Waterproof Chart Cases: Transparency, Legibility and the Backup Nobody Can Afford to Lose

Why paper charts persist, and what that demands of the case

A waterproof chart case exists because paper charts still exist, and paper charts still exist for reasons that are regulatory rather than nostalgic. International navigation rules administered through the International Maritime Organization require vessels to carry adequate and up-to-date charts for the intended voyage, and where electronic chart systems are used as the primary means of navigation, a suitable backup arrangement is required. In commercial practice that backup is frequently paper. On private vessels there is no such formality, but the reasoning holds: a chart plotter depends on a power system, a GPS constellation and a display, and all three can fail independently and simultaneously in a bad moment. Everything in marine navigation chart storage follows from that one requirement.

That status imposes a specific standard on the case, and it is a higher standard than most buyers apply. A case holding a spare snack can be slightly hazy and nobody cares. A case holding the navigation backup must not degrade the information through it in any way, because the entire value of the object is the information. The test is simple and it is worth stating on the product: if a crew member has to lift the chart out of the case to read a sounding or a buoy symbol in low light, the case has failed at its only job, no matter how well it keeps water out.

The consequence is that the product should be specified the way an optical component is specified, with numbers for light transmission and haze and with an expected service life before those numbers degrade. That is not how the category is usually sold, which is precisely why the products in it vary so wildly in real quality while looking identical on a shelf.

Chart sizes: A1 and A0, and why folding is not an option

Charts are large, and the size is not negotiable because it is set by the chart publisher rather than by the bag designer. Formats vary by publisher, with sheets commonly around 700 by 1000 millimetres and larger, and with folded sizes and sheet sizes differing substantially between hydrographic offices; the UK Hydrographic Office publishes its own sheet and folded dimensions, and any case intended for a specific publisher should be dimensioned against that publisher’s actual sheet rather than against a nominal A-size.

For planning purposes the ISO A series gives a useful frame: A1 is 594 by 841 millimetres and A0 is 841 by 1189 millimetres. A case sized to accept A1 flat will take most folded chart formats and a good number of full sheets. A case sized for A0 will take almost anything and will not fit on most chart tables, which is the practical constraint that decides the range. Any case that is smaller than the chart forces either folding or cropping, and both are unacceptable in navigation use.

Folding a chart is not an acceptable workaround for a case that is too small. A fold line through a chart obscures whatever runs along it, and because charts are dense with soundings and symbols exactly where you might choose to fold, the loss is real. Repeated folding along the same line eventually wears through the paper, and a chart that has been folded and unfolded a few hundred times develops a crease that lifts and catches a pencil point when plotting. A chart that has to be folded to fit its case is a chart that is being degraded every time it is stowed.

• Dimension the case against the actual sheet size of the charts your customers use, not against a nominal A-size.
• A1 flat is the practical maximum on most chart tables; A0 flat will not fit on most boats.
• Never require the chart to be folded to fit; fold lines destroy information and wear through paper.
• Allow clearance around the sheet so the case can be welded and sealed without compressing the chart.
• State internal usable dimensions, not external, because weld width and seam allowance eat into both.

One size decision that is easy to miss: the case should be slightly larger than the chart, not exactly its size. A case cut to the exact sheet dimensions will not seal, because the weld line and the closure need material outside the paper, and a chart forced into an exact-size case will buckle at the edges. Ten to twenty millimetres of margin on each dimension is the usual allowance, and it should be stated as internal usable size so the buyer knows what actually fits.

Transparency is the specification itself: haze, yellowing and legibility

Transparency in this product has two distinct components that are routinely confused, and they are measured differently. Light transmission is how much light passes through. Haze is how much of that light is scattered, which is what makes a transparent material look cloudy even when it passes most of the light. A film can transmit 90 per cent of incident light and still be unusable for reading fine print if its haze is high, because the scattering blurs the detail rather than dimming it. Both matter and only one is usually quoted.

The standard test method for both is published by ASTM International as the widely used haze and luminous transmittance method for transparent plastics, and it is the right method to specify on a technical pack because it produces two numbers rather than one. A reasonable specification for a chart case is luminous transmittance above about 90 per cent and haze below about 3 per cent when new, with a stated maximum haze after defined UV and salt exposure. Those numbers are achievable with a good TPU film and are not achievable with a cheap PVC, which is the single clearest quality divide in this category.

