The Teleflex steering system I am employing is a push/pull type of single cable design, which requires the end of the outer cable to be anchored so that the inner cable can push or pull the tiller. This is achieved by a support tube which screws into the outer cable, and which in turn is anchored by a clamp block. There are different sorts of clamp block made for different types of boat. One, which is meant for boats with inboard motors, is mounted onto a horizontal platform, but another, which is designed for use with outboards, mounts onto the inside of the transom.
The one shown here is the transom mount, illustrating the mount itself, and the clamp for the support tube. The clamp is tightened around a ball on the post of the mount, so that the whole mechanism can move slightly as the tiller passes from side to side. It can also accommodate a little vertical movement such as might be experienced with a standard outboard, but that will not be necessary in my situation. The inboard clamp block is less mobile than this one, and would also be a possibility.
In any case, I was faced with having to build a platform for one of these types of block, and the one I chose was the transom mount. So now I have to build a false transom, onto which to mount the clamp block, to hold the support tube. The tube should be at the same longitudinal level as the point on the tiller where the steering cable attaches to it via a clevis pin. That is some 150 mm. forward of the centre of the rudder stock, or about 220 mm. forward of bulkhead F. The depth of the clamp block itself is such that it holds the centre of the support tube 135 mm. forward of the false transom.
In other words, the false transom has to be 85 mm. forward of the bulkhead. It seem that the simplest way to construct such a platform is as a 50 mm. thick plate mounted on a 35 mm. thick base piece, and the whole then bolted through the bulkhead. The mounting bolts for the clamp block are 2-1/2" long, which will be sufficient to reach through the plate, and short enough to terminate before the bulkhead. The base piece then has merely to be designed so as to give access to the locking nuts and washers which secure the bolts.
The mount part of the clamp block is shown here bolted to the 50 mm. portion of the false transom.
Although the base of the clamp block is quite small, 65 mm. x 55 mm., it is clearly advantageous to make the surface area of the false transom larger than that for its fixation to the bulkhead, as it is the latter which will absorb some of the sideways force of the rudder, via the tiller to the steering cable and on to the support tube.
All this extra weight of the steering mechanism is acting on the starboard side of the boat alone, but it does not need to be counterbalanced, because the action of the right handed rotation of the propeller does that anyway.
The steering cable with support tube and clamp block, and clevis pin attached,
ready for screwing onto the tiller and mounting on the bulkhead.
I called on my friend Lindsay Armstrong again to supply a tiller. He acquired the rudder for me back in May '06, and has come through for me again this time. The tiller is slightly different from the design, which specifies an M9 bolt to be welded to it for the attachment of the steering cable(s). With the Teleflex system a clevis pin is supplied which is 3/8", so I have asked for the bolt to be left off and a 3/8" hole made instead.
With the tiller fixed to the rudder, and the steering cable fixed to the tiller, and with the support tube clamped in the block, the rudder compartment hardware is complete. Now all that has to be done is screw the rack onto the helm, with both steering wheel and rudder in mid position. But that requires that an appropriately angled helm support be built in the motor compartment, and that, in turn, means that the steering column and its bearings have to be fitted. That will be a job for next month, because I want to finish the rear end deck stringers and make the rear deck hatch.
Top of Page
58. The Rear Deck Stringers
The laying out of the rear deck
stringers requires that the appropriate camber be cut into the top of
the bulkhead frames. To measure it I employed a batten again, but it
immediately showed me how far above the existing transom inner frame
the camber of the deck would lie, if the actual curved part of the
transom were to avoid the bow-tie look which I first alluded to in May
'06. It is now obvious, that, even with the 2 metre radius I have used
for the transom, there will be a dip of about 25 mm. in its middle if I
proceed with the flat transom frame.
The alternative is to build up a camber on the transom frame and allow the transom itself to be horizontal. The amount of build up in the camber has now to be measured.
The batten clamped onto the transom misses the transom frame by quite a lot.
Before the dimensions of the camber of the transom frame can be measured, the existing bulkhead top frames have to be
grooved for the correct lie of the batten.
