Thru hull Transducer Question

I am the proud new owner of a 1975 E27. It is in pretty good shape and it sails like a dream. It presently has the thru hull transducer for the Data Marine instruments that I think came with the boat. The gauges are shot so I am going with a Raymarine unit that came with the boat but has never been installed.

My question is this, should I pull the old transducer out and try to put the new one in its place, or just leave the old one and drill a new hole. Pics of the existing transducer are attached.

Thanks very much.

I guess an obvious question is, are both of the transducers the same size i.e., requiring the same through hull size. I don't know. But, there are enough holes in the e27 already that I'd try not to make a new hole. Some of these thru hull openings have a tapered plastic ring/insert. I don't think the thru hull you are working on will have it since the transducer flange is not flush to the hull, but I'm not 100% certain. Memory fails and I don't have pictures.

Are these datamarine instruments the same or similar to the signet instruments that came with my 77 e27? If so I have some recent experience replacing them. But I replaced with new signet instruments.

Jay

I still have a Data Marine depth gauge and apparent wind indicator on my E32-3 and had it repaired once at DMI Marine.
http://dmimarine.com
They even sell new gauges that fit the same space as old Data Marine gauges. BUT.....If you have your heart set on Raymarine there's nothing wrong with that! I have a Raymarine auto helm with the control squeezed into the old pod where the water speed gauge use to be. (See my photo) I think my choice would be to see if you can get a Raymarine transducer in the same hole. IMHO, the less holes you put in a boat below the water line the better. Can't imaging it not working and running a new cable to that spot will be easier, maybe, cause you can use the old cable as a messenger line of sorts, attaching the new cable to one end and pulling though whatever tight spots it might go through in your boat.

Back in the 90's I replaced the OEM Datamarine instruments with new Raymarine stuff. I recall the the new pair of thruhulls fit the old holes.
I installed the new Raymarine cables in place of the old stuff, too.

I'd vote no new holes. Hard enough to maintain the existing ones. Even if the new transducer isn't the right size. If its too small, you can get a larger diameter transducer which till be cheaper than filling the old hole properly at least time wise. If it is too big you can drill out the existing hole. A decent way to do that is to get a wood block like from a 2x4, drill a hole in the center same size as the hole-saw pilot bit. Then have someone inside the boat hold the block over the existing hole pressed down on the hull (hands clear of the pilot hole of course), then you can work with your helper to center the hole saw over the existing hole, tell them to press really hard then drill away. I use the highest speed and lightest pressure to start with to avoid snagging the saw. If the new hole is significantly larger than the previous hole I usually use drywall screws through the material into the wood block, inside the new diameter, to hold it all in place once centered, You could also use a drill press to make a center-drilled tapered plug that fits the old hole snuggly to center your hole saw.

I'm not familiar with the Datamarine transducers, so I can't say for sure. But I'd also be in the camp of trying to use the existing hole if possible. A picture of the transducer from inside should help us. Also, if they're like the Airmar transducers, if you measure the diameter of the transducer on the inside, that should tell you how big the hole is.

debonAir said:

If it is too big you can drill out the existing hole.

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Here's another idea for centering a hole saw. This arbor takes two different hole saw sizes and uses the internal as your "pilot" while the external cuts. Mine was called a 'hole enlargement arbor'. Doesn't work for every use case, but I've used it with success.

I had the same experience as Loren, only more recently. 2 years ago new depth transducer, and speed paddlewheel, from Raymarine i50/60 sailing instrument combo kit, were a direct swap for the original datamarine through hull sensors in regard to hole size.

And as Bolo suggests I ran mouse lines when I removed the old sensors and that made pulling the new wires a cinch.

Do you know the condition of the existing thru hull? I installed a new thru hull and DST800 sensor in my Ericson 25 in the same location as the original Data Marine unit. I had the display but nothing else, and installed a lightly used ST60 display. The original/old thru hull was not difficult to remove and had very little sealant on it. It also seemed to be a bit brittle. It was not leaking, but I was glad to be replacing it with a new unit. The thru hull was tapered into the hull and the new thru hull was not, so I needed to fill that taper before installing the thru hull - the hole was otherwise the right size. Rather than just use extra sealant for the gap. I sanded the area back a bit and used the new thru hull as a mold, temporarily taped the threads and flange and installed it inside out and used the flange nut to hold thickened epoxy I spread into the flange gap. Then I removed the "mold" and installed the thru hull correctly. The hole was otherwise the correct size, just tapered instead of straight.

I see some cracking in the area in your picture, so further investigation there is probably warranted anyway. You may have some repairs to do while you are at it.

Congrats.

Thanks for the help folks. I have attached a picture of the transducer from the inside. Its the one on the top.

It looks like there's a depth transducer and maybe an old speed transducer there. I don't see both of them on the exterior picture. Are they under that large circular protrusion? Regular transducers are usually maybe an inch bigger in diameter on the outside than the inside.

driftless said:

were a direct swap for the original datamarine through hull sensors in regard to hole size.

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@driftless Tyler - is that what yours looked like on the outside?

If you wish to save time and money on this project, there is a chance your existing transducer can communicate with the new Raymarine display.

KS Dave said:

@driftless Tyler - is that what yours looked like on the outside?

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Yes - the Datamarine depth transducer looked just like that. Mushroom style. I'm looking for photos but I don't think I have any. I'm pretty sure I still have the old transducer though, so if I can dig that up I'll post a photo. I don't remember the "wing nut" style interior nut, but I may just not remember. I'll look for them this evening.

jtsai said:

If you wish to save time and money on this project, there is a chance your existing transducer can communicate with the new Raymarine display.

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I would not count on that. Everything I read lead me to believe that the Datamarine system would not "talk" to anything else.

driftless said:

I would not count on that. Everything I read lead me to believe that the Datamarine system would not "talk" to anything else.

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My former boat's Data Marine's depth gauge had a transducer like programza's post #9. It communicated with a Raymarine ST60 display. All I had to do was soldering pair of tiny butt connectors. I was happy to be able to view the bright large display.

Perhaps it’s worth considering the location? Normally you want it in a flattish section if the hull, forward of the keel. If it’s mounted too far forward it won’t work while you are sailing (could be out of the water). It’s hard to tell in the photos. They also don’t work well when on a steep angle unless you get a transducer made for that.

Things worth considering.

Also, it’s not hard to fill an old transducer hole. A bit of glass and some epoxy. People are commenting on that, but imo better to locate it in the right spot than try to use the old hole if it’s not ideal. If the new sounder isn’t a combo like the DT800, you can just glue it to the inside of the hull and it will work through the hull with no hole.
-p