Nasa Skin fitting & Silicon? Did anyone resolve this fitting issue?

[squidge]

Hi I am about to fit a Nasa log skin fitting, after a search on the forum i found that others have had questions regarding the sealant to use during installation.

As it appears that Nasa will only endorse the use of a "Silicon Sealant"and a Mastic base must not be used. The instructions also suggest the use of GRP on the inside of the hull up to the top of the "tube".

Did anyone find out what silicon sealant to use? Or has any one used epoxy?

Thanks

 

[Equinox]

I installed my log skin fitting as per the NASA instructions. I used this type of silicon sealant to seal the base to the outer part of the hull.

http://seamarknunn.co.uk/catalog/items/item1485.htm

I then used West's epoxy resin and hardner on the inside of the hull and taped over the threads to avoid getting the mixture on them. It's had one seasons use to date and it seems to be doing the job.

Hope this helps.

 

[DanTribe]

Hi
Having had one of these snap off after 2 seasons use I would say it's imperative that you glass them in as shown in Nasas instructions.
If you do that, I dont believe it makes any difference what goo you use because the resin internally gives the seal.
People worry about the liitle splosh of water you get when you withdraw the impellor. Thats nothing to what you get when the whole thing comes off in your hand!
Dan

 

[jimbouy]

On my previous boat I'd sika'd and glassed in and after one season all seemed to be OK. The boat's sold now and I haven't heard that she sunk!!

However, some of what I heard scared me, so for Blue Moonlight I had a phosphor bronze fitting made up. Not especially cheap I know. Arguably I could just have used a different manufacturers log. But I wanted a) to use all Nasa instruments as they seem to be good value for money. b) have a sender unit that is not too expensive to replace if needed.

PM me if you'd like to know more.


Jimbouy

 

[AndCur]

Hi

I had a NASA log skin fitting fail last season which can only be put down to the fitting being bedded in silkaflex and not the sealant NASA recommend. I was told by NASA to use the sealant that smells of vinegar. I fitted a new skin fitting sealing it with marine silicone and glassed it in place inside using West epoxy and woven mat. After a season everything is fine. But it is a must to glass the fitting to the inside of the hull to ensure that even in the event of a failure the fitting stays in place. This should also apply to all hull valves.

Regards

Andrew

 

[squidge]

Crikey! a 1 in 2 fail rate. Dont like those odds much.
Jimbouy you have a PM. The risk may be reduced with the correct installation (thanks to your advise) but for the sake of a few bob for a bronze fitting i would sleep more soundly.
Thanks again.
Best regards
Squidge

 

[steve6367]

I have the NASA log fitted with Sikaflex, it has been there 4 or 5 years and I have not expereinced any problems.

 

[sailorman]

Re: Nasa Skin fitting & Silicon? Did anyone resolve this fitting issue?

possible they have been "over-tightened" when installed.
i have Ratheon they dont req. backing-up with resin.

 

[jimbouy]

Got your pm mate. I'll try and dig out the details tomorrow and I'll let you know


Jimbouy

 

[roger]

Back it up with Bridger

Epoxy may be the gold plated treatment for a NASA tube. I used car bodging "Bridger" compound. Its a mixture of polyester resin and short glass fibres. Its a wonderful bodgers material. Its good tempered and easy to work. You get it from car accessory shops.

 

[VicMallows]

How exactly did yours fail? DANTRIBE says his 'snapped' which seems to suggest tensile weekness, (and possibly overtightening) rather than any degredation of the plastic due to the sort of mastic. Either way, from the many stories it does seem there is something questionable about the material/moulding of the skin fitting.

Very interested, since still have my log fitting to install! Old fitting (Navico) had larger hole, but still perefect after 20years.

Vic

 

[jimbouy]

If you do a search back a while you should find details where NASA have stated that the solvents in mastic such as Sika effect the particular plastic they use in their thru hull fitting.

So I suppose overtightening wouldn't help. But too loose and you may not get a good water tight seal!!

