TITLE 2309.24 - REGIONAL FACILITIES HANDBOOK
FSH 9/85 R-10 TRANS
CHAPTER 500 - ANCHOR BUOYS
This Chapter establishes guidelines for design and location of buoys and associated
hardware for anchoring small boats under 40 feet.
A maintenance plan for installed anchors and buoys must be developed during the
design. Maintenance, with its associated costs, is mandatory to assure safety for
boaters. A diver shall inspect the chain and anchor for wear and movement. Size
and weight of the buoys shall be designed to enable inspection by Forest Service
work boats, although contracting may be used in some cases.
510 - Location.
1. Highest priority shall be the placement of buoys at existing developed
trailheads, cabins, and other marine related recreation facilities.
2. Buoy locations shall conform with the adopted ROS classification for the
area, as approved in LMP's. In some cases, buoys detract from the natural setting
and are not desired by the public. Not every anchorage needs a buoy.
3. Priority shall be given to locating buoys in areas where new anchorages are
created due to conditions preventing relatively safe anchorage. This applies, for
example, to situations with a hard or steeply sloping bottom or a lack of "swing
room" where a boat normally would not anchor, although protected and relatively
ice-free. These conditions also dictate a rigorous site evaluation and design.
4. Do not pre-empt existing natural anchorages. There have been cases in the
past where a buoy, located in the center of a good anchorage, has prevented boats
from utilizing adjacent areas because of the wider swinging area required with
normal anchor gear on those boats.
5. Locate buoys in areas relatively ice-free most of the year. Ice can carry the
buoy away as the ice pack moves out in the spring. We know of no practical way to
design for ice loading.
6. Locate buoys outside normal travel lanes, within the anchorage area.
520 - Specific Site Conditions. The following guidelines shall be used as a starting
point in the selection of a location for an anchor buoy:
1. The site shall be protected from a fetch length that exceeds one mile against
prevailing summer winds. This is a general guideline. Many other variables must
be considered.
2. The site shall be protected from excessive ebb and flood currents.
3. The site shall be free of underwater obstructions and adhere to the
following:
a. Minimum water depth shall be 12 feet at 4.5 minus tide.
b. Maximum water depth shall be 90 feet.
c. Minimum clear entrance width shall be 50 feet into anchorage.
d. For buoys, scope of chain should be 1-1/2 the high tide depth for
protected anchorages when using a typical deadweight anchor.
e. Avoid cable crossing areas.
4. Determine soil types and sediment depths of site (examples: sandy silt,
uniform sand, mud, bedrock, gravels 4 feet deep over bedrock, etc.).
5. Determine if slope of seafloor is suitable for safe anchorage.
6. Determine any hazardous/unusual seafloor conditions. For example:
a. Small sediment channels, local extreme bottom slopes, or cliff-like
topography.
b. Erratics from ice-deposited glacial detritus.
c. Sloping seafloor greater than 10 degrees.
d. Thin sediment layer above rock.
e. Layered seafloors--soft sediment over stiff/dense sediment, or vice
versa.
530 - Anchors. Anchor type shall be determined on a case-by-case basis. The
deadweight type meets most needs. The deadweight concrete sinker, or squat
clump, has proven successful and is relatively cost efficient to construct and install.
Four types are discussed below and in Chapter 1000, Appendices 1-4. The
deadweight type shall be most frequently used. Others are shown in case special
situations warrant such designs. Although this information may not be directly
applicable, it should initiate design ideas more appropriate to a local situation.
Engineering must be involved in the design of anchors for specific sites.
531 - Deadweight Anchor Type (See Appendix 1).
--Large vertical reaction component, permitting shorter mooring line scope.
--Reliable holding force, because most holding force is due to anchor mass (weight).
--Simple, on-site construction feasible, tailored to task.
--Size limited only by load-handling equipment (boom size).
--Economical; weighting material readily available.
--Reliable on thin sediment cover over rock.
