Transducer - To Replace or Not Replace

The boat is scheduled for haul out Jan 22nd, which gives me a chance to plan for some repairs and upgrades. The boat still has the original depth sounder, a Simpson spinner type, which does work. It's located in the cabin, which is fine for crew and for checking anchoring depth, but not very useful while at the helm. The transducer also protrudes pretty far into the water. I'm considering replacing with a modern, 2" style digital gauge to be mounted beside the companionway, visible from the helm position. Thoughts? Can a new transducer replace the old one without major surgery? Will it stick out less into the water? Pros and cons?

Thanks in advance,

Most of the new chartplotters accept a glue-on transducer (just Lifeseal it to bare fiberglass low on the interior hull), which also provides water temperature.

Compatibility always needs to be confirmed, but there is about zero reason to drill through a hull for depth/temp today. (On Ericsons, with solid hulls. They don't work on yachts with cored hulls).

Existing hole

Picture from the inside.
Is inside the hull as reliable / accurate? How about any noises emitted in the cabin?
Possible to plug the existing hole?

I found a very good reason to go thru-hull on my 34-2. The old depth sounder transducer was in hull and didn't work vey impressively. When it died, I got a Raymarine depth sounder with an in hull transducer and it didn't work at all. The unit worked when it was placed near the prop shaft stuffing box. I went to a thru hull at the original location ant I could suddenly read to 1,200'. As it turned out, the core at that point is just shy of 1 1/4" thick. At the shaft, it was 3/4" thick. The 1 1/4 thickness was just too thick to shoot through.

Gotta love the way these boats are built.

DS trivia

The same forward "V" in the Ericson hull that makes for such a soft ride in rough seas, also makes a DS install a bit more complicated - up there in the bow.

It is desirable to have the face of the DS transducer parallel to the sea surface, and that's why the prior owner used a long-reach transducer thru a shaped piece of teak(?) on the outside of the hull.
This does create a couple of concerns, albeit low-percentage worries... one is that the protruding piece will be whacked by a piece of drift wood and knocked off or bent. The other is that it is large enough to slow the boat by several nano-knots.

I have done two installs where I glued the faced of the DS "puck" to the inside of the much flatter hull just behind the keel. As long as the angle is, say, under 5 or 6 degrees -give or take- your sound beam should still have a good shot down at the sea floor. Like my boat, yours has a solid layup hull, and the thickness will be less along the aft half of it.

Sand off the gel coat and clean the surface well with solvent first. If using the liquid-filled 'cup' provided by many major DS vendors it has a way to align it before it is glued down so that the actual face of the transducer is parallel to the water surface.
Otherwise you can epoxy the face to the inside of the hull.... but be really sure you have no air bubbles trapped in the thickened epoxy.

I note that many owners will put a small water-filled plastic bag against the hull, and hold the puck against the bag first -- just to verify that the instrument reads OK.

I note that some owners worry that locating the DS transducer aft will reduce the "warning" that the keel is about to costact the ground. Since you will normally be moving slowly when in shallow waters the difference in notice to you will be about a second, or less.
If moving at full speed, no matter where the transducer is located, you will not have enough time to effectively take an evasive maneuver anyhow....

Ask one of our members about the rock he nailed at warp speed! First 'notice' is usually the loud sound of the boat hitting something unyielding.

I have not hit a rock, but have grounded at about 7 kts in very hard sand. While we were aware of the nearing channel's edge, we did not allow for the steepness of the underwater ledge we could not see.
Buried our keel a full foot deep in a heart beat, and had to be towed off.

It's all good clean fun!

In hull, and located aft

Last year I also replaced my depth sounder transducer. Filled the hole of the thru-hull (properly, with mat, chopped strand and polyester resin), and installed a Raymarine in-hull sounder aft of the keel, in an area easily accessible.

I’m not worried about hitting ground because the sounder is “way back aft”. If your relying on your sounder to keep you from running aground, then you need to spend more time studying the charts.

Raymarine has various transducer produced by Airmar, make sure you get teh correct one. These are compatible with various systems.
CTO

My two installs work fine too.

The current one loses the bottom at 100 feet or so, whereas the former was good to 700 feet (both glue-ons).

