|
CHAPTER 1 GENERAL
Pram
To get the most of boat from the provided
material, a Pram design is an obvious solution.
The Pram can serve three
purposes: as a tender,
as a sail trainer, and/or as a little gunkholer that is
carried on top of a car. In
this last case, to save weight, the hull is constructed from 1/8"
Philippine mahogany plywood, a.k.a. Lauan, albeit on the same inside
measurements as the hull for the first two purposes.
Simplified
Construction
The hull is developed from a constant-flared,
15-foot Double-Ender by reducing the Overall Length to nine feet as
described in the article Boat Building with a Difference I in
Duckworks Magazine. The
worked-out mathematic calculations are explained in the Appendix.
1.
The provided material allows for a maximum bottom width at Beam
of 36". The
maximum length of the expanded bottom panel is 96",
or 94" with the rocker taken in account, and a maximum side
panels’ width of 15.7".
2.
Based on a Double-Ender with an Overall Length, LOA = 15 Feet,
the Breadth at Beam is ¼ x 180" = 45".
The half-Breadth at Beam is 22.5".
The constant flare angle is 16.7º.
This is based on the ratio Profile Height/half-Breadth = 0.3 =
6.75"/22.5" (Tan 0.3 = 16.7º).
3.
In the set of plans of the Double ender, station Beam is
given the number 8. This
explains the numbering sequence of the stations of the Pram as is shown
in the half-Breadth illustration below, and in the set of plans
of the Pram on page 7.
4.
The sheer lines circle arc segments are allowed to go straight
fore at the bow, and aft at the transom boards. This makes the bevels of the straight sides of the boards an
easy-to-cut constant bevel of 17.7º for the bow board,
and a constant bevel of 11.5º for the transom
board.
5.
The chines run parallel to the sheer lines.
In the expanded side panel’s drawing, the sheer and the chine
lines are straight lines.
First
Project for Amateurs
The constant flare of
the sides, the constant bevel angles of the bow and transom
boards, and the straight sheer and chine lines of the expanded
side panels, simplify the layout, and the cutting of the parts.
These simplifications make building the Pram especially suitable
as a first project for aspiring amateurs.
Model
Build a to (1/6) scale
model first from inexpensive 2-mm thick cardboard found in art
stores in panels of 32"x40" (less than C$7, inclusive
taxes), and a 2' piece of (scrap) 2x4 lumber as a jig.
You become familiar with the different parts and their layout.
“At least, it will prevent having to buy wood twice.” (Harold
“Dynamite” Payson).
Building
Method
The full-sized hull is
constructed upside down on a jig with the help of four cross frames.
Four small, triangular longitudinal frames facilitate the mounting of
the bow and transom boards. It
keeps these boards perfectly in place during the time that the hull is
assembled.
Also, these longitudinal
frames keep the cross frames fore and aft exactly plumb on the jig
during the construction. The
two cross frames amidships are kept plumb with triangular brackets that
can be made of any kind of scrap (ply) wood.
Before the hull is lifted off the jig, put on the
guardrails. Then, at Beam, immediately place temporarily a hull spreader,
which is also made of scrap wood, to conserve the correct hull shape
until all the thwarts are in place.
Warning
Do not cut any of the
boards and/or the other thwart parts until the side panels are set onto
the four cross frames on the jig and the exact measurements of the
thwart parts are verified on the setup.
The layout of the timber is such that it allows for small
corrections!
DRAWINGS
Set
of Plans, Measurements Adjustments
The three drawings of the set
of plans give the dimensions to the outside of the hull.
With exception of the bottom panel, the measurements of the
temporary construction cross frames, the bow and the transom boards, and
all the thwart parts are reduced to allow for the thickness of the side
panels that are ¼" (0.25") thick.
LAYOUT
Wood
Dimensions
The actual
measurements of a 1x12 are ¾"x11½".
For a 2x4, the actual dimensions are 1½"x
3½". In the
layout drawings, the adjusted actual measurements are used.
Layout
The snags in the
layout puzzle of the parts are the two 2x4s!
The solution is to rip each beam into two planks.
Since that cut is 3½" wide, it has to be done with a
band saw, or a regular 12" table saw blade.
