Dock Types

(The following content is taken from the Fisheries and Oceans Canada website from the section entitled A Cottager's Guide To Waterfront-Friendly Docks produced by Fisheries and Oceans Canada in association with Cottage Life)
 
Although nature considers all docks to be removable, floating docks and pipe docks are the only ones cottagers usually consider removing, either for repairs or to protect the dock from the ravages of winter ice and spring breakup. Given Canada’s climate, that means removable docks are extremely popular.

REMOVABLE DOCKS

Floating Docks

Floating docks are relatively easy and economical to build, adaptable to most shorelines and, because they are held up by the water, the distance between the top of the dock’s deck and the surface of the water - known as freeboard - remains fairly constant, varying only with dock load and high seas (being minimal on a well-designed and well-built floater). Since a floating dock is not dependent on submerged lands to hold it up, the added benefit is that there is no maximum water depth that prevents its use. 

From an environmental perspective, floating docks cause minimal direct disruption to submerged lands; disruption typically caused by anchors, spuds, or pilings (the most popular ways to moor a floating dock in place). In fact, if secured to the shore only, there may be no contact with submerged lands at all. However, floating docks can block sunlight to aquatic plants - altering fish habitat - and they may also cause the erosion of shorelines. This means that floating docks will not work everywhere. To minimize damage to the shoreline, a floating dock must have sufficient buoyancy to keep its floats resting on water, rather than bumping into submerged lands (which can harm both the dock and aquatic habitat). A depth of 1 metre (approximately 3.3 feet) (measured at the low-water mark) is the normal accepted minimum however, less depth may be possible if the water level never varies and the area is not subject to harsh wave action. 

Floating docks often lack stability but it is not impossible to make a stable floater - hundreds of good designs exist; some so stable a user could mistake the dock underfoot for a waterfront boardwalk. Unfortunately, the number of unstable disasters out there is great due to poor construction practices. When it comes to stability, a floating dock works best when it is made long, wide, low, and heavy. Remember to look for a design that will achieve this stability without causing harm to fish habitat.

The consensus among dock builders is that 1.8 metres (approximately 6 feet) x 6.1 metres (approximately 20 feet) is the minimum size for a stable floater; this single section weighing in at about 450 kilograms (approximately 1000 lbs) minimum. And bigger is even better for stability. 

As usual, the drawbacks to bigger are increased initial cost, increased labour for installation (and removal) and of course, greater impact on the shoreline’s ecosystem. A pipe dock - which can be made smaller and still remain stable - may be a preferable choice in shallow water.

In areas where ice conditions prohibit a four-season solution, the floating dock offers the advantage that it can be removed from the water in the fall and replaced in the spring (albeit with no small effort in some cases). That said, many floaters are left in all year where wave action and ice conditions permit. In addition to size and shape, float type and float location also contribute to stability. A discussion of float types is beyond the scope of this booklet but as a general rule, installing floats towards the perimeter of the dock, rather than set back towards the dock’s centre line, greatly enhances stability.

Floating Dock For maximum stability, a floating dock should be heavily built and solidly anchored.

Pipe Docks

If you can imagine a 1 metre wide wooden ramp sitting about a quarter of a metre above the water, supported by long skinny legs running from the ramp down to submerged land, you have just mentally built a pipe dock. Building one in reality is only a little more difficult, and not a lot more expensive (pipe docks are typically the least costly dock option). As most of the dock sits out of water, contact with the land and shading of aquatic vegetation is typically held to a minimum, making a simple pipe dock the least disruptive to the environment of all the dock types.

Unlike the floating dock, the pipe dock is stationary, therefore, the distance between the dock and the water varies as the water rises and falls. Should the lake or river at your shoreline do a gentle retreat through the season, the pipe dock’s deck can usually be lowered on its legs to accommodate moderate fluctuations in water levels, and even more extreme fluctuations can sometimes be handled by relocating the dock further out on the shoreline. (The dock’s light weight is a real advantage here). Some pipe dock legs can also be fitted with wheels to make moving the dock an even easier task. Be aware that the slightest amount of ice movement can fold up a pipe dock like an accordion, so plan on moving the dock at least twice a year (the more favourable option), or on buying a new one each spring. 

Because a pipe dock’s deck and framing remain elevated above the water, there is very little surface area exposed at the waterline for nature to damage. This makes the pipe dock a good candidate for situations where plenty of surface activity is experienced, such as on busy river channels where the wakes from passing boats may be a problem. However, with waves passing under the dock unobstructed, any boat moored to the opposite side will be exposed to the full brunt of wave action. 

