CSC 30 Catamaran- the coastal passage

That is good to hear about the beams. That's a lot better than the pictures on the designer's page would lead one to believe. Much more like the wooden beams I've seen on other boats.

Thanks for clearing that up.

I'd also have to agree with the wood vs foam/glass comments above.

 

bridgedeck clearance

Here's a link to an evaluation of the consensus on bridgedeck clearance by a number of catamaran designers.

http://www.multihulldynamics.com/news_article.asp?articleID=204

 

That's a good link.

It should also be noted that the dynamic buoyancy of the hulls plays a factor in slamming a bridgedeck. Also that seamanship can keep even the lowest clearance from pounding. Heavy chop is most likely to cause problems, as opposed to large seas, as is going to windward or motoring directly into chop.

To stop slamming, alter your course.

 

Thats an interesting summary of standards (opinions?), thank you for providing it. There have already been several threads of messages about bridgedeck clearance and I am not sure this is the right point from which to start another one. You can find the older threads by searching for 'bridge deck clearance' with the search facility provided by this forum.

I notice that only two out of the seven 'standards' listed give minimum bridgedeck clearance as a function of other boat dimensions. I would expect mimum bridgedeck clearance to be a function of at least the spacing between the hull centrelines since a wider catamaran has to span larger variations in water surface height for any given wave profile. I suppose there is also the effect of the inner bow waves converging in the middle of the bridgedeck, maybe that would determine a minimum clearance for small narrow catamarans.

The design I sketched earlier this year is pictured in simplified form here:
http://www.boatdesign.net/forums/multihulls/post-your-design-ideas-37103.html
I have done a little more work on it since then, the stern view in particular now looks a bit different. The bridgedeck clearance for this 10m LOA design is drawn at 650mm, but with fairly narrow 'shelves' at 500 above the water along the inner sides of the hulls, these being to improve the accomodation within the hulls. According to the scatter graph on the above link, this clearance is significantly above average for a 10m cruising catamaran, it is also right on the trend line drawn on the graph, yet it is less than the minimum clearance stipulated by 3 of the 7standards. I wonder if some of these standards are intended for catamarans larger than 10m?

I assume that there are decimal points missing in the standards for Westlawn Institute of Marine Technology - should be 8% and 6%? Mind you, 8% of waterline beam overal (presumably measured accross the lateral outer extremities of the water surface penetration?) gives quite a low bridgedeck clearance, the 30" requirement will overide this, other than for large wide boats.

 

Hi Dean, welcome to the forum! I love seeing another Italian surname in cyberspace Post some pics of your build if you have any I would love to see how you're doing (and live vicariously through you lol).

In the pics on the coastal passage, the LAR keels appear to be just narrow, solid timber planks with no foil shape to them. I don't think they would be strong enough to dry out on or even ground on, at least from the pictures. Are you thinking of modifying that, or using a daggerboard or something for upwind work?

As for all the other posts, are there any actual examples of a boat built with non-marine plywood actually falling apart at sea? I have had plenty of failures on my exterior-grade plywood boats, but the hulls seem to be the one part that never gives any trouble (caveat- they have been relatively small boats). As far as I'm concerned, the only structural difference between marine ply and good exterior grade ply is the lack of joining and voids in the center layers of the marine stuff. Other than that the glue type and rot resistance is about the same. These center voids would be outright dangerous in a race boat, where the tolerances are so tight (ie "the perfect racing machine falls apart the moment it passes the finishing line"). But in practice, so many boats have been built of exterior grade wood but I haven't heard of any falling apart due to that fact. Let me know if I'm wrong about that please because such an example would probably change my thinking on the issue!

