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Algedugen - et alternativ til bundmaling ?
The concept in this method, called algae-sheet, is to avoid light to reach the
underwater parts of the hull, hereby reducing the photosynteze and therefore the growth of
algae. By minimizing the amount of fresh water around the underwater hull, the amount food
particles required for the growth of barnacles and mussels is reduced. This is obtained by
making a cover that fits to the underwater hull. This cover is placed in the marina, where
the boat normally is placed.
The method is tested during the sailing season from the end ofApril 2000 to the mittle
of October 2000.
After this test it is proved that the concept has an effect.The amount of
"life" underneath the hull was not at a level that spoiled cruise or pleasure
sailing.
The time consumption over the season was about 1 hour - also a reasonable level. In
addition to this it takes about 1 hour to remove barnacles and seaweed from the outer side
of the algae-sheet, but on the other hand the work with other anti-fouling products is
reduced.
The pattern of the effect of the algae-sheet is pretty clear. In the areas where the
sheet is close to the hull there is not any algae, barnacles or mussels.
The reasons are the lack of light, lack of food and maybe the small movements of the
algae-sheet against the boat, initiated by waves and wind also has an effect.
The concept is now ready for a major part of the pleasure boats, and especially in
freshwater areas where barnacles do not exist.
A further problem has to be evaluated.
If a more common use of the algae-sheet is taking place, a visiting boat will have to use
the algae-sheet of another boat.
The solution on this problem is partly integrated in the design of the algae-sheet as
the mooring in the harbour is carried out in elastic material, and the alga-sheet is open
and ready for arrival when the owner has left the place.
If the visiting boat is smaller than the owners boat, there is not a problem. If the
visiting boat is of same size, but with long keel design, the algae-sheet will simply be
pressed below the surface. This is not a problem. The same will happen if the visitors
boat is larger than the owner, but often it will not be possible to enter between the
mooring posts, and the problem is non-existing.
But anyway, sometimes a very small algae-sheet will be placed where it is possible for
a large vessel to enter, and here it would be reasonable to move the algae-sheet, when
leaving.
The use of propellers in the algae-sheet will result in damaged propellers and damaged
algae-sheet.
The waste from the annual cleaning of the vessel and the algae-sheet is not toxic, and
is to be treated as waste from the ordinary housekeeping.
The selection of material is a matter of resistance to the environment, the dissolution
and the enviremental load after end use.
If PVC is chosen the algae-sheet will withstand the load for at least 10 years, and in
the next 10 years if we are able to do a 100% PVC-recycling, it is a fair choise.
If reinforced Polyethylene is the choise, a "guess-estimate" on the resitance
will be 3 years. Therefore the use of material, and thereby resources will be at least 3
times larger.
But on the other hand, when dumped, the rest-product from polyethylene is water when
burned.
The tested algae-sheet is made of 30 sqr.meter PVC, with a weight of about 13 kg. This
will develop 18,5 kg Calcium- or NatriumChloride depending on the smoke treatment
procedure, and the waste will have to be stored at a deposit.
The final choise of material could be a Polyethylene with a better resistance (at least
10 years) or a PVC softener with a phthalate with a short half-life time and a low toxic
effect.
In the season 2001 a PVC without phthalates is tested as material for the algae-sheet.
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