The alternative is to build up a camber on the transom frame and allow the transom itself to be horizontal. The amount of build up in the camber has now to be measured.
The batten clamped onto the transom misses the transom frame by quite a lot.
Before the dimensions of the camber of the transom frame can be measured, the existing bulkhead top frames have to be
grooved for the correct lie of the batten.
Once that is done and the batten is lying fair on all the bulkheads, the gap from transom frame to batten can be measured,
and a camber can be developed.
Once the measurements for the transom frame camber have been taken, the slope can be cut into the bulkhead top frames. Here, the top frame of bulkhead E has been planed to the correct angle, and the batten now lies flat on top of it.
The same can be done to the top frame of bulkhead F, and then the calculated and already cut addition to the transom frame can be fitted.
The extension to the transom frame is glued on after being roughly shaped.
After removing the
clamps and sanding the spills a smooth camber is ready for final
shaping to fit the battens and make a continuous deck slope with the
other two bulkheads and the curved transom. There is a final choice to
be made here: whether to plane a slope onto the real transom, or to
build up a wedge on its forward surface. I think that a generous epoxy
bog will perform the latter operation nicely, so I will leave it
unshaped.
The final shape of the rear deck emerges from the cambered top frames.
The final shape of the rear deck emerges from the cambered top frames.
The
actual fitting of the rear deck stringers is more difficult than the
fore-deck. For a start, the slope of the deck is much steeper, so that
angles are needed on the ends of the stringers if they are to fit into
their bulkhead frames without protruding. Those angles cannot be
accurately measured, only guessed at. Some trial and error is necessary
to get them right. Secondly, because the curve of the deck slope has to
be forced onto the stringers, because they are originally straight, the
cuts into the stringers for the halving joints with the frames have to
allow for a change of angle as the curve is accommodated. In other
words, the cuts cannot be straight, but more bell shaped. This leaves
the halving joints rather loose when they are put together, so as one
end is tightened down, the other one wants to spring out.
The best approach seems to be to lock in the central joint, (on bulkhead F), and then tighten down the joints at the front and back a little at a time sequentially. Plenty of epoxy is used and the squeeze out is formed into a small fillet alongside the joint members.
A small epoxy fillet surrounds the joint at the transom frame.
At 60 mm. wide these stringers are about at the limit of what can be bent into the deck slope shape too. They very nearly split, and anything stiffer than usual might need steaming. I kept reminding myself that the sheer clamps took the strain, but they were only 50 mm. wide. Nevertheless, after some anxious moments the first stringer was in position and clamped down.
The first stringer fitted is the starboard intermediate, which will support the hatch.
The best approach seems to be to lock in the central joint, (on bulkhead F), and then tighten down the joints at the front and back a little at a time sequentially. Plenty of epoxy is used and the squeeze out is formed into a small fillet alongside the joint members.
A small epoxy fillet surrounds the joint at the transom frame.
At 60 mm. wide these stringers are about at the limit of what can be bent into the deck slope shape too. They very nearly split, and anything stiffer than usual might need steaming. I kept reminding myself that the sheer clamps took the strain, but they were only 50 mm. wide. Nevertheless, after some anxious moments the first stringer was in position and clamped down.
The first stringer fitted is the starboard intermediate, which will support the hatch.
In
the photo at right above it appears that the stringer is taking a
straighter course than the sheer, but that is a photographic illusion.
Behind bulkhead F, which has the rudder tube, the stringer and sheer
are almost parallel, but in front of that the stringer becomes steeper
than the sheer to ascend the camber of the bulkhead frame on bulkhead E.
However, I can see a problem coming up: the rear hatch will lie immediately forward of bulkhead F, which means that aft of that the central stringer will only need to stretch between the transom and bulkhead F. Two points of support for a curved shape are not enough. It may be better to leave the stringer sitting proud of the bulkhead and transom, and plane it to shape later.
The outer two stringers are glued in to complete the rear deck framework.
The hatch frame is glued up.
However, I can see a problem coming up: the rear hatch will lie immediately forward of bulkhead F, which means that aft of that the central stringer will only need to stretch between the transom and bulkhead F. Two points of support for a curved shape are not enough. It may be better to leave the stringer sitting proud of the bulkhead and transom, and plane it to shape later.