Yellowing is the failure that ends the product’s life and it is worth understanding mechanistically rather than treating it as inevitable. Aromatic TPU yellows under ultraviolet exposure because the aromatic structure absorbs UV and forms chromophores; aliphatic TPU does not yellow appreciably and costs substantially more. PVC yellows and additionally loses plasticiser, which makes it stiff, then brittle, then cracked. In practice the yellowing clock on a case kept on an exposed chart table in the tropics is measured in single-digit months for an aromatic film and in years for an aliphatic one. That is the entire argument for specifying aliphatic TPU and it is the question a buyer should ask first.

A cost option worth considering is a hybrid: a coated fabric body with a bonded transparent window, rather than a fully transparent sleeve. This works well for cases where the chart is slid in and read through one face only, and it lets the brand use an expensive aliphatic film only where it matters. It also improves durability, because the fabric takes the abrasion and the film only has to be transparent. The trade-off is that only one face is readable, which matters if the chart is used double-sided or if the case gets flipped.

Writing on the case: pencil erasability and coating compatibility

Navigation is a pencil discipline. Positions, course lines, tidal vectors and dead-reckoning marks are drawn, checked and rubbed out dozens of times in a passage, and the case has to accept that without being damaged. That means a pencil has to write on the outer surface of the film, the mark has to stay put while the boat moves and the case is handled, and it has to wipe off cleanly with a soft eraser or a thumb, leaving no ghost that could later be misread as a real line. A ghosted position line is a genuine safety hazard, not a cosmetic issue.

This requirement drives the surface finish, and it is where a lot of otherwise good products fail. A very smooth, glossy film takes pencil poorly; the graphite sits on the surface and smears. A slightly matte or micro-textured surface takes pencil well. Conversely, too aggressive a texture holds graphite in its valleys and resists erasing. The working window is narrow and it is a surface-energy problem: the film needs enough tooth to accept graphite and not so much that it retains it. Specifying a target surface finish, and testing with the actual pencils crews use, is the only reliable way to land in that window.

Pencil hardness matters and is worth stating. A soft pencil, around 2B, marks more readily on a film and erases more completely, and it is what most navigators prefer for chart work anyway. A hard pencil, around 2H, gives a finer line but is more likely to score the film surface permanently, and a scored film scatters light and becomes permanently hazy along the line. Recommending a soft pencil and warning against hard ones is a small piece of instruction that materially extends the life of the product.

• Specify a film surface with enough tooth to accept graphite but not enough to retain it.
• Test with real pencils under real conditions: a 2B should mark and erase cleanly, a 2H should be discouraged.
• Require erasing without ghosting; a residual line can be misread as a plotted position.
• Check that erasing does not polish the film into a locally glossy patch that catches glare.
• Confirm that salt water on the surface does not make pencil marks permanent.

There is a compatibility question that catches people out: the same coating that makes a film resistant to plasticiser migration and easy to clean can also make it resist pencil. Anti-graffiti and easy-clean surface treatments are designed to reject marking, and a film with such a treatment will take pencil badly. If the supplier has applied a surface treatment, it needs to be tested for pencil acceptance rather than assumed compatible. This is the kind of detail that never appears on a datasheet and always appears in field use.

Reading through the case: parallax, glare and the lamination question

Even a perfectly transparent film degrades a chart by two mechanisms that have nothing to do with the material. Parallax is the apparent shift of the chart detail when it is viewed at an angle through a film with thickness; a 0.5 millimetre film over a chart viewed from a steep angle shifts fine detail by a small but visible amount, and when plotting a position to the width of a pencil line that shift can matter. Glare is the reflection off the front surface, which on a bright day in a cockpit can wash out the chart entirely.

Both are reduced by keeping the film in contact with the chart rather than letting it float. A case that is much larger than the chart allows the film to lift and bow, which introduces an air gap that makes parallax and glare dramatically worse. That is an argument for a closer fit than the margin discussion earlier might suggest, and the resolution is a case with a modest margin plus a closure that pulls the film flat, rather than a generously oversized sleeve.

Anti-glare and anti-reflective surface treatments exist and are worth evaluating, because they address the single most common complaint about reading charts through a case. The trade-off is that they usually reduce surface smoothness and can affect pencil acceptance, which is the conflict described in the previous section. A matte finish that kills glare and takes pencil well is the ideal combination and it is achievable, but it has to be specified and tested rather than assumed. Where it cannot be achieved, glare is the priority in a cockpit and pencil acceptance is the priority at a chart table, which is again an argument for two formats.

