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GPS / Sounder questions

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visio
Deckhand

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USA
12 Posts

Initially Posted - 01/02/2003 : 01:47:11

Greetings everyone,

My family all pitched in and gave me a great Christmas Present this year: West Marine gift certificates for a gps / sounder of my choice. I've picked out the Garmin GPSMAP 168, but I'm having trouble with the options.

Transducer:
I'm not sure whether to shoot a transom mount transducer through the hull or cut a hole in the boat for a thru-hull tranducer. If I do decide to cut the hole, what is the difference between the plastic and bronze transducers? (West Marine catalog pg. 146) Will bottom paint or epoxy barrier coats damage / affect the transducer? What would be a good location for the transducer?

Mounting Location:
I'm considering a swing arm mounted over the galley sink that can swing out into the companionway. Any other suggested locations?

Antenna:
Will the internal antenna model work OK in the companionway, or should I get the external antenna?

Thanks,

Dave Laws
1981 TR/SK C-25 #2580 "Visio"
Stillwater, OK

Edited by - on

osmepneo
Past Commodore

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USA
1420 Posts

Response Posted - 01/02/2003 : 07:07:32

Merry Christmas Dave! <img src=icon_smile_cool.gif border=0 align=middle>

What a great gift. I sailed with a friend last summer and he had a portable Garmin GPS mounted on a swing devise that positioned the GPS in the companionway. He had no external antenna and the unit quickly picked and maintained necessary satellites.

The unit my friend had was not a Garmin GPSMAP 168, but some other model.

I bought a GPS E-Trex Legend in the fall and it does not have an external antenna. I have not used it on the boat yet, but in the car it works fine. Picked up and maintained satellites for a three hour trip. [*D]

From this simple sample of 2, I'd guess you won't need an external antenna.

Don Peet
c25, 1665, osmepneo, sr/wk
The Great Sacandaga Lake, NY

Edited by - osmepneo on 01/02/2003 07:08:03

Edited by - on

lcharlot
Master Marine Consultant

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Antigua and Barbuda
1301 Posts

Response Posted - 01/02/2003 : 08:32:12

I have a Garmin 135 combo GPS/Sounder on "Quiet Time". The transducer for the sounder is mounted on a piece of aluminum extending down froom the skeg, so as not to have another thru-hull. I hate punching holes in my boat below the waterline. The antenna for the GPS is mounted on the stern pulpit, and the instrument panel is mounted on a West Marine swingarm on the starboard side of the companionway, so that I can use it both from the cockpit and inside the cabin. The VHF is also mounted on the swingarm. When anchoring out somewhere overnight, the "anchor drift alarm" function is very nice. You can set it for any distance you want, I usually use 0.200Km (200 meters), and if the boat moves more than that, the unit sounds a very loud alarm. It works best if you are using two anchors; on one anchor with a lot of rode, if the wind or current reverses overnight, your boat could swing enough for the alarm to go off, even though the anchor is still firmly set. On a single anchor with a lot of rode out, you might need to use 400~500 meters as the alarm point distance. The battery drain is about 0.5 amp, about two anchor light's worth.

Larry Charlot
Catalina 25 #1205 "Quiet Time"
Sacramento, CA
<lgcharlot@hotmail.com>

Edited by - on

dlucier
Master Marine Consultant

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Virgin Islands (United Kingdom)
7583 Posts

Response Posted - 01/02/2003 : 11:59:55

"Transducer: I'm not sure whether to shoot a transom mount transducer through the hull or cut a hole in the boat for a thru-hull tranducer." - Dave

There is a third option other than a transom mount or thru-hull mount transducer. A glue on puck-style, in-hull transducer.

Don Lucier, 'North Star'
C25 SR/FK
On the hard, 200ft from Lake Erie

Edited by - on

visio
Deckhand

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USA
12 Posts

Response Posted - 01/02/2003 : 17:10:18

Wow, thanks for all the input guys!

Don P.: Sounds like the internal antenna model should work OK. Thanks!

Larry: The GPSMAP 168 has shallow and deep alarms. Would you set them both for an anchor alarm, or is that a separate feature? I was looking for the Garmin 135 on their website http://www.garmin.com/marine/products.htm, but couldn't find that particular model. Is it similar to one of the current products? How many boat units is that model?

