Rigging advice needed

[Dickj]

Hi folks

I put the following post up on a forum called Multihulls4us, one of the members mikereed100 suggested this would be a good forum from which to gets some answers so here goes!

I wonder if you could help with some questions/thoughts on rigging.

In many respects Butterfly (44ft Fastcat catamaran) has a fairly standard catamaran sail rig with a large(ish) roachy 75 sq m main and small(ish) 39sq m jib. Shrouds placed aft. No inner stays. Mast approx 56ft. Cruising weight around 10-11 tonnes.

However, the rigging is unusual in that the shrouds are primarily PBO with the lower 4 ft being Dyform wire. The wire used is 10mm and the PBO has an OD of 14mm; it has a black protective covering so the actual PBO is probably 12mm dia.

Even more unusual and certainly bad engineering practice is the attachment of the toggle to the chain plate. The clevis pin is approx 15mm dia but the hole in the chain plate is approx 18 mm dia.

I assume from this that the chain plate was originally designed to take 12mm Dyform shrouds.

Although we have had no issues with the rigging so far - what I have described raises a number of questions:

A 15 mm clevis pin in an 18 mm chain plate hole is very bad practice and creates an almost point load. Is the solution as simple as sleeving the pin so the pin and hole are the same size?


What is the typical shroud Dyform wire diameter for cats of this size – 10mm or 12mm?


My understanding is 12 mm PBO is as strong as 12mm Dyform. Does than mean that the strength (working load) of the PBO is not an issue?


How do you calculate or estimate the loads that rigging needs to withstand?

Thought and advice welcome.

Dickj