Designing a High Seat

Designer High seat

Having sat in several home built and shop bought high seats for over four hours at a session, I had begun to wonder if the people designing them had ever actually used one? Or perhaps I was just so old now that my arse and my back could no longer tolerate poor ergonomics.

I found vertical back rests which made me squirm in pain after an hour, poorly positioned foot rests, gun rails which meant I had to adopt some hunch backed position to shoot a rifle, some of the seats had ladders that would buckle under my 16 stone and others had no inherent stability, so any failure of the strapping meant falling from a great height whilst holding a loaded rifle. Most were open sided so I would take a camo net to drape around me for both stealth and to act as a wind break.

Most if not all had some redeeming feature and some were even comfortable but all had something about them I felt itch at my personal image of perfection.

So with an engineering background and an obvious old farts self-indulgence for comfort and practicality, I set about designing my perfect open high chair.

Part 1: The Learning Curve

Cost was a consideration but not an end game, so having done the calculations I ended up spending around £100 per seat. That said, in order to do this, certain items like the 10mm bolts had to be Screwfix bulk buys for more than one seat. Buying individual nuts bolts and washers is daft expensive. I also negotiated a deal on timber with TP.

Again on the cost issue I decided I wanted 10mm bolts on the main seat structure rather than cheaper screws. I am sure screws would work but I have more faith in bolts and I feel it allowed me to avoid further expense cross bracing to make the seat ridged.

My first attempt was a learning curve for both ergonomic and cost issues. I calculated the width for two people and space for bags without considering the implications on materials. As a result, I needed two sheets of Sterling board to form the wind break and that was a waste of money. I also didn’t provide any specific anchor points for the seat nor did I consider the issue of clamping a seat to a tree with a 4 X 2 cross brace. My final seat design didn’t allow for any off vertical positioning of the seat, the foot rest (final rung of the ladder) was too low and the gun rail was too narrow to rest a rifle on without supporting the rifle butt.

All these issue became apparent on erecting it. Due to a branch we couldn’t cut, the seat was leaning back ever so slightly but there was no adjustment on the shooting rail height so it was too high to see over properly. Another unexpected issue was that the size & weight of the seat meant two strong people struggled massively to walk it up to vertical once assembled on the ground.

So it was back to the drawing board…

The Mk 2 seat

High Seat Design 2
High Seat Design drawing (click to enlarge)

The MK1 seat did have some good points, but its biggest virtue was that it gave me a physical thing I could sit in and re measure to get Mk2 much closer to perfection. Many a happy hour was then spent measuring myself and the seat in order to improve things.

No it can’t be perfect for everyone, but I am Mr average at 5’ 10” so I made it to fit me which was I felt the best compromise in the ergonomics area.

First off the 1.6m width of Mk1 was way too much. Mk2 was 1.2m wide which was plenty for two stalkers to sit comfortably and happily worked out as a cost saving by offering 3 rungs out of a standard 3.6m length of timber and for a 8 X 4 (1.2 X 2.4) sheet to fit perfectly with minimal cuts and minimal waste.

The critical dimensions I felt were:

  • Height from the base of the seat to the gun rail (600mm)
  • Distance from the base of the seat to the foot rest (360mm)
  • Distance from the back of the seat base to the front of the ladder rail (1.0m)

In the sketch below the rear vertical 4X2 and horizontal 4 X 2 are shown as dotted lines so the seat design can become clear

Seat Detail Drawing
NOTE: If you feel it might be nice to have some variation in the rifle rail height, make it 500 and then you can add on 4 X 2 to raise the final rail to your perfect height. For me 600 was spot on

The depth of the seat was in part dictated by the width of my chosen 150mm decking board, but it was also close to the dimension I had calculated for myself at 460mm with a small gap left between the planks for rainwater drainage. With clearance for the rear back support vertical planks, it became 490mm. This worked out nicely at three 150mm planks + clearance. The dimension to the back of the seat was calculated against the hand rail and 1.0m was decided upon. Allowing a further 100mm for the rear supporting 4X2’s in total the side rails for the seat were 1.1m long.

