Installing Nasa Log skin fitting

[Tech_help]

Fit the paddlewheel unit according to the instructions - it will give many years of trouble free service.

The Skin fitting should be sealed with SILICONE sealant (the one that smells of vinegar). ON NO ACCOUNT SHOULD MASTIC OR OTHER PETROLEUM BASED SEALERS BE USED. They can cause embrittlement of the plastic which will ultimately cause it to disintegrate. We recommend that the assembly be glassed into the hull. if it isn't, in some instances the fitting can come into contact with fuel residue which can also degrade the plastic. Glassing the fitting in will also maintain the integrity of the hull should the fitting be struck by a submerged object.

The 'O' ring seals should be lubricated periodically with silicone grease. ON NO ACCOUNT SHOULD WD40 OR ANY PETROLEUM BASED PRODUCT BE USED. WD40 in particular should not be used on any plastic parts - by its very nature it penetrates the surface and can cause parts to become brittle.

In areas where fouling of the paddlewheel occurs the impellor wheel can be removed and coated with a thin layer of antifouling - and reassembled when dry. Do not antifoul the skin fitting itself.

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[jimbouy]

Can i suggest that as your product is clearly going to be fitted by a large number of ignorant DIY types such as myself that you make your fitting instructions even clearer.

I had no idea as to what a mastic is and found it hard to believe that bathroom silicon would do the job. Can I also suggest telling the retailers who sell the fitting. As I phoned a supplier and said " i need some sticky stuff to fit my NASA" ... and was sold Sika.

Finally Did you ever ask Sailing Today(sorry IPC) to retract their article showing how to do the job.....with sika.

Jim

<hr width=100% size=1> "It is a pleasure to give advice, humiliating to need it, normal to ignore it"

 

[chriscallender]

I'm with Jim here - the wording of the instructions is

"It is advisable to avoid the use of mastic materials- use a form of proprietary silicon sealant."

Now I like Jim had no idea what a mastic material actually was, it was my fault of course not to find out, but the sentence above doesn't really convey the seriousness of the consequence of using a mastic material - potentially the fitting cracks and your boat sinks! I would suggest that you give consideration to a much more strongly worded warning in the instructions, so that at least we get the hint that its really important to comply with this instruction. "Advisable" isn't really strong enough in this case.

Don't get me wrong, I am otherwise happy with the Nasa instruments I use (depth + log) and HF radio I have and think Nasa are to be congratulated for making good and usable products at a very good price. But I think its in everyone's interest that the instructions are improved along the lines of

"WARNING, NASA only recommend proprietary silicone sealant and failure to comply with this may well cause failure of the skin fitting. In particular mastic sealants such as the Silkaflex brand are not suitable for this application"

I think that would have stopped myself and Jim using the wrong product. Maybe you feel you can't mention Silkaflex brand by name in the warning, but at least a sterner warning is needed to make us do our homework!

Oh well still afloat after 1 year with Silkaflex and I checked the fitting when I dried the boat out a few weeks ago. I'll replace it at next haulout, which will be once all the other boats are back in.

Chris

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[Trevor_swfyc]

Instructions

Checked my NASA instructions that were on the boat yesterday, they said use a<pre> PROPRIETARY SILICON SEALANT</pre>

This is available in B&Q or Homebase cannot remember where I got mine but knowing I used the right stuff has made me feel really buoyant. /forums/images/icons/smile.gif

Trevor



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[junksailor]

Re: Instructions

I'm seriously thinking of machining an identical thro' hull fitting from marine grade bronze. Would this anyway affect the function of the paddle wheel? Someone mentioned mentioned polishing the internal bore in another post. Is this for the rubber seals or some sort of accuracy issue?

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[chriscallender]

Re: Instructions

Personally I would not feel too happy with drilling a hole in my hull, and then depending on B&Q/Homebase bog sealant to keep the moisture out of the glassfibre.

