Ahoy mates one and all,steve-nacra58-MAC36 wrote:Mast head floathttp://www.thebeachcats.com/index.php?m ... emId=11941
There it is. Thanks again for the info. Do you know if a skin of glass is wrapped around the float or is it just a moulded piece? I'm going to owe my soul by the time this is all over.
I think that I might design something that may reduce windage and be a better system for the mast head float. I need a couple of days to think it over and then I'll run it by everyone for discussion.Today, we get a little bit deeper in the muck but once it is all said and done, we will come out on the other side dirty and tired, but alive. Like I always say, every day above ground or floating on water is a good day. I have yet to find any imperial information for this design and hopefully Steve or someone else will come through, so here are the results.
The design carries a single spreader approximately half way up the mast dividing the column into two panels. The normal distance above the deck is 50% -52%. Regardless of length, this approximates 10 degrees for a shroud to mast angle so this assumption is used. Also, the lower shrouds bear 60% of the load on single spreaders and the uppers bear 40%. The dolphins striker, well, everyone knows what that does. This leads to certain acceptable rules and guidelines for calculating the loads paths and tracing them down to the hull. They are that:
1. Double lower fore/aft spreaders should be equal in size.
2. One double lower shroud is designed to bear the entire lower shroud load,
3. The head stay should be greater than or equal to the largest shroud size,
4. The back stay should be equal to the size of the head stay.
5. Mast loads are always equal and opposite.
With this in mind the traverse sail forces and compression/torsion loads arecalculated:
Mainsail: This calculates to 23837 f/lb
Foresail: This calculates to 19286 f/lb
Genoa: This calculates to 3948 f/lb
Apparent Velocity : This calculates to 3.16 mph
Mast compression: This calculates to 33,376 f/lb
Boom Torsion Load: This calculates to 3803 f/lb
Mast Ixx Min: 10.62in^4 - 442cm^4
Mast Ixx Eff: 22.29in^4 - 928cm^4
Mast Iyy Min: 10.62 in^4 - 442cm^4
Mast Iyy Eff: 12.74in^4 - 530cm^4
To put this in perspective, a Z701 US Spar mast would do the job.
Boom Ixx Min: 0 .53in^4 - 22cm^4
Boom Ixx Eff: 1.11in^4 - 46cm^4
Boom Iyy Min: 0.38 in^4 - 16cm^4
Boom Iyy Eff: 0.46in^4 - 19cm^4
To put this in perspective, a Z160 Us Spar boom would do the job.
Now we have some sections that we can compare with, and if unable to corroborate, then we have a good idea of where to begin. Obviously, it would be prudent to provide specific measurements and weights to mast manufacturers and request their recommendations before purchasing.
For simplicity purposes, we know there are 3 cross beams, one of which carries the mast compression loads. This by the way was also genius. These can also be designed to different levels of strength such as cantilever, simply supported, load at center or equal loads at ends etc, and sections also may vary such as circles, squares, ellipses etc. The design uses a cylinder and it is probably designed to simply supported. The manual said it has 6-5/8" (outside diameter) tubes, so knowing the loads, we can solve for the inside diameter and we can then complete the triangle.
Center Beam Ixy Eff: 36.082^4 - 1502cm^4
6-5/8" OD x 5-7/8"ID - 3/8" wall
Fore/Aft Beam Ixy Eff: 25.475^4 - 1060cm^4
6-5/8" OD x 6-1/8"ID - 1/4" wall
I think that my safety factors could be close because these sure appear to be seriously heavy duty for their span. Anyway, best to be safe than sorry. I think the beams on board are 1/8" walls for the fore/aft tubes and 1/4" for the center tube if my memory serves me well, but I just don't know if someone changed them out correctly or just decided to negate the designers safety factor and purchase the cheaper smaller wall thicknesses.
Lower Shrouds: These calculate to 9/32" and they should be tensioned to 389#
Upper Shrouds: These calculate to 7/32" and they should be tensioned to 864#
Lower fore/aft Shrouds: These calculate to 9/32" and they should be tensioned to 518#
Forestay: Calculates to 9/32" and should be tensioned to 648#
Backstays: These calculate to 9/32" and they should be tensioned to 432#.
Wow, these also are heavy duty wires unless my safety factors are indicative of my enthusiastic will to survive
Spend the extra $160.00 and go all 9/32" and carry only 1 replacement wire diameter and associated fittings and relax knowing that the rig has been upgraded for offshore use. It does however add weight. One thing is for certain…that baby is going to be in a blow and when the skipper pulls his head out of the sand, he is going to find a stick standing there. Based on these loads, the clevis pins are 1/2" diameters, and that at least agrees with the manual.
Okay. There we are so far. If anyone happens to have first hand knowlege of any of the above scantlings without having to go outside and measure it to confirm, I would appreciate your input. If it is off, I appreciate that as well. Blocks, winches and mainsheet will be next. The running rigging will be based on the block loads depending on the deck design so sheet diameters will not be called out and is subject to the different deck layouts.
Talk later. I gotta run,. Literally.
Whoops... had to edit. I mixed up the lower and upper shroud designations so I fixed them to reflect the correct diameters. The diameters did not change, only that they were asigned to the incorrect shroud, upper or lower. It is now accurate. Sorry.
DOH 
Rob 
