Boats have a bad tendency to leak. Old wooden boats leaks both from below and from above. (Did you ever wonder why old sailors (and pirates) are ever so frequently scrubbing the deck? It's because the wood should not dry up and crack and start leaking. Or so I thought, until I did some few minutes of research - it may be a myth). Almost all boats with an inboard engine and a fixed propellor shaft leaks a little bit where the propellor shaft goes through the hull. Small open plastic boats nowadays usually have an air-filled hull so they will float even when capsized ... but they are also often leaking, so it's quite often some water inside the hull. Inflatable rubber boats and RIBs are leaking air, except when they are brand new. Some sailing boats leaks by the keel bolts. While most boats have a reasonably water tight hull, the deck is another story. Whatever material the boat is built from, screws are a source of frustration, as are windows. When it's raining heavily, water will enter. Some ventilation shafts and other openings may be well-designed to keep vertical rain out, or horizontal rain coming from the front, but quite often water will find the way into the boat.
It can be very wet at the sea, even when it's not raining
When sailing in rough conditions, waves will engulf the boat and throw big amounts of water on deck. In my previous sailing boat (made from glass fibre), sometimes I would keel so much that parts of the sidedeck would be under the waterline - I learned the hard way that the boat wasn't completely water tight. Not to forget all the winter problems ... while rain usually falls either vertically down or diagonally (sometimes near-horisontal) dependent on the wind, snow can really move in unpredictable ways dependent on the wind and the size of the snow particles and enter everywhere. If the boat can be covered with wet snow, that's really nasty stuff, it can behave a bit like standing water. If it's frosty, trapped freezing water will expand and will make small cracks bigger. Admittedly, most people don't have those winter problems. Here in Norway most boat owners park the boat on land and cover it with tarpaulins for the winter season. It's probably smart, but I want to be able to use my boat.
This design works well against sea spray and diagonal rain while staying at anchor, but every now and then we're getting rain water or snow through this funnel
What was that guy thinking when he made this? It is indeed protecting against water coming horizontally or diagonally in from the front (like sea spray or rain when it's windy and the boat is by anchor), but quite often the water goes straight into those gills
It's not only leakages that is a problem - humidity comes from the inside too, people breathe and sweat, cooking may releases big amounts of humidity, we even have a shower onboard ... and water that has leaked in without being mopped up will contribute to the humidity. All this humidity has to either be ventilated properly out or collected in some dehumidifier. When using the boat in cold conditions, there can be huge problems with condensation on the windows, and I was also wondering if some of the moisture problems in the wood may be due to humidity coming from the inside (probably not).
With leakages comes moisture. Since my boat is wooden it starts rottening (it's actually layers of wood glued with epoxy, and epoxy tends to be water tight, so it's a bit cheating - nevertheless I do have problems with rotten wood). Even glass fibre boats may have problems, they often have wooden details, interior, teak deck, etc - some boats are even built with a sandwich construction with a thin sheet of balsa wood surrounded by glass fibre, sooner or later there will be some leakages and the balsa will start decomposing. Water entering the boat also causes humidity inside, which will affect everything - tools gets rusty, books gets ugly, wood may rotten, other metallic surfaces starts rusting, there may be electrical problems, etc.
My moisture problems
both handles are leaking and dripping when it's raining. Do you have any clue on how to fix this? Pleeease write something in the comments field!
I actually wasn't aware of those black spots, saw them just now. Bad stuff ...
I haven't been very good at fighting moisture problems. During my first years as the owner I did very little maintenance ... why should I, everything worked just fine and I didn't have much clue about what was needed to be done. The first hints that something was wrong came with varnish that would fall off. Some of the spots was probably because I hadn't been good enough at maintaining the varnish itself - it's important to put an extra layer or two every year, but other places it was due to humidity under the wood. So, on the unprotected wood there should be seven layers of varnish. It's a lot of work. And then, after going through all this work with the varnish ... the varnish would just peel off. I was naive enough to believe it was because my varnishing work wasn't good enough, so I would just keep on varnishing. I never really had a proper understanding of where the water enters, where there are problems with humidity and how to get rid of the humidity.
I believe most of the moisture comes from leakages in my teak deck. I've started removing the strands of glue from between the teak planks and replacing it with new glue. In the beginning I would just apply new glue to make sure no more water would enter, but I've realized that I need to get rid of the humidity in the wood, that means I have to keep it open for a longer while and let the wood dry. That's rather non-trivial in a location where it's raining every so often.
I bought some moisture meters. There are actually parts of the boat that is in OK condition, but I realize that the problems are a bit out of hand. I think I have no option except putting the boat under a tent or a roof, open it properly up and let it dry for a longer time. The current plan is to "park" the boat inside a hangar or something from the autumn.
Summing it up
Almost all boats are leaking (more often from above than from below), it's difficult to locate the leakages and deal with them, and leakages are a major problem. I've considered that to keep this boat in a (relatively) good condition, I should park it under a roof after the summer seaon and try to dry it up properly.
Everything else, own work, cc-by-sa 4.0 license applies.