Building is starting. Several questions in here. Answer any you like! :)

Interesting. I have also read about some catamaran builder or designer (was it Oram? Who used greased up plywood to just drag the boat out of the shed at the end.

I am thinking the female might be best because you do the deck at the same time. Seems like that might save a lot of work.

 

In the old days those were called butterboards, even before plywood, just boards greased with tallow or lard.

 

The mold/form only has to be reversed once, say you make two port halves and then two starboard. My shed walls are 4.2m high so have plenty of clearance to lift a hull from the mold and rotate while its above the mold.
If you dont have enough height you would need wider gantry frames so the rotation is done next to the mold and not over it. Gantry beams do not have to be very substantial as I am guessing that even your larger half hulls would only weigh ~500kg.

In the photo you can see that the two port halves are supported on recycled 4 x 2 attached to the shed walls. When the 3rd half thats in the mold was finished and joined with the one above, the top outer laminate was done. This joined hull was then lifted out rotated and placed down on low pads next to the mold so the other half of the outer laminate could be done.

After the final half hull was made then the very first one which is on the left of the photo was simply dragged across on some 4 x 2 that was joined up with the existing 4 x2 seen in the photo.

Many Oram boats are dragged out of their sheds on some form ply greased with liquid detergent. But these boats have a flat bottom with additional 6mm ply glued and glassed over on top of the balsa panel. They can take that kind of treatment, I would not do that with round bilge foam core hulls.

 

Last Major Question (Andrew, I had asked you privately too):

If you build a female mold and produce a couple of "half hulls", one with bulkheads already pre-installed, how do you do the layup of the joint at the keel and mid deck?

My keel has a complicated layup with structural bog and overlapping biaxial, etc... (see keel joint diagram below) How can I do this complicated internal layup if I am joining the keel together as the bulkheads are also joining at the same time?

I don't even see how you can do the inside biaxial tape joint for the deck with the bulkheads in. There must be a way...

Anyone ever seen this done?

Keel joint layup----------

 

catbuilder.
email me via website please.

Bob Oram

 

Thanks, Bob. I emailed you.

Word has it that the way to do this keel layup (and tape the halves of the decks together) is to just skip under the bulkheads.

Does anyone see a problem with that?

 

keel reinforcement

Catbuilder,
I consider continuing the keel laminates and reinforcement under the bulkheads [preferably laid down as a continous run] from end to end as crucial in fore and aft stiffness in the keel area.
Consider the loads imparted on a hull if for any reason one hull was stranded on a single rock or the like, [these things do happen in the cruising world].

My understanding of the keel reinforcement shown in the drawing [given the tri-ax glass is warp tri-ax] is that a third of the laminate runs at 0 dgs to the centreline [a uni directional beam] therefore acting as a load path fore and aft, ie spreading the keel loads along the hull and out into the ends.
If there is no reinforcement under the bulkheads then all loads are localised and the bulkheads then become the hard [fracture point] point in the load path.

If it is required to fit the bulkheads prior to reinforcing the keel area then scallop out the bottom of the bulkheads by the laminate width and approx 50mm [2"] high and pass the laminates under the bulkheads.
It will be easier with 2 people to do this.
Fit and tape the piece of bulkhead back later.

All our boats have the fore and aft tapes inside and out laid down in one length.
With the flat panel building method it is quite straightforward.
Our boats are renown for their stiffness, strength and robustness and they have landed in some awkward and less than desirable places occasionally with none or very little damage.
Best wishes with your build.
regards
Bob

 

The base laminate is under the bulkheads already so there is continuity of the 0 deg fiber on either side of the core.
The design is bringing the inner and outer laminates together along the keel line and then toping up with structural bog rather than a core.
So in my mind the question is, is the bringing of laminates together really necessary? and if you want a higher sheer strength material in there why not put in a strip of ceder as a part of planking in the first place rather than bog.

 

I am attaching some design detail improvements. Most are class standard. I have to draw in excel as I do not like copying and posting from the book.

