CSC 30 Catamaran- the coastal passage

Epoxy is the bees knees

Gus - it is poly that eats polystyrene foam. Epoxy can go over any foam. I do know people who have used extruded polystyrene on stern extensions which have held up well.

 

Steve W. Sorry but I'm a lot sceptical of the "each block is sealed" story with the balsa, I've cut out a lot of wet balsa from stink boats, once the water is in it travels big time. They were all poly though. Still the evidence that each block is sealed is scant. On e the boat has a few different owners drilling holes willy nilly the seals are well and truly breached.

 

The point was it only holds true for infusion. I doubt an old balsa and poly stink boat was infused. I would not believe it under usual circumstance either, but with infusion it could well be true?

 

It's possible to get great results with hand layup & contour balsa, by applying the principles on the installation guide. Particularly if bedding to core bonding/bedding adhesive with appropriate calcs to materials and application tools & well rolled & jiggled into the bedding, resin priming procedure and also resin squeegee to inner face before continuing lamination, this will pretty well get between the contour splits.
As apparent many boats/items are not built to this standard with dry unprimed core pushed with a hopeful hand into a layer of choppy then inner laminates bondline resin scavenged by core..... only takes one uncaring or untrained mug on the floor to mess it up.. the thing is every box of core used to have the instructions laying on top of the first sheet of core. Comes down to lack of knowledge or application of such right up the management chain of the builder, maybe the bean counters only care about shiny sales off the floor & early warranty issues, the big issues come later.

Not bagging infusion, just laying out that hand layup can be very effective and reliable when instaaling core materials correctly. The health benifits such as lower fumes and accidental skin contact look great.

Jeff

 

Or you can just use foam which is lighter and doesn't rot.

 

Kelsall's KSS boat building system

I'm surprised that no one has brought up this excellent reference on home building system,....developed over a long number of years by a very well known multihull sailor, Derek Kelsall

http://www.kelsall.com/TechnicalArticles/SummaryOfArticles.htm

Brian

PS: He does not utilize or recommend balsa, even though he utilizes a vacuum infusion process.

 

Polycore, Nidacore

Alternatives to balsa if you really want to avoid all possible problems that might be encountered with balsa.

Have a look thru several other discussion subjects on this forum,....just a few that I have entered:

1) http://www.boatdesign.net/forums/fiberglass-composite-boat-building/polycore-21319-2.html

2) Infusion Grade PP Core & Kelsall Method

3) http://www.boatdesign.net/forums/boat-building/steel-hulls-composite-superstructure-topsides-47349.html

 

Agreed, foam is a better choice but at least where I live balsa is less expensive, a lot easier to get and with infusion is an excellent product without the problems associated with hand laminating. I too have removed more wet balsa compost than I care to remember but it is completely different when used with infusion. I realize that if you have not actually done infusion and dissected samples it is hard to accept but if you cut off a skin and inspect it you will find that every space between blocks is filled with resin creating a vertical wall of isolation from the surrounding blocks. After previously dismissing balsa as a viable core I now would be happy to use either balsa or foam. Foam used for hulls is typically H80 (80kg/m3) or 5lbs/ft3, standard balsa is about twice that its true but balsa is also available in a lighter version which is about 6lbs/ft3, so not much different to foam, according to my baltek rep the resin uptake is less for the light balsa than it is for the standard but I have not tested it myself yet.

 

Groper mate I read every page of your build and learnt some things had a laugh a cry it was great well done. Hope now years later youve got enough enjoyment out of it for the hassle. But like when your a kid building a billy cart that takes you days and days. Even if it falls to bits in a fiery on your first ride Im sure it was all worth it. And to do the design yourself must have made you chuffed that it all works and provides you with what you wanted. by the by how did the pyramids go at stiffening the bridge now youve been user her over time? Thats one issue Im having trouble deciding on as theres so many differing opinions. But as soon as I saw your I thought now theres a good Idea. did think that alot if boats used the half PVC idea though.. Anyway Again well done.
I must say that you really really went for it in the planning stage which I loved. I don’t have the smarts for that Im just following what Ive learnt from working with boat builders years of payed work repairing dodgy jobs. And years of sailing. Then Ill transfer my carpentry to the build and we will see what happens. Even if Im left with a floating apartment at the end at the very least Ill have somewhere to live while I follow the advice of others and go out and buy a plan a do it again. Then Ill sell her for materials cost and sail away.
Cheers

 

Increase length by % right or wrong?

catsketcher cheers for info on the foam Im thinking of that as it gets really hot here and the insulation properties I reckon would help a lot. Any idea on something other then plexiglass with a very dark film on it for hatches if it lets in to much heat??