Severe wave action can put some of the lighter aluminum pipe docks at risk. However, lighter construction also means less labour to install and remove the dock, and less initial cost to purchase. And in the right situation - a protected bay for instance - a lightweight pipe dock is certainly up to the task of mooring smaller boats. For larger vessels and harsher wave action, boat lifts or marine railways are a better choice. 

Because a pipe dock is propped up on legs, it can be built smaller than a floating dock yet still remain stable. The basic rule for pipe docks is that the width of the dock should be at least 1 metre (approximately 3.3 feet) and never less than the depth of the water. Because stability suffers as legs get longer, about 2 metres (6-7 feet) is considered the maximum water depth for pipe dock installations. Choose one of the other dock types - such as a floating dock - for deeper water.

Pipe DocksBecause they have little contact with submerged lands, pipe docks are easy on the aquatic environment.


PERMANENT DOCKS

Residential permanent docks (as opposed to commercial wharves) can be divided into three categories: crib docks, concrete piers, and permanent pile docks. The term “permanent dock” is more a reflection of objective than reality, because permanence is not a concept recognized by nature. Shifting ice can topple cribs, lift piles right out of submerged land, and push concrete piers up onto shore. However, blessed with sound construction techniques and the appropriate conditions, a permanent dock can serve faithfully, perhaps even for several generations.

Because freeboard will vary with fluctuations in water level, permanent docks are often used in conjunction with floating docks, the floaters attached to the more permanent structure in a manner that permits the floater to move up and down in concert with changing water levels.

Crib Docks

A “crib” is a container. In the context of waterfront construction, a crib holds a few tons of rock and stone. Cribs should not be confused with gabions. Gabions are inexpensive wire or plastic mesh baskets designed to hold stones, rock, or concrete; the baskets wired together to serve as unattractive retaining walls. At first glance, they may seem like a good idea for dock building, but time has proven gabions to be better at tearing skin than retaining rock under siege by strong currents, waves, and ice, all of which will distort the basket’s shape, causing the gabion to sag and flatten.

A proper crib is built from new, square-cut timber, not wire or driftwood or round logs tacked together with small nails and hope. (Occasionally, steel or concrete castings are used in lieu of wood). The timbers are assembled in opposing pairs, one pair laid out on top of the next, creating a slatted, box-like affair with an integral floor. Threaded rods run the full height in each corner to secure the timbers in place. The box is then filled with rock. 

Maximum water depth for a crib is about 2.5 metres (approximately 8 feet). For optimum stability, a crib’s total height should at least equal its total width. Obviously, this can make for a very large container, which in turn needs a ton or more of rock to fill it, and all of this rock must be taken from onshore sources, not from close-at-hand submerged lands (which would disrupt fish habitat). For this reason, and from an environmental standpoint, cribs should be placed above the ordinary high water mark, using the strength of the crib as an anchor or attachment point for other structures such as floating docks, cantilever docks or pipe docks. (On a lakeshore, the ordinary high water mark is the highest point to which water customarily rises, and where the vegetation changes from mostly aquatic species to terrestrial). If however, cribs must be placed in the water, leave at least 2 metres (6-7 feet) between them, and locate them at least 2 metres from the ordinary high water mark. This will allow near-shore water to circulate around the structures.

From an environmental perspective, floating and pipe docks are preferred to crib docks, since crib docks can cover over sensitive spawning habitat and result in the removal of rocks and logs that provide shelter.

Dock Foundation

Where ice and currents permit, rock-filled cribs can make a solid dock foundation.

Concrete Piers

The concrete pier is basically a big block of cement and aggregate, bound together, often with an integral boat ramp. Most often, they are found in commercial or municipal settings. As with crib-based docks, practical water depths are limited to about about 2.5 metres (approximately 8 feet), and the piers can be merged into shorelines to provide a shoreline interface for other types of docks. 

However, concrete piers are expensive to construct, and no dock does a better job of disrupting the environment. Erosion of submerged lands at the base of the pier can often be a problem too, and unlike the slatted sides of the crib, the concrete pier provides no substitute home for refugee aquatic life. Because they take over the areas where fish feed, rest, and hide from predators, you should only consider designing a concrete pier when no other alternative is feasible. 

In most cases, there are better solutions for residential docks.Permanent Docks 
Concrete piers are expensive and environmentally destructive.

Permanent Pile Docks

The permanent pile dock is a heavyweight, long-term version of the pipe dock - still a ramp on long legs, but definitely not portable. Instead of resting on the surface of submerged lands (as the legs of pipe docks do), long poles of wood or tubes of steel or plastic - all referred to as piles - are sunk into the earth, either by force or by being set in pre-drilled holes. Either way, because of the heavy-duty equipment required, a pile dock is not the stuff of home workshop projects.

