Blue bark texture background

Standard raft

This raft is made of 3m tanalized soft wood and is 3m square. The design includes chick shelters, a re-entry ramp and an optional security fence.

How to build a standard raft

Buoyancy for a standard raft is provided by two high-density polystyrene blocks. The raft is anchored to concrete blocks by a chain attached to a marker buoy. It is covered with gravel and rocks, and any plant growth is removed each winter.

Raft platform

  • Mainframe: 100 x 200mm timber, bolted together in each corner through overlapping ends (two upper, two lower), one top inset 150mm to allow for re-entry ramp. 
  • Deck: 25 x 150mm planking, laid on and nailed (75mm galvanised nails) to lower mainframe timbers. 
  • Sub frame: 50 x 75mm runners to support flotation and strengthen deck, nailed (150mm nails); main flotation holders/deck support 50 x 100mm runners; slides 25 x 150mm planking, nailed flush with top of upper mainframe timbers along the lower sides to hold in gravel etc, and flush with the bottom of the mainframe timbers along the upper sides to hold the flotation devices in place. 

Buoyancy

  • Blocks of 380 x 600 x 2,700mm high-density polystyrene foam, painted (optional) with BP Aquaseal 44 bituminous paint (as suitable for use inside cold water tanks) to water seal and strengthen the polystyrene; two optional straps per float block, 1,420mm strips of polystyrene webbing (or 50mm chair webbing as a temporary measure, for example during launching) with eyelet holes for nailing to frame.
  • Once in the water, the weight of the raft is sufficient to hold the polystyrene in place without any additional fixings, even in extreme conditions.

Mooring

  • Mooring ring bolted through centre of mainframe timber (bolt fixed with two nuts so that it can swivel freely), connected preferably to a chain (expensive) or a 20mm diameter hawser-lay polypropylene rope (which will not rot but can be chafed), with hard eyes and shackles each end. 
  • Tether a 30in circumference marker buoy to the raft end of the chain or rope with a length of polypropylene rope to allow the raft to be detached, without having to pull up or lose the anchor.

Anchor

  • Multiple small weights (up to 1 cubic metre concrete as a total) for ease of transport. Four buckets 250mm high x 300mm diameter of concrete, eyebolt set in centre; weights connected in pairs by shackles to 300mm lengths of chain; fixed to mooring by placing two pairs of weights together with the connecting chains forming a cross, and attaching the mooring rope shackle to the point where the chains cross.
  • Exposed sites where wind and waves are strong may require more anchor weights.

Shelters (to protect from rain)

  • These comprise 1m-long 25 x 150mm planks located in opposite corners, nailed flat on to end of upper mainframe timber, side plank and 50 x 75mm end block.

Gravel covering

  • Preferably of 15–25 mm gravel with larger pieces and rocks to provide shelter, and give sufficient weight to push running board down to water level.

Re-entry system (for chicks falling overboard):

  • These are located on opposite (lee) side of raft to the mooring ring: running board 3m, 25 x 150mm plank nailed to bottom of the two lower mainframes. Ramp (1.5m, 25 x 150mm plank) sloping up to top corner of mainframe, supported by up stand, nailed. Block gap under raft behind ramp with 25 x 150mm skirt plank. 

Optional removable security fence

  • These comprise four frames measuring 230mm x 0.3m, made from 50 x 50mm planks covered with 25mm chicken wire, bolted along each side and fixed at top corners.