Mounting a FF on my Tarpon 120

My experience with the putty...

I used about 1/3rd of the putty chunk from Home Depot.
Rolled it into a ball with my palms.
Flattened it with my palms.
Pressed it onto the bottom of the hull.
Pressed and wiggled the transducer into the putty.
Peeled/rolled up the edge of the putty pancake and pressed against the sides of the transducer.

I haven't had any problems all last season. I transport my yak right-side-up, but hang it in the garage upside down.

My DSI transducer is designed as a skimmer transducer, and came with a bracket for transom mount, and that will go nicely on my 16' PB.

I don't want the transducer protruding back from my Tarpon's  stern, since it might foul my lines, collect seaweed, or bump into something and get knocked out of its horizontal plane, skewing the readings. In hull would be the best.

So I am still going to try to concoct an in-hull install with a water filled puck so I can move the transducer between boats. It will have to be something that holds it firm and does not allow it to roll at all.
 I have submitted the problem to both my subconscious and the cosmos, and am waiting to be blindsided with a reply whenever it gets around to flashing me.

So I am still going to try to concoct an in-hull install with a water filled puck so I can move the transducer between boats. It will have to be something that holds it firm and does not allow it to roll at all.
 I have submitted the problem to both my subconscious and the cosmos, and am waiting to be blindsided with a reply whenever it gets around to flashing me.

It's easy.  Make the foam reservoir slightly smaller than the transducer, then it is a press fit.  Fill the foam reservoir with water, press the transducer into the foam until it contacts the hull.  You may need to rock the transducer back and forth to let the excess water squirt out.  It works quite well and the foam holds the transducer securely.  Had mine mounted this way for a full year and the transducer never moved except when I added water.

The link below may be the original Plumber's Putty (Duct Seal) report:

http://www.hobiecat.com/forums/viewtopic.php?f=26&t=34526

I hope this isn't too late, but I don't believe you can use a dsi transducer thru haul.  I just bought the mark 4 for my PA, and that was the only reason I didn't get that ducer.  Hope I'm wrong or you aren't mounting thru haul.  That's an awesome fishfinder though.

Thanks demonick, That's exactly the route that I ended up taking. A tight squeeze holds it in firm.
I found a big chuck of foam and cut it to shape. Have yet to glue it down.

 Power went out here before noon and didn't get back on until 9:30pm, so I didn't have any good lighting in my shop. (Wind blew a power pole down just to the north of my place, blocking the hwy for a few hours and I couldn't even head into Westport until they got one lane open around 5pm)
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It's easy.  Make the foam reservoir slightly smaller than the transducer, then it is a press fit.  Fill the foam reservoir with water, press the transducer into the foam until it contacts the hull.  You may need to rock the transducer back and forth to let the excess water squirt out.  It works quite well and the foam holds the transducer securely.  Had mine mounted this way for a full year and the transducer never moved except when I added water.

You may be correct about this, flyry. I don't know.  Indeed, it looks like it was designed to be only a skimmer transducer. Somebody told me that it might not be an issue with the thin plastic hull of a yak. In my mind, the question remains, so I'll be the guinea pig and try it. 

I googled "dsi thru hull" and found a couple of forums "down under" where members have discussed this, with a couple of them saying that they have installed their DSI transducers below deck, and still get clear readings shooting thru the hull. They may have epoxied 'em down, though. I'm going to try water.

If it doesn't work thru-hull, then I'll use a transducer arm to hang it off the slide plate on which I'm mounting the head. The long, torpedo shape of the transducer looks streamlined, so the drag might not be too noticeable with the arm hanging off the starboard side, especially if I'm trolling off the port side.

I hope this isn't too late, but I don't believe you can use a dsi transducer thru haul.  I just bought the mark 4 for my PA, and that was the only reason I didn't get that ducer.  Hope I'm wrong or you aren't mounting thru haul.  That's an awesome fishfinder though.

You may be correct about this, flyry. I don't know.  Indeed, it looks like it was designed to be only a skimmer transducer. Somebody told me that it might not be an issue with the thin plastic hull of a yak. In my mind, the question remains, so I'll be the guinea pig and try it. 

I googled "dsi thru hull" and found a couple of forums "down under" where members have discussed this, with a couple of them saying that they have installed their DSI transducers below deck, and still get clear readings shooting thru the hull. They may have epoxied 'em down, though. I'm going to try water.

If it doesn't work thru-hull, then I'll use a transducer arm to hang it off the slide plate on which I'm mounting the head. The long, torpedo shape of the transducer looks streamlined, so the drag might not be too noticeable with the arm hanging off the starboard side, especially if I'm trolling off the port side.

I hope this isn't too late, but I don't believe you can use a dsi transducer thru haul.  I just bought the mark 4 for my PA, and that was the only reason I didn't get that ducer.  Hope I'm wrong or you aren't mounting thru haul.  That's an awesome fishfinder though.

It works fine. I also got the Lowrance Mark 4 DSI sonar/gps DSI from Cabelas and mounted it last week using goop. Fished with it Friday and Saturday and it worked great through the hull.

Thanks,Noah. Good to know. I am not going to goop or epoxy mine down, but use the "foam cup and water" method.

I am going to use a very thick-walled cup and bevel the inner bottom edges at a 45 degree angle to a point that meets the rim of the transponder, level with its center (halfway up). This way, the bottom edges of the cup itself (which is closed cell foam and has air bubbles) won't get in the way of the 120 degree cone angle and mess up the signal. I don't know if that would happen without the bevel, but I imagined how much clearance a 120 degree cone would need, so I thought I'd ensure adequate clearance by adding the bevel.
If, for some reason, that doesn't work, I'll have to go for the transducer arm, since I will be using my Mark 4 on my 16' john boat, as well as on my Tarpon.

I already shaped a 1st prototype foam cup, and it came out pretty good, but not quite perfect. My second attempt is going to be precisely measured and cut (instead of freeform eyeballing it like I did with the prototype), and should work as imagined.

Sounds good. One of there days I'm going to pull it up and see if I can notice at difference between my currect goop install and mounting it on an arm.

I have a battery box that will require a little customizing, and now I just need to go get some thru-hull fittings and connectors so I can run my cables into the hold. I also need to make a "split pigtail" for the leads coming out of the box. One set of wires for the Mark 4, and the other for backlighting my Ritchie in-dash compass. Also, still need to get 2 in-line 3-amp fuses.

If I can't find all the fittings and connectors I need in the marine supply outlets in Westport, i'll just head into RadioShack in Aberdeen. I should be able to find it all locally, though. Gonna check Englund Marine, since I know the people there.

I can screw the Mark 4 base directly to my slide track "side board" with self-tapping screws.