sonar

[albin43]

anyone here have sonar? what are the startup cost and the pros and cons of sonar? some guys here in the great lakes use a side sonar system to find ships from the 1700's.. pretty wild stuff. deff intresting.

-- Edited by albin43 on Thursday 29th of April 2010 07:51:57 AM

 

[Marin]

We all have sonar. That's what a depth finder is. The degree of sensitivity, the type of display, etc. is a major variable, but they're all sonars.* The multifunction unit on our GB displays numbers, but the "fishfinder" on our 17' Arima fishing boat paints a graph with most larger details on the bottom.* For example, years ago I took a co-worker and his son out on the Arima to do some scuba diving (them, not me).* They wanted to dive on a sunken ferryboat.* They knew the approximate location and we cruised back and forth until the ferry's structure showed up on the display.* Dropped the anchor and they did their dive on the wreck.* This was with a Lowrance unit that we still have on that boat.


-- Edited by Marin on Thursday 29th of April 2010 12:19:57 PM

 

[albin43]

I understand the fish finders are sonar I guess im not really sure what im asking here. Forward looking sonar? vs side sonar? how accurate are they?

 

[Marin]

I don't think it's so much a question of accuracy as it is a question of usefulness. The claimed advantage of forward-looking sonar is that you can "see" what's ahead of you and so not hit it. Based on my experience, for a cruising boat it's not much value. If you have a decent chart plotter and a depth sounder that's all you need not to hit anything in front of you. You can see where you are on the chart, you can see what's in front of you on the chart, and the depth sounder tells you how much water is under your keel. The chart tells you what the depth is going to do as you move forward.

For fishing I can see where a forward-looking sonar might be of some value. Our here we fish with downriggers. So we've got heavy cannonballs down 100', 150', 200' on a wire dpending on what we're fishing for. Given the rocky nature of the bottoms here, it would be nice to know in advance if the bottom was going to start coming up, or if there was a narrow ledge up ahead so I could crank the weights up enough to clear the obstruction rather than risk hanging them up in the rocks. Without knowing what the bottom's doing out front of you, the first you know of a rock ledge or rise in the bottom is when you're over it and it's painted on the depth finder at which point it might be too late to get the weights up to clear.

By the same token, I could see where forward looking sonar might be useful if you cruise in real shallow water, or waters in which you have to follow narrow, twisting channels through shallow water. Even though the channels and shallow spots should be on the chart, if there's not much margin for error a forward-looking unit could be helpful.

But in all the boating we've done starting in the mid-80s with the Arima and now with the Arima and the GB, I have not once found myself wishing we had forward looking sonar, other then the downrigger issue I described.

Side-scan sonar I believe is primarily used for finding stuff, like wrecks, downed planes, the Loch Ness monster, or missing H-bombs. As I understand it, it lets you "see" a much larger swath of the bottom as opposed to a conventional straight-down sonar. So you cover more ground with each pass. I'm guessing a good one is Not Cheap.




-- Edited by Marin on Thursday 29th of April 2010 01:25:28 PM

 

[Codger2]

I think that Marin pretty much nailed it.

If memory serves me correctly, Jeff, on Arctic Traverler has one and loves it! He pokes his head into a lot of coves and can see if he's going to hit a rock, shelf, etc. I had one and loved it for "paddy fishing." I could look under kelp paddies to see if there were any fish, before getting too close to the paddy. By standing off and casting to the paddy, we were really successful.

For normal cruising, etc......you really don't need one. Charts (electronic & paper) and a good sounder are all you really need.

 

[Keith]

I looked into those when they first came out. At that time, they could only see as far ahead as the depth under them. So that would be good for deep water, but around here where I boat in 10' of water (when I'm lucky) they wouldn't even see to the bow!

I understand they are better now, and some are "aimable" but still pretty useless in shallow water.

 

[johnhinshaw]

When we purchased SeaHawk there was a Wesmar sonar installed. Very expensive unit. It worked at first then cratered probably because it wasn't used much. As a non-commercial customer it's very tough to get these units repaired and because it was older technology (mid 80s) there are fewer techs who have the knowledge to work on them. When it worked it was very impressive - side scan, adjustable angle etc. I think it must have been a great tool for locating fish schools etc.

I have removed the console and video display although the radiosond and hoist mechanism is still installed. I rely on a simple depth sounder that seems to work very well.

 

[Doc]

I have an Interphase side scanning sonor. Pretty useless.

 

[albin43]

Doc wrote:

I have an Interphase side scanning sonor. Pretty useless.

*why??

 

[Doc]

For one thing, it is on the hull with the keel stopping it from looking to port in side scanning mode. In the up and down scan mode I have never noticed anything except a gate in front of me when I was locking. I guess if I was going to suddenly run aground it might warn me if I happened to be looking at it. I just don't care for it that much. Probably just me.

-- Edited by Doc on Sunday 2nd of May 2010 10:59:15 AM

 

[Conrad]

Recently Humminbird and Lowrance (plus their Simrad etc.*brethren) introduced their new side scanners that look quite interesting, particularly in the detail that they apparently show. I believe that they are good down to around the 100' level and would be fun to explore for wrecks etc. as Marin mentioned. For actual navigation purposes though I doubt that they add much.*And as Doc suggests, transducer location could be quite tricky if you wanted the full scan capability.