Re: [BCC Forum Post] Bil: Re: Thru-Hull Locations for transducers

Interesting that you mounted Sonar Transducer in the
keel forward of the mast. Is it offset (to pt or
stbd)? or How and where is it mounted. We have on
that sticks out like a big wart on the port side. I
wonder how much it costs in turbulence/speed??
Appreciate your insights.

nathaniel berkowitz, sausalito california
tel: 415 331 3314 fax: 415 331 1854

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Nate: Hi!

The sonar transducer (it’s an Interphase, see is mounted on the keel (ie not offset), so it looks forward and to port and starboard without any shadowing.

In rough seas, especially head seas, the transducer can be in the wave zone - so it can lose signal. It has detected floating lumber and also dolphins. And the transducer has occasionally picked up floating nets or plastic bags (but so has the prop!).

I have not detected any loss of speed (ie it adds a tiny proportion of wetted surface area; it must add some drag, but again it would be a tiny amount compared to, say, the drag of our 3-blade fixed prop).

I’ve appended a photo taken at our last haul-out. You’ll note that I carefully specify, to the straddle crane operator, just where the forward sling must run! See Zfls.jpg.

The in-board end of the tranducer is in the forepeak bilge. I follow Roger Olson’s practice of hauling as much of my primary chain anchor rode aft into the forepeak bilge when on passage, so I made a teak surround for the transducer so it does not get abraded by the chain. I also have my forepeak bilge set up as a shower sump (ie I have a shower head in the forepeak, but I have not to date needed to use the shower), so I have a pump in that bilge plus a softwood plug that would be used should the transducer be sheared off. The transducer is mounted on a stock standard Interphase fairing block.

Our FLS works well, and is in much use when we nose our way through coral or into shoal anchorages (but I have to admit that since the 26 December 2004 tsunami, I’ve been choosing anchorages that are around 8 m depth instead of my former practice of aiming for 4 m!!).