Sailing Dry Bags Compared: Zhik, Gill and OverBoard

This is an objective, spec-led comparison, not a hands-on test. Figures are the makers' published specs and independent bench numbers where cited, not our own measurements. On genuine submersion engineering OverBoard leads, and we say so plainly.

A dry bag is a coated-fabric pressure vessel with a labyrinth seal, and the whole category divides on one honest engineering line: welded-tarpaulin holdalls that hold out spray and green water, versus film-over-scrim roll-tops rated to survive going under. Everything a professional weighs — fabric chemistry, weld versus tape, IP rating, fold-seal mechanics, hardware — flows from which side of that line the bag sits on. This compares three makers who solve it differently, and sets out where a Melges 40 programme should actually spend. It pairs with our note on race crew backpacks and the guide to what to wear sailing for what goes inside.

At a glance

The engineering that actually separates them

Coated fabric: TPU film vs PVC tarpaulin

The base fabric decides weight, cold behaviour and how many fold cycles the bag survives — and the two dominant chemistries fail on opposite terms.

PVC tarpaulin is a PVC-coated polyester scrim; Gill's Voyager range is stated at 85% polyvinyl chloride, 15% polyester, in roughly 500-denier weight. Denier is grams per 9,000m of yarn, so 500D is the sensible middle — heavier and far stronger than the 210–300D used on packable stuff-sacks, lighter than the 840–1000D of expedition tubes. PVC's virtues are real: it takes high-frequency welds beautifully, resists abrasion and puncture, and costs little per square metre, which is exactly why it dominates large, cheap holdalls. Its weakness is equally real and directly relevant to a roll-top — PVC plasticiser migrates with age, UV and cold, so the sheet stiffens and eventually micro-cracks, and it cracks first along the fold lines that a roll-top flexes on every close. Left folded in the sun on an Australian summer campaign, that is the failure mode.

TPU — thermoplastic polyurethane film laminated to a nylon scrim — is what the premium end uses, and Zhik's 35L Waterproof Backpack is built from welded TPU for exactly this reason. Per gram it carries more burst strength than PVC, it stays supple well below 0°C where PVC goes brittle, it welds cleaner with less flash, and it resists hydrolysis, UV and fuel/oil contact markedly better. It costs more, and that cost is the whole reason the class splits. OverBoard sits in between by design, combining TPU, nylon ripstop and PVC across its range so each panel gets the film best suited to its job. For a Grand Prix bag that is rolled hundreds of times a season, dropped on non-slip and stored hot, TPU's fatigue and cold-crack margin is the technically correct call; PVC remains the right economy for a big soft holdall where the fold count is low.

Seams: high-frequency welding vs seam-taping vs stitching

A dry bag is only as waterproof as its seams, and there are three constructions in this group — they are not equivalent.

High-frequency (RF) welding fuses the two coated faces into a single homogeneous, hole-free join using radio-frequency dielectric heating. Gill states its Voyager seams are "stitch-free" and welded; OverBoard welds throughout and adds its Fold Seal System at the closure. This is the only construction that is inherently waterproof at the join, because there is no needle penetration to seal — the seam becomes parent material. It is also why these bags carry burst pressure: the weld is typically as strong as the panel.

Seam-taping over stitching is the tier below, and Zhik's 25L roll-top is explicit about it — "seam taped construction to minimise stitching holes and leakage." Here the panels are sewn, then a heat-activated tape is laid over the needle line to bridge the perforations. Done well it is genuinely water-resistant and cheaper to produce, but every stitch is still a potential path, tape adhesion degrades with flex and age, and it will not hold static immersion head the way a weld does. This is precisely the construction difference that places Zhik's 25L in the splash/spray tier and its welded-TPU 35L in the submersible tier — same brand, two deliberately different builds. Plain stitched seams with no tape are spray-only and out of scope for a genuine dry bag.

