Catamaran: Protruding shelves in the tunnel and resistance

[masalai]

Hi Mark Cat,
Design criteria are influenced and relevant to where one will cruise ... and personal preferences/money etc... Avoid the midships mini-V... It won't work as well as you expect and adds weight - when a little extra height of less beam will serve you better...

Ocean conditions on the Queensland coast of Australia are different to those across the 'top end' of Australia (Cape York to Dampier/Karratha) and different again in the west... and I am no masochist, therefore will not sail to the South of Australia (TOO BLOODY COLD)... I gather the seas are different in the Atlantic... All have a different fetch, height and duration/distance crest to crest... as well as cross patterns... (I should know the terms but failing memory.......)

Take a ride in as many different configurations and you will appreciate the difference in ride...
- When at anchor in relatively calm lee, one does NOT want a peaceful nights rest disturbed by an annoying slap or jerk...
- When there is a short steep swell one does NOT want to be bounced about whilst making reasonable progress...
- Not too much beam, as the extra engineering adds an undesirable weight penalty, or risk of being split in half, (in extremis)...
- Work out the "magic-length" for you (the smallest that will meet your needs) ... longer costs LOTS MORE to build and maintain...

Maximum LOA & LWL for me is 11.99 metres, beam sits comfortably at about 21 ft.... I can carry a tonne (or a little more) in fuel... CNO - admirably suits my purpose, needs, and cruising region... I have eliminated the forward 2 double berths and only have 2 double berths aft... If you are a charterer, do day charters... better margins and still live aboard...

[Mark Cat]

Masalai,

Great suggestions, unfortunately the range of charter/circumnavigation Cats I have been focused on are 65 to 74 feet in length.

Actually for aluminum structures if you combine the mini m with an aluminum cabin, the two together form a complex truss. Add to this small frame spacing and a welded on aluminum skin, we get a very interesting and strong monocoque structure.

In order to finalize the structure we look at per welded strength in how to stagger weld the frames to distribute complex shear, especially for openings.

Then we look at metal fatigue. But I minimize the areas of reinforcement.

Mark