Redundancy for Chartplotter & Sounder

[Drew]

Have a 2004 28TE with the C120 Raymarine chartplotter, sounder, autopilot and radar. Considering adding redunancy for the chartplotter and sounder. Maybe the A series Raymarine or for a few more bucks the Garmin 700 series hocked up to a separate transducer. My question...any experience with the "in-hull" transducers? My current transducer is a through hull.

[RobS]

My question...any experience with the "in-hull" transducers? My current transducer is a through hull.

By "in-hull" I assume you mean "shoot-thru" ?

This needs to be in a solid glass installation, not a cored-hull like our Albin's. I took a standard transom mount ducer and epoxy'd it in the bilge of my Pursuit and it worked flawlessly as a shoot-thru. I guess you could pick your location and remove the core and solid fill with epoxy and it should work. If not you have a great start for pepping for a thru-hull install

[joe.baar]

I just purchased an Airmar P79 in-hull. The installation manual shows and describes exactly what Rob says: remove a 4" circle of the inner hull fiberglass and core, then thoroughly sand the inside of the outer hull down to bare glass in the exposed area. "Glue" the receiver part/antifreeze reservoir down using some simple geometry to align it correctly with the keel and taking account of the deadrise - Albin says 16 degrees but I measure 15 - then backfill with a solid epoxy. The manual has recommendations for what kind of "glue" and epoxy filler to use but I left it on the boat this week. You could try for the manual on Airmar's web site.

The issues I can foresee right now are 1) how to control a 4" hole saw without using a center bit which would puncture the outer hull, and 2) there might be tight clearance between the transducer unit as installed on the receiver part/antifreeze reservoir and the epoxy fill if the core is too thick. I imagine the fill could be dished enough to clear the unit if necessary.

Finally, my '95 28TE has a left-hand prop, probably because the Yanmars in these boats are installed tranny forward. Airmar is clear that the 'ducer needs to be mounted on the side of the hull where the prop's blades are moving down, away from the hull, otherwise the pressure waves they generate will interfere unnecessarily with the sonar's readings. This is probably true for any style of transducer. In my case it means the old transducer is mounted on the starboard side about a foot out from the centerline and the new one will be mounted to port. Either the old transducer was positioned on the wrong side or the previous engine ran a right-handed prop, who knows?

Have fun with it.

[Carl]

Joe, this might help with your question as to controlling a 4" hole saw without pilot bit. Find a scrap piece of lumber that will fit in the bildge at the desired drill location. If you can get it to fit so it will not move in a clockwise direction, even better. Mark the scrap lumber where you want the hole. Remove it and drill it out with the hole saw. Put the board back in place and remove the pilot bit. The hole in the scrap board is now your guide and will keep that saw from walking. Make sure you have a handle on the drill motor, and even better someone else to hold onto it. Let the saw do its job and dont rush it. Good luck!

[joe.baar]

Carl,
Thanks so much for the hint about how to use a hole saw. It would have taken me days, if not weeks to come up with that technique on my own.

My electrician neighbor suggested a method I think I'll try instead: the RotoZip. With a template I should be able to cut any size or shape hole with no fear of puncturing the hull.

I'll try to remember to document with photos as this progresses. The boat gets hauled for repacking the shaft gland, bottom paint and removing the old transducer October 7.

[RobS]

.....the RotoZip. With a template I should be able to cut any size or shape hole with no fear of puncturing the hull...

Never under-estimate the RotoZip !

[DougSea]

The template as suggested by Carl can be invaluable. I use that technique all the time, especially when i have to drill a new hole where there was one already and there's no material for a pilot to even sink into. You can also set the center, pilot bit in a hole saw shallow and even with the blade to help guide it without piercing the skin. Either way you'll be glassing in the hole so penetrating the skin is really not a big deal. In fact, you can use the pilot bit to help make sure you don't "oversaw". Have the pilot set 3/8 below the edge of the saw and when your helper sees it penetrate you should be 1/4" from the skin. Glass it in and you're good to go.

[joe.baar]

Thanks very much to both Doug and Carl. I'll keep you posted.

[Drew]

New question...with my 2004 flush deck the existing thru the hull transducer is located port side, just behind (towards stern) and to the left of the transmission. Any thoughts/experiences on where to place the second transducer so as to not be impacted by other through hull applications.