Dear Philippe, I could not agree more ...
In our case, we had to cut out a part of the big steel frame. What was cut out was the central "spine" with the upper plate. The lower plate (which was not corroded) stayed in the boat and was ground down to a plane. The new frame part has a lower plate of its own which is bolted into the old one. Plus, of course, there are the fore and aft plates.
The keel is bolted through the old lower plate which stretches along the bilge sections. So, there is a longitudinal support which also holds the keel bolts.
Regarding the mast drain but on a completely different ball game ... in the meantime, I have heard from someone who not only put better drainholes in the mast in his boat (not a Swan), but who also computed the volume of the mast and ordered the appropriate amount of ... ping-pong balls. The mast is now completely full of ping-pong balls, and while they do not add any mentionable weight, they allow water to pass. New cables and lines can be easily drawn using the old ones as guides, and nothing in this mast ever makes a sound when the boat is rolling. What an unusual idea!
Dear Philippe
There is a very strong backbone for the center section of the hull - the lead keel on the outside. The mast step does therefore not see much longitudinal load in the keel area, but at each end of the keel the loads need to be considered, in a grounding situation they can be extremely high.
The transverse bending loads from the keel are best taken on floors in the center section, and the loads are cyclic meaning that fatigue is an issue.
Dear Martin
Ping-pong balls in the mast is certainly a new approach. It can be assumed that the balls move out of the way when a halyard is tensioned. In tall masts there might be fairly high pressure on the bottom balls from all the others on top.
Tried to calculate the allowed ball stacking height, but get rather strange results.
Daniele, would you be able to help with finding the proper calculation formulas for stacked ping-pong balls?
It could be commented that earlier attempts to use shaped pieces of foam inside the mast for preventing halyard noise have not been very successful.
Kind regards
Lars
Dear Lars,
thank you for thinking of me and yes I probably can help. What are the quanties of interest? 1) number of balls per unit meter in height given the internal mast surface and 2) pressure exerted on the single ball at a certain distance from the top?
The problem of crushing occurred to me too as soon as I read the post: the balls at the bottom might be particularly subject to this effect and will eventually end being an hodgepodge of compressed plastic matter.
Daniel, 411/004
Dear Daniele
The matter of interest is how much contact load is needed to dent the balls. One ball weighs 2.7 grams, and their dimensions are determined by rules. With this information the number of balls stacked on top of each other can be estimated.
Kind regards
Lars
Dear Martin
The main concern is that the bottom ping-pong balls in tall masts would collapse under the stack weight. The conclusion of the research efforts is that the bottom balls can stand the short-term static loads, but long-term effects are quite uncertain.
It is likely that the celluloid ball material will creep slowly under continuous load and vertical accelerations, and the phenomenon becomes faster in hot and moist atmosphere. The load test reports suggest that after initial slow denting the ball will then eventually suddenly flatten, i.e. collapse totally.
Would appreciated to hear how tall the mast filled with balls is, and if the internal halyards are affected when they are embedded in balls - are they stiffer?
Celluloid is highly flammable, and it is important to avoid any action which may cause the balls to heat up. Warning - hauling halyards at high speed causes friction.
It can be noted that since 1st July 2014 celluloid balls are not any more allowed in big table tennis events, instead other plastics must be used. It would be advisable to use the new balls also in masts.
The research and warning above referred to celluloid, the new plastic materials may behave differently.
Rather peculiar that a Forum for sailing yacht matters discusses table tennis balls!
Kind regards
Lars
