Note the angle of the coaming, especially at the wind-
screen. It parallels the inclination of the cabin side walls.
April
'06
11. The Carlings
12. The Rear Seat
13. Rollover Day
14. Filling and Fairing
In the plans the carlings are 25 mm thick and 50 mm. wide. They run parallel to the hull at its top, and are placed in a vertical plane in their intersection with the bulkhead top frames. In other words, they need to bend in two directions, just like the sheer clamps.
Eventually
the coaming boards will be attached to the carlings, and if the
plan were to be followed, the coaming would be in a vertical
plane as well. However, traditional slipper launches have the
coaming flaring out as it goes forward to meet the windscreen,
and roughly following the inclination of the hull. The rakish
angle at the windscreen level adds a lot to the appeal of the
launch. I intend to diverge from the plan and make my coamings incline
off vertical.
Note
the angle of the coaming, especially at the wind-
screen. It parallels the inclination of the cabin side walls.
So the carlings need to be installed with the same cant on them as the coaming will have. This means they will have to twist longitudinally as well as bow and warp at the same time. The chances of getting a 25 mm. thick piece of wood to do that I rate as remote, so I propose to laminate the carling out of two pieces of 12.5 mm. each.
The carling apertures in the bulkhead top frames were all marked so that their sides were parallel to the side of the bulkhead, and their bottoms were perpendicular to the sides. This means that the carlings and coaming will lie almost vertical at the level of bulkhead E, which will be needed for the eventual fitting of the canopy hardware to the outside of the coaming.
One problem which soon became apparent was that these timbers like to take the straightest line to their destination. While the sheer was being installeded it could be held in the required position by clamping against the hull, however, with the carlings being supported by only three contact points at the bulkheads, the long stretch between bulkheads D and E (the passenger compartment) allows them to sink below the level of the sheer. An additional support point has the be provided temporarily, or perhaps permanently between D and E.
The
passenger compartment between bulkheads D and E, showing the
amount of
curvature in
the sheer, and the straight line wanting
to be taken by the carling.
The obvious place to provide support to the carling will be in the vicinity of the half bulkhead which makes up the seat front. Even so, the pressure exerted on the support point at bulkhead D will be great, and it is a good thing to have a widely glued deck support here to spread the load.
Deck
support attached to the front of bulkhead D, showing the cutout
for the
carling,
and
the eventual location of the coaming. Any internal lining boards will
sit against
its cut end to the
left, immediately
below the inboard side of the carling.
(Above)
the support post sits on top of the half bulkhead seat front,
(right) the two carling laminations glued up.
In the event, the support did prove to be necessary to attain a smooth curve, but because the carlings were laminated from two lengths of 12.5 mm. stock there was very little spring back when the clamps and support were removed.
With both carlings fitted it was time to do some work on the interior while waiting for rollover day, which is calculated to need the help of five strong bodies. A barbecue and beer day is promised after Easter to lure the workers. Meantime the hull under the passenger compartment sole is being epoxied, and some light weight additions to the rear seat are progressing.
The
carlings before and after removal of the clamps.
The plans have been
altered to allow for a seat with more rake and area. The half
bulkhead which makes up the front of the seat is already in
place. Two fillets were attached to the hull inside between
bulkhead E and the half bulkhead, to support the side of the
seat, and two additional struts were run from bulkhead "E" to bulkhead
"1/2" to provide support under the passengers and to
allow for a removable hatch in the seat for access to the locker
under it. An athwartships beam was run between the fillets to
carry the back of the seat at the correct angle. These members are all
connected by halving joints.
Only
the central hatch will be liftable. The rest of the seat
will be
glued to to its frame.
The seat bottom for the space behind the back is attached.
The back of the seat will be thrust forward at its base by a batten lying on top of the rear of the seat platform. The platform itself was fitted in separate pieces, which makes for much easier shaping around the epoxy fillets and the curving hull. Here, the rear end of the platform is installed, ready to have its positioning batten added.
Rear seat with
hatch
closed (above) and opened (right).
I am not happy with the idea of plywood being used as a hatch and being repeatedly opened and closed, even with epoxy coating . So I am putting a hardwood beading around the approximating edges of the moving parts.
The
central hatch of the rear seat with a beading of
padouk.
After painting the inside of the locker, and the underneath of the seat with copious epoxy resin, the rear section of the seat platform was glued down to the frame, followed by the side panels, leaving the opening panel to drop into place.
Next, the positioning batten was glued down to the platform, after being grooved for the placement of back support struts corresponding with the position of the seat platform struts.
The positioning batten
is clamped down.
Support
struts behind the seat back
stop
it sagging
under weight. The
piece of scrap represents the
athwartships coaming.
Capt.
Jack surveys progress.
