Be very careful before changing anything with the original geometry. There are a lot of factors involved. The height of the maststep will affect the height at the partners (deck) and every stay, not just the headstay. There are deck ties which hold the mast to the deck, they will be good guides as to the appropriate height of the step. The mast typically pivots at the partners so moving the foot makes a big change to the head and shrouds. Our rigs are not typically swept but these factors are even more exasperated on swept spreader rigs.
Josh Muckley S/V Sea Hawk 1989 C&C 37+ Solomons, MD On Mar 25, 2017 3:12 AM, "RANDY via CnC-List" <cnc-list@cnc-list.com> wrote: > Listers- > > Seeking your input here. I'm in the middle of the mast step rebuild > project a la http://cncphotoalbum.com/doityourself/maststep/maststep.htm. > Lots of pictures of the project at https://drive.google.com/open?id=0B- > NqAxQ6JxFTSzRLbFo0NDl6U1E. > > I'll be cutting new supports from laminated GPO-3 slabs Saturday night or > Sunday morning. Before installing the new supports, I have to decide on > the elevation of the aft support. Of course I took careful elevation > measurements from the cabin sole before removing the original supports. > But the question is, what was the original shape of the top of the aft > support? > > I believe the middle of Grenadine's aft support, under the mast step > block, was compressed down from its original elevation due to a combination > of weakness in the support and standing rigging tension (especially > backstay). Have a look at the pictures and you can clearly see what I > mean, e.g. https://drive.google.com/open?id=0B-NqAxQ6JxFTLXZuXzd1T1pkR28. > This compression has the effect of pitching the mast step aft, thereby > moving the masthead aft, thereby increasing weather helm (which I've > definitely noticed under enough wind and sail - it was strong under full > main and #2 genoa in 30 kts, not surprisingly). > > However I also believe that the original elevation of the aft support may > have been carefully tuned for helm balance, prior to compression below the > mast step block due to weak wood and standing rigging tension. > > The reason this elevation question matters so much is because, using > trigonometry, I can calculate the distance by which different elevations of > the aft support will move the masthead forward or aft, which in turn will > affect helm balance. Each quarter inch of aft support elevation difference > could move the masthead about three inches I believe. > > The last picture (https://drive.google.com/open?id=0B- > NqAxQ6JxFTU3hRNmZoMUU1MFk) in the Google Drive folder linked above shows > the templates from which I'll cut the new supports, traced from the > original supports removed from Grenadine's bilge. I hypothesize that the > dashed line I drew at the top of the aft support template may have been the > aft support's original elevation. > > I'm halfways tempted to split the difference and cut the new aft support > to have that elevation. Of course, I could be full of crap, because I tune > the mast rake using the stays after all, which probably influences helm > balance more than mast step pitch. And of course I can control the sail > selection and sail trim, which probably influence helm balance more than > mast step pitch. However, for a given sail selection close-hauled, with > neither the backstay nor forestay over-tensioned, the mast step pitch would > certainly influence the masthead position and therefore the combined center > of effort of the sail plan. > > What say ye? Does anyone out there know if the top of the original aft > mast step support on a 30-1 was flat all the way across, or did it come > from the factory with a little elevation drop to tune helm balance? I'll > be committing an assumption about that to a GPO-3 slab with my jigsaw in > the next day or two. > > Thanks in advance, > Randy Stafford > S/V Grenadine > C&C 30-1 #7 > Ken Caryl, CO > > _______________________________________________ > > This list is supported by the generous donations of our members. If you > wish to make a contribution to offset our costs, please go to: > https://www.paypal.me/stumurray > > All Contributions are greatly appreciated! > >
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