OK the skin fitting might last very nicely but I have an older hull that was epoxy treated as a precaution when it was young, moisture readings are still nice and low and no osmosis blisters and that is the way I'd like to keep it!

Although, yes the hull will get pretty damp if it sinks! /forums/images/icons/laugh.gif

Chris

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[chriscallender]

Re: Instructions

Polishing was just so that the O rings would seal in my understanding. Seems to be not too hard to make one from the description in the other thread, luckily its 1 1/4 " BSP and at least 1 person has done this successfully. I'm planning to do this myself (since I used Silka my fitting is suspect and needs replacing anyway so I might as well do it in bronze).

Chris

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[Althorne]

Stirred up a right little hornets nest a couple of weeks ago when I wrote the first of these posts about Nasa in hull fitting and Sikaflex. Feel quite proud of myself that it's been one of the better lasting subjects and fired so many of us up. Wonder what I'm going to do next????? Feeling a bit anti-climatic now.
Thanks to all who had an input.
Really surprised it took Nasa so long to respond though!

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[misterg]

Just hang on....

"Sikaflex" isn't sufficiently specific. They make many different sealants, including silicone:

http://www.sikaindustry.com/ind/ipd-marine/ipd-marine-products.htm

For more specific info, try:

http://www.sikaindustry.com/ind/ipd-tds_msds.htm

Having said that, the ubiquitous 291 is a polyurethane.

Three posts in a day... must shut up now.

Andy.

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[VicMallows]

Was puzzled by your instruction that 'mastic' should not be used, since have always understood this to simply mean a 'pliable soft material'. However, here's the Oxford Dictionary definition:

1. mastic •n. (100%)
an aromatic gum or resin exuded from the bark of a Mediterranean tree, used in making varnish and chewing gum and as a flavouring.


Now, I don't think I'll be using that on my skin fitting! The bronze idea is favourite.

Vic

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[Jools_of_Top_Cat]

Just a few points to the nasa engineer who has entered the forum.

1. Thank you for coming in to respond.

2. Why the hell have you produced an item that will sit in the bilge of boat that will often have contaminants such as fuel oil, lubricating oil and other such petroleum products, knowing full well your product will be harmed by these products. I understand you are aiming at a budget conscious market but this in my opinion stops your product being fit for service.

3. would it really add a large amount to fit a phosphor bronze fitting?

4. To those of us who read the sides of the silicon sealant tubes and make a note that they say do not use under the waterline then feel anxious when a company with what now appears a dubious product tell us to ignore that information and use silicon bathroom sealant anyway.

5. I used sikaflex 291 and am now fairly anxious to remove the fitting and replace. Are Nasa willing to replace these fittings to those of us who now apparently need to change them do to contaminant weakening. Your instructions are unclear to say the least.

6. If you are unwilling to add a bronze skin fitting I would suggest you add a few pence to the purchase price and add a tube of the correct and recommended sealant and some glass fibre with resin. This then will allow you to continue selling plastic that can be damaged from petroleum.

7. In the event of a fuel leak on board, which can happen, what is your recommendation with regards to a fitting that has been previously immersed in diesel for example?

And to the forum,

Does anyone know if the same warnings apply to the silka and Raymarine plastic log fittings?


<hr width=100% size=1>Julian

<A target="_blank" HREF=http://www.topcatsail.co.uk>Top Cat Homepage</A>

 

[poter]

Julian

"I used sikaflex 291 and am now fairly anxious to remove the fitting and replace. Are Nasa willing to replace these fittings to those of us who now apparently need to change them do to contaminant weakening. Your instructions are unclear to say the least"

I would not be that concerned the previouse plastic fitting was also sealed with 291 & it was in the boat for at least 10 years.

I have just fitted a nasa log with sikaflex 291 which is a polyurethane based mastic,
& I agree with you I would not use a 'bathroom sealent' below the water line, that would be asking for trouble, & at least the 291 will seal. I wonder how long the thru hull fitting takes to go brittle??

