Thursday, 1 December 2016

Refit Tech - Re-Bedding Hatches With Threaded Epoxy Fasteners

Cracking The Hatch Frame Off The Deck
We sailed over 11,000 nautical miles in the past two years, so now we're working through a fairly major work list on Crystal Blues.

As always, just as fast as we tick something off a new item is discovered and added to the list - at last count 35 items were completed,  with only 40 to go (!).

Among our major jobs is the refurbishing and re-bedding of our six Goiot deck hatches.

My Grandfather's Anvil Was Used To Straighten The Frame
These have not been touched since the boat was launched, and still don't leak at all, but the aluminium base rings (attached to the deck) are corroding badly in some areas.

As a trial, we've removed one hatch completely, cleaned up the frame and had some of the larger corrosion holes filled with alloy weld by a skilled local welder. Then, after some inspired sleuthing, Ley located a small anodising plant in the south of the island, run by a group of local motor cycle racing enthusiasts. They've re-anodised the frame and we're now ready to refit it to the deck.

Tapping The Epoxy
The original fastening system was somewhat uninspiring - we wanted a better way to securely screw these hatches down while also maintaining a perfect water seal for the interior of the boat. After considering various options, including adding a welded stainless steel flange to the deck, we've opted for a simpler and less intrusive option, that doesn't involve damage to the paint systems on deck.

With generous help from our friend Peter Laine, a shipwright and boat builder based at Chagauramas in Trinidad, we repaired the epoxy fairing compound that provides the level bed for the hatch on the curved deck.

Recoil Inserted Dry, Pulled Out @ 300kg
We used West System epoxy modified with microfiber for this task. Then we drilled and tapped "blind" holes directly into the modified epoxy and tested the result - it was reasonably strong but did not survive multiple fastener removals or insertions - the thread tended to "crumble" away with multiple use.

Test Recoil Inserted Wet, Could Not Be Removed In Our Test
Now we've improved on the original idea, running tests here in Australia to prove the new process. We're using Recoil thread inserts, made from 316 stainless steel, to create a permanent metal thread inside a tapped hole in the epoxy bed. Note that standard Recoil inserts are made from 304 stainless, but 316 can be obtained on special order.

We found that a 5mm Recoil insert screwed dry into the prepared hole would handle more than 300kg of load, applied with a short pinch bar, before pulling out.  Better still, if we coated the insert with wet epoxy before insertion, we simply couldn't extract it with our simple "pinch bar test" - it was plenty strong. When we return to Crystal Blues we can now continue the refitting task - only five hatches and one hundred holes to go.

1 comment:

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    Kevin - Clark Boats


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