Transom mounted Transducer

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Dimitri-2000X-Tampa
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Transom mounted Transducer

Post by Dimitri-2000X-Tampa » Wed May 10, 2006 5:28 am

After 7-8 months, I finally got my motor fixed I'm pretty sure. Had to rip the whole dang thing apart. After I test drive it wide open in the bay to confirm, I'll post pics back in the motor overheat thread.

But this thread is about my new depth finder (digging into shallow sand areas probably didn't help my overheat problem much). I sent my old L265 unit back to Raymarine and they said it was working fine, which left my in-hull transducer as the culprit. After thinking about it, I decided to get a whole new A-series HD digital unit (DS400x) as it was cheaper than just trying to replace the broken transducer. The kids love watching the fishies anyway, and Dad thinks over the water speed and temperature are cool gadgets to have. Raymarine says the color display is very easy to read in the sun.

After reading all the archived threads on mounting, my question is whether you can epoxy a piece of starboard or wood to a bottom painted transom? My guess is that it won't stick right unless I sand the paint off but I thought I would ask for some other opinions. There are other holes below the waterline so I don't think its a big deal to screw it into the transom as long as the screws are properly bedded in 5200. I had another boat which once had some leaky screws below the water line, but I don't think those had any sealer on them.

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Post by Nettech » Wed May 10, 2006 6:59 am

I have my transducer and speed senser screwed to the transom. No leaks, works great. I see you are in Tampa, we are in Lakeland and I think we are going to put in at Ft Desoto Saturday and sail out and around Egmont Key. Maybe we will run into you. Well, maybe bump is a better word.

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norbert
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Post by norbert » Wed May 10, 2006 10:36 am

dimitri, i NEVER EVER would drill holes below or near the waterline and only seal them with marine sealant as 5200! you re asking for trouble!

okay, first i would not drill below the waterline at all. if ever i had to, i would seal the holes very accurately with epoxy. 5200 is not a durable solution (although i fear the the factory did it like that :x ).

nettech, leaks are not the question when you screw a little item like a transducer on the transom. but you puncture the gelcoat, and water intrudes the grp. you will have a serious osmosis problem after several years (the problem will occur later if the boat sits on her trailer). i'd recommend to take the scres out, let it dry for several weeks, fill it with epoxy and set the screw in again immediatly. this should fix it.

i voted for the glued cutting board solution. remove the antifouling in the glueing area until you reach the epoxy barrier coat (hope you have one :wink: ). the glue the (predrilled) piece of board with epoxy. repaint the board (but not the transducer!) with antifouling.

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Captain Kimo
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Post by Captain Kimo » Wed May 10, 2006 5:37 pm

norbert wrote:dimitri, i NEVER EVER would drill holes below or near the waterline and only seal them with marine sealant as 5200! you re asking for trouble!

okay, first i would not drill below the waterline at all. if ever i had to, i would seal the holes very accurately with epoxy. 5200 is not a durable solution (although i fear the the factory did it like that :x ).
I with norbert here dimitri. Recommend trying first to shot thru the hull.

I mounted my little fishfinder transducer in plumber's putty just forward of the CB trunk in the bilge area. Plumber's putty remains soft, therefore if the location isn't right you can relocate it without the problem of epoxy removal. Water ballast needs to be in to get a reading. It works on my 96' :macx:. Side benefit, depth readings start to display when the ballast is filled and no air bubbles :)

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Why not?

Post by robertw » Wed May 10, 2006 6:24 pm

I mounted my transducer that way. Sealed it up and it never leaked, its only a tiny hole to mount with a couple of screws. And even if you get a small leak, what does it really matter, its going right into the water ballast tank anyway.

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Dimitri-2000X-Tampa
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Post by Dimitri-2000X-Tampa » Wed May 10, 2006 7:39 pm

Norbert, I thought this method you speak of was only required when you are drilling through fiberglass with a wooden core? I'm surprised you have such a low opinion of 5200...I thought that was the premier sealant for below the water line. I had always heard that above the water line, you can get away with using 4200 which is more flexible, but below, it should be the more solid 5200. I'm curious if anyone who has used 5200 has had this sort of osmosis problem?

As for mounting position, I have the airmar P-58 and if I don't use any shims, the bottom of the triducer is pretty level with the bottom of the boat. Seems like the best place to put it is right inside of the fill valve on the starboard side. It is barely 3 inches out of the prop radius there but I wouldn't want to put it further outside or else it will come out when heeled. Also, it can apparently be completely level with the hull or drop slightly below. Can anyone confirm that with a completely flush and level installation at this location, it will read well at all speeds?

I've thought about putting it in the putty, but I like the idea of having speed over the water to compliment my gps and calculate currents. Temp gauge is kinda cool too...what can I say, I'm a gadget type.. I talked to the folks at Raymarine about this too and they said you lose a lot of power shooting thru the hull although I suppose that only affects deep water performance, which we don't have much of around here.

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Dimitri-2000X-Tampa
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Post by Dimitri-2000X-Tampa » Wed May 10, 2006 8:01 pm

Nettech wrote:I have my transducer and speed senser screwed to the transom. No leaks, works great. I see you are in Tampa, we are in Lakeland and I think we are going to put in at Ft Desoto Saturday and sail out and around Egmont Key. Maybe we will run into you. Well, maybe bump is a better word.
That's a top notch area. I was there last weekend with the kids..sans boat unfortunately. Did you know that the North Beach at Fort Desoto was voted the number 1 best beach in the U.S. last year? When I was there on Saturday, it was like being in the Bahamas. Of course with the boat, it is better to go to a less populated beach like Shell Key to the North or Egmont to the South. I'm surprised we don't get more visiting Mac's around here as gorgeous as it is. 8) Someone should organize a Mac regatta and subsequent beach cruise!