Don L.: I was thinking that one could shoot the transom mount transducer through the hull, since Garmin only seems to list thru-hull and transom mount transducers http://shop.garmin.com/accessories_for_product.jsp?sku=010-00199-00. Do you think either the transom mount or thru-hull model would work OK glued in-hull style? Would a different manufacturer's puck transducer work as long as it was 200khz? What kind of glue would be best?

Also, does anyone know how the speed sensors on thru-hull transducers work? I was hoping that they were doppler (i.e. no-maintenance), but I've heard some people mention paddle wheel speed sensors that could be affected by algae and other critters.

Thanks again for all the help. This community is great! <img src=icon_smile_big.gif border=0 align=middle>

Dave Laws
1981 TR/SK C-25 #2580 "Visio"
Stillwater, OK

Edited by - on

ClamBeach
Master Marine Consultant

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3072 Posts

Response Posted - 01/02/2003 : 17:46:22

Can't answer all your questions but...

"Would you set them both for an anchor alarm, or is that a separate feature?"

Setting depth over/under alarms is the "old fashioned" way of doing an anchor alarm. If your depth changed outside a pre-set window, the alarm would go off.

With the advent of GPS, you can now set distance-based anchor alarms too. If your reported position changes beyond a certain distance, the alarm goes off.

With a full-time GPS and depth sounder I guess you could be really safe by setting both alarms. Depth and position...

Currently maintaining two holes in the water...'77 Venture 23 and new to the family,
'78 Catalina 25

Edited by - on

Walt
1st Mate

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USA
37 Posts

Response Posted - 01/02/2003 : 19:52:54

Get the transducer that reads through the hull. Then clean the hull where the unit is going to go and then put down a very large glob of silicon with no bubbles. Then press the unit down in the big gob of silicon. Make sure that the silicon is all the way around the unit and about as tall. There will be about 2% differance in readings but NO HOLE!

Enjoy

Walt Dudley

Edited by - on

Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts

Response Posted - 01/02/2003 : 20:12:37

Dave: If I were replacing my depth sounder and didn't already have a hole in the hull for it, I'd definitely go with the puck. From what I've read, you set it into a "pool" of silicone sealer, making sure not to get any air bubbles under it--I don't know exactly how. (I'd also look hard at the fishfinders.)

On my paddlewheel speed log, I use the special antifouling paint that's made for thru-hull depth transducers, and I've had no animal growth. This year the slime got it toward the end of the season, but that was due to lack of use. Anyway, not being a racer, I prefer to use my GPS for speed. (If I didn't have a speed log, I wouldn't add one.)

One of these days, they'll make fish finders that measure speed just like optical mice do--if they haven't already. At our speeds, it should be simple.

Dave Bristle - 1985 C-25 #5032 SR-FK-Dinette-Honda "Passage" in SW CT

Edited by - on

ssteakley
Captain

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USA
467 Posts

Response Posted - 01/02/2003 : 21:03:58

Dave,
My in Hull puck Depth transducer is a standard Horizon. Relatively simple to install. It has a small plastic cylinder that you caulk (i used Life Caulk) to the hull. After is sets for 24 hours then you pour about 2 ounces of Mineral Oil in the cylinder and the puck snaps in the top of the cylinder extending into the mineral Oil. Mine works great. I have a 250WK and I installed it just forward of the water tank.
Steve Steakley,
Moon Chaser #385

Edited by - on

dlucier
Master Marine Consultant

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Virgin Islands (United Kingdom)
7583 Posts

Response Posted - 01/02/2003 : 21:37:13

The Garmin GPSMAP 168 Sounder/Fishfinder that Dave is considering does not have the option of an in-hull transducer, only transom and thru-hull mounted transducers. They do have a transom mounted plastic transducer that includes both speed and temperature for $99.99 or a thru-hull bronze transducer with S/T for $299.99.

Dave, what are your priorities for this device or the main feature you are wanting? GPS navigation, fishfinding, depth sounding, speed log, chartplotting,...etc?

Don Lucier, 'North Star'
C25 SR/FK
On the hard, 200ft from Lake Erie

Edited by - on

visio
Deckhand

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USA
12 Posts

Response Posted - 01/03/2003 : 01:14:02

Hi Don,

I'm most interested in depth/tree finding in my shallow lake and GPS speed to help me learn to trim my sails better. The speed/temperature transducers, chart plotting and fish-finding gizmos all look neat, but aren't a priority.

