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hydrophones

plankton

New member
Joined
3 Oct 2006
Messages
35
Hi has anyone tried hydrophones as an assistance (alarm) to napping sailors? Low power portable models are available that can be used with an amp to give an audible alarm/indication of a prop nearby...apparently picking up noise from a couple of miles?
 

Noddy

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Joined
22 Jun 2005
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Thames Estuary
This is not a very active thread.

Probabbly because we are all flumuxed by the technical questions.

Sounds like a good idea but:
How do you tune out background noise? (Waves etc)
How deep does it need to be?
Is it good for your mental health to have whales wispering in your ear while you sleep?

These and other questions make it difficult to start a conversation.

Any submariners out there?
 
G

Guest

Guest
An ingenious idea - but even if the technology could be ironed out to make this possible - a ship travelling directly towards you ('worst case' - but the only one worth worrying about) at 16 knots, if detected 2 miles away will give you just 7.5 mins advanced notice of the impending collision.
In that 7.5 minutes you'll need to fully wake-up, get-up, get-out and try and establish a fix accurate enough to determine the appropriate avoiding action. At night, in a lumpy sea (and probably scared witless), this won't be at all easy. How much time will then be left to put the avoiding action into practice ?

I think at least double that detection distance is required, and a lot more if possible - which implies equipment such as radar, AIS, and/or the Mk.I eyeball.

Colin
 

Aeolus

Active member
Joined
3 Aug 2004
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802
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Sussex
But if you are asleep out at sea, 7.5 minutes warning is an awful lot longer than no warning. I think that that would be enough time to get on deck, see the approaching ship, start the engine (if necessary) and change course (if necessary).

One big question would be how much power such equipment would consume. Some sort of amplifier would presumably be necessary since sleeping with headphones on might not be very restful.

Another big question is whether the gradually increasing engine sound would wake you - if you're a deep sleeper, perhaps not.
 

Noddy

Member
Joined
22 Jun 2005
Messages
621
Location
Thames Estuary
Can't work out the qoute thingy

"The ship heading directly towards you"

What we are really interested in is the ship on a collision course. This might be a ship that is nearly parralel to your course, at the same speed but gradually getting closer.

Visually (and I guess on radar) we identify these by their bearing. If the bearing is steady and the ship is getting closer you are going to hit it. (try watching the relative bearing of another car as you approach a roundabout - not my responsibility if you hit it etc etc). You can tell whether you will pass in front of, or behind the other ship just by monitoring the bearing.

This means that an approaching ship could be a threat for a long time before contact.

Aside from all this I think it would just be interesting to hear stuff as you sail. In the same way that a fish finder is pretty useless for finding fish but jolly interesting.
 
G

Guest

Guest
[ QUOTE ]
Can't work out the qoute thingy

"The ship heading directly towards you"

What we are really interested in is the ship on a collision course. This might be a ship that is nearly parralel to your course, at the same speed but gradually getting closer.


[/ QUOTE ]

A ship doing 3 or 4 knots in mid-ocean (?) With current financial pressures, that skipper would soon be sacked !
Relative to a much faster-moving container ship or military vessel, a 20ft sail boat making 3 or 4 knots is - for all practical purposes - more-or-less stationary in the water. That's what I meant by "The ship heading directly towards you".
If we're being pedantic, yes then by all means - "the ship on a collision course with your own vessel."

[ QUOTE ]

Visually (and I guess on radar) we identify these by their bearing. If the bearing is steady and the ship is getting closer you are going to hit it. (try watching the relative bearing of another car as you approach a roundabout - not my responsibility if you hit it etc etc). You can tell whether you will pass in front of, or behind the other ship just by monitoring the bearing.


[/ QUOTE ]

Thanks for the 101 on taking bearings. But in order to take a visual bearing you have to be able to actually see the approaching vessel. If you're in the trough of a deep swell, your visibility will be zero (or if we're still being pedantic, a few tens of feet). You'll only be able to do a 360 sweep when your boat is lifted up by a wave. The visibility from the deck of a small boat at sea is - except under calm conditions - severely restricted.

