FIELD ENGINEERING
=1109.= The following, from the =Engineer Field Manual=, together with
the elements of field engineering covered in Chapter XI, on
=Obstacles=, will give the company officer a good, working knowledge
of those parts of field engineering for which he is most likely to
have need.
Bridges
=1111. Dimensions and guard rail.= A roadway 9 ft. wide in the clear
should be provided to pass infantry in fours, cavalry two abreast, and
military wagons in one direction; a width of 6 ft. will suffice for
infantry in column of twos, cavalry in single file, and field guns
passed over by hand.
The _clear width_ of roadway of an ordinary highway bridge should not
be less than 12 ft. for single track, or 20 ft. for double track.
The _clear head room_ in ordinary military bridges should not be less
than 9 ft. for wagons and cavalry; for highway bridges not less than
14 ft.
Ramps at the ends of a bridge, if intended for artillery, should not
be steeper than 1 on 7. For animals, slopes steeper than 1 on 10 are
inconvenient.
If the bridges are high, hand rails should be provided. A single rope
may suffice, or it may have brush placed upon it to form a screen.
A guard rail should be provided along each side of the roadway, near
the ends of the flooring planks. In hasty bridges it may be secured by
a lashing or lashings through the planking to the stringer underneath.
Otherwise it may be fastened with spikes or bolts.
=1112. Spar bridges.=--This name is applied to bridges built of round
timbers lashed together. Intermediate points of support are provided
by inclined frames acting as struts to transmit weight from the middle
of the bridge to the banks. The single-lock and double-lock bridges
with two and three spans of 15 ft., respectively, are the ones of most
utility.
The first step in constructing a spar bridge is to measure the gap to
be bridged and select the position of the footings on either bank.
Determine the distance from each footing to the middle point of the
roadway if a single-lock, or the two corresponding points of a
double-lock bridge. Next determine and mark on each spar except the
diagonals the places where other spars cross it. The marking may be
done with chalk, or with an ax. If possible a convenient notation
should be adopted. As, for example, in marking with chalk, a ring
around the spar where the edge of the crossing spar will come, and a
diagonal cross on the part which will be hidden by the crossing spar.
A simple way to determine the length of spars is the following: Take
two small lines somewhat longer than the width of the gap, double each
and lash the bights together. Stretch them tightly across the gap so
that the lashing comes at the middle as at _A_, Fig. 8. Release one
end of each and stretch it to the footing on the same side as
indicated by the dotted lines. Mark each line at the footing _C_ or
_C'_, and at the position chosen for the abutment sill, _B_ or _B'_.
Cut the lashing and take each piece of rope to its own side. The
distances _AB_ and _AB'_ are the lengths between the transoms, and
with 2 ft. added give the length of road bearers required. The
distances _AC_ and _AC'_ are the lengths of struts from butt to top of
transom, and with 3 ft added, give the total length of spars required.
For a double lock bridge, a piece of rope of a length equal to the
length of the middle bay replaces the lashing. If the banks are not
parallel, a measurement should be taken on each side of the bridge.
If desired, a section of the gap may be laid down on the ground in
full size and the lengths of spars determined by laying them in place.
This method, though given as standard by all authorities, requires
more time and more handling of material than the other and gives no
better results.
The construction of a frame is shown in Fig. 1, and the system of
marking in Fig. 2. The arrangement of frames to form a single lock
bridge is shown in Figs. 3 and 4, and a double lock bridge in Fig 6.
[Illustration: Fig. 1]
[Illustration: Fig. 2]
[Illustration: Fig. 3]
[Illustration: Fig. 4]
[Illustration: Fig. 5]
[Illustration: Fig. 6]
[Illustration: Fig. 7]
[Illustration: Fig. 8]
[Illustration: Fig. 9]
=1113. Construction of single-lock bridges=, Figs. 3, 4, and
5.--Suitable for spans of 30 ft. or less. The two frames lock together
at the center of the span; their slope must not be more than 4 on 7.
