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Barrel & Drum Raft

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Parent
🏗️
Simple Raft Building
Log rafts for river crossing and cargo
Current
🛢️
Barrel & Drum Raft
Salvaged containers as flotation

A sealed 200 L drum displaces 200 kg of water when fully submerged and, with a 20 kg drum, supports 180 kg, but that is the figure at zero freeboard; at half immersion each drum supports 80 kg and at three-quarters 130 kg. Four to six drums therefore carry 320 to 480 kg at half immersion, a pallet of goods, and a vehicle ferry for a 1,500 kg vehicle on a 400 kg frame needs about 24 drums at half immersion or 15 at three-quarters, which is far more than the 4-6 the overview suggests.

Part of Coracle & Small Watercraft

A drum raft uses sealed barrels or drums, lashed to a frame, as the floats of a platform, with a lift fixed by the volume of the drums and how deep they sit.

The Lift Per Drum Depends On How Deep It Sits, Not Only On Its Size

The carrier says sealed 200-litre drums make excellent pontoons: each supports about 180 kg, 4-6 drums are lashed to a frame of poles or lumber, caps must be sealed tight (a small leak fills the drum over time), and the result is a flat, stable platform suitable for vehicle ferry service on rivers. The first number is the maximum: 200 L is 0.200 m³, which displaces 200 kg of fresh water; subtract the drum’s own mass, about 20 kg (an assumed figure; weigh yours), and 180 kg is the load at which the drum is exactly submerged, with no freeboard at all. A working raft sits higher.

For a drum lying on its side, the displaced volume at a depth is a circle segment: 50% of the volume at half the diameter and 75% at about 0.69 of the diameter (a 0.58 m drum, an assumed size, then has about 29 cm and 18 cm of drum freeboard).

What You Need

Method: Size The Raft

Step 1: Weigh a drum to find its own mass m (here 20 kg).

Step 2: Choose an immersion (50%, half, for a margin of safety; 75%, three-quarters, for a heavy load) and compute the net lift per drum = 200 × fraction − m.

Step 3: Divide the total load (cargo plus frame) by the net lift, rounding up.

Step 4: Compute the lashing force and size the rope.

Step 5: Build, test each drum for leaks, and float the raft empty before loading.

Worked Example: Drums For A 1,500 kg Vehicle

Net lift per drum (20 kg drum): fully submerged 200 − 20 = 180 kg; at 75% immersion 150 − 20 = 130 kg; at 50%, 100 − 20 = 80 kg. Load: a vehicle of 1,500 kg (assumed) on a frame of 400 kg (assumed) is 1,900 kg. Drums needed at 50% immersion: 1,900 ÷ 80 = 23.75, so 24; at 75% immersion: 1,900 ÷ 130 = 14.6, so 15. The overview’s four to six drums (4-6) carry 4 × 80 = 320 kg to 6 × 80 = 480 kg at 50% immersion, 520-780 kg at 75%, and 720-1,080 kg at full submersion, none of which reaches 1,900 kg. The 180 kg figure is therefore a ceiling, and a vehicle needs a raft of fifteen to twenty-four drums.

Lashing: a drum lifted by 180 kg of net buoyancy pulls up on its cradle with 180 × 9.81 = 1,766 N. With the corpus’s 5:1 safety factor for a line (Rope Strength Testing), the lashing for each drum needs a breaking strength of 8.8 kN. At 50% immersion the pull is 80 × 9.81 = 785 N.

Common Mistakes

  • Reading 180 kg as the working load — it is the load at zero freeboard.
  • A drum with a bad cap — it floods and the raft tilts; test each one.
  • Weak cradles — drums try to float out of the frame.
  • Mixed drum sizes — the raft rolls.

Safety

Drums that held fuel can explode, and a flooded drum sinks one corner

Never cut, weld or heat a drum that held fuel or solvent, even when empty and apparently clean: residual vapour explodes. Do not use drums that held chemicals as floats on water people drink. Test the caps, tie the load down, wear flotation, and stay out of strong current; see Safety & Capsizing Recovery. For ferry loads, the stability checks in Ferry Platform Design apply.

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