JOY

Kuai Lei

This is Kuai Lei, at my mooring in Ladysmith Harbour. She is my iteration of a chinese junk. Why a junk you might well ask . I like the look of them and the ease of hoisting and reefing sail. How and why did I design her the way I did?

Kuai Lei is a cross between long micro and a chinese junk. I found a picture on the Cheap Pages of a junk hull that showed a large sliding rudder balancing a large dagger board

which was fitted just ahead the mast. In another picture, on another site, the dagger board was again forward of the main mast, between that and the forward mast. So I thought why not? No keel to get in the way when grounding and no great lumps of leeboard to knock off on the dock.

This was the first go around,

but the thought of that high stern and the forward daggerboard made me think that perhaps there just might be to much weather helm or that I might have to double the size of the rudder.

The second try was better, at least I thought so.

JimMichalak's writings had turned my mind to stitch and glue for the hull. Then I realized I had no idea how to develop the panels. All my building in the past had been the old way, frames, stem, transom then stringers. Scribing was the way to develop side and bottom planking.

Much thought ensued but I finally came up with a solution and no the web was not helpful. To test it out I got some basswood, printed the developed panels and glued the print to the basswood. I cut the panels out and made a model. Ha, it worked, what do you know about that. But then there were second thoughts. Five bucks worth of basswood is one thing four hundred dollars worth of plywood entirely another.

More indecision. So I designed a small dinghy just to test everything out

It's just a small, two sheet, pram style dinghy based on the sampan but it became my test bed and yes the panel development did work full size.

More on the design process 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.

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.

Construction Redux

Construction Redux

When we finished last we had drawn the construction profile to the gunwale and added an outline of the keel. This time we'll look at the construction plan view.

I transferred all the construction details from our previous drawing to this one.

You will notice that I've only drawn in half, why draw two things that are exactly the same? Anyway the other side is for the deck plan once we decide what sort and size of house we want.

Next we need to deal with the transom and we should draw that in detail and then transfer it to the construction plan, Once it's drawn in detail you can later add specifications. To draw you take the height of the transom off the lines plan in profile and the width at the top and bottom from the sections.

I've added a sculling notch, framing around the edges and a centreline backing block for the rudder attachment. When drawing the transom , or any other detail view for that matter you should show two views as a minimum.

The bevels cannot be taken off the lines plan as the transom is sloped 27 degrees and the sides slope outwards making a compound bevel so draw the transom as if it was square and let the builder do the bevel in situ. However having said that you can draw in the bottom to transom bevel as that is not compound and the bevel can be taken directly from the lines in profile.

Once all that is done then the transom can be added to the construction plan in plan and profile.

Now comes the question of floorboards. Are you going to have any at all? If not then it makes no sense to have a keelson as that becomes a tripping hazard, not good in a small boat. I lean toward full length floor boards which are removable for cleaning then a keelson makes sense.

Next time we'll drawn up the out board profile and then the deck plan and return to the construction plan to add those features

Stringers and wales

Stringers and wales

Hog, keel, keelson, stringer, inwale, outwale, gunwale, cap rail, rub rail, these are all longitudinal frame members which add to the stiffness of the hull. These must all be laid out in your construction drawing. The builder will then either follow your plan or do what he knows is better than what you've drawn.

In out last discussion we had laid out the frames and the stem and transom. We will now draw in the longitudinals.

Here's our salmon boat as we left it,

So first we'll draw in the chine log, this is the longitudinal that goes along the chine of our boat. Our scantling calculation tells us that this should be sided 15/16 ths and molded 1”5/16 ths so we'll round up to 1x1 3/4 and draw it in,

Now this is an internal chine log so it looks like this,

Once you've drawn in the planking you can add an external chine log to protect the plywood edge or you can specify fiberglas tape. Me, being a belt and suspenders kind of guy, I go for both.

Moving up to the head of the frame we can draw in the inner and outer wales which, with the rubbing strake and the cap rail make up the gunwale. The scantlings calculation calls for just short of 1x2 so that's what we'll use.

