How does a wave attenuator work? A floating wave attenuator is a wide, heavy concrete float placed on the exposed side of a marina. It reduces the energy of incoming waves, so only a smaller “transmitted wave” reaches the boats and docks behind it. A marina needs one when the site is too exposed for the slips to stay calm on their own.
What a wave attenuator does
A wave attenuator is a structure that reduces the energy and impact of waves to protect vessels and waterfront property. Bellingham Marine builds concrete floating wave attenuators that are custom-engineered for the wave patterns of each site.
From the dock, an attenuator can look much like a large floating dock. The engineering behind it is different. Wave energy at a real site is rarely one orderly wave arriving square to the structure. It is a mix of waves of different heights, directions and periods, plus reflections from around the harbor. The attenuator also has to keep working as tides and seasonal water levels rise and fall.
The transmitted wave: the number that drives the design
Attenuator design starts with one decision: how large a wave is allowed to pass through to the inside of the marina in worst-case conditions. That is the transmitted wave. Once the limit is set, engineers work out the attenuator beam (width) and depth that meet it. Those two dimensions relate directly to the size of the structure.
The design case is an extreme event, the kind that may occur once in 50 or 100 years. For most of its life, a protected marina sees far calmer water than the design limit.
What engineers look at
- Wind speed and direction
- Fetch, the distance of open water the wind blows across
- Water depth and bottom conditions
- Tides, currents and flood levels
- Wave length and wave period
- Wakes from ships or ferry traffic
When a marina needs a wave attenuator
Most naturally protected waterfront sites are already developed, so new marinas are often built on more exposed water. Boaters also expect calmer slips than they used to, because they spend more time on board at the dock. Both trends make wave protection more important to a marina’s success.
A pre-construction feasibility study answers the question for a given site. It can show that:
- a floating concrete wave attenuator is the right solution, which is often the case;
- a fixed breakwater is the better fit;
- a standard-duty concrete floating dock on the perimeter gives enough protection, which is common on lakes and rivers where waves are milder;
- no special wave protection is needed, in well-protected areas;
- the water is too deep or the fetch too long for an affordable solution. It is better to learn this before committing to a project.
Bellingham Marine and SmithGroup developed an Attenuator Planning Tool for this early stage. With basic site data such as wind, water depth and fetch, it gives preliminary attenuator dimensions in a few minutes. It is offered free to owners and developers, guided by a Bellingham Marine representative.
More than wave protection
A floating wave attenuator is also usable space. Bellingham Marine attenuators can serve as transient moorage or fuel docks, and finger piers can be added to the protected side for additional slips. They can be built straight or curved, with internal utility routing, and can be reconfigured later if site conditions or operations change. They also support marine habitat and help water circulate around the site.
Construction and service life
Bellingham Marine wave attenuators are solid concrete on all six sides, with a compressive strength of 5,000 PSI or greater. They are fire and rot resistant and are built for a service life of 50+ years. Maintenance is light: regular inspection and cleaning.
Frequently asked questions
What is a wave attenuator?
A wave attenuator is a structure that reduces the energy and impact of waves before they reach the boats and docks behind it. A floating wave attenuator does this with a wide, heavy concrete float that is held in place by piles or an anchoring system.
When does a marina need a wave attenuator?
A marina needs wave protection when the waves that reach the slips in normal or storm conditions are larger than the boats, docks and guests can accept. Exposed sites with a long fetch, deep water or regular ship and ferry wakes are the usual cases. Well-protected sites may need none.
What is the difference between a floating wave attenuator and a breakwater?
A breakwater is a fixed structure built up from the bottom. A floating wave attenuator sits on the surface and moves with the water level. A pre-construction feasibility study shows which of the two fits a site, or whether no special wave protection is needed.
Can a wave attenuator be used as a dock?
Yes. Bellingham Marine wave attenuators can be used for transient moorage and fuel docks, and finger piers can be added on the protected side for additional slips.
How much maintenance does a floating wave attenuator need?
Very little. Regular inspections and cleaning remove debris and catch early signs of wear so repairs can be made before they affect performance.
Planning a marina on exposed water? See our floating wave attenuators, read the wave attenuator design conversation, or talk to our team about your site.
