What shrink wrap does that a tarp does not
A tarp sits on the boat rather than over it. Wind lifts it, the grommets tear out, the tie-downs chafe against the gelcoat and rub through to the laminate at every contact point, and snow pools in the middle until the low spot holds standing water. By February a tarp is usually loose on at least one corner and funnelling meltwater straight into the cockpit it was put there to protect. The boat ends up wetter inside than it would have been bare.
Shrink wrap is heat-shrunk onto a frame so it finishes drum-tight and sheds instead of collecting. Nothing flaps, there is nothing loose for the wind to get under, and the loads go into the frame rather than into the boat's own fittings. It seals against wind-driven snow and it keeps pine needles, sap and squirrels out of the interior. The honest trade is that it is single-season material: it is cut off in spring and does not go back on next year.
Ventilation is not optional
A sealed boat is a terrarium. Any moisture still in the bilge, the carpet, a cushion or a damp locker evaporates during a mild spell, condenses on the cold underside of the wrap when the temperature drops again, and rains back down onto the interior. Repeat that through the winter and you get mildew through the upholstery, black spotting on the headliner and a smell that does not come out of foam once it is in. The boat is worse in April than it was in October.
Vents go into the wrap for exactly that reason, positioned to move air along the length of the boat rather than merely letting it in at one end. A zip-in access door is worth having as well, so the boat can be checked mid-winter without cutting the wrap open and taping it back. A wrap with no ventilation will do more damage over six months than no wrap at all, and it is the most common thing we see done badly.
The frame, the peak and snow load
Snow load is the whole reason the frame exists. Wet New Hampshire snow is heavy, and a flat or shallow wrap collects it, holds it, and then holds the meltwater that refreezes into a solid slab on top in the next cold snap. Freeze-thaw cycling repeats that process all winter, each time adding weight the wrap was never meant to carry. A frame with a proper ridge and real peak height sheds the snow before it can build; a low one turns into a bowl.
The frame is built from strapping run fore and aft over padded uprights, with the ridge high enough to give genuine pitch down both sides. Every point where the frame touches the boat gets padded, because a bare strap end under a loaded wrap will mark or crack gelcoat over a winter. The transom and the bow both need support, since the wrap is tensioned over each end and an unsupported wrap pulls down hard on the rails, the windscreen and the bow rail.
Wrap, canvas cover or indoor storage
Indoor storage is the best outcome for the boat. No snow load, no ultraviolet, a stable temperature and access whenever you want it. A fitted canvas or poly cover on a good frame is reusable and reasonable for a boat under a roof or in a genuinely sheltered spot, but canvas absorbs water, sags under wet snow and needs checking and clearing through the winter rather than being left alone until spring.
Shrink wrap is the middle option, and it is why most boats stored outdoors here wear it: it takes the winter unattended and it comes off in one pass in spring. What it cannot do is rescue a boat that was put away wet. The preparation matters more than the covering, and a well-prepared boat under canvas comes out better than a damp one under a perfect wrap. We prepare boats for shrink-wrap or covered storage; ring us on (603) 941-5836 and we will confirm exactly what is included and how the wrap itself is handled.
Preparing the inside before it is sealed
Everything that is going to be shut in for half a year should be dry before it is closed up. Cushions come out, or at least get stood on edge so air can pass behind them. Carpets and the bilge are dried out rather than merely wiped. Lockers are left open. Food, drink and damp gear come off the boat entirely. The fuel system is dealt with before the wrap goes on, and the boat should not be sealed smelling of fuel, because a vapour that vents harmlessly all summer is trapped under a wrap.
The drain plugs come out and stay out, so that meltwater and any rain that finds a way in drains away instead of sitting in the bilge and freezing solid. We put them somewhere they will actually be found in spring rather than loose in the boat. Batteries come out, get charged and are stored where they will not freeze. This unglamorous part is what decides the condition the boat is in when the wrap comes off in April.