Installing a new depth sounder transducer

[Thalassa]

I'm in the process of replacing my old Signet depth finder/transducer with a new Airmar transducer P7 (part of the Raymarine i40 package). The transducer is designed for a 12º hull curvature where the transducer is mounted (they also have a transducer for a 0º and 20º hull curvature). Now wondering what the hull curvature at that spot is for a 1985 Ericson 32 Mark III.

 

[Kenneth K]

I think there is pretty good access to the depth transducer below the screwed-in cover plate at the bottom of the port-side setee cabinet.

Just go down there with a pencil, sheet of paper, and a small level. Hold the level till it's at the same slope as the transducer and mark this on the paper. Then draw another line after tilting the level until it shows "level." These two lines will give you the angle.

 

[Thalassa]

Thanks Kenneth, the only problem with that is the lack of accessibility on a 32’ one.

 

[peaman]

My transducer is under the vee berth. On the aft face of the vee berth cabinetry, there are two drawers plus a bottom-hinged panel which accesses a plastic access port which in turn accesses the bilge. If you can reach the hull bottom through the cabinet, you could drill a pilot hole through the hull to mark the center location for drilling the hole for the transducer. Also, it's easy enough to get the correct angle from the hull exterior. That is a centerline location with a pretty low angle, perhaps closer to 0 than to 12 degrees.

 

[Loren Beach]

A bit of a suggestion from our ten years with the prior 26 foot boat: The location of the depth transducer can be somewhere flatter and easier to access -somewhere aft - than the V in the bow section. While the concept of having depth info from somewhere forward is valid, it's good to remember that the "advance warning" of a shoal that you want to avoid is little different if the device is located mid ships or even aft.

Usually... when worried about hitting a rock we are keeping speed down to a couple of knots and and the difference in warning from a sensor located aft 20 feet or is maybe a second or less. Your reaction time to hearing the alarm or viewing the screen is a LOT more variable and subject to delay.

Intuitively I want that sensor up forward, too, but sometimes the boat construction and inside access may dictate another location.
On our model the bottom has a softer V up forward, at the rear of the v-berth and both KM and DS are happy there. When we added a second DS transducer for the depth display in our chart plotter, we put it under the quarter berth. In a decade I have never noticed either reading being different. Certainly we would want warning of a pinnacle rock or an old piling top as soon as possible (!), but odds are that we would still have to be looking at the numbers at exactly.... the right moment. (sigh)

Good luck on the project. I have to remove two drawers under our V berth to access that area, and reaching around the slider track is tricky.

 

[Thalassa]

All excellent points! Thank you all and feeling much better to tackle the project. Ps. I’m planning to replace the old signet transducer with the new one at the same location. It looks like the new one requires just a 1” larger hole so, after some grinding, that should work I think.

 

[Bolo]

Just a suggestion. I recently installed a new transducer in my E32-3 (1987) and it’s part of a video on my YouTube channel “Sailing Vesper”. I replaced the transducer “core” which goes into a housing (Airmar) so it’s not the same as a new through hull install but there are some still shots of the transducer area that might interest you. I could look at the transducer I was replacing or feel it but couldn’t do both at the same time. So my install was all by feel and a bit “exciting” since the boat is still in the water.

 

[tpcorrigan]

Just as an aside, We installed a "in hull" transducer with no through hull needed. We also moved it to just in front of the keel and a little to port. the hull is solid fiberglass so you can use a in hull. when I ran into the problem of what angle of the hull is appropriate I took some measurements and actually made a wedge shaped spacer that brought the unit to the correct level. I made sure there were no air bubbles in my glassing so no odd signals in the Garmin. Now we not only have a new depth sounder but with the newer Garmin I can map our river entrance way more accurately every spring. Have a great season, _/)

 

[Stuphoto]

Just a suggestion. I recently installed a new transducer in my E32-3 (1987) and it’s part of a video on my YouTube channel “Sailing Vesper”. I replaced the transducer “core” which goes into a housing (Airmar) so it’s not the same as a new through hull install but there are some still shots of the transducer area that might interest you. I could look at the transducer I was replacing or feel it but couldn’t do both at the same time. So my install was all by feel and a bit “exciting” since the boat is still in the water.

Bolo,
Thank you for the video,

I am installing one on my 25 after it arrives next week.
I am thinking of the center compartment in the V-berth, however will have to see when it arrives.

Oh, I am your 48th subscriber.

 

[Bolo]

Bolo,
Thank you for the video,

I am installing one on my 25 after it arrives next week.
I am thinking of the center compartment in the V-berth, however will have to see when it arrives.

Oh, I am your 48th subscriber.

Thanks for becoming a subscriber! My channel will never come close to becoming a "famous" as some of the other one's on YouTube because I'm doing it for pure fun and to share my knowledge and my mistakes. Glad you enjoyed it.

 

[TKBLACK]

Just a suggestion. I recently installed a new transducer in my E32-3 (1987) and it’s part of a video on my YouTube channel “Sailing Vesper”. I replaced the transducer “core” which goes into a housing (Airmar) so it’s not the same as a new through hull install but there are some still shots of the transducer area that might interest you. I could look at the transducer I was replacing or feel it but couldn’t do both at the same time. So my install was all by feel and a bit “exciting” since the boat is still in the water.

