12v foghorn system?

differentroads said:
I'm with you on that. Mostly because of the thought of big b*ggers like you scraping small b*ggers like me down the side!!
Kidding aside, AIS has been a game-changer in fog for me. Being able to call up a ships bridge, check they have me on radar and who will do what is a huge help. The professionalism of merchant mariners always impresses me. I'd be interested to hear if and how well watch officers hear fog signals from small vessels like yachts and fishing boats.
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This has come up before, and the consensus view was that we can't make a noise loud enough and if we could it would permanently deafen us. The consensus was supported by professional mariners, who had amusing anecdotes about being required to wear ear defenders when using fog signals!
 
AntarcticPilot said:
This has come up before, and the consensus view was that we can't make a noise loud enough and if we could it would permanently deafen us. The consensus was supported by professional mariners, who had amusing anecdotes about being required to wear ear defenders when using fog signals!
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Aye, a 139db air horn sits in category of 'painful and potentially damaging to hearing' that I saw on a number of websites earlier today. Careful with your testing dolabriform!
If an airhirn could hurt us and anyway won't be heard on the bridge of a ship a mile away, maybe there's no point in going further than the frankly ineffective gas foghorn I use (sporadically) nowadays. I've always been one to turn away from ships rather than stand on my rights to cross their bows. Radar, AIS and bridge to bridge VHF make that a safer manouvre. The rest is in the lap of the gods.
 
I was considering this a bit back using a car horn after I got caught a couple of times in fog while short handed. Scouring the depths of the bilge for the air horn seemed precarious at the time, yet in fine weather it seemed an entirely reasonable place to leave the thing. It'd be handy to have a button near the helm... Maybe one of those red things with a flip-up top... :D
The current boat has it tucked in the nav table cubby hole where I tend to lean on it.

Obvs. over 12m you must have a squeaky 120dB whistle complying with annex iii anyway. Presumably such opulent craft all ship with that?

Do we really expect to alert a 100,000 tonne bulk carrier to our presence with a small boat horn at all?
 
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I have a hand held car horn, push button operated, mounted on a board with a hand grip. Power lead plugs into a 12v socket. Only used a few times. Works for me.
 
ithet said:
I have been considering something similar, but using a small horn mounted on the mast rather than a loudhailer, e.g. Stainless Steel Compact Horn

Anyone have experience with these?
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I've no experience of those, but from the look and the price I'd guess it's just a standard car horn chrome plated. For more serious horns see e.g. Horns and accessories - EXCLUSIVE from Nippy Normans, No 1 Supplier of BMW motorcycle accessories! (unfortunately you'll have to trawl through other horn accessories and combination sets with horns & lights etc., but the horns themselves are c£25-£50 ) . Other suppliers are available.
 
Just how reliably do human ears determine direction of a sound in fog? Does the fog make this more difficult than in clear vis?
 
The one time I listened to a ship's foghorn I knew it was somewhere to starboard, and forward of the beam, but couldn't place it any better, just knew it was getting closer. It's the most scared I've been at sea.

Reading the comments from those with ship rather than boat experience, I'll stick to the letter of the law with my little lung operated gadget and scuttle off into 5m or less water if fog comes down unexpectedly. If it's expected, look for me in the bar.
 
Roberto said:
Try and make a sort of hearing cone with a stiff piece of paper, it helps indeed figuring out where the sound comes from.
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Stemar said:
The one time I listened to a ship's foghorn I knew it was somewhere to starboard, and forward of the beam, but couldn't place it any better, just knew it was getting closer. It's the most scared I've been at sea.

Reading the comments from those with ship rather than boat experience, I'll stick to the letter of the law with my little lung operated gadget and scuttle off into 5m or less water if fog comes down unexpectedly. If it's expected, look for me in the bar.
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The problem is that foghorns operate at low frequencies with long wavelengths - assuming that it's about 128 Hz (lower C) then the wavelength will be around 2.5 metres - and that's probably at the upper end of frequencies for foghorns; I'd guess 60 Hz is more like it. The distance between our ears is far too little to distinguish the direction of a sound at those frequencies except in the most general sense. The horn idea works by collimating the sound over a somewhat larger aperture, but it still isn't going to be very directionally sensitive. It's worth noting that in the 1930s a vast amount of effort went into locating aircraft by sound, and they used enormous (several metres across) concrete mirrors to capture the sound, with widely spaced pairs of reflectors to determine the direction. The results were at best indifferent, and even the first experiments with radar were so clearly superior that sound locating systems were dropped very quickly. The other thing is that it is very easy to get the direction 180 degrees wrong...

