Could a whale cause this?

[Naughty Cat]

We put out from Imperia (Liguria, Italy) a few weeks ago to head up the coast with an ok breeze, and a frustrating current from the north. A few miles offshore the depth sounder showed we were over the shelf at 200m+. The charts, as you would expect showed no rocks, obstacles etc..

Then the depth gauge showed 6.5m. Then blank, then 5.8m, blank, 6.5m etc and so on between 5.8 and 6.5m for 20 minutes or so. Eventually we tacked and it did the same at around 10m for about 5 minutes and then went blank again. There were no further anomalous readings that trip. I checked the depth sounder that night and it was clean.

Imperia is well known for whale sightings. We did not see any but it got us wondering whether we had something under us. Anybody else experienced something similar. Are we just wishful thinking?

[hpeer]

I’m inclined to a thermocline.

[a64pilot]

I’ve had similar and thought it maybe Dolphins, but only for a few seconds. My depth alarm goes off, I look and see the depth change it’s so fast.
So I do believe a marine mammal can definitely be under your Boat, but for 20 min.? That is a long time.

[SSgtPitt]

Mating season?? Does the underside of your boat look a little like a whale when you look up from underneath? Did you hear any sweet nothings followed by irritated grumblings after 20mins?? Just a thought.

[Don C L]

I’m thinking a school of fish. One night I saw an enormous blob of bioluminescence swirl under my boat for a good 20 minutes. My first thought was a whale too... until nothing ever came up to breathe.

[newhaul]

Whale is a possibility in your area . Here it would be a bit of a different critter made out of steel.

[danielamartindm]

To quote a character in Melville's "Moby Dick,"

"Why bless me, a whale can do anything!"

Why do I find myself wanting to believe that?

[DeepFrz]

Russian sub?

[Jd1]

What is the range for your depth sounder? I get that sort of thing happening regularly when depth is more than 600 ft or about 200 meters !

[Peregrine1983]

This happens with our depth finder occasionally. Kelp, fish, whales, dolphins... who knows.

We recently had a humpback swim right under our boat just off Brooklyn, but as you might imagine I wasn't focused on the depth finder. The fat mammals have come back and it's pretty awesome!

Please excuse my cussing... we've seen plenty of dolphins, but we'd never seen an urban humpback. I cut the video short as my cussing gets a bit out of hand and the whale disappears under the boat.

https://www.youtube.com/watch?v=pyuoDMeVY6o

[belizesailor]

Yes, a whale (or lots of otherthings), could cause odd behaviour on your sounder.

I had my sounder go to about 6' when sailing thru the Windward Passage in moderately heavy weather...Holy Carp! Checked my navigation quickly...nope we're fine...then some variety of beaked whale (like a Pilot Whale) rolled out from under the boat and looked at me...like he knew exactly what he was up to...smart ass. [emoji6]

[Lost Horizons]

Originally Posted by Naughty Cat

We put out ...

A mating season indeed.

[barnakiel]

Big fish, seaweed, thermal turbulence, etc. Whales off course too.

Or else the instrument playing up.

b.

[Pete7]

Originally Posted by newhaul

Whale is a possibility in your area . Here it would be a bit of a different critter made out of steel.

Indeed a very good reason for having the echo sounder on plus playing a bit of ACDC loudly on the hifi so they know you are there.

As a diver, I could always recognise my own rib by the unique V4 engine sound when underwater. The scary thing was surfacing if there were yachts under sail in the area, often silent with big metal bits handing down.

Pete

[GTom]

Originally Posted by Pete7

As a diver, I could always recognise my own rib by the unique V4 engine sound when underwater. The scary thing was surfacing if there were yachts under sail in the area, often silent with big metal bits handing down.

Add the deeper draft of the sailing boats too...