Underwater Shipwreck Documentation: A Safe Guide

This guide explains how underwater archaeologists document shipwrecks without causing damage. You will learn the standard methods used to record a site—from baseline mapping to photogrammetry—so you can create an accurate record while leaving the wreck exactly as you found it. The steps cover the core techniques, the equipment involved, and the precautions that keep both the diver and the site safe.

What You’ll Need

• Diving certification and experience with underwater navigation and buoyancy control
• Dive computer, compass, and underwater slate or wet notes
• Measuring tape (at least 30 m / 100 ft) and a reel or line
• Baseline (a weighted line) and stakes or pins for anchoring
• Trowel or hand fan for gentle sediment removal (if excavation is part of the project)
• Underwater camera with strobes or video light
• Scale bars and color reference cards for photography
• Photogrammetry software (e.g., Agisoft Metashape, Reality Capture) for 3D modeling
• Underwater writing slate or a waterproof tablet for data logging
• Surface support: boat, dive supervisor, and a dry-erase board for communication

Step-by-Step

1. Conduct a pre-disturbance survey. Before touching anything, swim over the site to get an overview. Note the general layout, the extent of the wreck, and any obvious fragile areas. Take wide-angle photos and video from a distance. This initial record serves as a baseline and helps you plan where to place equipment without causing impact.
2. Establish a baseline and grid system. Lay a measuring tape or line along the longest axis of the wreck. Anchor it at both ends with non-invasive weights or pins that do not penetrate the hull. If the site is large, create a grid of squares (e.g., 1 m × 1 m) using lines and buoys. This grid gives you a reference for all measurements and ensures you cover the entire area systematically.
3. Record the site with trilateration. For each feature or artifact, measure its distance from two or three known points on the baseline. Use a tape measure, and record the distances on your slate. This method creates a triangle that fixes the object’s position in space. It is accurate and requires no physical contact with the wreck.
4. Create detailed drawings. On your underwater slate, sketch the plan view (top-down) and profile view (side) of the wreck. Use the grid lines as reference. Draw each feature to scale, noting dimensions. If you have a waterproof tablet, you can use a drawing app, but a slate is more reliable underwater. Always note the orientation (north arrow) and depth.
5. Take systematic photographs. Use a camera with a wide-angle lens and strobes. Shoot overlapping images of every part of the wreck, including close-ups of details and artifacts. For photogrammetry, take photos with at least 60-80% overlap, moving slowly and maintaining a consistent distance. Include a scale bar and color card in at least one photo per set. Never touch the wreck to move objects for a better shot.
6. Conduct photogrammetry (3D modeling). If you have the software and computing power, process your overlapping photos into a 3D model. This is a non-contact method that creates a highly accurate digital replica. The model can be measured, analyzed, and shared without ever touching the site. Ensure your photos have good lighting and texture; otherwise, the model will be incomplete.
7. Document sediments and environmental conditions. Record the type of sediment (sand, silt, clay), water temperature, visibility, and current. These factors affect the site’s stability and the preservation of artifacts. Note any signs of erosion or recent disturbance. This information is crucial for conservation planning.
8. Use remote sensing if available. For large or deeply buried wrecks, side-scan sonar or magnetometer surveys from the surface can provide a non-invasive map of the site. These tools can detect buried features without any physical contact. If you have access to such equipment, integrate the data with your ground-truthing.
9. Handle artifacts minimally and only when necessary. If an artifact must be moved for conservation or safety, do so only after documenting its original position thoroughly. Use soft tools like trowels and brushes to gently remove sediment. Place the artifact in a labeled container or bag, and record its exact location and orientation before lifting. Always follow the project’s conservation plan.
10. Compile the data on land. After the dive, transfer all notes, drawings, and photos to a digital database. Create a site plan using GIS or CAD software. Process the photogrammetry model. Review the data for gaps and plan follow-up dives to fill them. Publish or archive the results for future research.

Common Mistakes

• Poor buoyancy control: Kicking up sediment or bumping into the wreck can cause physical damage and reduce visibility. Always practice neutral buoyancy and fin slowly.
• Inadequate overlap in photos: For photogrammetry, insufficient overlap (less than 60%) leads to holes in the model. Take more photos than you think you need.
• Inconsistent measurements: Using different reference points or not recording the depth of measurements can make the data unusable. Always use the same baseline and note the exact point of measurement.
• Touching or moving artifacts without documentation: Even a small shift can destroy archaeological context. Always document in situ before any disturbance.
• Ignoring environmental conditions: Strong currents or poor visibility can compromise the accuracy of your measurements. If conditions are bad, postpone the dive rather than risk a poor record.

Tips

• Use a dive team with specific roles: one person measures, one records, one photographs. This reduces time on the bottom and minimizes disturbance.
• Mark the baseline with small floats so it is easy to locate on subsequent dives.
• Take a few test photos and check them on your camera screen before shooting the whole site. Adjust strobe angles to avoid backscatter.
• For photogrammetry, use a camera with a fixed focal length and avoid changing zoom during a survey.
• Always have a backup plan: extra batteries, memory cards, and a spare slate.
• When in doubt, do not touch. If an artifact is fragile, leave it and note its position.

Troubleshooting

• Poor visibility: If silt is stirred up, stop and wait for it to settle. If it does not, abort the dive and return later. Use a torch to improve visibility in dark water.
• Camera malfunction: Carry a backup camera or at least a spare battery and memory card. If the camera fails, continue with measurements and sketches; you can photograph on a later dive.
• Photogrammetry model has holes: This usually means you missed areas or had too little overlap. Go back and take additional photos of the missing sections.
• Measurements do not align: Check that the baseline was taut and did not move. If it shifted, re-establish it and re-measure the affected area.
• Strong current: Use a line from the boat to the wreck to help you stay in place. If the current is too strong, abort and reschedule.

Frequently Asked Questions

1. Can I document a shipwreck without any archaeological training? Basic documentation like photography and simple measurements can be done by recreational divers, but professional archaeological recording requires training and permits. Always check local laws; many wrecks are protected.
2. Is photogrammetry accurate enough for scientific research? Yes, when done correctly, photogrammetry can achieve sub-centimeter accuracy, making it a standard tool in underwater archaeology.
3. Do I need special permission to document a shipwreck? In most countries, shipwrecks are protected by heritage laws. You need a permit from the relevant authority before any documentation or disturbance.
4. What is the best way to measure a large wreck without a grid? Trilateration using multiple baselines is effective. You can also use a total station on land if the wreck is in shallow water, or a GPS buoy for surface mapping.
5. How do I avoid damaging fragile artifacts when taking photos? Use a camera with a macro lens and a small strobe. Do not move the artifact; instead, adjust your position to get the best angle. Use a scale bar placed gently beside it.
6. What should I do if I accidentally disturb sediment? Stop moving, wait for the sediment to settle, and then continue with extra caution. If the disturbance is significant, consider ending the dive to avoid further impact.

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