Ship Sheer Line

[RTNerd]

Two other factors related to this discussion are the load line regulations and the trend in recent years to increase hull depth for a given ship length (L/D). The freeboard calculations for load line assignment assume the ship has defined standard sheer curves forward and aft. This is to help avoid diving the bow into waves and the stern being pooped in following seas. Ships with insufficient sheer must have freeboard added amidships but increasing the depth of hull can offset any required reduction in allowable draft. If the L/D has been reduced to provide sufficient hold volume for coal then there is no need to add sheer to maintain the desired draft. An article in the June 1955 edition of Marine Engineering provides an interesting comparison of the Detroit Edison and John J. Boland (now Saginaw). The Detroit Edison was 33 feet shorter than the John J. Boland but its coal capacity was only .8% less. This was accomplished by increasing the hull depth 2.5’ from the Boland’s 36’ (17.8 L/D) to 38.5’ (15.7 L/D) for the Edison. While the John J. Boland was built with sheer and the Detroit Edison was not, the Edison had about 1’ deeper load line draft. Bottom line: Years ago, boats tended to be built with minimum hull depth (L/D about 19) and there was a draft penalty if sheer was eliminated but the expense of adding sheer to more modern hulls with depth increased for some other reason is not economically warranted.

[Guest]

I think sheer was primarily to increase buoyancy fore and aft as a vessel entered and left green water. Any strengthening caused by sheer would be negligible. Sheer has disappeared, I think, because the time and cost savings of reducing the loft shop time and the resultant bending, fitting, and fastening of curved plates outweighs today whatever seakeeping benefits sheer provided, especially with new innovations (bulbous bows, for instance) and better construction techniques.

Thanks for the reply. Do you think that the designing ships with a sheer was a largely a carryover from wooden ship (both sailing and steam powered) construction practices?

[William Lafferty]

I think sheer was primarily to increase buoyancy fore and aft as a vessel entered and left green water. Any strengthening caused by sheer would be negligible. Sheer has disappeared, I think, because the time and cost savings of reducing the loft shop time and the resultant bending, fitting, and fastening of curved plates outweighs today whatever seakeeping benefits sheer provided, especially with new innovations (bulbous bows, for instance) and better construction techniques.

[Guest]

Older vessels were built with a sheer line but this appears to have been slowly done away with as years went by. By the 1950s it appears that ship designers had started to minimize the sheer of their hull designs. Since the 1970s it appears that ships have been built with no sheer line. Did this evolve from new construction techniques or materials used in the building of lake ships? I'm assuming the sheer of a ship's deck was to strengthen the hull?