Conceptually speaking

Concepts

You are not going to find the ideal boat.
You are not even going to have it if you design it from scratch.
-Carl Lane

This is boat from the board of Tad Roberts, it was built by Barrett Faneuf, it's beautiful.

Years ago hundreds of these little launches plyed the waters of the BC coast, they were the main means of transportation mainly because there were no roads.

The reason I put this up is because in 2012 I saw a version puttering around Ladysmith harbour(it was nowhere near as good looking). So at that time  I thought that as a concept a low powered 15' plywood launch would be a great starting point.

So I drew these lines,

With that as a starting point I created the basic launch

Then added to that basic launch to make a yard boat,

Then modified the lines to produce a tug with a deeper body to allow for a heavier engine and scantlings and a horizontal prop  shaft.

The tug has a covered after deck and protection for the operator.

And then I thought what about a steam launch at which point I realized that a plywood boat would not be appropriate so I modified the lines yet again still keeping the original concept.

All that from a simple concept drawn from seeing a small launch puttering about.

Quick and not so dirty

Quick and Dirty

When I first approached this design I took the section lines of the skiff,

and simply rounded the chine corners. Then I adjusted the rounding so that the curves were parallel. I also narrowed the pram bow at the waterline to give a finer entry

I then went through the process of waterlines, buttocks and diagonals to get this,

 

Compare that to this, which is the hull we've developed over the past few weeks

 Here's a comparison of the sections side by side, the red being the lines developed from the skiff by rounding and the black being our skiff, and also superimposed.

On the face of it I can't see much difference and it was very much quicker. Our skiff is a little finer in the bows and the Q&D version has a bit more displacement, that's about it.

Now that that is done I will run some numbers on the two versions to see what difference, if any, there is.

Buttocks - not that kind!

Buttocks

Buttocks are also fairing lines and show the flow of water around the hull. Usually two buttock lines are used and are shown only on the profile as they will be straight lines in plan. They are drawn first on the sections, the blue lines,

and then the intersections transferred to the profile and then joined by curves.

You can see that we have the same hump at station 1 as we had in the diagonal. The flow aft appears good, perhaps we should have a third buttock line to better define that flow.

That third buttock shows a definite problem aft of station 5. This where the fiddly bits come in, adjusting all the lines so that they are fair to one another

Sections Redux

Sections yet again

In the last post we had drawn in the waterlines in plan now we can go back and construct the sections in the same way as we did here. The thing is here there are more intersections and instead of joining them with straight lines we join them with curves.

In the first iteration the sections look like this,

So we'll go with that as it looks good. You'll notice that I said the first iteration but now comes the tricky bit, buttocks and diagonals.

Changes yet again

The Look Astern and Other Changes

The stern on the original design was also quite complicated. It had a motor well for the outboard which could be sealed off when the motor was not fitted by a plate which was held in place by a bungee cord attached top a removable curved piece that fit into two slots in the side of the well. The space on either side of the well was for storage and flotation.

So in the new version the transom is flat across and the well is eliminated. And an electric trolling motor is fitted through a PVC tube right aft of the dead wood. The original also had a leeboard which in the new version I've traded for a centreboard.

Because all the spars had to fit into the hull for rowing they were quite short which constricted the sail area. It was about 49 sqft, a boomless standing lug sail, with sheets led to each quarter. There were no permanent stays or shrouds.

This is the new design with the old rig.

The previous design was more row, motor, sail. In the new design I wanted more emphasis on the sail and less on the motor so I increased the sail area to 80 sqft keeping the the same foot and yard as in the old sail which means that the mast is now some 17 ft tall which might require stays and shrouds. So here we have the new rig. You'll notice that the centreboard is located in exactly the same place as with the old rig. But, because of the shifted centre of effort of the sail, it is deeper.

The sheets also had to be beefed up a bit given the increase in sail area.

We'll look at the interior arrangement next time and that will determine how we can lay out the shrouds and stays or even if we need to use them.

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.

It's all about profiling

Outboard profile

The out board profile is what anyone looking at your vessel from the side will see. One of the perils of drawing outboard profiles by hand is the perspective effect caused by you looking at the profile with its top edge away from you. What appears to be a neat boat on the drawing board suddenly doesn't look all that swell when pasted up on the wall. The advantage of computer drafting is that you are already looking at the boat as it would appear on the wall.