The GPSMAP 168i looked like a deal at under 5 boat units, but I'd be very interested to hear of others experiences with similarly priced gps/sounders.

I'm thinking having the transducer mounted near the front of the boat would be most useful for depth finding, maybe in the head area in front of the keel trunk.

I was hoping that I could mount one of the available thru-hull or transom mount transducers "in-hull" style even though they are not designed for it. Has anyone had any success with this or should I just mount the transducer according to directions?

Thanks,

Dave Laws
1981 TR/SK C-25 #2580 "Visio"
Stillwater, OK

Edited by - on

dlucier
Master Marine Consultant

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Virgin Islands (United Kingdom)
7583 Posts

Response Posted - 01/03/2003 : 01:58:09

"I'm most interested in depth/tree finding in my shallow lake and GPS speed to help me learn to trim my sails better." - Dave

If you need to find trees in your shallow lake, then you might want to ask the family to chip in a little more so you can get the Interphase forward scanning sonar on page 147 of the West Marine catalog. <img src=icon_smile_wink.gif border=0 align=middle>

As for your questions about the GPSMAP 168i, I don't know. I use a Garmin handheld GPS (interfaced with the autopilot), Datamarine speed log, and Standard Horizon depth gauge.

Oh, and one more thing I never leave home without,...paper charts!

Don Lucier, 'North Star'
C25 SR/FK
On the hard, 200ft from Lake Erie

Edited by - on

visio
Deckhand

Members Avatar

USA
12 Posts

Response Posted - 01/03/2003 : 02:20:10

Don, I guess you and I qualify as the night owls in the group. Those Interphase sonar systems look very cool, but wow, look at the boat units! <img src=icon_smile_shock.gif border=0 align=middle>

There don't seem to be a lot of options in the 5 boat unit range, but I did just spot the Lorance LMS-240 Fishfinder/Chartplotter. It has an optional "pod-style in-hull" transducer. Maybe this would be the ticket if I want to keep from cutting holes in the hyll or hanging things off the back.

I would love to trailer to a locale that required chart-plotters and backup paper charts, but the current tow vehicle is ridiculous (V-6 Dodge Dakota). <img src=icon_smile_sad.gif border=0 align=middle> I should dig up my pictures of Visio on a trailer behind it. I'm sure it would give everyone a good laugh.

Dave Laws
1981 TR/SK C-25 #2580 "Visio"
Stillwater, OK

Edited by - visio on 01/03/2003 02:21:33

Edited by - on

ClamBeach
Master Marine Consultant

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3072 Posts

Response Posted - 01/03/2003 : 10:03:15

"... mount ...transom mount transducers "in-hull" style even though they are not designed for it. Has anyone had any success with this... "

I did this on a 18' powerboat... took a transom mount and used some epoxy to put it inside the hull... and it worked OK.

IMHO You lose some power (depth capability) shooting through the hull like that... but if you're on fairly shallow lake waters, it shouldn't bother you very much.

I think the other poster is right about the trees though.. by the time you see one with a conventional depth sounder... you'll be stuck in it already.

Currently maintaining two holes in the water...'77 Venture 23 and new to the family,
'78 Catalina 25

Edited by - on

visio
Deckhand

Members Avatar

USA
12 Posts

Response Posted - 01/03/2003 : 15:05:59

Hi Clam,

Thanks for the info on mounting the transom-mount transducer in-hull. I was hoping someone had had success with that configuration.

I know what you mean about the trees, but hopefully knowing the depth accurately will keep me in water deep enough that I'll only feel the gentle thud of a 1500 lbs. keel slicing through an upper branch instead of the blood chilling bang of the keel riding up and down over the think base of a tree trunk. I've often plotted late night scuba-lumberjacking missions after too many adult beverages. <img src=icon_smile_evil.gif border=0 align=middle>

Dave Laws
1981 TR/SK C-25 #2580 "Visio"
Stillwater, OK

Edited by - on

Ed Montague
Captain

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USA
499 Posts

Response Posted - 01/03/2003 : 15:16:43

I have my transom mount fish finder transducer mounted in a mineral oil bath shooting thru the hull as discribed in the tech section. This set up has worked fine for 5 years. I am ready for a new fish finder (my 10 year old unit is starting to fail) and I hope to use the same thru hull set up for the new one.

