Forward Scanning Sonar - Is It Any Good?

[DeepFrz]

Its a matter of refresh times on the screen. Because of the large amount of data and boat motion and wave motion it is impossible to see what is ahead of you except at slow speed in almost calm water.

[jeremiason]

Originally Posted by barnakiel

Do not count on it to warn you of containers happily bobbing on your course BUT they do perform well when e.g. entering a shallowing anchorage, etc..

b.

Try the Interphase... It has good horizontal scanning!

[Katiusha]

Originally Posted by resilientg

have you though about just getting a cheap fish finder and shooting the signal forwards (instead of downwards) to the angle you want?

Fish finders work by reading the echo from the stuff they've hit: send a signal straight down and get the echo back. When you send signal not straight down, the echo won't come back to the same spot (think refraction angles or snooker).

A good visual: How A Fish Finder Works

So I don't think your idea would work.

[David M]

Originally Posted by Katiusha

Fish finders work by reading the echo from the stuff they've hit: send a signal straight down and get the echo back. When you send signal not straight down, the echo won't come back to the same spot (think refraction angles or snooker).

A good visual: How A Fish Finder Works

So I don't think your idea would work.

A small portion of sound will reflect back to its point of origin if it bounces off of a contact. There is no refraction if the sound remains in the same medium, which it does. Did you mean reflection? There is a reflection if sound makes contact with something of a different density than water, or even water of a slightly different density such as a thermocline or a halocline.

A transducer for a depth sounder could be effective for looking forward if you want to spend all that time looking at a screen and the sea state is not so rough that the sound cone spends a lot of time pointed at the surface or looking down too far. Keep in mind that a transducer head pointed forward is very prone to damage from floating debris. Were it to shear off there would be the possibility of some relatively fast flooding.

Overall I don't think it would be worth it. Maybe as a novelty item for detecting fish ahead of you.

There is relatively primitive side scan sonar for fishermen now. But this shows fish off to the side of the boat, which would be "what did happen" type of information.

[DeepFrz]

Why don't you try it David and let us know how it works?

[David M]

Originally Posted by DeepFrz

Why don't you try it David and let us know how it works?

It's not worth the trouble or the expense nor is there any research that calls for it. If you want to fund it I will take it into consideration.

[DeepFrz]

Sorry David, I thought it was you that raised the question about fish finders. Looking back I see I was mistaken.

[DeepFrz]

Originally Posted by barnakiel View Post

Do not count on it to warn you of containers happily bobbing on your course BUT they do perform well when e.g. entering a shallowing anchorage, etc..

b.

Try the Interphase... It has good horizontal scanning!

jeremiason, can you give us some examples of how you use the system in rough water?

[Jim Cate]

G'DAy all,

I've posted on this subject several times before, but will try to summarize here.

We have had an Interphase Probe on both Insatiables, starting in 1996. We spend lots of time in poorly charted areas, some of which do not enjoy clear water. We explore anchorages new to us frequently.

Our findings:

1. The display does require some experience to interpret usefully... just like a radar display does. It isn't rocket science, and a few hours of paying attention to the forward picture in known waters will sort out most issues.

2. The useful forward range is a function of the depth. Under most conditions one gets a useful view of the bottom at somewhere between 3 and 5 times the depth. Note that this is looking at the bottom. In deeper water one can see things like a bommie sticking up from the bottom much further ahead. We have seen coral reef walls from around 800 feet distance, for instance, in a lagoon that was on the order of 50 feet deep.

3. Surface waves make "noise" that hides things like floating objects that do not protrude deeply into the water, things like logs or in rough conditions, even a container (no data, just a guess).

4. The alarm system is useless IMO. If you set the gain low enough to avoid frequent false alarms the detection range approaches zero. This means that one needs to watch the display for it to be useful. Note: ours are older models. They may have improved the alarm algorithms in later editions.

5. Our bottom line is that we find them useful and in fact essential for our sort of cruising and our degree of cowardice in strange waters. They are perhaps not as good as shown in the glossy brochures, but they are sure as hell better than nothing.

As for using a fish finder pointed forward: a waste of time and money.

HOpe that this has been helpful. A bit of searching should find some earlier and more detailed posts on the Probe.

Cheers,

Jim

[HopCar]

A little off topic but Garmin is buying Interphase. It will be interesting to see what new products they come up with.

[carstenb]

Thanks Jim,

I'm thinking about using as you do. For coming into shallow anchorages or bays.

Any other experiences?

[Jim Cate]

Originally Posted by carstenb

Thanks Jim,

I'm thinking about using as you do. For coming into shallow anchorages or bays.

Any other experiences?

Any other experiences?? Well, I remember dating this amazing chick in highschool...

But that's likely not what you were after! Our probe has allowed us (a number of times) to get into anchorages that we'd not have dared to attempt , it kept us off a completely hidden and unexpected reef in the Morova Lagoon in the Solomon Islands (murky water, no useful charts), and generally has reduced the tight pucker string factor in more everyday situations. Due to the physics of sound propagation in water there are some failure modes possible. I've posted about this before... but with some care they do provide an otherwise unavailable security blanket.

I was so fond of the one we had on Insatiable I that I ordered a new one before we hauled I-2 for survey so that we could install it whilst on teh hard!

As far as we are concerned, if it keeps you off just one reef/rock/other ugly thing during its tenure on your boat it has been worth its fairly high price!

And we've put our money where our mouth was!

Maybe Garmin will bring the price down??

Cheers,

Jim

[HopCar]

Jim, Does the Probe have a horizontal scan or a vertical scan?

[jeremiason]

Here is a link to the Practical Sailor Review of the Interphase Sonar

For those of you talking depth... According to Interphase, forward looking depth is 5 to 6 times the depth of the water. So if the water is 20 feet deep you should be able to look forward 100-120 feet. This has been my experience with my unit.

As far as the question about horizontal scanning, the unit will scan forward horizontal, but will not pick up floating debris, like vertical floating logs. It will pick up anything with depth, like deadheads and containers. The is a detailed explination on the interphase site explaining

[jeremiason]

Originally Posted by HopCar

A little off topic but Garmin is buying Interphase. It will be interesting to see what new products they come up with.

So far Garmin and Interphase have been pretty silent since the purchase in February 2012.

Neither company web site references or mentions the other and no new or renamed products have been released.