The bridge can be erected by two or three noncommissioned officers
and 20 men, one-half on each side of the gap. Heavy spars require more
men.
The footings at _A_ and _B_ must be firm, horizontal if possible, and
at right angles to the axis of the bridge. In a masonry pier they may
be cut out. In firm soil a simple trench will suffice. In yielding
soil a plank or sill must be laid in the trench. The frames are made
of such length as to give a slight camber to the bridge, which may be
increased to allow for probable settlement of the footings. The inside
dimension of one frame is made slightly greater than the outside
dimension of the other, so that one frame may fall inside of the other
when hauled into position. For a 9 ft. roadway the standards of the
narrow (inside) frame should be 9 ft. 6 ins. apart at the transom and
10 ft. 6 ins. at the ledger, in the clear, and the other (outside)
frame 1 ft. 6 ins. wider throughout.
A frame is constructed on each bank. The standards are laid on the
ground in prolongation of the bridge, butts toward the bank. The
ledgers are lashed on _above_ and the transoms _beneath_ the standards
at the positions marked. The diagonal braces are lashed to the
standards, two butts and one tip above the latter, and to each other.
Before the braces are lashed the frame must be square by checking the
measurements of the diagonals.
If necessary, pickets for the foot and guy ropes are driven, the
former about 2 paces from the bank and 4 paces on each side of the
axis of the bridge; the latter about 20 paces from the bank and 10
paces on each side of the axis. The foot ropes, _CC_, Fig. 5, are
secured by timber hitches to the butts of the standards and the back
and fore guys, _DD_ and _EE_, to the tips the fore guys are passed
across to the opposite bank. The guys of the _narrow_ frame should be
_inside_ the guys and standards of the wide frame.
The frames are put into position one after the other, or
simultaneously if there are enough men. A man is told off to each foot
rope and one to each back guy to slack off as required, two turns
being taken with each of these ropes around their respective pickets.
The other men raise the frame and launch it forward, assisted by the
men at the fore guys, until the frame is balanced on the edge of the
bank. The frame is then tilted until the butts rest on the footing, by
slacking off the foot ropes and hauling on the fore guys, Fig. 5.
After the head of the frame has been hauled over beyond the
perpendicular, it is lowered nearly into its final position by
slacking off the back guys. When the two frames are in this position
opposite each other, the narrow frame is further lowered until its
standards rest upon the transom of the other. The wider (outer) frame
is then lowered until the two lock into each other, the standards of
each resting upon the transom of the other.
The center or fork transom, Figs. 3 and 4, is then passed from shore
and placed in the fork between the two frames. This forms the central
support to receive a floor system of two bays, built as already
described.
The estimated time for construction of such a bridge is about one hour
if the material is available and in position on both sides of the
stream. The construction of the roadway requires about twenty minutes;
forming footings in masonry about one hour.
=1114. Construction of double-lock bridge=, Fig. 6.--Suitable for
spans not exceeding 45 ft., and consisting of two inclined frames
which lock into a connecting horizontal frame of two or more distance
pieces, with cross transoms, dividing the gap to be bridged into three
equal bays of about 15 ft. The force required is two or three
noncommissioned officers and 25 to 50 men; the time for construction,
except roadway, about two and one-half hours; extra time to be allowed
for difficult footings.
The width of gap is measured, the position of footings determined, and
the length of standards from butt to transom determined and marked as
before.
The inclined frames in this case are built of equal widths, launched
as before, and held by guys just above their final position. Two
stringers are launched out from each bank to the main transom. The
distance pieces, Fig. 6, are put into position inside the standards,
using tackle if necessary, and the road transoms are placed and lashed
to the distance pieces at the places marked. Both frames are now
lowered until they jam.
=1115. Roadway of spar bridge.=--For infantry in fours crowded the
transoms should have a diam. of not less than 9 ins. for a span of 15
ft. Five stringers 2 ft. 3 ins. c. to c., and 6 ins. diam. at the tip
will suffice. If the sticks vary in size, the larger ones should be
notched down on the transom so as to bring the tops in the same plane.
