SSensei,
Below are some dictionaries I consulted. Surf lingo may have never made it into such works. It struck me that paipo may be a variation not of surfboard but being prone. I’d be interested to hear from someone who is knowledgeable in this area.
Since my original comments on this, I remembered to have a look at the Surf Research site (early prone boards are refrred to as bellyboards or lamaroo - probably an Australian term):
http://www.surfresearch.com.au/h_AncientBoards_0000_Menu.html
In the Hawaiian Islands, there were two distinct board designs based on their cross-section.
Depending on the local conditions and the available materials, both were built in an extreme range of lengths.
The Alaia or the Thin board was flat in cross section and generally wider.
It was more suitable for steep waves and, when conditions were suitable, riding in a standing position.
The Olo or the Thick board was elliptical in cross-section and narrower.
It was better in flatter waves and usually ridden prone.
http://www.surfresearch.com.au/h_AncientBoards_1779.html#Table
"The two designs are identified by their Hawaiian names by another native historian John Papa I’i, circa 1870:
“The ‘olo’ is thick in the middle and grows thinner toward the edges.”
and
“The ‘alaia’ board, … , is thin and wide in front.”
Bob
http://www.wehewehe.org/gsdl2.5/cgi-bin/hdict?a=q&r=1&hs=1&e=q-0hdict–00-0-0–010—4----den–0-000lpm–1en-Zz-1—Zz-1-home—00031-0000escapewin-00&q=alaia&j=pm&hdid=0&hdds=0
alaia
n. Small thin surfboard, as of breadfruit or koa wood, and heavier than the olo board. Also omo.
olo
- n. Long surfboard, as of wiliwili wood. (Laie 449.)
http://books.google.com.au/books?id=bHdRhjL9Y9EC&pg=PR21&lpg=PR21&dq=%22Hawaiian+dictionary%22&source=web&ots=bvzb86LKT-&sig=PLj9lSipXbNieEDJbSDuWVsvveI&hl=en#PPA154,M1
kT.papa -prone position on a surfboard
kT.oe small surfboard
http://ulukau.org/elib/cgi-bin/library?a=p&p=frameset&p2=search&p3=word&r=1&e=q-0ped-000Sec–11en-50-20-frameset-search–1-010escapewin&t=0&q=surfboard&summarise=1
kī.'o’e - kipa.pani : Prone position on a surfboard; to assume such.
Pae-loa-hiki - pā.hema.hema : A kind of surfboard.
pā.paha.paha - papa kuhi.kuhi : Surfboard.
http://wehewehe.org/gsdl2.5/cgi-bin/hdict?a=q&r=1&hs=1&e=q-0hdict–00-0-0–010—4----den–0-000lpm–1en-Zz-1—Zz-1-home—00031-0000escapewin-00&q=surfboard&j=pm&hdid=0&hdds=0
Papa heʻe nalu. Of special kinds, the most common were olo (of wiliwili wood, as long as 5.5 m, for chiefs) and alaia (of koa or breadfruit wood). Other names: kīkoʻo, kīoe, omo, 'onini, 'ōwili, paha, pu’ua. To ride a surfboard, he’e nalu. Prone position on a surfboard, kīpapa.
