Tag Archives: scout engineering

Prestressed Triple Walkway Bridge

STRONG Bridge!
STRONG Bridge!

For information, contact: Albert Crowsky, 847-809-4593

Sound engineering, deliberations, and a dose of creative improvisation entered into the picture during the building process.
Sound engineering, deliberations, and a dose of creative improvisation entered into the picture during the building process.
The finished bridge is decorated with pennants.
The finished bridge is decorated with pennants.

JAMBOREE PIONEERING AREA: BRIDGES

JAMBOREE PIONEERING AREA: MAIN PAGE

The Monkey Bridge at the 2013 National Jamboree

Modified Double A-Frame Monkey Bridge
Modified Double A-Frame Monkey Bridge

For those familiar with the traditional Double A-Frame Monkey Bridge design, a couple of noticeable modifications will be apparent from the outset. (Click on the photos for larger views.) Scout Engineering is a fluid undertaking, and frequently variations are necessary. Just as frequently an alteration or change can be deemed a desirable improvement. In the case of this double A-frame design, the consensus of opinion is these modifications are really neat, and I’m sure Adolph Peschke would concur.

  1. Instead of  separate shorter ledgers for each pair of adjoining A-frames, connect four legs with one longer ledger. The length can actually be the same as that of the legs, e.g. four 8-foot legs and one 8-foot ledger at the bottom, or for a larger structure, 10 or 12-foot legs and ledger. (A spar longer than the legs does yield more flexibility when lashing together the four legs.)
  2. Ladder rungs! Lashing a couple of cross pieces between the legs of the left A-frame cancels the need to climb on board the bridge using the foot and hand ropes! Same thing of the other side. Crossers use the rungs and have a safe and easy way to get on and off the bridge, AND eliminate the often awkward balancing act on the ropes between the A-frames and the anchors. There’s an added advantage too: no more excess stress and strain on the ropes near the anchors.
Crossing the Monkey Bridge in the Pioneering Area of the 2013 National Jamboree
Crossing the Monkey Bridge in the Pioneering Area of the 2013 National Jamboree

JAMBOREE PIONEERING AREA: BRIDGES

JAMBOREE PIONEERING AREA: MAIN PAGE

 

A Better Clothes Drying Rack

You’ve got to love this design. It’s compact, it’s sturdy, and it’s ingenious!

This drying rack is based on suspending two concentric, equilateral triangles to make six cross sections for hanging wet clothing or towels during a long term encampment, and there’s no reason you can’t put it up on an overnighter if there’s a practical need. All that’s been said before regarding the advantages of this kind of campsite improvement apply to this simple camp gadget:

  • It takes up less space while drying more wet things.
  • It eliminates the clutter of clothing and towels haphazardly strewn around on tables, tree branches, tent platforms, or overcrowded on a disorganized array of drooping clothes lines.
  • It can be set up in a location where there is the most sunshine.
  • It’s especially useful when camping in an open area with few trees.

Materials (adapt these as you like)

  • three 4-foot  x 1-inch sticks
  • three 5-foot x 1-inch sticks (Scout staves are ideal)
  • one 6-foot x 1-1/2 to 2-1/2-inch straight pole for the upright (or an additional 5-foot Scout stave)
  • one 30-inch pioneering stake
  • eight camp gadget lashing ropes (6 to 10-foot)
  • three 15-foot lashing ropes
  • three small stakes
Two Equilateral Triangles

Procedure

Lash the triangles. Start by lashing together two equilateral triangles, one smaller for the top (three 4-foot sticks), and the larger one for the bottom (three 5-foot staves). Use square lashings. One easy way is to lash two at 90° and then bend them in and tie the third square lashing to make the triangle. This yields a nice, tightly-lashed triangle, (but be careful you’re not putting too much stress on the ropes and poles when preparing to apply the third lashing).

Pioneering Stake
Pioneering Stake

Erect the upright. Pound in a pioneering stake and lash the 6-foot pole to it securely with two tight strop lashings or round lashings. Making this upright stand up vertically without moving or wobbling at all is a key to a good and sturdy clothing dryer. So, solidly pound in the stake and make sure it’s as straight as possible. Also, make sure the lashings are well-tied and tight.

—> ALTERNATIVE APPROACH: A clothes drying rack can be erected without having to either pound in a stake or sink the center pole, by using the same principle as when erecting a flagpole. The key is using the support ropes as guylines. SEE PHOTO.