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Post by Nettech » Thu May 11, 2006 5:28 am

Dimitri-2000X-Tampa wrote:
Nettech wrote:I have my transducer and speed senser screwed to the transom. No leaks, works great. I see you are in Tampa, we are in Lakeland and I think we are going to put in at Ft Desoto Saturday and sail out and around Egmont Key. Maybe we will run into you. Well, maybe bump is a better word.
That's a top notch area. I was there last weekend with the kids..sans boat unfortunately. Did you know that the North Beach at Fort Desoto was voted the number 1 best beach in the U.S. last year? When I was there on Saturday, it was like being in the Bahamas. Of course with the boat, it is better to go to a less populated beach like Shell Key to the North or Egmont to the South. I'm surprised we don't get more visiting Mac's around here as gorgeous as it is. 8) Someone should organize a Mac regatta and subsequent beach cruise!

There are a lot of nice beaches and sailing areas here. I love it. As to the transducer, being a native Floridian, I have owned three sailboats, bassboats, saltwater fishing boats, canoes, and anything that floats. I have always mounted mine to the transom with screws. Of course sealing it up is just common sense. I have NEVER had a problem. In my opinion, you only mount things below the water line with putty or epoxy that you can afford to lose.

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Post by Paul S » Thu May 11, 2006 6:28 am

on our powerboat..I mounted the transducer to the stern without issue. Never had any blistering or anything. When it failed..added another one (didn't take the old one off).

That said, on the Mac, I couldn't get myself to do it. I glued (4200 I think) a 4" pvc pipe segment, fill it with water..have the depth transducer in the center held down with a dab of 4200. Works like a charm .. as long as the water is still in there.

I tried the putty trick. didn't work. But the water worked like a charm.

Paul

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Bobby T.-26X #4767
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Post by Bobby T.-26X #4767 » Thu May 11, 2006 8:50 am

but if you have a sensor for temp and speed, you "gotsta" put it on the transom, right???

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Post by Paul S » Thu May 11, 2006 10:35 am

If you have a temp sensor ( I do not) then it would measure the hull temp, which I can't imagine would be far off from the water temp. The GPS gives over the ground speed, which is what I care about. I don't have much need for through the water speed. If you want/need through the water speed, you need to mount it externally from what I understand.

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Dimitri-2000X-Tampa
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Post by Dimitri-2000X-Tampa » Thu May 11, 2006 10:25 pm

Water speed is nice to have to measure currents. Not sure why putting some screws in the transom of a Mac is different than any other boat. I took a good look at mine this evening. Crawled down into the claustrophobic stern of the boat and took the cover off. There are already plenty of holes in the transom that look to be sealed with 5200. About 5 holes for each rudder, 4 holes for the engine mounts, two holes for the ballast valve stem guide, and the lowest 4 holes are the two each for the lower rudder line fairleads. If I remember the days I used to use my boat more, those fairleads are frequently underwater. And many of the holes are underwater when launching/retrieving the boat on the trailer. I didn't see the signs of any leaks. Of course the transducer would be lower than all the other holes.

The interesting thing is that the stringers are not as deep as I would have expected them to be if the ballast tank area near the valve only went through the stringer. I can't see the backs of any of the 4 screws that hold the valve in. I think this may imply that there is ballast tank all the way across the transom and the triducer screws in fact would go into the ballast tank down that low...if they get all the way through. Can't really tell what the hull thickness is there.

So I thought about glueing something to the transom, but the screws probably need about 1.25 inches so that means it would be something more like a 2X4 I would be sticking to the hull unless I wanted to use shorter screws. Just seems like it is a cleaner and stronger installation to screw it directly to the boat using the longer screws with sealant in the holes.

Seems like folks here are pretty divided on whether to drill or not to drill. :wink:

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Post by Paul S » Fri May 12, 2006 7:23 am

I have no problem drilling below the waterline.. I just don't like to do it if I can avoid it.

I just put a water fill on the stern. Drilled a 2" hole for the fill.
Water fill picture click hereI could not believe how thick the hull was there. I was somewhat impressd. I should take a picture of the plug.


If done right, drilling into the boat below the waterline should not be a big deal. Sometimes you have to. I wouldn't do it just for a water speed sesnor. But to others it might me a lot more important.

Paul

Frank C

Post by Frank C » Fri May 12, 2006 10:48 am

Dimitri-2000X-Tampa wrote: ... Seems like folks here are pretty divided on whether to drill or not to drill. :wink:
I'm not too concerned about drilling these small holes below the waterline. And I much prefer the transom-mounted ducers ... that's where my dealer originally installed them, both depth skimmer and and paddle-wheel. But I removed them since I wanted the option to beach the hull stern-to. Unfortunately, the shoot-thru depth ducer simply doesn't work as well as the skimmer, which gave constant readings in any seas and at any speed, sail or motor.

Adding them back onto the transom, I think I'd try hinged mounting boards that could be raised for beaching ... and also to keep the ducers slime-free. In the case of hinged boards, seems it would be pretty easy to mount them above the waterline, with something like a hasp & pin to hold it down, and release for lifting. Anyhow, that's what I'd ponder for starters

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Post by Dimitri-2000X-Tampa » Fri May 12, 2006 2:29 pm

Frank, the bracket that the triducer is mounted with is already hinged and designed to kick up if it hits an obstruction. Unless yours is a different design, couldn't you just manually kick it up when you need to beach?

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