SHIP
SKIP
SKIS
SKYS
SAYS
SACS
SACK
SOCK
DOCK

Of course, this fails if you count Y as a vowel, or if you disallow words with an apostrophe (sky's). But it's good enough for me.

Thankyou

sfwc
<><

PS if you take the view that Y can serve either as a vowel or as a consonant, I can't see an obvious way in which to tell which role it plays in SAYS. I would claim it is a consonant there on two grounds:

1. it plays a similar role in the word to the R in YOURS, and R is a consonant.

2. (selfish) it would mean that the above counterexample is valid.

Nope, I had to use a less categorical "might be wrong".

Without further ado:
>
>SHIP
>SKIP
>SKIS
>SKYS
>SAYS
>SACS
>SACK
>SOCK
>DOCK
>
>Of course, this fails if you count Y as a vowel, or if you
>disallow words with an apostrophe (sky's). But it's good
>enough for me.

It may not pass by a purist, but I appreciate having it. Thank you.