Keith-i
Well-Known Member
Here's a couple of close-ups in case it helps. The tinge of blue in the background is where some antifoul came off with the sample.
White deposits on rudder
- Thread starter Keith-i
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Hydrozoan
Well-Known Member
No obvious structures in those lumps, I accept - I confess myself stumped, but will just ask a few more questions:
(1) What is their rough size?
(2) Did the acid alone give a much less intense and/or less orange flame colour than the acid which had dissolved the deposit?
(3) Is the boat moored in ‘full strength’ seawater, or is it heavily diluted with fresh water?
(4) When the boat dries, are the areas of the deposits in mud, or just dry?
(1) What is their rough size?
(2) Did the acid alone give a much less intense and/or less orange flame colour than the acid which had dissolved the deposit?
(3) Is the boat moored in ‘full strength’ seawater, or is it heavily diluted with fresh water?
(4) When the boat dries, are the areas of the deposits in mud, or just dry?
Keith-i
Well-Known Member
The accretions vary in size on the rudder but for scale in those photographs the background is standard A4 paper with feint lines so perhaps 8mm per line space.
I could not discern any appreciable colour difference between acid alone and solution.
The boat is moored in St Helier old harbour on the mud, floating for about 5 hours per tide. Full strength seawater but obviously the likelihood of contaminants in the mud from surface water run-off from adjacents roads and the like. This is not the first year it has happened.
The depsoits are above the mud when the boat is dry.
I could not discern any appreciable colour difference between acid alone and solution.
The boat is moored in St Helier old harbour on the mud, floating for about 5 hours per tide. Full strength seawater but obviously the likelihood of contaminants in the mud from surface water run-off from adjacents roads and the like. This is not the first year it has happened.
The depsoits are above the mud when the boat is dry.
Hydrozoan
Well-Known Member
Thanks. That being so, as I explained before we cannot rule out that any colour in the flame came from (say) calcium in the acid, and not from the deposit. So given the fizzing but no H2S odour, it could perhaps be calcium carbonate, or perhaps a zinc carbonate or hydroxy-carbonate.
Do any boats on adjacent moorings get similar deposits – and if so, what are their rudder materials?
Keith-i
Well-Known Member
Well, I've been practising my flame tests and can fairly confidently say that the acid alone gives a very faint yellow flame whereas the deposit in solution is much more pronounced. Photos below show the two tests. I've yet to inspect my neighbour's rudders.
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Hydrozoan
Well-Known Member
That difference looks pretty convincing - though to 'make assurance double sure' I'd dissolve a similarly sized bit of a shell just to confirm the colour you get from calcium under the particular conditions of your flame test.