Internal Framing

After installing the coaming and determining the deck beam curves, I marked out and cut the deck beams.

Marking out one of the deck beams

 The deck beam curves were cut with a jigsaw after which their exact positions on the boat were determined. I was recommended to leave at least 400mm between the transom and the rearmost deck beam to allow room for the engine to be tilted up. Some of the compound angles made cutting the deck beams accurately to size a challenge. I am beginning to rely more and more on my angle grinder with sanding disk to trim wood quickly and easily to size. The angle grinder is such a useful tool! You need a dust mask when using it! 

Laying out deck beams in position

The front deck beam was supported by blocking to the sheer and an upright from the stem.

Deck beam and vertical support

Vertical support

Front deck beam with blocking to sheer

There were two deck beams installed in the vicinity of frame 1. One deck beam is angled for the seat (left in picture below) and the other will form part of the hatch structure.

Deck beams for seat and hatch

Blocking for seat and hatch deck beams

Looking from the front gives a nice perspective of the curve of the deck.

Another piece of wood was added to the deck beam on frame 2 for added strength. These frames get notched for the deck battens and therefore loose some of their strength.

Frame 2 deck beam strengthening 

The glue-up of the rear deck beams was a bit tricky because I did not bother to create blocking for the 2 deck beam segments either side of the coaming. Hence in the image below there is some complicated clamping going on.

Epoxying the deck beams in position

 I have a tendency to underestimate how long it takes to do glue-ups. Mixing epoxy, doing neat fillets and cleaning off excess epoxy it quite time consuming.

Epoxying the deck beam in place.

I used a router free-hand to notch out the deck beams for the deck battens and strongback(center longitudinal). An auxiliary dash beam to which the actual dash will attach was installed. It was a bit of playing around to get the dash in what I thought was an appropriate position and angle for the steering.

Auxiliary dash beam, strongback and deck battens

The deck battens were too thick to be able to bend down to the sheer so I laminated another piece of wood under them to eliminate the need to bend them. The plan is to simply plane (or angle grind) them down to the curve of the deck. The strongback bends down to the breast-hook relatively easily. The strongback was tapered to fit the breast-hook in about 1 minute using the angle grinder. I am not gluing the battens and strongback in place yet because I need to add flotation foam to the front of the boat.

Deck batten and strongback

Extra pieces of hoop pine were added between each of the battens on the floor of the boat. This is to act as flooring. I still need to shape these extra floor battens to the curve of the hull which will be another angle grinder job. A seat was created by resting a piece of plywood on the chine timbers and then adding supports to the keel and battens.  The supports are perpendicular to the battens and angled where they meet the seat. In hindsight it would have been more aesthetically pleasing to have them perpendicular to the seat. I am considering adding a decorative piece of wood to the front of the seat to hide the supports.

Seat and flooring

The seat is in two parts, There is also a support for the seat along frame 1.

Seat in two parts

An angled piece of wood was cut and glued in place to support the back rest of the seat.

Backrest support

The finished seat structure.

As I am intending to power the boat with a 20 horse power engine, I decided to beef up the transom with some more transom knees. These transom knees are scaled down versions of the larger knee and should serve to transfer the force of the engine onto the battens without any excessive stress concentrations. They are each held in place with epoxy and silicon bronze screws.

Transom knees

The router table and flush trim router bit was used to create the transom knees.

Transom knees

Some supports were also added to strengthen the joints between the transom-sheer and transom-coaming. 

Sheer and coaming supports

Curved bracing was added between the coaming and the rear-most deck beam.

Deck beam and coaming bracing

Building the frame was a lot of  fun and it felt like I was achieving a lot!

The next step is to determine how much buoyancy foam needs to be installed and this will be followed by sanding the interior of the hull and giving it a good coat of epoxy.

Cheers!

Deck Beam Maths + - / x

Before I ordered the timber for the internals of the boat, I drew the following sketch showing the lumber that would be needed. 

Sketch of interior lumber

There are quite a number of pieces of wood (in green) going across the width of the boat which I have called 'deck beams'. These pieces of wood cannot be straight. They need to have curves that are consistent with the curves defined on the plans for the the Transom, Frame 1 and Frame 2.

Frames & Transom

The quandary is how to know what curves to cut. The simplest solution would be to simply copy Frame 2 for the forward deck beams and then 'eyeball' the aft beams based on Frame 1 and the Transom. I suspect this 'eyeballing' method would have been fine especially given it all needs faring anyway and that epoxy can fill gaps admirably. I wasn't satisfied with that approach and wanted a more analytical way of developing the deck beams. Glen L Witt's book, 'Boat Building With Plywood' gives some methods of developing deck beams.

Plate 8-J from 'Boatbuilding With Plywood'

Initially, I considered making the jig shown in the bottom half of the image above but I decided it would be easier to do the maths to work out the formula for the curve the jig would scribe. The development of the formula is shown below.

I think maths is beautiful because it can describe with infinite perfectness the truths of geometry.

With these formulas I can now plot a deck beam for any width and any given crown.
The concept is that you have a consistent β angle across your whole deck. The crown of the deck changes as the width of the boat changes but the β angle remains the same. The curvature of the deck is defined by the β angle.

Measuring the crown and width of transom on the plans.

Using the plans, I measured the width and crown of the deck beam on Frame 2 which allowed me to calculate the β angle which will define the curve of the deck. With the β angle I could then generate a curve for any point on the deck of the boat by simply measuring the width at that point. (Obviously, at the very front of the boat the width is 0 so the height of the deck beam is zero at that point. The formula makes that clear as the term  (W+2d) will equate to 0 when the width W = 0 and d therefore by necessity equals 0.)

Frame 2 was calculated to have the following crown and width.

The forward deck beam at its measured width W was then developed using the β angle of 84.7degrees and the formula above.

The Beams

I was expecting the β angle for the deck beam of Frame 2 to match the curves of both Frame 1 and the transom. This was not the case however.  Furthermore, I found it difficult to find a β angle that would match the transom and Frame 1. In the end, I chose the following:

For the beam between the Transom and Frame 1

For the beam at Frame 1 (this beam will be the seat backrest)

Ironically after I finished cutting out the beams I read the instructions which say:

Pro Tip - READ THE INSTRUCTIONS!

Apart from using this analytical overkill to develop the forward most deck beam, the whole exercise was a bit pointless. BUT I like maths! I enjoyed exploring this and had some good conversations with my friend Jeremy (maths teacher) about it. I also used the geometry explained in plate 8-I above to develop the deck beams. This method was much simpler to calculate. I suspect both methods yield the same geometry. The results were slightly different in excel but I expect that is due to rounding errors in the trig functions. I would like to check to see if they are the same but I would like even more to just keep working on the build.

Next post will be all about the internal framing!