Considering sonar

[stickinthemud57]

I sail a MacGregor 26S with a swinging centerboard. WIth plans to sail in unfamiliar and potentially very shallow waters (Texas Gulf Coast Laguna Madre and waters surrounding the ICW), I am considering the notion of adding a depth sounder, but have reservations.

1. I am not very keen on the idea of thru-hulls.
2. I am thinking that anything short of forward-looking sonar could be too little too late, but forward-looking sonar transducers protrude from the bottom and would have to be removed for trailering. Not an option I am thinking.
3. Money

I would be interested to know if there are solutions I am not aware of. Ideally, I would like to know if anyone knows of a forward-looking sonar rig that does not require a thru-hull, or one that fits flush to the hull.

Thanks!

 

[PaulK]

Forward-looking depth sounders only seem to work at slow speeds - in the range of less than 5 knots. They are not likely to be much help in your situation. Since water depths tend to change gradually in the Texas Gulf -- you're not dealing with sudden rock peaks or cliffs - a standard depth sounder should work well enough to tell you when the water is getting thinner and you need to tack. Depth sounder sensors can be mounted on the inside of the hull and still work - check with the dealer or manufacturer.

 

[Davidasailor26]

Not forward looking, but you can definitely mount a traditional transducer in the hull without a thru-hull. I think there’s still value to that just for seeing the exact depth under the boat. If you draw 3 feet you’ll know when the water is starting to get skinny as you see the sounder drop toward 5 feet, then 4. The forward looking feature might be nice in some cases, but it’s not the only way to get a better sense for where you can and can’t go.

 

[Ralph Johnstone]

I would think by now, through hull transducers are almost a thing of the past. The only place for them is in the bottom of a cored hull.

I am thinking that anything short of forward-looking sonar could be too little too late,

Use your charts as well as your depth sounder to see what to expect up ahead.

 

[dmax]

There are some inexpensive depth sounders that should work for you by Hummingbird and Hawkeye and maybe others - just make sure the transducer can be mounted inside the hull as others have pointed out.

 

[stickinthemud57]

Not forward looking, but you can definitely mount a traditional transducer in the hull without a thru-hull. I think there’s still value to that just for seeing the exact depth under the boat. If you draw 3 feet you’ll know when the water is starting to get skinny as you see the sounder drop toward 5 feet, then 4. The forward looking feature might be nice in some cases, but it’s not the only way to get a better sense for where you can and can’t go.

At 5 feet, I will feel/hear my centerboard dragging the bottom (I draw 6' with the C-board down, 1.5 with it up). I have a hand-held device that I can use when in doubt/curious.

@dmax - I will look into those. Thanks!

 

[dlochner]

Forward scan transducers are cool and expensive. At least the Navico version has a range of 8 times the water depth, at speed in shallow water they won't be much help. In deeper water to see the bottom beginning to rise up they will be more helpful. In a an anchorage they will be helpful in seeing the bottom and knowing how flat or steep it is, which helps with determining where to anchor.

A B&G chartplotter has a feature which graphically tracks depth which can help predict shoaling. It is helpful, its shortcoming is it shows where you have been, not where you are going.

If you opt for a through hull transducer, you might as well get the speed/depth/temp transducer. The extra cost is minimal and you get speed, not additional displays will be necessary. At least the B&G displays can show both speed and depth on one display.

 

[stephen_i_w]

I sail on shallow Lake St Clair. The chart plotter, with an updated map, shows the minimum depths ahead and all around me. With a standard depth sounder you can calibrate the depths on the map to the actual depth. So, if my chart plotter shows 5' and my depth sounder shows 7', I can simply add 2' to what I see on my chart plotter. I think that will work a great deal better than SONAR.

 

[Davidasailor26]

I sail on shallow Lake St Clair. The chart plotter, with an updated map, shows the minimum depths ahead and all around me. With a standard depth sounder you can calibrate the depths on the map to the actual depth. So, if my chart plotter shows 5' and my depth sounder shows 7', I can simply add 2' to what I see on my chart plotter. I think that will work a great deal better than SONAR.

It can, in some places. In many places the depths shown on the charts are soundings that are multiple years (or decades) old, even in areas with shoals that move yearly or monthly.

I often compare my sounder to the chart and find notable differences, much more than the tide would account for. Sometimes the chart is too shallow, and sometimes too deep. My general approach around anchorages or when deciding how much to cut a corner is to stay away from areas the chart says are too shallow, and stay even further away if the sounder is reading lower than the chart as I approach.

