Alternatives to Floating Structures

Some alternatives may be more suitable than floating structures.

Cantilever Docks

A cantilever dock typically relies on the shoreline or on a shoreline structure for its entire anchorage (figure 9). Some docks may have intermediate supports very close to the shoreline. The end of a cantilever dock juts out over the water, appearing to float on air. Cantilever docks are suitable for almost any type of environment and have a very small environmental footprint. The shoreline anchorage and framing must be strong enough to support the weight of the dock and its users. Consult a qualified engineer to develop a design suitable for your application.

Figure 9—Cantilever docks do not float on the water.

Crib Docks

A crib is a framework of large timbers (made of a durable wood such as Douglas–fir, larch, or hemlock) filled with rocks (figure 10). Timbers continually submerged in water can last 50 years or longer without treatment. A traditional crib dock extends from the shoreline out to a crib. Cribs can also be used for shoreline supports, anchorage, foundations, and landing platforms (figure 11). Crib docks are not suitable for deep–water applications.

Figure 10—Drawing of a typical crib. Underwater cribs should be constructed
from square timbers that are bolted together securely. Crib frameworks
are commonly filled with rocks.

Figure 11—This aging crib dock continues to provide sturdy recreation
access in a lake that is subject to icy conditions.

Concrete Piers

Concrete piers are hard to beat in terms of strength. However, the cost, complexity, esthetic considerations, and environmental footprint—these are massive structures—make them problematic. If you are interested in a concrete pier, consult an engineer.

Pile Docks and Piers

Pile docks are very similar to traditional boardwalk structures. They rely on large wood, steel, or concrete piles to support them above the water (figure 12). Piling design must be left to a qualified engineer. The MTDC report, Wetland Trail Design and Construction (0123–2833–MTDC), contains some discussion about installing piles.

Figure 12—Small pile–based docks (finger docks) reaching out from the
main dock offer access during periods of high water.

Pipe Docks

Pipe docks are similar to pile docks. However, the deck and frame rest on 1.5– to 3–inch–diameter metal pipes rather than on large piles. The metal pipes rest on supports placed on the bottom of the waterway (softer bottoms need wider supports), as shown in figure 13. Pipe–supported decks are not suitable for deep water. Water depth should not exceed the width of the deck. The frame and deck ride above the water level, making the pipe dock an excellent means of crossing swift water (be aware of possible scouring at the pipe's base) and areas with environmental concerns. Only the metal legs come in contact with the water. Pipe legs should be cross braced and bracketed on the frame for added support. Most pipe dock designs are easily adjusted and removable.

Figure 13—A drawing of a dock supported by pipe legs. Pipe–leg–based structures
are one of the most environmentally gentle ways of crossing wet areas.

Suspension Docks

Picture a suspension bridge cut in half and you have a suspension dock (figure 14). The shoreline end is hinged to a solid landing. Cables are run from a shoreline anchor over a tower to connection points on the dock. Suspension docks are suitable for most settings so long as anchorage is adequate and the structure is strong enough. Use engineering assistance to design a suspension dock.

Figure 14—Suspension docks, when properly designed and built, can provide
many years of use. A suspension dock can be designed so it can be
raised and lowered.