Catamaran Hull Construction Questions

I was thinking about the above layers for the hull of the catamaran.....

• All foam mentioned in the exterior skin would be Corecell Foam considering it's economical price. Is there any material you would use instead? and why?
• What layers of this cross-section would you add or remove? And why?
• What thicknesses of each layer would you recommend, and why?
• What thickness is sufficient for fiberglass exterior skin? that can be fared, sanded, etc.?
• I was thinking about adding corecell foam between each stringer to add bouyancy/safety flotation. What are your recommendations?

What is the Best Material to bond fiberglass with marine grade lumber?

 

It depends on the overall structure. However, for composite sandwich construction there shouldn't be any need for ribs (frames).

 

I should have mentioned this when originally posting........the hulls will be pointed on both ends, forward and aft (like the typical bows of a catamaran hull). They will be roughly 60 feet long, 8 feet above the waterline, and 8 to 10 feet wide, at their widest points. The hulls will support short (16 feet) masts on each end (forward and aft). They may see unusual torsion due to the masts.

My plans included ribs placed every 36 inches, as redundant bulkheads to compensate for the torsion stresses caused by the masts. Each rib is made from a 3inch foam core, sandwhiched between 1/4 inch -- 1/2 inch marine plywood (depending where they are located longitudinally along the hulls). After construction, the ribs would be cut internally to accomodate living arrangements.

Thanks much for the replies!

 

If you are using foam core, there is no need for plywood. However, to get a laminate schedule, the whole boat, beams, deck, etc. has to be engineered as a whole structure. There is no proper answer to your question as posted.

 

Not to sound ingnorant, heh! But what would be the best way to approach this?? Should I start a new thread asking.....if anyone be willing/able to help me put together a laminate schedule for my experimental catamaran project? I can provide drawings, dimensions, and answer most questions.....

 

Since when is Corecell economical
... it's one of the most expensive foams!

 

That is something you cannot get free from a forum like this. That is design and will cost you money. If you ask a specific question about design, maybe the knowledgeable members would be able to answer your Q.

Your basic design idea is flawed. I suggest you refresh yourself and read something simple about how to put it together. ISO 12215-5 perhaps would guide you the proper way.

 

I would estimate about three weeks of work for a design that is not too "experimental". That means it is relatively normal in shape and dimensions. You could find a smaller design office to charge about $140/hr., which would bring the cost to about $18,000. That wouldn't include any interior details or rigging. If the design is truly experimental and outside the norm, the cost may triple. Unless your budget is large (it may be), using a stock design with minor modifications is a better option.

 

Thank you, Gonzo, for the information. That gives me a good idea. I'm going to have to get someone to fund this (sponsor). I think the design has merrit. Can anyone tell me specifically what information needs to be in the "Laminate Schedule". Thanks, so much.

 

The laminate schedule is generated by the whole engineering of the design. Once you have calculated all the forces, deflections, etc. the laminate schedule is calculated. It is one of the last sections of the design. As a analogous to designing a floor on a storage room. You wouldn't start by designing the floor joist, but by calculating the static and dynamic loads. The joists are then calculated for those loads. A boat is much more complicated, but follows the same process.

 

Complicated, yes. I am seeing that. Wow. Getting started by calculating the loads sounds good though.

 

One of the first things that you should estimate (not calculate) is the weight of your boat and for this it is essential to have calculated the scantlings. So, the scantlings are in the first steps of the design spiral. And I have not seen anyone, in my life, calculate the deflections before calculating the scantlings. Moreover, I think it is not possible to do it because, if you do not know the dimensions of, say, a beam, how are you going to calculate its deflection?
Before calculating the loads, define how the structure will be, that is, the elements that it will have, although you still do not know the dimensions of each element.

 

I have a very good idea of the vessel's dimensions already, I am currently undergoing the process of designing the vessel in my 3D software. I will post images of the 3D model when completed. The images will also show cut-away sections revealing the scantlings. I'll do my best. It may take another week or two, but I'll post here when the design is drawn out.

To help me with the 3D model, what elements do I need to include in the scantlings besides, bulkheads, ribs, stringers, foam cores, and fiberglass layers?
Thank you!!!

 

If I were in your place, first of all, would do a very detailed SOR and a General Arrangement plan to check that there is enough space on the boat for all the equipment, people, etc. that the boat must carry. Then I would make a body lines plan and then, if you want to dazzle friends, it would make a nice 3D render, although to move forward is still not necessary.
Excuse me if I am not very positive because I am afraid that you need a lot more help than that from this forum can be given. Then, a piece of advice, carefully analyze the recommendations that we can give you because may be some of them can waste your time and increase your doubts.

 

Sounds like a lot of money for the estimate. I used to work at an overseas international engineering office and we charge about USD 50/hour. Takes me a day to get the scantlings right and about a week to do a full 60 pages of composite analysis for a Classed design. ACAD drawings cost less but takes longer.