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Catalina/Capri 25/250 Sailor's Forums

Catalina 25 Specific Forum

Transducer

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tweekes
Deckhand

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USA
14 Posts

Initially Posted - 03/28/2003 : 13:50:27

I have been having a problem getting a consistant reading out of my fishfinder after installing the thru Hull transducer inside a 3" PVC pipe which was Epoxyed to the hull and in 2 ozs of mineral oil.
I read about this application first in this forum and then saw it again in Sail Magazine.
I have trid two positions on the boat, one foward and one in the aft area, both as flat as possable.
If you have any ideas I will gladly listen.
Thanks,
Tom

Edited by - on

John Mason
Admiral

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USA
687 Posts

Response Posted - 03/28/2003 : 14:15:50

Do you have the PVC completely filled with oil? Air inside might make it slosh around introducing air bubbles into the oil, which could give inconsistent readings.

The only other things I can think of that can cause inconsistent readings are voids in the fiberglass layup or a bad transducer. I think a cored hull would give you consistently wrong readings (depth of 1" maybe).

Can you get a shoot through the hull type transducer? I'd think that would be the easiest mounting solution (as long as you didn't have any air bubbles in the epoxy you bedded it in).

John Mason
<img src="http://www.users.qwest.net/~jamason/ali.jpg" border=0>
pronounced "Ali Paroosa"
1982 - FK/SR #3290

Edited by - on

Douglas
Master Marine Consultant

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1595 Posts

Response Posted - 03/28/2003 : 14:25:54

How deep are we talking about ? If you can push down on the top of the puck does it get better ? What type of botom is under the boat?
These things will also give trouble. Deep water with temperature variation (Thermal barriers in the water) Also what type of fish finder ? I also hope you did not shorten the wire from the puck. They are very sensative and can not be cut or spliced.

Doug&Ruth
Triska (Alberg 29)
Tacoma Wa.

Edited by - on

John V.
Admiral

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USA
559 Posts

Response Posted - 03/29/2003 : 23:38:04

You can check spots for the transducer with water, or any where the water will collect. The transducer will shoot right through the fiberglass and to the best of my knowledge the C25 is a solid hull.
After doing several through hulls last season I found no core on my 77. If you bed the puck in epoxy it should read right through the hull and you don't have to deal with PVC pipe full of oil. This is just my opinion but I think the best place for the transducer on a C25 is right ahead of the V berth bulkhead on the flat spot. The transducer should be as far forward as possible so you can see what is comming rather that what you just hit.

John V. Nin Bimash II
77 C25 sk/sr #153

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RichardG
Admiral

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USA
990 Posts

Response Posted - 03/30/2003 : 01:21:07

<BLOCKQUOTE id=quote>quote:<hr height=1 noshade id=quote>voids in the fiberglass layup or a bad transducer <hr height=1 noshade id=quote></BLOCKQUOTE id=quote>

You can test the transducer by lowering it over the side of the boat into the water -- readings should be consistant.

Assuming the transducer is fine, there may be something to this bubbles in the hull fiberglass thing. I've been testing my fishfinder off and on for about three years at various hull locations using water, bags of water, putty, etc as testing media with the same results as you (depth = 0). I'm convinced there's minibubbles in my hull preventing this from working. Nevertheless, I'm sure I'll keep trying.

RichardG 81 C25 SR/FK "Sanity"

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tweekes
Deckhand

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USA
14 Posts

Response Posted - 03/30/2003 : 07:58:26

Thanks to all,
I finally gave up trying to find consistant readings and went sailing yesterday.

To my amasement once I left the marina the unit worked great.

I can only conclude that the dredge in the marina was the problem.

Thanks for all your help, your input was excellent.

Maybe, sometimes the solution is to just go sailing.

Edited by - on

John Mason
Admiral

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USA
687 Posts

Response Posted - 03/31/2003 : 19:13:16

Sounds like a great solution.

Richard, I just mentioned the possibility of tiny voids in the fiberglass 'cause I'm in the process (pain) of removing all my boat's bottom paint to do an epoxy barrier coat, etc. and am finding small voids all over the underwater portion of the hull. Funny thing is though, I've ground out several of these "blisters" and they are bone dry underneath. No water, no black pressurized acidic ooze, no RESIN. Just really dry-looking fiberglass mat. I'm puzzled as to what to do with them. They don't conform to all the info I've read about hull blisters.

Tom, anytime the water is aerated, the fishfinder will give funny readings. Backing up does it really well. Going across other boats' wakes can too. Sometimes I'll be sailing along and my fishfinder shows about 2' of depth. I immediately look over the side and invariably the water is either aerated or has a high level of particulates in it.

John Mason
<img src="http://www.users.qwest.net/~jamason/ali.jpg" border=0>
pronounced "Ali Paroosa"
1982 - FK/SR #3290

Edited by - on

Leon Sisson
Master Marine Consultant

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USA
1893 Posts

Response Posted - 04/01/2003 : 01:18:40

John Mason,<BLOCKQUOTE id=quote>quote:<hr height=1 noshade id=quote>... finding small voids all over the underwater portion of the hull. ... they are bone dry underneath. No water, no black pressurized acidic ooze, no RESIN. Just really dry-looking fiberglass mat. I'm puzzled as to what to do with them. They don't conform to all the info I've read about hull blisters.<hr height=1 noshade id=quote></BLOCKQUOTE id=quote>

I found the same thing when doing a thorough blister repair and barrier coat on my 1979 C-25. I forget now where I stumbled on a possible explanation, but here's what I think I remember. During layup, it was not unheard of for the interface between the mat and the first layer of roving to end up resin starved. This can occur in small patches, or over much larger areas. So long as the roving got wetted out, there doesn't appear to be a structural weakness. It does, however, promote blistering.

The only sure fire solution I've read about is a deeper version of the gelcoat peel process. On my boat, I just used a 7" disk sander to remove the dry mat back to good roving, and refaired the affected area. In spots where the damage extended into the roving, I ground away the weakened fiberglass with a 4" right angle grinder, and relaminated the resulting shallow depression with epoxy and fiberglass cloth. I then sanded the patch back to the original surface profile before applying the barrier coating.

I've had the same experiences you describe regarding fishfinder confused by water aerated by reverse or powerboat prop exhaust path.

-- Leon Sisson

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John Mason
Admiral

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USA
687 Posts

Response Posted - 04/01/2003 : 12:35:03

Thanks for the info, Leon. I was afraid that might be the case<img src=icon_smile_sad.gif border=0 align=middle>. I guess splash time just got pushed back a bit.

John Mason
<img src="http://www.users.qwest.net/~jamason/ali.jpg" border=0>
pronounced "Ali Paroosa"
1982 - FK/SR #3290

Edited by - on

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