Ed Montague on 'Yahoo'
1978 #765 SK, Stnd, Dinette ~_/)~

Edited by - on

Leon Sisson
Master Marine Consultant

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USA
1893 Posts

Response Posted - 01/03/2003 : 15:58:51

Dave Laws<BLOCKQUOTE id=quote>quote:<hr height=1 noshade id=quote> I'm thinking having the transducer mounted near the front of the boat ... I was hoping that I could mount one of the available thru-hull or transom mount transducers "in-hull" style ... anyone had any success with this ... ?<hr height=1 noshade id=quote></BLOCKQUOTE id=quote>Yes. I mounted a transom-style depth transducer puck inside a large PVC cleanout fitting. I trimmed the unthreaded end of the PVC to match the inside of the hull under the V-berth, and drilled & tapped it for the transom mounting bracket screws. I then attached the PVC to the hull and liner with epoxy mush. I drilled a hole in the threaded cleanout cover to pass the transducer cable connector. After installing the transducer and its bracket, I poured in enough clean water to cover the transducer, but not enough to slop out the cable hole when heeled over.

When selecting that location, I tested hull transparency first by placing the puck in a puddle of water there. I've also heard of testing using a zipper baggy of water, or a fist full of modeling clay.

The PVC cleanout method has the advantage of protecting the puck from getting damaged by other stuff in the same locker. It also makes removal and replacement nondestructive. Some people use oil to reduce evaporation, but with the lid I've only had to add a few ounces of water a year. If the liquid ever got loose in the bilges, I'd rather it were water.

Some people have had success mounting the puck with lots of silicone sealer. The manufacturer of my fishfinder specifically said not to do that, because the soft flexible silicone absorbs too much of the accustic energy. They recommended using epoxy with no air bubbles or low density fillers. I asked them how would I remove or change out a suspect transducer? They said to use a sledge hammer, but then they're in the business of selling new transducers.<img src=icon_smile.gif border=0 align=middle>

-- Leon Sisson

Edited by - on

RichardG
Admiral

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USA
990 Posts

Response Posted - 01/03/2003 : 16:17:42

Before you mount the transom style transducer in the shoot-thru fashion, you might want to test it with a bag of water (or patroleum jelly) to make sure it works. I've been periodically testing my Raymarine fishfinder transducer (regular transom mount type) at various places inside the hull -- under v-berth, under quarterberth, near thru-hull under stove, etc. It often doesn't work at all, sometimes works a little, but never works all the time. Someone suggested small bubbles were trapped in the fiberglass when the hull was made.

RichardG 81 C25 SR/FK "Sanity"

Edited by - on

RichardG
Admiral

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USA
990 Posts

Response Posted - 01/03/2003 : 16:25:20

<BLOCKQUOTE id=quote>quote:<hr height=1 noshade id=quote>transducer for the sounder is mounted on a piece of aluminum extending down froom the skeg<hr height=1 noshade id=quote></BLOCKQUOTE id=quote>

Laurence:

Can you give more details on this installation? Does it create much drag?

RichardG 81 C25 SR/FK "Sanity"

Edited by - on

Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts

Response Posted - 01/03/2003 : 17:12:09

<BLOCKQUOTE id=quote>quote:<hr height=1 noshade id=quote>
The transducer for the sounder is mounted on a piece of aluminum extending down froom the skeg
<hr height=1 noshade id=quote></BLOCKQUOTE id=quote>
Dave: One consideration here is that the new balanced rudder extends below the skeg. However, the way I mounted mine, there's several inches of clearance between the skeg and the "step" in the rudder, so I might be able to get a sounder below the surface there, depending on its dimensions. I've been thinking about a fish finder in place of my shaky depth sounder, and am interested in the transom mount option, even though I have a hole in the boat. The few feet fore-to-aft difference won't matter much to me--if a big rock (that's our problem around here) appears on the sounder, it's too late either way. I use charts for rocks, and the sounder to help locate myself on the chart or pick an anchoring location.

Dave Bristle - 1985 C-25 #5032 SR-FK-Dinette-Honda "Passage" in SW CT

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Notice: The advice given on this site is based upon individual or quoted experience, yours may differ.
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