Deep reads were formerly very useful for navigation, but with GPS chartplotters now seem only a backup.

We are told to test several potential location points before installation. But test how? Not easy for sailors on the Chesapeake to find a 700-foot test depth, as I recall.

Farlander,

My original Signet depth sounder transducer (an Airmar mfg transducer) was silicone caulk sealed/glued to the inside of my hull, never drilled and installed as a thru hull transducer. It was working fine when I upgraded my 35 year old Signets to Furuno in 2015, note typical Chesapeake depth is < 50 feet, max depth is like 200 feet in one spot. I assume it worked normally from new install as my boat lived in MDR and Santa Barbara until I bought it in 2011. It was actually the ONLY one of the three (wind and speed) still working. I resealed it with new silicone and bought a used Raymarine ST-50 depth display on Ebay for $50 and now have a totally redundant second depth sensor. So you can certainly install a "typical" depth only transducer inside the hull with no drilling and have full function.

So what do you do with the existing hole? You can certainly install a new depth transducer in the existing hole just to fill it. Are you planning to upgrade other functions - speed and temp? (NOTE: most everybody will agree you really only need depth, I added speed, water temp and wind just for fun. I went the first four years with just depth and it really IS all you NEED.) My new Furuno transducer, a combo depth, speed and temp (an Airmar DST-800) went in my existing Signet speedo transducer hole in the hull. But it was larger in diameter and not flush to the hull so I had to over-drill a larger hole in the hull and then epoxy fill the taper area. All easy with a few tricks and techniques.

In the near term, you can add a new depth transducer INSIDE the hull and leave the existing transducer in place. Next haul out you can add something else in the existing hole if you'd like, fiberglass the hole or move the new depth transducer to the existing hole if it doesn't work inside the hull.

Mark

Using a in hull transducer does drastically reduce the depth that the depth sounder reads to. On my boat the difference was between 120-140 feet in hull and 1200 feet thru hull. In the south and east that might not make any difference but in the north west, where we can get 1200 feet short distances offshore, it is appreciated.

If you already have a hole for a thru hull hole, it makes sense to replace it with another thru hull transducer. It's much easier than trying to fill the 2" hole in the hull and getting a much less sensitive instrument in the bargain.

supersailor said:

Using a in hull transducer does drastically reduce the depth that the depth sounder reads to. On my boat the difference was between 120-140 feet in hull and 1200 feet thru hull. In the south and east that might not make any difference but in the north west, where we can get 1200 feet short distances offshore, it is appreciated.

If you already have a hole for a thru hull hole, it makes sense to replace it with another thru hull transducer. It's much easier than trying to fill the 2" hole in the hull and getting a much less sensitive instrument in the bargain.

Click to expand...

Please do note that a "flush" mount on the very angled bow section will point the beam off center too far, IMHO.

And do not give up on the aft flatter inside install.
On our previous Niagara 26, that mounting gave us good returns up to 200 feet, and when we in the Straits of Juan whoever, it once got a good return at 600..... bottom there is hard rock and probably makes a perfect reflector.

It's all just choices and compromises, like everything else.

I had good luck with an in hull install on my old E27. Found a spot on the bow forward of the keel that was flat enough with a little bit of sanding to work just fine. Probably had about a 2 degree forward cant which didn't significantly change the depth readings enough to be of any concern at the less than 200' depths. ( If it's too deep to anchor in, I generally don't care how deep it is).

One thing I will do if/when I need to install a new one in my E35 is put in a charting fishfinder like I did on my E27 instead of just a digital depth sounder like I have now on my E35. Being able to 'see' the bottom makeup and know if it is hard, soft, weedy, rocky, etc. is very helpful in anchoring (and locating that wreck to dive on, and fishing, etc, etc, etc. That's why they put the cup on the bottom of the old sounding leads). And frankly fish finders are usually way cheaper than 'sailboat electronics' and just as rugged and dependable. You used to be able to get a good guess as to bottom type with the old flasher types, but I'm of the firm opinion the straight LED digital depth readouts are a big step backwards.

Grumble, grumble.

Kevin Wright
E35 Hydro Therapy