A rush of new buildings could throw off estimates of how big the scrubber-equipped fleet might be come 2020, manufacturers said on a Deutsche Bank conference call hosted by analyst Amit Mehrotra Wednesday.

CR Ocean Engineering president Nicholas Confuorto said he expects 4,000 ships, or 10% of the world's fleet, to be outfitted with the exhaust gas cleaning systems ahead of the IMO 2020 emissions regulations set to...