2" Hole 1.5 inch transducer

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yachtorion

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I think in reality I know the answer to this.... fill the whole properly by grinding a long (12:1) overlap onto the hull and glass over...

but I've got a 1.5 inch transducer I want to put into a 2" hole... is there a quick and safe shortcut? The flange of the transducer actually covers the hole - but obviously a fair portion of the flange is over the hole.
 
robmcg said:
Leave the old transducer in situ and mount the Nasa one inside the hull with the kit they sell. No filling, no mess, no worries.
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+1 for that process. Even a straight silicon gob (no air pockets though) to 'glue' transducer to hull rather than the oil filled bath route as recommended by NASA. I tested it first using 'blue tack' new out of the packet to ensure that the super thick 1978 Westerly layup was not too much for the pings to deal with.

Jobs a guddun!!.
 
Sadly it's a log transducer so it has to go through the hull and needs a clean flow... on this twin keel boat the previous transducer is in about the only suitable location.
 
taper as you stated, then + do similar on the inside so there is a bond from both sides.
make a paper template of circumference of extremity of the grind back then mark with ever decreasing rings of approx 6m/m ( like annular rings in a tree trunk) pin on the glass mat & cut the first line. repeat this process. this will give you the mat layers working from the smallest to the outside layer. by doing it this way all the glass strands will be embedded within the resin.
 
Find a plastic cap such as is used on aerosol cans that has the correct diameter.
Mount it on a square of plywood and smear all with release wax such as Meguiars.
Grind the edges of the existing hole to a taper on both sides (no need for a long taper like when we do structural repairs; just a half-inch will do).
Prop the plywood over the existing hole, centring the plastic cap within the opening.
Fill gap with thickened resin and cut glass fibres, pushing well into the corners and the bottom taper. Some people advocate using epoxy but I have always used plain thixotropic polyester without any trouble. Continue adding as required.
When the new fibreglass has cured thoroughly, say after one day, remove the prop and knock out the plywood and the plastic cap.
You will then have a neat hole of the correct diameter and all that you'll need to do is to grind the inside parts to be reasonably flat for receiving the flanged nut that secures the transducer.

When mounting the transducer do remember to use a sealer that is meant for underwater use.
 
I have exactly the same situation on a Sadler29. Original log (which I fitted) was 2" (Navico DL something-or-other). I bought a NASA Duet to replace it. The new NASA skin fitting would fit perfectly INSIDE the existing skin fitting with a suitable sealant (maybe grind the exterior of the old fitting flush with hull if you are concerned about excessive turbulence).

HOWEVER, the Nasa fitting is much shorter that the original Navico, and the surgery necessary to install it on my Sadler is simply too much trouble.

Personally, I don't miss having a paddle-wheel log at all (clogged so often that you could never trust it anyway) and am perfectly happy with SOG from the GPS. After all, before GPS we used to work in reverse to derive SOG from the log reading!

I have simply left the old redundant log transducer in place to seal the hole.

Edit: Be aware that some years ago there was quite a bit of concern about the NASA through-hull fitting. Some instances of the external flange parting from the through-hull part of the fitting. HOPEFULLY this issue has long since been resolved.
 
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VicMallows said:
Edit: Be aware that some years ago there was quite a bit of concern about the NASA through-hull fitting. Some instances of the external flange parting from the through-hull part of the fitting. HOPEFULLY this issue has long since been resolved.
Click to expand...
I'd be very nervous about drilling a hole in my boat and filling it with anything that says Nasa on it.
 
VicMallows said:
Edit: Be aware that some years ago there was quite a bit of concern about the NASA through-hull fitting. Some instances of the external flange parting from the through-hull part of the fitting. HOPEFULLY this issue has long since been resolved.
Click to expand...

Wasn't it something to do with sealants? I seem to remember NASA warned about using some types as they could degrade the through hull plastic.
 
sailorman said:
polysulphides
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That's no excuse! Indeed my original NAVICO fitting instructions even suggested polysulphide for their fitting. Horrible stuff to work with but still my sealant-of-choice for underwater fittings if working between tides. That fitting is still in perfect condition at 30 years.

I have no expertise whatsoever in plastic moldings, but it certainly looks to me that my (unused) NASA skin fitting was fabricated from two components (flange and threaded tube). There is certainly an undercut where the tube meets the flange which cannot help as far as strength is concerned


If the length of the fitting is not a problem, it is possible to use a standard bronze or DZR skin fitting with the NASA transducer. You just need to grind off the internal protrusion(s) with a dremel and possibly use slightly thicker O-rings.
 
When I bought my present boat the previous owner had fitted a NASA log in place of an old 2" one. Having read on this forum of the danger of exterior flange falling off I examined the housing tube (from underneath) and found a crack extending 2/3 of the way around the fitting. It was easy to remove!

To repair the the defect I filled the hole in the hull with West epoxy loaded with 404 high density filler; the through hull hole having been carefully scraped and sanded to expose fresh GRP. Next day I redrilled through the new epoxy for the replacement NASA housing and bonded it in place using CT1 (another tip from this forum). I glassed the inside in accordance with NASA's instructions as extra security but to date four years on there is no evidence of failure in the housing.

I should say the previous owner had used Sikaflex and of course there was a thick bed of it trapped in the annular cavity probably for some time before it cured. This could possibly have initiated the stress crack failure.

I would recommend this method to the OP
 
basil421 said:
When I bought my present boat the previous owner had fitted a NASA log in place of an old 2" one. Having read on this forum of the danger of exterior flange falling off I examined the housing tube (from underneath) and found a crack extending 2/3 of the way around the fitting. It was easy to remove!

To repair the the defect I filled the hole in the hull with West epoxy loaded with 404 high density filler; the through hull hole having been carefully scraped and sanded to expose fresh GRP. Next day I redrilled through the new epoxy for the replacement NASA housing and bonded it in place using CT1 (another tip from this forum). I glassed the inside in accordance with NASA's instructions as extra security but to date four years on there is no evidence of failure in the housing.

I should say the previous owner had used Sikaflex and of course there was a thick bed of it trapped in the annular cavity probably for some time before it cured. This could possibly have initiated the stress crack failure.

I would recommend this method to the OP
Click to expand...

That sounds like a plan - thanks!
 
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