Forward looking sonar

[Benjay]

Does anyone have experience with forward scanning sonar?
I’m considering installing for the purpose of navigating shallows at slow speed (<4kts) - in for example the Exumas -where the charts may be outdated due to shifting sands, or the charts may simply be inaccurate.

Yes I know visual navigation is required in the Bahamas.

Have a Raymarine system on board…

Thanks in advance.

[Insequent]

Here is a somewhat dated review of some options.
https://www.pbo.co.uk/gear/5-forward...r-tested-29321

I have an older system, an Interphase, that was installed by the PO. They were bought-out by Garmin, and it is no longer available.
https://www.sail-world.com/Australia...?source=google

The systems do take some learning. I was using it in coral reef areas where stuff you want to avoid is often vertical, so perhaps an ideal use-case. But I had it in the pilothouse and I preferred to navigate near reef's from the flybridge, so was not using it much. The Interphase unit worked well enough but visual from the flybridge was better. A few hours before and after midday when sun angles were high gave a better perspective. I have not even turned the Interphase on in the last 4 years. I might have the transducer removed at next haulout and sell the system if anyone was interested.

[AlanT]

Originally Posted by Insequent

Here is a somewhat dated review of some options.
https://www.pbo.co.uk/gear/5-forward...r-tested-29321

I have an older system, an Interphase, that was installed by the PO. They were bought-out by Garmin, and it is no longer available.
https://www.sail-world.com/Australia...?source=google

The systems do take some learning. I was using it in coral reef areas where stuff you want to avoid is often vertical, so perhaps an ideal use-case. But I had it in the pilothouse and I preferred to navigate near reef's from the flybridge, so was not using it much. The Interphase unit worked well enough but visual from the flybridge was better. A few hours before and after midday when sun angles were high gave a better perspective. I have not even turned the Interphase on in the last 4 years. I might have the transducer removed at next haulout and sell the system if anyone was interested.

Likewise, I inherited an installed Interphase from a PO and after experimenting with it for a season I decided it is useless for detecting Logs (the only real use I would have for it in my cruising area). I have no idea of the capabilities of more up to date systems, although I suspect for most use cases one would be better looking out the window than down at the screen!

~A

[FWT]

I can't help you yet, but will later in the year. I have a new build delivery in the spring and am having it installed. Simrad. On the east coast the water is murky so just picking your way visually isn't an option.

But the shoaling isn't vertical

We shall see.

[GFC]

I have no experience with forward looking sonar but had a Garmin Down-Vu on a Boston Whaler I had. The clarity is spectacular, as you can see in the pics below. In the first pic, it looks like the boat is running across land. It's really not, the water level had come up and it just looked like I was on land.



In this pic you can see that I'm in ~64' of water, moving at 5mph and you can see individual weeds on the bottom. You can also see that I have flipped the two screens, putting the sonar screen at the top.


In this pic you can see I'm in 170' of water, moving at 6mph and you can see all of the bottom contours.


I can't say enough good about the Garmin's resolution, screen refresh rate, and its ease of use.

[Flatswing]

I had the old Interphase twin transducers) on my previous boat and once I learned to use it properly, found it useful for staying in a narrow channel. My present boat came with a (now 8 y. o.) Simrad forward looking sonar which is virtually useless. In fairness, it may be because the transducer is mounted fairly aft and close to a sizable keel. Having cruised the Bahamas only twice, I don’t think it added much over common sense and using Explorer charts. Navionics charts tend to be erratic in their accuracy in the Exumas ime.

[MYTraveler]

Originally Posted by AlanT

Likewise, I inherited an installed Interphase from a PO and after experimenting with it for a season I decided it is useless for detecting Logs (the only real use I would have for it in my cruising area).

Surface chop will prevent even a $25K searchlight sonar from detecting logs, but for finding gamefish, rockpiles and other submerged obstructions, and more, is way better, in most circumstances, than the old interphases or any of the other phased array units I have seen. In shallow water (like typical freshwater lakes), the "mega" frequencies of the newest units offered by Humminbird, Lowrance and Garmin can reveal amazing detail, but the signal strengths at those frequencies are quickly attenuated so that the useful range really isn't more than 90', or arguably even only 50'.

[Mako]

Why don't you experiment with a used fishfinder from eBay, and temporary mount the transducer inside the bow area (in a bag of water), perhaps facing downward at about 22° angle? Fool around. If you're putting along at 4 knots it might work for you, at about 1/100th the cost than an actual FLSonar system.

[IRENE]

The folks that produce the SAILING AQUARIUS series on YouTube did a video on their Echopilot sonar, which was favorable. Take a look.

