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  1. #1
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    Default Poor old Sixpence

    As therapy from the poxy coating dramas with Redback's sailing bits (see the grrrrrrr thread), I've also been doing the brass rubbing strip along the keel of Sixpence (my Yellowtail - see my avatar).

    Whitworths have a 'special' on at the moment, selling 6' lenths of semi round brass strip for under $20 a piece. Perfect length for Sixpence. I bought two and didn't have trim either - one for in front of the centreboard slot right up to the stem and one for behind the centreboard to the end of the skeg. And very nice to work with too - I was surprised at how easy it was to shape the ends and the quality job old fumble fingers here was able to achieve.

    I carefully drilled the holes for the screws, countersunk them, then got some fine paper and 'polished' the strips. No, I didn't go for a 'see your face in the thing' polish - hell, these strips will be under the boat and are there to take the bangs and scrapes.

    Then to fitting them. I wanted to use brass screws, the old brass on brass rather than stainless on brass business of mixing non alike metals which I don't understand except to know that it's not a good thing (deliberate non-use of grammar to develop that breathless, 'I haven't a clue what I'm doing' feel). Knowing that brass is rather soft, and I'd be screwing into kapur, and that I'd need the screws to pull the brass into place, I predrilled every hole and pulled the strips into place using stainless screws first. Worked perfectly ...

    ... until I decided it was time to fit the strips properly.

    Nice thin line of Sikafex along the bottom of the strip. Dip the screws into poxy to seal the hole in the timber, start screwing. I did the front strip first. Started at the centreboard slot, worked forward, got partway around the curve of the stem ... and twisted the top off a screw :mad:

    The dog chose to disappear.

    Not sure what to do and knowing I couldn't remove what I'd done without causing dramas, I tried the next screw - this one screwed the head BELOW TIMBER LEVEL :mad:

    The dog ordered an aeroplane ticket and passport.

    Being an overly confident (translated to mean 'stupid') boat builder, I'd already laid Sikafex along the rear strip so I decided to fit that one while I decided what to do with the front one.

    You guessed it, the first screw I tried to put in broke below the surface :mad:

    A rescue team of SAS Dogs came to rescue my quivering mutt.

    Back to the front strip.

    I was able to get a pair of pliers onto one of the broken screws and extract it. For the second, I wound up getting a stainless screw and digging a new hole down the side of the broken screw. I then enlarged the remaining screw holes. As it turned out, I was able to get the front stip on without further dramas and it looks fine - every screw well bedded in poxy, the strip bedded with the Sikafex (yes, I know it'll be hard to get off but don't anticipate removing it very often). The strip doesn't fit as well as it did originally (my messing about put a bend at a screw hole and it doesn't quite sit tight on the timber, but you have to go looking hard to find the gap).

    She looks really trick now.

    That left the rear strip. First step was to get out the turps and clean up the Sikafex - off the boat where I'd laid the strip and off the strip which still waited to be fitted. Once clean, I dry fitted the strip again with stainless screws, larger than the ones I'd used originally, and had a hell of a time.

    This is where a bit of hindsight works well.

    You see, I wanted the holes premade so I didn't over stress the brass screws. But because I wanted these screws to hold, I'd used stainless screws a little smaller than the brass ones to follow, thinking the brass would have an easy entry but would still get to cut their own thread in the timber. The timber is a kapur strip glued to the oregon skeg. The stainless screws were a little shorter than the brass. That's right, the stainless screws stopped short of the epoxy layer between the two bits of timber. The brass screws would dig in happily until they hit the poxy layer, then bind up and ping. :mad:

    So the holes have been threaded using the right sized stainless screws now and after I've gone to the shops to buy some more brass screws, I'll fit the final strip.

    The thing that does annoy me about this is that I'd predrilled all the holes and I'm darned sure I drilled through the poxy layer - the rear strip was the second one I predrilled so I'm guessing I'd learned to judge the depth 'properly' by then, as opposed to having the drill run away and dig too deep like what happened at the front, and didn't actually get through the poxy.

    Ah well, another leason learned - two actually, make sure you cut the threads with the right sized screw first off and that brass screws are a looootttttt more fragile than realised.

    But Sixpence really does look cute with that white bottom and the brass stip.

    Piccies to be posted when I get the second strip on (which won't happen if I stay here on the forum for too long will it )

    Richard

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  3. #2
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    Default

    Richard

    Shouldn't a boat called sixpence have a "silver" rubbing strip? Or are you going to re-christen her "Thrppence".

    Jeremy
    Cheers

    Jeremy
    If it were done when 'tis done, then 'twere well it were done quickly

  4. #3
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    Default

    Richard,
    go and let the dog out, he's out of earshot? Good....

    For depth critical applications like this you could always set up a stop block on your drill bit to ensure you get the right depth every time. (you know, chuck drill bit, making sure the shank is bottomed out in chuck so it can't go anywhere, measure how much bit is still protruding, cut small block to appropriate length and run drill into it.)

    The reason you don't want dissimilar metals in contact is electrolysis. Two metal in an electrolytic solution (salty water) will create an electric current. It will eat out the more base metal. If your SS screws are insulated from the brass with the sika or epoxy then you should be fine. Brass and salt water is an other story though, brass = copper + zinc and zinc is eaten out by salt water in no time flat. You may find that your rubbing strips will be pitted in a very short time:eek: . Hopefully not (especially for your dog's sake ). Bronze ( copper and ??) is more usually used in marine applications.