Our ears are so bad at determining the direction of a sound, especially a pure tone, that emergency vehicles these days emit bursts of white noise (the sort of "scrunch, scrunch" sound between the tones) as well as the two-tone sirens, as it has been shown that we do better at determining the direction of white noise than a pure tone.
 
Refueler said:
the signals designated for each type of vessel are initial .. once you make audio contact with another - you both would then change to frequent blasts to give indication of where you are as well as any turns you make ...

Now some smart arse is going to argue that ..
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Apologies if I'm missing an elaborate joke but if i'm not...which part of the colregs do You believe you are referencing there?
 
laika said:
Apologies if I'm missing an elaborate joke but if i'm not...which part of the colregs do You believe you are referencing there?
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Not a joke ... and its actually something that gets discussed in Marine College about manoeuvring clear of each other when visual is so bad ...
Believe it or not ColRegs and what is done - occupies a large amount of time when studying for tickets ... we do not just learn them parrot fashion to spit out as some ... they actually get debated and scenarios introduced to see and understand how they work.

Anyway - my post was based on the guy creating an auto sequenced horn. Which led me to mention the use of the horn to know where the other vessel is and to manoeuvre.
 
Refueler said:
Not a joke ... and its actually something that gets discussed in Marine College about manoeuvring clear of each other when visual is so bad ...
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So you're referring to a practice which is neither in the colregs nor taught on rya courses? Do you expect people in small yachts to follow this practice?
 
laika said:
So you're referring to a practice which is neither in the colregs nor taught on rya courses? Do you expect people in small yachts to follow this practice?
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One toot turning to starboard, two to port I imagine. Its what I'd do if I only had sound signals to communicate. And is in the colregs and RYA courses. Thank goodness for VHF and AIS though.
 
AntarcticPilot said:
The problem is that foghorns operate at low frequencies with long wavelengths - assuming that it's about 128 Hz (lower C) then the wavelength will be around 2.5 metres - and that's probably at the upper end of frequencies for foghorns; I'd guess 60 Hz is more like it. The distance between our ears is far too little to distinguish the direction of a sound at those frequencies except in the most general sense. The horn idea works by collimating the sound over a somewhat larger aperture, but it still isn't going to be very directionally sensitive. It's worth noting that in the 1930s a vast amount of effort went into locating aircraft by sound, and they used enormous (several metres across) concrete mirrors to capture the sound, with widely spaced pairs of reflectors to determine the direction. The results were at best indifferent, and even the first experiments with radar were so clearly superior that sound locating systems were dropped very quickly. The other thing is that it is very easy to get the direction 180 degrees wrong...

Our ears are so bad at determining the direction of a sound, especially a pure tone, that emergency vehicles these days emit bursts of white noise (the sort of "scrunch, scrunch" sound between the tones) as well as the two-tone sirens, as it has been shown that we do better at determining the direction of white noise than a pure tone.
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Thanks AP, interesting.
I simply tried closing one ear and putting the cone in the other, while turning/sweeping the horizon around the general direction, so it was rather trying to detect the direction the maximum sound level came from, I had the impression of an improvement but it was maybe just an impression.

Otoh, while coastal I always use the mouth fog horn, of course not for ships but for small boats which might be around like scuba diving, sport fishing, other sailboats which might not be visible on the radar. Funny effect in the total silence of fog, sometimes one waits a little before using the horn, then when one begins blowing after a few minutes other weak horns can be heard from the fog. On the days pre-plotter, I once had a couple of sportboats approaching, then ask if I had he radar on, then "can we queue behind you and follow you to the port". :)
 
differentroads said:
One toot turning to starboard, two to port I imagine. Its what I'd do if I only had sound signals to communicate. And is in the colregs and RYA courses. Thank goodness for VHF and AIS though.
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I'm familiar with rule 34 (actually *both* rule 34s but let's not go there). What I was questioning (and I may have misunderstood) is the implication in refueller's earlier post that your own sound signals should somehow be different after you "make audio contact". If nothing else I'm not sure how I would know if/when another vessel could hear me. I'm sure there are plenty of conventions applied by masters of large commercial vessels which arent In the colregs but that doesn't make them best practice for small yacht sailors
 
laika said:
I'm familiar with rule 34 (actually *both* rule 34s but let's not go there). What I was questioning (and I may have misunderstood) is the implication in refueller's earlier post that your own sound signals should somehow be different after you "make audio contact". If nothing else I'm not sure how I would know if/when another vessel could hear me. I'm sure there are plenty of conventions applied by masters of large commercial vessels which arent In the colregs but that doesn't make them best practice for small yacht sailors
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IRPCS annex V - read the rules, understand and follow, not what some bloke says on a web forum :)
 
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