Composite Tang/ bracket construction methods for fwd crossbeam??

You can do it anywhere and everywhere on a load in tension. Works like a charm.

 

If that is what you think, rather than can demonstrate by relative stiffness, that is your prerogative.

However, this is contrary:

The other hull wont rotate as you describe, its is out of plane form the other.

So, this inward movement, is not movement?

It seems you have assumed there is no movement rather than demonstrated, fair enough, that's your prerogative.

 

The new sig 45 built here in Cali has used the same setup for crossbeam attachment... My point about having a tang vs a laminated attachment is that if and when you do have an instance of movement at this point if even ever so slight you would have stress cracking that would occur in the finish.. I believe that by going the tang route you can accommodate any possible movement that may occur but still have a strong attachment point that will take upward crossbeam loads as well as compression loads from walking up forward onnthe tramps in addition to keeping the hulls stiff and inline with one another going through seas.?

 

Ok, we're close... we might just be splitting hairs, or splitting paint at the spot the tang joins the deck.

Maybe my wording is not correct. That is just how the bows and beams work, but not worth arguing over. I'll stop at this point.

 

You can employ what ever method you like, a tang is one. You just need to ensure that the strain is being distributed smoothly and with enough shear area and load paths available. In your pic it shows 2 main cross beam, one approximately midships and the other aft. There is a very long lever from the fwd beam to the bow. This midships beam must be very very stiff indeed to prevent ANY movement of the 2 bows relative to each other.

The pic you show indicates you have done some analysis??...if so, what load case did you apply and what is the relative movement you calculate?

 

That was just a generic catamaran load path image from shuttle worth site. He deserves the credit for mapping the loads in that amage. There are indeed many forces at play here. I believe most designs that have a solid wing deck attachment between the hulls are using the crossbeam mainly for additional support and headstay loads as the torsional loads are handled mostly by the main crossbeam, wing deck, and aft crossbeam. Of course the fwd crossbeam helps add stiffness to torsional loads between the hulls as well.
However, there are some designs that do not incorporate a fwd crossbeam like dazcat as well as few others. Not sure what is better but mainly looking for advice on building this composite tang for my project.

 

Boy, does that picture ever show what I was talking about:

1) The port hull is depressed into the water.
2) In response, the starboard hull and port hull rotate about about the boat's overall centerline. They do not move relative to each other.
3) There are absolutely no structural loads on the bows other than tension from the forestay, attempting to pull the bows toward each other (they don't move). All movement of one bow (the port one in the picture) is carried through the connective beams (aft) to the other bow via the hulls.

This picture shows exactly what I was talking about. It would appear they use a system of small cables to carry the forestay loads to the bows of this boat.

Again, the aluminum beam and seagull striker across the bows of catamarans do nothing but take the forestay load.

I would look at composite chainplates for your answer... same thing. Just copy those.

 

It seems your observational skills are so advanced, why not propose an actual size, thickness/layout and material for Ismotorpsort's tang?

 

That I would indeed like to see... Perhaps someone could enlighten me on how the layup for such Tangs. Is it mostly uni cloth with some db mixed in and what laminate weights are used in say a 50ft catamaran crossbeam as the photos show?

 

Don't give me a hard time just because you didn't understand how a catamaran is designed and how the stresses and forces on one work.

Material is dead simple: You use glass or carbon in many layers, just like a chain plate. Actual lamination is more complex because you will need to know how much tension load is transmitted from the forestay to know how many layers to put on. It will always be a lot of layers.

Just Google composite chain plates and look at the pictures to see how it is done. It's nearly all uni and you carry the material out in a big fan pattern to allow the stress to carry into the hull and or bulkhead.

 

I’m sorry, but you misunderstand me.

I’m not giving you a hard time at all. You have clearly stated there are no loads & no movement. That is your position, fine. Doesn’t bother me one bit.

So, I could suggest that Ismotorsport simply use a bit of cheap plastic he can buy from his local hardware shop. You are so adamant that there are no loads nor movement,…so why don’t you tell him to use a bit of cheap plastic? Since a bit of cheap plastic will easily suffice in the absence of movement and loads.

What is wrong with that?

 

Adhoc and cat builder, I think it is suffice to say that both of you are knowledgeable guys by the number of posts you each have here in this forum. Cat builder was making the point that the tang mainly serves to distribute forestay loads to the hulls and adhoc was noting that there is also a benefit served by the beam to keep the hulls in line and movement limited.
No sense in arguing about that.... Would prefer to discuss how to attach tang to hull... My project calls for the tang to be incorporated to the fwd most bulkhead and not sure if the tang should taper into the entire bulkhead or just the top half? Any suggestions there?

 

Longer is better.....

 

How about laminating the striker strap to the front beam and them joining just the beam to the hulls.
You could make the beam and induce a bit of pre-bend before mounting the striker and strap
The core of the bracket could be multi-directional and then change to uni once the laminate is stretching/fanning down onto the bulkhead

 

In green is the generally consistent view that I've had expressed by a few Different NAs, it also makes the integration of the fore beam a simple bolt up arrangement. I've been on cats that were real "jelly fish" in regards to apparent "stiffness" of the platform & also really stiff "rock solid" carbon beamed machines with "no" apparent movement- these I still believe do move the bows relative- you just don't "see/feel" it.
As much I reckon the trend of composite chainplates & stanchions & even cleats integrated & faired into hull structure laminations is cool & clever & non leaking etc etc it comes at the disadvantage of being time consuming & down the track of collision damage etc might lead to much more complex repairs compared to simple bolted metal bracketing that interfaces the composite structure with good bedding & core close outs etc. Jeff.