Write-up · Exhibit A (What fouls a hull) · IMO: 2023 Guidelines for the control and management of ships' biofouling, MEPC.378(80); Frontiers in Marine Science (2024): Capture efficacy test method for in-water cleaning using artificial barnacles)_

**Q: By how much can heavy calcareous fouling raise required shaft power, per Schultz (2007)?**  
A: Up to 86% at cruising speed. _(Source: Write-up · Exhibit B (The drag penalty) · Schultz (2007), Effects of coating roughness and biofouling on ship resistance and powering, Biofouling)_

**Q: Which body issued the 2023 Biofouling Guidelines?**  
A: The International Maritime Organization. _(Source: Write-up · Exhibit D (Cleaning risks) · IMO: 2023 Guidelines for the control and management of ships' biofouling, MEPC.378(80); IMO: Biofouling)_

**Q: What's one risk of in-water cleaning?**  
A: It can release organisms and coating debris. _(Source: Write-up · Exhibit D (Cleaning risks) · IMO: 2023 Guidelines for the control and management of ships' biofouling, MEPC.378(80); IMO: Biofouling)_

**Q: What usually forms on a hull before barnacles?**  
A: A microbial slime film. _(Source: Write-up · Exhibit A (What fouls a hull) · IMO: 2023 Guidelines for the control and management of ships' biofouling, MEPC.378(80); Frontiers in Marine Science (2024): Capture efficacy test method for in-water cleaning using artificial barnacles)_

## Sources

- [Schultz (2007), Effects of coating roughness and biofouling on ship resistance and powering, Biofouling](https://doi.org/10.1080/08927010701461974)
- [IMO: 2023 Guidelines for the control and management of ships' biofouling, MEPC.378(80)](https://wwwcdn.imo.org/localresources/en/KnowledgeCentre/IndexofIMOResolutions/MEPCDocuments/MEPC.378%2880%29.pdf)
- [IMO: Biofouling](https://www.imo.org/en/ourwork/environment/pages/biofouling.aspx)
- [Frontiers in Marine Science (2024): Capture efficacy test method for in-water cleaning using artificial barnacles](https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2024.1404472/full)

## Cite this case file

Easterling, Marcus. "Battling Barnacles." The Detail Department (DetailEnjoyer), case file DD-705, last updated Mar 18, 2026. https://detailenjoyer.com/case/battling-barnacles/