Mounting hardware in the cockpit sandwich - advice

[Ed]

I have searched the forum but havent found what i am looking for.

Basically i have removed all the fittings on the boat and I am rerouting some of them.

The deck is carbon nomex laminate and the fittings i need to mount which will see higher load are.

- spinnaker halyard block
- spinnaker halyard block (the one the crew pulls on)
- Tack line
- forestay cleat (3:1) clamcleat.

Where the fittings were before the core was replaced with foam, but some of them were bolted not screwed.

I cant see if there are nuts set into the foam or what.

Some of the fittings had carbon plate ontop of the foam and then screwed.

Any suggestions on how to do this gratefully received.

[Clive Everest]

I would cut off the top skin either using a router or vibrating multitool.
Cut away the nomex back to the second skin.
Bog in some carbon plate at least 5 or 6 mm thick.
skim and sand flat with more bog.
carbon over top skin.
Tap into carbon plate to bolt on fitting.
We did this on the deck of A+E. All fittings appear bolted to the deck but are actually tapped into carbon plate that is sandwiched between the skins.

Most stainless bolts will show rust stains when in contact with Carbon and salt-water.
If you are feeling flash and want to save a few grams as well use titanium bolts.
There will be no corrosion.
http://www.pro-bolt.com/titanium/titanium-bolts-dome-head.html?dir=asc&order=price&thread_washer_dia=160

[Ed]

Thanks clive,

what size should the plate be roughly?

[Clive Everest]

A bit bigger than the fitting.

[Phil Alderson]

Have you seen this page: http://www.uk-cherub.org/doku.php/tech/fittings Perhaps it could do with an update if anyone has pictures of the tapping a plate.

I have not tried tapping a carbon plate, I was never sure about the strength left in the the fine detail of a thread cut into a disparate matrix like carbon laminate. Do you use any particular technique or lubricant when cutting the thread? How thick a plate is needed, and can you use wet layup plate with clamps, or does it need to be vacced?

[Clive Everest]

I managed to get hold of some 6mm machine pressed plate.
It was far harder than anything that I could home make and tapped very nicely with no lubricant.
Because the swarf breaks it does not bind up like tapping metal.

FibreFusion have a heated 100 Ton press and will make up plate to your spec. They can also water jet / CNC cut out bits that you need.  http://www.fibrefusion.com/composite-panels/

If you only need a small amount you can get pressed glass epoxy plate that will also tap readily.
eg http://www.ebay.co.uk/itm/10G40-SRBGF-Epoxy-Glass-Fabric-laminate-4wep-8-x-70-x-112-mm-/360876165825?pt=LH_DefaultDomain_3&hash=item5405e54ac1
This seems a bit expensive but if it is just one or 2 fittings that you need to attach it is not so bad.

[Ed]

Thanks for all the advice.

I went for a halfway house because i cant easily buy the sugfesred carbon plate from Norway.

 g10 at the back and home made carbon plate, it stands a little proud.

Will see how well it taps.