Inquiry for information from experienced boatbuilders and boat designers

Ivan, it's really simple. The crossbeam must reach from the outside of the ama, across the main hull to the outside of the other ama. You fix it down at every gunwhale on each hull, so six attachment points per beam.
Now if for some reason the crossbeam can't be one single piece (for example you can't find the appropriate lenght for sale, or it is to heavy to maneuver alone) you can make the crossbeam from two pieces. This two pieces can be spliced into one and fixed to the hull like a one piece beam, or you keep it in two pieces and fix it like in the Astus example because that's the simplest way of doing it.

Hi Rumars,
I've seen some examples of crossbeams which are only fixed at one point on the mainhull. But the 6-point fixation for each beam is would then be more suitable, of course. Thanks for the additional explanation

SolGato said:

You can geek out a bit more on that style folding system by studying the Seaclipper trimaran which also has a simple and straightforward hinged kick-up rudder design that may be of interest.

Beams sliding past one another like the Atsus is a simple and straightforward method that makes trailer sailing a breeze.

A more “seasonal” method that uses tubes for beams would be something like this Condor 30 which has beam pass through tubes glassed into the main hull, so the one piece beam is passed through the main hull, fixed, and then the floats are clamped to the tubes in the same way as my Catamaran.

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Hi SolGato thanks for your response,

this is a great example and if it were not for the two half-beams and if one beam would be intended for the amas then this system would be the best solution. It would avoid the splicing, too. The weight would still be possible for one person mounting/dismounting (although on the limit).

SolGato said:

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On the tri you mention, are these inspection holes used to set the nuts in place, for the bolts, inside the ama hull? Or just for inspection

Rumars said:

...Now if for some reason the crossbeam can't be one single piece (for example you can't find the appropriate lenght for sale, or it is to heavy to maneuver alone) you can make the crossbeam from two pieces....

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Been reading your and SolGato's last responses for a lot of times recently.

The 4-metre beam is just at the limit of what would be possible to maneuver alone, and since the dismounting would be intended as seasonal, ...

It would really simplify the matter of attaching the amas to the mainhull.

I would be interested to know whether a two-part beam spliced into one is inferior in strength (or rather, how much inferior) to a single-part crossbeam, if dimensions are the same. There is certainly an additional mass of the splicing tube.
And if this difference is not negligible for the intended dimensions, in which aspect of stress does it manifest the greatest in pitch or torsional connecting moments or in transverse bending. Perhaps because of the lateral "cut" at the middle, the simple shear stress would be the largest difference between these two crossbeam types.

Anyway, thanks