Hull Inspection and Haul-Out: A Practical Guide to Dry-Dock Preparation

Planning the Haul-Out

Most marinas and boatyards in Ontario, Nova Scotia, British Columbia, and Quebec operate travellifts with rated lift capacities ranging from a few tonnes to over eighty tonnes for larger vessels. Scheduling the haul-out several weeks in advance during peak fall season is standard practice; yards typically fill their daily lift schedule by late September in most Great Lakes locations.

Before the vessel arrives at the sling area, the yard will need the beam measurement, displacement, and keel configuration — whether fin keel, full keel, or twin keels — to position the sling correctly. Incorrect sling placement can concentrate the vessel's weight on an unintended area of the hull and cause delamination on fiberglass boats.

A vessel blocked out in a dry dock storage yard. Correct cradle placement distributes the hull load evenly and prevents distortion over a long winter. (Source: Wikimedia Commons)

Initial Hull Wash and Visual Inspection

As soon as the vessel is clear of the water and before the hull surface dries, a pressure wash removes bottom paint fouling, weed, and growth so the hull can be inspected properly. The inspection window while the surface is damp is brief — bare fiberglass shows stress cracks, osmotic blistering, and delamination zones more clearly when wet than when dry.

Osmotic blistering

Osmotic blistering occurs when water migrates through the outer gelcoat layer of a fiberglass hull and becomes trapped between the laminate layers. The blisters appear as domed protrusions on the hull surface, ranging from a few millimetres to several centimetres across. When punctured, they release a yellowish or brownish fluid with a vinegar-like or acidic odour — a characteristic sign of the hydrolysis reaction occurring within the laminate.

Minor surface blistering can be ground out, dried over a full winter, and filled with an epoxy barrier coat in spring. Blistering that extends deeper into the laminate structure or covers a large surface area warrants a more detailed assessment by a boatyard with fiberglass repair capability.

Keel attachment inspection

On fin-keel sailing vessels, the keel is typically attached with stainless steel keel bolts running through the hull and secured with nuts in the bilge. A small amount of movement at the keel-hull joint is common with age, but significant play — or rust staining and crystalline deposits on the bilge nuts — indicates that the joint needs attention. The keel bolts should be torqued to the manufacturer's specification during every haul-out cycle, and the bedding compound around the base of the keel should be checked for separation.

A vessel being lifted clear of the water for a hull inspection. The haul-out moment allows access to every part of the underwater hull. (Source: Wikimedia Commons)

Through-Hull Fittings and Seacocks

Every hole through the hull below the waterline — for engine water intake, cockpit drain, head intake and discharge, depth transducer, and bilge pump outlet — is a potential failure point. Through-hull fittings are typically bronze or glass-reinforced plastic (GRP) depending on the vessel age and builder.

During the haul-out inspection, each through-hull should be checked for:

• Dezincification — a pinkish, weakened appearance in bronze fittings caused by selective leaching of zinc from the alloy
• Corrosion at the junction between the hull and the fitting flange
• The condition of the seacock handle — stiff or frozen handles indicate that the seacock has not been exercised regularly and may fail to close under load
• Hose clamp condition — double-clamp installations should have both clamps tightened and positioned so the slots are offset, not aligned

Sacrificial Anodes (Zincs)

Sacrificial anodes protect underwater metal components — propeller, shaft, rudder fittings, and outdrive lower units — from galvanic corrosion by providing a less noble metal that corrodes preferentially. In freshwater, aluminium anodes are typically used rather than zinc, because zinc alloys can passivate in freshwater and provide inadequate protection. In saltwater, zinc or aluminium anodes are both common; magnesium anodes are specified for freshwater use by some manufacturers.

At haul-out, any anode that has worn to less than approximately half of its original thickness should be replaced rather than carried through another season. Replacing zincs in fall — rather than spring — means the new anodes are in place and ready from the first launch day.

Cradle and Jackstand Placement

Once the haul-out inspection is complete, the vessel needs to be blocked out on cradles or jackstands for winter storage. The blocking must support the hull at its structural hard points, not in the middle of unsupported spans of fiberglass.

Keel-stepped sailboats

Sailboats with a ballasted keel normally rest on the keel itself, with the vessel sitting vertically. Jackstands are placed on either side of the hull at appropriate angles, with rubber pads at the contact points, to prevent lateral movement. The stand angle should allow the hull to push outward against the stand — if the vessel leans, the stand on the low side prevents a fall while the stand on the high side would need to be repositioned.

Powerboats and runabouts

Powerboats typically rest on custom cradles built by the yard or owner. A correctly fitted cradle distributes load along the hull's longitudinal stringers and not across the unsupported hull panels. Trailer storage using the boat trailer is common for smaller vessels, though a trailer is not always ideal for a full winter because the trailer suspension and tyre sidewalls experience static compression for months.

Bottom Paint Assessment

The existing bottom paint should be assessed while the hull is accessible. Antifouling paint on Canadian Great Lakes vessels is typically an ablative formulation that wears away through the season, releasing biocide as it erodes. After several seasons, the ablative layer becomes thin enough that growth control is compromised before spring relaunch.

If the old paint is sanding down to fiberglass or a hard-paint substrate, a new coat should be applied before launch. Applying bottom paint in fall — after the hull has had a few weeks to dry out — rather than in spring can improve adhesion and allow more cure time before the vessel goes back in the water.