Bruce Roberts
Yacht Design

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BACK to METAL   BOATS

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’.

"FRAMELESS" POWERBOATS:

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 hull.

FRAMES 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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