Who left the diesel tank cap off?

[penfold]

Tanks without sumps and/or drains are just rubbish; as several others have already said heel the boat so the water gathers to one side of the tank(whichever is easiest to access from the filler) and suck it out, then treat with bug killer. Would be a good idea to consider having inspection hatches and drains fitted this winter, then dealing with this kind of thing is so easy it's not actually a problem.

 

[howardclark]

The filler hole is just the normal size - water doesn’t run in from the deck and given the wind direction the hole was partly shielded by the pilot cabin. Only significant rain in the period was the Monday night storm. Tank is about 600mm tall so 12mm represents 2%. Agree the water has accumulated over the 16years use of the tank. Good reason to clean it out!

 

[Mistroma]

The filler hole is just the normal size - water doesn’t run in from the deck and given the wind direction the hole was partly shielded by the pilot cabin. Only significant rain in the period was the Monday night storm. Tank is about 600mm tall so 12mm represents 2%. Agree the water has accumulated over the 16years use of the tank. Good reason to clean it out!

Yes, it would seem that way. I estimated 5-10 litres of water based on a guess at your tank dimensions. A 205 litre 600mm high tank with 12mm of water works out around 5 litres. A steady 25mm of rainfall per day would be lucky to collect 50mls and you said that the hole is actually sheltered.

It would take more like 4 months of non-stop rain to collect 7.5 litres, rather than a few days, if no water is funnelled into the open filler. I agree that it is time for a good clean out as it is highly likely to have collected water over years, not days.

Water does run down past my fuel filler and I always make a point of applying excess grease to the o-ring after lift out. I also apply a little during the year. I haven't been on board since October 2019, fingers crossed that I won't have a tank full of water when I do eventually get back.

Have you checked the other tank for water? Leaving the filler open prompted a check on one tank. It seems likely that the other would be worth checking.