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Author Topic:   First time BW owner - depth finder question
bobbyrd posted 03-05-2002 09:53 AM ET (US)   Profile for bobbyrd   Send Email to bobbyrd  
I have just purchased a 1991 15'GLS side console with a 1993 50 hp evenrude. The
boat has never had a finder mounted. I'm
sure this question has come up before, but
i do not see how to do a topic search. I would greatly appreciate recommendations.
I just need something functional and would
liek to know how others went about mounting
the transducer to the hull.
DJS posted 03-05-2002 09:59 AM ET (US)     Profile for DJS  Send Email to DJS     
Go to Look at Mounting Depth Sounder Tranducer. David
dburton posted 03-05-2002 10:00 AM ET (US)     Profile for dburton  Send Email to dburton     
Try here. This is a much larger web site than just the forum. Take some time to look around.


SteveC posted 03-05-2002 10:03 AM ET (US)     Profile for SteveC    
I epoxy/fiberglassed the bracket to the transome without screws. It broke off after about 2 years. I think I hit something. If I had to do it again I would make a pad out of fiberglass and resin about 1/4 or 1/2 inch thick. embedding the screw heads into the pad, then epoxying the pad to the transom. There is no way I would ever drill holes in the transom for this.
kingfish posted 03-05-2002 10:07 AM ET (US)     Profile for kingfish  Send Email to kingfish     

Also,go to the "Repairs/Mods" section of the forum, and with from drop-down menu in the "show topics for the last 10 days" (upper right hand corner), choose "show topics for the last 2 years" and click on the "Go" button. When the page has expanded to show 2 years, go up to "edit" on your browser toolbar (if you're using MS Internet Explorer), choose "find[on this page]" and type in a search key-word like "transducer" and the search function will show you all threads that had that word in their title.

Good luck-


where2 posted 03-05-2002 01:03 PM ET (US)     Profile for where2  Send Email to where2     
On my 15' Sport, the PO had removed his electronics. So, I had holes with silicone around the screws, that wouldn't match up with the new transducer I bought. So, I removed the screws, fabricated up a piece of 1/2" Starboard to fit the screw pattern, and mounted my transducer to the Starboard. If I ever replace the unit, I just drill new holes in the starboard, rather than the transom. No matter if I hit something, or what may cause the transducer mounting screws to be unseated, I should get no water problems with the transom, since the transducer is likely to break free from the Starboard, before the starboard comes off the transom. Starboard is on with #10 SS screws, the transducer is using #6 or #8.

The Unit I have is an Eagle 128+ with speed and water temp. (no longer made) Water temp is a novelty for snorleking, speed is handy to have when you have an ICW with a 25mph speed limit. Yes, I can also do speed with my GPS, but that's another thing... I can't complain about it, it works for what I use it for which is checking depth, and reading speed. I don't use the fish finder as a fish finder. Don't expect most "fish finders" to read accurately below 3' of depth, they don't. I chose the Eagle because it reads to less than 3'.

LKS posted 03-05-2002 01:13 PM ET (US)     Profile for LKS  Send Email to LKS     
Welcome aboard, Bob. For your future reference, the forum currently does not have a built-in search function. One way to find information you may need is to expand forum listing to show the time-frame you want to search (such as "Show most recent 2 years), and then use your browser's "find" feature -- Control-F in Netscape -- and enter in variations on your primary search term. There's lots of information here and I'm sure you'll learn a lot. Again, welcome! -- Lor
bobbyrd posted 03-05-2002 07:18 PM ET (US)     Profile for bobbyrd  Send Email to bobbyrd     
Thanks to all for taking your time to respond
to my questions. And thanks for the welcome aboard. Afew months ago I had never given much thought about buying a BW. But I can truely say that I get a "OH what a feeling"
when I see my new 1991 15' in the yard waiting for me to get it ready. This is a great site! I look forward to launching my boat!
David Livingstone posted 03-05-2002 07:44 PM ET (US)     Profile for David Livingstone  Send Email to David Livingstone     
Bob, congratulations on your new whaler. You'll like the 15'. I towed mine 2600 miles south to the Florida Keys. Also pasted 20' boats going out the inlet and had a dryer ride then they did in the surf coming in from the gulf stream. Towed the boat behind a 3.3 litre V6 Plymoth Grand Voyager mini van. At home I tow it all the time behind a 4 cyc. 1/4 ton. The depth sounder that I use is a Raymarine 365. It has depth, bottom lock, fish alarm (that works), speed, trip log, and surface temp. The transducer will kick up if you hit anything. Best to mount it on a starboard and epoxy it to the stern. Also use a Raymarine 45 VHF. Fish on salt water in all kinds of weather and no problems. No, I don't work for the company, I just needed something that was fairly water proof, lots of features (I use to fish commerically), small enough to fit on the center console, and reasonably priced.
All the best with your new boat, David
fireball posted 03-05-2002 11:25 PM ET (US)     Profile for fireball  Send Email to fireball     
tell your supplier you want a thru hull transducer with the unit you decide upon. He will protest but will get this for you. The whaler wash messes with transom mounted transducers (as well as some fish). A THRU HULL IS THE WAY TO GO. G
Tom Byrum posted 03-05-2002 11:34 PM ET (US)     Profile for Tom Byrum  Send Email to Tom Byrum     
My transom mounted transducer will read fish at 40mph. I also know that a friends Montauk will read fish at over 25. I mean fish not just the bottom. Could be a real mess on a Whaler and a thru hull.
whalerron posted 03-06-2002 12:19 AM ET (US)     Profile for whalerron  Send Email to whalerron     
Tom, I am with you. I would never use a through hull transducer on a Whaler. My Garmin shows fish, structure and bottom at any speed up to 32 mph. With my old 70, that is as fast as the boat would go.

