In, out, what’s it all about?
Q
We have a 10.4m (34ft) motor-cruiser built in 2000, and have received conflicting advice on whether to take it out of the water for the winter or not. On the one side, the argument is that taking it out once every two/three/five years (the number varies depending on who we talk to) reduces osmosis. The counter argument is that the best shape of the hull is when it is in the water, and that taking it out can overly stress it. In addition, there is greater danger from freezing and damage to inlet/outlet valves (and therefore serious leaks) when it is returned to the water. And finally, GRP manufacture is well refined now, and boats the age of ours are not at risk from it. Colin Brown replieS: Taking a boat out of the water when it is not in use is considered good practice because it allows the moisture which inevitably passes through the laminate to evaporate. Water in the laminate will attach to unbonded polyester chains, which can weaken the resin and the resin-to-glass bonds. The by-products of this process collect in tiny voids in the laminate. Osmosis is the process by which the fluid in voids attracts water through the laminate. This can generate enough pressure to separate the laminate and form blisters.
The good news is that building standards and materials have improved since the early days of glassfibre boats, and blistering and other water-related defects are much less common than they used to be: a boat left in the water for several years may never blister. The advent of sheltered marinas has led to more boats staying in the water over winter or even multiple years. This is driven partly by convenience and the understandable avoidance of spending more money. I don’t think that preserving and supporting the hull is considered by many people.
If a boat is lifted out of the water and shored up properly there should be no damage or stress on the hull. There are, however, several ways that damage can be done by poor lifting and shoring. Slinging from a single point without a spreader bar can squeeze a hull enough to cause damage. Poorly-placed keel blocks can allow the middle or ends of the keel to sag, particularly on straight-keeled motorboats. The weight of the boat should be borne by the keel with shores applied to strong parts of the hull to keep it level. This might be along the chines or lined up with internal structures. Shores or cradle pads pushing against unsupported panels can distort the hull skin.
If a boat is out of the water over the winter it is important to winterise the engine and systems so that frost damage is avoided. This includes draining the fresh water system and plumbing, and putting antifreeze in any water that stays on board. Don’t put antifreeze in any drinking water tanks. Seacocks should be left open to release any water. The bilge should be dried and kept dry over the winter. Ventilation should be arranged to allow air to circulate to reduce condensation.