Trying to design my own cat.

Rick, thanks for the pics. It's very clear to me now what you mean by 'fullness'. I'll do that to my boat (along with 2 motors).

I slept in a narrow bed once, in a Nolex 22, and hated every second of it. Bad air, and worst of all, no room to stretch my legs out. For me, the main goals have always been the following:

* great panaramic views for everyone on deck....no matter where they sit

* reasonable speed in light air (it's not windy most of the time where I'll be living).

* FULL size beds for everyone sleeping....with good ventilation

* a dry ride in choppy conditions

* good comfortable seating on deck

* most of all....the ability for everyone to socialise without disturbances (eg. people chatting with a hot drink, without healing or bending over to see someone's face.)


All other issues of practicality take a lower rank of importance for me. My friends are 'rough and ready' like me. Even the girls won't mind a tight squeeze for something so temporary as going to the toilet.

I'm sure there are heaps of things I haven't thought of, and I know you are full of good ideas Rick, and you can probably see lots of things that I can't....but at this stage I am definitely happy with where the design is at.

I've got another 2 years to think about it! (don't worry, I won't be hounding you for 2 years!)


Thanks for everyone's help so far

- Richard

 

Rick, you say it's just a hobby for you....do you have any commercial interest in boat design? Would you like to market your electric boat if it proves to be successful? Or does the business side of things bore you?

No reason for asking....just wondering

 

No commercial interest.

It will be an odd looking boat so I doubt that it will have wide appeal.

I did find this boat:
http://wolfeboats.com/
My concept is a stretched version of this so will be faster and more easily driven at speed. I am aiming to come in well under the price of this one but it is still early days. Sparky has the same motor and controller I am likely to use. I will have a more efficient prop. It still seems I will get 7.5kts with 1.5kW in calm weather.

Rick W.

 

Thanks Richard, would both you and Rick like to look at my similarly "in process stage" with my route to finals different to meet my needs (the software you guys use is not yet ported to Linux (except spreadsheets which I can use easy).

My efforts are in the member gallery. Comments are sought, PM please as I am shy. or comment on the image. I will make a thread when things move on a bit (I.E. I know where the design is going? - have a set of objectives and needs)

 

Brian
I am looking forward to a video of the model in operation. The underwater portion is almost identical to the RA_Opt that I posted earlier. Just a bit fuller in the ends because you have a higher target speed.

When do you do the first run?

Rick W.

 

Soon, possibly this Sunday.

 

Looks great to me Masalai. I don't know much about boats, I'm still learning heaps, so don't expect me to give you any educated comments! I'm still trying to understand what it is that I have designed lol.

Hmmm...do models behave like the bigger version? or do all the physics change with funny square laws (that question goes out to you and Rick in particular).

I know that models are made for testing Americas Cup boats in wind tunnels etc. I think my boat would be simple(r) to build as a model. (well....maybe not. I've never done it before). It looks like a lot of work.

- Richard

 

Modelling has its own issues, converting model performance to "full size" is still a mystery to me. but I am more comfortable with something to touch.

I may put my relevant PM's on the forum for those wishing to review my processes LATER. I paid for mine to be done. materials not cheap and still overweight (wanted 6.5kg came in at 10kg) for a tenth scale model.

Thanks for your interest.

 

Richard
The model provides a good deal of information.

If you have a reliable performance prediction method then you can do comparitive analysis as long as the wave regime (Froude Number) is in the ballpark. You need to take into account all the scaling factors though. Basically what I am saying is that if you can accurately predict the performance of the model then you can also accurately predict the performance at full scale. There are some difficult to scale elements like breaking waves but these are not a serious issue with efficient hulls.

If the model does not perform as predicted then you need to narrow down the causes. Often this is appendage drag that gets forgotten about when you do the initial prediction and it typically needs to be allowed for. Could be surface roughness, etc.

Sailing balance can be directly scaled. If the model balances well then the full size will behave similarly. You can observe how stiff the boat will be. How well it points and so on.

The model also enables better appreciation of the 3D space. Layout of drives, steering, rig etc.

A model can help you work out how the full size boat can be built most efficiently.

So my personal view is that models are very useful and the bigger the better.

All my pedal boats have been models aimed at understanding hydrodynamics and I have learnt some things about hydrostatics I did not know before I started.

Rick W.

 

Okay, Masalai, I hope you do.

Cheers Rick...it sounds like a good excuse for having some fun. I imagine those little sails could be a headache though. Can you buy model spare parts, like complete mini sail rigs that just fit on to your home-made hulls?

Rick, would it take much time for you to send me the Godzilla optimised 28 ft hulls as a .fbm file so I can do a really good rendering of my design in Freeship? If it's not too much hassle, that would be awesome. I'll get Michlet soon.

- Richard

 

Here is the original Michlet output and the Opt.fbm that I have done the deck on. So you can choose whether you start from scratch or just cut out the bits you do not want from the fbm.

 

Far out Rick, how helpful can a person be! This is GREAT! There's no need for me to start from scratch. As you say, it's similar to my design. Thank you VERY much for being such a big help, yet again.

Richard

 

Richard, check out the model racing clubs in your area, there is a special fabric/plastic used for sails.

Batons are applied rather than inserted in pockets and sheets are all adjusted by r/c but rigging and lots of other adjustments are made on land.

Easier that way. Enjoy the r/c model sailing!

I may join the club that is helping me. It is mainly social sailing/realistic models, power too. Also a group of younger members who race their electric powered speedsters.

 

Richard Atkin wrote "I am an absolute amateur but I am designing my own catamaran as much as I can (admittedly I will get it checked over by people with more experience)."

Later he says "I don't want to do any building. I think this part of the process is best left to people with a lot of experience."

Now I will probably annoy a lot of people (but I find that is easy to do when I speak my mind) when I say that I find it strange that Richard is prepared to design his own boat but not build it. It always seems to me that visulising the shapes and strengths of boats is much easier when you are building them than when designing them.

Having said that, who does Richard plan to use to "check over" the design and give it the OK?

For that matter which professional boatbuilder will be prepared to build an amateur designed boat even if very full working drawings are provided. (So far all we have seen are some rough sketches. As a guide I would expect working drawings for a one off 28ft catamaran to take me 500 hours to draw, once I had decided on the final concept. I would assume that someone who hasn't spent 30 years designing catamarans will take much longer).

And who will be responsible if the resulting boat either doesn't have the performance, seakindliness or basic strength/seaworthiness that Richard expects? The builder?? The ones who gave the OK??

I have designed and sold more small catamarans than most, so might well be on a list of those suitably qualified to assess Richard's catamaran. But I wouldn't do it, if nothing else because of the potential liability problems. James Wharram would be another very experienced designer one might use to assess a design, but I am sure he would say the same as me.

Just something that needs thinking about soon.

Best wishes

Richard Woods of Woods Designs

www.sailingcatamarans.com

 

Richard Woods (to differentiate from other Richards - a popular name here?),
I am pursuing a similar path, essentially, my objective is to understand the lines for sailing comfort, accommodation, load carrying capacity for personal use and needs. I would like to use Kanga or Robin, as it was their efforts that inspired me to try and meet my particular needs/application, because I recognise there are engineering issues and build experience issues Professionals best understand and incorporate into the design for professional build. I guess Richard is following a similar track.