The
second stringer goes in without incident, and this is now sufficient to
get started on the next phase of construction, namely the hatch. As I
have not yet finished work inside the rudder compartment it will be
unnecessarily crowding to put in the outermost stringers right now.
59. The Rear
Deck Hatch
With the hatch
complete the last two stringers can be fitted. These ones have the
greatest amount of curvature, and some serious clamping is needed to
keep them in place while the epoxy dries.I
agonised over ways to avoid putting a hatch into the rear deck, but in
the end I had to submit to function. The steering mechanism has to be
accessible, and there is just not enough room to squeeze through any
passage made in the bulkhead behind the rear seat. The distance from
bulkhead E to the tiller and steering mechanism is too great to reach
from the passenger compartment, so the only alternative is a hatch.
The 50' slipper launches also had this problem, and they used openings similar to the foredeck hatches, but there is a picture of one Meekes launch available which shows a neat but tiny hatch, which could serve the purpose provided that there is no need to get into the rudder compartment physically.
Two possible rear deck hatch treatments.
The 50' slipper launches also had this problem, and they used openings similar to the foredeck hatches, but there is a picture of one Meekes launch available which shows a neat but tiny hatch, which could serve the purpose provided that there is no need to get into the rudder compartment physically.
Two possible rear deck hatch treatments.
I
have spaced my stringers far enough apart to allow the larger hatch to
be built, but a smaller one could also be accommodated by them. In the
end, the location of the support tube for the steering cable was what
made my mind up. It is close to the hull side. So I have elected for
the large hatch, which will be the same as the foredeck one.
The first job then is to build the surrounds for the hatch. That starts with the transverse member, which has to be cut on the slope, and cambered as well. In the foredeck the camber of the transverse member was virtually the same as that of its nearest bulkhead top frame. But with this rear deck construction the camber is changing so quickly that the nearest bulkhead cannot be used. Instead, an additional camber piece will have to be fitted after measuring the gap, as was done for the transom frame.
Using the batten again to define the shape of the camber piece for the transverse member.
A gap filling strip is placed on top of the transverse member. It will need to be shaped to a feather end at the stringers.
A bit of forethought here would have saved me some
work: as soon as I started building the hatches themselves I realised
that they would not open in their current configuration. The acute angle at the underside of the rear hatch
frame needs to be enlarged to a right angle before the hatch can clear
the deck, assuming it is to open sideways like the foredeck hatches.
This is seen when the side frame pieces are fitted into the opening.
The side frame pieces are seen sitting inside the hatch opening, but when you try to hinge the piece sideways you can
appreciate why it won't open.
In order for the
hatch to open, the side frame pieces have to be trimmed to 90°., as
seen drawn left. However, if the hatches are to be trimmed to that
shape the support will need to be made narrower so that the lip of the
hatch overhangs the gutter and not the support. Otherwise water will be
attracted in between the hatch frame and the support, and will drip
into the rudder compartment. So now I have to face the prospect of
manually narrowing the
support, since it is already glued into position!
A simpler solution is to make the hatch a one piece drop-in structure, not a hinged one. (That would also avoid the difficulty of getting a hinge to work on a curved surface). The plan actually calls for a "pot type" hatch with lifting rings, and I assume this is why. It will be a fairly easy task to make a fastening device to stop such a hatch from bumping around, even though I think it is unlikely to. A catch could be fixed to it which would be accessible from the passenger compartment via a hole in the bulkhead.
That is the best option I feel, so the hatch will now be made up of three fore/aft frame members, and two joining athwartships members. The fore/aft frame pieces are first scribed to the hatch supports on which they sit, and then to the deck stringers. That is fairly easy for the lateral frame pieces, but the central one does not conform to the stringers. Instead it has to be shaped with the help of the batten.
Before and after scribing and cutting to the shape of the support.
Planing the slope and camber of the stringers onto the hatch frames.
but now the batten is put back for the shaping of the central frame member.
