Trimaran Design Concept with longer foils than the main hull

I'm vaguely aware of his work, via articles I sometimes read. But I don't follow him or his work as a rule. If it's presented to me, via a magazine/technical paper etc...then I read it, but I don't go out of my way to follow him.

Why?

 

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Well, there was an article on his site a few years ago where he described his type of planing ama in a fair amount of detail. But it's gone now-sorry.

 

Planing Hull

Planing sure puts things into a different dimension. I like the idea of planing for recreation, and possibly for good weather sailing if the risk factor is considerably low. But right now, I think that as fun an exercise as it might be to design something cool like that - especially for a model that I could R/C, it is overwhelming for me to try to comprehend !!! Remember guys, I am new

Great idea, though, but I would not feel confident about trying planing until I have a few designs done and tested first.

As a kid, I wanted an R/C sub! I had a cheap plastic sub (non-r/c) that I bought as a kit, and I added a motor to it and stuck some vaseline on the shaft to make it repel water lol! It didn't work out very well - alas. At least I got to try it

 

You are of course right, not pedantic. I read the post fast and replied even faster.

And I agree with Adhoc re the slamming of a planing flat bottomed outrigger

Richard Woods

 

Quite a few post while I was off cruising! In part I went off to see a R/C model yacht championship. Talking to the designers made me realise they face very different problems to full size boat designers. So I'd be wary of taking too much notice of model trimarans (its been discussed here before)

Thank you for the Banshee compliments. That 35ft catamaran was designed in 1984/5 and the first was launched in 1986. It won the multihull class in the 87 AZAB, and was 1,2,4 in the YM Triangle race the following year. The first two catamarans ever to do the Fastnet race were Banshees. Many have sailed oceans, two have sailed UK to Australasia. Speeds in the high teens in flat water are common. Tacks through 80deg

It has four double cabins (two with queen size bunks, a big galley and heads. Chart table is full size

Richard Woods of Woods Designs

www.sailingcatamarans.com

 

Queen sized bunks

That is amazing that you could be queen sized bunks (plural) on board a cat and still have her be that fast and yet of a size that is still compact!

 

Parametric Hull Shapes

Okay, I am learning! I did some more research, inspired by Tom Speer's design methodologies, on Bezier Curves and how I might use them to simplify the spline process for designing transverse hull shapes. My idea is simple: to create half-breadth transverse hull shapes using a composite of two Bezier Curves that share some common control points. I think I can do this...

I just created a preliminary set up using Excel and one Cubic Bezier Curve. I got the parametric formulas from: here.

Notice that the control points in the formula correspond to the following scheme:

P0 ={a,b}, P1 = {c,d}, P2 = {e,f}, P3 = {g,h}

The formulas for X and Y, respectively, are just sums of smaller equations dealing with each point, therefore, for simplicity's sake, I created a separate column for each control point's sub-formula, and summed them into their corresponding X and Y values for each parametric value, T.

I am new to parametric equations - so when I first set this up, I was running T = 0 to 9 and I had some extremely large X and Y values. Then I recalled Tom Speer's article about his boat, Basiliscus, and I remembered that he was using a Sin function for something. I still don't understand exactly what he was doing, but I thought perhaps from having tried Microsoft's graphing software earlier today, and having watched the animation of how the T values were located on the Bezier curve graph I ran there, that values for T would make more sense if they happened to range from 1 to 0 - just like a Sin function does.

So I changed my T-values (linearly for the time being) to range from 0 to .9. I will look into the merit of using a Sin function later - especially if it can give me round values on one of my axes!

At first, I wasn't sure if I would be able to graph this properly in Excel so that I could see what the curve looked like. But after some trial and error, I discovered that the X Y Scatter Plot function will work for my purposes, and that I can add a second series to it using a single point to force it to have the same scale for both the X and Y axes. I just set the single point close to the maximum values for both X and Y, and set the X axis to show the grid for its sub units so I could make sure when I manually sized the graph that everything looked squared away properly (that the graph looked like squares - not rectangles).

I can see from Tom Speer's Basiliscus hull design how he was using control points at various places on the hull. I think he is using more than I was intending to use, but since I am still learning about this, I think I can start off by grouping two Bezier Curves together just to prove that I can do it, and from there I can graduate to more complex hull designs.

Right now, what I have doesn't really look like a feasible hull, because it is only using one Bezier curve. But I am going to post it so everyone can see what it looks like!

I think that setting up the formulas for the hull shape can simplify the other calculations because once I have the formulas set for each section of the hull shape, I should be able to use those same formulas to calculate, section by section, each length of the hull shape's curve and sum them for a total hull shape curve length which I can then use for calculating displacement, WSA, and so on and so forth.

I have never tried adding an image from my desktop before so I'll have to see how this works. But I did add it as an attachment!

 

Hull Shapes Again

So here is my question to all of you:

What are the pros and cons to the following hull shapes:

1. Conventional
2. Bell
3. Flared

?


I see Tom Speer showing these three hull shape types on his site: here.

Are these the main hull shapes that are used these days?

Are there any others?

Thanks !


PS - What I am thinking I can do is to spline together any hull shape given its control points. I believe that what I can do is use Bezier curves to create smooth splines by using the last two control points for each preceding Bezier curve as the first two for the next...

