Ahoy,
Gaff boom spar pretty much covers it: Two specifics and a generic. In rigs such as my catboat Marmalade - Ted Brewer's Chappequiddick 25 - the boom has stiffeners with holes only for the strops for the sheet blocks and various lifts. I think that lots of contact between the stiffeners and the boom is needed to evenly distribute the considerable strains such a rig can have. Even in really lightened T beam construction, one generally sees a web of round holes rather than long gaps.
G'luck
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