DF/SF Transponders

[Shane]

I don't want to rehash old threads, but searching on DF, SF, or transponders didn't turn up loads (other than the Seachamp2000 thread).

Ordered a Lowrance LMS-520, in a nutshell it's 5", 480x480 Sonar/GPS/Chartplotter that comes with the external antennea and a single freq. (900ft) transponder. I hummed and hawwed, but the dealer said that if I wasn't worried about the wide beam angle for fishing, that there's not much difference between (even though the DF is almost double the wattage, and claims up to 2500' depth).

I know Duane (Allegro) has commented on only getting around 300' on his Eagle DF, but what are others' experiences? If there really isn't much benefit depth wise I'd don't think I'll bother, but the LMS-525 is the same unit with the SF/DF transponder. If users find a noticeable improvement with DF over SF for depth shots I'd gladly pay the $60 more, but not you don't actually get the results.


Regards,
Shane

[Frank C]

Actual depth can sometimes be a benefit in navigation, say recognizing one island from another because of the channel depth -- pretty rare in my area. Otherwise, unless one was trying to sail a coastline at a constant depth like 100 fathoms (600') who cares? Once I know it's at least 8 feet or so ... deep enough to clear the centerboard ... I just want to make sure it doesn't shallow-up, unexpectedly.
As long as that display stays at 20+, it's all good!



BTW ... I noticed that too, that the dual-freq units suck lots 'o watts.

[Shane]

Hi Frank,

I guess knowing the extra depth would be more as a second positional confirmation, so to speak. If you know your running on a contour line, to have that reconfirmed would be nice. Although I suppose that's just old habbit, given how accurate GPS is.

One other thing I forgot in the previous post. Rather than drilling bracket holes in the stern, I was thinking of shooting through hull; how much loss have people noticed with going that route?

Regards,
Shane

[DLT]

Going through hull, you will not get an accurate temp reading (my transducer has a temp sensor). That may not be important to you, or your transducer may not even have that capability...

But, you don't have to drill holes below the water line (or anywhere near it) just to mount the transducer. You can expoy a piece of cutting board to the transom and mount the transducer to that... You will still need a hole for the cable to enter, but that can be well above the water line...

[Duane Dunn, Allegro]

I'm going to fiddle around more on our next trip with the different transducers. I'll try to make a note of the power consumed with each one on. I doubt there will be a significant difference.

The 50khz one is suppose to go much deeper than the 200khz. I'm going to do some more tuning to see if it does better crossing the sound next week.

My temp sensor is part of my paddle wheel speed sensor, not the depth transducers.

The mounting hole issue really isn't a big deal on our boats. The place you need to drill on the transom to mount the transducers is actually in the aft end of the ballast tank. Any leaks due to improper sealing will just end up in the tank. My cables enter the boat well up in the transom next to the motor cables where there are already open holes.

If you do shoot through the hull be sure to avoid the ballast tank area's. On my previous boat I epoxy'd on the transducer shooting through the hull and had no signal loss at all.

[March]

I glued a piece of fiberglass on the aft end of the transom, like Duane suggests, and I mounted the transducer on another one--the two interlock together. I had already lost a transducer when at anchor one night. The boat turned around and somehow the transducer got caught either in the anchor rode, or the line that went to the dinghy. Lost the sucker. Now I remove the transducer and keep it in the cockpit when at anchor

Wonder of drilling aft will take you into the tank though. Is the ballast tank part of the lower hull, or is it added on top of the lower hull, in which case water might dribble in between the hull and the tank--which would not even be the bilge?

[Shane]

Duane,

Did you have a chance to check on transducer (50 vs 200) depths while you were out on the weekend?

Regards,
Shane

I'm going to fiddle around more on our next trip with the different transducers. I'll try to make a note of the power consumed with each one on. I doubt there will be a significant difference.

The 50khz one is suppose to go much deeper than the 200khz. I'm going to do some more tuning to see if it does better crossing the sound next week.

[Duane Dunn, Allegro]

I played with a variety of setting with no greater success. I had both transducers pinging away in side by side sonar view and both lost the bottom as we crossed the Sound. No adjustment to any of the parameters on the 50 khz transducer would make it aquire the bottom.

Unlike what I understand should happen, it does not have any deeper penetration than the 200 khz transducer.

If anyone else get's it to work in 200' to 300' and deeper water let me know.

[Frank C]

... Wonder of drilling aft will take you into the tank though. Is the ballast tank part of the lower hull, or is it added on top of the lower hull, in which case water might dribble in between the hull and the tank--which would not even be the bilge?

The ballast tank is a fiberglass half-shell that's fully adhered into the bottom of the hull. These two parts, the hull and the upper shell, are completely sealed together, forming the ballast tank.

The "bilge" is those portions of the hull bottom where ballast tank is absent. A leak between the ballast tank and bilge would be due to a failure of that bottom seal, or a hole drilled through the side of the shell. One reason the factory long-remained stuck at a max 50 hp was the risk to that seam.

[beene]

One reason the factory long-remained stuck at a max 50 hp was the risk to that seam.

How long have I got Doc

[Captain Kimo]

.... Once I know it's at least 8 feet or so ... deep enough to clear the centerboard ... I just want to make sure it doesn't shallow-up, unexpectedly.
As long as that display stays at 20+, it's all good!



BTW ... I noticed that too, that the dual-freq units suck lots 'o watts.

Agree with Frank. I am a Lake Mead sailor with water level down some 80+feet from normal 1210 feet of elevation above sea level. So the chart contours mean nothing here. I use the 60 foot contour line as the shore line for the lack of anything better.

Installed my Humingbird SX 100 transducer (SF) just forward of the CB trunk (on ) in the bilge using plumbers puddy, just in case it could not shot through the hull and I had to relocated it. Was trying to 1) avoid drilling ANY additional holes in the hull, 2) wanted the depth reading coming as far forward as possible rather than from the transom.

Able to get readings down to 400 feet in fresh water. Beyond that get reading of the transducer depth from the surface .

It must be shoting thru the filled ballast tank as I get NO readings until ballast tank is filled.

Like Frank, I am more concerned about the shallow depth readings, especially sudden reductions in depth, rather than the great depths.