Forward looking sonar.

[Rohorn]

Hi people,
Running aground and sinking half of one's catamaran focuses the mind on ways to stop such a shocking and extremely expensive experience ever happening again. The circumstances are banal. It happened one mile from home. I am a statistic.
Perhaps a fishfinder (historic depth meter), as opposed to our old classic one-shot would up have prevented this, but at five and a half knots we hit a rock 70 cms below the surface sticking up out of a flat sandy bottom four to five metres deep. This faily typical of Aegean terrain. At that speed, say two point five metres a second, given we would need say 15 to 20 seconds warning to wake up, see which way to turn and get the boat around the obstacle, the warning should be triggered at a distance of about forty to fifty metres from the rock.
Does anyone out there have experience to share with Forward Looking Sonar?
I've got info from both Echo-pilot and Interphase. The latter have a side-to-side scanning system as well as the better kown fore and aft sweep. You can even have both systems and switch between them. Both have normal fish-finder views on a split screen with their FLS displays.
I'd really appreciate informed opinions on this (expensive) equipment.
Cheers...R

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[LORDNELSON]

There was some discussion about this subject about (I think) five years ago. Not sure if it is possible to search that far back but, if so, it would be worth while. I have often pondered about buying a forward looking sonar but whilst it would be useful if one was aware of the peril approaching and thus had someone concentrating on the sonar screen, how useful would it be if one did not lookat the screen for say 30 seconds before a rock was due to be under you? My recollection of the earlier discussion was that the sonar response and clarity was very dependent upon the type of bottom the boat is traversing.

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[BrendanS]

There have been several discussions in the past year,

Do a search on FLS and forward looking sonar on 'all forums' for the past year
I

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[Rohorn]

Hi...thanks for that info......I just looked back using search-all forums and got a few more insights, but I'd like to talk to someone who has real experience using both vertical and horizontal scanning. Echopilot sent me brochures which seemed to indicate that they concentrated on vertical rather than sidescan. Interphase market both and from the screen images they show, the combination of the two would be ideal. Like many people I like to explore coastlines and hop between islands. The Interphase Sea Scout sidescan , sweeping 45 degrees either side of the track but to a limited depth, would be excellent for finding safe passages into narrow bays and fiords, or where best to anchor off a beach. It includes a standard fishfinder (historic echosounder) function, which is displayed on a split screen.
The question of an alarm function giving adequate warning time is critical. Echopilot are clearer on this, saying that with their system you can set a depth warning level, ie, 2, 4, 6 or 8 metres depth, up to say 100 metres ahead if that is the range you have selected. Interphase say you can set an alarm that will warn of floating containers or even whales, which some posts in the search were sceptical about.
If that really worked it would be phenomenally useful in the context of my accident, or similar ones. The cost of such a unit is minimal if it avoids the protracted shock, effort, aggro and bureaucracy resulting from such a drama.
So, anymore comments, anyone? Would be much appreciated.
Cheers.....R

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[SteveGorst]

Hi I used to go out regularly on a boat with an Interphase forward facing Sonar. To be honest I found the display of very limited value. It would pick up all sorts of clutter in the water, thermoclines, weed, shoals of fish(maybe!) the only thing it didn't see was the rock my mate hit whilst circling the bay as I was putting the trailer away.

The best way to avoid rocks in my opinion is to read the charts properly and get to know the water you are sailing in. Take a look at it at low water and note where the hazards are. Although you don't get much tide in the Aegean. Your best bet maybe a pair of Polaroids, imho they would be cheaper and more effective than forward looking sonar in the clear waters of the Aegean. I have always seen the Rocks showing up as dark patches against the white sandy bottom long before the sonar sees them. A rock 70cm from the surface should also create a noticable disturbance on the surface of the water in the form of breaking waves or upwellings and whirlpools.

My advice would definately be keep your money in your wallet. Gadgets are no replacement for experience.

Steve

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[Rohorn]

Hi....Thanks for those comments...it's good to have the negatives brought out, because what seems clear to me now is that the forward ALARM system is perhaps more important than the screen display.
Your comments about buying some polaroids , learning the charts and so on made me feel even worse...I've been sailing these waters for 35 years, we were one mile from where we'd set off four days previously, we'd had an idyllic cruise to Amorgos, experienced 41 knots of wind off Karos, and raised the cat's fastest speed record to over twelve knots. The last two days were flat calm and we motored across from Heraklion to Paros, all sitting in a line across the bows with our toes in the water on Autopilot. We were back in the cockpit just finishing tea and discussing what to do that evening. The evening sun was in our eyes and there was a slight popple which made the surface opaque when we hit.. Thats the first serious grounding in all those years...! Like I said in my first post, I'm a statistic, and I hate it. Statistics have always been for everyone else......
So a reliable forward alarm is the most importants function. Anyone had a similar experience...and would you agree?
Cheers....R

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[wallu]

Hi
I have been using Interphase probe in Finnish archipelago for years and been very pleased. My boat is a slow 11 ton Dutch vlet with typical 6 ... 7 kn cruising speed. Our archipelago is scattered with rocky islands, typical depth varying from very shallow to 50 m. When I'm cruising outside marked fairways, my speed is naturally slower and typically this gadget have saved me hitting a rock a few times during sailing season. Our charts are basically OK for fairways and close by, but other areas there are unmarked rocks and in order to benefit from this part, you need some tools or good luck.

Interphase is not very fast re-newing the screen and you have to know how to interpretate what you see in the sceen, but if in doubt, reduce the speed. Last summer I had some problems with the measuring part and had to go without the unit... and I noticed how useful it is to widen my useful boating area.

I have not used the unit in really deep water with temperature inclines or whales, but for me it's been a good choise for 6 years. I have not used the alarms (for natural reason of the type of archipelago).

In a way, it is funny to read very strong comments from fellow sailors who obviously have never used the type of unit in real situation and this is not particularly referring to forward looking sonars. Some gadgets are useless gadgets in some type of sailing, but could be very useful help in other situation. The thruth has varying gray shadings and it is so much depending everyone's preferencies.

best regard
m/y Merikihu
Wallu

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[Rohorn]

Hi Wallu....many thanks for your interesting reply. I have a lot of good memories of Finland from a previous life.
You note that the Interphase screen refresh is a bit slow. The Echopilot people say their unit works "in real time", which I suppose means a very rapid screen refresh. They also make a big point about their alarm system, which sounds good.
Since my boat is a fairly wide catamaran (5m30 wide) I am puzzling over where to mount the transducer probe. The existing echosounder transducer is under the starboard hull, to the left of the front edge of the keel. Ideally a forward looking sonar should be on the centre line of the boat which in my case is possible to do, but only if I put it on a leg mounted like an outboard on the middle of the transom. Put it on a lifting bracket and one could lift it in or out of the water at will. Not only that but if I took an actual outboard leg and mounted the probe in the underwater gear case, I could pivot it side to side as well, a sort of mechanical sidescan arrangement..
Sounds like a good winter project but a bit mickey mouse!. Would it be effective? Where is your transducer situated?
Cheers.....R

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