displacement question

[Gold Rock]

Is it universally implied that when a given design's displacement is stated that the rig is included? I was thumbing through some books and noticed the number of designs shown with multiple rigs drawn. I'm sure that a gaff schooner's rig would substantially outweigh a sloop of comparable sail area.

[Ian McColgin]

The rig is normally included. Certainly the weight of a mast can affect the boat's trim. Just think of all the sloops that float a little bow up till the stick is in. But especially as the boat gets larger the weight of rigging choises is not different enough that it will make a big difference in displacement. Rigging choises can make a difference in weight distribution - a hollow versus solid spar, net effect on metcentric height, etc. But not a huge impact on total displacement.

[CByrneiv]

Unfortunately, also, some commercial boat builders disingenuously quote the displacement as bare, dry, and empty.

This makes them look artificially lighter than boats of similar volume and construction; solely for marketing purposes.

[bucheron]

I might add that for smaller boats built for class racing, when the hull is weighed to see if it conforms to class rules, it is often done with rigging and all moveables removed. Probably this has come about because it is easier to hang the boat off scales with the rig removed.

[TR]

Gold Rock....

Usually the figure quoted on plans (and in sales brochures) as displacement represents the calculated volume of the underwater portion of the boat (in either salt or fresh water). Also usually this is calculated to a DWL, or design waterline. Sometimes the DWL is the designers best guess, or an honest wish.....and sometimes it has nothing to do with reality.

Exactly what the boat really weighs is always something different than the volume calculated to an arbitrary line.....it may be a lot different or just a little different. As you surmise the schooner will for sure come out floating at a different level than the sloop.

[Gold Rock]

Thanks Tad, and sorry to all for having lost track of this thread. Sheesh. Tad, I guess the gist of my question is then, when figuring the location of the DWL, I presume a number of separate factors are calculated. I don't know exactly what they are, but I'd assume the volume of the hull vis a vis it's shape, the weight of materials from which it's constructed, etc. I just wondered if the actual weight of the rig (spars, fittings, standing/running rigging, etc.) are tallied up and thrown into the equation?

[Lewisboats]

Yes they should be... as they affect not only the overall displacement but a number of other factors too.