Garmin 'In-Hull' vs 'Thru-Hull' Transducers

[Fishspearit]

Originally Posted by SeaKing

I don't think I would have used 5200, I will have to experiment with some other easier to clean up stuff. Maybe the 4300 ( i think that is what it is), for a more temporary permanent install.

I just used silicone, that's what the transducers manual recommended.

These new in-hull transducers are pretty slick. Years ago we used to have to build PVC dams or epoxy the transducer into the hull, now they've made the installations amazingly easy. Pick your spot, measure the deadrise, put the deadrise angle marked on the housing perpindicular to centerline and silicone in place. Once that dries, fill with mineral oil, snap the transducer in place, and you're done.

Cleanly running the cable through your boat and up to the chartplotter is far more difficult than mounting the transducer.

[AnchorageGuy]

Originally Posted by David M

When responding to threads, it is always helpful to check the date of the original post and the date of the last post. In this case, this thread was created on July 30 2008. The guy who created the thread probably hauled out months ago and is back in the water with his new transducer already installed.

David, As you can see the original poster may have no more use for the information but others obviously do and would like to continue the discussion. That is what we are all here for. I have seen discussions resurrected that are 5 years old.

[gbillman]

Anyone have a preference for what to fill the well with--I've heard both mineral oil and ethyleen glycol. Appreciate inputs.

[David M]

Sound travels quite efficiently through all liquids. So long as it is a relatively safe liquid and does not adversely affect the rubber or plastic then I would think either would be fine.

As was suggested earlier, I would give silicone sealant a try first. If it does not work its real easy to remove and try another method.

[Phil A]

Like the first post here, I am considering the Garmin 545s for my Beneteau 323. Practical Sailor rated it the best choice, but for any of them it comes down to installilng the transducer. From what I have been able to determine here , most feel that constructing a well filled with a suitable liquid allows the transducer to be inside the boat close to the hull rather than drilling which I want to avoid. I would like to do it right the first time, so any help would be appreciated. I'm thinking a stubby length of say 3" PVC mounted away from the keel and angled to be plumb when motoring? The other sender is mounted forward but is there any reason not to position this one Aft ? Is the transducer siliconed to the boat or should I somehow mount it to the side of the PVC? Thanks, Phil

[David M]

Transducers have a cone measured in degrees that extends from the transducer head. If you do a little geometry, you will be able to keep the cone away from the keel so it does not reflect off the keel.

Ideally, you want to have the transducer head in the water, because a percentage of the sound will be attenuated as it transmits through and once again is attenuated as it comes back through the hull. Its quite common to mount a transducer head in the hull so as to avoid having to drill yet one more hole through your hull...a definite advantage. If you want to do this then the goal is to mount your transducer head directly to a medium that transmits sound. Water inside the hull works best but the problem is you will have to build a well of some sort. By the time you build a well of some sort, you are probably better off by mounting the transducer head to a medium like silicon sealant or some sort of soft bedding compound which is relatively easy to remove, for the day when the transducer head has to be replaced.

You can have two transducer heads on board, one aft and one forward but you cannot have them operate at the same frequency. They will interfere with each other caused mostly by phase cancellation and phase amplification. You could put a 50/200Khz one forward and a 50/200kHz one aft then set the two sounders to operate them at two different frequencies.

Ideally, you want the transducer pointing downwards when the boat is level. For most sailboats, the cone is wide enough to bounce the sound off the bottom even when the boat is heeling, within reason. If the transducer is pointed off to one side when the boat heels, you may only be able to read the depth on one tack but not on the other tack. You can make up a wedge inside your boat to compensate for the boats deadrise at the point where you want to mount your transducer so the transducer head is level. If you do this, then make sure there are no air gaps between the transducer head and the water. Using a hard plastic such as Delrin would work fine as a material for the wedge. Of course, do a dry test using Vaseline as your sound transmission medium to see if this works before bedding down the transducer.

[s/v Jedi]

Here's how to install an in-hull transducer on boats with a cored hull.

First check that the spot for the transducer is indeed cored. Many cored hulls have solid laminates in areas like around the keel. Might save some work, but not much.

If you are not confident with fiberglass and epoxy work, you better do this during a haul out. The project is simple however, and can be done in the water as long as you keep thinking ;-)

This is a fun project and perfect to learn how to use fiberglass and epoxy!

First thing to do is get a foot of fiberglass pipe for exhaust systems (Centek industries, from the waterlift mufflers), 3" internal diameter. Now, find a way to put the pipe in the chosen spot straight up, using a bubble level, laser or whatever. Measure the max. distance between the pipe's lower end and the hull. Find something, like a book or piece of wood, as thick or high as that distance plus, say 1/2". Put it on the hull against the pipe and transfer the deadrise angle onto the pipe with a felt tip marker this way.

Cut the pipe, sand the outside and inside of it and put it back. Don't worry too much about 100% fit as it will have to be fine tuned later on anyway. Now, draw the outline onto the hull and remove the pipe.

Now decide the height of the pipe. Look carefully at the pipe and the transducer plus thru-hull fitting. Figure 1/2" between emitting-surface of transducer and end of pipe. Cut the pipe straight at the desired length.

Now we need to close the top of the pipe: fun! Put some clean pastic wrap on a work surface and cut a piece of fiberglass cloth round with 5" diameter. Put the pipe onto it and use scissors to cut V's out of the cloth around the pipe so that the flaps can be folded onto the outer pipe wall. Take the pipe off and wet out the cloth using a spreader. Put the pipe on and use a brush to first wet out the outer surface of the pipe and next fold the flaps onto it.