    Mick
    "If you need a machine today and don't buy it,

    tomorrow you will have paid for it and not have it."

    - Henry Ford 1938

  5. #4
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    How's the dog after Mick's post?

    I agree with him entirely!

    I think it may be of some consolation to know though, that in a small boat kept out of the water, (and cleaned with fresh water after use), the chances of damage through electrolytic action are slim indeed.

    In all seriousness, I'd use an aluminium strip and ss screws next time! (Gruff has brass with SS screws and no sign of damage except abrasion from boat ramps. The screws were dipped in Epoxy on the way in.

    Cheers,


    P

  6. #5
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    Default

    Brass and salt water is an other story though, brass = copper + zinc and zinc is eaten out by salt water in no time flat. You may find that your rubbing strips will be pitted in a very short time . Hopefully not (especially for your dog's sake ). Bronze ( copper and ??) is more usually used in marine applications.
    Oh bugger off Mick

    The strip was bought from Whitworths and advertised as 'Brass D strip ideal for dinghy skegs, gunwales or other points of chafe'.

    I thought it was brass you used so didn't think anything of it. Pah. Doesn't matter. The boat will not be living in the water - just used and washed and seeing this'll be under the boat, getting a bit ratty won't be a problem. Besides, it's a tad smaller than I'd have liked, but I got it at a good price ... and have recently listened to Glenn's dramas in finding a strip to do the same job on Rusty (he wound up having to restore a second hand strip at greater price than I paid). Even if it doesn't last as long as I originally imagined, it'll do the job for long enough to get some good use out of the boat - maybe when it comes to replacement time I'll be able to afford (or find) the wider strip ... in bronze.

    The only permanent things in boating are the water and the expense - in my case, the latter is trying to stop me facing the former . Still, it's nice to get it right in the first place, but why do that all time - it's boring

    Richard

  7. #6
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    Default

    Typically, I can't get more brass screws locally ... as I found out this morning Looks like a trip to the other side of the city. Job for monday (when I'm already halfway there) and yes, I did try the specialist fastener mob that supply my local boat shop.

    Richard

    now I'm going out to do some sanding. Oh joy. Oh bliss. Clap paws with joy

  8. #7
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    Default Drilling Brass Strips

    I don't know what happened to my post, but here is the subject matter again.

    If the brass strips need to be permanently bent to fit to the boat - bend them first then drill the holes.

    If you do it in the opposite order - when you bend - it will break across the holes.

    Bitter experience!

    MIK

  9. #8
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    Default

    Well, she's upright and sitting in her cradles (thanks Glenn ) And she looks a treat. Now to fit out the insides. The inside is cleaned out, sanded and filletted, but Mik'll be happy to know I'll coat her with poxy first. I collect the coach house from Pt Elliot on saturday where it's been living for the last couple of years (divorce does that ya know). Thinks should start moving fairly quickly now ... but we all know about that don't we

    Richard

  10. #9
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    Default

    Quote Originally Posted by Daddles
    Ah well, another leason learned - two actually, make sure you cut the threads with the right sized screw first off and that brass screws are a looootttttt more fragile than realised.
    Beautiful boat!

    My impression (from experience rather than engineering/scientific knowledge) is that silicon bronze is considerably stronger than brass. It might not be a perfect match but looks much better with brass than does stainless steel. It is probably also less of a potential electrolysis problem.

    Anyone have any facts on this?

  11. #10
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    So youve finally sorted it Richard? How about seein to the poor dog whos quite probably shivering and shaking in some dark corner of the shed tryin to get up the courage to escape from the maniac its master has turned into!!

    Great faq thanks fellas and Mik we all learn by our mistooks eh!... cheers!!
    Believe me there IS life beyond marriage!!! Relax breathe and smile learn to laugh again from the heart so it reaches the eyes!!


  12. #11
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    Default

    Quote Originally Posted by onthebeachalone
    Beautiful boat!

    My impression (from experience rather than engineering/scientific knowledge) is that silicon bronze is considerably stronger than brass. It might not be a perfect match but looks much better with brass than does stainless steel. It is probably also less of a potential electrolysis problem.

    Anyone have any facts on this?
    In published tables of most noble to least noble metals both Stainless Steel and most marine bronzes are more or less the same - ie up at the top.

    Problem with Brass is that the zinc is from the opposite end of the table. And because of the metallurgy (I don't know exacly why - probably a crystal geometry effect) the zinc and copper remain more seperate so it tends to dezincify in contact with salt water - the copper component eats away the zinc.

    Contact of brass with EITHER stainless or bronze will speed the electrolysis.

    Thus the post above where someone suggests using sikaflex or epoxy between the screws and the brass strip.

    It is an acceptable solution because a brass strip is just there to take wear and tear. If you you brass fastenings to hold your boat or rig together or fasten the rudder to the back of your boat - you are asking for unexpected problems later. Particularly as you can't actually tell whether the zinc is still in the fitting or not - still looks hte same, but might only be a porous copper shell with all the zinc leached out.

    Michael

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