--Mooring line connection easy to inspect and service using divers.
--Good energy absorber when used in conjuction with "non-yielding" anchors (piles,
embedded plate anchors).
--Good reaction to vertical load components; works well in combinations with drag
embedment anchors permitting short mooring line scopes.
--Lateral load resistance low compared to other anchor types.
--Usable water depth reduced.
532 - Drag Embedment Anchor Type (See Appendix 2).
--Broad range of anchor types and sizes available.
--High capacity achievable.
--Standard off-the-shelf equipment.
--Broad use experience.
--Can provide continuous resistance even though maximum capacity exceeded.
--Anchor is recoverable.
--Usable with wire or chain mooring lines.
--Anchor does not function in lithified seafloors.
--Anchor behavior erratic in layered seafloors.
--Low resistance to uplift. Therefore, large line scopes required to cause near
horizontal loading at seafloor.
--Penetrating/dragging anchor can damage pipelines, cables, etc.
533 - Plate Anchor Type (See Appendix 3).
--High capacity achievable.
--Resists uplift as well as lateral loads, enabling short scope moorings.
--Anchor dragging eliminated.
--Higher holding capacity to weight reaction than any other type of anchor.
--Handling is simplifed due to relatively light weight.
--Installation is simplified due to possibility of instantaneous embedment or
seafloor contact. (Propellant-embedded anchor.)
--Accurate anchor placement possible.
--Does not protrude above seafloor.
--Penetration is controlled and can be monitored. (Screw-in anchor; vibrated-in
anchor; driven anchor.)
--Susceptible to cyclic load strength reduction when used in taut moorings in loose
sand, coarse silt, seafloors.
--For critical moorings, soil engineering properties required.
--Anchor plate typically not recoverable.
--Anchor cable susceptible to abrasion/fatigue. (Propellant-embedded anchor.)
--Surface vessel must maintain position during installation. (Screw-in anchor;
vibrated-in anchor; driven anchor.)
--Operation limited to sediment seafloors. (Screw-in anchor; vibrated-in anchor.)
534 - Pile Anchor Type (Appendix 4).
--High capacity achievable.
--Resists uplift as well as lateral loads, permitting use with short mooring line
scopes.
--Anchor setting not required.
--Anchor dragging eliminated.
--Short mooring line scopes permit use in areas of limited sea room.
--Drilled and grouted piles especially suitable for rock seafloor.
--Does not protrude above seafloor.
--Driven pile costs competitive with other high capacity anchors when driving
equipment is available.
--Drilled and grouted piles incur high installation costs and require special skills
and installation equipment.
--Drilled and grouted rock bolts can be used for lighter anchorage systems. Divers
required for installation.
--Wide range of sizes and shapes are possible (pipe, structural shapes).
--Field modifications permit piles to be tailored to suit requirements of particular
applications.
--Taut moorings may aggravate boat response to waves (low resilience).
--Taut lines and fittings must continually withstand high stress levels.
--Costs increase rapidly in deeper water or exposed locations where special
installation vessels are required.
--Special equipment (pile extractor) required to retrieve or refurbish the mooring.
--More extensive site data is required than for other anchor types.
535 - Anchor Design Considerations.
1. Site specific geotechnical evaluation may or may not be required.
2. Determine drag forces caused by wind and water. Typical calculations are
shown in Appendix 8.
3. Determine typical holding power of deadweight and drag anchors (see
Appendix 9).
4. Determine holding power needed by type of use, site, vessel size, drag and
wave forces.
5. Determine how the anchor will be transported and dispatched on and off
the boat. This may influence design of anchor.
6. Refer to Appendix 7 for a typical deadweight block set-up, and Appendix 7A
for a typical rock anchor design.
7. Refer to Handbook of Ocean and Underwater Engineering by Meyers, Holm
and McAllister (McGraw Hill); NAVFAC DM-26; and COE Technical Report No. 4.