Ingress ratings: what IP66 and IP68 actually certify

Professionals see "waterproof" and "IP" on the label and conflate them; the IEC 60529 codes are precise and the two second-digit regimes are not interchangeable.

• IP66 is a jet test: a 12.5mm nozzle delivering ~100 L/min from 3m for at least three minutes. It certifies heavy spray and boarding green water — a good proxy for a deck bag — but it makes no submersion claim.
• IP67 adds temporary immersion to 1m for 30 minutes.
• IP68 is continuous immersion to a depth and duration the maker defines; OverBoard rates its phone and tablet cases to IP68. There is no universal IP68 depth — always read the maker's stated figure.

The trap: a jet applies dynamic pressure at a moving point, immersion applies static head over the whole surface, so passing one does not imply the other. OverBoard's Pro Sports bags are dual-rated — IP66 main compartment, IP65 zip pocket — an honest acknowledgement that the zip is the weakest ingress path and should never carry your phone underwater. The practical rule for this comparison: if a bag does not publish a submersion figure, treat it as spray-class regardless of how "waterproof" the marketing reads. Gill's Voyager and Sail Racing's Bowman make no submersion claim; OverBoard and Zhik's 35L do.

Fold-seal mechanics and trapped air

Every roll-top is a labyrinth seal, and its performance is governed by fold count, closure-strip stiffness and internal air — three things partly in the user's hands.

Each fold presses the coated fabric against itself and lengthens the tortuous path water must travel while tightening the contact pressure along it. Below three folds there is not enough sealed length to resist static head, which is why every maker in this group specifies a minimum of three rolls before clipping the side-release buckles. A stiff, wide closure strip (the flat rigid batten sewn into the mouth) rolls cleanly and holds the labyrinth compressed; a floppy strip creases, opens micro-channels and leaks if you rush it.

Trapped air is the second-order variable a lot of crews get wrong. A ballooned bag holds internal pressure that pushes outward against the fold, and if it goes over the side that trapped air gives it buoyancy that floats the sealed mouth to the surface — exactly where wave action and dynamic pressure attack the seal. Purge the air before the final rolls; some designs fit a one-way valve so you can pack, seal, then squash the air out for both compression and seal integrity. Clip the buckle across the roll, opposing the fold direction, so load draws the fold tighter instead of peeling it. On a wet 40 with cold hands, the design that tolerates a hurried three-fold-and-clip is worth more than a theoretically better seal that needs care you will not give it at the leeward mark.

Format, hardware and carry

Format matters as much as capacity on a crowded foredeck, and the hardware is where saltwater durability is won or lost.

Gill's Voyager splits into flat-based cylinder/dry bags (5–50L) and wide-mouth duffels (10–90L); the cylinders add a mesh-reinforced clear window so you can read the contents without unrolling, six external D-rings for lashing, a non-slip flat base for cockpit stability, and — on the duffels — a Velcro-plus-side-release closure. This breadth of format and lash points is the range's genuine strength. OverBoard covers dry tubes, Pro Sports backpacks and rated hard cases within its submersion focus, with a proper padded harness and ergonomic back panel on the pack. Zhik runs two carry stories: the 25L roll-top is a light (0.2kg empty), touch-screen phone-pocketed, D-ringed personal bag, while the 35L is a submersible backpack with padded straps, ergonomic back panel and an internal elasticated laptop sleeve behind a 400D nylon mesh front drain pocket — sized for what a crew hauls down the dock hands-free. Sail Racing's Bowman is a wide-mouth tarpaulin holdall/backpack with a padded harness, back protection pad and a neoprene laptop sleeve, built to carry as one piece with the rest of a matched kit. Across all four the hardware that lasts is corrosion-resistant acetal/Delrin buckles and welded-in D-rings; metal spring hardware is the first thing to seize in salt and is worth avoiding.