I had made the first seat all of 4 X 2. Whilst this was cost effective I felt the front supports were too flexible and for MK2 I upgraded to 6 X 2 and set in the footsteps to full depth for greater support.

The top hand rail was also enlarged to 6” to allow a rifle to rest on it without further support and with comparative safety.

hooks-on-sideThe other issue I found when using 4 X 2 as a frame was clamping down with the ratchet strap to secure the seat to the tree. The design of the seat left no timber open for the strap and using a 5-ton strap on a 4X2 felt like it would snap it.

To resolve this, I did away with the 4 X 2 cross member and used a 6X2 screwed to the verticals behind the seat. I then drilled holes in it and mounted two large U bolts on square washers and nuts.

I set these at a width which I knew was ideal for the tree I intended to mount the seat on as they would become the hook points for the straps.

Supporting it this way proved to be very effective but left a small problem of the exposed bolts. So a 2X2 strip was added to allow for this and provide the top support for the seat back. Mounting the cross members of the seat immediately in front of the verticals left a natural 50mm slope on the seat back which I found very comfortable. In order to support the verticals for the seat back a 100 X 25mm strip was added to the seat support. Obviously a 4X2 would have worked fine.

The height of the seat back was settled on 700mm. This seemed to provide adequate support without overhanging the top of the chair in a way which would stop the seat going back against the tree.

For my high seats I have fitted a 13mm Sterling board wind break. Painted green this also provides a nice almost camo patterned panel to hide behind. Some will prefer the full visibility of an open seat and the panels can be left off, but I fitted a panel to within 150mm of the first step / foot rest and filled in the side panels of the seat for added stealth and protection from cutting winter wind.

I haven’t been through the winter with one yet but I am sure they will be warmer than fully open seats.

The final design change related to the bracing legs.

The original required extra-long bolts to allow a triple beam fix on the rear horizontal and vertical support and a further two bolts to clamp it to the sides of the ladder support.

In order to avoid this, I used the hip rafter technique found on roof trusses. By increasing the dimension of the second step to 100 X 100mm I presented a brace point. Simply bolting the side

brace just inside the seat support with a standard 110mm bolt I was able to mark out the end of the timber so it would angle on to the enlarged step and present a flat surface for screwing back to the ladder support. I could have used 150mm No6 screws for this, but for extra support I used 200mm bolt headed deck screws.

Side Brace Detail

The end result of these modifications meant a significant weight reduction and on assembly two old, overweight but strong blokes were able to lift the seat and walk it up to vertical against the tree.

CONSTRUCTION TIPS

Job one is to mark out the seat heights cross member heights and step heights on the main vertical ladder supports. Not forgetting to allow 50mm,for the gun rail mark out 550mm in from the end of the side ladder support.

Then mark down a further 360mm which will be the top of your last step / foot rest. Finally mark out the top of each step at 400mm centres.

Personally I cut in the steps for additional support using a jig saw. If you choose not to do this, I would at the very least cut in the 100 X 100 step which supports the side braces.

Having cut my 1.2m long steps I screw in the top and bottom step to the ladder support to provide a working frame.

Then the frame is laid on the ground steps upmost and the 1.1m vertical side supports are positioned, clamped with G clamps and drilled for 10mm bolts

Once bolted up tight they are knocked vertical to a set square and the rear 650mm long verticals are clamped in place, drilled and bolted

Taking my 3.0m length of 6 X 2 I cut off 1.2m for the rear brace and set the remaining 1.8m aside for the gun rest and front brace. This section is then drilled and screwed in place against the rear verticals.

Having determined the width of the tree it is going to be mounted on, I position two U bolts out from the centre line, hold them in rough position and hit the top of the U bend with a hammer to mark the plank with the bolts. These marks are drilled and the U brackets pushed through just enough to mount a 2” square washer and a nut.

A 2 X 2 strip is then cut and screwed on above the square washers to form the back support.

A 1.0m length of 4X2 is cut and inserted between the horizontal supports and tight up against the rear vertical post position. This is screwed in place with 100mm No6 screws in the end grain, through the lower side support timber.