540 - Buoys. Designs may vary (see typical design in Appendix 7), depending on
site specific situation, but shall conform to the following:
1. Must support mooring deadload, mooring cable weight, and function under
the drag load it will face.
2. Must have positive stability (remain upright).
3. Be resistant to damage during transport and installation.
4. Be durable in marine environment; theft and vandal resistant.
5. Must be filled with foamed polystyrene, or similar, so it is unsinkable.
6. Include heavy rope pennant for easy pick-up by boats.
7. Bumper strips, or similar, on steel buoys are optional, but highly
desirable. Fiberglass buoys are encouraged, where possible.
8. Must be labeled in neat 2-inch-high black letters, with design load of
anchor in terms of maximum boat displacement and length, and identified with:
"Maintained for public use by the USDA Forest Service" using 1-inch letters, or
substituting a small Forest Service Shield.
541 - Mooring Hardware. Size for design loading shall be increased to allow for
corrosion and be hot-dipped galvanized fittings.
542 - Chain. Refer to Appendix 5 for typical sizes, weights, and strengths of chain.
When ordering, standard 90 feet (15 fathoms) are called "shots." Coil or high-test
chain is recommended. Do not use BBB chain.
543 - Shackles and Swivels. Use safety shackles, including nut with cotter pin.
Normally, 3 are used on each buoy and anchor installation. The anchor end of the
chain shall also include a swivel. An additional shackle is needed for each shot of
chain added, and one for the buoy end of the pennant.
544 - Thimbles. A shackle and thimble shall be used on the buoy end, and a thimble
on the out end of the pennant. Where rope is used instead of chain between anchor
and buoy, additional thimbles will be required.
545 - Pennants. The short section of line for accessing the buoy shall be a minimum
of 3 feet in length, and 1 inch in diameter, nylon or dacron braided rope, spliced
both ends to a thimble. Three-stranded nylon is easier to splice, but less resistant
to abrasion, if that is a problem.
550 - Rope. Typical sizes, weights, and strengths are shown in Appendix 6. Rope is
not normally recommended for the anchor line due to abrasion, theft, and
vandalism problems. However, in some instances, it is preferable to chain because
it allows for smaller buoys, is easier to handle, and has some shock absorption
characteristics. The anchor end shall include a section of chain to reduce abrasion
adjacent to the sea bottom.
555 - Color Requirements and Painting. All buoys shall be painted white above the
waterline, with a 4-inch-wide blue stripe, located half-way between the top of the
buoy and the waterline. Painting methods and specifications are found in Appendix
10.
560 - Pile Floating Docks. The Forest Service shall normally not install floating
recreation docks. In most cases, buoys will fill the need for safe anchorage. In
dispersed recreation areas (ROS classes R, SP, SPNM, SPM, RN), the Chief's
direction is to provide facilities for the safety and health of the visitor, and a
minimum of developed facilities for the comfort and convenience of the user.
Floating docks may cause a dramatic shift in the recreation experience toward the
developed end of the ROS spectrum. Consistent with this National policy, we shall
defer to the State where there is a public demand for this type of dock facility. The
State shall be encouraged to meet ROS objectives for the area involved, so that
upland and water related areas are managed consistently.
565 - Review and Approval. Forest Land Management Plans and MAA's shall
reflect the general criteria for location and management guidelines for these
facilities. An EA shall not be required if the MAA is site specific regarding buoy
location. Where not covered in the MAA, anchor buoy installations will normally
require an EA. We recommend an EA cover several planned buoys, rather than
preparing one for each buoy. A "categorical exclusion" may be used if there is a
closely associated development already constructed under an existing EA, and the
recreation experience is not changed by the anchor buoy installation. For example,
this would apply to a buoy installed to service an existing visible cabin or trail. A
separate EA shall be required where the buoy is an intrusion in a natural setting, or
the recreation experience is changed from one of higher risk to a more secure one.
All project EA's shall be reviewed by the Regional Office Engineering and
Recreation Directors. A Corps permit is not required.