Javelin advice
I have a 1979 Day Sailer II, but am familliar (sort-of) with the Javelin. If you look on the O'Day Owners Unofficial Website there are pictures from the 1978 Javelin brochure, look under info by model (I think?) the boom vang is pictured. I have also posted a pic of the boom vang on my DS II, it should be the same type you have on your Javelin. I can explain how to reef the sail using the roller-reefing on the boom, but you will need a reefing claw to use this feature. If you have one, you reef by unhooking the mainsheet from the boom bail. (reefing is usually done with the sail raised) then pull the boom aft slightly to disengage the gooseneck swivel from the slider on the mast, as you twist the boom ease the main halyard allowing the sail to lower at the same rate that it is being rolled onto the boom. When the sail is rolled up to the point where the lowest batten is almost touching the boom, release the boom and let it re-engage and lock the gooseneck. now hook the mainsheet block to the hole in the reefing claw and slip the claw allong the boom to the normal fore 7 aft location of the mainsheet. Now, after describing all this....I'll let you in on a "secret", the roller-reefing doesn't work very well on these boats! I took my mainsail to a local sailmaker and for $67 they added a set of reefpoints, these allow me to tie in a reef and still use the boom vang (rolled sail covers the mounting bracket on boom if roller-reefing is used).I'm unsure about how your mainsheet is getting caught on the outboard if you have the standard mainsheet rigging for a 1982 Javelin, the 1975 and later Javelins had the mainsheet located at mid-boom to among other things, avoid tangling the outboard. If your boat has the older style mainsheet that ran from the end of the boom, down to one corner of the stern, across the stern, back up to the end of the boom, then forward along the boom to mid-boom and down to a block and camcleat on the centerboard trunk, I could see the problem. I had that set-up on my old (1969) O'Day Widgeon (12') and it was a bit of a pain to tack! I never really did come up with a way to avoid that, maybe you could move the blocks forward along the side decks far enough to avoid the motor?