By undertaking a sea voyage one losses caste. Such people should be avoided at Sraddhas as said in Smritis like Manu etc.
The Baudhayana Dharma Sutras (BDS) also gives the remedy of that sin.
1 Next, the sins causing loss of caste: stealing a Brahmin’s property
or a deposit; undertaking a sea voyage; bearing false witness with regard to
land; trading in all sorts of merchandise; serving S ´udras;
fathering children by a S ´udra woman; and becoming a child of a S
´udra.* When people have done any one of these, they should eat a
little at every fourth mealtime ; bathe at dawn, noon, and dusk; and
remain standing during the day and seated at night. In three years
they wipe off their sin.
Fourth mealtime--- two mealtimes a day are acknowledged for humans, morning and evening. Eating every fourth mealtime amounts to
eating one day in the morning and the next day in the evening, thus
skipping two mealtimes between meals
As additional information I am quoting from the book "Essence of Dharma Sindhu" which states that Samudra Yatra is prohibited in Kali Yuga:
Kali Yuga Nishiddhas:
The following are the avoidable and unnecessary acts of Kali Yuga
viz. Samudra Yatra, carrying of Kamandulu to misdirect the Public ,
remarriages, begetting children from husband’s brothers; Go Vadha;
Mamsa Bhakshana at Shraddhas; performing vivaha to a physically imm
ature girl; Chira kaala Brahmacharitwa; Naramedha Ashwamedha Gomedha
Yagna; Madya Paana, Abhakshya Bhakshana, Apeya paana, Agamyaagamana
or wandering aimlesly Rahasya Prayascittha, Devata Puja and Pashubali
for evil ends; Kula Bhrashtata; Extreme Profiteering and narrow