When it comes to building a dock, you want something extremely durable that can stand up to punishment, particularly if you’re in an area prone to storms. You need a dock that can endure high winds, towering waves, and the strain of any attached boats.
In addition to strength and stability, you also want a dock system that can quickly expand, accommodating growth and a variety of configurations. A modular system is ideal since it can be easily expanded or contracted.
The Unifloat concrete dock system, in which walers connect modules, meets both the strength and configuration test, able to endure punishing storms as well as the need for expansion.
In this article, we’ll explain what the Unifloat concrete dock system is, as well as the purpose of walers.
The Unifloat Concrete Dock System
The Unifloat Concrete Dock System is the product of Bellingham Marine and was first developed in 1958. Since its introduction, the Unifloat system has become the industry standard for modern marinas. It is a dock system made up of individual, modular concrete blocks, all of which connect with a through rod/waler system. It is the walers which give the Unifloat dock its unique ability to expand to almost any size or configuration.
The Origination Of The Waler
The concept of the waler-connected concrete dock was patented in 1958 by Ernest M. Usab, from Long Beach, California. After receiving the patent, Usab then licensed it to Bellingham Marine the same year. Bellingham Marine then demonstrated the technology to the world when it manufactured and built Shilshole Bay Marina in Seattle, Washington. As the years went on, it became apparent that the waler technology would be critical to the marina industry, and Bellingham Marine wisely purchased the patent.
Since constructing the Shilshole Bay Marina, Bellingham Marine has continued to hone and improve waler technology, building and installing more than 20 million square feet of docks in thousands of locations around the world. Proving just how durable the original walers were, the floats installed at Shilshole Bay Marina were used for fifty years until they were finally replaced to accommodate larger boats. Once again, Bellingham Marine did the job, using new concrete docks at Shilshole Bay Marina. The original floats at Shilshole’s were not scrapped, with many still used in private residential and marina docks.
How The Waler System Works
Walers are structural beams mounted flush to the deck of the Unifloat concrete floating dock from Bellingham Marine. Also referred to “through rods,” they span the width of each concrete float and are secured by washers and nuts. They attach to the float by long rods threaded at the ends.
Walers are made from a variety of materials depending on the structural requirements of the marina. They can be constructed from structural timbers, composite materials, steel, and other materials. Most Unifloat systems use structural timbers although Bellingham Marine has built marinas with walers of other materials.
As mentioned above, concrete floating dock marinas utilize a modular construction. This particular modular layout allows the docks to bend and twist at the float connections, providing the flexibility necessary for a water structure that will be in rough conditions. Additionally, it is significantly easier to manage the building and installation of the docks when the floats are built in modules. Finally, the modules can be removed, replaced, refurbished, and even expanded upon. The modular construction offers a variety of repair and expansion options.
The primary purpose of the walers is to join the modules. The waler system has proven itself to be so durable that no other connection methods, such as hinges are necessary. In addition to joining modules, walers perform two other functions. First, they offer protection for the dock in the event of a collision with a docking boat. Second, they provide a soft surface for the hulls of ships which are mooring. This surface is especially soft when the walers are composed of structural timbers and used in conjunction with protective rub rails.
Why The Waler System Works So Well
The brilliance of the waler system is in its ability to distribute loads. In the original patent, Ernest Usab described the purpose of the walers as: “…to support the bolts or other fastening means, and to distribute the forces received there from throughout the structure.”
Why are distributed loads so crucial to docks and marinas? To gain clarity, let’s consider others types of float connection systems used. Many systems employ heavy-duty hinged steel bolts or thick wound cables at the corners of the floats. Unfortunately, there are two significant problems with these systems.
First, the hardware connecting the floats can, and often does, break down. Repeated bending and stretching, as well corrosion can significantly weaken the connections. Second, and perhaps more importantly, forces on the floats are not evenly distributed. Rather, they are concentrated at the corners of the floats. The result? Massive shear loads directed to locations where they can cause irreparable damage to the float.
Understanding Load Distribution
There is a quite a bit of complicated science behind stress analysis of structures, but we can at least discuss the fundamentals to gain a clear understanding of the different systems. The following example will demonstrate why distributed-load systems are superior to point-loaded systems.
Let’s say a sizable powerboat is moored to a concrete floating dock. A powerful storm hits the area, causing significant disturbance in the waves. The boat’s large “sail area,” the currents in the water, and the repeated push of waves against the ship are all sent through the mooring lines into the floating concrete dock. These forces run through the dock and act as shear forces at the connection points for each module. For our example, let’s say that the shear force at the contact points between the floats is 10,000 pounds. In a real storm at a real marina, it could be more or less, but 10,000 lbs. gives us a simple number to analyze.
Figure A. Hinged Connection System
On the hinged or cable-connected system, the shear load of 5,000 lbs. is applied equally at the corners of the floats. The pressure is transmitted through the hinge or cable to the concrete at the corners. This means that concrete floats must handle a shear load of 5,000 lbs. at the easily-damaged corners of the floats.
Figure B. Waler Connection System
By contrast, a Unifloat system, using a typical setup of 10 through rods, is hit with the same 10,000-pound load. However, unlike the hinged system, where shear loads are focused at the vulnerable corners, the shear load is translated the full length of the waler and distributed even among all the through-rod entry/exit points. This means that each of the entry/exit points in the concrete float only needs to be able to handle 1,000 lbs. of shear force. The waler system has reduced the load on the concrete structure by 80%.
Distributed Load Systems Are Everywhere
Of course, distributed load systems are not limited to walers. These types of engineered structures are everywhere around us. Donald Douglass and John Northrop revolutionized airplane design by distributing loads across the entire skin of the aircraft. We also see load distribution in cable-stayed bridges. For an everyday example, look at your house. The lumber is sandwiched between exterior plywood and interior sheetrock, making it quite the marvel of distributed load technology. They show off their incredible strength in earthquakes.
Why Structural Timbers Are Superior
Why do most Unifloat marinas use walers made of structural timbers? Is a wood-waler marina as strong as should be? Aren’t floats connected by steel bolts or cables stronger? Actually, using structural timber for walers is a deliberate decision. Timber walers create the most durable, longest lasting, most practical and most attractive marinas on the market.
Why is timber the best choice? Several reasons. Wood is all over the world and is easily and cheaply available. It holds up well in corrosive environments that are always moving. Wood is also a natural, organic material, with a cell structure that has adapted to constant motion. Even with repeated bending, it maintains its strength. Compare this with metal structures which would degrade and break under the same conditions. Wood is capable of absorbing sudden impact without the permanent damage similar metal structures experience. Wood is also not subject to galvanic corrosion.
Most importantly, timber has shown its toughness in marinas everywhere. From the East Coast down through Florida around the Gulf of Mexico to Texas - it’s all testing ground for marinas with wood walers.
These marinas have seen some of the most horrific storms recorded, and the wood-waler system has easily survived them all. Hurricane Ike pounded Galveston Bay on September 13, 2008, battered the Unifloat-equipped Bayland Marina in Baytown, Texas. The massive storm was the third costliest hurricane ever to hit the United States. The Unifloat Marina handled everything the storm threw at it until a tide surge finally took the floats over the pilings. And yet when the storm passed, the marina was found mostly intact on the beach across the bay…with the floats still joined with wood walers!
The Unifloat waler system may appear to a simple idea. And yet history has shown that using a distributed-load concept is a brilliant engineering solution. Bellingham Marine has built marinas with walers of other materials over the years. However, the structural-timber waler is the industry standard by which all other float-connection systems are measured.