Rolling Hitches
Rolling Hitches

Attach the triangles. Lay the triangles on the ground over the upright, first the larger triangle, and then the smaller one on top.

Using rolling hitches, tie the three 15-foot support ropes to the top of the upright. (Roundturns with two half hitches also work just fine.)

Tie each corner of the smaller triangle to a support rope so it will be suspended about 5 feet above the ground. Use clove hitches which can be adjusted as necessary to assure the triangle hangs evenly and the 4-foot sticks are horizontal. Continuing with each of the three support ropes, repeat this process for the larger triangle so that it will hang about 4 feet above the ground.

Clove Hitch
Clove Hitch
Tautline at Stake
Taut Line Hitch at Stake

Anchor the support ropes. Hammer in a small stake a foot or so out, in line with each corner of the bottom triangle. Using the remaining length of the support ropes, attach them to the stakes with a simple taut-line hitch. This will further stabilize the clothing dryer and enable you to make fine-tune adjustments to the way the triangles lay. (You can also just make them fast to the stakes with a roundturn with two half hitches, or another clove hitch.)

Better Clothes Drying Rack
An assembled clothes drying rack at the 2013 Jamboree gets the once over.

Making a Trestle

Lashing together a Trestle from Bamboo Spars
Lashing together a Trestle from Bamboo Spars (note the friction tape)

Link to: Older Pamphlet InfoThe following text is by Adolph E. Peschke as presented in the 1998 printing of the 1993 edition of the Pioneering Merit Badge Pamphlet:

A trestle is the basic component for building a bridge in a pioneering project. It is used to support the walkways.

The most basic form of a trestle is an H-frame. It consists of two legs, two ledgers, and two cross braces (see figure 125). When building a bridge, the top ledger is also called a transom. This is the part that supports the walkways.

To make an H-frame trestle, the two ledgers are lashed near the top and bottom of the legs and the cross braces are added, lashing them to the legs.

Figure 125
Figure 125

All of the lashing on the H-frame trestle is done with two types of lashings: a square lashing and a diagonal lashing. The ledgers are lashed to the legs with square lashings. Although it might not look like it, the cross braces are also lashed to the legs with square lashings, not a diagonal lashing. A diagonal lashing is used to lash the two cross braces together where they cross in the center.

When setting out to build an H-frame trestle, choose the two spars for legs first. These spars can be most any length, depending on the type and height of the structure you’re building.

To build a basic H-frame, lay the two legs on the ground with the two butt ends of the spars at the same end and even with each other. Then add the ledgers.

Ledgers. The ledgers are spars that are typically 2 to 2-1/2 inches in diameter. They are lashed to the legs with square lashings. Any of the three square lashings (shown in this pamphlet) can be used. The position of the ledgers on the legs will depend on the structure you’re building. There are a couple of general rules to keep in mind.

Assembling the X-Brace Side
This Trestle is One of Several Subassemblies in a Larger Project

First, always keep the legs parallel and the butt ends of the legs even with each other as you’re lashing on the ledgers.* If you don’t, the trestle will stand crooked when you stand it up. As you add the ledgers, they should not stick out too far beyond the legs. You must leave enough room at the ends to tie the lashing, Any more will get in the way.

When using a Traditional Square Lashing or a Modified Square Lashing to tie the ledgers to the legs, be sure the starting clove hitch is placed on the leg so it’s beneath the ledger. When the clove hitch is below the ledger it will support it when the trestle is stood upright. As you tie the lashings, make sure they ar all very tight.

If you use a Japanese Mark II Square Lashing, you can start this lashing with a clove hitch in the middle of the rope to help support the ledger.

Cross braces. Next, the cross braces are added. The cross braces are spars that are usually 2 inches in diameter. They are lashed to the legs in a particular sequence.

First, flip the trestle over and work on the opposite side from the ledgers (see figure 125). Lash one cross brace to the back side of both legs. As mentioned before, use a square lashing (not a diagonal lashing) to attach the ends of the cross braces to the legs.

The second cross brace is added so that the bottom end is on the same side as both ends of the first cross brace. The other end is placed on the front side, the side with the ledgers (see figure 125). This is done so that the cross braces are standing slightly apart. There will be a gap where they cross at the center.

