Hull

 
   

   

Specifications

Dimensions in cm/m
2.52m - LOA - Length overall
  1.7m - LOD - Length on deck
  1.46m - LWL - Waterline length
 
  46.8cm - Beam max - Greatest width
  46.1cm - Beam WL - Waterline beam
 
  31cm - Draft - Depth of hull below waterline
 
 ?kg - Weight - Measured weight of boat including sails
 
 16.40kg - Displacement - Weight of water equivalent to the immersed volume of the hull.
 
Lateral dimensions measured along the waterline from the bow
51% - Centre of Gravity including sails (1.4cm below WL)
51% - Centre of Bouyancy
50% - Centre of Effort of full sail plan (94cm above WL)
56% - Center of Lateral Resistance (12cm below WL)
54% - Centre of Floatation.
 

 

Keel

The Keel is made up of 3 seperate ply sheets. The inner single piece 6mm core gives the overall shape. This is part covered both sides by 6mm pieces to thicken the keel to 18mm where neeeded. This is then covered with 1.5mm ply pieces to make up the keel thickness to 21mm (plan = 200mm).
Making the keel from three 6mm ply pieces reduces weigh and cost. It also allows the rudder tube to be easily fitted into the central core with only slight alteration to the outer pieces.
The keel was cut from 1800 x 610 x 6mm and 1200 x 610 x 1.5mm ply sheets using a fine tooth metal jigsaw blade.

The top deck edge of the keel was drawn using a battern and pins, both ends were straight. The enlarged picture shows the removal of 1mm to allow the rudder tube to fit.

drawing out the keel and removal of 1mm for the rudder tube

The central 6mm core gives the overall shape locating the frames, cutouts and mast support. A part is removed to locate the rudder tube.

keel central core

The central core is then clad either side by 6mm pieces creating the keel thickness and stiffness. Dowels were used to locate the separate parts accurately when gluing and trimming to match the central core. 1mm is removed either side to allow the 7.5mm rudder tube to fit as it is slightly bigger than the central core.

keel outer parts

Notches were cut from the bottom of the keel for the lead ballast blocks.

keel core and outer parts glued

The central core was used to mark out the bottom edge of the 1.5mm ply. The inner edges form the planking rabbet.

1.5mm
1.5mm glued on

The rabbet was deepened by about 1mm along the edge of the 1.5mm ply and the area around the aft part of the keel was thinned as the planking is flat in this area. The bow of the keel was chamfered 100 x 50.

Tapered bow

The bow is tapered to give a cleaner entry into the water.

bow stiffeners

6 mm ply pieces were added at the bow to strengthen the planking to keel nailing.

The completed keel weighs 2.5kg and cost £25.

 

Frames

Frame Lines

This is one of three inter-related line drawings used to design the hull. The horizontal "Waterlines" were drawn 450mm apart, The frames were drawn using 300mm spacing to be more accurate. The lines were the outside of the planking, so a new set of lines were drawn for the frames allowing for 50mm planking above the whale and 30mm below.
A "Table of Offsets" was produced from these lines which were then used to draw up the frame drawings. The frames can be cut out by either using the drawings as a template or by plotting the points from the Table of Offsets.
 
Using the frame drawing as templates Cut the frame drawing into individual frames leaving 10mm around the outline
Arrange these on 6mm ply to get the most economocal arrangement then rough draw around them and cut out using a fine metal blade in a jigsaw.
The paper templates were stuck down on the ply using slightly watered down wood glue on the ply. Do not smooth out the air bubbles as this will stretch the paper template out of shape, distorting the frames in various directions.
Check the major dimensions for accuracy. Crown height, Sheer width & height, Waterline width and Keel cutout. If inaccurate use the Table of Offsets to plot the correct dimensions. When I did not smooth out the bubbles, the lines were 0.5mm larger in some directions.
Cutout using a band saw or Jigsaw and file down to the line. I was taught to file half the line away, the remaining is left as a "witness" of the line. You can file to an accuracy of 0.5mm but is this necessary for wood? The best investment I made is a £100 Bandsaw from ScrewFix.

