Originally posted by L1m3r:

And I think I've read recently that workbenches/etc don't protect dropped items from despawning if they're more than 2m below the water line.

(dunno where and can't find it)

Here: https://valheim.fandom.com/wiki/Player_base

in the first set of bullet points.

I still think the gulls fly away with them.

The only safe place to keep your boat is in a chest, sadly.

Maybe someday they'll add bollards and rope so we can secure our ships properly.

No. Singleplayer

Any mods installed?

Whenever you're in the vicinity of your boats and buildings and objects are loaded in, the boats become prone to damage sustained from colliding with them. This happened to me a couple of times, including their materials vanishing, so I guess the same is happening to your boats.
You mention having stone walls built around the boats and having poles and stakes placed in the water, likely to protect the hulls. Perhaps the masts are still able to hit the stone walls or poles whenever the boats rock on waves created by storms. This results in damage over time and can even sink the ship when sustaining too much damage this way.
I assume that materials vanishing is due to the new coding that unloads unused assets. They likely erase the ship's construction materials when they aren't near workbenches.

And I think I've read recently that workbenches/etc don't protect dropped items from despawning if they're more than 2m below the water line.

(dunno where and can't find it)

@the above two posts, if he's got a workbench and stonecutter on the dock, the mats would still be there. Only the nails would sink (and possibly despawn if deep enough).

No mods, vanilla... Also what I forgot to mention that when I lost my first boat I left some iron scraps there in the boat inventory. When I noticed my boat is missing later I went to look around. All I found was a crate floating on the water named "Cargo" and had all the iron scraps in it. No materials from the ship though...

Is it possible some gremlin swam in there all around the fortification, destroyed the ship and then swam away. Maybe this game is just trolling me

The best thing to do is just vanish the boat yourself. When you are done sailing use your axe on the boat, recover the materials, and store them in your main base. Rebuild the boat when you are ready to sail again.

Not a bad idea

Yeah, it’s unfortunate but you can’t have boats making your docks look pretty without risking them suddenly disappearing.

Gotta break them down and leave them in a chest for later

Originally posted by 654681631:

My boat and 2 longships have simply vanished. No materials left behind.
I have a base in black forest by the sea.
No trolls spawning around anymore and gremlins very rarely.
My ships were docked, protected by stone wall from 3 sides, 4th side blocked by 2x wooden pole against sea waves and weather+ dock is protected by stakewalls and sharpened stakes.

I have abandoned my base for 1 day to explore mountains, returned before sunset and ship was gone.

I don't understand what's going on and how to protect myself more in the future...

It literally just happened to me as well. Second time. One moment my viking longship was parked safely outside....... although greylings have started to make the loooong swim around my base to gnaw on it.............. and now it's gone. Not a sign of it. No wood, no iron nails, no deer hide... nothing. Poof. Vanished.

This is obviously some sorta glitch, so I felt no shame in using devcommands to spawn me a new one. But still........... yeesh.

I also had and still have workbench and stonecutter located in my dock. None of them took any damage

Do you play on a multiplayer server