Ditto, John. My M17 was radiused slightly to ease the mast stepping, about a 3/4 radius and everything has always worked fine. No crazing of the fiberglass, no damage to anything. I will say though that one needs to inspect the hull right at the ends of the sleeper boards both fore and aft. Depending on how far forward or back you position your hull on the sleepers you may find some collapsing of the lapstrakes right at the end of the sleeper boards. This means that you are "blanket folding" some portion of the fiberglass layup. Not good. My last Monty, back in '84 actually developed a crack along the fold right at the end of a bunkboard such that I had to prop up the hull, fix the crack and fiberglass in a half section of epoxy soaked cardboard tubing, such as that found in a "Sonotube" to reinforce the hull at that point. After that there was no crushing of the lapstrake at that point. Fair winds, Tom B On Sat, Mar 24, 2018 at 4:25 AM, John Schinnerer <john@eco-living.net> wrote:
On 03/23/2018 04:18 PM, David Rifkind wrote: ...
You're not stretching the shrouds or anything when you raise the mast. But if you radius it, the shrouds are _undertensioned_ until the last moment when it rocks onto the high spot. The tradeoff for that is significant reduction in the footprint of the mast, i.e. higher pressure.
My tabernacle is a stainless "U" with vertical slot for bolt. Aluminum mast base rests on large stainless plate that is the bottom of the "U" shape. So whatever part of the mast base contacts the plate, the plate spreads the pressure somewhat.
The total pressure exerted is what it is. Question is, how concentrated or spread out is that pressure (over how much/how little surface area does it pressure the cabin top)?
Anyone ever tested how much of their mast base (and where) actually contacts their tabernacle base when raised and static? When in use sailing? Some thin automotive feeler gauges or just a strip of paper would do.
Altering mast rake would shift the pressure point...if my mast base is flat on tabernacle plate at 1 deg. rake and I go to 2 deg. rake then that is going to increase pressure exerted at aft edge of mast base.
My hunch is that for our small boats, the forces involved are not a problem in the vast majority of cases.
cheers, John
-- John Schinnerer - M.A., Whole Systems Design -------------------------------------------- - Eco-Living - Whole Systems Design Services People - Place - Learning - Integration john@eco-living.net - 510.982.1334 http://eco-living.net http://sociocracyconsulting.com