How to NOT do a whack job on the underwater weeds, the new art and science of mooring your boat

Image of anchor chain on sea bed, new boat mooring

Ah, the piercing call of the string trimmer, a sure sign of spring.

I’ve never embraced weed whacking. The smell of the gas engine, the weight on my shoulder … I finish the job sick and stiff necked.

Plus I don’t like the way I think when I weed whack. Something about the vibration or the sound puts me in a primitive “must-conquer-nature” mental state. I push the cutter farther and farther into the wild verge, knocking down perfectly good native plants like salal just because I can. And I’m not very good, I leave circular patches of scarred earth in my wake.

Anchor chain weed whack

When I heard boat anchors and mooring buoys described as huge weed whackers on marine vegetation, I immediately wondered if my son’s boat anchor was doing a number on the bottom of Puget Sound. The analogy is perhaps a little hyperbolic, but I’m already concerned about the condition of the eelgrass in my harbor, I don’t want our mooring lines and anchor chains to add to the problem.

According to Seagrass Long Island, “setting any kind of anchor in an eelgrass meadow will result in disturbance to the adjacent plants. Temporary anchoring can result in “tilling” in a meadow until the anchor sets. Then, when the anchor is removed, a large turf of grass is usually uprooted with the anchor. Boat moorings placed in eelgrass meadows will also cause disturbance. Not only is the anchor sitting in the eelgrass, but the chain that connects the anchor to the mooring buoy drags through the eelgrass, resulting in an unvegetated area around the anchor.”

Changing the way we moor

The typical mooring or anchor features a large, heavy (hopefully stationary) object such as an anchor or concrete block. Attached to that immovable object, a chain or line acts as a shock absorber, lifting and sinking as the boat rides the waves and tides. As the boat swings and moves with currents it lifts and lowers that chain across the bottom, striking against the vegetation in its path. Marine biologists and inventors of boating related gear are looking for new ways to moor to reduce the damage to the underwater habitat.

In the case of my son’s boat, which is on an anchor, the easiest change I can make is to move to deeper water. The maximum depth at which eelgrass grows is 30 feet. Moving the boat out well beyond the fringe will fix at least some of the problem. My rowing distance will increase, adding to the time I spend messing about in boats. And to the biceps.

To keep the boat closer to shore I need a new mooring technology. The latest innovation I’ve heard about is the use of elastic mooring rode, essentially a huge Bungee cord. This has been used successfully where tides aren’t much of a factor. It may not be the answer for Puget Sound where typical tidal range is 11 to 14 feet and in extreme conditions can be 19 feet. I’m curious whether the elastic can stretch to suit our needs here in the northwest.

Another upgrade to the traditional system is the augur, or helix style mooring, which replaces the anchor or hunk of cement or metal with a screw drilled into the sea floor. This is the type favored by the Washington State Department of Natural Resources, and is the only type allowed on DNR tidal lands.

These types of systems also help with the issue of scope – the amount of chain or line needed to keep the boat from pulling on the mooring or dragging anchor, while also staying clear of other boats, docks, and buoys. The scope needed depends on the shape and material of the bottom, the tides, currents, storms, size of the boat, size of the anchor, etc. Books like Chapman Piloting go to exhaustive detail on how to figure all this out.

The amount of chain needed can sometimes be reduced by employing various shock absorbing mechanisms. The elastic mentioned may be one, another is a length of concrete pipe through which the chain is threaded. This reduces the damaged area to the pipe’s length. Better is an intermediate float, which hovers midway between the bottom and the surface and lifts the line off the bottom. The DNR brochure linked above shows this method.

The bottom line is, this yachting season – which has just opened, and which happens to coincide with the eelgrass growing season – there are good reasons to think how we drop the hook and some new, better ways to do it.

For us boat lovers there’s a side benefit of taking on a mooring retrofit project. It offers us one more chance to head to the chandlery, use lots of salty slang and try out more techie marine gadgets.

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