The Mink Raft

Mink rafts and cage traps are provided by the Norfolk Mink Project to our volunteers. However if you wish to build your own or live outside the county of Norfolk this guide will help you through a step by step process from start to finish.

Our mink rafts are based on the game conservancy trust mink rafts, but we try to use recycled plastic stokbord when possible instead of plywood. Plywood can be used but we recommend treating it with a garden paint, such as Cuprinol garden shades or at minimum varnish the edges as otherwise the plywood will delaminate. DO NOT treat plywood with oil as this can contaminate the water.

Materials Required To Build Four Mink Rafts

It is more economical to make four rafts at once since you will get four base sheets out of one large polystyrene board. We have therefore provided a list of materials to make four mink rafts. Most of these can be purchased from hardware shops or building supplies merchants. We estimate an approximate cost of £150-200 to build four rafts.

Mink raft

2x 2440mm x 1220mm x 6mm Stokbord black
1x 2440mm x 1220mm x 9mm Stokbord black (will make 16 tunnel tops, alternative such as plywood can be used)
1x 50mm expanded polystyrene insulation boards 2400mm x 1200mm x50mm sheets
8x BZP eye bolts nuts & washers 152mm x 6mm
16x M6 x 70mm BZP roofing bolts & nuts (Screwfix or CPC), other suppliers might only do 80mm which is fine but they will need cutting down once fitted.
2x 3.6m x 22 x 200 sawn imported softwood red/whitewood FSC (with spare for one raft)
Spax 4CUT or Screwfix Turbo Ultra screws 4x40mm pk200 (or equivalent) if you can get a pk100 do that as only 32 needed
Spax 4CUT or Screwfix Turbo Ultra screws 4x25mm pk200 (or equivalent) if you can get a pk100 do that as only 64 needed
16x Corner brackets 1½” x 1½”
3x M6 large flat washers pk10 (24 needed)
4x 1m length of 12mm doweling
*Plastic barrier mesh or equivalent, usually comes in a roll of 100cm width (cut to size)
*Staples for staple gun (hand stapler works just as well)
*optional but recommended

Tracking pad

4x 25cm handy basket (can be tricky to source, try school supplies shops. I purchase from Ebay in bulk, search for “Whitefurze 25cm handy basket”. There are some shallow versions (6.5cm) of the 25cm baskets on the market so be careful, you want 25cm x 8cm x 16cm)
4x Oasis florist foam, 25cm brick (local florists or Amazon)
School clay, comes in 12.5kg block, 650g per raft (local supplier or www.glsed.co.uk)
Kiln dried sand, comes in 25kg bag, 350g per raft

Mooring

4x Machine turned round pointed posts 1.50m x 50mm p/treated HC4 green FSC
4x 6” nails
12 meter of 6mm diameter polypropylene rope, 3m per raft

How To Build a Mink Raft

Mink raft base

The base of the mink raft is made out of two 1220 x 610 x 6mm sheets of stokbord which sandwiches a sheet of 1200 x 600 x 50mm expanded polystyrene in the middle. The stokbord comes in a large sheet of 2440 x 1220 x 6mm which is then cut to the dimensions mentioned, and the polystyrene comes in a 2400 x 1200 x 50mm and again cut to the dimensions previously mentioned. Some suppliers may cut this to size before delivery so it is worth asking, this also makes it easier to deliver and handle. The picture below shows a sheet of stokbord cut into four pieces, do the same with the polystyrene but at the required dimensions. I recommend a circular saw for the stokboard as this will give you fairly straight cuts but a jigsaw can also be used. For the polystyrene you can use a sharp knife, hacksaw, fine tooth woodsaw or something similar. Personally I find a hacksaw blade in a handle works well for the polystyrene.

Step 1. Cut sheets into four.

You now need to cut a 237 x 152mm rectangular hole for the tracking pad in the center of one of the stokboard sheets. Take one of the stokbord sheets and find the center, to do this I measure in 305mm on the short side, making some marks and 610mm on the long side again making some marks; now join the marks with a long straight edge to make a cross which will give you the center. From the center of the cross we can now measure out the hole for the tracking pad. The width is 76mm and the length is 118.5mm. Measure this out as in the picture and join it up. I find a chalk stick or a yellow/white colouring pencil good for marking marks on the stokbord.

