Deck fixings for a Bimini -- self-tapping?

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gr1mb0

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Well, I managed to order my Bimini from the US and get it brought over by a friend visiting the country -- £180 for a 6ft 3 bow Sunbrella Bimini is a lot cheaper than anything I could find here!

Whilst I'm still hoping that I can adapt the bimini to fit the standard hood fittings on my Cranchi Ellipse, if push comes to shove I may have to fit extra brackets on the outside of the screen...

Now I have no experience at all on DIY with GRP -- would I be able to use self-tapping screws to fit the brackets, or is it nut and bolt territory (which might prove a problem, since a cursory glance shows a double skin where I'd want to put the fixings)? Do you need to use any adhesive or will the screw/nut fixings suffice?

Any advice would be greatly appreciated -- I'll need the Bimini for all this sun we're just about to have over the next month !!


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A bimini takes a great amount of stress and needs good fixings. I have always used Stainless steel bolts. To avoid cracking the gel coat when drilling I generally put a piece of masking tape over the hole to be drilled and set off very slowly. It is not a hard job if you are careful!

Paul

<hr width=100% size=1>Will I ever find the perfect boat?
 
Should be fine with self tappers but make sure you drill the pilot hole big enough. If you are tempted to drill a small hole with the theory that the screw will hold better you will find that the gelcoat will crack like a bitch. Drill size should be same as screw shaft. No adhesive required however a white silicone applied around the mounting plate will finish the job off.
Ian

<hr width=100% size=1>Play the best game you can with the cards you've been dealt ! ! !
 
Not disagreeing with Nartorious but most commercially are fitted with self tappers. Obviously pick a thick moulding, not a yoghurt pot bit

Use big fat self tappers, not weeny ones. You need to drill a pilot hole of correct size, then countersink the gelcoat to a dept of maybe 1mm - otherwise as you start the self tapper a shard of gelcoat can be split off.

Tighten the screws - remeber what holds a component like this in place (so far as shear loads are concerned) is not the screws per se, it is the friction between the fitting and the boat created by the downforce from the screws.

You can bed the fittings down on silicone if you want, acts as a decent glue, so quite a good idea and easy to do

If you prefer nuts/bolts/penny washers, that's a top job. The issue is getting access. Sometimes it is worthwhile fitting those 4inch dia dinghy hatch lids to get access behind, to get to nuts. But feasibility of this depends on the specifics of your job

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I m not too clear quite where you might be fixing this, but Id say that as long as the fibreglass layup is thick enough (say thick enough to walk on if its on the deck), then self tappers would be fine. My bimini is tapped into the alloy frame of the windscreen, and I think that only got a little stresses when i towed it at 60 mph.
If alloy is adequate for normal use, id think a fibreglass deck will be fine. Add a little silicon sealent to the drilled hole to keep it tight and waterproof.
Cleats would sure need bolting, but I guess you wont be using your new sun top for warps!
Id be somewhat more wary if you were trying to fix it to the (probably much thinner) sides.

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All the fittings for my canopy are self tappers and if you size them right, SS self tappers will do a good job. Even if one strips, you can always ream the hole out one size bigger and fit a one size bigger self tapper. Also, my bathing platform is held on with them - as it always has been. Try using Sikaflex as an adhesive / filler just before you drive the self tapper home. GRP is brilliant self tapper meterial.

<hr width=100% size=1>Madoc Yacht Club
<A target="_blank" HREF=http://www.madocyachtclub.co.uk>http://www.madocyachtclub.co.uk</A>
 
I would echo Dave's comments re using Sikaflex rather than silicone as it will act as an adhesive. It is important to use a sealer of some sort because water will get into the boat through the fitting and down the screw threads without it - this also tends to soften the edges of the hole that the screws are seated in over time and eventually they will pull out easily.....
I also suspect there will be a 'right size' screw for the fittings so just get the right size, CS or pan head as appropriate and drill the pilot hole correctly the first time. If you do screw up (sry) fill the hole with araldite or resin (not gel coat repair) and re drill. Fill whole with sealant before screwing in the final time.

ps hope you are right about the weather!

<hr width=100% size=1>madesco madidum ..../forums/images/icons/smile.gif
 
Maybe it is wise to have a look <A target="_blank" HREF=http://www.yachtsurvey.com/more_on_cores.htm> here </A> before you start drilling holes !





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A product called riv-nuts, insert a threaded tube into a hole and pull up as you would a normal rivet, you can then use bolts as small as 4mm to fix your brackets. You cant beat it and they aren`t going anywhere!!! Thunder bolts in southampton sell them and the tool to insert with.

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