A second 1.0m length is cut and fitted in the same way approximately 450mm forward of the first. A “noggin” is then cut to fit at the midpoint in the two beams to form a cross support. A 100mm strip is then screwed to the back of the rear section with 50mm showing above the timber to allow fixing of the vertical seat back timbers. It is advised that multiple 6mm diameter course thread screws are used to fix this timber as it will take the weight of the person sitting back in the seat.

seatconstructiontipsThree 1.2m long strips of decking can then be cut and 7 X 700mm decking for the back support. The back support should be installed first and then the seat decking. The back support will have 12mm gaps between the planks and the seat was spaced out to allow drainage using the flat washers. Three planks laid in this way should just overhang the seat support

If sterling board panels are to be used, they should be cut at full board width 1.2 X depth 800mm for the front panel and cut to fit for the side panels. I hold the panels in positon and mark around the seat planks and cut a rough slot to clear them. The side panels are supported on the top and bottom side rails and the front panel on the gun rest and side ladder supports. As a result, these are best assembled on site. Finally, the side brace timbers are held in position, marked up and cut to fit. I will ensure the seat is square and then pre drill the bolt holes so on assembly with the brace the seat is forced back to square

The timbers are then marked up for position for final assembly and the seat taken apart for painting.

In the MK1 pic above I fully disassembled the seats for transportation and assembly on site. However, with the MK2 seat I only removed the ladder section (four bolts) from the completed seat and managed to easily get two ready assembled top section seats on my 6ft 6” trailer
In the MK1 pic above I fully disassembled the seats for transportation and assembly on site. However, with the MK2 seat I only removed the ladder section (four bolts) from the completed seat and managed to easily get two ready assembled top section seats on my 6ft 6” trailer

ASSEMBLY ON SITE

Position the ends of the ladder section at the base of the intended tree a distance out, slightly in excess of 1.1m.

seat-assembly1Laying the ladder section, rungs upwards it is important to identify the left and right hand vertical ladder supports. As I use coach bolts and keep the dome heads internal to the seat to avoid getting scratched by the bolts, I can see the square indentations on the internal side of the timbers which allows for easy ID.

Insert and fix in position all of the ladder rungs not forgetting to install the 100 X 100 rung in the second step position.

If the seat section was transported assembled, you can now stand it up on the side arms seat facing downwards and bolt it to the ladder section, if not then first assemble the seat support section prior to assembly. The rear support is then screwed to the rear vertical sections before the two side braces are fitted. If carried out in this order when the side braces are fitted the seat can be manhandled back to square without further measuring.

NOTE This is the MK1 seat in the photos but assembly is the same
NOTE: The two photos above show the MK1 seat, but assembly is the same.

If I owned the land, I’d probably fit a roof and heating  😀

In theory these seats can be disassembled and moved about, but they are heavy and that’s a lot of work so I have only positioned them in gold star locations.

On a new permission, I use a portable metal high seat to decide upon the best locations and only once that’s established will I erect one of these. The metal one is reused for the next recon operation.

I also have used pad stones under the vertical legs to reduce the water wicking from the soil and potentially rotting the vertical ladder supports. I intend on drilling a 13mm hole 100mm up from the floor and inserting 12mm Boron Rods. These solid rods of disodium octiborate dissolve in water to release a very powerful fungicide. They are used on telegraph poles. The 13mm holes are loosely plugged with a timber dowel or plastic plug and every two or three years a new boron rod is inserted. In this way the soft wood can outlast the most durable hard wood.

I used 5ltrs of very reasonably priced (£11.00 for 5ltrs) Cuprinol “Ducks Back” timber treatment to paint the seat and found this was just enough for two generous coats.

high-seat-mk2-b
The Mk2 High Seat in Situ

It took a day to build the seats at home (including painting), then a further two hours work to erect them on site.

I am sure there are many cheaper ways to do this but for me It was an investment as I am not getting any younger. I do find it odd when people are happy to spend serious money on a rifle and scope but balk at a few extra quid to build good high seats.

I am sure I’ll be tweaking the design in the future and that many will find it extravagant or have better ideas, but I hope it can at least provide a starting point on dimensions & construction for anyone considering building one for the first time.

ATB
Mark Chase