The first job then is to build the surrounds for the hatch. That starts with the transverse member, which has to be cut on the slope, and cambered as well. In the foredeck the camber of the transverse member was virtually the same as that of its nearest bulkhead top frame. But with this rear deck construction the camber is changing so quickly that the nearest bulkhead cannot be used. Instead, an additional camber piece will have to be fitted after measuring the gap, as was done for the transom frame.
Using the batten again to define the shape of the camber piece for the transverse member.
A gap filling strip is placed on top of the transverse member. It will need to be shaped to a feather end at the stringers.
From the front end the first of
the hatch support/drip channel strips can be seen screwed onto the
bulkhead. Because of the steep deck slope in this part of the boat only
the lowermost corners of the drip channels will need to be drained, as
water will readily run down to them from above.
With the camber piece shaped,
the rest of the hatch supports can be added to the structure.
The completed hatch opening.
The completed hatch opening.
With the hatch frame
completed it is time to finish the central stringer. The segment
between the front of the hatch frame and bulkhead E is so close to
straight that it does not need to be shaped, but the longer segment,
between bulkhead F and the transom, is first curved to the
slope of the deck and then fitted. The curve is taken off the lateral
stringers. Once again, the difference between them is so little that a
bit of hand planing will be sufficient for any necessary fine tuning of
the camber and slope, although it is a different matter forward of
bulkhead F. Here, the central portion of the hatch itself does rise a
little from the lateral section, so the hatch frame's central member
needs to be shaped to accommodate the curve.
Now there are just the two
outermost stringers to fit before the deck framework is complete, but
for ease of access they can be delayed until after the hatches and drip
channels are done.
The drip channels are formed (left), and after removal of the clamps (right).
The drip channels are formed (left), and after removal of the clamps (right).
The side frame pieces are seen sitting inside the hatch opening, but when you try to hinge the piece sideways you can
appreciate why it won't open.
In order for the
hatch to open, the side frame pieces have to be trimmed to 90°., as
seen drawn left. However, if the hatches are to be trimmed to that
shape the support will need to be made narrower so that the lip of the
hatch overhangs the gutter and not the support. Otherwise water will be
attracted in between the hatch frame and the support, and will drip
into the rudder compartment. So now I have to face the prospect of
manually narrowing the
support, since it is already glued into position!A simpler solution is to make the hatch a one piece drop-in structure, not a hinged one. (That would also avoid the difficulty of getting a hinge to work on a curved surface). The plan actually calls for a "pot type" hatch with lifting rings, and I assume this is why. It will be a fairly easy task to make a fastening device to stop such a hatch from bumping around, even though I think it is unlikely to. A catch could be fixed to it which would be accessible from the passenger compartment via a hole in the bulkhead.
That is the best option I feel, so the hatch will now be made up of three fore/aft frame members, and two joining athwartships members. The fore/aft frame pieces are first scribed to the hatch supports on which they sit, and then to the deck stringers. That is fairly easy for the lateral frame pieces, but the central one does not conform to the stringers. Instead it has to be shaped with the help of the batten.
Before and after scribing and cutting to the shape of the support.
Planing the slope and camber of the stringers onto the hatch frames.
but now the batten is put back for the shaping of the central frame member.
Initially the central frame
member is cut full length so that is will hold itself in position while
it is being shaped. Later it will be trimmed to size to fit into the
completed framework.
The central frame member with and without the batten.
Rebated joints are used in this hatch. Finger joints on a slope
are too difficult.
The central frame member with and without the batten.
Rebated joints are used in this hatch. Finger joints on a slope
are too difficult.
The outer two stringers are glued in to complete the rear deck framework.
The hatch frame is glued up.
Forward to November '07
Back to Ariadne front page
Back to Monthly Progress chart
Back to January '06
Back to February '06
Back to March '06
Back to April '06
Back to May '06
Back to June '06
Back to July '06
Back to August '06
Back to September '06
Back to October '06
Back to November '06
Back to December '06
Back to January '07
Back to February '07
Back to March '07
Back to April '07
Back to May '07
Back to June '07
Back to July '07
Back to August '07
Back to September '07
Problems shows higher resolution shots as well.