Trying to design my own cat.

Wow, where do I start! This is all great advice. Thanks guys!!

Fanie, I like to sail with many passengers, so they will be doing most of the fiddling around...but most of the cushions are tied down and fit precisely to the deck. The 'cabin' tents have built in frames which fold open and closed, but never fully dismantle. I do want to sail at night occasionally. The sleeping tents are little more than tarpolines which are tied down firmly and touch each sleeping person's shoulder. I agree my boat is a bit 'fiddly', but that gives me something to do during the journey.

OldYachtie, after JCD mentioned the outboard boards, I started thinking about putting them on the inside, but I think it would be far more simple to put them on the outside. As far as reading a good book on yacht design....you got me. I've never read any books at all on boat design. And yes I know I should, especially for getting familiar with certain terminology. However, less than a year ago I didn't know anything at all about sailing catamarans other than the fact that they have 2 hulls and a sail. Since then the internet has provided me with a fun way to learn in my own way, rather than wading through a formiddable sea of text. I mean...hearing people's personal experiences and opinions is invaluable to me. I think it is time that I knuckled down into a good book though.

Rick (the ever-helpful), right from the start I have always wanted the boat to be all fibreglass and aluminium as much as possible. Maybe even a carbon fibre mast. Ofcourse I have a budget...so I will need to look into the cost of things. I want the boat to last a long time cos it's a lifestyle thing for me......probably the only expensive toy I will have.
As I will be getting professionals to build it, that shouldn't be a technical problem (I hope).
My rudder is crap.....great! I'll change it and learn a bit more about % aspect ratios etc. I wanted it to skim over rocks...but now I'm thinking to hell with the rocks....let it kick up.
Fuller sections at bow and stern....If you mean overhangs...I don't like the look of that. I like the simple rugged 'campercat' appearance of my boat. Am I being rediculous? How bad do you think the pitching/nose burying could be? Do you mean changing the curve of the hulls on the plan view so they are closer to eliptical?

J, I agree I shouldn't have an unstable boat, but because I am cramming a lot of people on to such a small boat, I think it will be a bit 'wobbly'. On the other hand, it does have a low centre of gravity and all those people can position themselves so the weight is used as an advantage (like you said). So the stability is not innate.....but I think it'll be safe enough. As you say, it's still evolving. You may ask..."why such a small boat for 6 to 8 people?" I did some outlines of my old 28 ft design on the lawn outside, and tried to imagine what it would feel like. It just felt too damn big. I have always liked the 'Huckleberry Finn' feeling that you get from smaller boats. And I will always want to be able to take friends without saying "maybe next time". Actually that sounds like the beginning of a disaster movie.....lol

Masalai, I'm glad you like this thread. Merry christmas


thanks to all
- Richard

 

A mast under the mast (so to speak) could also be an option for your tent...

If you would consider longer hulls they would add to stability, you can still keep the deck area the same. Friend of a friend bought a deep V ski boat recently, first fishing trip already a disaster. They took along a heavy unexperienced guy who decided to join the others at the same side resulting in an almost tip over, people falling, breaking rods... no thanks. Stability is everything. Controlling people is like herding cats, you think everyone is going to stay put on one spot ? First time someone says 'look at this' the whole bunch is going to be on one place Also, most articles hint the longer the hulls the better...

 

LOL!! (laughing out loud for real). Fanie, I was lying in bed last night thinking about the stability (hope I'm not becoming obsessed!) You're absolutely right. If I have to ask everyone onboard to do as they are told....it defeats the whole point of a holiday. I want the boat to be relaxing. People should be able to do what they like (within reason). You guys have convinced me that I'm being too stringent with my size restriction. A compromise on the Huckleberry Finn feeling is better than a drowning feeling.

I'm thinking about how I will enlarge the boat.

- Richard

 

Richard
By fullness I meant more beam up high. As you put it the deckline becomes more eliptical. The waterline would be unchanged. This would increase bouyancy in the ends and increase damping of pitching forces.

Rick W.

 

Longer hulls and more beam. Rick has a good point there. You also have to think about when mother nature calls which is important if you take females along. They like to powder their noses in a bit of privacy. They also tend to take a lot of unusefull things along like clean clothes for every day, the hulls could provide for all of this. Whenever we go anywhere I tell the wife, don't bother to set the alarm, the thieves will think they were here already there's that little left.