When you are drawing the outboard profile you should include everything that you, as the designer, planned to have fitted on the boat, the builder/owner may have other ideas. So be it.

So we start with the outline of the hull as we drew it in the construction drawing. And remove any extraneous lines.

So we need to add a house. If you recall the original design called for a place to get out of the wet and an open cockpit. The design was also for up to three adults so two can be out of the wet and the other can steer. So the house should be at least half of the waterline length. And a way for those inside to see outside, a port perhaps and or a hatch. Now a comfortable seat needs to be about 15 or 16 inches high and with the same depth and minimum head room is 38 inches so the cuddy top should be some 4'6“ above the midship frame. A hatch needs to be a minimum of 2 feet square. The port can be any size or shape but should fit with the overall design. I always like a small foredeck, not that you would want to stand on it, but it gives a place for a substantial samson post forward and a small storage locker below.

So all that would look like this.

The cuddy would be open at the back for air in the cuddy and also to provide air for the engine which is air cooled. We could also decide upon a rudder at this stage.

The rudder could be transom hung or be under the boat on a rudder shaft. Because this is a small slow boat I think that a transom hung rudder would be better and fits with the type of boat.

OK you say but what about the propeller and engine. Well in this profile you can't see the engine but you're right about the propeller. The problem is you can't show the propeller until you decide the angle of the shaft and to do that you need to decide where the engine is going to go. Which brings us to the inside profile.

I lied when I said in the last post that we would do the deck plan, we really need to establish where the engine will go and what the shaft angle will be because then we can finish the outboard profile and the construction drawings for the keel.

Inboard Profile

We start with the almost completed construction profile, see why this is easier on a computer.

Then we add the cuddy that we drew on the outboard profile.The port, samson post, fore deck and some seating at the transom and in the cuddy.

Now for the engine. We have the specifications for our engine. It is 15.4 inches long, 12.6 inches wide and 13.6 inches high, the shaft height above base is 4.17 inches to the centre of the shaft. The propeller that we have is 8 inches in diameter so once we draw that in with the shaft exiting from the back edge of the keel and the propeller tip 2 inches away from the bottom of the boat, to stop thumping, we can establish a shaft angle of 5 degrees which will not interfere with the lubrication of the engine.

There is a little bit of a problem, the prop spins just a little below the keel which, if the boat takes ground, will cause damage to the prop so we'll put a skeg on the keel to protect the prop.

Now that we have established the shaft angle we can extend that back into the boat and determine where the engine will sit and draw in the engine bearers. But we have a problem, the optimal RPM for the prop is 600 RPM the engine runs optimally at 3600 RPM so we need reduction gearing. There are two ways to accomplish this, an actual reduction gear set up or v-pulleys. Given that this project is driven by cost, V-pulleys it is. A 2” steel pulley on the engine output shaft and an 8” pulley on the propellor shaft.

All of which means that the engine must be several inches above the shaft centreline probably, about a foot. There are calculators for this at http://www.gizmology.net/pulleysbelts.htm. For the purposes of this exercise we're going to place the two shafts 12” apart. Given that distance we get this,

The square box is the engine, the area under it is the engine mount, the beds should cover at least three frames to reduce vibration and strain on the hull. Covering the shaft coming into the boat is the shaft log. The concentric circles on the engine are the exhaust. We can extend the exhaust to show on the outboard profile and draw it in.

And there is the almost complete outboard profile and the almost complete inboard profile.

Outboard Profile

Inboard profile

Next time we'll finish both these drawings and move on.

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

The Tricky bit

The Tricky Bit

When we left off we had our boat in plan and profile. The job now is to see if those lines will match up in the third dimension and still have fair curves. This is done by drawing the sections.

In the cartoon the sections are drawn in the middle of the drawing about station 5 which is used to represent the centreline (CL). You can in fact draw it any where, the reason I chose that particular position was that I was doing this without most of the tools and no drawing board. So to lay off the sections I was using tick strips. You can read more about this method here (http://www.lackeysailing.com/daysailor/sidebars/tickstrip.htm)

In that application the person is using a large piece of wood as he is doing it full size, however you can use strips of paper to do the same thing on your scale drawing. In order to do this you must first draw in a waterline (WL) where you are going to put your sections drawing, in this case I put it mid way between the profile drawing and the plan.

In the following picture a small slip of paper is laid along Station 5 and ticks are made at the WL, the chine (the curve of he bottom) and the sheer.