The stringers should be long enough to overlap the transoms, and
should be lashed together at each tip. The floor is held down by side
rails over the outside stringers and lashed to them. If lumber can not
be obtained, a floor may be made, of small spars, the interstices
filled with brush, and the whole covered with loam or clay; Figs. 7
and 9.
Corduroy Roads
=1116. Corduroying= is done by laying logs crosswise of the road and
touching each other. The result will be better if the logs are nearly
of the same size. The butts and tips should alternate. If the logs are
large the spaces may be filled with smaller poles. The bottom tier of
logs should be evenly bedded and should have a firm bearing at the
ends and not ride on the middle. The filling poles, if used, should be
cut and trimmed to lie close, packing them about the ends if
necessary. If the soil is only moderately soft the logs need be no
longer than the width of the road. In soft marsh it may be necessary
to make them longer.
The logs may be utilized as the wearing surface. In fact this is
usually the case. They make a rough surface, uncomfortable for
passengers and hard on wagons and loads, but the resistance to
traction is much less than would be expected, and the roughness and
slightly yielding surface make excellent footing for animals. Surface
corduroy is perishable and can last but a short time. In marshes,
where the logs can be placed below the ground-water level, they are
preserved from decay, and if any suitable material can be found, to
put a thin embankment over them, a good permanent road may be made.
Any tough, fibrous material may be used to temporarily harden the
surface of a road. Hay or straw, tall weeds, corn and cane stalks
have been used to good advantage. Such materials should be laid with
the fibers crosswise of the road, and covered with a thin layer of
earth, thrown on from the sides; except in sand, when it is better to
dig a shallow trench across the road, fill it with the material and
then dig another trench just in front of and in contact with the first
and throw the sand from it back onto the material in the first trench,
etc.
Brush work
=1117. A fascine= is a cylindrical bundle of brush, closely bound. The
usual length is 18 ft. and the diam. 9 ins. when compressed. Lengths
of 9 and 6 ft., which are sometimes used, are most conveniently
obtained by sawing a standard fascine into 2 or 3 pieces. The weight
of a fascine of partially seasoned material will average 140 lbs.
Fascines are made in a =cradle= which consists of five trestles. A
=trestle= is made of two sticks about 6-1/2 ft. long and 3 ins. in
diam, driven into the ground and lashed at the intersection as shown
in Fig. 10. In making a cradle, plant the end trestles 16 ft. apart
and parallel. Stretch a line from one to the other over the
intersection, place the others 4 ft. apart and lash them so that each
intersection comes fairly to the line.
=To build a fascine=, straight pieces of brush, 1 or 2 ins. at the
butt, are laid on, the butts projecting at the end 1 ft. beyond the
trestle. Leaves should be stripped and unruly branches cut off, or
partially cut through, so that they will lie close. The larger
straighter brush should be laid on the outside, butts alternating in
direction, and smaller stuff in the center. The general object is to
so dispose the brush as to make the fascine of uniform size, strength,
and stiffness from end to end.
When the cradle is nearly filled, the fascine is compressed or
=choked= by the =fascine choker=, Fig. 11, which consists of 2 bars 4
ft. long, joined at 18 ins. from the ends by a chain 4 ft. long. The
chain is marked at 14 ins. each way from the middle by inserting a
ring or special link. To use, two men standing on opposite sides pass
the chain under the brush, place the short ends of the handles on top
and pass the bars, short end first, across to each other. They then
bear down on the long ends until the marks on the chain come together.
Chokers may be improvised from sticks and rope or wire.
=Binding= will be done with a double turn of wire or tarred rope. It
should be done in 12 places, 18 ins. apart, the end binders 3 ins.
outside the end trestles. To bind a fascine will require 66 ft. of
wire.
