Rig Attachment

[kimper]

Hello,
I have been working on a design for a while. I am currently doing the rig structure bit. I would like to know if anyone has an idea on how to fix the shrouds chainplate and how to do the appropriate reinforcement calculation? Knowing that I would like the chaineplate to be fixed on the intersection (deck-hull) and not in the middle of the deck.
Thank you in advance
kimper

[Eric W. Sponberg]

Kimper,

I address this in general terms in my article "Engineering the Sailboat, Safety in Numbers" which you can read on my website at:

http://www.sponbergyachtdesign.com/A...ngineering.htm

Skene's Elements of Yacht Design addresses this a little. And Principle of Yacht Design by Larsson/Eliasson also has a short piece on chainplates. Basically, you need to calculate the strength at the top of the chainplate around the pin hole, the shear strength and number of through-bolts that hold the chainplate to the structure, and the thickness and shear strength of the structure along either side of the chainplate.

Eric

[kimper]

Attachment of chainplates to FRP structure

Thank you for your quick answer.
I have been reading your article. If I have no problem to design a chainplate I am wondering:
• How to make sure that the hull and/or girder will be locally strong enough to handle the load
• How to make sure that the structure will be stiff enough in the transverse plane (for the shrouds case).

For the first point, I learn from the Germanischer Lloyd’s Rules that “the bearing stress in way of the bolts (for a bulkhead or a girder) should be calculated on the basis of 1.6 times the breaking load of the attached and should not exceed the ultimate compressive strength of the GRP”. But is it sill enough if the chainplate is attached very close to the hull or on the hull (see pictures attached).


Regards
Kimper

1: chainplate
2: shrouds
3: Ring frame / Bulkhead

[Eric W. Sponberg]

It looks like you are attaching the chainplate to a frame which you can consider is a type of beam. In the figure to the left, the shroud attached at the middle or thereabouts, puts a point load on the beam which will try to make it bend. The beam has to be strong enough to take the bending load. There will also be a component of compression above the attachment point and a component of tension below the attachment point, so these have to be taken into account. There will be some peeling of the frame from the hull, and also some shear, so the bond of the frame to the hull has to have enough bonding area to make sure it does not peel or shear.

In the figure to the right, the arrangement is simpler, and all you are dealing with is tension on the frame and shear of the frame at the hull.

It is very difficult to isolate any one component away from the others, so frequently you can assume that all of the load is taking one particular path. Momentarily, in actual sailing conditions, that may happen, who knows? So by coving a number of different senarios, you cover the bases. And since the structure is redundant, that builds in some safety factor. Take this all with a sense of reasonableness because you don't want to over build the structure either.

Generally, try to figure out the various load paths (tension, compression, bending, shear) and apply the appropriate amount of material in way of the load path. That's all engineering is.

I hope that helps.

Eric