Transducer installation question.

[BlueDart]

I'm in the market for a depth finder and have seen many recommendation on best makes but get confused when it comes to transducer location.
My boat is a 16 foot fiberglass bow rider.

I realize there are three types ... thru hull which is not for my skill courage, in hull which with no holes to drill is attractive but read that location can be a challenge and transom mount which requires holes for the unit as well as for the cable.

I have not been able to score the In Hull vs. Transom mount higher.

From the experiences of those reading which is the easiest install for a semi handy chap along with greatest accuracy?

Thanks.

 

[alldodge]

The "in hull" or what most call shoot thru hull is not that hard to find the right spot. So long as the hull is not hollow you just add some water to the bilge. Then use a sand bag to lay on top the transducer and move it around until you find the spot. In most cases it is about anywhere under the motor area. Dry area up, put a blob of silicone and push the transducer in it. Both my boats they are on the starboard side in front of the motor.

The transom mount is real easy to just drill and screw it into the hull to one side of the outdrive and clear of anything in the hull which can create turbulence. To do it better is to glue a block on the bottom edge of the hull with 5200 and then drill mounting holes in it instead of your hull

 

[Chris1956]

The inhull transducer requires you mount it on a part of the hull that is solid fiberglass. Foam or wood in the hull will distort the accuracy. Also the transducer must be wet to operate properly. You can place a transom-type transducer in your bilge and wet it and see if you get a good reading. If so, just epoxy a piece of wood to the hull in that spot and screw the transducer in. Most hulls have enough water splashing around to keep it wet.

If you cannot get it to work well in the bilge, install it on the transom. Normally you drill 1/8" pilot holes for the transducer unit, backfilled with silicone to seal the screws. Drill a hole for the transducer wire, above the waterline, Install the transducer cable thru the transom, and connect it to the head unit. Now fill the transom hole with silicone and cover with a clamshell cover.

 

[TruckDrivingFool]

install it on the transom. Normally you drill 1/8" pilot holes for the transducer unit, backfilled with silicone to seal the screws. Drill a hole for the transducer wire, above the waterline, Install the transducer cable thru the transom, and connect it to the head unit. Now fill the transom hole with silicone and cover with a clamshell cover.

Just want to add no silicone for sealing holes. Use 3m 4000,4200, 5200.

 

[alldodge]

Disagree they do not need to be "wet" there just cannot be any air bubbles between the transducer and the solid core hull. Silicone works just fine and has been for several years in my bilge. True epoxy will be more secure but if you ever need to change it you got a job

 

[Texasmark]

I used the inboard mount in all my boats.

First of all we are talking about sound waves, usually 200kHz and later on 50 KHz. The piezo crystal in the transducer is an electrical to mechanical conversion device. Upon transmitting the electronics sends an electric current to the ducer and it vibrates at it's cut frequency. These vibrations are mechanically transmitted to and through the water.

In time (depending on the distance) the sound waves will strike an object and some will be reflected back to the transducer making it vibrate. In doing so it generates an electric current which is sent back to the electronics and displayed on your viewer. That's how it works.

Sound travels easier (less loss) through solid objects and you can consider water a solid for this discussion.

For maximum signal strength in sending and receiving, hard surfaces are required: fiberglass, aluminum, epoxy, molded plastic suited for the purpose. RTV is not a hard set and as a result will offer more attenuation of the signals than something that sets up hard like a 2 part epoxy. If you only boat in reasonably shallow water and have large objects to detect, the "glue type" doesn't really matter nor does shooting through a balsa sandwich hull or air or any other attenuators.

Water presence in the boat is not a necessity. It merely provides a solid link between the case of the ducer and the hull. Your epoxy installation glue does that for you.

I always preferred to mount close to the transom and as vertical as I could get it for best accuracy and near as I could get it to the keel (boat centerline) for max depth readings. I realize that some deep V hulls with high transom dead rise present a problem but not that big of a problem. In shallow water the slope isn't that big of a deal as the cone of signal operation is like 20 degrees in a lot of units. Dead rise is on the order of 15 max give or take so you are still within your cone. Or you could build a shelf out of epoxy that is horizontal on the top (wedge shaped) allowing your ducer to sit vertical.

OEM ducer mfgrs usually recommend a bubble-less epoxy (no bubbles, no air, less attenuation of the signal) but a regular epoxy stirred slowly and carefully will keep them to a minimum. I like to clean both surfaces thoroughly, and usually take some 100-220 grit sand paper and rough up the bottom of the ducer and hull where I'm making the installation. Coat both surfaces and press in place.

If you want to know what kind of result your intended location will get for you the following will help:

1. Get to a protected cove or such and at a depth where you are the most interested in a reply.....10-20 ft, more....... Bring along a 1 gallon zip lock plastic bag.