 

Thanks Peter for the welcome,
I guess I'll have to take some more pics of my boat to post here now that I have actually told everyone that I am building it :-} And yes the Lar Keel in the plans is just a 2x12 glued and lag bolted to the bottom of the boat. My keels will be Lar Keels but will be fatter with a foil shape. Although dagger boards would be better for sailing performance, I want this boat to be as simple to sail and handle as I can make it.
Dean

 

peter, the voids in any core material under a fibreglass or resin covering, can cause other issues besides strength concerns... The air in the voids expand and contract with temperature variations and in extreme cases, you will see bubbles form in the covering/coating. This not only ruins the surface finish near the affected area, but the constant cycling of these expansions and contractions the bubbles grow larger and causes delaminations or seperation of the epoxy/glass from the plywood or other core material. Once this happens, strength is reduced and water ingress is now much more likely thru tiny holes in the stretched surface. Voids also act like a mini set of lungs allowing it to draw a larger volume of air in and out of the core and water ingress will occur just from absorbing humidity from the air and trapping it, if the core isnt completely and perfectly sealed on all sides.

Coating wood with epoxy, i find it difficult to acheive a perfect seal, there is always a tiny pinhole somewhere...

 

After owning wooden boats for 30 years, I figured out a few years ago not to worry about it. I remember thinking a scratch would get water under the glass, and after all the stuff about the build conditions, I figured that would be the end of the world. I do think that it takes more experience than is conveyed in the average plans to figure out what details do and don't mater, but overall it is fairly resilient, and fairly easy to repair wooden boats, though I have to say all my experience is with the trailer-able boats that one can actually get after cheaply enough.

I have had a few major repairs and some minor ones. I have built with premium materials, and not so great (always good epoxy). The major ones resulted from jobs started that I could not get back to, and then water got in. This is a real problem with boats, because life often interferes and a wooden boats can't survive what some pure composites may. Often builds take longer than one would like and that also leaves a boat unprotected.

I think that wood/epoxy may not last as well as some other materials, but it sure does last longer than most builders will. I'm a big believer in building up to 30 feet at sub resale prices, so cheap it doesn't mater whether you sell or not. Designers are often brokers and can resell boats. But I couldn't get the price of a Canoe for my tri when I tried to sell it a few years back. . Good thing it didn't cost more than a Kevlar canoe to build.


http://www.youtube.com/watch?v=BnLmKXY-FCg

 

Dean, my name is Jim O'Brien I am an exile/retired from the Big Island Hawaii now living/fishing on the South China Sea the Philippines. I am also doing a day sail version CSC build for my oceansports business here. I am not yet into the build and do appreciate your input. You mention your beam has been increased to 20' in proportion what effect if any has this had on your overall length ?

 

Jim, could you give your thinking in choosing this design?

Will you take tourists out fishing on this boat, set up as a sailor?

 

What really struck me was the simplicity of the design and construction method. I would like to do the build expanded longer and with more beam. Along the same lines as the Gold Coast open deck day sailers Web site:

http://www.goldcoastyachts.com/Commercial-Sailing/CS-index.htm

Basicly a large sailing platform with on deck seating, bar area, restrooms etc. nothing fancy to write home about! Will be inspected to carry
passengers on snorkel trips to and from islands.

Very protected water here ,we are located off the South china Sea Norrthern Philippines inside the Gulf of Lingayen (same place Gen. Mc Arthurs forces landed in WW2). In fact several dive sites have WW2 war ships and artilary tanks We have 123 islands of various sizes within an area of 4 sq miles each with its own white sand beaches & lagoons much like offshore Thailand very beautiful.
Building materials are very inexpensive Epoxy / Resin / cloths / all good quality (60% less) as compaired to Hawaii / US all manufactured here in PI. Good quality marine ply (we call cigar box cedar) is available factory direct
9mm @ 600pesos per sheet Or $13.50 US good hardwoods also cheep
(bad marine ply is also availible)
Day labor carpenters 250 pesos ($5.75) per 10 hour day.

 

yup, its the construction method that caught my interest as well. Kinda like a light-bulb going off actually. How simple can it get. A couple flat panels bent over two bulkheads with a multi chine bottom on it. Looks good, obviously works, all he needed to do was improve his materials.

Basically one of the easiest forms of building I've seen yet. Kinda made me want to reevaluate my own desires to get a little silly with the cold molding thing.

 

Would probably be just as easy with foam sandwich glass panels !
RR

 

sounds expensive, I can get 32 sq ft of ply all day long for about $50 a sheet. How much are those panels your suggesting ? Ive never priced them but it sounds like it would be kinda pricey

 

And how many days to glass, fill weave, undercoat, gloss ?