Anchors Update 4-8-13

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    Waves can be very powerful. They can push your island a long way away from where you want to park it. For centuries, men have used anchors to hold their ships in place.

    To the experienced sailor all this may seem as normal as blue berry pie, but to the greenhorn, this logic may seem all new.

    At first they drilled a hole in a big rock, attached a line (rope) with its other end attached to their ship. For us, itís easiest to imitate it in conventional reinforced concrete about 3 feet around and a foot thick. Make sure you include steel rebar to hold it together and take up the tensile force. It works, but has handling problems that may require a crane. Itís heavy and hard to move around. It can be done, as mass can work as an anchor for your island, but there is a better way.

    Then they invented the anchor. It has the traditional shape to keep it digging into the bottom more and more as each wave tries to pull it away. It worked, and was much lighter and easier to handle. However, it can be improved a little for your island, if you have a way to work with steel, cutting and welding.

    This shape as shown should dig into the bottom real well, to hold your island against the relentless force of strong waves.

    Traditionally, there were two places to grab into the bottom, but one was up and not used, while the other one did the work. That was because they had no other way to hold it upright and digging in correctly. At the top of the anchor was a 90į cross piece. Its purpose was to keep the anchor reasonably upright and digging into the bottom. It worked. However, even that can be improved.

    You need a strong line (rope) attached both to the anchor, and wrapped a ways around your island. Consider that all the force of the waves, especially during a storm, pulls on that connection, so it needs to be strong. Rushi had two of his islands picked up by a storm, and slammed onto a beach. Obviously you donít want that to happen to your hard work.

    So the connections should be strong. You can double the anchorís force by building two of them, but keep their connection to the island as far from each other as you can to spread out the force during a storm especially.

    This design is easy to build. It is made of strong steel, is made to dig into the bottom more and more as the waves force it along. Obviously, it works best when placed up-stream, that is to hold your island against the waves. You can dissipate some of the waveís energy with a Tricter, or funnel to redirect each wave upwards into a holding tank for the generation of wave energy into a constant and more useful form, such as electricity. But waves are big and your ability to do this is small. Plus it makes a lot of noise, it can be pleasant, but sometimes not. But, energy-wise itís a good idea anyway. It beats pounding your island to pieces. Please read my article on wave power.

    At night this sound can alert you to an approaching storm.

    The connections between island segments need to be strong, because thatís where wave force tends to concentrate, especially on your islandís edges that face each wave. You may have to use Brianís rubber tire island segments on that side of your island to make them strong enough, or make the NFRC thicker on those pieces and the inter-piece connection stronger. It depends on where you are located, but even on a lake, waves during a storm can be big.

    The connection to the anchor also needs to be strong. Big ships use a line a couple of inches in diameter. There is a reason for that. You can imitate it by putting multiple lines together, and wrapping them several times around the anchor connection. If you have a marine store handy, and can afford it, they may have a good supply for your needs.

    If you use plastic rope make sure it isnít destroyed by the UV rays of the Sun. It may take a while, but its action is relentless, and can prove irritating or even expensive.

    This applies to all rope used to hold your island together, that can be exposed to the Sun.

    In the illustration, the purpose of the attached plastic bottles with tight lids, is to assure that the anchor lands properly so the bottom-digger will land on the bottom. Think about how much your anchor weighs in the water (the weight of the anchor less the weight of the water it displaces.) You want your anchor to stay upright as it goes down, but you donít want it to float.

    The holder is to reduce bending when the force of the waves is strong. And the line tie is big enough to allow the anchor line to wrap several times around the steel.

    It should use good strong steel, because the force of waves against your island during a storm is strong.

    Put a point on the end of the bottom-digger, and at the bottom of the bottom-digger has a pointed plate. It spreads the force of the bottom-digger out in sand, so you donít just dig a trench if your island moves. Make it at least 3 inches across, and triangular shape with one point down, welded tight.

    The cross-piece helps keep the bottom-digger pointed down. It is at right angles to the main anchor, but bent down somewhat to hit the bottom when the anchor is twisted sidewise, to keep the anchor from falling over. (Itís hard to show in the illustration.)

    But this type of anchor should be easier for you, or the welding shop, to build. Plus you have this explanation on how it works.

    Paint the whole thing with a thick, waterproofing paint, to prevent rusting, which can happen surprisingly fast, when you are having a beer or two.

    When placing it in the sea, place your island a bit up-stream from where you want it, so when the anchor digs in, and your line becomes tight, your island is where you want it. Remember, that the line goes down straight, but as your island moves away from that spot, then the line becomes tight. And there must be enough line, so that when the water gets deeper during a hurricaneís storm serge, the anchor doesnít just pull up. Plus, it may not dig into the bottom exactly where you want it, but skip along a bit.

    Make sure the water isnít deeper than your anchor line, laid at an angle from the anchor to your island.

    You should have a GPS receiver, and a navigatorís chart map to decide where you can safely park your island, and where that can be done. Consider storms, and ask the Coast Guard for help is laying it out. Just anywhere is seldom the best choice.

    Have a fruitful day.


Meet the Scientist

Meet the Scientist
Meet the Scientist
    John N. Hait

    Thanks for reading.