2. Put the ducer over the side at the transom adjacent to where you wish to mount it in the boat. Let it hang such that the bottom surface is in the same orientation as will be in the boat. Take a reading on your monitor.

3. Fill the bag with water, immerse the ducer, and while holding the bag to retain the water, set it on the hull where you intend to mount. Take your second reading. The difference is what the inboard installation is costing you.....but you need to weigh that to the benefits and I'll take that miniscule loss for the benefits.

4. If you buy a side looking ducer this will not work. Side looking are popular with Bass fishermen who mount ducers on the bottom of their trolling motors and do things like look under piers they intend to fish to see if any fish are present.

5. Current ducers come with temp sensors/displays. My last installation was a couple of low ball priced simple systems. One was at the helm of my alum boat with the ducer at the transom (inboard) and the other was at the bow with the ducer clamped to the bottom of the trolling motor. The max difference at any given time between the two was 2 degrees due to the mounting location. Reading 80 degree water, 2 degrees is only 2 ? % error and you aren't going to notice that personally. So inboard mounting isn't a problem from a temp standpoint. Yes glass boats aren't as thermally conductive as alum so if you go blasting across the lake where temps vary and shut off the engine and toss the trolling motor over the side, you will read more than that error...but give the boat a little time to cool/heat to the new water temp and things will settle out.

Want any references on the above just ask!

Mark

 

[BlueDart]

Thank you to all that provided information on this topic and Mark in particular for a all the detail.
I'm sure I will be better prepared to take on the challenge and now to compare makes of finders and spend some money.
Note when I was thinking of the need for such a device my wife reminded me of the time last summer when kayaking in a northern Ontario lake that I ran onto a shoal with the kayak.
Would be much worse with a stern drive.
Safe boating all.

 

[JimS123]

The instructions for every depthfinder I ever bought were clear enough to understand. I personally like a transom mount better. They make good sealers so water intrusion can never be a problem as long as you follow the directions. Chrome plated hardware is available to cover up the wire entry point. People are perfectly content drilling a dozen holes in their transom to mount trim tabs. The transducer only requires 2 little holes.

Don't think a sonar unit will prevent you from running into a shoal. If that's an issue you need a chart not electronics. The time you first see the shoal on your screen will correspond exactly to the time your outdrive hits it!

 

[bruceb58]

Typically, trying to find a place in the bilge that aims directly down can be an issue. In a boat my family used to have, we built a box that was fiber glassed to the bottom and was filled with water and some mineral oil on the top that the transducer mounted in.

 

[dingbat]

Transom mount:
Pros: No loss of sensitivity (ability to see objects in the water column)
Cons: Overly sensitive to turbulence

Installation tips: Starboard side, 18” min. from center of prop. Eliminate sealing problems by drilling 3/8" diameter holes and fill them with epoxy. Allow to dry, and then drill your mounting holes in the epoxy. No sealing required

In-hull mount:
Pro: Not as sensitive to turbulence
Con: Loss of sensitivity (Frequency shift as signal passes thru the hull)

Installation tips: Minimize sensitivity loss by purchase or building an in-hull transducer mount ("wet" box&#148. Cut a piece of 4” diameter PVC pipe to match the deadrise of your hull. Silicon PVC pipe to the bottom of the hull. Suspend transducer inside housing and fill with castor oil. Use a 4” flexible pipe cap to seal the top.

 

[poconojoe]

If your unit gives you water temperature, I don't think that feature will work if you Mount the transducer inside the boat.
I bought a kit called "stern saver". It's basically a piece of starboard with the glue and everything you need to mount it (with the glue) to your outer transom. Then you screw your transducer to it instead of making holes in your boat.

 

[poconojoe]

Oh, and I didn't even make any holes for the wire. I ran the wire up to the rubber rub guard. Pealed the rubber partially off and snuck the wire behind the rubber all the way around the boat near the helm.
After I snapped the rubber back in, you don't even know it's hidden behind there.
My transom has no aftermarket holes in it at all.

 

[dingbat]

If your unit gives you water temperature, I don't think that feature will work if you Mount the transducer inside the boat.

Temp is surprisingly accurate using the wet tank method.

 

[JASinIL2006]

I installed a transom mount and I really like it. As long as you are careful and seal holes with one of the 3M sealants listed above, you don't need to worry.

In my boat, installing a shoot-through-the-hull model would more or less be something that would be tough to do unless I pulled the motor, so I went with a transom-mounted model. It has a water temp indicator, which is actually kind of cool. Some of the inside the hull models have temp probes, but you'd have to put holes in the transom for the probe anyway.

 

[JoLin]

I had a transom mount on my previous boat, and when I needed to install one on the current boat, I went with a transom mount again. They work fine and they're easy to install. Most 'deals' on fishfinders and combo FF/GPS units come with the transom mount, too.

