Thanks to all who replied, I'm beginning to wish I'd never seen the BT. It was part of the package when I bought shares in NB Tranquility. Last year The BT stopped working when we were on the R. Nene and I decided to take a look to see if there was anything I could do to get them going. They've been weak for a long time and we've seen frequent brush replacements. I then discovered the wrong brushes were fitted, 24 volt type (single bonded braid) instead of 12 volt. (Twin bonded braid). I managed to clamp what was left of the burnt out braid between the leaf spring and the brush, and that got it going again for a short while. Since then the BT has been removed for a professional service and within a month of that new brushes were fitted again, because they were damp - probably from condensation. I've spoken to a couple of electrical engineers and they both said the brushes would only need replacement if the unit had been immersed and there was evidence of corrosion or degradation inhibiting the performance.
The way I see it is this:-
24 volt brushes = twice the resistance = half the performance = over heating of the braid - and a bill fast approaching £1000.
Thanks again,
K