Well, you left out a lot of details that might make a diff. For
example, what kind of boat? Classic wooden? Racing dinghy? Oldie but
goodie clorox bottle? Not that you will lose sleep over the decision
but form follows function, right? An extension is not a tiller but is
used when holding onto the tiller itself is either awkward of
disadvantageous to performance when racing. If you are making an
extension I suggest you scratch the idea and invest in an after-market
one instead. Among the benefits of these are a wide array of lengths
and materials (carbon-fiber, alloy, fiber-glass) as well as design
(think telescoping). My tiller extension folds back nicely on the
tiller and is held out of the way with a clever grip.

Now if you are not discussing an extension, but an actual tiller, then
my suggestion is that you try to mimic the original design. Most naval
architects take pains to work out even the smallest of details,
including the tiller. As for material, heck you aren't making an
heirloom here. I would not worry too much about laminating something as
it is not going too buy you a whole heck of a lot. A stout piece of
white oak with a good varnish (I like Captain's, YMMV) on it should
serve you well. And when the varnish fails and the oak turns black it
just adds character. Sand off the varnish and redo for the pleasure of
adding more "character" to your tiller. And last but not least.
remember that the tiller must attach to the rudder somehow, and where it
does is your most likely source of failure so pay particular attention
to reinforcing this area. I used 1/4" SS angle iron - it worked great
for 10 years and for all I know may still be working now, 15 years down
the road.

Have fun and good luck ...

Renata wrote:
I'm gonna make a new tiller extension handle for a club's sailboat.
What's the best (and cost effective) wood to use? White oak? I'm
thinking teak might be too $$.

Thanx
Renata