Dingbat's installation tip is good. Drill the mounting holes oversize, fill with epoxy, let it cure, redrill to mount.

My .02

 

[BlueDart]

Great support with excellent advice.
Really appreciated and already feel more confident with the project.

 

[Texasmark]

Typically, trying to find a place in the bilge that aims directly down can be an issue. In a boat my family used to have, we built a box that was fiber glassed to the bottom and was filled with water and some mineral oil on the top that the transducer mounted in.

That's why I included this comment: "Or you could build a shelf out of epoxy that is horizontal on the top (wedge shaped) allowing your ducer to sit vertical." Once it's done it's done. Through fooling with it.

On JimS's comment, I got enough knocked off by the trailer bunks (driving on, cross winds and current large waves....common here), running into/banging docks and piers for numerous reasons, skiers bending them and knocking them out of adjustment when boarding...used the engine AV plate and engine hood for a ladder, fishing in standing and floating timber and who knows what else. That's why I moved my later installations inboard. Problems solved. But what works for me works for me!

 

[bassman284]

I'm in the market for a depth finder and have seen many recommendation on best makes but get confused when it comes to transducer location.
My boat is a 16 foot fiberglass bow rider.

I realize there are three types ... thru hull which is not for my skill courage, in hull which with no holes to drill is attractive but read that location can be a challenge and transom mount which requires holes for the unit as well as for the cable.

I have not been able to score the In Hull vs. Transom mount higher.

From the experiences of those reading which is the easiest install for a semi handy chap along with greatest accuracy?

Thanks.

Here's a link to my post a couple of weeks ago.

It's a plastic mount board that doesn't require holes in your transom. Also in my my boat, the transducer cable runs over the transom with no holes required.

OK, ignore the link. I can't remove it for rattza krattza reasons. Here's a c&p of the post I was trying to link.


http://www.iboats.com/12-Lx4-W-Horiz...view_id.167626

Us this and you won't need to drill holes. Yeah, I know it comes with 2 screws but you don't need to use them. I have one on my boat that is glued on with 3M 5280. Been there 14 years and no sign of coming loose. So you drill your holes in the plastic.

All right, another edit: ignore the link way at the bottom, not the one in the middle (if that makes any sense).

 

[Texasmark]

Transom mount:
Pros: No loss of sensitivity (ability to see objects in the water column)
Cons: Overly sensitive to turbulence

Installation tips: Starboard side, 18” min. from center of prop. Eliminate sealing problems by drilling 3/8" diameter holes and fill them with epoxy. Allow to dry, and then drill your mounting holes in the epoxy. No sealing required

In-hull mount:
Pro: Not as sensitive to turbulence
Con: Loss of sensitivity (Frequency shift as signal passes thru the hull)

Installation tips: Minimize sensitivity loss by purchase or building an in-hull transducer mount ("wet" box&#148. Cut a piece of 4” diameter PVC pipe to match the deadrise of your hull. Silicon PVC pipe to the bottom of the hull. Suspend transducer inside housing and fill with castor oil. Use a 4” flexible pipe cap to seal the top.

The picture used as my Avatar is of the boat mentioned herein and would do 48 GPS on a cool day in calm water, me alone.....condition when pic was taken. I can get a quasi reading on my helm monitor at that speed....enough to know my depth.

On delta F, The AN/APN 81 and associates through the SN/APN 108 airborne Doppler radar systems operated with a carrier frequency of 8800 MHz. The antenna radiated forward and aft beams such that you captured + Doppler (frequency shift) on the forward beam and - Doppler on the aft. Signals were summed for 2x frequency shift for the existing ground speed. The frequency shift for a 178 mph test frequency (from the test set) was 4 kHz. I really doubt Doppler is of a concern and if it were to what extent? To the extent of the bandwidth of the receiver and gonna bet it's more than wide enough to tolerate any doppler at 200kHz transmitted frequency with a boat traveling 40 mph. However, if Doppler shift is a problem and the doppler exists from boat speed and reflections from the bottom, then inside or outside, the boat speed is a common as is the depth so it's a wash as I see it. Besides, the depth finder operates in the time domain, not the frequency domain usually, or did. It looks at the time delay from the time a signal is transmitted.....sweep starts...on some of today's systems....dot at top right of the screen, descending down the screen as time passes waiting for any reflections and as they occur they are noted. When the next beam is transmitted a new data line, previous moves to the left, process repeats. Even if the current system is using FM (Frequency modulation) the detection mechanism is on the same platform moving through the water at the same depth and the same speed so no difference there. Any Doppler shift change resulting from installation resistance differences in the signal path would probably be with in the tolerance of the system's accuracy.

 

[bruceb58]

Besides, the depth finder operates in the time domain, not the frequency domain usually, or did.

You might want to look up what CHIRP means.

Best place to mount is on the transom.