Curved draw knife v straight?

I'm ready to purchase a draw knife and I see there are at least 2 kinds, curved and straight. Can someone please explain the different uses and/or why you might choose a 5" instead of a 10"?

After 2 1/2 years my quick down and dirty bridge has failed. I used birch and later found they will rot quickly if unpeeled and/or not split. Version 2.0 will be made of peeled logs. Species will depend on what it handy.

Length is pretty obvious: for narrow workpieces, a short drawknife is easier to handle and control. For wide workpieces, you need a drawknife big enough to fit over it.

By curve, are you referring to the profile of the edge, or the whole blade being bent up or down? General purpose drawknives have the blade in one plane, and my experience is that the edge has a slight sweep to it so that angling for a deeper cut will concentrate the cut toward the center. Curved blades are made for specialty jobs, like hollowing out the inside of barrel staves. You wouldn't want to use one of those upside down for peeling logs, because the angle of the edge and handles is coordinated for use right side up.

I would suggest a first drawknife to be big enough to comfortably handle around the logs you want to peel. You can later get a larger or smaller one as you find tasks that require it. My preference is to look in antique stores and flea markets for old tools... if they have survived a century, they are probably high quality, and refinishing and using a good old tool just feels good. In some cases, old tools are designed better than modern mass-produced ones, too.

Peeled or not, birch rots quickly, and I would only use it as a last resort. Black locust is the gold standard, as it can last 50 or more years in the ground, but oak, hickory, black cherry, maple, ash, beech, and many others could work for a number of years depending on conditions.

Great advice here! I'll add my 2 cents and suggest you develop good footings. If you have to scrimp anywhere, that's not the place. Move a few stones in place to support your bridge; whatever wood you choose will last a lot longer.

Absolutely right! If you have enough good stone to have at least two layers of it between wood and ground, you will have a dry base for beams; a single layer of stone sunk into the ground as will happen under a bridge will tend to stay moist and possibly affect the beams.

It's not the kind of bridge that needs footings. This lasted 2 1/2 years. If I can make version 2.0 last 5 years I'll be happy. I think pretty much any species is better than Birch and peeled will be better than unpeeled.