New Advances in Forward Looking Sonar

[J Clark H356]

When I outfitted Persistence in 2003 I looked at an Interphase unit and passed. I tilted my transducer slightly forward on the standard Raymarine unit then available and mounted it about 10 feet from the bow. If I am going into an anchorage or in shallow water I slow up and it has helped me immensely avoiding going aground. I split screen the chart plotter with the chart and sonar showing.

At normal cruising it doesn't help so I am glad to see some improvements in FLS. The newer chirp systems certainly have better resolution and I think it will only be a matter of time when the forward range will be enough to help . I would like to have had a good FLS last month returning up the Tenn-Tom from Mobile to Demopolis as I was dodging logs and debris for a lot of the way. There are also snags that you see at lower water levels that would be nice to be warned of near the channel edges . It would also have helped in the GICW where sand shifts near the edge of the channel and I did run aground but softly with no consequences .

[Randy]

It does seem like it would work for nosing into atolls, avoiding coral heads.
We use the side-scan sonar at times on my ship similar to what they're using for flight 370 and it is slow incredibly tedious work, moving at 2 kt.

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[Don1500]

Originally Posted by skipmac

Sure. You will pick up the container about a nanosecond before you hear the loud crash.

Seriously, you might get a few seconds warning or none at all, depending on the sea state at the time. A partially submerged container might sit 8-10' down in the water. If the seas are running 4-5' the pitching of the boat, and the container rising and falling in the waves plus all the surface turbulence the chance of getting any significant warning of a floating container are pretty much nil.

I agree completely. We should (at this level of the technology) just do nothing because it won't help anyway. But, maybe, if you have this it just might give you more warning than the thud of the box hitting your hull.

[Dan316]

What is the reason you cannot just use a depth sounder facing forward?

[Randy]

Originally Posted by Dan316

What is the reason you cannot just use a depth sounder facing forward?

Lack of resolution.

[DeepFrz]

I have found the Probe to be very useful in entering strange anchorages, especially under poor visibility conditions or at night. They are not useful for avoiding floating containers or other such hazards... no question about that! But for slow speed exploration of unfamiliar waters they are VERY useful, at least in our cruising experience, and it has kept us off uncharted and invisible shoals more than once. IMO, even once paid for the instrument well and truly.

This is essentially the same report I have seen from others who use FLS. It can be a great tool for feeling your way around a new anchorage or for negotiating a narrow steep channel that you might find on the BC/Alaska coast or feeling your way into a reef opening. Any chance of spotting something while cruising in any sort of chop will be negated by the false alarms caused by the boat pitching.

[skipmac]

Originally Posted by Don1500

maybe, if you have this it just might give you more warning than the thud of the box hitting your hull.

Not according to all the reports I recall reading by cruisers that have them and the math confirms it. Just go back to post #11 by Roy who has one and seems to like it. Remember these units do not look straight ahead but at a down angle. Roy reports 100' range in 20' of water under ideal conditions in a harbor. A shipping container is 8' high. Maybe one end sits lower in the water so it's 10' down. That would give a maximum range of detection of 50' under ideal conditions in quiet water in a harbor.

At 6 kts you would cover that distance in 5 seconds. I assume you use an autopilot or some sort of self steering on a long passage. I believe the great majority of sailors on passage do. I see 0% chance of getting to the helm and altering course in 5 seconds if the AP is driving. Even if you don't have any sort of self steering and have both hands on the wheel, do you think after a few days at sea, standing at the helm you hear an alarm sound, look for the source, figure out what it is and decide to go hard to port or starboard to miss the container in max 5 seconds?

Also, I have read that they can give false alarms from wave turbulence when the seas pick up which would mean you would be doing frequent 180s on every passage since 5 seconds would not leave you enough time to decide if the alarm you hear is real or false.

I think a forward sonar would be a great tool to use like Jim Cate describes and if I had a couple of unused boat bucks around I would add one. For now I'll have to make do with what I've got.

[leftbrainstuff]

None of the affordable forwardscan sonar options will provide reliable detection of containers. Do the math of a yacht moving around in even a mild sea state.

While radar may detect floating containers, particularly where a corner is above water, it's not going to be avoidable in practice.

Wave action causes huge detection issues for defence grade active systems let alone low power recreational systems.

We are preparing for a full instrumentation upgrade on our Liberty 458. BandG Zeus2, 4G radar, forwardscan and related infrastructure. Container detection isnt even a use case worth considering.

There is very little test data available on these systems. Even the vendors info is woefully lacking. We'll be completing our own testing. If we can detect a bottom contour 20' ahead at 1 knot we'll be satisfied. Anything else is a bonus.

Many years of defence system testing and certification makes me wary of any specific performance claims.


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[Paul L]

Originally Posted by leftbrainstuff

.....
There is very little test data available on these systems. Even the vendors info is woefully lacking. We'll be completing our own testing. If we can detect a bottom contour 20' ahead at 1 knot we'll be satisfied. Anything else is a bonus.
...

You can easily do this. We used our Echopilot FLS reliably at 1 boat length when going slow.

[leftbrainstuff]

Originally Posted by Paul L

You can easily do this. We used our Echopilot FLS reliably at 1 boat length when going slow.

We've completed out instrumentation refit. Initial experience with the B&G forwardscan sonar are positive.

We'll conduct some detailed testing over the winter and post our findings. There is zero decent reviews online apart from a few marketing and press release artefacts.

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