You can also mark where you need to drill the holes for the bolts at this time; these are simply 2” in from the edge as shown in the pictures (for plywood we recommend 3” – 4” from the edge).

Step 2. Mark the sheet for the tracking pad hole.

Step 3. Mark bolt hole locations.

Step 3. Mark bolt hole locations.

Now that you have marked out one sheet, you can take another sheet and clamp them together using spring or G clamps. I just use a couple of old chairs to rest them on so I have free cutting room below for my jigsaw. You could also use some blocks on a bench to raise it up and achieve the same thing. Now drill small holes in the corners and cut out the rectangle in the middle with a jigsaw. I find cutting two sheets (one raft) at once is best. Once the tracking pad hole has been cut out on one sheet you can use it as a template for the rest. Make sure to check that the basket for the tracking pad fits and does not drop out. If the hole has been cut slightly too big a strip of metal builders band can be used to make the hole smaller again ( e.g. Builders band – Screwfix ).

Step 4. Clamp two sheets together.

Step 5. Drill four holes to cut out the tracking pad hole.

Step 6. Cut out the tracking pad hole (finished raft).

If tracking pad hole to large use a strip builders band.

There is also an option to add a couple of finger holes when cutting out the tracking pad hole; this is to aid in pulling out the tracking pad when checking for footprints. The easiest option is to drill two large holes in two opposite corners and then cut out the tracking pad hole, I use a 19mm spade drill bit to do this but a similar size will be fine.

19mm spade drill bit (similar can be used).

Drill two holes in opposite corners and cut out the tracking pad hole.

Finger holes in two corners.

Finger holes can also be added at each end instead of the corners, they can be a little trickier to line up nicely but you can tidy them up with a dremel for example.

Three holes cut in a line at each end.

Finger holes in each end.

Now that you have cut the hole for the tracking pad, unclamp the two sheets of stokbord. Place a 1200 x 600 x 50mm sheet of polystyrene between them, making sure that they are roughly lined up and clamp them all together. Drill a 6mm hole through all three sheets at the positions marked earlier – 2” from the edge. Bolt them together using two eye bolts and four roofing bolts to form the base of the raft. The clamps can now be removed. (Note: Plywood rafts drill 3” – 4” away from the edge).

Step 7. Sandwich the polystyrene between the two sheets and Clamp together.
Use a 6mm drill bit and drill all the bolt holes.

Step 8. Bolt holes drilled.

Step 8. Bolt holes drilled.

Step 9, Bolt the base together.

Step 9, Bolt the base together (finished raft).

Step 9, Bolt the base together (finished raft).

You now need to cut a hole into the polystyrene for the tracking pad. I find a hacksaw blade works very well and gives a clean cut but other tools can be used as previously mentioned.

Step 10. Cut out the polystyrene for tracking pad, I use a hacksaw blade.

Tracking pad hole complete.

Tracking pad hole complete.

Turn the raft over and trim down the bolt threads to within a few mm of the nut using a grinder with a cutting disc. A hacksaw can also be used but will take a little bit longer. If you used 70mm roofing bolts you will not need to cut them down, you will only need to do the eye bolts.

Step 11. Turn the base over and cut down the bolts close to the nut.

Bolt cut down (finished raft).

All that is left for the base of the raft is to fit some mesh. This is optional but it does provide grip for an animal (e.g. mink) to climb up onto the raft. I use plastic barrier fencing mesh (green) 1m wide roll, but any similar plastic mesh will work. The approximate size is 50cm x 25cm but with the barrier mesh it is easier to count 3 holes down and cut across the 1m roll on the 4th hole down, leaving a strip with 3 clear holes. You then count in 12 holes and cut the strip in half on the 12th hole making two pieces of mesh for one raft, which can then be stapled onto the raft base with a staple gun.

Step 12. Cut out the mesh.

Step 12. Cut out the mesh.

Step 13. Lay the mesh in place.

Step 14. Staple the mesh to the base.

Cut the extra lengths of the plastic mesh off so it looks neater.

Base of the mink raft complete.

Mesh on finished raft.

The base of the mink raft is now done!