These cuts are 1/8" wide.
1.
Rip the first 2x4 into two halves of equal thickness: 1½"
- ⅛" (the cut) = 1⅜".
Divide by 2. The result is two planks each 8' – 11/16"x3½"
actual.
2.
The second 2x4 is ripped into one plank of a standard 8'
- ¾"x3½" actual and a thinner plank of ¾" -
⅛" = ⅝" actual thickness.
3.
In Canada, a special multi-tooth blade for cutting plywood costs
C$15 inclusive sales tax. This blade makes 1/10" (0.1") wide cuts.
With such a blade, the thin ⅝"x3½" plank
is ripped into 6 equal slats of ⅝"x½".
(6
x 0.5" + 5 x 0.1"= 3" + ½" = 3½").
4.
The bevels of the bow and the transom boards, and of the thwart
parts, are exploited to gain an extra critical inch in the layout
pattern.
6.
The length over the bottom (LOB) of the hull is 94".
Taken in account the curve of the chine line, and the thickness
of the bow and transom boards, the chines can be made from 8'-long
battens.
When the above-mentioned
conditions are adhered to, and precisely executed, a 9-foot Pram can be
constructed from the provided material!
Safety
Usually, the cockpit depth
for such small boats is approximately 12 inches.
In this design, it is increased to 15 inches.
The extra 3 inches add to the safety, especially, for its
use as a sail trainer.
SAIL
PLANS
Standing
Lug Rig
One 8'x10' tarp is cut
into a simple standing lugsail. Only
the head (the top yard side) of the tarp needs some modification.
Although this can be done with double sticking tape, try to do it
with a not-too-hot-set, ordinary clothes’ iron.
It looks neater, and it is a lot stronger.
Buy your wife a new iron; use the old iron for this job. Experiment first on some pieces of scrap material until you
get the “knack” for it. Too
high a temperature melts and crinkles the material.
A too-cold iron does not glue the new seams properly.
Lay a piece of rope inside of a new seam.
Reinforce the corners with large patches. The grommets for attaching the head to the top yard
strengthen the seam further.
Perfectly round holes for the grommets are made with a hot
soldering iron. Push in the
iron quickly, pull it out immediately.
The edges of the holes melt, and then solidify again into a hard
edge. With plastic grommets, they are corrosion free and sturdy.
Maximum
Sail Area
The safe sail area for
a 9-foot pram is maximal 60 square feet.
This area is obtained by using one of the 10-foot, 1½"
dia wood poles as a slanted top yard for the lugsail. It reduces the tarp area from 80 square feet into
exactly 60 square feet. Make
allowances for the new seam!
The right triangular rest of the tarp is used to reinforce the
corners of the sail, to patch round holes for two rows of reefs, and
some scrap material to get the ‘knack” of gluing the new head seam
of the sail with the clothes’ iron.
Other
Sail Plans
The second tarp can be used
for a different sail configuration, i.e. a lateen sail, or a spritsail
with a small jib.
Reefing
If you sail on water where
windy conditions prevail, make two rows of reefing points in the sail, 15",
and 30" above, and parallel to the boom.
Tuning
By adjusting the location of
the halyard onto the top yard of the standing lugsail, the pram is tuned
for (slight) weather helm. Underway,
fine-tuning for weather helm is done with the in/outhaul fore on the
boom, and/or by shifting the weight of the crew.
For other sail configurations, changing the angle of the jib
stay, the size of the jib, and/or raking the mast forward or backward,
do the tuning.
HARDWARE
Screws
Very little of this small
hardware is used to hold the parts together.
This material is only a (very) small part of the total costs.
Stainless steel screws are not that expensive either.
Rigging Fittings
A good functioning rudder is very important. Buy the best quality set of pintles and gudgeons that you can
locate.
For the mainsail halyard, use a fairlead with a ½"
ID hole. Screw the fairlead at the top and on the side of the mast.
The black nylon material is very slippery.
The line never jambs. The
weight of the yard added by the weight of the sail, guarantee a smooth
sliding-down movement.
Also, use a fairlead on the bow deck for the in/outhaul of the
boom for the fine-tuning for weather helm.
Use a set of blocks for the mainsheet.