• Keep the film in contact with the chart; an air gap multiplies parallax and glare.
• Use a modest margin and a closure that pulls the film flat rather than a loose oversized sleeve.
• Evaluate anti-glare finishes, and test them for pencil acceptance before committing.
• Prefer a matte or semi-matte surface in cockpit use and a smoother surface at a chart table.
• Check legibility in low light at an angle, not straight on in a showroom; that is the real reading condition.

Salt spray, UV and the yellowing clock on deck

A chart case lives in the harshest environment any soft product faces: full sun, salt spray, constant flexing, and temperatures that range from a cold night passage to a tropical afternoon on an exposed table. The two mechanisms that end its life are ultraviolet degradation and salt crystallisation, and they interact. UV attacks the polymer, salt crystals form in the closure and abrade the sealing surfaces, and the combination of a degraded film and an abraded closure is what finally lets water in.

Salt deserves particular attention because it is a mechanism rather than a circumstance. Salt solution wicks into any gap, water evaporates, crystals grow, and the crystals are hard enough to abrade a film surface and stiff enough to prevent a closure from seating. A chart case that is rinsed with fresh water after each passage lasts several times longer than one that is not, and the difference is larger than any material upgrade. That instruction should be printed on the product, because very few owners do it unprompted.

UV exposure is cumulative and irreversible, and it is the reason the case has a service life at all. A film that starts at 2 per cent haze will drift upwards with exposure, and the point at which it becomes unusable is not a sudden failure but a gradual loss of confidence in what the crew can read. That argues for stating an expected service life and for designing the case so the film is replaceable or the case is cheap enough to be replaced, rather than pretending the product is permanent.

• Rinse with fresh water after every passage; it does more for service life than any material upgrade.
• Store out of direct sun when not in use, even a shaded cockpit locker doubles the life of the film.
• Choose aliphatic TPU where the budget allows; it is the difference between seasons and years.
• Accept that the film is a consumable and design the product so replacement is cheap and obvious.
• Avoid dark interiors behind clear film; they heat the chart and accelerate condensation inside the case.

Condensation inside a sealed case is a specific and frequently reported problem. A case sealed in cool evening air and then brought into a warm cabin will condense on the inside of the film, and the condensation forms between the film and the chart, exactly where it destroys legibility. A small vent, a breathable patch, or simply instructing crews to open the case when conditions change all mitigate it. Our note on condensation in sealed cases covers the mechanism in more detail, and the material side of salt and sun is set out in our review of UV resistance in outdoor materials and in our note on chemical and salt resistance.

Fixing the case: chart tables, instrument surrounds and one-handed access

A chart case that is not fixed down is a chart case that slides off the table on the first tack, and this is the most under-designed aspect of the category. Chart tables are typically smooth, often angled, and frequently wet. A flat welded sleeve on a smooth surface has almost no friction and will move. The product therefore needs a fixing system, and the right one depends on where the case lives.

On a chart table the best solution is a case with fixing points at the corners and either a set of suction cups, a non-slip backing, or eyelets for screws or shock cord. Non-slip backing is the cheapest and works well on a dry table; suction cups work on a smooth table but fail on a textured one and lose grip as they age; eyelets with shock cord are the most secure and are what most serious crews end up fitting. Offering more than one option, or a case with both a non-slip face and corner eyelets, covers the range of boats without requiring the buyer to guess.

In a cockpit the requirement is different: the case has to be reachable and readable by the helmsman, which usually means fixed near instruments, and it has to survive being rained on and sprayed. A lanyard or a clip lets it be hung within reach, and a stiffened back panel keeps it flat enough to read when hung. There is a specific interference issue worth flagging: a case fixed over or immediately beside an instrument display or a radar repeater can obscure it, so the fixing points should allow the case to be positioned clear of the instruments rather than only in one predetermined spot.

• Provide corner fixing points; a flat sleeve on a smooth angled table will slide on the first tack.
• Offer a non-slip backing plus eyelets, so the case works on textured and smooth surfaces.
• Use a stiffened back panel if the case will be hung, or it will curl and become unreadable.
• Keep the fixing system clear of instrument displays and radar repeaters.
• Make the closure operable one-handed, because the other hand is holding something more important.

The closure itself needs a note because it is the most common failure point in service. A zip on a chart case is a zip exposed to salt, and salt crystals in a zip are the standard failure described in our review of waterproof bags for sailing. A roll-top with a clip, or a hook-and-loop flap with a stiffened lip, both survive salt better than a zip, and both can be worked one-handed. Hardware families and their behaviour in this environment are compared in our guide to hardware selection.

