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

Going Whole Hog

Going Whole Hog

Last week we ended on the thought that maybe we should have a second stringer, I though some more and put it in.

We are going to draw in the hog, the hog sits atop the bottom planking and is fastened directly to the keel through the planking. It's partner is the keelson which sits atop the frames and is through fastened to the keel through the frames and hog. It is not strictly necessary in this small a vessel but we will discuss it later when we decide on decking.

The hog is let into the stem knee and the transom knee in a similar manner.

Then I did some tidying up. When you look at the construction drawing in profile you're actually not looking square on, in this boat, to the stringers as the side has some flare to it. In actual fact you would see the bottom edge and bottom of the stringers and wales so I've drawn them in. Similarly the frame ends would stick up beyond the top of the inwale.

Then we'll add the bottom planking, the scantling rules suggest 5/8 planking however plywood doesn't come in 5/8” and 3/4” ply would be too heavy so 1/2” will have to do. 3/4” ply weighs about 75 lbs and 1/2” only 50 lbs.

We'll draw in the keel next but leave it in profile and develop a detailed drawing of its construction once we know the shaft diameter and angle.

Keel

The last bit for today is to draw in the cap rail.

Next time we'll look at transferring the construction in profile to the plan view.

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.