Piles should always be braced to prevent sway, and although there are no theoretical limits to depth, if the exposed portion of the pile extends 7.5 metres (approximately 25 feet) or more above supportive soil, construction costs will skyrocket. 

The permanent pile dock shares many of the environmental advantages of the pipe dock - minimal contact with submerged lands, free flow of water underneath, and the ability to build a relatively narrow dock that is still quite stable. Dock Piles Sunk deep in the ground, piles made of wood, steel, or plastic make a great base for a stable dock.


SPECIALTY DOCKS

Specialty docks include cantilever docks, suspension docks, and lift docks. These docks can be dramatic to behold and expensive to purchase. Some design and construction similarities exist between specialty docks and the docks discussed above, but specialty docks are more complex, typically making their construction and installation beyond the skills of even many professional dock builders. These are not docks that lend themselves well to the average tinkerer.

Cantilever and Suspension Docks

The cantilever dock works in the same manner as an overhanging apartment building balcony: the dock’s frame stretches from shore, over the fulcrum point, and then out over the water. The maximum length of the dock, and the proportion of the length that is land-based, is determined by how well the land-based end - the end that supports the load - is tagged to the shore. Customarily, a cantilevered dock requires 0.5 metres (approximately 2 feet) of onshore dock for every 0.25 metres (approximately 1 foot) hanging beyond the fulcrum, although cantilever docks can be incorporated into wood bulkheads (walls built parallel to, and usually at, the shoreline) using a leverage ratio as little as 0.25 metres (approximately 1 foot) on shore for every 0.25 metres of overhang, and even less when the land-based end is embedded into a concrete bulkhead or solid bedrock.

The suspension dock, on the other hand, has more in common with a massive suspension bridge than an apartment balcony. Picture half a Golden Gate Bridge but instead of connecting two bits of land together, it connects one bit of land to water and your boat. Think of it as the “Golden Gate Dock”. Cantiliver Docks  Cantilever docks do not disturb the water or submerged lands. Unlike the cantilever dock, a suspension dock’s deck does not rely on large chunks of shoreline for support. Instead, a rectangular tower holds up a pair of cables anchored well back on shore to keep the deck suspended over the water (just like the entrance to the aforementioned bridge). Both cantilever and suspension docks sit completely out of the water, so neither dock demands a minimum depth of water for installation. Since freeboard will vary with water level fluctuations, cantilever and suspension docks are not the answer for locations that experience extreme water level fluctuations.

Both dock types have practical limits to the length of overhang: About 2.5 metres (approximately 8 feet) for cantilever docks (which normally equates to a minimum of 5 metres (approximately 16 feet) of onshore decking), and about 15 metres (approximately 50 feet) for the suspension dock. Greater distances are not considered cost effective. 

A short cantilevered overhang of about 0.25 - 0.5 metres (approximately 1-2 feet) can work very well along bulkheads, cribs, and the like. When a large, shore-based deck is desirable (such as over a boulder-strewn shoreline), the cantilever dock again becomes a reasonable option. 

Cantilever and suspension docks cause the least disruption to the water or submerged lands - it is difficult to disrupt what you do not touch. However, as with floating docks, the resulting shading of the aquatic environment could alter aquatic life. Also, both dock types will disturb the shoreline, particularly the cantilever dock, which in turn has the potential to disrupt both aquatic and land-based life. Suspension DockA tower and thick cables keep a suspension dock up in the air.

Lift Docks

Lift docks come in three styles - lift pipe docks, lift floating docks, and lift suspension docks - each based on the style of the dock being lifted. The freeboard of each is the same as for non-lifting versions.

In concept, the lift dock appears to function much like the classic drawbridge. Yet while the drawbridge was historically raised to protect the castle from unwanted weekend guests, the lift dock gets raised for its own protection, hoisting it up out of reach of winter ice.

Size restrictions and environmental impact for the three versions of lift Lift Pipe Dockdocks are the same as for their non-lifting counterparts.

With its decking removed, a lift pipe dock can simply be winched up in the air to escape damage from winter ice.
 
 
(This pages content was taken from the Fisheries and Oceans Canada website from the section entitled A Cottager's Guide To Waterfront-Friendly Docks produced by Fisheries and Oceans Canada in association with Cottage Life.  The reproduction of this content on this site has not been produced in affiliation with, or with the endorsement of the Government of Canada.)