[Insequent]

Originally Posted by MYTraveler

Surface chop will prevent even a $25K searchlight sonar from detecting logs, but for finding gamefish, rockpiles and other submerged obstructions, and more, is way better, in most circumstances, than the old interphases or any of the other phased array units I have seen. In shallow water (like typical freshwater lakes), the "mega" frequencies of the newest units offered by Humminbird, Lowrance and Garmin can reveal amazing detail, but the signal strengths at those frequencies are quickly attenuated so that the useful range really isn't more than 90', or arguably even only 50'.

Useful ranges of 50' or 90' only? For that kind of money? Hell, the old Interphase, for all its deficiencies, does that easily.

[twistedtree]

I got a bunch of time on a search light sonar last summer and really like it, but like all tools, you need to understand what it can do and what it can't do.


I think the first thing worth noting in all the screen shots in this thread is the relative length of the boat icon vs the distance ahead. The icon looks like a 60+ foot boat, but it scales out to be 10-15m. And the look-ahead is 20-30m. So you are really only seeing at most 2 boat lengths ahead. That's not much. Especially with a fixed transducer, in shallow water, which is when you want to use it, they just can't see very far ahead before it's picking up the bottom, even if the bottom is flat. With a search light you can aim the beam up to see further, but then it's harder to get a return off the bottom because it's such a flat angle to the beam. Plus you start to pick up surface noise. In deeper water they do better, and will clearly show something rising up abruptly, but the low power of the fixed units still limits distance.


As for detecting surface hazards, forget it. I'm note sure if a fixed sensor can really pickup much of the surface, and with a searchlight you get surface noise before you will detect anything.


Personally, I wouldn't bother with a fixed unit, and only consider a search light. And only consider a search light if your mission really justifies it. They aren't cheap, are complex to install, and take a commitment to learning how to use them. But mine took me places I never would have gone before, or would have gone with great worry. Just being able to scan your anchor circle to be sure you have clear depth is a great convenience.


Oh, here's one example from this past summer. We went to anchor at the head of one of the glacial fjords in Glacier Bay. We had been their 5 years earlier and I had my old track including depth soundings in a circle around our anchor zone, so I knew what was there. I also had used the radar to mark the shoreline at low tide, so I was pretty confident in what was there, or so I thought.


Like many active glacial outflows, they often have a very abrupt "cliff" where the silted mud flat drops off. If can go from zero to 100' in a boat length, and of course the visibility through the water is zero. I had previously anchored in 100' of water, comfortably away from the shoreline.



As I approached this time, I started seeing something on the sonar, but it was way short of our previous anchoring spot. Long story short, the mud flat was had advanced over 500', and my previous anchoring spot was high and dry. Were it not for the sonar, I probably would have run right into it, believing I still had over 500' before my anchor drop point..... Sonar saved me..

[Insequent]

TT, thanks for clarification.

Scan of the anchor swing circle is my main use case for FL Sonar. Up in the Great Barrier Reef I can readily find a clear space visually, and see sandy bottom directly below, but at 20 to 30m depths. The issue is that there are around 7 ages of reef development and one of the older ones was at a time when sea level was about 15m lower than it is now. I can't easily see them visually. I've had my rode hangup on those older reef's several times as I've swung at night. I've always managed to get free without diving, but have spent uncomfortable nights anchored with annoying swell at a much shorter effective scope than I intended.

In theory I could pivot the boat through 360° to search for those older 15m deep reef areas, but it isn't all that practical to do. So a searchlight would be good. However, my plan is to get quite a lot longer chain when I replace my current 110m length. That way I can be out away from the reef, in 30m or so water depths with nothing but sandy bottom for large distances, and have a 5:1 scope to sleep soundly. The fishing trawlers up there anchor away from the reefs, but they typically use rope rodes, very long ropes I believe.

[twistedtree]

Originally Posted by Insequent

TT, thanks for clarification.

Scan of the anchor swing circle is my main use case for FL Sonar. Up in the Great Barrier Reef I can readily find a clear space visually, and see sandy bottom directly below, but at 20 to 30m depths. The issue is that there are around 7 ages of reef development and one of the older ones was at a time when sea level was about 15m lower than it is now. I can't easily see them visually. I've had my rode hangup on those older reef's several times as I've swung at night. I've always managed to get free without diving, but have spent uncomfortable nights anchored with annoying swell at a much shorter effective scope than I intended.