Now I hope I explain this so all can follow as I want to make sure that these calculations are checked. I just noticed that the plan is a 30 foot using 4 sheets of 2400x1200 even taking into accout scarfing the sheets itd be hard pressed to get to 30ft.
So Ive done a percentage increase for the boat as I wanted to add an extra sheet of 2400x1200 for a bigger boat in length. I am not going to take the scarf joints into account for simplicity so lets just agree that the panels will be joined with scarf joints that will reduce the length by 400mm per join 200mm per sheet. Unless you guys think this is to large on a 9mm board.
Ok so I have the correct percentage increase I worked on the assumption that I had been working with a boat 9600, now don’t start on the O you idiot its there in front of you and all that I know that already I was busy reading about other ply build and its not that big a deal as it is only now I am sitting down to nut out final design.
So I increased the 9000 by 600 which then gave me a increase of 600 / 9000 = .0666666666666 I then increased in by another 2400 which gave me an increase of 2400 / 9600 = .25 adding together at 31%. Now you may ask why didn’t I just go from 9600 to 12000. And the answer is I wanted my increase from 9600 not 9000. If I did it from 9000 the increase would have been all wrong at 33%.
Now thats My theory Im hoping that I am correct as it effects the bulk head spacing which in turn effects this and that and then the boat just drifts of to Africa by itself because its had enough. But you guys know what I mean as to how it could be bad to have this wrong.
So skipping all the in between bits I am including a diagram of the spacing of the two main bulkheads for the original and the 12000 spacing. Now if any smarty pans out there can let me know if I a fool or I need to be institutionalised please please let me know. The diagram, again a bad on is below.

 

Scarfing - 12 or 10 to 1 is fine. It can be hard to scarf in situ so you may better butting. I like butt joins on hulls sides.

As to deck hatches - you make them out of scraps, glass and foam. The edges and the radius is done in solid glass - about 3-4 layers of 600gm is fine for me and then I get a piece of foam for the middle. One player 600 each side. No pespex anywhere. Did most of my deck hatches this way. Works well. Don't make them out of ply with ply edges - did that once and replaced all of them with the glass method.

cheers

Phil

 

Gus - i think you need to slow down a bit... and lay off the rum or VB or similar...

You cant just scale up bulkhead spacings like that. As a carpenter you will know that floor joist spacings are 300-450mm depending on the flooring your laying - however have you thought about why? The reason is the stiffness of the floorboards your laying. If the floor boards are 25mm decking timber for example - yuo can get away with 450mm spacing. If they are 19mm decking boards - well now you should go down to 300mm spacing right?

The same theory applies to your boat hull. The unsupported spans of hull area are determined by the hull skin stiffness. The stiffer the hull material and thicnkess is, the further you can space the stiffening grid.

2 main properties determine stiffness - engineers call it the E and the I - which are represented in their equations to engineer the strutures they design. The 2 properties are known as modulus - the E - and the moment of inertia - the I. Sounds like mumbo jumbo but it basically means the physical properties of the material your using, the E, steel is much stiffer material than say softwood, so the E of steel is high and the E of softwood is low. The I, is all about the physical dimensions of the structure. THe main thing worth thinking about in this context is the hull material thickness - so a material with a large thickness will have a large I, and visa versa. So consider a plate aluminium hull of say 4mm, it will have a small I compared to a hull thats 25mm thick - irrespective of the material its made from - wood perhaps - the I is still much higher as the thickness is greater.

So the hull stiffening grid is determined by the type of material your using - wood, steel, fiberglass etc - and by the hull thickness. So in summary - to arrive at the same stiffness hull with the same stiffening grid, you might use a 4mm plate aluminium hull skin or to get the equal stiffness in solid fiberglass - which has a lower E than aluminium- it might have to be 8mm thick - just as an example...

So - you cant keep the hull thickness the same, and expand the stiffening grid without the hull becoming more flexible - you must keep the grid spacing the same OR increase the thickness of the hull to compensate. By how much? - this can be calculated by the methods the engineers use in their equations... funny that hey ?

Or the quick and simple way to figure it all out is to look at some well engineered boats, and use their hull thickness and stiffening grid specs for your own consideration and apply due diligence when considering them for your own boat and its intended usage

Remember - the loads the boat is designed for differ depending on a number of factors - if you wish to use others scantlings as a basis for your own design - the intended purpose, area of operation, typical speed, displacement, rigging loads and righting moment must also be comparable to your boats design criteria or the scantlings wont be valid.

 

Gus, it is for a sail boat?

you're more or less fine but need to know the mast length, the sails center of effort and place in line with the keel.
You need know the mast inclination degrees, the mast place, in this case, in top to the front bulkhead, and move the bulkhead down to the mast.

The bulkheads in the Leon's plans are 1200mm, like the plywood lenght, you need scarf the bulkheads in two sheets for a 12 meters boat.

These are some pictures about the mast near finised in this model:





Oh!! this is the aux:




The mast is wood and carbón self constructed, the cable connections may be different, for avoid wind resistance.

 

isladelobos, you have done a great job with your model!

 

More info on extention of length

Sorry I didnt explain that to well obviously. I understand the spacing ratio's in regards to span over distance. Meaning that I do understand you cant just increase the length without increase in bulkheads. I was just working on the plan as is and extending the hull length the bulkheads marked are not the only bulkheads that go in her. I was working on the assumption looking at other cats made with ply that a full of partial bulkhead would be placed every meter. As I was planning on making it stronger then it proberbly needs to be I was planning on placement of bulkheads full and partial at 850 or so giving me 14 instead of the 12. But Im going off other ply boats that seem to space there partial/full bulkheads at a spacing of 1000mm or one foe every meter of hull length.
Anyway I am building a model with the exact specs given for the hulls. And for the rear beam am going to try a boxed beam that has bulkhead shape at either end that will slot into two bulkheads that are glued together like a box ready to receive the beams. This seems to be the best method Ive seen used on a ply boat giving you a nice stiff end.
Yeah sorry after looking back at the post should have provided more detail. I'll post some pics of the standard model soon for comments. Beware its out of cardboard so I can easily make alterations as I go.

Cheers