For hulls and decks, my advice is always use marine grade.
It is the water resistance of the type of glue used to laminate the
piles, which determines the grade of the ply, as well as wood of the
veneers.
When boat building with plywood always use the best quality you can
afford.
Any extra you pay for a better grade will be repaid by the longevity
of your boat, reduced repair bills, a reduction in building time and
the resale value.
Marine Plywood is made with waterproof adhesive so that it can be used
under water.
It is normally laminated with a ‘phenol-formaldehyde resin’ which,
sets permanently under heat and pressure.
The bond is permanent and will not deteriorate under wet conditions,
heat or cold.
There should be no voids in the core or crossbands, though these may,
on lower grades have been patched with synthetic material.
The better grades will have been pressure-preservative treated for
resistance to decay.
Marine grade is produced in soft woods such as Douglass fir or larch,
and in a variety of hard woods.
While the softwood plys are strong and light they do have a tendency
to ‘checking’.
Hardwood plys, on the other hand are heavier, and that little bit more
expensive.
Mahogany plys are probably the best, though Meranti is strong but
heavy.
Okume or Gaboon is a lighter hard wood but it doesn’t have the same
rot resistance as Mahogany or Meranti.

Mike

On 8 Apr, 22:45, gudi wrote:
( From recent *rec.boats NG post )

To build boat hulls ( 30 - 50 feet length cargo /fishing/
displacement
work boats) in plywood which resins are recommended to bond the
plies/veneers of (Gurjan) plywood together...

Polyurethene, epoxy, resorcinol, vinyl ester or phenol formaldehyde?

What are the costs and availability? Is a hot water boil test
adequate? What is the needed test spec?

These need to withstand salt water immersion for many years without
degradation. Also, which marine grades can be used for outside
personnel accomodation ( shelter on deck/ bridge or on wharf ) and
which for deep seawater immersible hulls?

TIA
Narasimham