Steeleye Span recorded an arrangement of the traditional version noted by Ralph Vaughan Williams from Mr. Hilton of South Walsham, Norfolk, in 1908. I believe that I sent a midi of the tune as published in The Journal of the Folk Song Society (vol.IV, issue 15, 1910) to Mudcat MIDIs nearly a year ago, but it doesn't seem to have been added. Here it is in abc format. You can convert it to midi or staff notation at Concertina.net. You'll need to remember to remove the spaces that will appear at the beginning of each line if you copy-and-paste it from here.

X:1
T:Lovely on the Water
S:Mr. Hilton of South Walsham, Norfolk, 1908. Noted by R. Vaughan Williams.
B:Journal of the Folk Song Society, vol.IV, issue 15, 1910.
L:1/8
Q:1/4=100
M:3/4
K:G
(E3/2F/)|G E A2 (GE)|G2 E2 E F|G A B2 g2|(e2{fe}d2)
w:As_ I walked out one_ morn-ing in the spring-time of the year,_
g2|e3/ 2e/ d2 (B3/2G)/|A B D2 (EF)|G A B2 (AG)|E4]
w:I o-ver-heard a_ sail-or boy, Like-*wise a la-dy_ fair.

Steeleye Span changed a note or two, and altered the rhythm, so this is a bit different from their recording; but it is authentic. I think that their recording was transcribed in the first "Steeleye Span Songbook", probably with suggested guitar chords, but that's long out of print. Perhaps someone round here has it and can help you more specifically.