Lamination Schedule

If you have any engineering background or are good at maths then read Larsson and Eliasson, Principles of Yacht Design (it's in the book store here). Its about yacht design, and doesnt go into cats but gives some procedure and explanation about structural design. I would suggest its just a primer for someone with a good engineering background that understands material properties, forces and at least basic stress analysis.

You could also peruse the multitude of threads here by "catbuilder". There is all sorts of debate about various layups though some of what is posted in reply is unqualified opinion and could consume many hours of reading time. Among all of that are some usefull lessons for the prospective amateur builder.

Once you get beyond the scoping stage one of the good folk here who design boats for a living could no doubt turn your ideas into a useable set of plans for a reasonable fee which will give you lines, laminate schedules etc so you have a craft that is the right shape, the right weight and has a good chance of resale.

 

it annoys me that this forum sometimes seems more like a fishing ground for naval architects trolling for customers rather than a learning resource... many people come here because they want to "do it themselves" rather than pay someone to do it for them - which is all this bloke is looking for...

Now whilst the rest of you are correct on engineering a laminate schedule should be carefully calculated and so on, not one piece of help has been given other than "go and pay someone" with the single exception of JRD`s post.

So ill offer what i can in the limited nature of the info we have been given - "its a 50ft CAT"...

Sailing cats (and powercats) have to be built light or they do not perform well. This reinforces what the others have said as ideally it should be engineered well for this reason and not over built where it turns out too heavy. If you use good quality materials, this isnt hard to acheive but avoid trying to do it with cheaper, heavier materials or you will end up with a slow, worthless junk cat that doesnt sail well.

So we will assume your looking for a composite PVC foam core or end grain balsa sandwich construction of around 1/2" - 5/8", 12-15mm thickness? You will be looking at Core density ranges of 80-155kg/m^3 roughly.

The skins of the hull can be quite thin, some sailing cats are built with only 600-800gsm fibreglass on the outer skins if high a performance very lightweight, racing type fast boat is what your looking for.... of course they get punctured easily if you hit something and they are generally fragile of you knock them around but they are strong enough to take the ocean in - just dont hit anything...otherwise a more typical hull skin laminate of a cruising cat would more like 1500-2000gsm of glass on the outside skins, slightly less on the inside skins around 1200-1500gsm. Its important to use stitched cloths rather than wovens or CSM (other than for a print layer) as its stronger, and has better fibre weight ratio... 2 layers of 750gsm triax is a good option thats also reasonably cheap and you might add a 200gsm woven cloth to the outside for easier fairing and less print...

The typical bulkheads and hull stiffeners are generally built from the same laminate as the inside skin, so around 1200gsm both sides will be plenty in a typical cruising cat, extra 300gr UNI cloth is wrapped around the edges of openings that you walk thru in the hulls.

Its the main connective bulkheads that join the hulls together and take all the concentrated sailing loads that need to be much stronger than the hull skins and std bulkheads/stiffeners. Now this all depends on the size and weight of the boat, size of the rig etc and most of these loads are dynamic anyway so engineering them is only a very careful estimation regardless of how many mathematical formulas you run, what type of safety margin you allow etc etc... there are many successful cat builders and designers that have used trial and error to know what was strong enough and what wasnt and i see this as perfectly fine as yacht engineering never has been an exact science anyway and still isnt....

What you can do here is look at other similar boats of the type you're looking for and ask people who are building them how much of what they are using where in the chainplates, mast bulkheads etc... basically lots of unidirectional fibre and you lay it up to make giant I-beams that join the hulls together and the chainplates are built into the bulkheads like giant straps to hold the rigging down. You can see in detail what im talking about in places like this --> http://buildacat.com/bblog.html

Theres plenty of info out there, and try to talk to as many people that have built or are building good quality cats, you will start to see a pattern on what is required where, and you can then decide whether you go for the lighter build for better performance or a heavier build for safety and longevity depending on whats most important to you and where you will be sailing.

Good luck

 

Lam Scheds

Great stuff Groper and many thanks, I now have something I can really get my teeth into.