There’s a common sentiment in the sailing community when it comes to groundings; there’s three types of sailors – those who have run aground, those who haven’t yet and liars.
While this may be said tongue-in-check, grounding do happen more often than you think. In fact, even with today’s advanced electronic charts and GPS accuracy, groundings remain one of the most common incidents reported worldwide.
Understanding how groundings happen, how to avoid them and what to do if the boat were to be grounded is all part of the mental emergency toolkit any crew or captain should form, to help ensure the safety of the people and vessel.
Navigational errors that lead to groundings
Despite all the wonderful technology available to us, the human element combined with a misunderstanding of that technology often introduces risk. Groundings typically occur due to poor lookout, fatigue, or key errors in route planning.
Lookout and fatigue
When people are tired, mistakes happen, but on a boat that can be costly. Before setting out ensure that your crew understands:
- Who is meant to be looking out when
- What the rest or sleep periods will be like
- What areas along the route may require greater vigilance
It’s also important to check that all electronics are working, such as the radar, depth sounder, GPS and charts, and that everyone knows how to use them.
Zooming in on digital charts
One common issue is the incorrect use of digital charts, especially by viewing them at the wrong scale. When you zoom out, the chart plotter automatically declutters the display, often hiding isolated dangers, small rocks, or crucial depth soundings that were shown on the larger scale. This zooming bias can make an area look clear when danger is lurking just below the surface.
Software issues
A momentary GPS dropout, software glitch or electrical issue can leave a boat in a perilous situation without a physical reference or electronic charts of the surrounding area. As a result, don’t discount paper charts as a backup tool for route planning and position checking.
Chart information and tides
The sounding on displayed on hydrographic charts are reduced to Chart Datum, which is usually the Lowest Astronomical Tide (LAT). This means the depths shown are the lowest level that can be predicted to occur under average meteorological conditions. It is important to keep in mind that LAT is not the lowest possible level that can be reached; storm surges and unusual weather patterns can cause considerably lower levels to occur.
Drying heights, which show objects like exposed rocks or sandbars, are given above Chart Datum. This is why careful, constant monitoring of the current tide relative to Chart Datum is essential for navigation in shallow or unfamiliar waters.
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- The noforeignland map is a helpful resource to check for unmarked grounding hazards
Squat effect
One of the most interesting aspects of shallow water navigation is a phenomenon known as ‘Squat’. This is a hydrodynamic explanation for why a boat suddenly touches the bottom in waters that the depth sounder suggested was safe.
Squat occurs when the water beneath the moving vessel is squeezed between the hull and the seabed. This restriction causes the water flow to accelerate, creating an area of low pressure directly under the boat. The vessel is effectively drawn down into this lower pressure zone, meaning its dynamic draft increases dramatically while underway.
The faster the vessel is moving, and the shallower the water, the more pronounced the squat effect becomes. The important technical takeaway is that the vessel does not actually increase its draft, but the surrounding water level drops, making it possible to ground the boat when the static draft should have been clear. Therefore, slowing down drastically when entering depths less than two-and-a-half times your static draft is the single most important preventative measure against squat-related groundings.
Reacting to a grounding
If a grounding does occur, crew safety and damage assessment are the first priorities. This is a moment where clear thinking is needed, and having a previously discussed or thought about plan can help.
1. Initial assessment and alarm
Immediately put the engine into neutral to prevent damage to the propeller or further grounding.
Raise the alarm aboard and have crew members immediately inspect the bilges and hull for signs of a breach. Simultaneously, someone should be preparing to notify surrounding vessels or local authorities using the VHF radio.
- If in immediate danger: MAYDAY
- If not in immediate danger but requiring assistance: PAN PAN
- If conveying a safety hazard to other vessels: SÉCURITÉ
Even if the situation appears minor, things can snowball quickly, and you can always notify the organization or person you alerted if the situation is resolved quickly and there is no damage.
2. Vessel stabilization and damage control
Assess the situation, and if it is safe to do so, try to stabilize the vessel and enact damage control plans.
Start by surveying the surrounding area and conditions, then use that information to formulate a plan.
- Are you in a dangerous position? (i.e. a busy seaway, near reef or rocks)
- What’s the sea-state like?
- Is there a swell?
- Is night approaching?
- Is there bad weather approaching?
- Is the tide rising or falling?
- Has the vessel been holed?
- Is the area isolated, or are there resources nearby?
If being driven by waves or wind, you could deploy ground tackle to try to stabilize the vessel and prevent movement further onto the hazard. If the tide rising, it may allow for a self-float, while a falling tide requires stabilization. If night is approaching, organize appropriate lighting.
In your planning, also consider the liquids you have aboard and how to minimize the sloshing. Completely fill or completely empty all tanks (water, fuel) to prevent the shifting weight from causing imbalance and instability.
Refloating techniques
Often, if the grounding occurred at slow speed and the conditions are calm, the vessel can be maneuvered off the bottom almost immediately. On monohulls, including a heeling moment can be enough to lift the keel enough to clear the obstruction. This is often done by swinging out a weighted boom or by raising a sail to leeward.
A technique for removing a larger vessel is to kedge off. This involves deploying an anchor (via the dinghy) into deeper water and using the anchor rode and main winches to physically haul the boat off the bottom. If successful, it is vital to immediately and carefully check the hull and bilges for damage or water penetration before continuing the trip. If severe damage has been sustained and the vessel is sinking, it may be better run the boat aground again in a location that is safe for the crew to evacuate, and easier for the wreck to be salvaged later.
Groundings – Are they inevitable?
In the end, preparation and knowledge are the greatest tools any cruiser possesses. By understanding both the technological limitations and the fundamental physics of hydrodynamics, a sailor is best equipped to prevent a stranding, and to safely manage one if it happens.
Share your own best practices for shallow water navigation or how you handled a grounding down the comments; your experiences make the noforeignland community stronger.
Michaela Claes is an experienced yachtswoman, currently based in Sydney Australia where she likes to spend time cruising on her motor yacht Joan B. She is a senior executive with Pantaenius Insurance and offers expert insights into cruising in the Pacific, and managing the safety and wellbeing of boats in this region.