This then transferred to the new WL and CL by lining the strip along the CL with the WL tick at the WL. Then the strip is laid out on the plan to take off the widths and the widths laid out in the same way along the WL. Lines are drawn from the ticks parallel to the WL and CL and where they intersect are the sheer and chine points. You draw lines through those points and you have a section. This is time consuming and prone to error.

There is another way. To the right, or if you prefer left, of the drawing extend the WL and draw an new CL perpendicular to the WL. Extend the plan CL to intersect with the new CL and from that intersection draw two 45 degree angles.

Then using your triangles transfer the plan and profile measurements. First the plan,

You will probably have to extend the line of the second triangle using a ruler, make a tick mark on the diagonal slide your triangle down and do the same for the chine line in plan.

Then slide your triangle along the yard stick and draw two perpendicular lines through the marks.

Now go to the profile and draw Two lines parallel to the WL from station 5 at the sheer and chine.

Join the intersections, erase all the unneeded lines and you have the half section at station 5.

Now do that for all the other stations with stations 0 to 5 on one side of the CL and 6 to 10 on the other. Draw a line parallel to the baseline from the bow to the CL. You end up with this,

And now for the tricky bit. Join the ends of the section lines at the chine and at the sheer to see if you have a fair curve. In most instances, when drawing by hand, you won't on the first try and will have to alter the lines in plan and profile to make the curves fall fair. That can be exceedingly time consuming.

Once that's done you have this,

In this case the curves fell fair on the first go and there is a reason for that, we'll discuss that next time.

More tools of the trade

More tools of the trade

In the last post I said to make a line parallel to the yardstick 6” up, that was six real world inches not scale inches and the same for the center line. All other measurements were to scale 1/2”=1'. In this post all measurements are scale unless otherwise specified.

We ended the last post with the following grid,

On this grid we will construct the lines in plan using the centerline (CL) marked in red and in profile using the waterline (WL) in green. From the cartoon we know that the proposed draft is 6”, and it appears halfway between station 5 and station 4. Measure down from the waterline 1' on stations 4 & 5. Draw a line from the intersection of the WL and station 4 to the mark on station 5 and vice versa, that will establish the point of maximum draft thusly.

Now we need to construct a fair curve from the intersection of Station 10 and WL through the point of maximum draft to the intersection of station 0 and WL.

This brings into play new tools, french curves, ship curves and splines and ducks otherwise known as spline weights. The basic drafting set contains french curves but in order to get long fair curves you really need ship curves or a spline and ducks.

A spline is a narrow sectional piece of wood or plastic which can be bent through several points to construct a curve. The spline is held in place by lead ducks,

These things are hard to find and when you do find them they are expensive. When I was doing the Westlawn course I carved two male molds and took then to a local foundry and had them cast ten for me which was way cheaper than trying to buy them, Or you can try to make them yourself, there is a good article at Duckworks on how to do this. (http://www.duckworksmagazine.com/06/howto/splineweights/index.htm)

Once you have all your ducks in a row then you can use the spline to draw the curve of the bottom.

And then remove the X from between stations 4 and 5. Which brings up another tool the eraser, get a good one you'll be using it a lot and you'll also need an eraser shield to protect the parts of your drawing you don't want erased and a drafting brush to sweep all the eraser bits off the drawing so it doesn't smudge.

Once the bottom curve is drawn turn your attention to the bow and stern. From the cartoon we know that the top of the transom is 1' aft of station 10 and 2' above WL, using dividers mark out those points.

Problem! The cartoon length over all (LOA) is 17' but we only want 16'. If we whack 1' off the LOA will we still get the sheer (the curve of the gunwale in profile) that we wanted? The only way to find out is to draw it in and look at it. So, again using the dividers, mark out a point forward of station 0 3' up from WL and 2' forward of station 0. Then draw a line from the mark aft of station 10 to the intersection of station 10 and WL. Do the same at the bow.

From the cartoon we know that the sheer is at it's lowest point at station 7, 1' 9” above WL so using the spline and ducks we'll construct a curve from the bow to the stern through that point on station 7.

Now take a good look at that line from all directions, is it fair, does it look good. I think so, in fact I think it looks better than the cartoon. So 16' is good.

Using the same process of taking measurements off the cartoon and using our spline and ducks we can draw in the sheer and bottom line in plan.

So far so good but the real test of all this will come when you draw the lines in section like the center portion of the cartoon. We'll discuss that next time.