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TECHNICAL LIBRARY

GENERAL ITEMS

STAINLESS STEEL

      There are several types of stainless steel with different properties and therefore suitable for different applications in the marine environment. Stainless steels have varying quantities of Chromium, Nickel, Molybdenum and Nitrogen resulting in different properties and yield strengths.
      The more common types are Austentic - 300 series. They have excellent ductability, good strength, are non magnetic and have good weldability. Grade 316, known as marine grade, is generally superior to grade 304 and both have good corrosion resistance. The chart below shows the different marine applications for these grades.
     Duplex stainless steels are a separate group which have been used for many years in the chemical, petrochemical& oil & gas industries. However it is only recently that these grades have become available for general use. For marine applications the most common of these grades are SF2205 and SF2207. In general their properties far exceed those of 304 and 306 grades for a marine application.

	APPLICATION	304	316	SAF 2205	SAF 2207
HULL	Hull Construction	x	x
	Keel	x	x
	Keel Bolts	x
	Nuts & Bolts	x
	Fuel / Water Tanks
ENGINE	Prop Shaft	x	x*
	Hydraulic Cylinders	x
	Heat Exchanger Tubes	x	x
	Cooling Coils	x	x
	Brine Coolers	x	x
	Exhaust Piping	x	x
	Seawater - Cooled Exhaust	x	x	x
	Skin Fittings	x	x	x
RIGGING	Chainplates	x
	Rod Rigging	x
	Shackles
	Screws & Fastenings	x
	Rigging Screws	x
	Spreaders
	Mast Fittings
FITTINGS	Pulley Blocks
	Bow Rails
	Ladders
	Staunchion Posts
	Deck Fittings	x

x = unsuitable

Empty boxes or ticks = suitable

x* - Only suitable if galvanically protected. eg. Zinc Anode or Aluminium Boat

As a General Rule
304 - May be used for fully exposed components, frequently washed with fresh water
316 - May be used for all hull and deck fitting applications above the waterline
SAF2205 - Offers higher strength and lighter weight for the same applications as 316 and can be additionally used up to 60 degrees C in wet exhaust systems and in all submersed applications.
SAF2507 - Offers higher strength and weight savings and can handle all marine applications with no risk of corrosion in tropical waters (above & below the waterline) and hot, wet exhaust systems.

DINGHY CONTROL

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For the times when the dinghy is being towed and the waves get bigger that anticipated there is a way to reduce the tendency of the dinghy to surf and thus reduce the risk of it banging into the mother vessel. Simply fix a stout funnel to the tow line with the spout facing forwards - the positioning of the funnel along the painter will need to be found by experiment with the dinghy to be used at the normal towing speed. A snap hook attached near the funnel might be useful for quickly shortening the tow prior to mooring or berthing.
Of course a dinghy should not be towed in the open sea. Where there will be swell and waves a dinghy should be stowed securely on board.

Normal tow - with tension on the painter

The line tension reduces - funnel into the water

Dinghy over-runs funnel which reverses

Reversed funnel exerts drag on dinghy and slows it down

FENDER BOARD

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A useful item to have on board is a multipurpose fender board. A piece of oregon between 200 & 300mm wide and 30mm thick is suitable with a length to suit the boat and the main purpose for its use. Aside from a fender board it can

also be used as a ladder, gangplank, makeshift table and a platform for washing dirty feet.
Cut a series of elongated holes (about 180mm long & half the total width) along the entire length at about 300mm between the edges of the holes. Round off the inner edges of these holes. Drill a pair of holes at each end of the board for attaching control ropes. Round off all edges and paint.

SIGNAL FLAGS

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SIKAFLEX PROPERTIES

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......Sikaflex comes in a variety of different forms for specialised purposes.. To bond materials two properties are essential in a marine environment - both materials must be adhered to and there must be no breakdown from water and UV radiation. Unfortunately Sika or no other product will bond a polycarbonate to alloy in an external environment subject to UV radiation. Sika 295UV comes close but preparation agents need to be applied and a UV protection strip also needs to be added. An important technique when using these type of products is to ensure that a bead of the sealant stays between the two surfaces. This means that fittings should NOT be tightened all the way down. Tightening should be done in a uniform fashion until the sealant starts to ooze out from the whole edge. Then stop and allow curing before final tightening or stressing.. Specialist advice would be useful before use. The following is a short summary of different Sikaflex products.
    #..221 - Polyurethane sealant most commonly used for caulking as it will withstand deck movement up to 10%
    #..291 - Polrurethane sealant is a fast curing, sealing & bonding compound developed for manufacturing and repair applications. It has excellent adhesive properties and can be sanded and overpainted when cured.
    #..298 - A bedding & bonding compound designed for use with large horizontal areas such as deck laying. Has and extended working period and spreads more easily and smoothly than 291.
    #..292 - A high strength polyurethane based adhesive & sealing compound - used specifically for constructed applications such as bonding deck to hull, bedding in deck hardware such as hatches, chainplates, toe rails & all-through hull fittings.
    #..295UV - A glazing sealant. It is a fast curing high performance adhesive, designed for bonding windows and portholes. It is suitable for use with all types of glass including polycarbonates.

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