Improvised binders may be made from rods of live brush, hickory or
hazel is the best. Place the butt under the foot and twist the rod to
partially separate the fibers and make it flexible. A rod so prepared
is called a =withe=. To use a withe, make a half turn and twist at the
smaller end, Fig. 12; pass the withe around the brush and the large
end through the eye. Draw taut and double the large end back, taking 2
half-hitches over its own standing part, Fig. 13.
When the fascine is choked and bound, saw the ends off square, 9 ins.
outside the end binders. After a cradle is made, 4 men can make 1
fascine per hour, with wire binding. Withes require 1 man more.
=A fascine revetment= is made by placing the fascines as shown in Fig.
14. The use of headers and anchors is absolutely necessary in loose
soils only, but they greatly strengthen the revetment in any case. A
fascine revetment =must always be crowned= with sods or bags.
[Illustration: Fig. 10]
[Illustration: Fig. 11]
[Illustration: Fig. 12]
[Illustration: Fig. 13]
[Illustration: Fig. 14]
[Illustration: Fig. 15]
=1118.= In all brush weaving the following terms have been adopted and
are convenient to use:
=Randing.=--Weaving a single rod in and out between pickets.
=Slewing.=--Weaving two or more rods together in the same way.
=Pairing.=--Carrying two rods together, crossing each other in and out
at each picket.
=Wattling.=--A general term applied to the woven part of brush
construction.
=1119. A hurdle= is a basket work made of brushwood. If made in
pieces, the usual size is 2 ft. 9 ins. by 6 ft., though the width may
be varied so that it will cover the desired height of slope.
A hurdle is made by describing on the ground an arc of a circle of 8
ft. radius and on the arc driving 10 pickets, 8 ins. apart, covering 6
ft. out to out, Fig. 15. Brush is then woven in and out and well
compacted. The concave side of a hurdle should be placed next the
earth. It wraps less than if made flat.
=In weaving the hurdle=, begin randing at the middle space at the
bottom. Reaching the end, twist the rod as described for a withe, but
at one point only, bend it around the end picket and work back. Start
a second rod before the first one is quite out, slewing the two for a
short distance. Hammer the wattling down snug on the pickets with a
block of wood and continue until the top is reached. It improves the
hurdle to finish the edges with two selected rods paired, Fig. 16. A
pairing may be introduced in the middle, if desired, to give the
hurdle extra endurance if it is to be used as a pavement or floor. If
the hurdle is not to be used at once, or if it is to be transported,
it must be sewed. The sewing is done with wire, twine, or withes at
each end and in the middle, with stitches about 6 ins. long, as shown
in Fig. 16. About 40 ft. of wire is required to sew one hurdle. No. 14
is about the right size, and a coil of 100 lbs. will sew 40 hurdles.
Three men should make a hurdle in 2 hours, 2 wattling and the third
preparing the rods.
=1120. Continuous hurdle.=--If conditions permit the revetment to be
built in place, the hurdle is made continuous for considerable
lengths. The pickets may be larger; they are driven farther apart, 12
or 18 ins., and the brush may be heavier. The construction is more
rapid. The pickets are driven with a little more slant than is
intended and must be anchored to the parapet. A line of poles with
wire attached at intervals of 2 or 3 pickets will answer. The wires
should be made fast to the pickets after the wattling is done. They
will interfere with the wearing if fastened sooner. Two men should
make 4 yds. of continuous hurdle of ordinary height in one hour.
=1121. Brush revetment.=--Pickets may be set as above described and
the brush laid inside of them without weaving, being held in place by
bringing the earth up with it. In this case the anchors must be
fastened before the brush laying begins. The wires are not much in the
way in this operation.
=1122. Gabion making.--A gabion= is a cylindrical basket with open
ends, made of brush woven on pickets or stakes as described for
hurdles. The usual size is 2 ft. outside diam. and 2 ft. 9 ins. height
of wattling. On account of the sharp curvature somewhat better brush
is required for gabions than will do for hurdles.
