[Public-list] Chainplate knees and mast pad

[Don Campbell]

Peter;
    I am not an engineer,  but the removal of the knees and additions to the hull of more mat and plywood would not increase strength to the hull in proportion to the amount you propose due to the loss of the 90 degree angle that the knees add to strength. For added strength why not use 45-45  unidirectional fibers sewn to mat and go over all that is there with this? Your additions here  will  reduce the strength since the right angled braces will have been removed. Thus, you will  have increased forces wanting to deflect the hull from the addition of chain plates on the outside of the hull. Only the deck ( which is relatively weak if there is any water
damage) is resisting this additional force towards the centre of the boat. It can only deflect so that the deck moves up or the keel moves down, and it will go whichever is least resistant. Your suggestion of through bolting new chainplates to the outside of the hull will do a couple of other things you might not like. The first is that they and the stays will be available for every wharf or pier to catch on, which is now not the case. As it is now, the spreader is out to about 8" from the edge of the hull and can easily hit other boats' rigging while moored on finger wharves in a storm, or walls of locks if even one person is misbalanced on the deck. (I
have seen both with the loss of a rig in the first case.) They will also allow for possible leaks to develop from 10 holes on each side of the hull which are not now there, especially with the increased flex with no knees,  and you have seen the comments on leaks in Albergs on this site. You will also change the angle of tension on the stays by some small amount which may change the internal forces in the mast. Lastly, you will have created three areas of turbulence on each side of the hull that will affect the performance of the hull. I hope you have considered that these are your desired outcomes of your chain plate improvements.
    Why second guess engineers and designers who have calculated the forces as they have designed the hull  and deck to optimize performance, given the compromises they have had to make within the design?
Don

Peter Amos wrote:

> The next time TaitTait is hauled in the U.S.,hopefully November,the mast will be unstepped so that I can fix that irritating dent in the deck aft of it.From the pic. in disorganized maintenance it appears the deck pad thickness is tapered being thicker  at its closest point to the mast.Is this so or is it an optical illusion in the pic.?
> Also I have always been concerned about the chainplate knees.Compared to those I have seen on other boats of a similar size they appear lightweight and not well finished.Although I have never heard of them being a problem,except the 1/4 bolts,while the mast is down it would be a good opportunity to do something about them.I have in mind to remove them,and after preparation add a couple of layers of heavy mat to the hull along the length between the lowers.Then add three strips of 1/4" marine ply over the same area so there is a thickness of 3/4".Finish up by fixing new sturdier chainplates inside bolted through the hull from the outside with 5/16" bolts.
> Constructive comments welcome,cries of "heresy" will be disregarded.
> Peter Amos
> Tait Tait #478
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