Trestle built with 5' Scout Staves
Trestle built with 5′ Scout Staves

Diagonal Lashing. After the ends of the ledgers and the cross braces are lashed to the legs, stand the trestle up on end. Adjust the trestle so that the legs are parallel. Also check to see that the top ledger is parallel to the ground. If it is not, lower the trestle, untie the lashing, and adjust it.

When the legs are parallel and the top ledger is parallel to the ground, you’re ready to tie the diagonal lashing to the cross braces while the trestle is standing upright. This lashing is very important to the strength of the trestle.

The diagonal lashing creates triangles that are important to stiffen the arrangement of the spars and to keep the trestle from racking. Look around at steel towers, bridges, or buildings being erected and you will see the triangle used in many places for the same reasons as we use it to build a trestle.

When the cross braces are lashed to the legs, there is a slight gap between them where they crossed at the center. A diagonal lashing is used here because it starts out with a timber hitch. The timber hitch pulls the cross braces tightly together. This adds strength to the whole trestle. You have to keep a strain on the lashing rope as you complete the diagonal lashing with three wraps in each direction around the X. Then make two frapping turns between the cross braces to pull the wraps tight. Finally finish by tying another clove hitch on one cross brace.

Once the possibility of racking has been taken care of with the diagonal lashing, the trestle’s vertical legs provide support for a large downward load. Since this is a downward force, also known as a shearing force, the legs don’t have to be very big. In fact, the overall shape of the trestle is an engineered structure that is able to support quite a bit of weight with rather small-diameter spars for legs.

* An exception is building a Single Lock Bridge when the top of one trestle has to fit between the legs of the other.

 

Hand Wash Station

This Wash Station is a Great First Class Camp Gadget!
Washing up before lunch.

This wash station is the ideal First Class Camp Gadget! It’s sturdy, portable, and very useful when camping away from washroom facilities. Inherent in its design is a sound approach to a variety of pioneering concepts and skills. When this project’s built with all the lashings tight and all the legs, cross bar, and support pieces properly positioned, it’s a fine example of a well-engineered, highly functional camp gadget. Each of the three legs making up the tripod gets a lashed on support piece, and the wash station’s stability stems from the fact the design contains three triangles.

Scouts sharing the work to lash together a wash station.
Getting it done!

To start, you’ll need six good, straight sticks as follows:

  • two 2-foot x 3/4 to 1-inch for the leg braces
  • two 4-foot x 3/4 to 1-inch for the back leg and crossbar
  • two 5-foot x 3/4 to 1-inch for the front legs

For the lashings, you’ll need:

  • one 10-foot x 1/4-inch manila rope for the tripod lashing
  • six 6-foot x 1/4-inch manila ropes for the square lashings

NOTE: This and several types of camp gadgets can be happily lashed together simply using binder twine!

You’ll also need

  • bar of soap in a sock with a 3-foot cord
  • small to medium-sized towel with a 3-foot cord
  • No. 10 can with a bail or 4-quart cooking pot with a bail.

Here’s the assembly procedure:

The design for making a wash station.
Position of the sticks.

Make the tripod. Using the 10-foot rope, lash the two 5-foot sticks and one 4-foot stick together with a tight tripod lashing. The 4-foot stick should be in the middle. Make sure the “butt” ends of all three these sticks are even. Separate the legs and set the tripod up. The success of this project relies on a well-tied, tight tripod lashing.

Lash on the braces. Using four tight square lashings, with the 6-foot ropes lash one end of the 2-foot sticks to the 5-foot legs and the other end of the 2-foot sticks to the four-foot leg.

Lash on the crossbar. Using two more square lashings, tightly lash the other 4-foot stick to the top extended sections of the two 5-foot sticks to make a cross bar for the towel and soap-in-a-sock.

Add the soap, water, and towel. Tie the end of one 3-foot cord to the soap-in-a-sock and the end of the other 3-foot cord to the towel, and hang them on either side of the 4-foot crossbar.

Washing his hands before breakfast on a cold, winter camping trip.

Hang the can filled with water to the end of the 4-foot stick extending from the front of the tripod.

During the camping trip, change the water as necessary. See that the soap-in-a-sock is not left in the can after use as it will melt.

One of the beauties of using metal containers is that in cold weather, the can of water can be heated in the fire.