Following with interest. I'm planning a Shearwater hybrid and looking through the build manual there are NO combing risers on either the tight or loose layouts.

if you are building from a kit, the risers should be part of the kit.  the risers will be four pieces of 9 mm okoume -- see the link below:

https://www.clcboats.com/shop/kit_options/shearwater-sport/1081.html

unlike the coaming itself, the spacer/risers are for only half of the coaming (left side and right side ) so two pieces are needed to make it all the way around.  so the "rise" is ~ 3/4 of an inch (bottom of the coaming lip to the deck).  if you were not building from a kit, you would make the risers out of 4 layers of 4mm okoume.  

the shearwater hybrid kit would also include risers as part of the kit

hope that helps

h

   Building from plans. And the risers aren't on the loose or tight fit suggestions in the build manual. I'm sure I'll find some somewhere. Not buying another sheet just for that!

As Howard points out, if you build from kit, the risers (spacers) and coaming lip will be included.  From plan, you often only get the outline of the inside of the opening and the size/shape/construction method are left to the builder.

I use stacked plywood spacers and a plywood (Sapelle) lip even on my strip boats because I like the way it looks.  The spacers need not be 1/2 coaming shape.  They can be made of smaller sections and super glued together if you don't have large enough peice of wood.

If you are doing a hybrid build, you can make both the spacers and lip from cedar strips. 

Pages 97-99 of Nick's book covers both methods,

If you go the plywood route, make sure that you use the Lazlo Method outlined below.  It makes it very much easier to clean up the inside and under the lip.

Tape off the deck and glue the pacers together clamped but not glued to the deck.

Not pictured - Once the glue cures, unclamp it and remove so you can clean up both the inside and outside edges.

Next, Glue the lip to the risor assembly but do not glue it to the boat.

Unclamp again and remove for cleaning.  I use my belt sander clamped to a work bench for the cleaning.

Last, remove tape grrom the deck and glue the assembly to the deck.  Clean up the  inside and glass.

   Great, thank you all for the suggestions! I am making it from plans only, so I'll likely use the scraps left over to piece it together, or may buy a 2×4 sheet of plywood.