Cut out the keel slots, fit onto the Keel and adjust where necessary so the Waterlines align. Mark the centreline on the crown with a small notch. There are alternative aligning marks on the compartment and rear frames.
The tops of the frames can be chamfered to match the slope of the deck at the centreline at the keel.

Frame drawings

Frames 10 10a

Frame 10 is the point where the deck sheer and the continuation of the bulwark sheer diverge. Frame 10.6 shows the deck camber and the hull sheer.

Deck Crown

This shows that the deck camber for each frame is the same having been designed using the Deck Crown Calculator.

frame 8 showing locating jig

To accurately locate the frames to the keel before adding the planking, 240mm strips of 3mm MDF were cut accurately. This is the dimension between the wateline and top of the stem. A notch was cut on the centreline to fit the central batten on the 18mm baseboard.
Notches were cut to locate the 3mm solid decking edges and the 120 x 50 bulwark rail. The MDF was screwed to the frame. Two dowel holes were drilled to aid the relocation of the the jig to the frame at a lated date if necessary. Note the propshaft hole on the portside of frame 8.

 

Stern

This section has caused me the most grief. I know what it looks like, I have felt how it curves and have dimensions but I cannot see how to draw it.

stern

From the main line drawings I drew the stern developing the curve stern as a true projection. This was then drawn on 1.5mm ply and three pieces cut out over size. A jig was made to hold these three pieces in the correct 4.5m radius curve while the glue set.

stern

Getting the correct angle where the stern piece meets the underside of the transom rail matched its 2D curve was difficult, so I used Plastic Padding.

stern

Another jig was made to locate the transom at the correct angle and at the corrrect height from the underside of the tramsom rail which is 17m from the stem.

stern

 

Planking

A timber strip was screwed on the centreline of the 18mm chipboard base plate using a straight edge. A U shaped piece was cut to locate the stem and the other end of the strip was cut to the overall boat's length of 1.7m
The frames and keel were assembled and packing pieces added to get the frames parallel, square and verticle.

Planking 1

The whale edge was the first 9 x 5mm strip glued and pinned. It was interesting to see that it bent in only one direction as shown by the Aluminium strip.

Planking the hull

The second strip 9 x 3.5mm was added mid-way to the keel. This also only bent in one direction.

Planking the hull

Strip 3 9 x 5mm was added at the sheer. To locate this, the Deck Edge A 28 x 3mm laminate was fitted in its slot on the frame extensions.
The stem end of the sheer plank could not be glued or pinned to the rear frame 10.6 as the frame at this point was too thin.
When its adjcent strip 5 was fitted, the two strips were glued and clamped together with a small backing piece and then twisted into shape using a notched stick B and a rubber band to the top of the clamp.
Another clamp was used at frame 10 along with notched stick C to stop the plank twist.
You can see the underside of the Bulwark Rail.

Planking the hull

Planking the stern was still giving problems as the gluing area of the stern frame was still too small.
The next 9 x 5mm strip was glued and clamped to the two previous planks with a small backing piece. All three were twisted into shape and this time it held its shape. Reinforcing blocks were added at the frame.
The thich 9 x 5mm planks were glued one per side and allowed to glue for 24 hours. The thinner 9 x 3.5 planking was glued 4 per side.
The forward ends of the thin planks were planned down to 4 - 5mm from frame 5 and the rear end down to 3mm from frame 6. The side to be removed was the side that overlapped the previuos plank when it was bent to shape.
Small pieces were glued behind the planks to level the surface between the frames.

Planking the hull

The final strips were tapered at both ends.

Planking the hull

At the bow the added ply was cut back to suit the planking angle.

Planking the hull

The four mahogany strips nearest to the keel were tapered from 20mm to 5mm at the bow. Triangular pieces were added at the stern.

Planking the hull

 

Sheer/deck Edge

The sheer/deck edge was made from 3mm thick strips laminated to shape drawn on a 6mm ply sheet. When they were planned to size they both sprung out of shape due to the removal of the material, in hindsight, this must happen.
More material was added and the corrrect shape redrawn but this time I did not cut it out. The bulwark post holes were cut out without altering the shape. To be able to glue the sheer/deck strip in place, cross pieces were made to fit in the post holes.

Deck sheer

The sheer/deck edge strips were glued on using square stuff and rubber bands.

