Chartplotters with Sonar / Live mapping

[Minerva]

I've noticed a few chart plotters have joined hands with their fish-finder brethren and are now offering live mapping and forward facing sonar capabilities at what seems like quite reasonable costs - I was looking at the Lawrence Hook Reveal over my tea break earlier as an example.

Over the last couple of years we've been using Bob's Antares charts (Scottish West Coast) which have been frankly brilliant at opening up new, previously uncharted anchorages before and these two factors have me thinking...

Has anyone any experience of using the "Live mapping" feature of these chart plotters (not just Lawrence, but I note all the big players seem to offer similar capabilities) to good effect? How do they adjust their readings to account for the state of tide? Are these features just a gimmick and not particularly practicable in real life?

 

[harvey38]

I have an ancient Phase (or some similar name) LCD display forward facing sonar, a complete waste of time. A newer, colour unit might be helpful if wandering into a rocky area and should give to some notice before you hit something.

 

[lustyd]

Are these features just a gimmick and not particularly practicable in real life?

extremely useful in real life. Turn up at anchorage and turn on live mapping then drive about. It records the depth around the anchorage so when you're finished you can pick your spot much more safely. With Navionics app enabled you can also record this and upload so that others benefit, yes they adjust for tides based on the GPS timestamps in the data. There are some countries where this doesn't work as it's illegal to collect such data, these are detailed in the Navionics Ts & Cs.

In addition to this, forward facing sonar has the distinct advantage that you don't have to hit something before measuring the depth, as you have to with downward facing depth sounders which are usually in the middle of the boat.

 

[Neeves]

We have forward looking sonar, Interphase. I forget the model, but now ours is technically ancient, maybe 10 years old.

Ours is no use if you are gallumphing round an anchorage, but if you are patient - a god send.

It does tell you of imminent shallowing allowing you time to rapidly and effectively apply reverse. If you are travelling at speed - its all too late.

On mapping - as mentioned tides are factored in but this assumes the tidal data is correct. Tides are impacted by atmospheric pressure and weather (specifically strong and consistent wind), and I don't think these anomalies are catered for unless there are large numbers of data for specific areas - in which case outliers might be weeded out - don't know. The places that need more accurate data are places that are infrequently visited - time will provide better answers. The mapping facility is 'new' most people find old chart plotters, without the mapping function, perfectly adequate - it will all take time. Our children and grandchildren will be the beneficiaries of the mapping developments.

We visit places in Tasmania marked 'unsurveyed' we commonly don't see other yachts for days on end.

Jonathan

 

[lustyd]

and I don't think these anomalies are catered for

I think it's probably better that way. Boaters don't have access to that additional info either, generally, so if it's consistent enough to skew the data then the depth will be as expected for most people. If it's not consistent then it'll average out and not be a problem anyway. Finally, it's not like anyone sensible is using the chart data for anchoring anyway. You work out how much further the tide will drop and add a safety margin then find somewhere with the depth sounder. Those with safety margins too small very quickly learn to build more safety in!

 

[Minerva]

Thank you. That's given some food for thought @Neeves - what sort of speed do you find you need to be travelling for the Sonar to give a useful heads up?

As for atmospheric variations, any pilotage that needed cm precision to scrape out of feels quite reckless (to me); If it gets to less than 1m below the keel I tend to woose out!

 

[Neeves]

If the seabed is sand or mud then touching bottom in a cat is not an issue (better on a rising tide). Even if its a falling tide as you simply dry out and move when the tide comes back. We often dry our, intentionally - to clean props, wipe down AF, maybe change anodes.

We also have some very shallow passages, inshore of Fraser Island aka Sandy Strait or The Narrows at Gladstone that are navigable at high tide but not at low and skimming the seabed would not be uncommon.

Most of the time you can see the seabed.

When you are trying to find 'the way through' we are cautious and would be moving at 1-2 knots. More modern forward looking sonar will see further ahead and allow more warning of the seabed shallowing out.

We have places with 300mm tides - surges, or whatever the opposite is called) for whatever reason are important if you are intentionally drying out - as you might be there for an extended period if you get it wrong . Its not common practice but we had to take a prop off once and we spent the day before checking locations and tides. We draw 1m - so a 300mm tide made it only a little bit easier.

Jonathan