 

Boradicus,

This is where your current limited knowledge is perhaps frustrating you. There is no one perfect shape. The shape is dictated by the clients SOR and then ensuring you satisfy the SOR. Every aspect of design is a compromise simply to fulfill the SOR.

So what may be perfect or ideal as a "bell" for one client, may well be totally inappropriate for another client. And NOT because of hydrodynamic reasons.

And this is the point. Design, is a multidisciplinary process and which is why you need to learn many different subjects and, as you are doing the maximum or minimum effects of each aspect. So when you start putting a design together, you understand the implications of the SOR and its effects on hydrodynamics, the structure, the weight the cost etc etc. In essence you are juggling with many balls all at once. How you juggle them and in what order is dictated by the SOR and not by one sole objective. The more designs you do (that work and not just on paper) the better you become and trends start to emerge. Trends are the most important tool for any NA.

Not saying one objective never occurs, it does, but very rarely and such a client is also rare. Such as the fastest boat in the world...that is one SOR, or the best seakeeping in the world....one SOR. But the compromises that are required in order to satisfy the "simple" one SOR, is often far more challenging than any "standard" SOR.

 

Sor

Thanks, Ad Hoc. So what elements am I missing from my SOR that I should add that would help me to gauge the pros or cons of hull shape? I understand intuitively what you are saying. There are many parameters, and each parameter has a relationship with the other parameters such that when you design a boat you will need to nail down specific numbers and requirements in order to narrow down the scope of all those variables that are floating about.

You mention trends in design, and I am wondering, leaving considerations of passenger comfort aside, if any of these shapes (or all) conform more toward specific trends, and if so, which trends might they be, and if not, what relevant SOR considerations should I bring to bear to better comprehend the situation as the sum of its respective parts?

I know I am pretty ignorant about design, but I am doing what I can, given the present constraint being self-taught. I seem to be learning by picking away at various articles and things that I find on the net, and when texts arrive, I expect that they shall be of better use than the scattered resources I am sifting through at present :/

 

Would you have an example SOR from a multi-hull client I could look at for studying purposes or could you point me to a source that you would recommend as being good to learn about SORs? Thanks much! :^)

 

If I may interject, your Statement of Requirements is fundamentally a description of what you want, where you plan on using it, your objectives in terms of speed, comfort, work required, budget and cost of operation. It isn't a feature list, a specification of how the objectives are to be reached or even a detailed technical document.

The Naval Architect needs to know what you want - it is his/her job to determine how to reach your requirements. Placing technical criteria (like preselecting features and technology only serves to impede their process - in effect they prefer to start with a blank canvas - not one with owner-painted blotches already in place.

It is funny, but often people get caught up in a laundry list of technology and features before they actually figure out what they want to accomplish. You would be wise to first decide where you want to end up before you worry about how to get there. And remember to specify success for the real world time frame when the boat is complete - because your needs today may be very different than that you will enjoy four years from now. I speak from expensive experience on this.

--
CutOnce

 

An SOR is just a shopping list.

How fast
How long
How wide
How many passengers/berths
What hull material
What is total budget
What time scales to build/delivered by
What generator size/make
What engine size/make
Maximum fuel consumption
Range at s full speed (if powered by engines)
Propellers or waterjets..what size
What window sizes and make
What seats manufacture
What hatches
What…etc etc etc etc

The list is as long or as short as you want.

That’s it..no magic.

 

Well you might write one up yourself. You made a start in your first post

cheap
transportable
stable
30ftish

so you could add:

at least as fast as the ++++ design
I want my spouse to sail with me
I don't want to race, just have fun

and so on.

So for example 1) would rule out an all carbon boat. 2) a fully assembled boat

Then once those are agreed, you can start your design spirals. But without the SOR or if you change it then you'll never get the boat designed, let alone built.

I still think you're getting too into one facet of design. When I worked with Derek Kelsall we did try using mathematical curves, as did Hugo Myers (check him out, although he is no longer with us). But there's no point in reinventing a wheel if you've not actually seen one.

Try the freeware Delftship instead

http://www.delftship.net/delftship/index.php/delftship/delftship-free

But remember it is still only a glorified pencil. The design is the thing, not the drafting. Buying me this

http://www.sweetwater.com/store/det...g&matchtype=&gclid=COiz9ZrU2rcCFQ1xQgod2wMA9w

won't mean I can play Layla

Richard Woods of Woods Designs

www.sailingcatamarans.com

 

Sor

Thanks, Richard!

What you said about SOR makes sense - I thought that I sort of had one already - and I did, so I believe that it is not the absence of an SOR that is problematic to answering my question, but knowledge in general, that I shall obviously have to obtain by learning on my own.

Everything I have read from posts points to the the fact that designing is something that is highly individualized in terms of style. In other words, there are many ways to skin a Cat (bad pun lol) and a unique solution exists for every designer at different points throughout his or her career. Basically what this means to me is that I should try to study by a combination of learning and by practicing what I learn on the design table first, and later in models, and possibly even a real boat some day!!

Thanks to all of you guys - I understand what you are telling me to do: learn, learn, learn...