Deck sheer
Deck sheer

 

Bulwark

Bulwark

The bulwark capping was liminated from two strips 5 x 2 and 4 x 3mm creating a 120 x 50mm rail with a grove on the underside. Cross pieces were made to accurately align the capping.

Deck sheer

The bulwark posts were cut to fit into the post holes and into the groove on the underside of the capping.
1.5mm ply squares were glued under the holes to locate the post bottoms. Slots were cut to take the shroud supports.

Deck sheer

The capping was glued down and held in position with lengths of chipboard to keep the capping flat.

Bulwark

Both sides of the sheer/deck strip were cut down to the correct shape before planking the bulwark sides.

Rubbing down
Rubbing down

 

Casting Keel Weights

Spaces were left in the underside of the keel to add ballast at the lowest point.
Lead shot was melted in a home made laddle over a BBQ. The heat was just sufficient to allow the lead to be poured into a wooden mould.
The keel was blocked up so it was horizontal.. A small amout of GRP resin was added and the lead ingot lowered in. More resin was poured in to fill up the hole.
The total ballast weight was 1.92kg

Casting Keel weights
Casting Keel weights
Casting Keel weights
Casting Keel weights

 

Stern Posts

4 stern posts were cut to suit. The centre right was grooved in the back to take a twin cable for the stern light. The wire is run through a white plactic tube to the main compartment.

Stern Post

1.5mm ply under decking was added at the stern. "Plastic Padding" was put under the sides for support and waterproofing.
5mm curved mahogany deck piece was then added at an angle supporting the stern posts. "Plastic Padding" was used for support and infilling.

Stern Post

 

Rubbing Down

It seem that it took as long to rub down as it did to plank the whole hull.
The darker filler is "Plastic Padding" which gives sharp edges and the lighter colour is "Easy Sand" which is good for large areas.
 
The planking curvature generally followed the plan but some hollows occured between the frames as the planks had to bend to shape forcing a twist in individual planks. Much of this could be planned out.
The step where the hull thickness changed was a particuler problem as it had to be 1.5/2mm and that was achieved by much filling and rubbing down. The "Easy Sand" was not a strong so the shape edge was made latter on with "Plastic Padding"
It was pleasing to see the run off to the transoms bottom was straight as on the plans. The some more curvature was added at the point of max beam.

Rubbing down


 
The bit I was not looking forwards to was shaping the rear bulwark sides to the transom. The sweep up tp the stern rail was as the plan. The width was a straight line from the transom max width to a point where the the scupper started. The curvature was a natural sweep from the underside round to the Bulwark sides.
 
When you run your hands down the hull you can feel why she is so fast.

Rubbing down
Rubbing down
Rubbing down
Rubbing down

 

Priming

Rubbing down
Rubbing down

 

Painting

Painting took forever, that's how it felt. As soon as the first layer of sprayed black car paint went on, more imperfections appeared. So more rubbing down and painting. Eventually it was smooth as a babys bottom.
The anti- fouling is red primer, above the waterline is gloss black with a red line and then sprayed with clear gloss laquer.
The top was painted black first as it was easier the spray the red line. Some of the 3mm MDF panels used initially to set-up the frames were refitted using the dowels. The hull was then turned upside down and carefully leveled. The keel was painted with red primer to just above the waterline without masking. Masking tape was used to define the botttom of the white boot line 75mm (7.5) below the waterline using a jig. The hull was then sprayed upto the deck edge.
The top of the waterline was masked off and the boot strip sprayed white. Rubbing paste was used to smooth the painted edges when the masking tape was removed.
The bulwarks had to be repainted as the bulwark planking opened up and the gaps had to be filled. It's very thin in places. Next time I will make the bulwarks from 1.5mm ply planked over with 2mm strips to the bottom. This will also make it easier to cut the chamfer for the red line. Another benefit is that the inside surface will be easy to paint red.

Hull painting

 

Hull completed

The only design problem was frame 9 just above the keel will have to be widened as the planks could not be bent to touch it and still give a smooth line. The frame spacing allowed the planks to distort when bending, they need to be doubled up which would approximate the real hull.

Hull completed from above
Hull completed from waterline
Hull completed from below

 

Hull Stand

Hull on its stand
Link to drawing in pdf