The Basics on Aquaculture Mooring Systems
Capt. Eric Oransky
An important part of your LPA application and your farm planning is figuring out what mooring system is robust enough to maintain the constant tension of a longline while handling the dynamic forces of storms, currents, and wind, and that it’s individual components are capable of standing up to the marine environment. There are so many different types of moorings and anchors to choose from and you need to figure out the right system for your farm. So take the time to think about all of your options and conditions to figure out what is the right choice for you. If you aren’t sure which direction to go reach out to a marine contractor for a consultation.
Concrete and Granite Blocks will work well especially when you have hard/rocky bottom when other types of moorings and anchors are not able to “bite” or dig into the bottom. Concrete blocks are not overly expensive but are heavy and difficult to move around without the right equipment. Granite is more expensive but has a longer service life. Both will require a marine contractor or additional equipment to install or remove them. They can drag if overloaded or “creep” from the constant directional loading of a tensioned longline, but they will move slowly because of their mass.
Mushroom Anchors are small and mid-weight, they have a lower price point for holding-power when compared to blocks and can be set/moved by yourself from a moderately sized boat, but they need to be properly sized (weighted), dug-in or “set” properly to hold. They work especially well in soft and mud bottom, but are just a weight on hard or rock bottom if they cannot be dug-in properly. If the direction of pull from your surface gear changes too much the anchor can “trip” and disengage from the bottom but will likely catch again when loaded in a new direction.
Danforth or Plough Anchors are relatively light, inexpensive and easy to install but will have to be large enough to hold all of your gear in a winter storm. They work well in sand, shell and mud bottom, but not as well on really hard or rocky bottom if they cannot be dug-in, and in soft mud can drag when there is a large loading from a storm-surge, waves, wind, etc. Like mushrooms they can be “tripped” if the direction of pull changes causing your site to move off-station, and may not catch again if fouled.
Helical Moorings are a large helical plate on a shaft, like a big screw. They come in various diameters and lengths. They are relatively inexpensive with regard to holding power, but must installed by a SCUBA diver or specialized drilling equipment which can increase the total cost of installation if you hire a marine contractor to install them. The “round-shaft” helix can be installed manually in soft bottom and the larger “square-shaft” helix require a specialized hydraulic unit and experienced diver. They perform exceptionally well in soft, sand, shell and mud bottom, but cannot be installed in ledge or very hard/rocky bottom. They will not trip, or drag if sized and installed properly making them ideal for a constantly tensioned longline at the surface. They can also be used to “back-up” a mooring block to keep them from dragging/creeping. Removal is done by unscrewing them from the bottom.
When applying for your LPA, you do need to include a mooring system design in your application. If the drawings accompanying the application are not easy to read and incomplete (from an architectural and engineering standpoint) it can be a reason your application is considered incomplete. Below are sample mooring designs that were created by Capt. Eric Oransky's of Casco Marine, LLC and can be found on the Department of Marine Resources Limited Purpose Aquaculture (LPA) License Application page under sample mooring designs. Additionally, moorings are one of the few things you are legally allowed to change on a LPA license (see 2.90 (2)(5)(E)). So, if the system you originally proposed isn’t working, you shouldn't have concerns about reaching out to DMR to change what is on your license. It's easy and quick.
Capt. Eric Oransky