=The gabion form=, Fig. 17, is of wood, 21 ins. diam., with
equidistant notches around the circumference, equal in number to the
number of pickets to be used, usually 8 to 14, less if the brush is
large and stiff, more if it is small and pliable. The notches should
be of such depth that the pickets will project to 1 in. outside the
circle. The pickets should be 1-1/4 to 1-3/4 ins. diam., 3 ft. 6 ins.
long and sharpened, half at the small and half at the large end.
=To make a gabion=, the form is placed on the ground, level or nearly
so, and the pickets are driven vertically in the notches, large and
small ends down, alternately. The form is then raised a foot and held
by placing a lashing around outside the pickets, tightened with a rack
stick, Fig. 18. The wattling is randed or slewed from the form up. The
form is then dropped down, the gabion inverted and the wattling
completed. If the brush is small, uniform, and pliable, pairing will
make a better wattling than randing. If not for immediate use, the
gabion must be sewed as described for hurdles, the same quantity of
wire being required.
[Illustration: Fig. 16]
[Illustration: Fig. 17]
[Illustration: Fig. 18]
[Illustration: Fig. 19]
[Illustration: Fig. 20]
[Illustration: Fig. 21]
The gabion, when wattled and sewed, is completed by cutting off the
tops of the pickets 1 in. from the web, the bottom 3 ins., the latter
sharpened after cutting, and driving a carrying picket through the
middle of its length and a little on side of the axis. See that the
middle of this picket is smooth. Three men should make a gabion in an
hour.
Gabions may be made without the forms, but the work is slower and not
so good. The circle is struck on the ground and the pickets driven at
the proper points. The weaving is done from the ground up and the
entire time of one man is required to keep the pickets in proper
position.
=If brush is scarce=, gabions may be made with 6 ins. of wattling at
each end, the middle left open. In filling, the open part may be lined
with straw, grass, brush cuttings, or grain sacks, to keep the earth
from running out.
=1123. Gabion revetment.=--The use of gabions in revetments is
illustrated in Fig. 20. If more than two tiers are used, the
separating fascines should be anchored back. Gabion revetments should
be crowned with sods or bags.
The advantages of the gabion revetment are very great. It can be put
in place without extra labor and faster and with less exposure than
any other. It is self-supporting and gives cover from view and partial
cover from fire quicker than any other form.
Several forms of gabions of other material than brush have been used.
Sheet iron and iron and paper hoops are some of them. The iron
splinters badly, is heavy, and has not given satisfaction. If any
special materials are supplied the method of using them will, in view
of the foregoing explanation, be obvious.
=1124. Timber or pole revetment.=--Poles too large for use in any
other way may be cut to length and stood on end to form a revetment.
The lower ends should be in a small trench and have a waling piece in
front of them. There must also be a waling piece or cap at or near the
top, anchored back. Fig. 21 shows this form.
=1125. Miscellaneous revetments.=--Any receptacles for earth which
will make a stable, compact pile, as =boxes=, =baskets=, =oil or other
cans=, may be used for a revetment. =Barrels= may be used for gabions.
=Canvas= stretched behind pickets is well thought of in a foreign
service. If the soil will make =adobe=, or sun-dried bricks, an
excellent revetment may be made of them, but it will not stand wet
weather.
Knots
=1126.= =Square= or =reef knot=, Fig. 22, commonly used for joining
two ropes of the same size. The standing and running parts of each
rope must pass through the loop of the other in the same direction, i.
e., from above down ward or vice versa; otherwise a _granny_, is made,
which is a useless knot that will not hold. The reef knot can be upset
by taking one end of the rope and its standing part and pulling them
in opposite directions. With dry rope a reef knot is as strong as the
rope; with wet rope it slips before the rope breaks, while a double
sheet bend is found to hold.