I also mounted my transducer like "where2" did. It is a great way to solve the mounting problem as long as you seal the screw holes well.

- ron

jimh posted 03-06-2002 02:00 AM ET (US)     Profile for jimh  Send Email to jimh     
I don't think the advice from contributor fireball to use a thru-hull transducer on a Boston Whaler 15-foot hull is particularly good advice, but I would like to extend to him the opportunity to explain further exactly where and how to do it.

In my experience there are no problems with transom mounted transducers on the 15-foot hull and strong bottom echoes can be maintained at planing speeds with no difficulty.

The design of the transducer is important. The LOWRANCE Skimmer transducer is a particularly effective design, and it seems to be a favorite among the Whaler owners I have had the pleasure of cruising with. I have two LOWRANCE units with skimmer transducers mounted on the transom and have no probems with maintaining bottom echoes at speed.

I have even seen the LOWRANCE skimmer working at speeds of 55 MPH. Proper installation is important. Tweaking the height (or depth) can make a dig difference.

I actually have never seen a thru hull transducer mounted on a Whaler of any size, although I think that on some of the really large hulls, say 25-27, there may be a possibility of doing it, although the benefits are negligable and the risk (exposing the hull to constant water penetration) are enormous.

But fans of thru-hull transducers should jump right in and tell their experiences.

JEvans posted 03-06-2002 12:18 PM ET (US)     Profile for JEvans  Send Email to JEvans     
My 31 has a thru-hull transducer which I replaced soon after purchasing the boat. First thing you will need an extra long shaft on the transducer to take into account the thickness of a Whaler hull. Of course there is an extra charge for the unit. Fact is whaler moulded in a flat in the 31 just for the transducer. Don't think I'd have cut a hole in the hull if it wasn't already there.

fireball posted 03-08-2002 10:28 PM ET (US)     Profile for fireball  Send Email to fireball     
I can only post my experience. I fish the ocean only for gamefish, which sometimes requires high speed searching. A properly installed thru hull transducer allows no leakage, and gives excellent readings at 50+ mph. The guy that sees fish at 32 mph from the transom-mount drank too much salt water in my considerate opinion, Captain Glenn
Tom Byrum posted 03-08-2002 11:56 PM ET (US)     Profile for Tom Byrum  Send Email to Tom Byrum     
Fireballs you crack me up. Are you related to Whalerguy?
Guts posted 03-09-2002 12:52 AM ET (US)     Profile for Guts  Send Email to Guts     
I've seen a thru hull in a Whaler befor. a good way to go, but not for bobbyrd. use a transome mount. mount on the downward side of the prop.
Tsuriki BW posted 03-09-2002 02:19 AM ET (US)     Profile for Tsuriki BW  Send Email to Tsuriki BW     
Uhhhh. I have never understood why it is important that you can read fish while doing 40 55mph in any boat.

Maybe it's my fishing style but I rarely go over 5 - 6mph while fishing.

Even as a "sounder" I think if I "see" the bottom coming fast up while doing 40mph it's probably because my face has been slammed into the screen......

