2 1/2 feet!? That's too long, not too short.  For a crossbow with an 8 inch draw, I'd use a prod of just under 20 inches.  Make it very thick, and taper it well.  Some people say that is too short, but my crossbows definitely work.
  Most crossbow prods in Europe were actually made of wood until the late 14th century - the wooden prods were a lot cheaper than composite or steel bows, both of which take vast amounts of time and skill to make perfectly.  Composite crossbows were far from rare, and the draw length could be drastically reduced, but a wooden prod would be typical, and should be short.  Think about it, DtB - the draw length of a normal bow is just a little bit under half the length of the bow itself.  Why not the same for crossbow prods?  Wooden prods are mentioned as a majority of the crossbows produced certainly in England until about 1450, according to Alm.
  In south-east Asia, tribesmen have used crossbows with disproportinately long prods, but they are not efficient.  Or wieldy.  Chinese crossbows have most often used self-prods or bamboo laminate prods with long drawlengths compared to European crossbows.  They are more efficient, I believe, with a longer drawlength.

All my European crossbows - so all the crossbows I've shown so far - have really short prods.  They should still be up.  20 inches is more than enough.  It's within safe parameters, and it's totally efficient.  Half an inch is quite thick, depending on the width of the bow.  I couldn't tell you how thick it should be, of course - I don't know what the wood is like, what draw weight you want... etc.  Just do it like a normal bow, just make it short.
  Think about it though: 8 inches is obviously 2 inches less than half 20 inches.  2 inches is ten percent of the length of the prod, and a bow should be about 9 tenths bent according to many English bowmakers.  Bear in mind too that the string on a crossbow, especially a wooden-prod crossbow, is slightly slack, or at least, nowhere near as tight as on a handbow.  There should be practically no tension.  A short prod, therefore, is absolutely fine.  I've had no broken prods that were made properly.

Yeah, pretty much.  As long as there is practically no tension on the bow itself, then yep, keep them strung.

Why is the prod more efficient when it is shorter?

Actually, I don't think the shorter prod is more efficient.  You can just get more brute force packed into a smaller bow.  Just thicken it, and taper it a little (this is a very rough science), and attach a truly huge string.  The longer bow's tips would have more time to reach maximum velocity and hence be more efficient, but efficiency is not really necessary here, where you don't need to keep poundage down to around 50 pounds.

Rebel, definitely invest in a piece of hardwood! From all my experiences with Pine, you're very lucky or very skilled. Do you know what weight the pine draws at?

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9/10ths bent?! What the heck does that mean? That makes no sense. For the length of a longer bendy handle bow, take your drawlength, double it, then add at least 20 percent. Maybe as much as 30 percent if the lumber you are using isn't very good, like soft maple, some of the less dense elms, and black ash.

Maybe english, you are referring to the old longbow phrase- "a full drawn longbow is 9/10ths ( or 7/8ths) broken.". This means if you overdraw your bow by about two or three inches, more likely than not it will break.

DtB, I would suggest using all of the length you have, and adding another two or three inches to your drawlength. Another 6" of prod length isn't going to "slow you down" any- unless for some wierd reason you are hunting with it. A longer drawlength will shoot better.

Also, the reason you can have it "strung" with about a 1.5" brace height is that such a short heavy bow will take a significant amount of set, so there shouldn't be any tension anyway. DtB, I really suggest you make a bow first. It is easy, it will teach you about tillering, and if you can take some pics I'll walk you through it.


Rebel I can believe you are making them out of pine, if you are backing them with leather and linen as you say. I think a piece of hardwood like ash or elm would be better, but if they are working for you then its alright.