The Steam Packet Company says two sailings later will be affected by forecast bad weather.
The Manannan was due to leave Douglas for Liverpool at 3pm, but will now set out at 10am.
Her return voyage will also set off earlier from Merseyside - leaving at 6pm rather than the scheduled 7.15pm.
The North Irish Sea could see gale force winds of up to force 8, according to forecasters.
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