Why Place The DF Transducer Forward Of The Keel?

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J

Joe Mullee

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Jun 3, 2004
418
Island Packet Island Packet 29 West River, MD
Why is it so important to place the transducer forward of the keel? Is it because placing the transducer aft of the keel would block the soundings sent out by the unit? The keel on my 1983 Hunter 34 is maybe ten feet long (bow to stern). If there was a rapid change in depth that ten feet of advance notice wouldn't allow me enough time to stop the boat anyway. As long as I'm paying attention to the trend on the DF and watching the chartplotter I'm thinking I should be OK.

Am I wrong?

Thanks,
Joe Mullee
 
RECESS

RECESS

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Dec 20, 2003
1,509
Catalina 27 . St. Mary's Georgia
The transducer will be effected by turbulence of water coming off the keel and could give you false readings. Forward of the keel allows for less turbulent water for the signal to travel.
 
Tim R.

Tim R.

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May 27, 2004
3,626
Caliber 40 Long Range Cruiser Portland, Maine
You also want the transducer to be out of the wet bilges. That is forward on many boats.
 
Ross

Ross

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Jun 15, 2004
14,693
Islander/Wayfairer 30 sail number 25 Perryville,Md.
I use a transom mount transducer on a purpose built skeg aft of the rudder. There are no problems.
 
sailingdog

sailingdog

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Oct 22, 2008
3,502
- Telstar 28 Buzzards Bay
Finally, having the transducer forward gives you slightly more warning that the water depth is falling, and may save you from a grounding, if you're paying attention. :) If it was after the keel, you'd find out after you went thunk pretty much every time.
 
Ross

Ross

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Jun 15, 2004
14,693
Islander/Wayfairer 30 sail number 25 Perryville,Md.
Mine shows bottom coutours and trends as well as depths. I have friends that tell of having grounded on a submerged log and their DF showing 10 feet of water. There isn't much of a remedy for logs and boulders. I know that around Long Island there are large boulders left by the ice age glacier that are exposed at low tide in 10-15 feet of water.
We have a reef at the south end of Garrett Island that rises 50 feet from a bottom of 58 feet. I love to watch the contour go into a sudden nearly vertical line.
 
Warren Milberg

Warren Milberg

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Dec 1, 1999
2,391
Hunter 28.5 Chesapeake Bay
My 2 cents on depthsounders and transducers: given a moving boat, I think most depth sounders are telling you where you was, not where you is...:dance: Unlike knotmeters, I don't think turbulence impacts a depthsounder's electronic signal much or at all. I also think that placing the transducer anywhere forward, or aft, of the keel makes sense from the standpoint of where the unit can send its cone shaped signal straight down rather than having to avoid the potential of bouncing off the keel if it were mounted alongside it.
 
sailingdog

sailingdog

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Oct 22, 2008
3,502
- Telstar 28 Buzzards Bay
Ross said:
We have a reef at the south end of Garrett Island that rises 50 feet from a bottom of 58 feet. I love to watch the contour go into a sudden nearly vertical line.
Click to expand
You have a very twisted sense of humor... :)
 
S

s sauer

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Jun 4, 2004
844
Hunter 28.5 Tolchester, MD
The depth sounder or knott meter should be placed where you can simply core thru the hull and not thru the hull and the structural grid / liner pan which may have space between then that could be harder to seal.
 
Ross

Ross

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Jun 15, 2004
14,693
Islander/Wayfairer 30 sail number 25 Perryville,Md.
Stu Sauer said:
The depth sounder or knott meter should be placed where you can simply core thru the hull and not thru the hull and the structural grid / liner pan which may have space between then that could be harder to seal.
Click to expand
I don't believe that I can understand what you have written. If you choose to use a through hull mount then of course you must choose to use a place that is accessable from both the inside and the outside of the hull.
 
RAD

RAD

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Jun 3, 2004
2,330
Catalina 30 Bay Shore, N.Y.
Free Spirit has both, the po put the transducer right under the helm of a center-cockpit and the hull is pretty flat there so its looking straight down at the bottom but its almost right behind my keel and here on the Great South Bay you need to pay attention to the bottom when close to the shores so I think I'd be hitting bottom before the transducer sent the signal to me,now when I decided to get a sonar/depth finder for the GPS it said to mount the transducer forward of the keel but the only place to do that is where its looking at a slight angle towards the bottom and that seems to work fine too but there are times when going through rough water and wakes the aft depth sounder will go blank for a while
 
Ross

Ross

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Jun 15, 2004
14,693
Islander/Wayfairer 30 sail number 25 Perryville,Md.
I think that my DF has a 30 degree beam, in 10 feet of water it doesn't look at a very big slice of the bottom.
 
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