28' sail cat

Hi all,
I have been reading this forum for about a month now. A few months ago I got this crazy idea of owning a cat. A cruise cat.
I am thinking of designing my own. Budget is of the utmost importance, so buying plans is something I would prefer to avoid.
I am pretty good with my hands. I have built a pirogue out of 6mm okoume ply and also have epoxy-glassed a mayflower. So any kind of manual labor does not scare me. I have an engineering background, so I can probably overcome a lot of the design / construction problems that might come up.
The time frame I give myself for this cat is about 5 years. One year to design it and four to build it. If situation stays as is today, I will be working most weekends and maybe some afternoons. If things go worse than they are now with the economy, I will have all the time to myself to work 24/7 If business picks up, I will not have time to build it or even sail it.
Second pair of hands might be available on demand.
There are a lot of issues with the construction site that I will have to solve too, if I finally decide to build it.

Anyway, I am starting this thread as means of posting progress and attracting feedback positive or negative, all is welcome (preferably positive), as I have seen posts by people in here that know their stuff.

OK, wish me luck.

 

First great big discussion / decision:
FOAM vs PLY

I have not been able to get any prices of foam cored composites on the net, but I guess good stuff goes for steep prices. I am much more confident about working with wood, and I can get plywood in Greece. Either plywood or foam core would be both imported, as the only thing we actually produce in Greece is deficit... and dreams of sailing cats...

Performance is not the main thing about this cat, so if foam core was to cost me twice as much, then its out the window. If I was to finally use plywood I would go for okoume, as it is pretty cheap (of the marine plies), very light (450kg/m3 @ 10% moisture), and average to good mechanical properties. I have used it and I like this stuff.

 

Hi mihari,

Let me start by pointing out that the cost of stock plans is a very tiny component of the final price of a boat. Like, one percent or so. If the cost of plans will break the bank, well, sorry, you can't afford a boat that big. On the other hand, designing a 28 foot cat from scratch could take hundreds of hours. And it is a well known constant that the first build- the prototype- of any new design is always more labour-intensive (thus more expensive) than those that follow; the bugs get worked out of the build process once it's been done once or twice.

If your goal is to test your own skills as a designer, then by all means, go this route. But if your goal is to build and sail, a proven set of stock plans will bring with it a community of other builders and the knowledge that the boat will work as intended.

As for materials- Fancy high-tech stuff isn't much use if you can't get it locally. Once you've narrowed down your hunt for plans to a few designs that seem to suit you, the issue of materials can be addressed in more detail.

Happy hunting.

 

get some plans. wharram for romance, woods for practical are my favorites.

seriously, the time you save in not scratching your head will pay for the plans. and you can be sure it will sail to spec when you're done.

if you must have the ego hit of 'all yer own work', go for simple, then simplify and simplicate. the resulting boat wont be a symphony of intricate wordwork, but it will get done.

 

Suggest you check out Bernd Kohlers KD 860 for inspiration. Plans are reasonably priced too.
http://www.ikarus342000.com/P86page2.htm

 

I have just received a full sett of plans for my 28'tri by HARTLEY . worked out approx £50. so for the price of 1.5 sheets of ply is not even worth considering. I would think you will waiste more than that just by building a bit, having an Ouzo,returning and thinking "Yikkeeees thats horrible"Like every one else has stated if its to be "your own design" etc etc then fine.

Kim

 

Thank you all for the replies, I hope you all keep up and more of the forum members come in and pitch in.

Marshmat, I understand your concern. I think of this project as a combination of 2 major ones. The first one being the design part, I was hoping to turn this into a forum wide project, with everyone giving their two cents worth of advice. Eventually the plans would be available for everyone to use... since I am not into the ship building business.

bill broome, I am not the romantic type, so wharram is out. Out of the Woods plans, the saggita is the closest to my liking. When I first started dreaming about my cat, I had a shuttleworth 28' in mind, with the modification of an added saloon. The hull sections are also pretty similar.

jamez, kd 860 is not what I was looking for. Thanx for posting that.

kim s, that sounds like a bargain. Too bad hartley doesn't have any cats. The only inquiry I dared make was for a 45' cat and the plans were for AU$8000. That scared me away, and I have not asked for a price again.

 

Do yourself a favor buy some plans !

A project like this is too big , time consuming and expensive to gamble
on. Not to mention your life and resale value... They don`t have to cost $ 8000.00

Really , do yourself a favor.......

