Strange lines on hull antifoul

[Don C L]

Well somebody in the Navy seems to think aliens are dwelling in ocean depths. Maybe they have a taste for French boat scum… and they have two fingers.

[sinnerman]

Did you sail near any French or US Islands where nuclear bomb tests were once performed?

Could be a new specie like Godzilla..

[Capt Clark]

Baffling. Please let us know if you find out.

[boatman61]

Sea slugs...
https://opistobranquis.info/en/introduccio/visualcat/

[nofacey]

And the hull wasn’t cleaned/hand scraped while in the water?

[Kit_L]

Joining this simply to see is there's a credible explanation. I have never seen marks like this on a hull.

[MicHughV]

Well, I've been looking at this long and hard. I don't see any gouges. I see the pattern over what looks like old bottom paint, the brownish stuff.
I don't think any critturs are involved here.

Seems like someone was having fun with a paint brush and yanking your chain in the process.

[wyb2]

If some feeding animal explains it except for the parallel pairs, wonder if it could be an individual with an injury that causes a gap in its effective feeding area.

[MicHughV]

Why would any animal/creature want to eat bottom paint ?? That paint is poisonous to marine life. That is the whole purpose of the paint in the first place.
I simply don't see any marine critturs involved here.

[Sun and Moon]

Originally Posted by MicHughV

Well, I've been looking at this long and hard. I don't see any gouges. I see the pattern over what looks like old bottom paint, the brownish stuff.
I don't think any critturs are involved here.

Seems like someone was having fun with a paint brush and yanking your chain in the process.

This is an interesting idea. Could the marks be due to surface prep before launching? For example, did someone do a light sanding before launching, leaving the striped pattern invisibly in the paint? Then marine life attached to the areas not as well sanded and left clear stripes where the sanding was slightly better?

What happened when you power washed? Did all the stuff come off?

[longtermcruiser]

Intrigued with sea slugs, but still perplexed with the parallel lines
Nope, don't believe it was do with surface prep. We did nothing different than usual, only a few spots of hand sanding.
Didn't power wash when we exited the water.
Nobody cleaned the hull in the water.
We've lightly cleaned the hull with a green scrubbie and are relaunching tomorrow, hopefully. We'll be lifting for the winter in a month or two and will be curious if the lines reemerge.
It's REALLY perplexing!

[MicHughV]

Not that is of any value, but having spent some 35 years afloat, can't say I've ever seen this.
I have in the past had the anchor rode rub up against the hull in a wind against tide situation, and that was my initial though, but the paint on those markings appear to be " untouched" so to speak.

One more wild guess. Maybe the bottom paint was not mixed properly at the time of application, or a bad batch of paint ?? allowing the streaks ?

[boatman61]

Originally Posted by longtermcruiser

Intrigued with sea slugs, but still perplexed with the parallel lines

Couples on evenings dining out...

[rognvald]

Was the boat on the hard? Was the boat in the water when you picked it up? How long had it been in the water? Was the bottom being cleaned? When was the last time you sanded and painted the bottom before picking it up?
Rognvald

[longtermcruiser]

Boat was stored inside during winter (for the first time in 34 years). Launched in mid april, with new seajet paint, sailed along coasts belgium (quickly,), and liesurely along normandy, brittany and s biscay coasts. We had a transmission failure in ille d'yeu, so we lifted out there after 2 weeks in marina. The photos are what we found after lifting out. No washing or scrubbing.