CONCEPTS!

The concepts the thing

Practice safe design: Use a concept.

Petrula Vrontikis

So what was the concept for Kuai Lei? What I wanted was a small boat capable of carrying me around the Gulf Islands and possibly doing an overnight. As I mentioned last time it all started with this.

If you compare the sweep of the sheer in the above picture and the sheer of Kuai Lei here you'll see that they're almost the same. Further inspiration came from Jonque de Plaisance. The JRA magazine which featured Kuai Lei erroneously said that the sheer came from Jonque de Plaisance when in fact it came from this old picture.

With the sheer determined then came the question of square or round boat. The Jonques are round but I'm a fan of Phil Bolger so square was it.

Next question - how big? She need to be trailerable so nothing much over twenty feet. In fact she's twenty feet LOA but only 12 feet on the waterline not including the deadwood. From the stern post to the leading edge of the daggerboard she's 15 feet.

I wanted a small cabin long enough to sleep in with sitting head room and a large cockpit so essentially she was to be divided into two spaces.

So we had a concept, now came the work of actually designing the boat.

First came the lines.

Then once that was done it was on to what cabin height, what sail configuration. Should the masts be canted forwards as on most junks, can we cant the mast forward even if we wanted to? All design questions that need to be answered.

First and foremost form must match function. Lets look at cabin height. I'm 5'6 and a half (I used to be 5'7” but you shrink with age), the height of the sheer at midships is just short of three feet so another three feet on top of that would give me standing headroom but the boat would look clunky and boxy. At most another foot would be suitable. But taking that height out to the gunwale would also produce a boxy look.

Here is the main bulkhead as drawn and as built,

The left side is as drawn, the right side as built (the builder always knows better than the designer). The height to the top of the hatch is just over 4 feet which means that you cannot have sitting headroom except at the centre line. Them's the breaks.

To see what I mean by boxy, here's the bow of the boat as designed,

And here it is with the cabin taken to the gunwale without any slope.

Ugly ain't it?

We'll explore this concept thing some more next time.

A Rose is a Rose or maybe not

The Eye of the Beholder

Every boat is beautiful to its owner, you won't find anyone who will admit that their boat is a dog but what is beautiful to one eye is not to another.

If you're designing for yourself this little problem isn't a problem but if you're designing for someone else then it can be.

PhilBolger designed some very square boats, I happen to think that they are beautiful because they meet the design purpose. Similarly JimMichalak designs squareish boats and I like the look of them too. Other people don't. So at the outset you need to find out what the client wants the boat for and what he or she thinks makes a good looking boat.

You can do this using cartoons or sketches which you can discuss with the client.

TadRoberts has a website that shows his designs and a Facebook page where he discusses various designs of his and others.

I recently entered a design contest which asked for a design for a houseboat without really setting out the parameters. What they did was ask for a design and your reasons for selecting that particular design and how you would use it.

Here is the profile that I submitted,

I like the sheer to be at its lowest about 2/3rds of the way from the bow. I think that that is very pretty even on a squareish boat.

The interior layout should also suit the client, in order to get the design started I imagined a young, somewhat penniless, couple with a small child who wanted a weekend getaway. The idea was to use the vessel as a cottage for two on a large wilderness lake and it shouldn't cost a lot to build nor be too difficult. They also wanted it to be trailerable so they could use it as a travel trailer much along the lines of Roy Schreyer's Dianes Rose.

The boat is essentially a trimaran with a large center hull for storage under the cabin and two smaller hulls for flotation with a tiny house on top. It's not meant to go fast but it is meant to be beachable. It's 24 feet by 8 foot 6 inches, which is the maximum trailerable width.

I like George Buehler's idea that a boat that's meant to be lived on should do drinks for 6, feed 4, and sleep two. So the two chairs and the sofa bed seat six for drinks, the dinette table plus one chair is room for four for lunch or dinner and the sofa bed sleeps two. Because of the small child I made the dinette table able to lower to make a small bed. There is ample play space on the foredeck and high bulwarks to keep the child on the boat and not in the water.

My wife says that if you're going to do dishes by hand then you should be able to look out the window and since part of the reason for having this boat was to take a gander at nature in the wild we have lots of windows where they count.

The toilet is a composting one to keep the non-potable tankage to grey water only and eliminate the need to do major pump outs.

Now you may think that this little square houseboat is downright ugly and you're entitled to think that but my imaginary couple don't because it meets their needs and budget.

Next time we'll look at Kuai Lei, my Chinese junk, and why I designed it the way I did.

Stability at last

The End of Stability

Work, work, work! No time for blogging until now.

Let's look at a really round bottom boat first.

So first we'll join the chines which leaves us with a trapezoid, and finding the centre of that is described here (centre already marked). If we join the centre of that line with the centre of the curve we essentially have two almost triangles and finding the centre of those is described here.

Once we have the centre of each almost triangle

We can join those centres with a line.

Where that line crosses the line join the center of the curve and the chine line is the centre of the area as both almost triangles are the same size.

We then join the two centres of area and do the math set out here and that gives us the centre of buoyancy

Again if you overlay this hull with the other two the centres of buoyancy are almost the same.

Well what about a boat with no parallel sides. That's even easier than our square boat.

You can divide the underwater area into two triangles and we already know how to find the centers there so I won't go into detail. What is most amazing is that an overlay of this dory type hull onto the other three puts the CB in almost the same place as all the others.