Great Video! Thanks for sharing!

 

[frick]

I think there is pretty good access to the depth transducer below the screwed-in cover plate at the bottom of the port-side setee cabinet.

Just go down there with a pencil, sheet of paper, and a small level. Hold the level till it's at the same slope as the transducer and mark this on the paper. Then draw another line after tilting the level until it shows "level." These two lines will give you the angle.

Download a level app on your smartphone and it will give you the angles fast.

 

[Kif]

Hi going to jump in here with a related question as it seems about as good a place as any. I just bought into a partnership on an Ericson 32-2. We are having some issues with existing instrumentation. Notably depth sounder reading <3ft when we know it's deeper (but not always), and faster than possible knot meter readings (over 9 knots at one point). The transducer is through hull (Airmar DST800 I'm pretty sure). It's located in what I fear might be a very poor location - midship starboard of the keel (under the seat about 1.5 ft from the bilge pump location).

I've seen a few things about why a depth sounder / knot meter should be positioned forward of the keel. However my former partner said the new transducer was installed (same place as old) less than 2 yrs ago and was working fine previously. I would think if placement was a problem it would have been an issue from day 1.

Curious if folks have experience with a midship placement like this that works or if it's just going to give us trouble for years to come. Not super motivated to pull out and put a new hole in our boat, but bad readings are kind of useless too.

 

[peaman]

Notably depth sounder reading <3ft when we know it's deeper (but not always), and faster than possible knot meter readings (over 9 knots at one point).

Regarding depth, the transducer measures distance to bottom from itself. Out of the box, it probably will read exactly that, but you should be able to make an adjustment (electronic, or whatever, depending on model) to add or subtract some number from the displayed value. Some people like the depth to read from bottom of keel to sea bottom (basically 'how much water is there below me?'), others like to read depth from the boat's waterline. The first requires reducing the "default" reading, while the second requires adding to it.

As for speed through water, I can imagine that a paddlewheel transducer mounted close to the keel could read higher than actual speed through water. Check the manufacturer's literature to see if the reading can be calibrated.

 

[Kif]

Thanks for the suggestions. To clarify, the depth sounder is currently not adjusted at all to account for position or keel.

I checked manually one day and the depth at our slip was 14+ft. So there's no way this is measuring the bottom even if it was measuring from the bottom of our keel (6'draft + 3ft still off).

Speed is a head scratcher. I've sent some help request to Airmar directly.

 

[Roger Janeway]

Thanks for the suggestions. To clarify, the depth sounder is currently not adjusted at all to account for position or keel.

I checked manually one day and the depth at our slip was 14+ft. So there's no way this is measuring the bottom even if it was measuring from the bottom of our keel (6'draft + 3ft still off).

Speed is a head scratcher. I've sent some help request to Airmar directly.

I have an old Signet paddlewheel sensor (i.e., not integrated with a depth sensor) and the display has a calibration function that allows adjustments up or down as much as something like 50%. Calibrating it is very tiresome: you drive back and forth in calm conditions on flat water (back and forth to compensate for current) and compare its reading to known distances (or to your GPS). On my 26-foot boat with the sensor just off center forward of the keel, my usual calibration adjustment is about +34% of the uncalibrated reading. I have no understanding of the hydrodynamics but it's that clear that water flows by different parts of the hull at different speeds and this must be accounted for.

 

[Christian Williams]

With GPS, I don't think you have to worry about calibrating a paddlewheel nowadays. Value of paddlewheel speed is relative changes--headings, trim, sail plans.

 

[Roger Janeway]

With GPS, I don't think you have to worry about calibrating a paddlewheel nowadays. Value of paddlewheel speed is relative changes--headings, trim, sail plans.

Technically true, but you don’t want the dial on your bulkhead reading 4 knots when you’re really going 5. And the dial on the bulkhead is the thing we see while sailing, if we don’t have a Garmin mounted.

 

[ConchyDug]

My t-ducer is roughly even with back edge of my keel about 1.5-2' from centerline. It works fine just have to calibrate it, but it's a newer Garmin system. Is it a full signet system?

Chicago_Marine_Electronics

Chicago and Great Lakes, Dealer, Sales, Installations and Service for Marine Electronic Products, Speed, Depth, Compass, Wind Instruments, Autopilots, Radar, Satellite TV, Satellite Phone, Satellite Navigation equipment, VHF Radio Communication.

www.chicagomarineelectronics.com

I've seen this dude bring back some old systems, like an Ockam scoreboard mast display. Has a wealth of knowledge.

 

[Dave G.]

My Raymarine I60 wind instrument needs paddlewheel speed to calculate true wind speed and direction. According to all the "experts" SPW is the source you need to get true wind info. I personally don't understand why that is as it seems wave/current direction which greatly effects SPW has little to do with the sails moving through the wind. I also don't know that there is anyway to input GPS speed into my instrument but I sure would love to be able to try it.