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We have designed many boats using the Frameless building
technique. When we speak of small steel boats this can cover the size range from a 16 ft
dinghy through to an under 40 ft power or sailboat. Frameless is something of
a misnomer because even a frameless steel boat may contain some frames and most will
contain some fore and aft framing by way of stringers and perhaps chine bars. Steel is
certainly an excellent choice as a building material for any cruising boat,
but because of its inherent weight some special considerations must be given to keeping
the overall weight of the boat down to reasonable levels.
For instance several years ago, we would not
have considered it possible to design a 34 ft steel planing hull that would offer
excellent performance and behave in a similar manner to a comparably sized fiberglass
hull. We have changed our minds and we now have several successful small planing steel
power boats in service throughout the world.
Most boats of under 36 ft have a steel
hull shell that is so strong that it only needs the minimum of reinforcing to provide a
seaworthy vessel. This does not mean that one can take any steel design and simply omit
the frames and or chine bars and expect to have a satisfactory boat; frameless
construction requires careful consideration at the design stage. In the case of our
smaller designs like the Tom Thumb 26, frameless construction was always intended to be
the basic building method for this boat.
Many of our boat plans and patterns allow for
several different options and suggest ways that some or all of the frames may be omitted
from the final boat. Naturally some type of framing or formers must be used to allow the
shape of the hull to be formed. These frames are usually incorporated into the final hull
on a larger steel boat but in a smaller steel boat they are not required for strength so
it is preferable to eliminate as many frames as possible. Intermediate bulkheads will be
bolted to tags that are small pieces of framing material welded to the hull to
allow the bolting of bulkheads in place.
Once it has been established where the
frames may be usefully retained it is time to decide just how many frames are required to
provide a former that allow stringers and plating to be installed thus
creating a fair hull. Most frameless hulls are built upside down.
For example the boat plans for the Tom Thumb 26
show a total of 11 frame formers however an experienced builder may safely reduce the
number to 6 installing frames/formers at stations 0, 2 , 4, 6, 8 and 10.
You may prefer to install the keel webs in
place for the intermediate frames as this would be easier at the setting up stage rather
than trying to retro-fit the webs after the hull and keel plating is in place.
The frame patterns, stem pattern and other
information provided on the full sized patterns can be transferred to either steel plate,
later used for hull plating or to plywood, later used for bulkheads. The frames/formers
are then assembled over these more permanent patterns.
When placing the stringers and chine bars
( if used ) these should be kept 3/16" / 4mm proud of the frames. If you
have seen a steel boat that looked liked a starved cow, then this was caused by allowing
the plating to come into contact with the transverse frames and in some cases welding all
frames continuously to the plating ugh.
The webs in frameless
powerboats can have lightening holes as shown and these are useful for leading cables and
plumbing etc., throughout the hull. Note the stringers, chine flat and other items that go
to providing sufficient strength to allow the transverse frames to be omitted in this
FOR FRAMELESS HULLS
If you are
building a 'Frameless' boat, that is a hull with only a few frames, or one, which has no
transverse frames, then you, may use angle frames as a mould and these will not remain in
the boat. When you are building the 'mould' for a frameless boat, it may be possible to
eliminate every second frame when setting up the shape of the hull. When the designer
prepares computer designed lines it is usual to have only 4 to 6 control sections (similar
to frames) and the remainder of the hull is faired through these sections. Most light to
medium displacement steel chine hulls (not radius chine), under say 40 ft / 12.19 M, are
suitable for building using the frameless technique. Contact the designer of your boat, if
you are interested in building using this method. Ask if some frames may be eliminated
either in the finished boat or in the setting up mould. Some frameless hulls are built
over a timber framework; this may be helpful if you are building a metal hull under 35 ft
/ 10.66 M and have limited metalworking experience. You could build the timber framework
yourself, and then hire an experienced welder to weld up the hull.
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