As you can see, bulkhead joints requires scarf joints or high density core under the bulkhead. If you did not do this, a reinforcing layer can be laid up underneath to spread the load and reduce stress point. This is normally practised in high performance boat or where the bulkhead receives a lot of slamming. Note that Bob has also pointed this out.

I am also worried about your inner laminate. It is 1100 gr/m2 and you are going to butt joint it? Thats a very weak point and at the keel at that. Note that Lloyds would even require a center girder or stiffener in the keel centerline.

I have some tips on jointing two hull halves. Just plan early so you stagger the lay up at joints. Normally, joints (as they are secondary bonds, therefore weak) are laid up layer by layer. In your case, it is supposed to be a contnous layup using very heavy fibers all at once, but you are jointing two hulls. Stagger whenever you can.

 

Damn. Looks like the plot thickens. Kurt said it's OK to miss under the bulkheads because the outer laminates would take care of it.

The outer laminates (outside the bulkhead) are 4 layers of 750gsm and a keel reinforcement layer of 16" wide 600 gsm.

Did everyone notice that the laminate schedule for the entire keel goes like this, from water to bilge?

water
600 gsm biaxial - exterior keel reinforcement
750 gsm triaxial - normal exterior hull laminate
750 gsm triaxial - normal exterior hull laminate
(then hull laminates are brought together at join)
750 gsm triaxial - normal interior hull laminate
750 gsm triaxial - normal interior hull laminate
foam strip to 9" from center (probably could be wood, it doesn't matter much - filler)
Structural Bog to even it all out
2 layers of 10" wide biaxial tape lapped over each other 2/3
bilge

I have quite a bit of conflicting information now... the designer says it's OK to skip under the bulkheads because the load is in sheer. Bob Oram (another respected designer) above says it must be run under the bulkheads and provides a good way to do it. I'm going to look at RX Composite's Excel sheet in detail momentarily. Andrews says it doesn't need to be run under the bulkheads and it looks like RX Composite says it does (and gives alternatives to stagger).

I think that makes it a 2 to 2 on votes. It would seem it's something nobody agrees upon.

PS: Bulkheads are joined to the hull like the 3rd example for "Bulkhead" in RX Composite's Excel sheet.

 

Depends how the plans define the details... Like if there's "tightly" spaced floors under the cabin sole spreading the loads and joining the hull halfs together so I'd might go with Kurt and Andrew. If it's only the bulkheads then Bob and Rx.. just my 2c

 

Bulkhead jointing 1 & 2 is straight from LR design details. That is allowed for low speed vessel. Jointing number 3 is an option for bulkheads subjected to slamming. Other class rules. These are generally good design practice or improvement on existing practice. I have never come across where the keel laminate has been discontinous in way of bulkheads. In fact in steel ships, the keel is laid first, in composite, the keel is integrated into the laminate before the bulkhead is attached.

Keel laminate extent is also straight from LR. The method of joining is even more complicated but I did not have time to draw it. The bog was not mentioned in the rules but the computation for the keel thickness and breadth is fairly complex.

The drawing for joining the two halves was simplified but I can make a sketch based on the information you gave me.

 

I do not know exactly your lam schedule but based on my initial pressure calcs, pressure increases from a little after midship and judging by the shapes of your bulkheads forward, the turn on the bilge is greater than 150 degree. Meaning, the side is treated as a bottom laminate and the high density core extends far upward than the waterline.

 

Cat,

This is the layup according to what you have described. That is 4 layers of 750 gr/m2 outside of the bulkhead. Or that is the total, 2 layers reinforcement, 2 layers exterior hull lam?
Rx

 

RX: Not quite. Just scroll back up. I put the keel layup in above in a black and white diagram. Is there anything that's not clear to you in that diagram? It follows the sequence I put in words later on. The bulkhead (and more load carrying triaxial reinforcements) go on on top of all of that.

The above diagram in black and white is just the hull, just the keel layup. The bulkheads and their reinforcing additional interior triaxial strips are in addition to the keel layup. The "9 inches from center foam" is a foam filler when you pour the keel. It keeps you from wasting bog and potentially having an exotherm.