I don't really want to start that discussion again!!

Personally I thought it was a pity to "spoil" an otherwise good log unit by supplying a thru hull fitting that in their own words should not be fitted by using what is probably the most popular marine sticky stuff.

Anyway being a cautious sort of chap I had a bronze version made up.

If anyone else wants details pm me.


Jimbouy

 

[DanTribe]

Hi
In my case I noticed the problem when the boat was out of the water for a scrub.
The outside flange was standing slightly proud of the hull and I picked it of with a thumbnail. The tube part was only held in place by the mastic within the hull thickness.
When I offered up the two parts you can see that the material is actually VERY thin at the junction of the flange and the tube. I can't find the bits now but the material is thinner at that point than the main areas.
Removal & refitting the impellor for cleaning obviously puts some stress on the fitting at this weak point.
I had fitted it myself and had only used hand pressure sufficient to squeeze the mastic. I think I probably did use Sikaflex, but the plastic showed no signs of degradation, just a clean break. Silicone mastic probably would not have stayed put.
To be fair to Nasa, the instructions clearly show that it should be glassed in, but I thought I knew better. They supplied a new fitting FOC , the nice man I spoke to casually said that yes they supply a lot of these!
Dan

 

[chriscallender]

Here are my experiences with the Nasa skin fitting

- I fitted a Nasa log transducer in winter 2002-3 incorrectly using Sikaflex 291 as many other people seem to have done. I did epoxy the fitting inside the hull as suggested in the NASA instructions

-The boat was then launched March 2003

- After launching I became aware of the problem from this forum, and decided to keep a close eye on the skin fitting

- I checked the fitting visually whenever the boat was dried out and I had access.

- By August 2004 I could see that a hairline crack had developed around the bottom of the threaded tube where it connects to the flange, just as described in another post on this thread. So about 18 months after installation there was a visible problem.

- Based on that, I replaced the skin fitting during winter 2004-5, cleaned it all up carefully to remove any traces of the old sikaflex and used Dow Corning silicon sealant to fit the new one. Also epoxied the new fitting to the hull of course! When the old fittig was removed, it was clear that the crack had extended to roughly 75% of the diamater of the tube, I'm not sure to what extent the crack extended in my struggle to remove the old fitting though. But anyway it looked pretty scary after I got it off.

- Boat was relaunched with the new silicon sealed skin fitting last week, its still afloat!


So my recommendation to anyone fitting one from scratch would be to do what the instructions say and use silicon if you want to save risk/hassle in the future. Epoxying to the hull on the inside is also important.

Chris

 

[squidge]

Update , I have just ordered a bronze skin fitting from my local chandlers, TCS Greys very helpfull. The best match they can get is within 1mm larger of the internal diameter of the Nasa plastic fitting so i will have to increase the "o" ring size to suite.If it works it will be a great improvement over the plastic fitting and at a cost of less than £20.00 !

 

[jimbouy]

Does it have the correct external thread and is it the right length for the impellor.

If so I'm GUTTED.

I spent ages trying to find a match.
/forums/images/graemlins/crazy.gif


Any way best of luck.


Jimbouy

 

[VicMallows]

Do you have a manufacturers name / reference number. Also please post update when you eventually install on how it all goes.

Thanks,

Vic

 

[squidge]

Sorry Jimbouy, I guess it was just pure luck.I looked at a brass fitting which matched and asked an old hand in the chandlers if he could get a bronze one, after a bit of searching he came up with a supplier. The thread is identical although the tube part is a little long, maybe an inch, i am considering either cutting it down a bit or packing it out with something like stuffing box packing haven't decided yet?

Vic, I dont have further details at the mo but the fitting should be in next week so i will make sure that i get the part number and manufacturer details so that i can pass them on.

 

[jimbouy]

Don't apologies.

Good for you!! I guess you'll have to shorten it to get the paddle wheel sticking out the right amount.

I look forward to hearing the final update.

Jim