Forward scanning sonar on a catamaran

[Roy M]

I just finished another installation of an Interphase SE 200C scanning sonar. The first was on my own boat, a Searunner 40 tri (photos in the gallery), and this vessel is a Catana 431 catamaran. The units are fairly easy to install, the most difficult aspect being where to locate the units (port and starboard hulls, allowing 180 degree view forward).

I selected a spot just forward of the daggerboards, since those are generally down at least 6 inches to protect the props (also a new installation - see the props thread for details). This places them in the forward third of the hull to reduce bubbles and resulting image disruption.

The units haven't been bottom painted in the photos, for clarity of demonstrating the installation, but they will look just like the ones on my boat in the gallery shots. The shots are at a 45 degree angle inboard facing aft, in profile, to show the relationship to the daggerboards, from forward and from astern.

[sandy daugherty]

I haven't installed mine yet because I'm concerned about drag. I'm currently considering a pole mount that would tilt up to the trampoline on my PDQ 36. I'm worried about smooth flow of water around the head, and am toying with a cavitation plate like an outboard motor. Suggestions please.

[Roy M]

The drag is really minimal, if noticeable, in the position shown. The advantage is that it is always available, and providing a backup function to a standard bottom reading transducer. Mounting it on a portable stem, as well as including a cav plate, would really seem to increase turbulence and drag, don't you think? Plus, at 3 AM, do you really want to have to deploy something like this, single handed? Remember, this transducer is about the size of a streamlined grapefruit, next to the massive daggerboard and rudder and saildrive already hanging down there.

[dana-tenacity]

The Catana 431 I delivered had one. I saw a whale on it.

[imagine2frolic]

A WHALE!!!!!! that had to be a little unnerving?

[pilot]

Some questions on my mind:

For operation with daggerboards:

Are there any considerations of a kind of "protection" against floating debris? I.e. a "cage"?

Or would that produce to much interference?

Operation with cats with keel:

Any experience if the transducer (one only) is installed slightlý behind the leading edge of the keel (some protection)? Interference?

Is the transducer body (plastic) fairly resistant against any kind of unwanted contact, i.e. floating wood?

[Stranded Mariner]

Just out of interest, because I have been playing with the idea of a forward looking sonar as well, how far do they actually look forward?

[Roy M]

From my own experience, on a 40' Searunner tri with the 200C model (180 degree view), the maximum range in bluewater is about 1000+ feet. In shallow water of about 20 feet, I get about 2-3 boatlengths (80-100 feet).

Regarding the position of the transducer behind a daggerboard, one would have to use the Interphase 200B model which uses one transducer only, and has a view of 45 degrees port and starboard, 90 degrees total forward. Mine are located on each side of the forward part of the minikeel (see pictures in Gallery).

Regarding security against damage, they appear pretty tough, but as Josh Slocum observed, "You MUST keep your boat off the rocks!" As far as floating wood, I would think that the bows are going to have first impact. But if it's a floating log, deadhead or shipping container, let's hope you saw it first on the sonar because the transducer head will be the least of your problems.

Regarding a "cage", it would have to have a clear aperture for the sonar signal to ping out and return with no interference. And think of the drag that such a cage might induce.

[Stranded Mariner]

Originally Posted by Roy M

From my own experience, on a 40' Searunner tri with the 200C model (180 degree view), the maximum range in bluewater is about 1000+ feet. In shallow water of about 20 feet, I get about 2-3 boatlengths (80-100 feet).

Thanks for that Roy M. That's pretty good actually. Specially the bluewater range, which would be the most important for me.

[Roy M]

Interphase suggests operating the FLS in vertical mode with the alarm set, allowing you to focus on other stuff around you. If a target is acquired (upward sloping bottom, seamount or isolated rock, or submerged obstacle within the scanner's cone), an alarm is sounded drawing your attention. Then, you switch to horizontal mode and choose an escape path, having an idea of what the extent of the obstruction forward actually is.

[pilot]

Below the company link.
However, experience is worth more than "paper information"!

Thanks , Roy

Interphase: Manufacturer of Forward Looking Sonars, Navigational Chart Plotters, WAAS/GPS and Fish Finders