FINISHING
Hull
If
the boat is kept in the water 24 hours, 7 days
a week:
Cover all seams with fiberglass and epoxy.
Seal the hull inside and outside with epoxy.
Let the epoxy dry completely for one week before painting.
Paint the outside with three coats of a good quality alkyd,
exterior, white house paint. One
primer coat, with two regular coats to finish.
If
the
boat is dry stored, and only used for incidental (weekend) trips:
Cover all seams with Buckram tape.
Buckram tape in found in the curtain section of fabric stores.
It is a tough nylon material that is used to seam curtains.
There are two kinds of tape: with, and without pockets.
The tape with the pockets is used for the metal curtain hooks.
The tape without the pockets is set at the bottom of the
curtains. This last kind is the tape for our purposes.
It is attached to the hull with plastic resin glue. (Urea
formaldehyde) Resin glue is
a beige powder. It is mixed
with water by quantity. Mix
two parts of powder onto one part of water.
Follow the manufactures instructions to the letter!
Seal the hull inside and outside with the waterproof powder glue.
Let it dry for four days at the least before you start painting.
Paint the outside of the hull with three coats of good latex,
exterior, white house paint. One
primer coat, with two regular coats to finish.
In both cases, paint the inside of the hull with two coats of
flat, anti-slip porch paint.
Buckram and resin glue are a lot less toxic as fiberglass tape
with epoxy, and cost about half the price of fiberglass tape and epoxy. There is no offending odour to boot.
Hull
Attachments
For a nice contrast, cover all the parts that
are attached to the plywood hull with three layers of plain varnish at
least. The guardrails and
the inwales, the dagger board case, the dagger board, the rudder, the
tiller and the tiller extension, and all the thwarts are also finished
with plain varnish. Depending
on your taste, the outsides of the bow and transom boards can either be
varnished, or given any other bright color.
Waterline
Prop
up the hull on a horizontal, flat surface.
The joint of the bow board and the bottom, and the joint of
transom board and the bottom must
be at absolutely equal
heights above the surface. Be
finicky about this positioning. Secure
the hull tightly in that position.
Measure the height of the bottom joints above the surface.
Drill a hole into a piece of scrap 2x3.
A pencil stuck through the hole must touch the side panels at the
height of the joints when the block is placed on the table. Drill a second hole one or two inches above the first hole.
Place a second pencil in this hole also.
Push the two pencils against the hull.
Draw two horizontal pencil lines onto the side panels from fore
to aft by sliding the block over the flat surface.
The lower line is the (no-load) waterline.
The second line is used for decorative purposes.
Finishing Touch
Paint the sides under the lower line and the bottom with a bright
red color. In that case
paint the band between the two lines with a bright green color.
Another nice effect can be achieved by painting the strip between
the two lines a flaming red, and the bottom with a (very) bright green.
DO NOT USE ANTI-FOULING PAINT ON THE
BOTTOM. IT IS TOXIC!
On top of that, some of these
paints stay soft and cause smudges all over your hands and clothing!
SET OF PLANS
Table
of Offsets
The expression TBaS in the table of offsets
is an abbreviation for the (station) location Transom
Board at the Sheer. TBaC is
then the station location of
Transom Board at Chine in
the set of plans.
BBaS
stands for station
Bow Board at the Sheer, and BBaC means station
Bow Board at the Chine.
The half-Breadth at sheer is to the outside measurements.
All measurements are in inches.
The bevel angles are in degrees.
Only the needed
measurements are recorded.
*These measurements are adjusted to the
tangent line part of the sheer.
| Station # |
Half Breadth Sheer |
Profile Height Sheer |
Bevel Angle |
| 8 |
22.5 |
6.75 |
--- |
| 6 = 10 |
21 |
6.3 |
--- |
| 5 = 11 |
19.15 |
5.75 |
11.5 |
| TBaC |
19 |
5.7 |
11.5 |
| TBaS |
18.5* |
5.5* |
11.5 |
| BBaC |
14.15 |
4.25 |
17.7 |
| BbaS |
10.5* |
3.15* |
17.7 |
The sheer line is part of a circle
segment. That is the reason
why the half-Breadth and Profile height figures for station #5
are the same as for station #11 in the table.
|
