Buoyancy bags and their properties
  Due to safety regulations the wooden dinghy 12í is required to sail with sufficient extra buoyancy on board. The Dutch rules specify a minimum of 120 kg and the Italian rules specify a minimum of 140 kg buoyancy fastened effectively. Apart from the fact that this extra buoyancy increases crew safety, it also could prevent damage to the boat or the loss of equipment such as floorboards, paddles, oars, bailers etc. Think about how deep a capsized boat without extra buoyancy lies in the water. Exactly! She is almost completely submerged and it takes a rescue boat quite an effort to return the boat to harbour. During that operation all loose equipment is liable to be lost.  
With extra buoyancy, provided it has been attached properly, there is a different story. It will be relatively easy to turn the boat upright. Usually the gunwale will be about 5 cm above the water level with one crew-member onboard, depending on the amount of buoyancy. Personally I prefer 4 buoyancy bags of 50 litres, 2 running from the middle thwart forward and 2 under the side seats including the middle thwart. Of course the room under the seats is limited and therefore the capacity will go down to 30 to 35 litres. Together the capacity will be about 160 to 170 litres. By hauling up the centreplate the quantity of water coming through the slot is limited. With some energetic bailing one should be able to empty the dinghy sufficiently to be able to continue sailing.
This all sounds very promising, but is very much in contrast with reality. Very often the bags are not mounted in the proper way and thus are less effective. One should keep in mind that a 50 litre bag, when submerged, exerts about a 50 kg force trying to break loose. Usually the water temperature is lower than the air temperature thus reducing the volume of the bags and giving them more chance to escape, especially in waves.
Personally I use 3 mm braided nylon or dacron line, one end to fix at a timber just above the floorboard, then straight up over the bag and go behind the same timber and from then on zigzagging and threading behind each timber until the end of the bag. The last run going straight up or down again. Thus the bag cannot go anywhere. Make sure that there are no or almost no creases in the bag as these will become weak spots in the material and a source of future leakages. If one chooses webbing straps to fix buoyancy bags, donít use the easy grip type (Velcro). They let go at the critical moment. Use one belt for every 30 cm. This will prevent the frustration of seeing your bags sail away after capsizing.
There are several producers of buoyancy bags.
In Italy there are very strong buoyancy bags that can also be used as a roller to pull ones boat out of the water onto the beach. I donít know the prices. In Holland Kubus Sports sells yellow plastic coated bags (about Ä 40 per bag) or the cheaper all plastic white buoyancy bags (about Ä 22,50 per bag) including VAT ex works Holland. Other sources of bags include the UK companies Allen and Crewsaver.
Duuk Dudok van Heel
Duuk Dudok van Heel