At the other extreme from wood-chip carriers, ore-carriers have small, compact cargo spaces because the nature of their trade is concerned with heavy-dense mineral commodities. Not so many years ago there was an international fleet of these gearless vessels around 20,000 tonnes deadweight, but the introduction of the more versatile logger offered stiff competition at the time that ore-terminals worldwide were gearing up capacity to take cargoes in excess of 100,000 tonnes. Now ore-carriers tend to be in excess of 100,000 tonnes deadweight and the largest dry-cargo vessels in the world (in excess of 250,000 tonnes) are ore-carriers, designed for a particular cargo-run, equipped with specially strengthened holds and tank-tops and with no need for the self-trimming facilities of other bulkcarriers. Bulk Cement Carriers. There are a few sophisticated mechanical and pneumatic bulk cement carriers, and even those that act as ‘mother’ or ‘factory-ships’, off-loading from other vessels and storing or even bagging bulk cement aboard. Often these vessels are converted from suitably dimensioned bulkcarriers, and serve a particular trade route or are stationed in a particulars area, the better to meet the cement demands of a nearby market. Otherwise, for odd cargoes, ordinary bulkcarriers can be readily adapted for the carriage of bulk cement or cement clinker (part manufactured cement without the setting agent, gypsum), by the cutting of small holes in hatchcovers to facilitate loading and/or discharge without creating unacceptable dust pollution, these holes being made good to Classification Society satisfaction before the vessel leaves port. This operation is usually covered by an appropriate Charter Party clause, under the terms of which Charterers usually reimburse the Shipowner for the cost of the hole-cutting and rewelding operation, with time so used to count as laytime, if employment on a voyage basis is involved.