Nasa Target 2 Depth...suitability for wooden boat?

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gary3029

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I need a new depth gauge and don't want anything fancy. The Nasa Target 2 meets the criteria as basic and cheap. Given I have a wooden boat I don't want to be drilling holes for the transducer. Will this unit work if I don't put the transducer through the hull. As anyone got this unit in a wooden hull?
Thanks
 
No, AFAIK there is no sounder which will work through wood - its too soft and deadens the ultrasound. It either has to go through - and some authorities insist you use a bronze transducer housing, as timber swells and may crack a plastic housing with disasterous results - or you have to find some way of going round outside like with a transom mount.

But maybe somebody knows different?
 
No, you are right. Although a plastic transducer might be OK through stable Plywood - I have one for my log impellor, you need bronze to go through wood which might swell. Apart from the extra cost of the bronze transducer, there is no downside to having the hole through a plank, or better still through the deadwood in front of the keel with a shaped fairing piece so that it is vertical. It will not work inside anyway. So, bite the bullet and do it properly! or cast yourself a lead!
 
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No, you are right. Although a plastic transducer might be OK through stable Plywood - I have one for my log impellor, you need bronze to go through wood which might swell.

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The shipwright who was working on Border Maid recently opined that this stuff about bronze transducers is a load of nonsense. He has seen dozens of plastic through-hull transducers like mine in wooden boats and none of them were cracked. The only qualification might be that a new wooden boat (or a new plank) might possibly swell enough to cause a problem.

Cue dozens of posts from people whose old gaffers have sunk because of plastic transducers /forums/images/graemlins/wink.gif
 
I use one with a bronze fitting on a plywood full, fits lovely, but as always, holes in the hull are a constant source of concern. -Especially as I get enough water in through my leaky roof / deck!
 
I'd agree. I had plastic transducers in my old boat, and although one of them did break (my fault for over tightning it) they never leaked a drop. If in doubt, bed it on stickflex and leave the nut off until its been in the water a week.
 
Nasa seem to only offer a plastic transducer that can be used in-hull in GRP or as a through hull. Even if you are happy using it through a plank, there is still an issue of getting it vertical and clear of the keel for good performance.

I fitted mine by drilling a hole vertically through the stem just in front of the keel, counterboring inside to give a square bearing surface for the lock nut and fitted a fairing piece on the outside to take the head of the transducer. The hole is about 1mm dia oversize and when I assembled it I filled the hole with sealer so the threaded stem of the transducer is not in contact with the wood. Been there for over 15 years now! However, it is bronze from Raymarine. They now have a range of bronze through hulls with fairing blocks - details on their website, but don't know whether they work with Nasa.
 
On Kala Sona I have both log and depth sounder through the hull and they are both plastic. Six or Seven years ago I had to replace the log and found that the hole was too big so I turned some mahogany to reduce the hole to the correct size, glued it in with epoxy and followed NASA's instructions for fitting. I have had no problems at that end with either of them. The unit in the cockpit is a different matter as I did not seal the log unit properly and the consequent ingress of water ruined the head. More expense!!
 
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Even if plastic is proved to be 100% safe, do you really want your lovely wooden boat to be plugged with the stuff?

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Well all things being equal probably not. They are there however, have been for at least 15 years and I see no reason to mess with things that are working perfectly.
 
It has occurred to me the only the people who I have heard advocating using bronze transducers in wood, are the people who are selling them..... at 2 - 3 times the price of the plastic version!

Nasa fittings do have a reputation for snapping off the outer flange though, and I have had personal experience of it happening - fortunately in the yard, not afloat!
 
I have bitten the bullet and taken out the old transducer...PLASTIC and bought a Nasa target 2 and the transducer fits nicely. After reading the posts I think my old girl has found her point of wood swelling after 40 years and that did not damage the last plastic transducer so I feel happy this one will be ok!!!!
I can just see the headline in PBO ' Plastic Transducer Sinks Boat'
Thanks for the advice
 
If really worried about a plastic transducer breaking and sinking the boat could you build a box over it on the inside of the hull,make the top in two bits that can be fitted around the coax lead.?
 
