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Sea Kayaking: What Size Dry Bag Do You Need?

Start from the hatch aperture, not from the bag

Every sea kayak packing plan begins with a tape measure across the hatch. A typical expedition kayak carries a large oval hatch aft, a smaller oval or round hatch forward, and a small round day hatch behind the cockpit. The oval hatch on most production boats gives a clear opening near 44 x 24 cm, and the round hatches are commonly 20 cm or 15 cm in diameter. No bag wider than the minor axis of that opening is going in, however many litres the compartment holds.

That single measurement is why expedition paddlers use several medium bags rather than one enormous one. A single 60L bag will not pass a 24 cm minor axis; two 20L bags and a 10L will, and they also let you distribute weight along the length of the compartment. Measure the opening on your own boat before you buy, because aftermarket hatch rims vary by 10 to 15 mm between brands and that margin decides whether a bag slides in or jams.

What a sea kayak compartment actually holds

Compartment volume is generous on paper and deceptive in practice. A 5.2 m expedition kayak typically offers 60 to 90 litres in the bow compartment and 80 to 110 litres in the stern, plus 20 to 30 litres in the day hatch. Fill all of it and you have a boat carrying 35 kg of gear, which is well past what the hull was designed to trim around, and the handling goes from predictable to sluggish.

The realistic planning figure is 60% to 75% of total compartment volume, with the remainder left as void so bags can be pushed past the hatch rim and around the hull curve. In practice that works out to roughly 50 litres in the bow, 60 in the stern and 15 in the day hatch for a five-day loaded trip, which is where the 90 to 110 litre total comes from.

Volume per day: the expedition maths

Expedition volume scales with days because food and water scale with days, while clothing, shelter and cooking kit do not. On a temperate coastal trip the fixed kit — sleeping system, tent, stove, repair roll, spare clothing and safety gear — accounts for roughly 35 to 45 litres and 9 to 12 kg. Everything above that is consumables, and consumables are where the day count bites.

Add about 5 litres per person per day for food and packaging, and between zero and 4 litres per person per day for water depending on whether you carry it or filter it. A two-day trip therefore lands near 50 litres, a five-day trip near 100, and a ten-day resupply-free trip near 140 to 160, at which point you are planning a different kind of journey and need a different bag plan entirely.

Water: the decision that dominates your volume

Nothing moves the numbers like water. Carrying four litres per person per day is the conservative planning figure in warm weather, and on a five-day trip that is 20 litres and 20 kg for one person. Filtering or treating as you go removes almost all of it, at the cost of a 350 g filter, a 400 g dry bag for the treatment kit, and the discipline to stop and pump twice a day.

The middle path suits most coastal routes: carry two days of water in collapsible or rigid containers stowed low in the stern, and filter for the rest. That halves the carried weight while keeping a genuine reserve, and it changes the bag plan from three 10L water bags to one. On an exposed crossing with no reliable freshwater for 60 km, carry the full four litres per day and accept the weight penalty, because dehydration ends trips faster than a headwind does.

Bow, stern and day hatch: which size goes where

Assign bags by compartment and by what you need during the day. The stern takes the heaviest, densest items — water, food, cooking kit — because it sits close to your centre of mass and the hull is deepest there. The bow takes light, bulky items: sleeping bag, tent, spare clothing. The day hatch takes what you may need between landings: rain shell, snacks, camera, spare hat, repair tape.

The day-hatch rule is the one people get wrong. Anything you might want within five minutes of launching belongs behind the cockpit, not in a bow compartment you cannot reach without beaching. A 5L bag with a shell, a snack bar, sunscreen and a compact first-aid roll answers most of those moments, and a 10L adds a camera and a spare layer for a longer crossing.

Bag shapes that actually pass through an oval hatch

Shape matters as much as litres. A bag loaded to a stiff sphere will not deform enough to pass a 24 cm minor axis, while the same volume packed soft and squeezed will. Load bags with soft items against the leading edge and firm items in the middle, and expect to push rather than drop them through. A rolled closure helps here, because the rolled top is narrower than the body and goes in first.

Some paddlers use long, narrow sausage bags specifically for bow compartments, and they are worth considering if your forward hatch is tight. A 15L sausage bag with a 16 cm diameter slides into a narrow bow far more easily than a 15L cylindrical bag, and it wastes less of the tapered space at the stem. The trade-off is access: a long narrow bag is harder to dig through at camp.

Sleeping system, shelter and cooking kit volumes

These three items set the floor for your whole plan, because they are bulky and non-negotiable. A three-season sleeping bag compressed into a dry bag occupies 8 to 12 litres; a one-person tent packed in its own bag occupies 6 to 9 litres; a stove, fuel bottle, pot and mug set occupies 3 to 5 litres. Together that is 17 to 26 litres before a single item of clothing is counted.

Compress each of them before you size the bag around it. A sleeping bag shoved loosely into a 20L bag wastes half the volume; the same bag compressed in a sack and then placed in a 12L dry bag leaves room for a stuff sack of clothing around it. Fuel is the exception: keep it in its own container, never loose in a bag with food, and note that a 500 ml fuel bottle weighs about 450 g full.