Prepare the next layer on new plastic wrap and wet it out while waiting until the epoxy just starts gelling. Turn the pipe around and carefully remove the plastic wrap and put it on the next layer, making sure to stagger the V's cut into the fabric.

If you are experienced a bit or always go boldly, you can prepare multiple layers on the plastic, wet them all out while stacking them. Put the pipe on top and fold the flaps, layer by layer. Use slow hardener if you need more time.

Build up the same thickness as the pipe walls. Finish with first 2" wide tape around the pipe (2 turns) to cover the flaps, followed by 4" wide. If almost cured but still sticky, use peanut butter consistency with colloidal silica filler to put a fillet on the inside of the pipe.

Let fully cure and install the thru-hull fitting (holesaw, LifeCaulk or 3M 101 sealant). Drill a 2nd hole and tap it for a plug. This is to let air escape when putting the transducer in wile filled with mineral oil. You can also use it for pouring the oil in with fitted transducer.

Now the fun really starts. You need to cut through the inner fiberglass layer of the hull. You may touch the core, but never the outer layer of glass. There are many ways to do this, I'll describe some:

• If the bilge is almost horizontal, you can use a holesaw mounted on a longer pilot bit. The bevel of the pipe must be less than the hull thickness, or you will start drilling/cutting the outer layer. I would prefer another method, especially if you never cut a hole in your hull like this before.
• Rotozip tool is perfect. If the deadrise angle is big, you need shims to keep the tool upright. But if you are handy you can even do this by just holding the tool straight up.
• Jig saw. Use medium metal blade for curved cuts and put something under it to limit the depth of the cut.
• Dremel tool with cut-off disc for plastic.

Now you need to remove the cut inner layer. The core will break if you put pressure on. I always prefer to make additional cuts so I can remove smaller pieces. I put a flathead screwdriver in the cut to force the layer up, protecting the "good" glass with something so that the screwdriver doesn't crush it. This phase normally only takes minutes.

Now you need to remove all the core. Use whatever you like: wood chisel, Dremel etc. Sand the inner side of the outer layer, the sides of the core and the area around the hole.

Look at the cut away inner layer of fiberglass. It will probably be thinner than the wall thickness of the fiberglass pipe, but if not, you need to increase the wall thickness of the pipe so it matches. Use epoxy and wrap with 2" wide fiberglass tape. Use fast hardener when the epoxy gels. brush more on so that the weave of the tape is filled. Now, you need to enlarge the cut-out in the hull to make it fit again.

Fit the pipe. It must meet the outer layer of the hull everywhere. Use a file and sand paper to shape the pipe. Also, check that the edge of the inner layer doesn't interfere with the fit. File it away if so.

Now you are ready for assembly. Mix epoxy and wet out the cavity (hull, core and edge of inner layer) and the outside part of the pipe that goes in. Wait until this epoxy starts to gel (cigarette break). Make a new batch of epoxy with high density filler to make peanut butter consistency and coat the side of the core and just where the pipe meets the outer layer of the hull. Put it in place. Excess epoxy will squeeze out inside the pipe. Use it for a fillet, adding some mixture if needed. Make a fillet between outside of the pipe and inner layer of the hull too, with the same high density mixture.

Let cure and sand. Wet out the outer fillet and surrounding area and wrap 2" wide tape over the fillet and lower part of the pipe. Fill weave. Cut a piece of fiberglass cloth like 12" diameter round with a center hole that fits over the pipe. Drop it over the pipe so that it covers the fillet/tape and runs out into the bilge. Wet out and fill weave.

Ready. This area of the hull is now stronger than before the job. Even if the outer layer of fiberglass would be penetrated, the pipe and lid and thru-hull fitting act like a 2nd layer.

Another advantage of having an in-hull transducer is that you don't get growth on it. As for temperature: the oil will be very close to water temperature.

ciao!
Nick.

[sbrin]

So, I am going to bring back this thread with a few questions:

I have a Bristol 35.5 (Love this boat!) and despite 3 different transducers, my Signet unit continues to get confused, oftenreading 4.9 or 5.6 feet just when I need it most. It is mounted forward of my keel/centerboard trunk and in order for a level installation there is a small lip at the angle of the leading edge of the hull in that area. My hypothesis is that air or turbulence gets trapped in the lip causing false readings. Despite fairing the area, my false readings have erratically continued.

Thus, the idea of an in-hull transducer is quite attractive. What is the downside of this type of install (I do not really care about water temp - I'll dip my toe in)? Since my hull is a solid core, is this an easy thing to do?

I welcome any input from folks........

[motion30]

The down side is reduced maxium depth reading

[osirissail]

DavidM may be correct about the original poster - but there are a lot of others with the same or similar questions, problems and continuing the thread is making useful information available to them even thought the original person is long gone.
- - As to the "shooting through the hull" type installation. It is described in many sailing magazine articles and is rather simple. I had a Raymarine thru-hull depth sounder that never worked from boatyard launching until my next haulout to replace the defective transducer.
- - I had an "el-cheapo" little round depthsounder - 0-99feet - for a little speed boat with a transom mount transducer. Armed with concept from the magazine articles and a FRG hull (about 1.5 inches thick), I purchased a short length of PVC Pipe that was large enough for the transducer to fit into and also a "clean-out" cap adaptor. Then ground the paint off an area of the inside hull and epoxied the pipe to the hull. I cut the clean-out cap to allow the cable to pass through. The article said to use "mineral oil" - research resulted in finding out that "Baby Oil" is mineral oil. I filled the PVC pipe with Baby Oil, placed the transom transducer in and screwed down the cap to hold the transducer firmly against the hull.
- - It has worked great for 7 years and is still working and reading its full range even though it is shooting through the FRG hull.