With regard to Nasa, even with the prices for the products being at the budget end, a bronze thru hull fitting could be supplied as an extra, they make a profit & I for one would be a lot happier.

With regard to other plastic/nylon thru hull ftgs. I think they would all be chemically attacked to some degree.

poter

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[MainlySteam]

<<<Does anyone know if the same warnings apply to the silka and Raymarine plastic log fittings?>>>

I do not have alot to do with small end boat equipment, but my own Raymarine transducers (log and depth) are both sealed with Sika 291 as are all the other glass reinforced thru hulls on the boat. This is all common practice and I would be surprised to find that reputable manufacturers' materials have any problems, especially the glass reinforced ones eg Marelon.

The acid test is that there are plastics which are essentially inert to petroleum products - oil is sold in plastic containers and even approved petrol jerry cans all seem to be plastic these days. So it would seem to me that the correct plastic is a perfectly acceptable material.

John

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[ongolo]

I am now getting utterly confused!!

Many times I read that most people are using sikaflex because it is the best.

Now I read here that one should use silicon sealant (the one that smells like vinnegar - because of acetic acid).

Then a poster says, do not use bath room sealants which are all I believe silicon sealnts anyway?

I was going to use BOSTIC MARINE sealant, definately a silicon.

Never mind the fibre glass problems and the fuel on plastic problem, my steel hull has standoff pipes in which the fittings are sealed with a flange in case of hitting a miniature iceberg, but what is now the correct (proprietary) sealant on the outside to use?

I have auto helm depth/speed/temperature tridata, but where I live there is no agent and no proprietary anything available.

So please could anybody clearly tell me which sealant is safe to use?

John is of course right about not all plastics being affected by petroleum products, and those which do, react differently to petrol, diesel and paraffine. Parrafine swells almost any rubber. And what most people dont know, is that diesel dissolves copper!! slowly but surely, that is why copper pipes on a diesel engine are always nice and shiny. Have you noticed? But before anybody gets worried, the process is too slow to worry much about it.


thank you very much


ongolo


<hr width=100% size=1>1000 dream about it, 100 talk about it, 10 start and 1 completes it

 

[jimbouy]

Chris

Glad to see someone agreeing with me, it doesn't happen that often.

Just to pick up on "it was my fault of course not to find out"..

I thought I had found out when I phoned a chandlers and asked for a tube of something to stick it in with!

I also wonder if a small tube of something could be included. Just as the inhull fitting kit contains plastic padding.

Cheers

Jim

<hr width=100% size=1> "It is a pleasure to give advice, humiliating to need it, normal to ignore it"

 

[jimbouy]

Silicon from B&Q

Doesn't inspire me with confidence at all.

Check the silicon around my bath and double glazing!!!



<hr width=100% size=1> "It is a pleasure to give advice, humiliating to need it, normal to ignore it"

 

[jimbouy]

Re: Instructions

I use various engineering firms to make parts for equipment I work with. I have made a few enquiries about having a small quantity made up.

I am not holding my breath, but will post if it proves worth while.

<hr width=100% size=1> "It is a pleasure to give advice, humiliating to need it, normal to ignore it"

 

[JohnL]

Re: Instructions

Hi Chris. In a book I read by a GRP expert he said any hole cut in a GRP hull should be sealed with resin, (the cut edge that is)and allowed to cure before the skin fitting is installed. You can always pay extra for real marine sillicone, perhaps an expert can tell us the difference

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[kds]

I am advised by my friendly shipwright that reputable,major boat builders fit skin fittings with epoxy and have done for years. (Just use a hole borer to get it out !)
This was something of a suprise to me - but then I am only an amateur.
As I have a NASA log to fit over the next week or so - I too would like an answer from NASA !
Ken

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[milltech]

I think you can take it this was from Nasa, in covert mode. At least they told me they had posted a response and I'm certain this was it!


<hr width=100% size=1>John
<A target="_blank" HREF=http://www.allgadgets.co.uk>http://www.allgadgets.co.uk</A>