 

[BarryL]

Hi,

SONAR, Depth meter, basically the same thing. The main difference is the display. There are units that only display the depth, in feet, meters, fathoms, or whatever. Then there are units that show fish, the bottom, and also display the depth of the water in feet (etc.).

Personally, I want to be able to see the bottom. It makes is easier to anchor (sand or rocks) and you can more easily see the bottom getting deeper or shallower.

My current boat came with an Airmar DST800 triducer (depth, Speed, water Temperature). It was mounted in a throughull (uses a paddlewheel for speed through water) and broadcast the data via a NMEA2000 network. All I received from that was the depth of the water. My chartplotter is a B&G Zeus, which can use various SONAR transducers. I bought the cheapest one available and mounted it INSIDE the hull, up in the V Berth, so it could shoot through the hull. Now I can see bottom and easily see trends. With the transducer mounted inside the boat I do lose the ability to find the bottom in deep water. But I don't care about that at all. The airmar can find the bottom in over 200', the B&G unit loses the bottom in 150' of water.

I would not rely on it as a forward looking device so I can avoid rocks or other obstacles. I just it for the depth of the water and to get a better understanding of the trends. Since my boat draws 7' I get nervous any time the water is less than 10' deep. I wouldn't spend lots and lots of money for a SONAR transducer but for the $150 or so it was well worth it.

Barry

 

[dlochner]

It can, in some places. In many places the depths shown on the charts are soundings that are multiple years (or decades) old, even in areas with shoals that move yearly or monthly.

I often compare my sounder to the chart and find notable differences, much more than the tide would account for. Sometimes the chart is too shallow, and sometimes too deep. My general approach around anchorages or when deciding how much to cut a corner is to stay away from areas the chart says are too shallow, and stay even further away if the sounder is reading lower than the chart as I approach.

Yep, the charts, depths, and locations are not nearly as accurate as we would like.

Last year the chart plotter showed me motoring along about 100 yards off shore, er actually inshore motoring through a field.

Then there was the time the chart showed me clearly on the edge of the channel, a line drawn between 2 piling would have gone right across my boat. The charted depth was 8-9 feet, either my keel grew 3 feet or the depth was wrong as I sat there waiting for high tide.

If you use Aquamaps they upload the most recent Army Corp soundings for the ICW and other areas. These are probably the most accurate depth soundings available. The rest of them, not so much especially in tidal waters with a sand bottom.

Aqua Map

Most advanced Marine Navigation App

www.aquamap.app

 

[jssailem]

I am thinking that anything short of forward-looking sonar could be too little too late,

If you want to rely on Forward Looking Sonar, you are doing "Too Little practical navigation" and "too late to save your pocket book".

The concept sounds great, and on a US Navy Submarine with what seems like unlimited funds, probably is a practical addition. On a sail boat it is an expensive and after seeing used by a boat owner who regretted the purchase many time... Not a good use of limited cruising funds.

Spend you money on a good navigation training class. Then go out and practice these skills.

 

[stephen_i_w]

It might depend on where you sail. But, all I can say is that I have been using Navionics charts for many years on the Great Lakes and they never failed me yet.

 

[dlochner]

It might depend on where you sail. But, all I can say is that I have been using Navionics charts for many years on the Great Lakes and they never failed me yet.

Yes it does. Some areas have not be surveyed in decades and the initial surveys were not that accurate as they were all pre-GPS or satellite images.

 

[RoyS]

Last year the chart plotter showed me motoring along about 100 yards off shore, er actually inshore motoring through a field.

That GPS offset happened to me once. I was at my slip in the marina and my chartplotter indicated that I was about 100 yards away. This anomaly was gone the next day. Some time later I ran into a scientist who specialized in GPS issues. He explained that those events occur because of infrequent but natural distortions in the ionosphere. Think about that the next time you are sailing in a field of rocks guided by your chartplotter.

 

[LloydB]

You would be amazed at the destruction I have raised driving through those new subdivisions with my out of date GPS.

 

[jssailem]

You have been watching to many insurance tv commercials

 

[Tom J]

At 5 feet, I will feel/hear my centerboard dragging the bottom (I draw 6' with the C-board down, 1.5 with it up). I have a hand-held device that I can use when in doubt/curious.

@dmax - I will look into those. Thanks!
[/QUOTE
Exactly what I was going to say. The swinging centerboard on my O'Day 23 would just swing up whenever I ran over a shoal in Vineyard Sound off Cape Cod. Unfortunately, the fixed keel sailboat following me out of the harbor would run aground.