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JohnPJones

fishfinder sonar vs MCM sonar

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just wondering if anyone knows anything about the MCM sonar out and about in the world today, and how it compares to the upper end of fish finder sonars.

could it be possible for say a 3rd world nation to use a high end fish finder sonar on an improvised sweeper? for example if somalia ever got it's craptogether and began building a budget navy, could something like that work?

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34 minutes ago, JohnPJones said:

if somalia ever got it's craptogether and began building a budget navy, could something like that work?

There is a HUGE power consumption difference between the two, so while it may be a difference in scale only it is a significant one. I'm sure there are differences in sensitivity also but I've never been a sonar man so I wouldn't know about those.

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The range on a fish finder is pretty short, so if you set a mine off you probably need a new minesweeper. Depending on the type of mine, you might set it off before you detect it.

 

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Fish finders would be poor mine warfare units, and I think would be put to use only in the most extreme and bizarre of cases.

 

The main MCM sonar types out there are typically sidescan or synthetic aperture sonar to generate a wide (hundreds to low thousands of meters depending on the type, frequency, system and settings) swath of data to each side of a towed or hull mounted unit. Some high end military ones also have a forward looking sonar which seems primarily designed to detect moored mines ahead of the mine hunter, but if you're feeling brave it's probably not necessary, and MCM is something you can do with small boats most of the time. A mine set to take out a very small craft will not likely be effective against larger ones, having already been 'wasted' on some poor fishing boat. 

If a poor country wanted to develop a nascent MCM capability it would be best served by just buying cheap boats (30-40ft maybe GRP catamaran style launches), winches, and commercial off the shelf sidescan sonar which are typically pretty cheap, from a manufacturer such as Edgetech or Klein. The commercial sonar processing package I use most often even includes 'Mine like object' and 'non-Mine like object' among its default target selection parameters. I'm pretty sure few of those sonars are ITAR or otherwise export protected as the technology is fairly old, basic and is publicly pretty well understood science wise - any small manufacturing and research capability could start churning out home-made sidescan sonar pretty easily. The only slightly hard things are the ceramic transducers, but China produces them pretty cheaply. Here's a military example: https://www.northropgrumman.com/what-we-do/sea/aqs-24b-minehunting-system/

The other ways of supplementally sweeping for magnetic and acoustic mines (usually bottom mines which you can also just 'see' with sonar and identify) is to generate a falsely big magnetic field to trigger them, or basically simulate a ship acoustically by making loud sounds, blowing up mines at a safe distance. No role for fish finders there.

 

Mine warfare is pretty strongly limited by depth for ground/bottom mines that sit on the seabed, and moored mines (the traditional floating ball with horns on a chain) are also depth limited and tend to be fairly conspicuous, there are even ways to detect those with airborne LiDAR for instance. All that means what you need to counter them is lots of ground coverage, even the shipping channel into a fairly small harbor may be a pretty big area to clear in absolute terms, 'sweeping' a channel through it is very possible, but a fish finder would probably need to do hundreds instead of a handfull of passes to clear a corridor - or at least locate mine like objects to blow up or avoid.

Edited by mofton
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On 11/1/2020 at 8:17 PM, SgtBeltfed said:

The range on a fish finder is pretty short, so if you set a mine off you probably need a new minesweeper. Depending on the type of mine, you might set it off before you detect it.

 

...there are fishfinders that have a range of hundreds of feet...so i'm not sure what kind of range you think would be necessary....

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3 hours ago, JohnPJones said:

...there are fishfinders that have a range of hundreds of feet...so i'm not sure what kind of range you think would be necessary....

A hundred feet is probably close enough for a typical minesweeper to be in serious danger, owing to the wood and fiberglass construction typical of the type. Probably worse for a wooden civilian boat built in a third world country, which is the most likely candidate for being converted into an ad-hoc minesweeper.

I'd also expect that a fish finder wouldn't be as effective against a mine as it is with fish, because fish present a moving and fluctuating return, where's a mine is generally stationary.

Then there's the problem with bottom mines, which will be even less distinct.

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