converting hierarchical clusters to polygons

I have used hierarchical clustering to assign lats and longs (start and end positions of lines) to separate cluster IDs.
I now need to convert each cluster of points to a polygon.
My first attempt was with CHULL, with the aim to then convert each convex polygon to a polygon layer. However, I cannot get the hulls to plot by cluster and then save as an external object.
I think the easiest method would be to take the outside points of each cluster of points and connect them with a polyline and then convert it to a polygon.
I have 100s of clusters per year (13 years) so I do not want to have 1000s of separate polygon files, but instead one layer with all the polygons per year.

Dummy data to show approximate structure:
GISID     x             y             Attribute              Year       CLUSTER_ID
1             -129.24 52.994   Start                     2005      1
2             -131.26 52.73     Start                     2006      33
3             -126.02 49.297   End                       2005      5
...

Any advice, helpfiles, or vignettes would be greatly appreciated. I've read a variety of stackoverflow entries and r-sig-geo entries and have unsuccessfully adapted other solutions.
e.g. https://stackoverflow.com/questions/44928507/draw-polygons-around-clusters-from-hclust
https://www.nceas.ucsb.edu/scicomp/usecases/GenerateConvexHullAndROIForPoints
Thanks!