: Where I live, I have a hard time finding cedar boards that are relatively
: free of knots, but knot-free pine boards are much easier to find, and much
: cheaper. I know that pine is heavier than cedar,

That depends on the species of pine - as you don't say where you live, its
kind of hard to guess what is likely your local lumber.

I live in NE England, where Cedar is not common (though I am very fortunate
to have a small stock of recycled ceiling panels which are 5/8" cedar). I
have used both pine and spruce - both light coloured woods which darken quite
a bit in use. The spruce is mostly plantation grown and kiln dried and tends
to be quite knotty. In this form it is quite hard to work, but is OK in
small pieces. I made my milled-to-shape cockpit coaming with spruce.

The Pine I find is much more expensive, but is mostly clear. I tend to visit
DIY shops and sort through entire stacks of pine to find wholly clear boards
for possible future use in a skin-on-frame boat but for cutting strips, one
or two knots aren't a great problem. There is also a timber merchant further
away from me that tends to have quite a lot of clear pine, mostly in shorter
lengths. There are two types that I have bought - "Redwood" also known as
"Scandinavian Pine" which is actually Scots pine (Pinus sylvestris), a very
similar timber to Lodgepole pine (Pinus contorta) which you will find in parts
of the US. The other is "Southern Yellow Pine", which is a US timber. This has
a very nice grain pattern, but is a significantly heavier wood. I haven't
yet used this is a boat, but it seems to be easy enough to work and looks
good. The light parts of the deck of my Hybrid Cormorant were made with the
Scots pine which was just as easy to use as the cedar, and barely denser.
The deck also uses Brazilian Purpleheart, a wood much denser than any
species of pine or cedar. Nonetheless, the boat is the lightest I have ever
handled - a tad lighter than Geyrfugl, a 5/6 size Great Auk which is a foot
shorter than my 94.5% sized Cormorant.

: but is that small weight
: difference enough to make a difference after the boat is finished?

The straight answer is "Yes" - but it isn't that simple. If you are mixing
woods for a nice pattern, then all your strips must be the same thickness,
but if you are using a single wood, you could cut the strips a bit thinner
for a denser wood. Denser woods generally are a little stronger, especially
in compression, so you could equally use the same thickness as you would
use for cedar, but use a slightly lighter lay-up of glass and epoxy.

There are lots of variables, but these need only be of concern if you are
a light or small person seeking a boat you can lift onto a car roof without
help, or need a light boat for some other reason. Given that strip boats
are much lighter than all-fibreglass boats that most of the world get by
with, you can probably afford to have your boat three or four pounds
heavier ...

Andy