Can anyone explain this to me?


jimh posted 03-09-2002 09:04 AM ET (US)     Profile for jimh  Send Email to jimh     
In the case of the 15-foot Whaler, which was the specific boat mentioned in the original posters question, I would specifically recommend strongly against trying to use a thru-hull transducer for these reasons:

--the only mounting point would be in the small bilge sump at the stern and on centerline;

--putting a transducer in there would fill up the sump area and make it awkward to access the drain plug. Reaching in to access the drain plug would expose the transducer wiring to damage;

--mounting the transducer in the bilge sump would put it on the keel centerline where it would be exposed to damage from keel rollers on the trailer;

--wiring to the transducer in the bilge sump would have to run across the rear of the cockpit and into the center of the boat;

--it is unlikely that a 15-foot Whaler can be driven at the 50 MPH or greater speeds mentioned where the stated benefit of the thru-hull begins to be obtained versus the transom mount;

--it is unlikely that a 15-foot Whaler will be taken offshore in the ocean to hunt for pelagic game fish;

--if the 15-foot hull were driven to the 50 MPH speeds required, it is highly certain that not much of the hull would still be in the water and a thru-hull transducer mounted in the bilge sump area might, in fact, be entirely out of the water at this speed;

--because of the vee shape of the hull bottom and the flat level cockpit surface, the two mounting surfaces of a thru-hull transducer will not be at all parallel, and this will make it difficult to obtain good mounting without using a beveled shim or some similar approach.

--at 50 MPH in the open ocean on a 15-foot Whaler it may not be possible to read the screen of a fishfinder, so the discussion is somewhat a moot point.


Tom Byrum posted 03-09-2002 09:43 AM ET (US)     Profile for Tom Byrum  Send Email to Tom Byrum     
Tsuriki if I pass a school of salmon on my way to the fishing grounds I want to stop and fish over it. Surely you dont do 5 mph when you are on your way to a 15 mile run to your fishing grounds? It also has something to say about the quality of your fishfinder. Trolling for tuna is done from 8 to 15 knots.
bobbyrd posted 03-11-2002 12:49 PM ET (US)     Profile for bobbyrd  Send Email to bobbyrd     
I have a stupid question.
I see starboard mentioned in atleast one
previous post and epoxy to the boat. What
is starboard referencing? The location on
the boat or material that is then epoxy to
the boat? I am ready to buy a finder but before I start drilling holes in my boat
hull want to make sure I understand.
Tom W Clark posted 03-11-2002 01:30 PM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     

Starboard is a brand name of a plastic used as a substitute for wood in many boats. You can buy it like lumber and cut or mill it into whatever your heart desires. I do not recommend it for this application.

You are trying to mount a transducer on your 15 Whaler. There is no need to make this a difficult and complicated task. It is very simple. Disregard the absurd suggestions of fireball.

Mounting your transducer will most likely require drilling four holes in your transom for #8 stainless steel sheet metal screws. Mount the transducer where you want it and then remove each screw individually and reinstall it with a polyurethane caulk like 3M 4200 Fast Cure or a polysulphide caulk like 3M 101. It is really that simple.

whalerron posted 03-11-2002 01:46 PM ET (US)     Profile for whalerron  Send Email to whalerron     
Tom makes a good point that just mounting the transducer brackets to the transom is easy and leak free if sealed with a good sealant. The only problem with this approach is that if you ever change depthfinders or if the transducer is swapped for one that is configured differently, you will no longer have just 4 holes in the transom. You will most likely need to redrill new holes for each transducer. But, if you mount a piece of Starboard to the transom with 4 screws, you can always replace the StarBoard as necessary and reuse the 4 transom holes.

I have been through 3 depthfinders now and every single one of their transducers used a different mounting template. I use the StarBoard method and I have a small piece of StarBoard mounted to the transom. If I had mounted the transducer directly to the transom instead of to the StarBoard, I would now have 12 holes in the transom instead of 4.

You can buy StarBoard at almost any marine dealer. It is basically plastic lumber.

jimh - thanks for the rebuttal. I do indeed drink some saltwater in rough weather but I have never been under the influence...

- Ron

Drisney posted 03-11-2002 01:46 PM ET (US)     Profile for Drisney  Send Email to Drisney     
Hi all,
I just wanted to make a point for moderation...I don't expect to read fish at 40 mph, but I would like to see bottom structure or a large bait ball at 15-20 or even a bit more. Spotting a bait ball on the run out to the salmon "hole" is a great way to limit early. Also you might want to consider placing the transducer on the same side of the hull you drive from. My boat lists a bit to my side when I am alone...yes I am big (270 lbs)...Dave
Tom W Clark posted 03-11-2002 02:26 PM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
I understand the reasoning behind Ron's suggestion. With only one exception, I see nothing wrong with using a pad of something (Starboard) glued to the transom for accepting the screws. I just don't think it is necessary.

It is true that during ownership of any small boat it is likely that the transducer will be changed and new holes will need to be drilled. But so what? I have swapped out transducers many times myself and you usually only need two new holes, not four. At least two of the old can be reused. But regardless, the new transducer usually hides to old holes even if it's not using them.