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I have bitten the bullet and taken out the old transducer...PLASTIC and bought a Nasa target 2 and the transducer fits nicely. After reading the posts I think my old girl has found her point of wood swelling after 40 years and that did not damage the last plastic transducer so I feel happy this one will be ok!!!!
I can just see the headline in PBO ' Plastic Transducer Sinks Boat'
Thanks for the advice

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Previous discussions have suggested that the hole should be a little oversize with plenty of suitable bedding compound (sikaflex or whatever) taking up the slack and giving some scope for the plank to swell and shrink. Seems like a sensible way to approach the matter.
 
In my experience as a surveryor these fittings very occassionally sheer their flanges on both GRP and wooden boats, and this is because of poor installation. It is obvious that both the inner and outer surfaces of the hull must be flat and parallel where the housing is installed or unfair stresses are set up on the flange from day one. On poor installations where this is not the case cracks around the external flange start unseen, and the crack spreads around the perimeter in the angle between the flange and body. So fit it properly, get your plank as warm and dry as possible around the nut, then apply a thickened epoxy fillet over the nut and onto the surrouding plank, then if the flange were ever to sheer off the housing will at least stay in situ.
 
Scary stuff! Might use epoxy to make shaped fairing piece as in the West book, but would set the fitting in a flexible sealer such as Boat Life with a clearance all round. Tighten the flange nut up finger tight, leave it overnight and then harden up to make a gasket type seal. (Been using epoxy for over 30 years - but never to bond an underwater through hull fitting to a plank!)
 
http://www.ybw.com/forums/addfav.php?Cat...p;what=showflat
Last years thread......

'Flange faliure' can be due to, as you say, uneven or unfair surfaces of a GRP hull.
However in wooden vessels the main reason for faliure is over tightening of the nut, usually onto hull timber which is relatively dry. On launch the timber swells a small amount, which may overload the flanges. Usually the fitting has be fitted with a setting polyurethene or polysulphide sealant, so major failure is unlikely. The failed flanges are usually only apparent on removal.
Of far greater concern is the trend towards larger diameter through hulls, around the two inch mark, which can leave very little plank either side. In this case a carefully fitted backing pad to the same scantlings as a butt strap should be fitted. However the thread depth of the fitting usually prohibits adequate thickness of this pad. The advantage of the NASA range is that their tranducers are of the old style, and of a small diameter, unlike Raymarines range, for example.

I have to say I am amazed that you suggest bonding internally to the planking. To suggest that you can dry the surface to level that you can bond reliably with Epoxy is...incredible! Most underwater planking can range from 16 to 25%, which is far to wet for Epoxy, which requires 12% max m/c. Also, most bilge areas have been contaminated for many years with oil etc.

So in summary, simply don't over tighten your nuts!


And finally....I don't have a hairdryer-I'm not that sort of chap!
 
Wow, wow!!!!!!!!!!!!!!!

PLease EVERYBODY read what I suggested. Of course the fitting should be installed in the normal way retained by the large plastic nut, and this only gently tightened by hand as recommended by the manufacturers. That way any taking up should be catered for, unless the boat's been out for years. The fillet of thickened epoxy is only there as a bit of insurance in the very unlikely event of the external flange being sheered off and the entire fitting being free to come inward, as has occassionally happened.
Yes I agree about moisture content and epoxies but in the tests I've tried provided you clean and key the timber surface and dry as suggested a surprisingly good bond will be achieved. Of course this is not a structural bond, just a little bit of insurance in the very unlikely event of failure of the external flange, or to put it another way, better than doing nothing.
Since I built my first dinghy in 1965 I have tested new materials from other fields as they came along and in particular outside the conditons recommended for their use and epoxies were no different. This is of course not best practice but I belong to a generation who kept old wooden boats sailing on a shoestring however we could and tried all kinds of things. Having said that I never suggest anything on these forums that I haven't tried and tested first over a long period. This is just a simple bit of DIY insurance and not of course bonding a plastic through hull fitting to damp wood!!!!!!!

Oh and Seanick, I borrow the hairdryer from the missus
 
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