In January 2018 I reviewed Fenwick’s Tent and Awning Cleaner – a product chiefly marketed to caravan owners – to see how well it would perform at removing stubborn mould growth that had accumulated on my yacht’s Treadmaster-clad side decks. It did an excellent job, and at £5.70 for a one-litre bottle it did so at an excellent price too.

Job done? Well, not exactly. It’s one thing to find an inexpensive and easy-to-use solvent-free product that shifts the gunk, but quite another to stop the problem recurring. And what chance finding something at such an attractive price again?

But it got me thinking… I returned to the local caravan shop where I chanced upon another interesting product – Fenwick’s ‘Over Wintering’. Described as: ‘a coating for the winter months that retards algae growth, black streaks and makes spring cleaning easier’.

This was something I had to look into. Might it mean one less job come fitting out? I particularly liked the bit about making spring cleaning easier. More often than not, what’s good for the caravan is just as good for the boat.

The litre bottle of the water-based solution cost £10 and I applied it as directed: I washed the deck with warm, slightly soapy water then allowed it to dry. Mixing one part ‘Over Wintering’ with four of water, I applied the solution with a paint brush and then left it to dry, and that was it. I could just as easily have used a garden sprayer or a sponge. Once dry, the protection was invisible. A little alarming yes, but hey, reserve judgement.

Come spring, there’s no need to remove it, so I didn’t. There’s nothing there to see. The quantity I used is less than a quarter of the litre purchased, so it should be good for at least another three winters.

Usually there’s mould covering Treadmaster, adjacent deck and weathered wood

Condition of Treadmaster on October 15, same day as application…

…and it looks pretty much the same at the end of March after full winter exposure

PBO verdict

The solution was applied in early October on laying up. In a warm autumn breeze it dried very quickly and soon became invisible. I made no attempt to avoid walking on the side decks during the winter, not that there was much reason to do so.

Come the end of March, Easter weekend, the Treadmaster looked the same as it did during the previous autumn; and that’s the first time that’s ever happened!

Fenwick’s Over WIntering coating is readily available from caravan shops

Usually there’s mould all over the Treadmaster, adjacent deck and weathered wood – Keppel doesn’t have a winter awning.

Importantly, by avoiding the attrition of hard scrubbing the longevity of surfaces is increased. So there’s a long-term benefit too. 

At less than £2.50 a year, to deliver one less arduous job during the fitting out season seems like excellent value to me. I can’t fault it.

To put the quantity used into context, Keppel’s fore, side and aft deck Treadmaster extends along her 9.6m length.

Top tip

Winter mould accumulation on bare wood can be avoided by using a fungicidal wood preservative like Cuprinol. One application lasts for up to thee years.

First published in the August 2018 edition of Practical Boat Owner – download the issue from Zinio or subscribe with Magazines Direct.