Help with nasa depth sounder

[Crinan12]

Hi all
Issue with nasa depth sounder - was hoping someone could help.
It often gives totally wrong readings. I.e display says 10 metres when we are in 100 metres of water.
However in shallower water it seems fine. When on our mooring it gives the correct depth and the reading changes with the rise and fall of the tide and it seems quite happy.
I've taken out the transducer thing from the tube that is fitted on the hull but there isn't really much to look at. There is oil in the tube but only a little bit - maybe a cm. Should the tube be fill of oil?
Any thoughts would be appreciated
Thanks
Douglas

 

[Major_Clanger]

The transducer head must be completely submerged in vegetable oil, right to the top of the tube that houses it. Any bubbles or air gaps will cause spurious readings.

Bit of Fry crisp and dry and job's a good 'un!

 

[Crinan12]

Thanks major
I'll fill it up and see how it goes!
Ta

 

[pvb]

The transducer head must be completely submerged in vegetable oil, right to the top of the tube that houses it.

Why? Transducers will also work if just stuck to the hull. The whole thing doesn't need to be submerged.

 

[Poignard]

" Pour the oil supplied in the sachet into the tube until the tube has approx. 25mm ( 1 ") of oil in depth. Check that there are no oil leaks "

From the instruction leaflet that came with my NASA in-hull transducer mounting kit.

A drawing in the leaflet shows that that depth is sufficient to just cover the head of the transducer.

I remember reading somewhere that the oil supplied is castor oil but I can't remember where I read that.

 

[Major_Clanger]

Why? Transducers will also work if just stuck to the hull. The whole thing doesn't need to be submerged.

Only if the transducer face is absolutely flush to the hull with no air gaps. Anything that could provide an air bubble could cause an odd reading in the same way that if the boat's well heeled over and a part of the transducer head comes out of the oil. That's as I understand it anyway. Seems easier to be in the doghouse for pinching some cooking oil than possibly going aground!

 

[PaulRainbow]

Not wise to use just any old oil. Some oils go rancid, don't want those in the transducer. If in doubt, will it with anti-freeze.

 

[Major_Clanger]

Not wise to use just any old oil. Some oils go rancid, don't want those in the transducer. If in doubt, will it with anti-freeze.

Quite so.... Swan owners will only used cold, first-press Sicilian olive oil.

 

[mattonthesea]

NASA software very old and unsophisticated. But works?.

After a certain, variable depth they just play. Mine spent a month across the Atlantic displaying anything from 2.1 metres to out. I used it as a diversion: could I guess the next number! But in shallower water it does a fine job.

 

[Crinan12]

Hi Matt that's sort of my experience with it so far
Shallow fine,deep quite random
As long as i can trust it when shallow that's okay

 

[davidpbo]

I had exactly the same problem with our Nasa depth sounder on the Clyde. Seemed fine in shallow water but displayed erroneous readings in deep water. Someone mentioned it might be the oil in the transducer tube but I haven't checked it yet. On Windermere it was fine last season, max depth there less than 100M.

I also wonder whether if it is a bit rough whether the oil might not get air in it, especially if it is a bit low.

I don't think the new head and transducer I fitted came with oil. Maybe it comes with the tube if required.

Is Castor oil best? The boat is 30 years old so maybe I should replace the oil as it may be the same age.

 

[DownWest]

We use Johnson's Baby Oil, works fine and just enough to ensure the head is covered. Castor tends to go off.

 

[ghostlymoron]

We used mazola which didn't seem to deteriorate but as it's an organic product you'd expect to turn off eventually. Maybe change after a couple of years - it's cheap enough.

 

[LONG_KEELER]

We use Johnson's Baby Oil, works fine and just enough to ensure the head is covered. Castor tends to go off.

Can also pour a little bit down the toilet now and then.

Lubricates the seals.

 

[Poignard]

Can also pour a little bit down the toilet now and then.

Lubricates the seals.

And wipe it on your aluminium spars to brighten them up.

 

[Crinan12]

It does seem pretty poor that these things just routinely don't appear to work in deeper water
Almost not fit for purpose surely.

 

[Spirit (of Glenans)]

We use Johnson's Baby Oil, works fine and just enough to ensure the head is covered. Castor tends to go off.

Baby oil is based on mineral oil i.e. petroleum, better to use a veg-based oil which will not deteriorate the plastics involved. Castor oil is preferable as it does not go rancid, unlike cooking oil.
I still have an un-smelly half-litre of castor oil bought eighteen years ago, left over from when I installed a transducer in my first boat.

 

[Poignard]

I have just looked up the invoice for my NASA depth sounder and I see I installed it in July 1998. The castor oil I put in the transducer housing is still all there, it doesn't smell and the depth sounder still works perfectly.

 

[eddystone]

It does seem pretty poor that these things just routinely don't appear to work in deeper water
Almost not fit for purpose surely.

Agree with that - there could be times, e.g. in fog, when finding a depth contour to follow is essential. I had NASA pencilled in if my ancient Echomax stops working - not so sure now.

 

[Graham376]

Ours plays around in deep water (>100m) but so did the Stowe. Accurate enough in coastal waters and ours is glued to the inside of the hull with Plastic Padding fibre glass filler.