Standing rigging diameter

[CP-Mike]

I'm about to replace the standing rigging on my Mac 21, but I'm not sure what diameter wire to buy. The boat currently has 1/8" type 304 stainless (as far as I can tell, it's 304...it looks very, very dull) and I originally wanted to upgrade to 5/32", but I just found out that West Marine is discontinuing its 5/32" diameter rigging products. They still have it in stock online, but that means I'd have to order it and wait around until next weekend. So now the next size up is 3/16". That seems rather large for a 21' boat. The only reason I'm concerned about 1/8" wire is that for type 316, it's not as strong as 304, and the breaking strength for 1/8" 316 is only 1800 lbs. Although I really have no idea what is or is not a proper size; I'm just going with my gut feeling. Any opinions out there?

 

[bruce]

size

if you go higher in size, the hardware at the ends will have to be beefed up to get any good from the oversize. mac appears to have done a good job at building their boats and used 1/8. if you want 5/32, get it, but tighten to the 1/8 inch specs.

 

[CP-Mike]

yep

Yeah I've already purchased new beefier turnbuckles and pins, but I was also wondering about the attachment of the chainplates to the hull. The forestay and backstay are just held in by one bolt going through fiberglass. If anything had to fail, I'd rather it be rigging, so at least when the mast comes falling down, it'd only rip up the deck at the mast step and not the hull as well. Now I'm leaning more towards 1/8". What size wire is used by the larger boats? Mac 25 and 26?

 

[vwjon]

same stuff

My '85 M25 uses the same 1/8 cable as my 74 V21.

 

[CP-Mike]

thanks (nt)

nt

 

[bruce]

chainplates

had a loose bolt in the chainplate, went to tighten it and it broke in two, have replaced all the bolts.

 

[CP-Mike]

good advise

Yeah, I replaced all my bolts as well. I think if your boat is 20 years old or older, and you're not sure if the bolts have been replaced already, they probably haven't been, but should be.

 

[Greg]

Bolts

When replacing the bolts here are some simple things that will increase the rigs strength. 1; Add 3 layers of wolven glass to the hull where the bolts go through. The bigger the patches, the stronger it will be. 2; Use fender washers on the outside of the hull, and use a backing plate of marine ply, aluminum or even brass or bronze on the inside. Then use fender washers on the inside too. 3; Make sure you get grade 5 stainless steel bolts. The bolts should have at least 3 dashes on the head. Some Mac's just used machine screws, bolts are stronger, and grade 5 bolts will take more shear forces before cutting in two than any machine screw. 4; make sure to get new self locking nuts too. I still apply lock tight to these, and use lock washers too. If the chain plates get loose, you will lose a lot of strength. And of corse it would happen at the worst time too.