This just the out wale,

and is shown on the construction profile as,

The completed gunwale would look like this, What is not shown here is the planking which would be between the rubbing strake and the outwale.

It's my practice however to add a second rubbing strake so that the final gunwale would look like this, 

The little over hang acts as a drip rail and gives an edge to fasten clips for capsize lines.

The next longitudinal is the stringer. You can have internal stringers for fitting seats or just use cleats which are shorter pieces between two or three frames and you can have external stringers for nailing your plywood to. In either case I like to draw the stringer parallel to the waterline half way up the center frame and then add more if required.

This design would probably be OK as is, although I am tempted to add a second stringer above the current one to provide more strength in the bow.

Next week we'll deal with the hog and keel and planking.

Construction Plan

Construction plan

The Westlawn scantling plan is a series of calculations based upon the constant C which is derived from the length overall (LOA) and the extreme beam (EB) using the equation (sqrtLOA +EB)/16. That constant is then applied in other equations to determine the scantlings. Suffice it to say that what you get is this,

PART                                                                      SIDED                                        MOLDED
PLANK KEEL                                                      0-1-2-0                                           0-2-4-0
UPRIGHT KEEL                                                  0-2-4-0                                           0-3-1-0
STEM                                                                    0-2-1-1                                           0-3-6-0
HOG                                                                      0-0-6-1                              KEEL PLUS 2 TO 2.5 IN.
TRANSOM                                                           0-0-7-1
BENT FRAMES                                                   0-0-7-1                                            0-1-2-0
BENT FRAME SPACING                                   0-7-4-0                                            0-0-0-0
FLOOR TIMBERS                                               0-1-2-0                                            0-3-6-0
SAWN FRAMES (SIDE) HEAD                         0-0-7-1                                            0-1-7-0
HEEL                                                                    0-0-7-1                                            0-4-3-0
SAWN FRAMES (BOTTOM)                             0-0-7-1                                            0-1-7-0
SAWN FRAME SPACING                                  1-8-0-0
DECK BEAMS (UNDER WALKING AREA)    0-0-6-1                                           0-1-2-0
SINGLE PLANKING                                          0-0-5-0
DOUBLE PLANKING INNER                           0-0-2-0
DOUBLE PLANKING OUTER                          0-0-3-0
CHINE                                                                  0-0-7-1                                            0-1-4-1
SEAM BATTENS                                                 0-0-3-1                                           0-0-7-1 OR MORE
CANVAS COVERED DECK                               0-0-5-0                                           0-0-0-0
CABIN ROOF BEAMS                                        0-0-5-0                                           0-0-7-1
CABIN ROOF (NOT WALKED ON)                  0-0-3-1                                           0-1-7-0
STRIP DECK                                                        0-0-6-0                                           0-0-7-1
CABIN SIDES                                                       0-0-6-1
CLAMPS AND BILGE STRINGERS                  0-0-6-1                                           0-1-7-0
ENGINE BEDS                                                     0-2-4-0

which reads in feet-inches-eigths-sixteenths. The reason there is no molded for the engine beds is that that measurement depends on the motor.

Hang on, I can hear you say, what does sided and molded mean? Sided is width and molded is depth. Except for the hog where the opposite is true.

We now have to apply that to our design.

You'll notice that the suggested spacing here is 20 inches whereas our station spacing is 15 inches plus a bit. I like to start the spacing from station 5 so we copy our lines drawing and erase the station lines except for station 5 and draw in the frame spacing remembering that the station line at 5 is the centre of the frame at 5.

The sawn frames, which is what we're using, are sided 7/8 plus 1/16 near as all get out to an inch so we'll heft up to an inch.

You will recall that I said from here on in I would be doing all the drawing in the CAD program and here's how you do it.

