RETRO-FITTING AN IN-HULL TRANSDUCER
OUR 11M POWERCAT has an older model Lowrance HDS Fishfinder system, with an Airmar in-hull transducer installed several years ago. This works well, with a second display up in the flybridge which is networked – both units share the Navionics map data and use the same transducer.
Recently we were offered a secondhand side-scanning module for the system at a really good price. But it came with a transom-mount transducer, and the boat has stern drive propellers so there is no clear water out on the transom.
The through-hull version of the sidescanning transducer is fairly expensive, especially when adding the cost of hauling the boat for installation.
Instead, we installed the transducer so it could shoot through the hull. We knew the hull was suitable due to the existing transducer but the new unit was not actually intended for this kind of installation.
Embedding it in epoxy in the bilge looked to be the simplest solution, although we knew this isn’t recommended by the manufacturers and we’d lose some of the unit’s sensitivity. But it was worth a try!
First, we identified a suitable spot in the bilge – a flat, solid section of the hull. To check how well it will work we surrounded it with liquid and viewed the image quality. We were able to pour a small amount of water into the limited bilge space and place the transducer in the water. Another option is to use a very thin plastic bag containing water and the transducer and place this against the hull.
We compared the picture to the one we got by simply dangling the transducer over the side. The first location gave us a fairly poor picture but after trying another spot we got a much better image.
We drained the water and completely dried everything off. A light scuffing of both surfaces with 120-grit sandpaper, followed by a thorough cleaning with acetone ensured we had no contaminants, and the epoxy would hold. We removed the redundant metal transom bracket from the unit and ensured the base would sit horizontally.
The final step was embedding it in epoxy. We avoided the five-minute setting type as we weren’t sure how long it would take to position everything and did not want it to go off too quickly. We used masking tape to create a ‘dam’ a few centimetres bigger than the transducer face. This would prevent the epoxy oozing away and leaving a void.
Mixing up a generous amount of glue we spread it over the dammed-up area. The face of the transducer was also coated to eliminate any bubbles. We then placed the transducer into the pool of epoxy, wiggling slightly to get it touching the bottom and perfectly horizontal.
The next day we took the boat out and ran alongside a few known underwater structures to check the sensitivity of the unit. We had to crank the gain up a bit to compensate for the hull but on the whole we got a good picture. Success!