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how fast does rust attack hull at waterline, should i wait to take her out

my 34ft 1991 sringer is corroded metal at much of water line, shes due out for complete blacking [extremely overdue] etc at end of march [last dates for the 2 week for 1 week deal].
my dilemma is should i take her out sooner to treat the rust but have cold/wet weather delaying the bitumen drying or wait till end of march in hope of better weather and accept that the corrosion will meanwhile continue working

Asked by: mb  | 12.07pm, Sunday 3 November

WW says:

The speed at which rust forms on a hull varies depending on a number of factors. One is the quality of the water it is in. A relatively clean rural canal is less likely to attack the hull than one polluted by chemicals. Any salt in the water will also speed up the rusting process.
The quality of the steel also has a bearing. If the particles that make up the steel are fairly consistent, it will rust less than steel that has more varied particles. This is because, when immersed in water, the particles form a cell similar to those in a lead acid battery. Some particles act like a cathode while some act like an anode which is then depleted. The greater the variation in the two particles, the greater the corrosion.

  • How urgent the need to treat your hull is depends on the quality and thickness of the steel and how well it has been protected during its life. Taken as a percentage, five months compared with twenty eight years is not much so you might take a gamble on the delay not making much difference but this is something only you can decide. If the worse comes to the worst, you may have to consider over-plating around the waterline.

    Graham Booth  | 1.03PM, Thursday 7 November

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