[Illustration: Fig. 22
_Square or Reef_]
=1127. Two half hitches=, Fig. 23, especially useful for belaying, or
making fast the end of a rope round its own standing part. The end may
be lashed down or seized to the standing part with a piece of spun
yarn; this adds to its security and prevents slipping.
This knot should never be used for hoisting a spar.
[Illustration: Fig. 23
_Two half hitches_]
=1128. Clove hitch=, Fig. 24, generally used for fastening a rope at
right angles to a spar or at the commencement of a lashing. If the end
of the spar is free, the hitch is made by first forming two loops, as
in Fig. 26, placing the right-hand loop over the other one and
slipping the double loop (Fig. 27) over the end of the spar. If this
can not be done, pass the end of the rope round the spar, bring it up
to the right of the standing part, cross over the latter, make
another turn round the spar, and bring up the end between the spar,
the last turn, and the standing part, Fig. 25. When used for securing
guys to sheer legs, etc., the knot should be made with a long end,
which is formed into two half hitches round the standing part and
secured to it with spun yarn.
[Illustration: Fig. 24
_Clove hitch_]
[Illustration: Fig. 25]
[Illustration: Fig. 26]
[Illustration: Fig. 27]
=1129. Timber hitch=, Fig. 28, used for hauling and lifting spars. It
can easily be loosed when the strain is taken off, but will not slip
under a pull. When used for hauling spars, a half hitch is added near
the end of the spar, Fig. 29.
[Illustration: Fig. 28
_Timber hitch_]
[Illustration: Fig. 29
_Timber hitch and half hitch_]
=1130. Bowline=, Fig. 30, forms a loop that will not slip. Make loop
with the standing part of the rope underneath, pass the end from below
through the loop, over the part round the standing part of the rope,
and then down through the loop _c_. The length of bight depends upon
the purpose for which the knot is required.
[Illustration: Fig. 30
_Bowline_]
=1131. Bowline on a bight=, Fig. 31. The first part is made like the
above, with the double part of a rope; then the bight _a_ is pulled
through sufficiently to allow it to be bent past _d_ and come up in
the position shown. It makes a more comfortable sling for a man than a
single bight.
[Illustration: Fig. 31
_Bowline on a Bight_]
=1132. Sheep shank=, Fig. 32, used for shortening a rope or to pass by
a weak spot; a half hitch is taken with the standing parts around the
bights.
[Illustration: Fig. 32
_Sheep shank_]
=1133. Short splice.= To make a _short splice_, Figs. 33, 34, 35,
unlay the strands of each rope for a convenient length. Bring the rope
ends together so that each strand of one rope lies between the two
consecutive strands of the other rope. Draw the strands of the first
rope along the second and grasp with one hand. Then work a free strand
of the second rope over the nearest strand of the first rope and under
the second strand, working in a direction opposite to the twist of the
rope. The same operation applied to all the strands will give the
result shown by Fig. 34. The splicing may be continued in the same
manner to any extent (Fig. 35) and the free ends of the strands may be
cut off when desired. The splice may be neatly tapered by cutting out
a few fibers from each strand each time it is passed through the rope.
Rolling under a board or the foot will make the splice compact.
[Illustration: Fig. 33
_Short splice_]
[Illustration: Fig. 34]
[Illustration: Fig. 35]
=1134. Long splice= (Figs. 36, 37).--Unlay the strands of each rope
for a convenient length and bring together as for a short splice.
Unlay to any desired length a strand, _d_, of one rope, laying in its
place the nearest strand, _a_, of the other rope. Repeat the operation
in the opposite direction with two other strands, _c_ and _f_. Fig. 37
shows strands _c_ and _f_ secured by tying together. Strands b and e
are shown secured by unlaying half of each for a suitable length and
laying half of the other in place of the unlayed portions, the loose
ends being passed through the rope. This splice is used when the rope
is to run through a block. The diameter of the rope is not enlarged at
the splice. The ends of the strands should not be trimmed off close
until the splice has been thoroughly stretched by work.