Mink raft tunnel

The tops for the tunnels are made from stokbord. This time though we use 9mm which are cut from a 2440 x 1220 x 9mm sheet. If you are only making a few rafts this might not be the best option as a sheet this size gives 16 tunnel tops. A similar thickness of plywood can be used but the dimensions should be the same, particularly the width as you may need to fit a trap inside.

The tunnel tops are 720 x 242mm, and as before use chalk or colour pencil to mark it out. The best layout to get the 16 tops is shown below. Number 16 might be a touch wider once cut but this isn’t a problem. This sheet can be tricky to handle so I recommend two people lift it into place for cutting. I use a circular saw but a jigsaw can be used although you might get a few wavy lines.

Step 15. Layout for cutting the tunnel tops.

The sides for the tunnel are cut from a 3.6m length of pressure treated 22 x 200mm sawn softwood plank which is cut every 718mm (which allows for saw blade width). From one 3.6m length you will get five sides, so 2x 3.6m will do five rafts, leaving some spares. Once cut you can paint them with garden paint. This is optional as they are pressure treated but helps to darken them up so they are not as obvious. Fix the tunnel top to the sides with 8 x 4mm x 40mm screws, and two ‘L’ brackets on each side with 4mm x 25mm screws.

Step 16. Cut the tunnel sides and paint, (sides and top for the tunnel).

Step 17. Screw the top to the sides.

Step 18. Screw corner brackets to the sides and fix to the base.

Otter guard

There are two main reasons to have the option of narrowing the tunnel entrance on a mink raft. One – if you are using a trap which does not have a fixed otter guard and two – some otters can dig out the clay in the tracking pad which means it needs topping up quite often.

This is where you can make use of the leftover squares of stokbord cut out of the centers of the mink raft base. The picture below shows the layout, which will give you 6 x 1in x 20cm strips of plastic, enough for 3 mink rafts. Once cut out measure in 10cm and mark the center point. Measure out 1.75in on both sides of the center mark and make a mark. Cut out two 12mm holes as shown (not the center mark), this will give you a gap of around 3 inches from the edge of one hole to the other.

Step 1. Mark out six 1" x 20cm strips.

Step 2. Find the center and mark 1.75" away on each side.

Step 3. Drill two 12mm holes.

Now take the strip of plastic with the two 12mm holes you have just cut out and place it on top of the tunnel. Line it up with the front edge and the inside edge of the tunnel. Use a sharp tool e.g. a sharp nail to mark the center of each hole on the tunnel top. Use the plastic strip as a template.

Step 4. Use the strip to mark the tunnel top.

Drill two 12mm holes using the marks you have made on the tunnel top as guides. Repeat this process for both ends of the tunnel. Secure the strip of plastic with the two holes to the base of the raft between the tunnel sides, using two small screws (see picture). This also helps to prevent warping, making sure there is a 20 cm gap in the tunnel large enough to fit a mink trap. Cut some 12mm dowelling to fit into the holes, around 23-25cm in length. This will keep otters out but still allow mink, water voles and other small mammals through.

Step 5. Drill the two 12mm holes in the tunnel top.

Step 6. Place the strip between the tunnel sides and screw to the base.

Step 7. 12mm doweling in place.

Mooring

Take the 6mm polypropylene rope and cut a 3m length, remember to burn the ends to stop any fraying. Tie each end to the eye bolts on the raft using a bowline knot. The pictures below provide a how-to guide if you aren’t sure how to do this. If you cannot tie a bowline then use a knot you are confident with, which won’t come loose. Once complete, tie a simple loop in the center of the rope. I normally tie the loop once on site – in flowing water one side of the loop will need to be shorter to keep the raft parallel to the bank. This will be passed over a post hammered into the ground and used to secure the raft when it’s installed on-site. For each of the 4 x pointed mooring posts (1.50m x 50 mm) knock in a 6” nail approximately a foot from the at the blunt end (top) of the post. Blunt the point of the nail almost flat – this will stop the wood from splitting. Make sure the loop just fits through the post – it must not be too loose. It can also be a good idea to add a second rope to make sure the raft is secure.

Bowline knot, step 1.

Bowline knot, step 2.

Bowline knot, step 3.

Bowline knot, step 4.

Bowline knot, step 5.