function [msk] = findocean_fast( oldmsk );

msk=oldmsk;

[nx ny nt nk]=size(msk);
xp=[2:nx 1];
xm=[nx 1:nx-1];
yp=[2:ny 1];
ym=[ny 1:ny-1];

C=msk.*(msk+msk(xp,:,:,:)+msk(xm,:,:,:)+msk(:,ym,:,:)+msk(:,yp,:,:));
jj=find(C==1 | C==2 );
while size(jj)
 msk( jj )=0;
 C=msk.*(msk+msk(xp,:,:,:)+msk(xm,:,:,:)+msk(:,ym,:,:)+msk(:,yp,:,:));
 jj=find(C==1 | C==2);
end