more info

From: tom Hynes
Remote Name: 76.20.134.136
Date: 01/07/07
Time: 03:03 PM

Comments

I didn't word my previous post very well concerning the structural aspects of having small but frequent hatches. As can be seen in the photo of the Maumee's hold, there is a large structural girder running across the ship just below the main deck every 24 feet. These stiffen the hull and probably provide a lot of resistance to torsion (hull twisting), which is more difficult to control in the relatively shallow hulls used on the Lakes than in a typical deeper ocean-going hull. ************** Other reasons that small frequent hatches are still so prevalent on Great Lakes ships is that many switched early to being self unloaders. Because so many ships were unloading themselves, very few shore-based unloading systems have been built on the Lakes in the past 50 years. So the lakes don't utilize the massive grab buckets or continous ship unloaders that have been developed elsewhere and that need larger hatch openings. Many of the newer Canadian bulk carriers that operate both on and off the lakes do have larger hatches: often 6 or 7m or longer longitudionally.**************In summary, the small frequent hatches used on Great Lakes vessels originated from ore dock designs of the 1800's and have been maintained because of the need for new boats to load at old docks and for new docks to be able to load old boats. That combination limits changes in technology, even over vast amounts of time. But the 12 or 24 foot hatch spacing doesn't hinder bulk cargo loading, and most boats are now self unloading. Finally it provides an easy way to provide cross members that provide hull strength.


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