Use of Triple Block with Aluminium Cheeks Underwater.

My trailer sailer keel lifting mechanism comprises two triple blocks the lower of which is mostly submerged when the boat is in the water.
Every boat of the type that I know of has suffered a keel drop due to failure of the 6MM pin which comes with the shackle attached to the standard Riley triple block and also the RonStan equivalent rf51300. Strangely it seems always to be the pin on the lower block that goes even when the top block is identical. It is a nightmare to fix once dropped requiring gymnastics on a beach with the boat dried out or a trip to a marina with a crane.
Hasn't happened to me yet but I'm going to take some preventative measures and the only preventative measure apart from tricky annual replacement of the shackle seems to be to buy a block which comes with a shackle having an 8mm pin. I have spoken to three other owners all of him have suffered drops and no one seems to have tried this.
Although the keel only has 385 kg of lead and the blocks are rated for way higher than this the ratings are nonsense as the shackles won't take it and drilling out the swivel to take a bigger shackle does not leave enough meat in the swivel.

Harken and Wichard.do do high end 60 and 65 mm triple blocks respectively with 8 mm pins at more than twice the price - which isn't a problem - but rather than stainless steel and plastic cheeks which I think are used in the RonStan mentioned above the Harken has alloy cheeks and from reading between the lines I think the iWichard does too.

Obviously the swivel shackle and other components of these blocks are stainless steel so I am thinking that having the block underwater is an invitation to electrolytic damage and failure. I don't keep my boat in the water so maybe it isn't really an issue but I'm wondering what the brains trust thinks?

Thanks in advance.

Another question I'd have is does the purchase go block to block when raised?

Go down to a skiff club or look at a Moth or similar to see clever stuff done with low friction rings. A 4:1 purchase is easy to do with them. Using stainless underwater is a bit of a no no, but don't tell my rudder shafts that.

It's a 1.85m lift using the electric coach house winch in addition to the top and bottom triple blocks.

Despite the bifurcated appearance of the top of the keel - see picture - the bottom block and saddle attachment is buried down inside the hollow central fibreglass walls of the keel a full arms length down and a real bugger to get at through a small square top hole - no gym junkies need apply. The lead doesn't start until the solid bottom third of the keel.

Anyway I got impatient today as it's only 2 and a half weeks until I head back to the Whitsundays so mail ordered the Harken Element triple block with 60mm sheaves as it has an 8mm pin and the highest load rating of any blocks that size. I compared the Harken element blocks with the Ronstan and Selden blocks on display at with Whitworths today and decided it was a very nicely made unit. It has the aluminium cheeks but I will have to live with that. Strangely they say FORGED. I also spoke at length with the Ron Stan technical guy who is very accessible and helpful. At least the boat is not moored so spends most of the time out of the water. I will try and flush out the cavity in the keel everytime I bring it out of the water whilst hosing the trailer.

I was tempted by the blocks with dynema strops rather than shackles but they seem to be much more lightly built - and in fact are actually lower load rated.

If I could get the keel high enough I would love to drill an inspection hatch in the side just above the lower block attachment point. I'm told that the Sonata 26 keels have such a feature.

Another Clubman owner has added a big hook underneath the lower block to attach to the keel to make removal and inspection easier and to raise the whole thing a bit so as to minimise the arm stretch necessary. A picture of his setup, which also includes a secondary dynema safety arrangement, is also attached but I'm buggered if I can find a load rated hook of the type he is using and he can't remember where he got it. Any ideas? Not Whitworths or RTM - looked today.

Thanks for the help and comments guys.