Double Platform Monkey Bridge

Project completed in time for a Scout Expo by a Pioneering Crew for Chicora Chapter, Santee Lodge No. 116, Order of the Arrow
Double Platform Monkey Bridge

It’s a pretty safe to say most Scouts love to climb things. So, it makes sense that if a monkey bridge is combined with something to climb on, it will be even more fun. The challenge in constructing a project like this is to assure the structure can safely support not only the weight of those climbing on the platforms, but also the continual stress created by repeatedly crossing the rope bridge. Building this version of a double platform monkey bridge entails quite a few subassemblies and a procedure with many steps. Basically, with the materials listed, the ropes span a distance of 25 feet between two identical square platforms 4 feet wide and 8 feet high. At the front of each platform is an X-brace just under 5 feet high, providing a V for the foot rope. The hand ropes run through the junction where the X-braces intersect the top of the front legs, and then extend down joining the foot rope at a log-stake anchor 10 feet behind the back of each platform.

Bridge in operation during a Scout Expo
Bridge in operation during a Scout Expo

Here are the materials needed to construct the project:

  • eight 8-foot x 4-inch spars for platform legs
  • four 8-foot x 3-1/2-inch spars for X-braces
  • four 6-foot x 2-1/2-inch diagonal side braces
  • eight 4-foot x 3-inch spars for side base spreaders (4) and platform supports (4)
  • sixteen 4-foot x 2-inch spars for ladder rungs (10), handrails (4) and X-brace leg spreaders (2)
  • twenty-four 4-foot x 2-inch floor spars
  • two 4-foot x 4-inch log and stake anchor logs
  • sixteen 30-inch pioneering stakes for 2 log-stake  anchors
  • sixteen large wooden stakes for the 8 guy line 1-1 anchors
  • sixteen small tourniquet stakes
  • two rope grommets with large O-rings
  • one 70-foot x 1/2 or 3/4-inch manila foot rope
  • two 70-foot x 1/2-inch manila hand ropes
  • eight 8-foot x 1/4-inch manila spanner ropes
  • thirty-six 15-foot x 1/4-inch manila lashing ropes
  • twenty-six 20-foot x 1/4-inch manila lashing ropes (for X-braces, base spreaders and platform supports)
  • eight 25-foot x 3/8-inch manila guy lines
  • four 35-foot x 1/4-inch manila lashing ropes for floor spars
  • six burlap or canvas saddles (for the foot rope and hand ropes)
  • two large mallots
  • Binder twine
  • Tape Measure
Anchors are being built as sides are being connected.
Anchors are being built as sides are being connected.

Tips:

• Participants should be well-acquainted and experienced in the skills required for building this project.

• Select a project leader who will divide the participants into work groups, assign tasks, and oversee operations.

• Before proceeding, position the materials in proximity to the location where the project will be placed. It’s good to organize the materials by the tasks for which they’re needed.

• Depending upon how many Scouts are participating (will there be a small group of 6 Scouts, or a large group of 24), many of the subassembly steps needed to finish the project can be completed simultaneously. This division of labor can enormously streamline the project’s completion.

• If the opportunity presents itself, it can very  helpful to initially lay out the hand and foot ropes, in conjunction with completing Task E, before proceeding with Tasks A & B.

• The following tasks can be completed at the same time:

  1. Tasks A 1 & 2  /  B 1 & 2  /  Tasks D  1 & 2 and E
  2. Task C  1  /  Task C  2
  3. Task F 1 & 2 /  Task H 1 & 2
  4. Tasks I & J  /  Tasks K, L & M

• If one task is taking longer to complete, workers from other groups can lend a hand and help finish it up so the next step can commence.

• Placing a 4-foot spar underneath the spars lying on the ground, in a strategic position, will raise the project sides up and make lashing much easier.

• There are 64 square lashings in this project and, for stability and safety, they must be tight! For speed and efficiency, the Japanese Mark II Square Lashing is highly recommended.

Ladder Side
Schematic of Ladder Sides

TASK A – 1 & 2: Building the ladder sides of the platforms. 1) Lay out two 8-foot legs side by side. Space the spars apart so that the distance from the middle of each spar, at both the top and bottom ends, is 40 inches. Use a tape measure. Also, make sure the butt ends are at the bottom and absolutely even. Starting 6 inches up from the butt end, connect the legs by lashing on a 4-foot ladder rung directly above the 6 inch mark, with tight square lashings.

Using a tape measure, measure 5 feet up from the butt end of each leg, lash on another ladder rung, directly below, just touching, the 5-foot mark, ON THE OTHER SIDE (what will become the inside) of the legs. See the diagram on the right.

Right in the middle of these two ladder rungs, lash on another ladder rung, and then, between the middle ladder rung and the top and bottom ladder rungs, lash on two more. Use tight square lashings.