[Illustration: Fig. 36
_Long splice_]
[Illustration: Fig. 37]
=1135. Eye splice= (Figs. 38, 39, 40, 41).--Unlay a convenient length
of rope. Pass one loose strand, _a_, under one strand of the rope, as
shown in fig. 38, forming an eye of the proper size. Pass a second
loose strand, _b_, under the strand of the rope next to the strand
which secures _a_, Fig. 39. Pass the third strand, _c_, under the
strand next to that which secures _b_, fig. 40. Draw all taut and
continue and complete as for a short splice.
[Illustration: Fig. 38
_Eye splice_]
[Illustration: Fig. 39]
[Illustration: Fig. 40]
[Illustration: Fig. 41]
Lashings
=1136. To lash a transom to an upright spar=, Fig. 42, transom in
front of upright.--A clove hitch is made round the upright a few
inches below the transom. The lashing is brought under the transom, up
in front of it, horizontally behind the upright, down in front of the
transom, and back behind the upright at the level of the bottom of the
transom and above the clove hitch. The following turns are kept
outside the previous ones on one spar and inside on the other, not
riding over the turns already made. Four turns or more are required. A
couple of frapping turns are then taken between the spars, around the
lashing, and the lashing is finished off either round one of the spars
or any part of the lashing through which the rope can be passed. The
final clove hitch should never be made around the spar on the side
toward which the stress is to come, as it may jam and be difficult to
remove. The lashing must be well beaten with handspike or pick handle
to tighten it up. This is called a square shears are laid alongside of
each other with their butts on the ground, lashing.
[Illustration: Fig. 42]
=1137. Lashing for a pair of shears=, Fig. 43.--The two spars for the
points below where the lashing is to be resting on a skid. A clove
hitch is made round one spar and the lashing taken loosely eight or
nine times about the two spars above it without riding. A couple of
frapping turns are then taken between the spars and the lashing is
finished off with a clove hitch above the turns on one of the spars.
The butts of the spars are then opened out and a sling passed over the
fork, to which the block is hooked or lashed, and fore and back guys
are made fast with clove hitches to the bottom and top spars,
respectively, just above the each spar the distance from the butt to
the center of the lashing. Lay two of the spars parallel to each other
with an interval a little greater fork, Fig. 44.
[Illustration: Fig. 43]
[Illustration: Fig. 44]
=1138. To lash three spars together as for a gin or tripod.=--Mark on
than the diameter. Rest their tips on a skid and lay the third spar
between them with its butt in the opposite direction so that the marks
on the three spars will be in line. Make a clove hitch on one of the
outer spars below the lashing and take eight or nine loose turns
around the three, as shown in Fig. 45. Take a couple of frapping turns
between each pair of spars in succession and finish with a clove hitch
on the central spar above the lashing. Pass a sling over the lashing
and the tripod is ready for raising.
[Illustration: Fig. 45]
=1139. Holdfasts.=--To prepare a fastening in the ground for the
attachment of guys or purchases, stout pickets are driven into the
ground one behind the other, in the line of pull. The head of each
picket except the last is secured by a lashing to the foot of the
picket next behind, Fig. 46. The lashings are tightened by rack
sticks, the points of which are driven into the ground to hold them in
position. The distance between the stakes should be several times the
height of the stake above the ground.
[Illustration: Fig. 46]
Another form requiring more labor but having much greater strength is
called a "_deadman_," and consists of a log laid in a transverse
trench with an inclined trench intersecting it at its middle point.
The cable is passed down the inclined trench, takes several round
turns on the log, and is fastened to it by half hitches and marlin
stopping, Figs. 47, 48, 49. If the cable is to lead horizontally or
inclined downward, it should pass over a log at the outlet of the
inclined trench, Fig. 48. If the cable is to lead upward, this log is
not necessary, but the anchor log must be buried deeper.
[Illustration: Fig. 47]
[Illustration: Fig. 48]
[Illustration: Fig. 49]