Ugh.
Those blocks serve
one major purpose, and that is to wreak back and forth under load till the mounting holes work open, admit water, and contribute to the rot (or the rotting again) of the deck core. If I may appear knowledgeable and experienced at the risk of appearing also opinionated and arrogant, the halyard (and vang) turning blocks should
NEVER be screwed into or through the deck structure in this area. The area is too vulnerable; and this is one way to totally destroy its structural integrity. Whenever I see these blocks bolted through the deck like this (especially when caulked with silicone!), it makes me want to go back into the fixing-deck-core-rot business at twice my old rate.
The best way to mount mast-base halyard blocks is directly to the mast step metal itself. In this way the compression load of the mast nullifies the tensile load on the halyard blocks, essentially giving them a free ride. Nothing goes bad and nothing gets weakened. I cannot see any reason in the world why anyone wants to do it any other way.
I have one piece, and
ONLY one piece, of Garhauer hardware on my boat, and this is it -
http://garhauermarine.com/catalog_process.cfm?cid=68
(I have the 2nd one.) I made a proper welded-aluminum mast step and drilled out the Garhauer plate for the mounting holes. A Delrin plate 3/32" thick insulates the aluminum from the stainless. The whole thing is bedded in 5200. The back two bolts go into the compression post and the front ones go into a G10 plate atop a brace in the toilet room. This does
not leak and is far stronger than the original system, which was awful, especially after being compromised by-- you guessed it-- a PO attaching halyard blocks through the deck core (with silicone). That rotted out the entire center section of the cabintop. The water migrated down the front side and into the foredeck as well.
Here is the page of the mast-base plates made by Dwyer -
https://www.dwyermast.com/items.asp...milyID=19&familyName=Halyard+Organizer+Plates
These are very nice plates but I needed block-mounting holes on all sides so I got the Garhauer one. The Dwyer people are very nice and make very nice gear and deserve more of the market than they get. All my spar hardware for Diana came from them. At the Annapolis show one year they gave me a very cool keychain just because I was saying nice stuff about them.
My very fervent suggestion is to remove those blocks, fit a mast-step plate, and fill the holes and the neighboring core with epoxy. Remember that no patch job done from the top is sufficient for the mast-step area unless it involves something like epoxy knitting the surrounding core together with the block you just installed. I did not open up mine at all; I merely drilled numerous holes and filled them with epoxy (some thickened and some not) with the syringe. It let the existing (rotten) core be the epoxy's thickening agent. And it's rock-hard now. You could hold a dub-step dance party on it.
Relying on the bond between the new core material and the old via the edges of the materials is
not adequate. If you must effect a cut-out from above, the best is to make an all-new patch of deck that covers a
very large area (24" square is probably not big enough), copies the old in thickness and layup schedule, and is adequately supported from underneath. Better would be to fill it like I did with mine or, even better, to fix it from underneath, similarly to how it was first constructed, using only marine/yacht-grade materials (
NO pressure-treated, Starboard, silicone, or worse stuff). This is not a bathtub surround; it is the mast on a yacht. Treat it with appropriate concern.
'Prudent pessimism is the mark of a responsible yachtie.' --JC
