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Rocker Stoppers

STOP THE ROCK 'N ROLL!

© David Kerr 2001-2004

Introduction:

We have all had our share of roly anchorages. Sometimes, deploying a second anchor or moving to another spot can help. Most often, we just put up with it. Our worst experience was on the East side of Lord Howe Island, with a 35Kt Southerly and very big Pacific Rollers pumping in from the East. A stern anchor helped somewhat, but the rolling was still huge and unpleasant. After that experience, I decided to do something about it and made up stabilisers which we have used extensively with excellent results. The total cost of these was $107, an extremely modest outlay compared with the very effective reduction in roll that they provide.

The principle:

The principle is simply to apply resistance to the rolling at points as far away as possible from the centre line of the boat. I made up "ladders" of rectangular panels that provide a lot of resistance when they attempt to move through the water. These are shown in the sketch. The ladders are weighted down so that the lines attaching them rarely, if ever, go slack. We push the boom out to one side of the boat with a stabiliser hanging from the clew. This locates the stabiliser about 5 metres from the centre line of the boat. A preventer, the mainsheet/vang and the topping lift plus the main halyard at the clew hold the boom rigid. We put the other stabiliser on the end of the spinnaker pole, which is similar in length to the boom. The pole is held rigid by the down haul, topping lift & spinnaker halyard and a mooring line from the end of the pole to a cleat on the aft quarter.

How to build the stabilisers:

I purchased eight nylon cutting (bread) boards from a hardware store. I then drilled an 8mm hole in each corner and threaded 8mm silver line through each hole, with a knot on each side, so that I ended up with two "ladders" of boards, one for each side of the boat. I made the distance between boards approximately 400mm. However, this is not very critical. The four ropes above the top board and below the bottom one terminate in a stainless steel ring. The ring is convenient but is not essential. I made lead weights to hang off the bottom rings and a single line comes off the top rings for attachment to either the end of the boom or the end of the spinnaker pole. The lead weights are also used for the end of our Jordan Series Drogue and I made them by melting lead (using a gas camp stove) into 850g beetroot tins (minus the beetroot). This gave 8Kg lead weights and I suspended a stainless steel eye bolt, with washer and nut in each tin of molten lead to provide a rigid, rust proof attachment point. I did start with galvanised bolts, but they generated messy rust after a few months of use.

Other boats:

Our 11-metre boat has a relatively narrow beam of 3.2 metres and displaces approximately five tonnes. Larger and heavier boats will require more surface area on each side as well as a heavier weight hanging underneath each stabiliser. The more surface area you can get, as far from the boat as possible, the better will be the performance. I suggest scaling the weight linearly with the surface area of the stabilisers. 8Kg is just right for the 0.5 square metres of total area on each of our stabilisers (each bread board is 440mm x 260mm). You can have more than four bread boards per side, but remember that you will sometimes be in shallow water and you do not want the stabilisers to come out of the water nor do you want them to rest on the bottom, as happened to us when the tide went out at Great Keppel Island recently! If you put the boards too close together, you will also lose some of the effective surface area. A friend with a Roberts 53 ketch is going to use four stabilisers, two each off the main mast and mizzen. We have found that in general, there is a huge reduction in roll by at least 80%. However, it is still possible for the boat to pitch. You could also deploy stabilisers from bow and stern to minimise the pitching. In practice we have had no need for this. Pitching usually has a longer period than rolling and the damping is better. Don't use a whisker pole instead of a spinnaker pole or you may well damage it.

Upsides and Downsides:

The stabilisers pack away neatly in a small space and it only takes us about 10 minutes to deploy or retrieve them. The benefits are substantial in terms of roll reduction. Our boat does look like a fishing trawler (see photo), however this is a small price to pay and we often receive envious looks from people on rolling boats when they see how comfortable we are.

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