 

So, going on from here, I also agree that plywood is the solution for me. Woods likes it and uses 9mm plywood sheets for most of his structural parts, only rarely 12mm, as opposed to shuttleworth that seems to prefer composite construction.

I am convinced of a circular section bottom hull (as opposed to flat bottom) mainly for performance reasons. It is a lot safer, as it can slide down a sloping wave a lot easier than a hard chined hull. It also yields better maneuverability.

For the same reasons keels are out of the question. Daggerboards and pick up rudders are essential to bringing it close to a sandy beach. But that is a discussion to follow.

Instead of strip planking with softwood, I was thinking to make strips out of plywood to accommodate the round hull shape. Plywood is much more predictable than stripped wood with properties that are homogeneous throughout. Other than that, the same construction method will be followed. Is there anyone opposing to that?

 

OK, I get it. No one would dare building something that big without sharing the risk with the naval architect. But I do have some time to spare, and I would like to see this design project through. Even if it stays at that. In the beginning of this thread I said (I think) that I give myself 1 year to design this boat, and then I will decide if I will build it or not.

So think of this as a "What if" project. I think that the knowledge in this forum, if accumulated, is more than adequate to bring this boat to final drawings.

 

In your second post you said performance was not a main concern, then in post 9 that you would choose a round bilge design over a flat bottom for 'performance reasons'. What sort of performance differences do you think there would be?

I mentioned the KD86o because I think it gives a good compromise between simplicity, cost, accomodation and likely performance. An alternative would be the more proven Woods Gypsy. Another flat bottom design, although it does have an option to increase costs by building the bottoms round bilge in cedar strip. Dagger boards are another option too.

It is not my intent to sound patronising but from the content of your posts I can't help wonder where your information comes from. I would suggest you read widely on boat design, boatbuilding, look at a few sets of plans and get some sailing experience on multihulls before you attempt to design one, rather than expecting the members here to do it for you.

 

jamez, thanx for taking the time to respond to this thread.
Performance still remains of lesser concern, since it is going to be a family cruiser. I think, from what I' ve read so far (and I am still reading), that hard chined hulls are:
1. more difficult to turn
2. easier to flip over while sailing in severe weather

I am sorry if you think that I have taken lightly your suggestion for the kd860 but It seems to me that the layout is not for me. That cross section of the hulls does not convince me as being strucurally the strongest around. Just from the structural point of view, a straight section is expected to bend when a point load is applied to it, where as a semicircular load will just distribute the load. So in my humble and vague opinion, I think a round bilge is structurally more stable than its hard chined counterpart.

(Please excuse my poor use of marine and engineering english, and be forgiving. Feel free to laugh and correct me also. I am here to learn...)

I don't think that a round bilge would raise the cost of the boat that much. It would definitelly spread the time frame that it needs to be built.

I never said that I am an expert in anything. I am reading all the time (only that I have only recently started). I don't expect anyone to do anything for me that they don't want to. Please, anyone who reads this thread, feel free not to post any replies.

You are right on one thing: the only sailing experience I have had on a cat was a day cruise with a 35' cruiser around an island. I loved it. Also a couple of hours sailing a tornado.

 

Hard chine cross sections etc...

You are probably aware of the Richard woods article here :



http://wzus1.ask.reference.com/r?t=...tp://www.sailingcatamarans.com/hullshapes.htm


I would bet a large bucket of gold that the difference between a well designed multichine cat versus round bilge would not be apparent on a cruising cat given equal size , weight , displacement , sail area etc .

 

boat fan, thanks for posting that!!! I get marine smarter everyday, and that is also thanks to you.

No, I had not read that article before. According to that article, all hull shapes that are shown there (except the deep V hull) are of simillar behaviour. If that is so, then why does he use the knucled U shape hull only for his larger/newer designs? Is it a marketing thing? Is it because they are so hard to build that it is too much hustle for the e-z build gipsy that would otherwise take 1200 hours to build, with an implied U hull the build time would rise to 1800? Is it the expense factor (I don't think it would be much more expensive) that it makes it appropriate only for the longer hulls, as it would be a smaller percentage price rise compared to that of a chine hulled cat?

 

.


You can gain lots of extra internal volume for galleys double bunks etc....

On some boats you cannot get decent widths for double bunks ( take a look at a wharram for example they tend to have tight berths , even at 38 ft or longer...a direct consequence of hull shape..)

On the smaller hulls you cannot fit doubles anyway , best to stick to single berths or put doubles inboard on the bridgedeck