Food volume and weight per person per day

Plan food by weight and volume separately, because they do not move together. Freeze-dried meals weigh 100 to 130 g each and pack flat, while fresh food is heavier per calorie and takes more space. A workable temperate menu runs 1.0 to 1.4 kg per person per day and 3 to 5 litres, including packaging, with breakfast and hot drinks the biggest volume items relative to their calories.

Repackage everything into flat bags before it goes into a dry bag, and group by day rather than by food type. One dry bag per two days of food means you open one bag at camp rather than five, and it keeps the smell of dinner out of the bag holding your breakfast. Pack the food bags in the stern near the water so you are not carrying both across camp.

Trim, weight distribution and the loaded waterline

A loaded expedition kayak should sit level or very slightly stern-down when floating in calm water. Load it on the beach, carry it to the water, float it in waist depth and sight along the hull from the side: if the bow rides 4 cm higher than the stern, move 2 to 3 kg forward. If it sits stern-heavy, the boat will weathercock and require constant correction with a skeg or a paddle brace.

Keep dense items low and central. Water is the densest thing you carry at 1 kg per litre, so water belongs against the hull near the cockpit bulkhead, not at the extremities. Bulky light items go to the ends, where their weight has the least effect on pitch. A 25 kg load distributed this way feels lighter than a 20 kg load piled into the stern compartment.

Redundancy: splitting the load so one failure is survivable

Sea kayaking is the activity where redundancy matters most, because a capsize far from shore with wet gear is a genuine emergency rather than an inconvenience. Split critical systems across at least two bags: sleeping bag and spare base layer in separate bags, in separate compartments. If one seal fails, you still have a dry sleep system and a dry layer, and the trip continues.

The same logic applies to electronics and documents. A phone, a VHF radio and a chart should never share a single bag, and each should sit inside a secondary pouch. Two small dry bags nested give you two independent seals for the cost of 90 g, which is the cheapest insurance available on a multi-day crossing.

Weather, tides and exposure on an open crossing

Exposure changes the plan more than distance does. An open crossing of 8 km with a 25 km/h beam wind and a 1 m swell puts spray over the deck continuously, which is why deck bags should be small, lashed twice and rated IPX6 or better. A sheltered loch crossing of the same distance involves no spray at all and can be paddled with a single loosely stowed bag behind the seat.

Tidal planning is the other variable, because a spring tide running at 3 knots against a loaded boat halves your effective speed and changes where you can land. Check predictions before you commit to a crossing window, and note that NOAA publishes tide and current data for US waters alongside coastal weather. Failing that, plan to be off the water two hours either side of the predicted turn.

Cold water and what a dry bag cannot do for you

Water at 12 °C removes dexterity in about ten minutes and consciousness in roughly an hour, and a dry bag does nothing about that. Immersion protection, a means of calling for help that works with cold hands, and a plan for re-entry are the three things that matter, and none of them is a packing problem. Keep a radio or phone in a PFD pocket, not in a hatch bag you cannot reach while swimming.

The bag does contribute one thing: dry spare clothing, which is a genuine part of cold-water survival after a wet exit. That clothing belongs in the day hatch or on your person, not in a bow compartment you can only open on land. The CDC publishes cold-water safety guidance that is worth reading before an early-season crossing, and it reinforces the same point about access under stress.

A sizing checklist for your next expedition

• Measure the clear opening of every hatch on your boat and write the minor axis down.
• Size each bag to pass that opening when rolled and loaded soft, not to the compartment volume.
• Plan 5 litres of consumables per person per day, plus 2 to 4 litres of carried water.
• Put dense items low and central and bulky light items at the ends of the boat.
• Split sleeping system, clothing and electronics across two compartments each.
• Keep a shell, snacks, repair tape and a camera in the day hatch, not the bow.
• Float the loaded boat and sight the waterline before the first crossing of the trip.
• Recheck trim after two days, once food and water weight has shifted.

Run that list the evening before a launch and most packing mistakes surface before they cost you a day. The two that catch people out most often are buying a bag too wide for the hatch and loading water at the extremities rather than against the hull; both are visible in a five-minute check on the beach and both are painful to fix in a cockpit.

For the shorter end of the same sport, the day kayaking sizing guide covers the 5L to 20L decision in detail, and the hatch packing notes go further on aperture and loading order. If your trip is measured in weeks rather than days, the seven-day sizing plan and the full capacity guide take the maths further, while the multi-day sailing plan covers the same problem on a bigger boat.

One practical note on buying: expedition bags take far more abrasion than day-trip bags, because they are dragged across shingle and stuffed through hatches dozens of times per season. Choose 0.5 mm film and welded D-rings rather than the lighter specification you would accept for a grab bag, and look at the floating dry bag options if you paddle anywhere a lost bag could not be recovered. Our team has produced waterproof bags since 2014 in an SGS-verified 4,950 m2 facility with 137 staff, and the sizing questions above are the ones that come up in every expedition programme; we document the full process from sampling to bulk, and the full product line lists the sizes referenced here.