The only thing that is the same about the four hulls is their waterline at the beam. The dory shape is very much smaller displacement although the other three are about the same. I'm going to investigate this further and will comment on it at some later date.

Next time aesthetics or does it look good?

RMS Some More

What's the diff?

In the hull proper there isn't much difference. In the original version the bow transom was curved at the top and also curved athwartships. Working out the build for this little quirk was difficult and it may be beyond the experience of the typical backyard builder so I made the new transom flat.

In the original design the keel was a flat plate with a the keel  attached to it. This came out of a design I was toying with much earlier. Here is a picture of a model of that design. I have long since lost the actual drawings during several moves but the model remains. You can see in the picture of the bottom the space for the keel piece which is a tapered, curved and beveled 2x12. Again probably not the best design for a backyard builder. It took me quite a while to get the model right.

I am a great believer in models. When I did the design for the WoodenBoat competition I made a half model to make sure the design would come together off the paper.

In the next  picture you can see the keel piece.

The change to the keel, which adds a box to the keel was to get the flow right to the new motor which is electric versus gasoline and we'll delve further into that as we develop the design. I don't think that the box keel will be that difficult to build as long as the build method is ply or plank on frame versus stitch and glue.

My instructor at Westlawn commented that this would be a wet boat because the sides are almost up and down at the bow, he obviously hadn't spent any time looking at Phil Bolgers designs for small boats.

The short strokes

Finishing up (this one)

I have been remiss, my other work has dragged me away from this and put me behind schedule however I'm back at it and so we'll finish up.

The last thing to be done with this design is to add the finishing touches, to add to each of the drawings those things which are present in other drawings and which are relevant to a particular drawing.

So on the inboard profile we drew in the engine bearers those need to be transferred to the construction profile and to the construction plan.

To the inboard plan I added chocks at the stern for berthing lines, those need to be shown in other drawings.

Lastly it is usual to draw one or two typical construction sections and in larger designs furniture detail in this case we'll just do the mid section

You can add specifications directly to the drawings or do as Bolger did, number all the parts and draw up a specification list.

When your drawings are done you can either put them all on one big sheet or do up separate drawing sheets for each of the views.

Here' the sheet for one of my designs, Vole.

In this case I wrote a build document that specified all the parts and sizes and the building process.

Next time we'll throw a spanner in the works and have the client change his mind about what he wants.

So let's begin

Where to begin?

 In the last post I talked about deciding on a design ethic and the importance of doodling and I showed a picture of one of my early doodles. Before beginning a doodle or cartoon first decide what will you be doing with this boat you're drawing. In the case of the cartoon I showed in the last post I was very much into salmon fishing and so I was looking for a fishing boat, an ocean capable fishing boat for the Pacific Northwest above the 49th parallel. Where it rains, a lot.  So the design had to be a certain size, at least 12 feet if not longer, it had to have cover and a place to get out of the wet but also an open cockpit. It had to be ocean capable. Most importantly, for my design ethic, it had to be cheap and easy to build.

The easiest boat to build and also the cheapest is a single hard chine hull. The cheapest to operate, if not the fastest boat in the world is an inboard of low horsepower.

So there we have it  but what size. Jim Michalak, as I understand it, likes to start with a simple calculation based upon expected gross weight and the prismatic coefficient (pc). He likes a pc of about .66, that is an underwater shape of 66% of a prism of the same waterline length and below waterline beam area. So you want a boat that can carry at least three adults, 700 lbs, gear, 200 lbs, beer 12 lbs, engine 250 lbs, various odd and sundry things like propellers fuel and water tankage and pretty soon you're up to a ton total. So 2000 lbs divided by 62.5, the weight of a cubic foot of fresh water, gives a displacement volume of 32 cubic feet. Let's say we want the boat to be 16' because it fits in the garage, 32/16 gives us a midships area of 2 sqft so if the pc is 1 then an underwater area of 2 ft wide by 1ft deep would do it. However that would be a canoe not an ocean going fishing boat. Four feet wide would be better, with a draft of 6 inches.

A pc of .66 gives us an area of 1.32 sq. ft , 1.32/4 gives a draft of 4" but that is still with square sides. Now square is OK, Phil Bolger, one of my favourite designers now sadly no longer with us, designed many square boats  but in this instance we want some flare in the sides, not much but some and we want to keep the draft at 6". So we need to lose .68 sqft (2-1.32). It turns out that if we do some complicated math we need to make the bottom about 16" narrower that the beam. 16" = 1.33 ft, notice a coincidence there?

Any way that's Jim's way but he was a rocket scientist. Me , I'm more of a "if it looks good it is good" kind of guy. My way  is to decide max length, max moulded draft, and max beam at the gunwale and fly at it.

I start with the waterline in profile and decide on a waterline length let's say 14' and max draft 6" amidships, Green is the water line.

Then I sketch in the bow and transom profile and add a sheer pleasing to the eye

That sheer could be a little  higher at the transom.

 Then I sketch a midships shape that I think will give what I want, red is the centerline and blue the midships shape

From there we can play around with the cartoon some more or take it to the drawing board to refine the lines and see if it makes the grade as far as displacement.

Next week the drawing board or computer screen, take your pick. I've tried both and computer is the way to go for me. You may feel differently and we'll talk about both.