Okay facts people facts based on scientific research
I searched today literature and found what I am most interested in is called the flexural strength.
I want a spar that is stiff and resist bending without breaking.
Tension strength is of no concern whatsoever . Compression
strenth for a spar that isn't a mast
supporting a high load is also of little concern.
So if you are interested in facts based on actual research
continue reading. I will share with you my findings.
#1 Normally you hear only of tension and compression
strength, however for a gaff and boom it is flexural strength that is key.
#2 It is measured as follows:
Flexural tests are performed in accordance with ASTM D790-98 . Tests are conducted on an Instron-4204 testing machine with the cross head
speed set at 1.4 mm/min
#3 Spar flexural strength has little to do with the orientation of the fibers. Which direction should strains be oriented when a spar can flex in both X and Y direction? Yes yes, for a column supporting a weight from above I can see your points. Therefore, yes a mast should use oriented strains for higher strength.
This said remember this is not an airplane. I am a cruising sailor crossing the Pacific and not racing
an ultralight. I have a 70 ton vessel and don't give a hoot if my spar weighs twice or three times more then it can be made with ultralight materials in perfect arrangement.
(I have no vacuum machine and no access to a professional shop. Standing a mold
vertical seems logical. )
Please, don't get me wrong I do what your input and seriously still considering
Continuing with idea of random chop in epoxy (may use injectable epoxy which has extremely slow cure and seems logical to allow voids to natural bubble out via gravity.
Switch to wood.
Have professional shop in China
build spars using orientated carbon fiber as everyone is clearly suggesting despite fact no one mentions flexural strength.
See page 60 of this thesis which discusses flexural strength of carbon fiber compositions.
Notice in particular that flexural strength DECREASES after the volume ratio of fiber to resin exceeds 34%.
Flexural strength for carbon fiber in a PET matrix deceased from 240 mPa at 34% down to 140 mPa at 41%.
Obviously this shows packing as much carbon fiber as possible into a spar is detremental.