Lee Cloths, Sail Covers & Cockpit Cushions

Canvas Work · Fabrication

Canvas fabrication at the level required for offshore sailing is not a specialist skill — it is a learnable craft that rewards careful measurement, decent materials, and patience. The projects in this guide — lee cloths, boom tents, sail covers, cockpit cushions — are within reach of any boat owner with a Sailrite or walking-foot sewing machine and a willingness to make a template before cutting expensive canvas. The economics alone justify the effort: a professional quote for a complete dodger replacement runs to thousands of pounds or dollars; the materials for a DIY rebuild cost a fraction of that.

Lee Cloth Fabrication

The lee cloth is the most important safety item in a passage-making boat's interior. A crew member sleeping in a bunk at sea on a heeled, moving boat needs to be retained in the bunk — not held gently, but physically prevented from being thrown across the cabin if the boat lurches in a seaway. The lee cloth provides that retention, and it takes significant load in exactly those conditions.

The fabric specification for a lee cloth is Sunbrella 9.25 oz at minimum. Some offshore sailors use heavier canvas or a doubled layer, particularly for the attachment areas. The cloth itself is not the failure point in a lee cloth that fails — the attachment hardware is. The standard failure mode is the attachment point pulling out of the bunk structure, not the cloth tearing.

Attachment hardware must be through-bolted D-rings with backing plates. The D-ring takes the webbing loop from the top of the lee cloth; the through-bolt passes through the cabin ceiling or bunk board with a backing plate of adequate area on the far side to distribute the load. The backing plate — typically a piece of 4mm aluminium or stainless plate, 50mm × 80mm minimum — is the non-negotiable element. A D-ring screwed into wood without a backing plate will pull out under the load of a crew member thrown into the lee cloth at sea. This is not a hypothetical; it happens.

Snap hooks are not acceptable attachment hardware for lee cloths. Snap hooks — the spring-loaded hooks used for sail hanks and bungee cords — can open under the right combination of load and angle. A snap hook that opens while someone is sleeping behind the lee cloth defeats the purpose entirely. Use D-rings and Dyneema or Spectra webbing at all attachment points.

Measuring and cutting a lee cloth: measure the bunk length and the height you want the cloth to rise when deployed (typically 18-24 inches above the bunk surface). Add 3 inches on all edges for hems and attachment. Cut the cloth, hem all four edges with a double fold, reinforce the corner areas with a doubled patch, and sew the webbing attachment loops to the reinforced upper corners. The lower edge attaches to the bunk edge with a continuous webbing strip or snaps — snaps for the lower edge are acceptable because the load on the lower edge is compression against the bunk, not tension pulling the cloth free.

Boom Tent Construction

A boom tent — the awning that stretches from the mast aft to the backstay and down to the lifelines — transforms a cockpit in the tropics and provides rain collection capacity that can meaningfully supplement watermaker output. A well-designed boom tent is one of the most used items on a liveaboard boat in warm climates.

Use Sunbrella 10 oz for a boom tent. The awning takes wind load when it is up in anything above light air, and the heavier weight handles the mechanical stress of being raised and lowered daily across a season. Lighter canvas works but wears faster at the seams and batten pockets.

Measuring a boom tent starts with a cardboard or tarp template cut to fit the space between the boom, the mast, and the cockpit coaming. Work section by section: measure the boom-to-coaming drop on each side, the boom length from mast to backstay attachment, and the width across the cockpit at both ends. Transfer these measurements to the template with 2-inch allowances at all edges. A boom tent is not a simple rectangle — the boom angles aft and down, the deck curves, and the final shape is an irregular trapezoid. A template prevents expensive mistakes in the Sunbrella.

Framework options: stainless steel tubing (permanent, strong, heavy) or aluminum battens (lighter, removable, adequate). For a boom tent that is raised and lowered daily, removable aluminum battens sewn into batten pockets allow the tent to pack into a bag for storage in a seaway.

Sail Covers

A sail cover for a stowed mainsail is one of the simpler canvas projects: a tube of Sunbrella that fits over the furled sail on the boom, closes with a zipper or lacing at the aft end, and snaps or laces along the bottom to the boom. The measurement sequence: boom diameter, boom length from mast to end, the girth of the furled sail at its fattest point (typically near the clew end), and the taper of the sail toward the mast.

Cut the cover panels with an allowance for the boom girth plus the sail girth — the cover sits over both — plus 3 inches on all edges for hems and attachment. Taper the forward end to match the sail taper. Sew the panels into a tube, add a bottom lacing webbing strip with snap attachments at 12-inch intervals, and finish the aft end with a zipper (Delrin plastic tooth — see the dodger guide) or a lacing closure.

A headsail sun cover — for the rolled headsail on the furling foil — is a simpler tube construction. Measure the drum-to-halyard length of the furled sail, the girth at the fattest point, and taper both ends. The cover slips over the furled sail from the top and secures with lacing at the bottom. Match the Sunbrella color to the boat or the existing UV cover on the sail.

Cockpit Cushions

The foam specification for cockpit cushions is closed-cell foam. Open-cell foam — the standard upholstery foam used in household furniture — absorbs water and retains it. A cockpit cushion made with open-cell foam is permanently damp in any rain, slow to dry, and mildewing within weeks of tropical use. Closed-cell foam does not absorb water; it is structurally firmer, which is the tradeoff, but the firmness is acceptable for cockpit seating and the dry-out time after a rain shower is minutes rather than hours.