Value, honestly

Value here is really cost-per-litre against the ingress rating you are actually buying. Gill is the clear price-per-litre leader — welded PVC tarpaulin gives a genuinely capable spray-to-immersible bag at a fraction of a premium TPU roll-top, and its independent submersion numbers (below) are strong for the money. Zhik is sensible mid-market with a real submersible option in the 35L. OverBoard is a considered spend, but you are paying for a certified rating and independently verified submersion performance, which for the valuables bag is money well spent. Sail Racing sits at the premium end: the spend buys tarpaulin build quality, finish and a bag that carries as a coherent system — not a submersion rating it does not claim. The right question is never "which is cheapest" but "which ingress class does this content need, and am I paying for a rating I will use."

What the independent bench numbers say

Because we do not run our own submersion tests, the useful external data point is Yachting World's roll-top comparison, which ran a controlled dunk. Two figures are worth carrying into a buying decision. The Gill Cylinder 50L was the best-performing roll-top on test with 100ml ingress and an 8/10 waterproofing score — genuinely good for a welded-PVC bag at its price. The OverBoard 40L Dry Tube let in 500ml, a reminder that a simple tube is a spray-and-brief-dunk bag, not a submarine — while the OverBoard 30L Pro Sports backpack took zero ingress and was a joint test winner. The lesson maps straight onto the class line above: within one brand, the rated, better-sealed pack decisively out-performs the basic tube, and construction — not badge — predicts the result. Treat these as the makers'/testers' figures, not ours.

Our pick

Be straight about it: no single bag is right, because the category is genuinely two problems. Our pick is a two-bag system, and each half has a clear technical winner.

For the valuables bag — phone, wallet, camera, laptop, anything unrecoverable — buy on the rating, and here OverBoard leads on merit: a dual-rated IP66 body with IP68 cases, HF-welded Fold Seal construction, and independent zero-ingress submersion results on the Pro Sports pack. If you want that submersible protection in a hands-free crew backpack with a laptop sleeve, Zhik's welded-TPU 35L is the strongest single-bag answer and the better cold-and-UV performer over seasons. Gill's Voyager cylinder is the value play that punches above its price on the bench.

For the kit holdall — thermals, towel, soft gear that only needs to beat spray and green water — build quality and how it carries matter more than a submersion rating those contents will never need, and Sail Racing is the confident choice: welded polyester tarpaulin, a properly padded harness and back pad, and a bag that stows and carries as one coherent piece with the rest of a high-end setup. It earns that on finish and system design, not on a rating it does not claim.

Our pick: run two bags. A Sail Racing tarpaulin holdall for kit that carries as a system, plus a genuinely submersible roll-top for valuables — OverBoard for the certified rating (or Zhik's TPU 35L if you want it as a backpack). Reach for Gill's Voyager when value and format breadth lead. On the water, the seal is only as good as your three folds and a purged bag — the best construction still leaks if you clip it once and hope.

Who each is best for

• Sail Racing — crews wanting a premium, coordinated kit holdall with the build and carry to match. Spray/splash class; our pick for the big kit bag that carries as a system.
• OverBoard — anyone needing a certified submersible bag for phone, camera or valuables. IP66 body, IP68 cases, verified zero-ingress on the Pro Sports pack — the pick for the valuables half.
• Zhik — the welded-TPU 35L backpack for a submersible, hands-free crew bag with a laptop sleeve; the 25L (seam-taped nylon) for a light splash-class personal bag.
• Gill — sailors after value and format breadth across welded-PVC cylinders and duffels, with strong independent submersion numbers for the price.

The takeaway

Dry bags divide on construction, not branding: welded-tarpaulin holdalls that beat spray and green water versus film-over-scrim roll-tops rated and tested to survive submersion. Our pick stays a two-bag system — a Sail Racing tarpaulin holdall for kit that carries as one piece, an OverBoard (or Zhik welded-TPU) roll-top for the valuables that need a certified IP figure, with Gill's welded-PVC Voyager the value alternative that holds up on the bench. Match the ingress class to the contents, purge and roll three times, and the seal will hold. See race crew backpacks for how you carry it all, and what to wear sailing for what goes inside.