zz4gta, i decided to do same last winter. the first time attempt, is best done with cheap material as you say. the first thing i did is establish a 'base-line'. i used the center-line of the boom as the center-line of the boat (fore&aft). then i tied a
line from the center of the mast at the the top of the boom to the bottom of the forestay (that gives you a 'comfortable angle' that the cover will 'fade' into the deck over the fore-triangle). now you have a straight-line you can measure to from side to side. it's your preferance whether you want the cover to reach the gunwhales or stop at the lower life-lines. i chose the lower life-line cause it lets the boat 'breath' while still protecting it from the elements. now go back to the aft-end of the boom and take your first measurement to the gunwhale or lower life-line (you only have to measure one side of the boat-when you lay-out your tarp for the cuts, the other half will be a mirror image. obvious, i know but you never know what degree of skills the person has you're talking to). i found that if you measure every 24" all the way to the end of the
line you tied to the forestay, you will have a profile of half your deck when you 'connect-the-dots'. now go to the mast and measure how wide it is -aft, center and forward from your base-line (this should be done with the main cover in place cause that's how big the hole in the cover needs to be to fit over the boom,around the mast and mainsail cover ). now go home with your measurements and drawings and lay your tarp out and fold it in half. decide what end of the tarp you want to be the aft end of the boom and start your measurements from there-just like you did on the boat. work foreward making a mark with a felt marker as you go. when you are done making your marks (every 24"), take a long (10-12ft.) board or as staight as you can find lenght of 1/2" or 3/4" PVC pipe and bend it around as many of those points you've just drawn without 'wandering' off the
line too much (in the most basic sense you are lofting the hull from a plan-view). i added an extra 3"to the the cut so i could hem the edges and add a double thickness of tarp for the grommets. i installed grommets every 4ft. ( the more the better). when you get to the foretriangle, make a slit from the front of the mast to the part of the tarp that ends at the forestay. i folded the sides of the 'slit' over so again i had had double material and installed snaps. at the top and bottom of the 'slit' i installed grommets on each side of the 'slit' so i could tie each end off with 1/4' CORDAGE as insurance if the the snaps should ever fail. there's one thing left to do that you have to go back to the boat to do. that is to mark the location of the shrouds. lay the cover out over the boom like you would install it and un-furl it so it hangs at the angle it will be when it's finally in place. mark the shrouds with just a dot from a felt-marker where the cover contacts the shroud in each case. go home and once again lay-out the tarp and find your 'shroud-marks' and make a slit out to the gunwhale or edge of the cover. you can install snaps or grommets to close this slit- i waited until i had the cover on the boat before i added the snaps and grommets to insure i got as close as possible to a good fit. once again, it helps to add grommets at the end of every slit and tie them together like shoe laces to prevent any fasteners from 'blowing-out'. i am very pleased to find that she held-up thru this winter's blows and snows. and yes, i also talked to Fairclough and after considering how many hrs. re-finishing teak, scrubbing the nothwest green slime off the ol' girl each spring, buying cheap tarps, snaps and grommets, crawling around on the garage floor like a reptile and did i mention re-finishing teak? i'm going to cough-up the $1600. and get the fairclough cover-hey! after-all, our "buddy' GW bush is paying for 1/3 of it -if you can believe anything he says- hope this makes sense- it almost takes as much time to explain it as it does to make it -salty57