[ QUOTE ]

This means that an approaching ship could be a threat for a long time before contact.


[/ QUOTE ]

Sure - but they are not the ships to worry about - if closing slowly you will have spotted him during one of your periodic lookouts - and may even have dialed him up on 16 for a chat ....

Colin
 

Noddy

Member
Joined
22 Jun 2005
Messages
621
Location
Thames Estuary
I am disabled by my inability to do the qoute thingy. But a couple of points:

I used the idea of the same speed to make the constant bearing point. As you know, it works regardless of different speeds.

Who's talking 3 or 4 knots? some of us multihullers have been known to overtake commercial ships (admitedly little rusty ones)

Because the equipment is for collision avoidance when sleeping, the important question is; Could you actually get to sleep wearing a pair of hydrophones?

Paul
 

JREdginton

New member
Joined
15 May 2006
Messages
155
If it is a case of steadily increasing signal strength then why not use some sort of trigger, when the signal reaches X trigger a proper alarm? Not my field but am sure it is not rocket science.

On a side track, if the vessel is heading towards you is it's signal not reduced? Not up on hydrodynamics and all that stuff.
 

Noddy

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Joined
22 Jun 2005
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Location
Thames Estuary
I think we need some expertise to outline the technical possibilities.

I have a mental image of a guy in a submarine telling the skipper (who is standing behind him) what the enemy are doing in incredible detail. Then the skipper takes the headphones off of him and says something equally interesting.

We need a submariner!
 
G

Guest

Guest
[ QUOTE ]
If it is a case of steadily increasing signal strength then why not use some sort of trigger, when the signal reaches X trigger a proper alarm? Not my field but am sure it is not rocket science.

[/ QUOTE ]

You need to be able to isolate and identify the sound of a propellor from the background mush - that would take serious expertise in digital signal processing, as well as significant processing power, which in turn means a continuous power supply (on a small boat !). If you monitor unfiltered noise strength, then each time your hull slams - the alarm will go off !

[ QUOTE ]

On a side track, if the vessel is heading towards you is it's signal not reduced? Not up on hydrodynamics and all that stuff.

[/ QUOTE ]

Louder as the vessel gets nearer.

Colin
 
G

Guest

Guest
[ QUOTE ]
I have a mental image of a guy in a submarine telling the skipper (who is standing behind him) what the enemy are doing in incredible detail.

[/ QUOTE ]

Yeah - me too. But think on - that hydrophone is manned 24/7 by a shift of guys who only do THAT - they don't have sails to tend, or gear to watch for chafe (or meals to cook, charts to consult ....).

Also, remember that those guys are using state-of-the-art gear (for it's time), and have to concentrate fully as the sounds fade-in and fade-out. Sounds like a very demanding job to me.

These days survey ships tow hydrophones behind them, to eliminate their own hull noise - but surely that's not an option here ?

All-in-all I don't see acoustic detection offering anything that the Mk.I eyeball can't provide - and without all the complications.

My 2p's worth.

Colin
 

plankton

New member
Joined
3 Oct 2006
Messages
35
Hi,

I contacted a hydrophone manufacturer you may be interested in their reply below

"Yes, our C54XRS hydrophone could easily detect the sound of ships from 2 miles
away. The sounds could easily be played over an amplifier so that you could
listen for the sounds of the ships. However, if you will be towing the
hydrophone, then there will be flow noise that will limit the range that
you'll be able to hear the ships. The flow noise will mask other sounds"
 

Noddy

Member
Joined
22 Jun 2005
Messages
621
Location
Thames Estuary
Thats some great research.

This sounds like a job for NASA Clipper (or whatever they are called)

I think it would be fascinating to have another source of information about what is going on around the boat.

No time / expertise foir the development work I'm afraid. Still working on ideas for a trim tab driven autopilot for a lifting rudder.
 
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