What else goes in the case: pilot books, dividers and parallel rules

In practice a chart case is rarely carrying only a chart. A working navigation kit includes dividers, a parallel rule or a plotter, a soft pencil and eraser, a notepad, and frequently a pilot book or almanac for the area. Some of those are hard and pointed, and dividers in particular are a genuine puncture risk to a film sleeve. A case designed only for paper will be destroyed the first time someone puts dividers in it.

The design response is either separation or exclusion. Separation means a second compartment or a sleeve for the instruments, with a divider between it and the chart. Exclusion means designing the case for the chart alone and saying so, which is defensible for a case intended to live flat on a chart table with the tools kept separately. What is not defensible is a case that looks like it should carry the kit and then fails when it does, because the customer’s expectation is set by the photograph.

Puncture resistance is worth specifying explicitly for any case that might carry tools. Film thickness helps, but the more useful lever is a fabric-reinforced laminate or a fabric body with a film window, because a woven reinforcement layer resists puncture far better than an unsupported film of the same thickness. Our guide to film thickness by application sets out where the thresholds sit, and the material comparison is covered in our note on TPU versus PVC.

• Decide whether instruments go in the case, and design or label accordingly.
• If tools travel with the chart, separate them with a reinforced divider or a second compartment.
• Use a fabric-reinforced laminate or a fabric body with a film window where puncture is a risk.
• Round the internal corners; a sharp internal corner is where a divider point finds purchase.
• Keep the pencil and eraser in an external pocket so they never press into the chart.

Folded, rolled or flat: the three storage systems compared

Stowage is where chart cases are quietly won or lost, because a chart that cannot be stowed conveniently will not be kept in its case, and a chart out of its case is a chart getting wet. There are three systems and they suit different boats and different passages.

Rolling is underrated and worth advocating. Paper tolerates a gentle roll extremely well, a rolled chart takes a fraction of the space of a flat one, and a roll-top cylindrical case is easy to weld, easy to seal and easy to stow in a locker or under a berth. The one caution is the roll diameter: rolling a chart tightly around a 40 millimetre core puts real strain on the paper and on any printed fold lines, while a 100 to 150 millimetre diameter roll is gentle enough to be harmless over hundreds of cycles.

Folding should be restricted to charts that are published folded, and only along the fold lines the publisher printed. Those lines are chosen to fall in relatively empty parts of the chart, which is exactly why the publisher put them there. Any other fold is a fold through data. A case intended for folded carriage should therefore be dimensioned to the folded size, and should not require an additional fold of its own.

• Roll rather than fold wherever the chart is not already published folded, at 100 to 150 millimetre diameter.
• Fold only along the publisher’s own fold lines; any other fold runs through data.
• Store flat where space allows, in a semi-rigid case that prevents bending.
• Never leave a chart loose in a soft sleeve; it will be creased by handling within a passage.
• Label the outside of the case so the right chart can be found without opening every one.

Materials and seams for a transparent marine product

The material decision has largely been made by the transparency requirement: aliphatic TPU film is the correct choice for any case that must be read through, and its thickness should follow the size, because a large unsupported panel in a thin film will stretch and crease under its own weight. For an A1 case, a film in the region of 0.3 to 0.5 millimetres is typical, with heavier films for larger formats or where tools are carried. Thicker films transmit slightly less and are slightly harder to weld consistently, so thickness should be chosen to the minimum that holds its shape.

The seam strategy is straightforward because the product is small and simple: weld everything. High-frequency welding suits TPU well and produces a clean, strong, genuinely waterproof joint. Ultrasonic welding is faster and is viable on thinner films, but it is less forgiving on thicker material and can produce a brittle joint if the parameters are wrong. For a product whose failure mode is water on a navigation backup, high-frequency welding with visual inspection of every joint is the defensible specification.

The closure is the one place where the seam strategy and the salt environment interact badly. A welded body with a hook-and-loop closure is the most robust combination in salt, because hook-and-loop has no mechanism to jam with crystals in the way a zip does, although it does lose grip when contaminated with salt and grit and needs rinsing. A roll-top with a clip is the next best. A zip is the worst in this environment and should be avoided unless it is a genuinely sealed marine zip with a substantial pull, and even then it needs a rinsing instruction.

