Transducer in the Keel

[Reg Barker]

In the article “Centreboard water spouts”, the pictures of the centreboard also show a transducer. I would be grateful if fellow boat owners could explain how they fitted the transducer within the slot of the centreboard, and was it bolted in? I also can see it has a spacer - how is this attached?

[Graham W]

Reg,

I've just spent quite a lot of time under my boat taking off an old transducer and installing a new one. The SB yard's way of doing it is to install a long and quite large wedge of wood which they stick with Sikaflex to the shelf inside the bottom of the centreboard slot, just ahead of the slot opening. With the pointy bit of the wedge facing forward, this gives a small aft-facing "transom" above the front of the slot. A small (and it has to be small) transom-mounted transducer can then be screwed into the wood, so that the transducer sits in the opening ahead of the centreboard. This is the standard 8-pin one used by several of the newer Garmin fishfinders http://www.scubastore.com/scuba-diving/garmin-transom-mount-transducer-500-w-for-gsd24/132427/p  I'd say that the small one in James's photo is another make, possibly Lowrance. 

The Garmin's bracket can be adjusted up and down when the screws are loose to get the vertical position just right and the hinge on the bracket allows the transducer angle to be adjusted too, so that the beam points straight down. I've attached a photo showing my old one in place in 2011 - you can just about see the wooden wedge to which it is attached. Note the missing screws on the steel centreboard mounting bracket - since rectified.

Unless you have very small hands, it will probably be necessary to unscrew the centreboard from its steel bracket to give yourself access to the slot from underneath.  For a neat wiring job, you may also need to unscrew the top wooden capping on the centreboard case in the cockpit. This way of doing it is not a job to be undertaken lightly, as I now realise when wondering where the past two days went!

[James Bennett]

Guys
Please see the attached photograph that clearly shows the block of wood that has been set into the forward end of the centreboard casing. This is Sikaflexed in place. Andrew Denman screwed the transducer into this block of wood and ran the cable up the forward end of the centre board casing and through a cunningly placed cable slot located in the underside of the wood capping piece to the centreboard casing.
 
He may have lifted the centre board itself to improve the access. He did this by removing the wood capping to the centre board area and then unscrewing the screws (only the four immediately fore and aft of the pin, see pic') that hold the stainless plate over the centre board pivot pin. The stainless plate can be lifted slighty so that the board can be lifted away from the pin. This allows the the whole board to be lifted up (say 100mm) and thus improving access. 

The cable slot continues along the port underside of the wood capping so that the GPS/echo sounder display can be located right aft on the centre casing. On my boat I elected to locate the display at the forward end. I'll take a picture of that arrangement at the weekend. Hope the above makes some sense!

[James Bennett]

and the missing photo!

[Reg Barker]

Graham and James
Thank you, that has been most helpful and useful. I had been toying with the idea of a transducer through the hull, or placed on the hull of the boat.  This would have been in the cubby of the BRe. I was against drilling a hole through the hull, and sticking it to the hull where it could get knocked. I did not want it on the transom as the electrics and battery are positioned forward.  This is a great position as the cable can come straight into the cabin through the small wooden top of the centre board.

[Tony]

Hi Folks.
The transducer of my Echofish actually fires through the EP hull. (I dont know if it'll work through a GRP version. I suspect not. )
 The trick is to put some kind of water dam around it so that there no air between hull and transducer. I used one of those little aluminium cat food tins for pampered cats, with the bottom removed and epoxied to the inside of the hull. (The tin, not the pampered cat )
It works just as well as dangling it over the side - and gives the same readings and graphics - but still tells me there are a million fish under the hull.
The only advantage over a proper fixed mounting is that you can easily take it home or use it on another boat.
Disadvantages;
Easy to steal
Someone is bound to trip over the wire.
Forgetting how to turn off the depth alarm. The beeping drives you mad so you turn the damn thing off - then run aground and have  to get out and push. 

BTW If you DO epoxy a cat to anything (accidentally, I hope) the only way to release it is with scissors.....and armoured chainsaw gloves, if your cat is anything like mine.

[James Bennett]

Tony /Reg
Most modern transducers will work inside a hull whether it be GRP/EP or similar. The important issue is to make sure that the transducer is carefully installed on a bed of resin that has no bubbles or cavities. The same applies to the parent material of the hull. The position can be tested by using a Vaseline as a temporary gunk and manually hold the transducer in place and check that a good signal is obtained. Carefully mark the area and remove all traces of the Vaseline.
Using a dam to retain the resin is the best idea and I would recommend the use of a large yogurt carton or similar that has been carefully cut to the shape of the hull. This can be held in place with plastercine or heavy duty duct tape.
Most manufacturers recommend that the deadrise of the hull is less than 10 degrees as this minimises any angular error.
Installing the transducer in the centre board case of the BR 20 is easy as it offers a protected location, the transducer cable is easily installed without having to penetrate any watertight floors or decks and the transducer faces directly down.
Good luck!