In theory I could pivot the boat through 360° to search for those older 15m deep reef areas, but it isn't all that practical to do. So a searchlight would be good. However, my plan is to get quite a lot longer chain when I replace my current 110m length. That way I can be out away from the reef, in 30m or so water depths with nothing but sandy bottom for large distances, and have a 5:1 scope to sleep soundly. The fishing trawlers up there anchor away from the reefs, but they typically use rope rodes, very long ropes I believe.

Well there is a use case I never imagined.

[MYTraveler]

Originally Posted by Insequent

Useful ranges of 50' or 90' only? For that kind of money? Hell, the old Interphase, for all its deficiencies, does that easily.

Those limited ranges are at the 1 MHZ frequencies. The higher the frequency, the more quickly the sound energy is absorbed by water with the range correspondingly reduced. I have a bass boat that I use in freshwater lakes, equipped with Hummingbird displays and mega side-imaging, "live" imaging (basically meaning that it will scan back and forth in planes defined by the user by physically setting the transducer, and 360 imaging, meaning that it goes in a circle around the boat. The resolution is fantastic -- in ideal circumstances, the head, dorsal fin and tail of a walleye can be clearly seen. But I generally use it on about 50' of range, after which reliability and usabilty of a return echo quickly diminishes to worthless after 90 feet. That is is sharp contrast to the range of my Furuno CH-270 scanning sonar, which I use when fishing offshore. With that, range is easily 600 feet, although resolution will not reveal much more than the existence of something returning and echo. But, when fishing offshore, knowing where "something" is often makes all the difference between hookups and another beer while waiting.

[Insequent]

MY T
Ok, got it. Thanks for comprehensive explanation.

[North Baltic sea]

Hi,

here is my story FLS installation and experience with raymarine + echopilot platinum.

https://www.trawlerforum.com/forums/...eel-30042.html

NBs

[catalinajack]

Originally Posted by FWT

I can't help you yet, but will later in the year. I have a new build delivery in the spring and am having it installed. Simrad. On the east coast the water is murky so just picking your way visually isn't an option.



But the shoaling isn't vertical



We shall see.

I have seen (the Simrad). Pretty much useless. It cannot see far enough ahead in shallow water such that a timely reaction can be made. IMHO, don't spend the money. I did and have never used it for navigating shallows.

[Iggy]

When bought my used boat. The past owner installed a new forward transducer. I hardly use it!

First off, I hate going in shallow waters. Rocks or not that uncommon in the North East.

As TT mentioned, the shallower the water the less you will see in front of you! Even doing 2 to 3 knots. By the time you see a rock and try to stop, most likely you will hit it. Why put your self there unless you have too?

I do understand, that down south the depths are less. So the need maybe greater to have it?

[boomerang]

I’m hoping the OP can sort through the replies and determine that, unless you’re going to invest in a genuine omnidirectional sonar, you’ll be disappointed with the forward looking sonars marketed for the recreational fishing market. Those that use them for fishing swear by them and they truly do work…at extremely low speeds and at close ranges. They do a great job of showing fish holding on bridge piles and structure but much more that 100’ out, their performance drops dramatically.
Attached is a pic I snapped of targets from an omnidirectional sonar. It was at the dock and I wasn’t testing it for range so that’s why I don’t have on example of targets at a distance but this thing is the real McCoy and will show bottom structure hundreds and hundreds of yards away. You can clearly make out the individual piling of the dock and if I were to had zoomed out, the shoreline across the creek would’ve been clearly visible. If you ,like a couple others on here, were an offshore fisherman and used this to target a species in deep water at a great distance , this would be a great tool to use for locating ledges and shelves in shallower water for anchoring. To use it solely as an anchoring tool would be a pricy investment indeed!

[MYTraveler]

Originally Posted by boomerang

unless you’re going to invest in a genuine omnidirectional sonar, you’ll be disappointed with the forward looking sonars marketed for the recreational fishing market.

Just a point of clarification, since you mention omnidirectionals. Mine is a searchlight. It can sweep in a complete circle and paint a display like the example you show (and can be set to sweep in segments and at any tilt from 0 to 90 degrees (actually from +4 degrees, although anything higher than about -4 degrees returns a lot of surface clutter and is therefore only suitable for the calmest of conditions and relatively short ranges), and can even automatically follow a target. But it is designated a searchlight sonar because, like a searchlight, it shines where it is pointed. By contrast, a true omni will transmit and return in 360 degrees simultaneously. Those units are a head and shoulders more expensive than the searchlights. If I recall correctly, the installed price of a Furuno Ch-250 is about $25K, while the hardware cost for Furuno's entry level omni is about $80k. I have never even heard of a recreational fisherman with one of those.