Simple question about screws

[martinwoolwich]

A help with the basics please. For outdoor marine use what is the correct grade of stainless steel for screws, A4, A2 or 316 (which i can't find at the momement)?

These are just for general purpose use not for any single specific task but will certainly be exposed to the marine environment all the time.

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[AndrewB]

A4 stainless should be used for any underwater or waterline applications. It is a lot more expensive than A2 stainless which is suitable for most applications where it won't be constantly wet. Even A4 is subject to crevice corrosion and needs periodic checking, but is the best material if you need strength. Otherwise phosphor-bronze or silicon-bronze would be better.

P.S. A4 is approximately the same as 316 grade and A2 is approximately the same as 304 grade stainless, different standards. I think I've read somewhere that A4 and A2 are slightly stronger for small components.

 

[dickh]

Definately use A4 for screws in marine environment. A2 screws are OK for normal outside use or internally on a boat. Often ss screws sold are A2 so be sure you get the corect grade. Try Anglia Stainless Tel No 01359 251414 who will do mail order(also Silicon Bronze screws) or one of the online screw people such as www.Screwfix.com or another one www.marine-hardware.co.uk or www.a2a4.co.uk

<hr width=100% size=1>dickh
I'd rather be sailing... /forums/images/icons/smile.gif

 

[tcm]

Not simple question about screws

yes, A4 grade screws are made from 316 s/s - hence you can't findem. Best of course to specify nothing but A4 on the boat, otherwise screws can't easily be changed about, which you may want to do from time to time

Note also that any washers should also be A4, else poxy washers will go rusty and afect the screws. Best in lightish applications around the boat to have plastic washers, hence no galvanic effect twixt two bits of metal.

Oh, and tother thing is to be careful when scrw the thing in: using a wrong size carbon steel screwdriver and buggering the end will pass carbon steel to the s/s screw, and heyho the rust gets going at the head. Spose you could try covering the screw with ptfe before screw it in, altho it's getting a bit anal...

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[charles_reed]

A2 is either 304 0r 303, OK for above waterline use but corrodes rapidly in anaerobic conditions.

316 is A4.

IMHO chandleres who sell A2 (the cost difference is minute) should be prosecuted under the Sale of Goods Act.
Apart from the UK, I know of no other EC country where A2 is displayed for sale in those little packs thjat they mark up by 1200%.

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[charles_reed]

My goodness - ;-)

what a lot about a simple subject - you're not a marine surveyor by any chance?

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[charles_reed]

Yep

nasty, inefficient stuff all the stainless steels - the advantage of 304 is that it doesn't work-harden and thus fatigue FME.
I'd definitely suggest the archaic alloys of bronze - especially aluminium bronze which from every aspect (excluding cost) is superior to all the iron-chrome-* alloys. However there are some exotic ss alloys which are vastly superior to 316 which is, after all, the catch-all.

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[tcm]

Re: My goodness - ;-)

er, no, not a marine surveyor.

Now, I'm not sure if being wrongly suspected of being a marine surveyor is like being accused of being an estate agent, and if it is - how dare you!

Otherwise, I'm flattered, so thankyou

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[martinwoolwich]

Re: Thank you

As ever perfect information thank you.

Order placed with Screwfix today

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[AndrewB]

Re: Yep

I've had some trouble with electrolysis caused by AB2, which is why I didn't suggest it. But it is certainly a good underwater material.

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[charles_reed]

The reason I aimed the gibe

(not to be confused with going about before the wind) was that I've found an increasing number of marine surveyors pathetically eager to overawe yachties with their miniscule knowledge by dressing it up with jargon and (on occasion) genuinely misunderstanding the textbooks.

Happy motoring - and many more years of it.

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[martinwoolwich]

While you\'re here.....

What is the best thing to use to fill very small holes in GRP.

My instance is that I have a few canvas poppers that are coming out and if I just screw them back in again they won't hold. My two options will be to use a fatter screw or apply some filler into the original hole to make smaller.

Sorry this is all very basic but I've heard horror stories of water ingress into GRP and the resulting damage caused so I'm a bit paranoid at the moment

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[jhr]

Re: While you\'re here.....

On a Fleming? Tsk, tsk. /forums/images/icons/laugh.gif

I've had a similar problem and used some very small plastic rawlplug type things that were knocking around in my toolbox (haven't a clue where I got them from, I'm afraid), bedded on a dab of sealant.

Seems to have done the trick.

<hr width=100% size=1>Je suis Marxiste - tendance Groucho

 

[tr7v8]

Re: While you\'re here.....

I've used Aradite, mixed up and then wiped into the hole with a palette knife or stanley knife blade. Allow to set then redrill.



<hr width=100% size=1>Jim

Draco 2500

 

[tcm]

Re: canvas poppers

To replace the fixed male element on the grp, find (or nick from jhr) a small rawlplug would be good as it "spreads" on the inside of the grp layer. But it will need a distinctly larger hole, from which there is no easy way back if there is limited space inside the hole - so i'd try with a larger and slightly longer screw first, and the tiniest dob of mastic to fill the thread on the way in, and go on to the rawlplug later.

The female "popper" part needs lubicating with silicon grease, to keep out sea water which crystallises on the internal c-spring in the female part, which tends to sets the spring shut if the canvas is often taken, making it increasingly toiugh for the spring inside (have a look) to open and shut it's this that causes the popper to need increasing more force to get on and off, and hence pull out the male part of the popper attached to the boat.

On the male side (usually attached to the boat) you get better long-term performance if you fill in the middle bit with silicon mastic as this again reduces the chance of seawater getting in, and/or of any movement loosening the screw, after which the whole lot works loose of the grp soon afterwards, as it did. Make a bit of cardboard with a hole in to protect the mess as you clean and fill each one, and/or clean up using industrial wipes, the kind that sting a bit, which cleans unset mastic. I only put this bit in as i know it's a new boat...

oh, and er, to fill a hole, two-part epoxy will do the job. Acetone will clean up, but best to mask off first anyway

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[charles_reed]

If you want to go down the route

of filling and re-drilling - I'd suggest using GRP re-inforced poyester mastic,

If ourse the trouble with many male poppers is that they have a built-in screw so you can't make a change of fixing.

Certainly keeping the female salt-free is the way to go to prevent it happening in future, if it's been left any time you may have to use some penetrating oil as well.

I've replaced all my poppers with twin screw fixings - but that's partly because I'm on my 2nd dodger and each change needs a minute alteration in popper-position.

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[tillergirl]

Re: Thank you

Avoid the use of stainless steel screws under the waterline. Stainless needs oxygen to keep it stainless! Silicon bronze is probable the best bet if its under the waterline, otherwise I go with the advice on A4.

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