2) Repeat the whole process on two other 8-foot legs for the other platform.

Assembling the X-Brace Side
Assembling an X-Brace Side

TASK B – 1 & 2: Building the X-brace sides of the platforms.

The premise for these sides is the X-braces have to cross each other  just under 5 feet for the foot rope, and they have to intersect the tops of the legs equally on each side for the hand ropes. Because of the size of the spars involved, and the necessity for very secure connections that do not shift, use 20-foot lashing ropes and two Scouts for each X-brace square lashing.

1) Lay out two 8-foot legs side by side. Space the spars apart so that the distance from the middle of each spar, at both the top and bottom ends, is 40 inches. Use a tape measure. Also, make sure the butt ends are at the bottom and absolutely even. Starting 6 inches up from the butt end, connect the legs by lashing on a 4-foot ladder rung as a leg spreader, directly above the 6-inch mark, with tight square lashings.

Schematic of X-Brace Sides
Schematic of X-Brace Sides

With a tape measure, mark 56 inches up from the butt end of each leg.

Temporarily stretch a piece of binder twine over each 56-inch mark and tie it to each leg to help define where this intersecting line lies. It’s at the middle of this line where the X-braces need to cross so that the foot rope will extend just underneath the floor spars of the platform.

Lay out an 8-foot X-brace spar diagonally in such a way that the top end lays over one leg about 4 inches from the top of the leg, and extends out approximately 6 inches from the side. Angle the spar so that it will cross the middle of the intersecting line (56 inches up from the butt ends of the platform legs). Line up the bottom end of this X-brace so that it is positioned under the bottom of the opposite leg. Lash the spar in place with tight Square Lashings.

Lay out a second 8-foot X-brace spar on top of both legs so that it creates an X.  Angle this spar so that it will cross the middle of the intersecting line (56 inches up from the butt ends of the platform legs). Make sure this spar also extends out approximately 6 inches from the side and that it intersects the leg at the same distance from the top as the X-brace on the other side. Lash this spar in place over both legs with a square lashing. It’s between the top of the front legs and the extension of the X-braces that the hand ropes will be supported.

Now, with a diagonal lashing, lash the middle of  both 8-foot X-braces springing them together where they cross, using a 20-foot lashing rope.

2) Repeat the whole process with the two remaining 8-foot legs.

Schematic of Connecting Side
Schematic of Connecting Sides

TASK C – 1 & 2: Connecting the Ladder and X-brace sides. (If Task E has already been completed, before joining the ladder and X-brace sides, carry the two completed sides for each platform to the approximate location where they will eventually be positioned.)

1) Turn both a ladder side and an X-brace side up horizontally, parallel to one another. On the X-brace side, make sure the leg spreader and the X-brace spars are facing out. Space the legs apart so that the distance from the middle of each leg, at both the top and bottom ends, is 40 inches. Use a tape measure. Also, make sure the butt ends are absolutely even. With tight Square Lashings, join both sides by lashing a 4-foot side base spreader to the legs just below the bottom leg spreaders with a 20-foot lashing rope.

On the inside of the platform, using a 20-foot lashing rope, lash a 4-foot platform support to both legs so that the top edge comes up to 58 inches on both sides (directly under and as close as possible to the top ladder rung on the ladder side.). We will be laying the floor spars on top of this support.

Lash a 4-foot hand rail (same as ladder rung) to the top of both legs.

Lay a 6-foot diagonal side brace diagonally over both legs, between the base spreader and platform spreader, and lash in place using square lashings.

To join the other side, carefully lift and roll the platform over 180°, supporting the spars as much as possible, and repeat the above steps.

2) Repeat the whole process to join the ladder side and X-brace side of the other platform.

TASK D: Stand the platforms upright. With three Scouts lifting at the ground-level handrail, and two to three pulling on the other handrail, raise the platform to an upright position. If TASK E has been completed, we can proceed to Task G.

TASK E: Site preparation. Begin by stretching a length of binder twine along the center line of where the ropes will span. Drive a tent stake into the ground marking the center.

Working from the center, measure 12-1/2 feet toward each end and drive another tent stake to mark where the X-braces of each platform are to be placed. They should be 25 feet apart. Then with two other tent stakes, mark out another 14′ to where the anchors are to be built.

25' span, 4' platforms, 10' to anchors
25-foot span, 4-foot platforms, 10 feet to anchors
Log Stake Anchor Diagram. Click image for larger view.
Log Stake Anchor Diagram

TASK F – 1 & 2: Build the anchors. The foot and hand ropes will be attached to anchors at both ends.