 

Here's my old boat and the new one courtesy of Rick's optimised 28 foot hulls (see first page in this thread). If a fat woman needs to pee, she will only just be able to slide her hips into that 20 inch wide hatch....but she will be able to pee in privacy...so that's not a problem.

Overall I much prefer the new design. Lots of bonuses (speed being the most obvious), and not too much of a compromise....cos I want the hulls to be mainly for storage anyway. In fact, oddly.....when I walked about on deck (using my 3d architecture simulator), it didn't feel much bigger at all, because the hulls don't seem to be very dominant visually. The deck space is exactly the same size as the old boat. The new BOA is 15 feet.

Looks a bit meaner.....but that's okay

 

Looking good squire. If you're happy that is good

Seasons salutations and may your new year offer good sailing in fair weather and happy adventures.

 

Thanks Masalai.
It is looking like a wave piercer now. Maybe I should still make the hulls fuller at the ends. I don't think wave piercing is ideal on a cruiser. However its speed should be capped at about 8 knots, so maybe it won't pierce??? Or at that speed maybe piercing is good.....smoother ride?

Do I need to use a VPP to predict the bows tendency to dive and recover?

Note: the pics are done with software that does not draw accurate curves.

From bow to stern, the deckline is 30 inches from the waterline. I think thats a lot of reserve buoyancy, but after what JCD said about windage, I might need to lower that a little.

If anyone wants to comment on this new design...that would be great. I havent done a proper rendering in Freeship yet.
If anyone is getting annoyed because I'm asking instead of reading....I can understand that....but I am lazy....and you guys are very informative. Your comments are like turbo-chargers.


- Richard

 

Don't ask me I get others to do that if I can. non-compus-mentus in that area (freeship etc).

Just a little flare near the bows to allow some rounding to soften the "harsh" look. Then I suppose needs "balancing" look for stern. That is where I like pencil. it is easy to draw lines, step back (like an artist) to check the look/feel. All the technical stuff I presume is done so do not change that, I understand you are after a prettier look now.

The flare and rounding should look after reserve boyancy. From earlier posts a wet ride is not the objective.

Don't loose the current stage and redefine the area above waterline to let everyone express a view. So Far so Good. Well ahead of me.

 

Rick, I have read that 2 propellers is better than one, for catamarans: better steering and you have a reserve if one fails. But electric motors are so reliable that I think the rules could change? In my case, would just one motor and prop be more efficient on power? Mind you....2 would be nice for a tidy installation.

 

Masalai, I was asking everyone

 

Richard
I think you could do a lot more with this boat that would make it more practical with just a little added cost.

The attached image has a few ideas. The colour is not one of the ideas. The hulls are based on the original hulls provided.

With some attention to detail you could get 4 bunks in the hulls and two in the bridge. The hulls have 5ft of height at the bridge so room to stoop about to climb into bunks.

There are other things I would do but it all takes work to think about.

The boat is very close in proportions to a model I made. My model was self-righting and was fun to sail. It was the best sailing model I have made. It is fun to sail a cat that has no limits at least with radio control.

Rick W.

 

Sorry about that Richard, I had to take mum out and a bit of a rush etc. Just banged out my thoughts without editing etc. If it was a solo thing I am sure I would have got a PM (to tell me off etc?)

 

Richard
The biggest cat I have actually sailed on is a 24 footer. They do not turn as well as a monohull. Some of the small ones will not tack without a jib.

Point is if you intend to work in tight spaces they are more difficult to postion under sail than a monohull. If you have propulsion in both hulls you can turn the boat in its own length.

Also a centrally mounted prop has to be deep to avoid ventilating. With your high clearance it would be a challenging installation for a mid-mounted motor.

You would get a slightly higher efficiency with a single prop but I think you would regret not having the better low speed steering of two motors.

Rick W.

 

No problem Masalai...what you say makes sense. The technical stuff is not all done, but because the cat is looking more typical in proportions, I don't think it will be rocket science to balance the rig to fit the hulls (when that time comes).