Cut the foam to the seat dimensions with a sharp serrated knife. The Sunbrella cover is a simple box construction: a top panel, a bottom panel (often a lighter backing fabric — Sunbrella is not required on the underside of a cushion), and a gusset that wraps the perimeter and gives the cushion its depth. Sew the gusset to the top panel first, then attach the bottom panel with a zipper on one long side for removal and drying. Use V-138 for the Sunbrella seams; Tenara for any seam that will be exposed to direct sun.

Corner reinforcement: the corners of the top-panel-to-gusset seam are the highest-stress area of a cushion cover. Box-stitch the corners with two passes of stitching and trim the seam allowance diagonally at each corner before turning the cover right-side-out — this prevents corner puckering and distributes the stress away from the seam termination.

A Simple Sail Storage Bag

A hanked sail bag — for storing a staysail, storm jib, or spinnaker that is not on the boat's inventory — is a straightforward project from canvas offcuts. The bag needs to be large enough to stuff the sail into without careful folding (stuffing is faster and causes less fatigue damage to laminate sails than systematic folding), close securely, and be clearly labeled. A simple drawstring or heavy zipper closure works; Velcro is fast but loses grip in salt air over time. Label the bag with the sail name, area, and cut using a permanent marker on a sewn-on canvas panel — labels that rely on adhesive fall off.

The Economics of DIY Canvas

A professional dodger fabrication quote in the UK typically runs £2,000 to £5,000 depending on complexity, window count, and the canvas shop's location. In North America, $3,000 to $7,000 USD is a reasonable expectation. The materials for a DIY dodger rebuild — Sunbrella, Makrolon or vinyl windows, Delrin zippers, Dyneema webbing, stainless hardware — run £300 to £600 in the UK at current prices. The tool cost — a Sailrite LSZ-1 — is approximately £800 to £1,000 new, and the machine is a long-term asset that earns back its cost over the projects it enables.

The DIY calculation is not just financial. It is also the difference between a boat owner who can do a field repair in a remote anchorage and one who must sail to a port with a canvas shop. An owner who has built their own lee cloths and sail covers understands the construction well enough to repair them. The skill compounds with each project. Most offshore sailors who commit to learning canvas work find that within two or three projects — a set of cockpit cushions, a new sail cover, a lee cloth replacement — they have recovered the cost of the sewing machine in labour saved and are considerably more capable sailors for it.

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Frequently Asked Questions

What fabric weight should be used for offshore lee cloths? Sunbrella 9.25oz (Solution Dye Acrylic) is the correct weight for offshore lee cloths. Lighter Sunbrella weights (6oz or 7.5oz) are suitable for cushion covers and shade awnings but do not have the tear resistance and load capacity needed for a lee cloth carrying a sleeping person's weight through a seaway. The 9.25oz weight is UV-stable, mildew-resistant, and stiff enough to hold its shape without going slack under body weight — a slack lee cloth that allows the sleeper to roll into the passage is a safety failure.

How should lee cloth D-rings be attached to the berth structure? D-rings for lee cloth lashing must be through-bolted — never screwed — to the berth structure, with a backing plate on the underside of the plywood minimum 50×80mm and at least 4mm aluminium or stainless steel. A screw-mounted D-ring will pull out under the lateral load of a person thrown against the lee cloth in a 30-degree heel, typically taking the plywood with it. The through-bolt should be 6mm stainless minimum with a large fender washer under the backing plate to spread the load. Two D-rings per berth side are the minimum; three is standard for berths over 1.8m long.

What webbing material is correct for lee cloth lashing attachment? Dyneema or Spectra webbing is the correct choice for the lashing loops and attachment points on offshore lee cloths, rather than polyester webbing. Dyneema webbing has eight to ten times the strength of polyester at equivalent weight and does not lose strength when wet — relevant in a boat environment where the interior accumulates condensation and spray on offshore passages. The lashing itself (the line securing the lee cloth to the D-ring) should be 6mm Dyneema braid, long enough to allow rapid release but without excess slack.

What canvas weight is correct for a boom tent, and how should it be constructed? A boom tent should be made from Sunbrella 10oz, heavier than the 9.25oz lee cloth weight, because the tent spans a large unsupported area (the entire cockpit) and must resist UV degradation over years of daily use in tropical anchorages. The tent should have adjustable side panels that can be rolled up for ventilation and weighted lower edges to prevent ballooning in anchorage wind. Seams should be lapped and double-stitched with Tenara PTFE thread for UV resistance at the stitch line. A properly made boom tent extends the usable shade area of a 40-footer by 15–20 square metres.

What sewing machine capability is required for making offshore canvas? The Sailrite LSZ-1 (approximately £800–1,000 in the UK market) is the standard recommendation for making offshore canvas — lee cloths, sail covers, boom tents, and sail repairs. It uses a walking foot and zigzag stitch, which is necessary for sewing through multiple layers of Sunbrella and webbing; a domestic sewing machine with a standard presser foot will skip stitches and break needles on canvas work. The LSZ-1 is specifically designed for marine canvas and is capable of handling 10oz Sunbrella with webbing sandwiched in the seam.

What foam type should be used in offshore berth cushions? Closed-cell foam is the only correct foam for offshore berth cushions — open-cell foam (the standard upholstery foam used in land furniture) absorbs water and never fully dries in a boat environment, becoming a permanent mildew culture within months. Closed-cell foam repels water at the surface and dries quickly after spray or condensation exposure. Specifications for offshore cushions are typically 100mm closed-cell foam for the sitting surface and 75mm for backrests. Covering closed-cell foam in Sunbrella 6oz rather than a stretch fabric prevents the cover from absorbing saltwater that the foam successfully repels.