Marine corrosion

 That day when we went inland water sailing
 The galvanised main halyard pulled apart.
 I had not noticed that it had been failing
 It finally gave up before our start.
 The metals that we find in buried treasure,
 Like platinum and gold, without a doubt,
 Resist corrosion. But by any measure, 
 For boats, their cost-strength ratio rules them out.
 I made this part with hacksaw, file and drill,
 From stainless three one six — it’s for our boat.
 This alloy, though expensive, no doubt will
 Survive the fierce environment afloat.
 For ev’ry task some alloy is ideal
 And when you’re talking boats, it’s stainless steel