Transparent products generally, and the trade-offs between clarity, thickness and durability, are covered in more depth in our review of transparent TPU construction. The film thickness thresholds by application are set out in our film thickness guide, and the broader marine material environment is described in our note on marine-grade specification.

Testing a chart case before production

The tests that predict a season aboard are quick, cheap, and mostly about optics rather than water. Run them on production samples, because weld parameters and film batch are exactly what drift between a prototype and a run.

• Legibility test: place a chart with fine soundings in the case and read it at arm’s length in low light and at an angle; if any detail is lost, the film or the fit is wrong.
• Haze test: measure haze and luminous transmittance on delivery and after defined UV exposure, and set an acceptance limit on the aged figure rather than only the new one.
• Pencil test: draw twenty lines with a 2B, erase them, and inspect for ghosting under a lamp at a shallow angle.
• Score test: draw with a 2H and check whether the film is permanently scored along the line.
• Salt test: soak the closure in salt water, let it dry three times, then check that it still seats and opens.
• Spray test: hose the closed case for ten minutes, then open it and check for water at the seams and the closure.
• UV test: expose a sample to defined UV and record haze and colour shift at intervals, so a service life can be stated.
• Slide test: put the loaded case on an angled wet table and tilt it; it should not slide when fixed as instructed.
• Puncture test: press divider points against the film at a stated load and check for penetration.

The pencil test and the haze test are the two to run on every lot, because they detect the two substitutions that matter most: a film supplier change alters haze and pencil acceptance, and a surface treatment change alters pencil acceptance alone. Neither is visible in a visual inspection. Both take minutes. The inspection structure for catching them per shipment is set out in our note on pre-shipment inspection, and the sampling logic in our guide to AQL sampling.

Care, cleaning and when to retire a case

A chart case is a consumable with a definable end of life, and saying so is better for a brand than pretending otherwise. The end of life is reached when the crew cannot read the chart through it with confidence, and that is a judgement the crew makes long before the case leaks. Three care habits extend the life materially and cost nothing: rinse with fresh water after salt exposure, store out of direct sun when not in use, and use a soft pencil with a soft eraser.

Cleaning needs care because the two things that clean a film well also damage it. Solvents, including alcohol and most degreasers, attack TPU surfaces and accelerate both haze and cracking; a film wiped with solvent will look clean and will fail sooner. Abrasive cloths and paper towels scratch the surface, and a scratched film scatters light exactly where it matters. The correct cleaning method is fresh water, a drop of mild detergent if needed, and a soft cloth or a bare hand, followed by air drying rather than wiping dry.

Retirement criteria worth publishing are simple: replace the case when haze is visible as cloudiness when looking through it at a printed page, when pencil marks no longer erase cleanly, when the film has stiffened or cracked at the folds, or when the closure no longer seats after rinsing. Any of those means the case is degrading the information it exists to protect, and at that point it is worse than no case at all, because the crew believes the chart is protected and readable when it is neither.

Building a chart case range: sizes, branding and ordering

The range structure is governed by chart format rather than by capacity, which makes it unusually simple. Two sizes cover most of the market: one accepting A1 flat, and one accepting the folded format of the charts the brand’s customers actually use, which is frequently close to A2 or a publisher-specific dimension. A third roll-top cylindrical format covers passage makers and small boats. Three formats, one film specification and one closure across all of them, which is what keeps the tooling and the material buy efficient.

Sizing to a real chart rather than to a nominal A-size is worth the effort, and it is a genuine differentiator because most of the market sells nominal sizes that do not quite fit the charts people own. Asking customers which hydrographic office they use, and dimensioning to that publisher’s sheet, produces a product that fits and generates the word of mouth that this category runs on. Our note on size and dimension customisation covers how to specify internal usable dimensions so the fit is what the buyer expects.

Branding on a transparent product is constrained by the fact that most of the surface has to stay clear. The practical locations are the border area outside the chart, the stiffened back panel, and the closure flap, and a small woven label or a print in one corner is usually the right answer. A large print across the reading area is self-defeating on a product bought for legibility. Where a brand wants visibility, the back panel of a fabric-backed design is the best canvas, and the durability trade-offs by method are covered in our review of printing and embroidery options.

On cost, the film is the dominant line and it is where the specification decision is made: aliphatic TPU costs materially more than aromatic and dramatically more than PVC, and on a large flat panel that difference is the product. That is the correct place to spend, because the entire function of the product is optical and the failure is optical. Saving on the film to spend on hardware produces a case that seals beautifully and cannot be read through, which is the most common failure in the category. The component-level picture is set out in our bill of materials breakdown.

