Topic: Simple depth sounder

I've been having some difficulty finding a depth sounder that has an in-hull transducer that is simply glued on the inside of the hull and does not require a through hull fitting.  I don't want to drill another hole, especially for a plastic fitting.  The Raymarine ST-40 looks good but they only seem to offer a through-hull transducer.  Garmin has a simple in-hull/puck transducer that simply glues to the inside of the hull but doesn't seem to offer a simple depth display like the ST-40. 

Does anyone know of a simple depth sounder with an in-hull transducer?

Re: Simple depth sounder

You can use the raymarine ST40 transducer inside the hull one of two ways.  Building a spirit box(which I don't really like all that much) or siliconing the transducer to the hull.  I've seen that work with success, the only thing on our contessas is one would have to make a levelling block and bond that to the inside of the hull somewhere (under v berth?) and then goop the transducer to that.  Some small strap clamps would be helpful in holding the transducer down  as well.  Use nothing more than plain clear plumbing silicone, you can get the works apart if you ever have to.  This is my plan for when I ever finally get around to installing my instruments, never really had a need for them yet...

Re: Simple depth sounder

Bite the bullet and install a through hull transducer properly.  Lay up a 2" (or whatever the correct clearance hole size is) fibreglass tube with at least 1/4" wall thickness,  cut to length and to square up the ends and glass in place through the hull.  Build up a nice fillet on the inside and outside, glass taped at the root and on its surface, with a structural paste of milled glass fibres, microfibres and some silica gel to prevent sagging in between, then once that's reached a good 'green' cure, build up a fairing block in solid GRP and finish with gelcoat.

You may want to worm the transducer thread with a piece of stout whipping twine with a loop tied in the top end before applying sealant and bedding the transducer in place so you have a seal-breaker to cut the sealant if you ever need to get the transducer out without damaging the mounting tube.

You probably wont get good results from a levelling block and an in-hull transducer.  Varying acoustic impedance across the transducer face will disperse the beam.   The best bet is probably glass or sikaflex in a tube cut to fit the hull angle at the bottom and immerse the transducer in it in oil or low melting point grease such as Vaseline.  There must be ABSOLUTELY NO AIR BUBBLES, so if you use grease, melt it with a hot air gun!  The transducer face must NOT directly touch the hull.  To find a good location, put the transducer in a plastic bag full of water with a rubber band round the transducer thread, wet the hull with a sponge and hold the transducer in the bag against the hull and try  the depth sounder. Keep vertical!

The silicone solution is only good for thin hulls with a flat bottom (less than 10 deg from horizontal).

4 (edited by stefan_d 2012-11-18 16:41:51)

Re: Simple depth sounder

Different strokes I guess.  I'd just really rather not have another fair-sized hole in my boat.  Especially not for a "somewhat-essential" piece of equipment.   Or a 2" appendage sticking down way up front.   Not to say that a depth sounder doesn't come in handy, just that I'd rather have a half-dozen other things I can count on before I think about depth sounder.   Most times I've found that when I might use it (unfamiliar marina approaches, taking shortcuts between channel markers, etc) everyone else who has one is glued to it, oftentimes getting erroneous readings off weeds etc... and getting very concerned about depth of channel etc...  My approach is to try to know where you are at all times.  I'll admit though that I'm looking very forward to the day that I don't have to haul up (by hand) an extra 50-70 or so feet of chain for being just outside a depth countour at any given (new!)  bay.  At least I wouldn't have dragged out to deeper water in the night........

Re: Simple depth sounder

I wouldn't worry too much about the hole. Done right with a solid GRP fairing block, the area will be considerably stronger than the hull around it and with several inches of the thread on the transducer body bedded in permanent underwater sealent, you could take the fixing nut off and pound on it with a sledgehammer without it moving.  That's why I said to put a bond-breaking string down the thread or you wont get it out again without a core drill!

Mine is about 2' forward of the forward main cabin bulkhead on the port side as low down as I could get it in the locker.  It is protected by the start of the keel and the turn of the bilge so I don't have to worry when hauling out as the sling cannot bear on it.

My home sailing waters tend to be a bit skinny. There are some drying banks as much as 12 miles out and you generally want to stay out of the deep water channels whenever possible due to very heavy shipping. Also the banks move noticably.  If you frequently sail shorthanded, and don't have a depth sounder, you'd better be handy with a lead line or comfortable dodging anything up to supertankers and Panamax container ships.

Re: Simple depth sounder

So Ian, where exactly are you? Sounds like the Solent????
Sure isn't Lake Ontario!

7 (edited by Ian Malcolm 2012-11-19 05:43:59)

Re: Simple depth sounder

No. UK East coast.  Thames estuary area. It can be 5 miles between buoys outside the main channels so you cant just  buoy hop.

All the South coast drying banks are under a mile offshore.  There are some outlying shoals and rocks but they are usually well marked.

What the South coast has is far far more nasty overfalls.  There are many headlands that you don't want to be within three miles of in heavy weather.

Re: Simple depth sounder

Sounds like lovely sailing... I assume everybody has read Erskine Childers (Riddle of the Sands) and those great Maurice Griffiths sailing stories from the 30s.
My uncle took me sailing from his home in Essex back when. He let me steer and I promptly bounced over the Goodwin Sands on a falling tide..
He was a very exciteable guy!

9 (edited by Ian Malcolm 2012-11-19 09:02:02)

Re: Simple depth sounder

I don't go up-tide of the Goodwins less than 1/2 mile off! wink
Even that is cutting it a bit fine as on a spring tide I might only have 10 minutes to sort out a problem - 5 minutes to fix it and another 5 to anchor if I cant. sad

Re: Simple depth sounder

My old SeaData depth sounder finally stopped working after a few seasons of being fussy.  Turns out that some of the electronics in the had simply oxidized away.

The old transducer is installed in a piece of PVC that is cut at an angle and epoxied to the hull under the v-berth starboard side.  It's filled with mineral oil and fits so snugly that oils does not leak out.

I'm debating to go with a through hull or simply replacing the existing Faria in-hull.  Here's the thing: My boat is in Nova Scotia and I live 1,500 km away so I don't get a lot of time to work on her.  Much as I love working on my boat I don't want to build a Swiss watch to install my depth sounder.   It looks to me like a through-hull is easy to install but then it would be pointing at an angle whereas the in-hull points straight down.  From the above posts it sounds like the only way to get a through-hull to point straight down is to build something.   

My questions are does having a through-hull point at an angle cause the depth sounder to be inaccurate and to measure what is beside you?  Since my PVC and mineral oil solution worked in the past is there any reason not to continue using it?