mast loading for hull girder strength on a gaff rigged vessel

Thanks to all who replied to my post regarding the center of effort of a gaff rigged vessel. quite an interesting discussion resulted from that, from which I was able to get much input. I am now calculating the hull strength for my gaff rigged sloop. I need to calculate the estimated mast load resulting from sails, rigging, etc, such that I can find the maximum bending moment on the hull girder (waveloading notwithstanding, since my vessel will be a 20' lake sailor). Principles of Yacht design (Larsson & Eliasson) states that for a sloop rig: 85% of the vessel displacement would suffice. anybody care to comment and/or make recommondations??

 

Calculate for the maximum rightening moment.

 

Well...since what you want for longitudinal bending is the mast/forestay couple, not the mast/shrouds, max righting moment won't do it easily. Not without going through some sort of maxi-calculation where you calculate all the vectors from the sails to finally arrive at a forestay load.

On a 20-foot gaff rigged boat I wouldn't worry about it, unless the design is really unusual. Gaff rigs are typically not highly loaded, and small boats generally are plenty strong enough globally, just from being strong enough for local loading.

 

Low rigs make strong boats; gaff is about as low as it gets.

Step the mast from keel, through the deck ( if you have one) or a thwart.

Stays become almost optional from thereon.............

Sail a gaffer easy: let her pull through the wind with the boom out over the gunl, never centrelined like racing marconi rigs. No stress worries then!

Gaff rig is beautiful, good luck!