On ordering and timing, the minimum order quantity is 500 pieces per style, so a three-format range is 1,500 units. Sampling takes 6–10 working days per round and bulk production runs 35–50 days, quoted FOB Xiamen; because film selection and pencil acceptance usually need one round of adjustment, budget two sampling rounds for a first chart programme. Chandlery, charter fleet and training-school channels are the natural routes for this product, and the commercial framing for marine buyers is set out in our notes on marine industry programmes and hospitality and charter programmes. If you want this specification turned into a costed range, review our own process from first enquiry through sampling into bulk production and send your target chart formats, intended film grade and preferred closure. Minimum order quantity is 500 pieces per style, samples take 6–10 working days, bulk production runs 35–50 days, and quotations are issued FOB Xiamen.

Frequently Asked Questions

Q1. Why do boats still carry paper charts?

Regulations require adequate charts, and where electronic systems are primary a backup is required. Power, signal and display failures are exactly why the backup matters.

Q2. What size chart case do I need?

Dimension it to the actual sheet of the charts you use. A1 flat suits most chart tables; larger formats will not fit on most boats.

Q3. Should I fold a chart to fit a case?

No. Fold lines run through soundings and symbols, and repeated folding wears through the paper. Only fold along the publisher’s own lines.

Q4. Is rolling a chart safe?

Yes, and it is better than folding. Roll at 100 to 150 millimetre diameter, not tightly around a small core.

Q5. What film should a chart case use?

Aliphatic TPU. It has the transmittance and low haze you need, and it does not yellow the way aromatic TPU does.

Q6. What is haze and why does it matter?

Haze is scattered light. It blurs detail even when plenty of light passes through, so a case can look clear and still be unreadable.

Q7. What haze figure should I specify?

Below about 3 per cent when new, with a stated maximum after defined UV exposure. Transmittance should be above about 90 per cent.

Q8. Will the case yellow over time?

An aromatic film will yellow within a season of strong tropical exposure. An aliphatic film will not yellow appreciably for years.

Q9. Can I write on the case with a pencil?

Yes, and it should erase cleanly. Use a soft pencil around 2B and avoid hard pencils, which score the film permanently.

Q10. Why does my chart case fog up inside?

Condensation forms when a case sealed in cool air is brought into warm air. Vent it, or open it when conditions change.

Q11. How do I stop the case sliding off the chart table?

Fix it. Non-slip backing, corner eyelets with shock cord, or suction cups, depending on the table surface.

Q12. Which closure survives salt best?

A hook-and-loop flap with a stiffened lip, or a roll-top with a clip. A zip is the worst choice because salt crystals jam it.

Q13. Should I put dividers in the chart case?

Only if the case is reinforced for it. Divider points puncture unsupported film; use a reinforced laminate or a separate compartment.

Q14. How do I clean a chart case?

Fresh water, a drop of mild detergent if needed, and a soft cloth or a bare hand. Solvents and abrasive cloths damage the film.

Q15. How long does a chart case last?

It depends on film grade and exposure. An aliphatic case rinsed and stored out of sun lasts years; an aromatic one in the tropics may last a season.

Q16. When should I replace a chart case?

When you can see cloudiness through it, when pencil no longer erases cleanly, or when the film stiffens or cracks at the folds.

Q17. What is the minimum order quantity for a custom chart case?

500 pieces per style. A three-format range is 1,500 units, which is a realistic opening buy for most marine brands.

People Also Ask

Do boats still need paper charts?

Yes as a backup. Regulations require adequate charts, and electronic systems fail on power, signal or display.

What size is a nautical chart?

It varies by publisher, with sheets commonly around 700 by 1000 millimetres. Dimension a case to the actual sheet, not a nominal A-size.

Can you fold a nautical chart?

Only along the publisher’s own fold lines. Any other fold runs through data and wears through the paper.

Why do chart cases go cloudy?

Haze from UV degradation and surface scratching. Aromatic TPU yellows; PVC clouds and stiffens as plasticiser migrates.

Can you write on a waterproof chart case?

Yes, with a soft pencil around 2B. Hard pencils score the film and leave permanent marks.

How do you keep a chart dry on a boat?

A welded transparent case with a salt-tolerant closure, fixed to the table, rinsed with fresh water after each passage.