1 & 2) Build a log-and-stake anchor (also known as a log and picket holdfast), 14 feet from where the X-braces of each platform are to be placed. To make the log-and-stake anchors, place one of the 4-foot x 4-inch logs perpendicular to the pull of the line, 14 feet from where the X-brace side will be. Drive in a row of four pioneering stakes spaced evenly in front of the log, leaning them back at a 45° angle. Slip a rope grommet through an O-ring and then slip the ends of the grommet around the log (see diagram). Drive a second row of pioneering stakes 24 inches behind the front stakes. Then anchor the front pioneering stakes to the rear pioneering stakes with a tourniquet made of binder twine or rope using four tent stakes. After twisting the tourniquet tight, hammer the tent stake into the ground to keep it from loosening.

TASK G – 1 & 2: Position the platforms. All hands on deck! Move both upright platforms into position no more than 25 feet apart. Place them on the binder twine that marks the center line of the bridge, making sure the X-braces of each are facing each other 10 feet from the center mark.

Bridge in Operation at a Council-wide Scout Expo
Bridge in Operation at a Council-wide Scout Expo

TASK H – 1 & 2: Lash on the floor. Lay 4-inch floor spars on top of the platform supports so that the ends extend out evenly on each side. Using the Double Floor Lashing and the 35-foot lashing ropes, lash the floor securely in place.

TASK I – 1-8: Add anchors for platform guy lines. For added stability, we’ll be adding four guy lines to each platform. To start, measure 10 feet, 45° out from each leg and drive in a 1-1 anchor.

TASK J – 1-8: Secure the platforms. Attach one of the 25-foot x 3/8-inch guy lines to each leg, directly above the floor spars, with a roundturn with two half hitches.

Extend the guy line down to the corresponding 1-1 anchor and attach it to the anchor with a rope tackle. Repeat this process at each leg.

TASK K: Foot rope. First place a piece of heavy canvas (called a “saddle”) in the top V formed by the X-braces. This will protect the foot rope and allow it to slide a little as needed.

If the foot and hand ropes are not already laid out during Task E, two Scouts will be needed to stretch the foot rope out, aligning the center of the rope with the center stake along the binder twine.

Next, lay the ends of the rope over the saddle in the V formed by the X-braces on each platform. Then, maintaining the rope’s center alignment between the platforms, extend the rope under the platforms, through the ladder sides and pulling it somewhat taut, thread the ends through the O-rings attached to the log-and-stake anchors. Tie these off temporarily with a roundturn with two half hitches.

TASK L: Hand ropes. Two Scouts will be needed to stretch the hand ropes out on either side of the foot rope, aligning the center of each with the center stake along the binder twine.

Climb the platforms and place saddles in the crotch between the X-brace extensions and the front legs.  Maintaining the center alignment between the platforms, place one hand rope over its corresponding saddles. Then extend the rope down, crossing it over the outside of the top ladder rung, pull it taut, and thread the ends through the O-rings attached to the log-stake-anchors. Tie these off with a roundturn with two half hitches. Repeat the process for the other hand rope.

Good Show!

TASK M: Stringer ropes. Now add the stringer ropes that will go from the foot rope to the hand ropes. Start by tying the center of an 8-foot long stringer rope at the center of the foot rope, using a clove hitch. The stringer rope is tied around the foot rope so that both ends are 4 feet long. Add two more stringer ropes on both sides of the center stringer rope (so there are five stringer ropes in all), tying them about 4 feet apart.

Tie one end of each stringer rope to one of the hand ropes, again using a clove hitch. Then do the same with the other ends of the stringer ropes, attaching them to the other hand rope.

TASK N: Tighten the foot rope and hand ropes. Now you can put a strain on the foot rope. Undo the Roundturn with Two Half Hitches, and make a rope tackle on each end of the foot rope. Two Scouts will need to adjust the tension at each rope tackle so that the middle of the rope stays midway between the platforms.

As needed, adjust the tension of the hand ropes by tightening them at the anchors and retying the roundturn with two half hitches.

Final testing. With caution, one crew member can get on the bridge as all lashings, anchors, and knots are observed by the safety officer and all other crew members. Make adjustments as required.

Safe operation calls for only one Scout to be on the foot rope of the monkey bridge and up to two on either platform at a time.

7 thoughts on “Double Platform Monkey Bridge”

  1. Just found your site, and I have to admit being a bit excited by it (I miss the tall towers of old…)

    Anyway, I want to point out that your schematic for part B is off … it indicates (to me) the center of the X 56″ above the bottom bar, which would put it 62″ above the butt end (which is the wrong side of 5′). The directions clearly state 56″ above the butt end.

    Regardless, BEAUTIFUL project, and awesome site. I’m excited to see people doing pioneering in scouting still!

    1. You’re so right! The arrow on the schematic looks like it’s pointing to the base support when it should really extend down to a point level with the butt ends. Thanks for your astute observation!

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