At the intersection of the waterline and station 5 draw two circles, one a half inch radius and the other a 20 inch radius. The first gives you your frame siding and the second the frame spacing. Draw two parallel lines through the intersections of the 1 inch circle and the waterline, then copy those two lines to the intersection of the 20 inch radius circle and the waterline and tell the program you want 4 copies, do that in either direction and you end up with this.

You'll want to tidy the drawing up and move the frame at the bow back about 4 inches and the frame at the stern forward about the same amount to get this.

There you have your frames all laid out.

I do the stem next and then the transom and then work aft from the bow as this is how I build an actual boat.

Our scantlings show the stem as sided 2 1/8 th and molded 3 6/8 ths. This is can be easily constructed out of three pieces of 1x4 glued together with a filler piece glued to the after edge. Using this form of construction allows for a constructed knee integral with the stem. For example,

However, having said that, you can draw what you want but the builder will build it their way unless they're an absolute novice. Be prepared for questions if they are.

The transom is 7/8 ths and a sixteenth, again close to an inch, up is better than down so 1” ply for the transom. And again the built up knee for the transom. 

 

Then the bottom frames go in, sided 1”, molded 2”. From frame 5 forward, forward of the side frame and from frame 5 aft, aft of the side frame, like this,

You'll notice that I show the bottom frame at the final aft frame let through the transom knee and the one forward above the stem knee, this is the way I build it, others might do it differently, that's up to them.

Next time we'll talk about chines, gunwales and stringers.

My Old Boatshop

Weston Farmer

I was rereading my copy of Weston Farmer's book From My Old Boatshop over the week since my last post. I started out looking for a particular item, and ended up rereading the entire thing, it's a very instructive book and I would recommend it to you. If you have that and Skene's you're well on your way to understanding the fascination of small boat design. In that book Mr. Farmer states that in his experience the best riding sea boats come in at 64lbs per square foot of the waterplane, the waterplane is the plane surface where the waterline cuts the hull.

To obtain the area of the waterplane you draw the waterline onto the plan drawing by using the reverse of the process we used to draw the sections. You can then measure that area on the plan drawing and multiply it by 2 to get the area of the whole waterplane. If you're using a CAD program this is easy, else you must have a planimeter or draft in small squares and count them.

In the case of our salmon boat the area of the waterplane is 40.02 sqft and we nominally set a displacement of 2000 lbs. Divide 2000 by 40.02 and you get 49.98 lbs per sqft. Mr. Farmer opines that that would be a very lively boat. If we multiply 40.02 by 64, the per foot weight recommended by Mr. Farmer we get a displacement of 2561.28 lbs.

All this has been pretty theoretical so far. To get a better idea of the displacement as shown on the drawing we need to do a little math. I have spreadsheet that does all the math for me. All I have to do is put in the half breadths and half areas and what are those I can hear you asking?

Halfbreadth – the distance from the centerline to where the waterline cuts the hull at each section.

Half area – the area at each section encompassed by the hull below the waterline

The math is Simpsons Rule, and to read more about Mr. Simpson and his rule you need to get Mr. Farmer's book or google it.

Having plugged in all the numbers we get the following,

Displacement 913.2365 lbs, well that's not going to work so back to the drawing board, well maybe not. The calculations give us a prismatic coefficient of .53 but our earlier calculations were predicated on .66. Maybe, just maybe, our weight estimate was off.

This design is essentially a power dory and meant for a low power inboard such as the RATO 11hp, well that engine only weighs 31 Kg without oil or fuel add the oil and fuel and tops 40 kg or 88 lbs. 11Hp will push this vessel at hull speed, a little over 4kts. It is not a planing vessel there is too little bearing surface at the transom. According to this site, http://www.psychosnail.com/boatspeedcalculator.aspx we could get away with much less horsepower which would reduce the weight even further, the 6.7 hp engine only weighs 16kg plus 9kg oil and fuel 25kg or 55 lbs.

So lets review the weights.

