Open source 12-15m high performance/semi-cruising catamaran design

Can you post a drawing of the arrangement so it is easier to see the problem at hand?

 

Can we agree on maximum acceptable surface deflection?
weight of 2 adults (150 kgs) on area of 1 sq meter should not yield deflection greater than 1 in 400 (unsupported span)
this is taken from NZ building codes and one example they provide.
i.e. 1 mm deflection across 400mm span.
Any other definition or suggestion?

 

Adhoc- this is an old rendering, its changed slightly but see the cutout in the aft center of bridgedeck sole? A tender is to be lifted through this cutout area and there is not adequate stiffness in the floor directly in front of the cutout. So far my solution is to add a ring beam around the cutout and then i can run longitudinal stiffeners under the supported floor plate into the ring beam. Another option is to run another transverse beam under the floor in front of the cutout but this reduces bridgedeck clearance to the water. I could reduce this intrusion into the tunnel clearance by making thos beam arched instead of straight which will reduce the required section depth.

Accepted deflection i would accept as low as half that UOS- 1/200 would keep me happy.

 

Hmm...a bit too small to really give any comment.
Do you have a plan view and with dimensions?

 

good to settle this design point as it determines a lot of the structure.

 

As requested;

 

So the bridgedeck floor has an unsupported span of 5 meters athwartship and 4.2 meters from the front beam to the cutout area to raise the tender through. My solution at this point is to run an arched beam just forward of the tender cutaway area and then another beam fore/aft from this one to the front beam. Ill draw this later. In this way - there is only perhaps a 250mm intrusion below deck level into the tunnel area at the hull to deck join, and a 250mm protrusion above the deck directly in front of the tender platform which will taper down as you move athwartship.

Then the subsequent fore/aft beam is under-slung the arched beam in the center and runs forward under the floor. These 2 beams cuts the unsupported spans in half. Will probably have to run 2 more longitudinals either side to cut it in half again and then we should be able to design a floor plate with required deflection.

 

run just one transverse beam fwd of the opening. You'll need long' plates on both sides of the opening to prevent damage launching and retrieving tender. Try to do without long's fwd of the opening - umm. ok that longeron will need serious tie in.
Not sure of your winch placements.
Where are your wheels on this plan?

 

This is one potential solution

 

I'd be scared of that big flat spot ... that is why I had drawn an upper and lower BD, like a skid plate. Your BD is not that high to start with, you might consider flaring the hull on the inboard sides along the same lines of that beam.

 

Interesting, a champher panel arrangement to the under-wing might help break up the span, I also would envisage the thundercat tender set longitudinally into an indent/pocket in the deck - with a vertical component then an inverted L leg or T to stiffen the cutout and maybe as a seat.. for fishing or put the bbq on, could offer a little security when nothing in place... a net tramp could be a comfy addition. You could drop the stern of the tender & drive the whole boat.
The mast connective looks a long way aft- is the fore beam to control the long bow overhangs or is the mast beam to be doing that- just the further apart & the deeper in section you get connective bulkheads seems they work better- got a pretty good close up look at Raw Nerve after she broke, couldn't say anymore than the integrity was challenged catastrophically by the loads applied though..
If you bring the mast beam depth up to the notional sheer looks like and easy transition to a full cruise mode later, pop another 5' of steps on the back of your 50 & she approaches the big M mark for resale later on
J.

 

Hmmm..cant view images while writing posts like the old system (Images don't open in a new tab)- backwards step if you ask me!

So, there is a small tender, is this sited in the cutout region?...if so, what is fwd of this, just an open deck?

Sorry - im just used to working with a bit more info, and less assumptions/guessing, before making a decision.!

 

Yes adhoc- just open deck and thus no support for the floor plate as yet. Inevitably need a beam structure around the tender as waikikin suggested... theres a few ways it can be done, just weighing up the costs in terms of time, money and physical weight of each...

 

Are you really really sold on the aft deck well for tender? Seems to cut into the aft deck access, always making sure you avoid the corners of the well.

 

I wouldn't be completly sold on it if you list the negs of structural discontinuity and safety say of the kiddies/adults falling down the hole.. The complications move away from the concepts even moving the aft beam right to the back for more room.. I'd be more in love with a really really long boom to derrick the tender over the aft beam- the aft longerone
Not sure about the forward longerone unless it hold anchor winch & cable they look like a trend when there's other reliable ways to pivot or project a sprit when etras are required.

Jeff