The plans show the back of the rear seat meeting the coaming behind it at the level of the top of the coaming in the midline of the boat. This is not possible if the back is to be made of a straight piece, because as it moves laterally towards the hull the angle it makes with the seat platform would have to become greater and greater in order for it to continue to meet the coaming. That is because the top of the coaming is getting lower and lower on account of the camber of the deck. Therefore, a gap opens between seat back and coaming the further laterally you look. An alternative arrangement is to have the seat back meet the coaming in a straight line from one side of the cockpit to the other, and therefore somewhat lower than the top of the coaming in the midline, but flush with it laterally. The seat back cushion can then be designed to fill in the space in front of the exposed coaming in the middle.
One of the problems created by canting the carlings and coaming is that the cockpit lining will have to slope as well, to follow the changing inclination of the hull. At the level of the seat back, that means that the back itself will be wider at the top than at the seat base level, and will, therefore, not be able to hinge forward, because it will hit the lining as it does so. A three part back will be needed, similar to the three part base, but access to the E bulkhead needs to be broad enough to allow further access to the rudder compartment and adequate swing for an emergency tiller. (In the case of steering failure, an emergency tiller needs to be able to be attached to the rudder post and to come forward through bulkhead E with sufficient space to swing from port to starboard.)
A straight line from the surface of the
carling to
the seat
base shows the reason that the entire back of the seat will not be
able to hinge forward.
The location of the lateral seat back support struts is a bit tricky to determine. The folding-down seat back has to be able to clear the inside of the coaming at deck level and the inside of the cockpit lagging at seat level. Which is more restrictive?
To work it out, the coaming was represented by a scrap block clamped to the carling, and the lagging was represented by another one. The outside surface of the lagging scrap represents the inner surface of the lagging.
Lagging
represented by the leftmost piece of scrap and
coaming by
the rightmost.
The
stick on the seat platform shows where
the lagging will
meet the seat.
A line can be drawn on the seat where the lagging will meet it, and a plumb bob hung from the false coaming block will show which component will project further into the cockpit.
In this case
the
coaming will lie a few
millimetres medial to the lagging.
So, with this information the lateral seat struts can be placed so that the seat back clears the coaming as it folds down. It will also clear the lagging.
The lateral support struts however, will have to lie a bit further medial than this, because there will be a strip of cockbeading on the coaming which will cover the holes for the screws which attach the coaming to the carlings.
Note
contrasting cockbead.
These considerations raise the question of access to the rudder compartment between bulkheads E and F. The plans call for a hatch in the deck at this location, but no hatches are found in the traditional boats. They show just an unbroken sloping deck, which is very attractive.
Compare
that with the hatch:
The
stern end of a 16' Henley Slipper of Selway-Fisher.
However, the cockpits in
the traditional boats are positioned much further sternwards than
the Selway-Fisher design, and the distance between bulkheads E
and F might be less. Therefore, an access hole in bulkhead E
might give adequate reach to be able to adjust the rudder
mechanism through the cockpit. In my boat the distance between
bulkheads is 871 mm. which may well put the rudder post beyond
reach of the cockpit. I will only know when the rudder is
installed, so I will delay making a final decision about the
hatch until then.
The formula given in Sam Devlin's book for the number of helpers needed to turn the boat gives a figure of 5. I arranged 7, just in case. (It is very handy having a son who has kept in touch with all his school friends). It cost a bit more in beer, but was worth the expense. It also saved me from having to build a jig for the purpose, so may have been a cheaper option anyway. The first step was to jack up the stern, with the bow on a block, and remove all the supports from the platform. The boat was then lowered onto carpets on the platform. Because of the flatness of the hull at the stern it is very stable on the carpet, and inclines only a little.
The
boat self supporting on the platform.
With the help the imported muscle the boat was inverted onto saw horses ready for the second ply skin to be cold moulded onto the its bottom. After all the apprehension about this operation, it was all over in under 20 minutes.
A
touch
of glamour.
The bottom of the hull needs to have a second skin of 6 mm. ply moulded to it, but before that can be done the wire holes have to be filled with epoxy, and any dips in the first skin have to be faired. Some of those dips were significant enough to require two coats of microballoon thickened epoxy sanded between coats. The central seam of the hull also needed attention. There was very little evidence of epoxy on the outside of the seam despite the fillet on the inside, so it needed to be filled as well.
A
filled wire hole prior to sanding...and then after
.
The central seam showing very little epoxy(left) and (right) a dip is filled with microballoon mix
The filling of the dips proved to be a drawn out affair, and very unpleasant. In order to be able to sand these fairings easily I wanted to thicken the epoxy with microballoons only, but the lack of a thixotropic agent meant that the mixture developed sags, especially at the bow end where it was most needed, and the slope was steepest. So sufficient microballoon had to be added to reduce that effect as much as possible. A mixture that thick was impossible to even out without most of it sticking to the smoothing batten and leaving pits and ridges. That then needed sanding back, and yet another application of mixture, and so on. Some days were taken up fairing the hull, before it was fair enough for the second ply layer to be applied.
Sagging
mixture after the first coat, and pits and bubbles after sanding.
The
second coat.
Between coats of fairing compound I started to cut the strips for the cold moulding of the hull bottom. To use up left over 6 mm. ply, I made the strips 150mmm. wide and set them at 45 degrees to the keel line.
6
mm.
ply strips ready for cold moulding.
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