Hull construction roughly 400

Engine and fuel( including spare gas) 75

Prop and shaft 25

Gear 150

Crew (3 adults 225lbs each) 675

Total 1175

Less 913.25

Difference 261.75

Our calculations told us that the pounds per inch immersion were 240 lbs so if we increase the draft by an inch we should be right on the money. But that's the draft over the entire vessel but we don't want the transom to be immersed so lets drop the bow by an inch keeping the same waterline and increase the draft at station 5 by 2inches then we should be alright.

By changing the draft without changing the half breadths our recalculation is much easier and the displacement worked out to 1177 lbs.

Before we stop for the day lets look again at Mr. Farmer's 64lbs per sqft of waterplane, with a waterplane of 40 sqft the displacement would be 2560 lbs we could only accomplish that by greater draft and a longer waterline. Clearly that measure is not suitable to a small open boat.

Next time - where do we go from here/

Curves of the fairer kind

Fair curves

When I was taking the Westlawn course, well worth the money by the way, all the work was done by hand as we have been discussing in the posts until now. Much cursing and erasing was needed to get the curves to fall fair. The cause of all that is the limitation of the medium. A 1/16^th pencil line on your 1/2”=1' drawing is an inch and a half in the real world hence the need for full size lofting when building.

I just want to take a moment here to dwell on the need to actually build some of the boats you're designing. A sound knowledge of how boats go together makes you a better designer. I spend a lot of time building the boat I'm designing in my head. Imagining all the joints, frames, beams and ceiling which would all surround the interior design and really determine how that design would come together.

Back to the drawing, a minute error in transferring a half breadth or height above the waterline causes a cascade of errors in the curves and you'll get a flat spot or a hard spot which has to be smoothed out by subtly changing the lines drawing. All that can be avoided to a great extent by not doing drawings by hand.

When I was about two thirds of the way through the Westlawn course I bought a new computer, it came with a bunch of bundled software one of which was a 1985 or so version of AutoCadLT. I began exploring lines drawings using this program and rapidly learned that the accuracy of the drawings increased exponentially. And with accuracy came better lines.

I used that ancient version of AutoCad for the next ten or more years. Then along came Windows 7 and that program would no longer work. So I began to hunt around for another CAD program within my budget, AutoCad being stratospheric with respect to the budget at hand. I continued to use AutoCad on an old laptop until I discovered QCad. I have been very happy with this program, primarily because it is easy to master the basics and secondarily because it allows for the importation of AutoCad drawings and lastly because it was free.

Why am I enamored by CAD? Because you can do the basic things, like drawing the grid, very quickly and accurately. You will recall in the third post we constructed the grid and I spent some time talking about having to change the spacing because 13' was not easily divisible into ten spaces. With a CAD program you don't need to worry about that. You draw your waterline and then a perpendicular line at one end, tell the program that you want a circle of 1.3 feet radius, apply that circle at the intersection of the two lines and copy the vertical line to the intersection of the circle and the waterline and tell the program that you want 10 copies. Bingo. It takes longer to tell you how to do it than to actually do it. And erasing the circle is just a key click, no muss, no fuss.

Curves are dead easy, you establish the point at the end of the bow, the low point of your sheer and the end point of the transom, click on the curve and connect the three points, voila! a fair curve.

Transferring points from plan and profile to the sections drawing is done the same way as as I described in the last post only now there is little or no room for error. A line drawn from a single point, such as the intersection of station five and the sheer in plan can be drawn accurately perpendicular to the centreline of your transfer drawing, creating an accurate intersection with the 45 degree line and an accurate line from that intersection to the baseline of the sections drawing. Again erasing all these lines takes just a key click and if you erase the wrong line you don't have to draw it again you just undo the mistake.

In the last post I ended by saying that we would discus why the curves fell fair on the first go. It's because I used my CAD program to draw the lines and two fair curves in plan and profile will naturally produce fair curves in the sections.

From here on in I will be using the CAD program to develop our other drawings in this design, however everything I tell you can be done by hand just more slowly.

Next week – what are those other drawings?

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.