Envoy is in Lefkas Marina for the northern hemisphere winter and we are home for the New Zealand summer, heading back in April.Upcoming Posts – Stabilisers Part 3, Cruising in Auckland’s Hauraki Gulf aboard 48ft motor yacht Moritz, Using the title Captain, Envoy’s 2017 cruising plans.
Our last Posting introduced the subject of stabilisers, now we’ll talk more about passive stabilisers.
A passive stabilisation system consist of two poles each about seven metres long mounted near amidships on the vessel’s beam, which are stored vertically and when in use lowered to be deployed out from the vessel’s side using a downhaul, topping lift and fore and aft guy-wires to keep them in position. They are mostly made from aluminium or steel though less commonly using laminated timber.
A large metal plate weighing about 25kg and shaped like a delta-winged aircraft, known as a “paravane”, “bird” (the term we use) or “fish” suspends from the end of the pole using a combination of chain and nylon line, the latter providing some spring to reduce shock loads. The front of the bird is weighted to make it “fly” through the water in a nose-down position approximately five metres below the surface and the top of the bird has several chain attachment points to adjust the bird’s angle through the water. The further aft you attach the chain the more the bird tends to dive deeper and the more aggressive becomes the bird’s stabilising action at the expense of increased drag.
This image shows the port pole and bird deployed with the downhaul, topping lift and fore and aft guy-wires
Due to the birds’ weight and large awkward shape some form of winch is used to deploy and retrieve them (we use a light block and tackle) and with familiarity this process takes about 15 minutes.
When not in use we store the birds well out of the way on the boat deck, but if intending to use them we move them down to the cockpit so they’re ready for immediate use.
Centre-right is a bird stored on Envoy’s upper deck
The poles provide a distinctive fishing-boat-like appearance that won’t suit everybody but certainly creates interest among other cruisers.
Stabiliser poles provide a distinctive appearance – love it or hate it! Port deployed, starboard raised
On some boats the poles are stored in a near horizontal position along the superstructure and this probably makes for a tidier appearance.
This system’s big advantages are effectiveness – reducing roll by about 70 per cent, low initial and ongoing cost and reliability since there are no mechanical or moving parts – in the ten years we’ve owned Envoy no part of the system has needed replacement or maintenance. Just now we’re having the birds epoxy-painted over the galavanising which is rusting slightly.
It’s disadvantages are that it slows your boat down by about 10 per cent, there is some risk of the birds fouling flotsam or lines in the water (although ours never have) and the system cannot be rigged and de-rigged in shallow water or confined spaces.
Another huge benefit of this system is that by suspending a different type of metal plate the system provides highly effective stabilisation at anchor. Envoy’s plates, known as “flopper-stoppers”, each consist of two flat plates of stainless steel plate joined together along one side with a hinge. When the boat rolls downward the hinge allows the plates to close together and drop rapidly and when the boat rolls upwards the hinge allows the plates to open and resist upward pressure. This system is extremely effective enabling us to anchor in places where roll or wakes would normally make it too uncomfortable. Flopper stoppers are comparatively light and easily deployed and retrieved by hand.
They can be used in depths over four metres.
Laurie holds a flopper-stopper
Here the port flopper-stopper has been deployed alongside a jetty to reduce the effects of a side-swell during a gale in Cephalonia
Next posting will look at ACTIVE stabilisers and our view on what is the “best” option.