It is very simple to seal up an old hole and only a bit more work to patch them with gelcoat patch paste and make them invisible.

If you want to use a supplemental pad that's fine too but there is a drawback. You will want to use at least a 3/4" piece of Starboard and this will move the transducer away from the transom. Not all transducers are the same but some will be adversely affected by having this increased distance and the resultant disturbance to the water flow.

Even if you bevel the bottom edge and mount the Starboard perfectly flush with the bottom of the transom, the radius of the hullís edge where the transom meets the bottom will remain. In order to fill this void you will have to use an epoxy putty and fair it. Quite a bit of work.

jimh posted 03-12-2002 12:46 AM ET (US)     Profile for jimh  Send Email to jimh     
Another data point: I have four transducers mounted on the back of two Whalers (2xSONAR; 2xTEMP/SPEED) and they are all mounted as Tom describes, right to the transom.

On both boats I removed pre-existing transducers and brackets. I found them mounted with sealant and the screw holes dry. I was able to reuse most of the holes and others that were not were filled with epoxy and gelcoat.

A couple of fine points:

HOLE SIZE: enlarge the part of the hole that is on the gelcoat so that the sheet metal screw threads don't have too much bite. If you set a screw too tightly into the gelcoat it will crack. Let the screw get its grip on the laminates and wood below, not in the surface gelcoat.

SONAR TRANSDUCER HEIGHT: allow room to move the transducer face lower. On my most recent installation (on my 20-foot hull with twin engines so hence the transducer is right on keel centerline) I found I had less than great results initially. I lowered the transducer about 1/4-inch and got a huge improvement.

Later I was told that even with twin engines it is still better to offset the SONAR transducer slightly from keel centerline to get it out of turbulent water.

If you browse way back you'll find we had a big discussion wherein I also proposed--to many skeptical comments--that the boundary layer effect was influencing the readings of the speed transducer, particularly more so on the larger boats. This was quite a debate, but I still hold my ground and think it happens.

If you ever do install a thru-hull, it may be better to NOT use 5200 as a bedding. Read these experiences in removing one:


bobbyrd posted 03-12-2002 08:58 AM ET (US)     Profile for bobbyrd  Send Email to bobbyrd     
Thanks agin for all the replies to my questions. I plan to drill in the hull,
after I decide which finder to buy!
Best regards to all,
Bob Byrd
"New 15' BW owner in Greenville, N.C."
Tom Byrum posted 03-12-2002 09:43 AM ET (US)     Profile for Tom Byrum  Send Email to Tom Byrum     
The finder choice is a lot easier answer than where to mount it. Furuno makes the best fish finder.
whalerron posted 03-12-2002 10:00 AM ET (US)     Profile for whalerron  Send Email to whalerron     
Tom, I concede. When mounting something to the hull, you really need to use a procedure that you are comfortable with.

jimh is right about the hole size. Forcing a sheet metal screw through the fiberglass will result in nasty cracks further down the road. I used machine screws instead of sheet metal screws. I drilled and tapped the holes in the transom and then put epoxy in the holes. After cutting the heads off of some stainless machine screws, I put epoxy on the threads and threaded the studs into the holes. Then, I put mounted the brackets using stainless nuts. This allows me to adjust the brackets without the need to reseal the screw holes. It has worked out great.

Alan Hiccock posted 03-12-2002 10:15 AM ET (US)     Profile for Alan Hiccock  Send Email to Alan Hiccock     
I hate to drill ANY holes in a fiberglass boat even more so in my Whaler but whats the issue of installing a transducer on the transom as one would any other boat.
Just bed the thing properly { I would consider pure thickened epoxy resin}, use stainless screws of course and go find those fish. I wont be installing one in my 15 sport. To me unless I was venturing into unknown waters/area which Im not I dont need it because of the thousands of hours Ive racked up in my area. When I step up to my next Whaler & get a little "ocean range" I'll get a Sitex106 for schools of fish. On my 15 sport the deepest water I'll ever be in will be 3o' or so 1 mile out the inlet on nice days. I'd hardly use the thing & it's a pain in the neck to remove it everyday from the boat , simpler is better thats the whole Idea of me owning this 15 Sport for a season or 2,
Whalerdan posted 03-12-2002 12:00 PM ET (US)     Profile for Whalerdan  Send Email to Whalerdan     
Is there any problem, other than looks, with filling old holes with (my favorite product) 5200?
Guts posted 02-16-2003 01:28 AM ET (US)     Profile for Guts  Send Email to Guts     
right on fireball !

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