Longitudinal framing plays a very important part in maintaining the strength of your hull. After you’ve set up the frames, it’s time to install the stringers and chine bars. We prefer flat bar for stringers. For chine bars, both solid round bar and flat bar have advantages and disadvantages. We don’t recommend closed pipe for chine bars. Steel pipe can rust inside, and it’s difficult, if not impossible, to paint or otherwise protect the interior of the pipe. When it’s used in the leading edge of the keel, you can fill the pipe with lead.
At one time many designers and builders preferred to have the stringers stand proud of the frames by 1/8 inch (3 mm), thus avoiding every frame showing through the plated surface. If the frames are not touching the plating, it will be impossible to weld the plating to the frames; in our opinion this isn’t a problem, especially in boats under, say, 40 feet (12.19 m). Using this method, the stringers are welded to the frames and the plating is welded to the stringers. This ties the structure together and provides adequate overall strength. While the foregoing advice is well founded, it may run foul of some of the metal boat building rules and regulations of classification societies such as Lloyd's, the EU, or the U.S. Coast Guard. In any case, follow your plans with one eye on any rule that you may be required to follow to register or operate the finished boat in your area.
Check your plans and—if necessary—with the designer of your particular boat before welding or not welding frames to the hull skin; his calculations may require one or the other practice. In any case, it is worth repeating that the frames should be set up in such a way so as to avoid their showing through the plating; frames 0 through 5 (midsection) are set so the forward edge is on the station mark; frames 6 to the stern are installed so the aft edge of the frame is on the mark.
When installing the stringers, only tack-weld them into the slots. In most designs, the plating will take a fair curve and the stringers may need to be “relieved” so they’ll make contact with the plating throughout the hull. It is a fine judgment whether to pull the plate into the stringers or let the stringers out to lie neatly against the plating. By now your eye should be developed sufficiently to make it obvious which course to follow. In some places, the stringers will need to take the strain while the plating is pulled into place; again your eye will help you to make the right decision.
The order of installing the stringers and chine bars (if present) can be as follows. First, install the sheer or deck stringer, making sure that you keep the ends of the frames equally spaced and square off the centreline. Next, in the case of a chine or radius-chine hull, install the chine stringers (chine bars). Although there is room for discussion as to whether you should fit flat bar, round bar, or have no chine stringers at all, your practical choice is limited: follow the recommendations shown in your plans.
RADIUS-CHINE STRINGERS
In a radius-chine hull, fit two stringers, one each side of the radius. They should be just a little inside or outside of the radius-flat joint; and as you’ll need to be able to weld the plates from inside as well as outside, the stringer must be a small distance from the intersection of the radius plate–flat plate line. One reason for having these two stringers, one each side of the radius-flat intersection, is to provide a fair guide for the actual radius plate–flat plate intersection. See your plans or full-size patterns, where this line should be clearly marked.
We do not recommend having the radius-chine stringers right on the line that intersects the flat and radius section. If you choose this method, you would need to make sure that the plate-to-stringer weld attains full penetration from outside. Also this welding from one side only may contravene the appropiate classification societies' rules.
Intermediate Stringers
After you have installed the sheer, deck stringer (if it’s present as a separate item), and chine stringers, check your hull for fairness. Again, use your eye (and perhaps the eyes of other more experienced builders) to ensure that the hull is progressing without being pulled out of line. Now install the intermediate stringers. The number of intermediate stringers in each chine panel will depend on the size of the hull and the particular metal being used. In most cases, a minimum spacing of 12 inches (305 mm) will be adequate.
Under no circumstances should you permanently weld the intermediate stringers into their slots at this time. You may want to release them later, to allow the stringers to take up the same line as the plate.
This is a good time to give you the first warning: We strongly recommend that you tack-weld the entire hull, including the plating, before running any final welding; don't do any finish welds until the whole structure is completed. In the case of hulls built inverted, you need to complete the welding before turning the hull over; in boats built upright, you can assemble and tack-weld the hull, deck, and superstructure before running the final welds.
When all the chine bars and stringers are in position, the next job is to check over the structure again to ensure that it’s fair in all aspects. A timber batten, sized approximately 1 by 1/2 inch (25 by 12 mm) and about 6 feet (2 m) long, can be laid diagonally across the hull at various locations, and your eye will probably give the best indication of the overall fairness up to this point. Check over the whole structure and make sure there are no unfair areas. On a round-bilge hull a longer batten will be needed to achieve the same results.
Before you start plating you’ll need to decide if you’re going to install the stern and rudder tubes at this stage. It’s reasonable to install the rudder tube(s) before the plating is in place. The stern tube(s) for the propeller(s) are more difficult to place correctly at this stage. If your hull is upside down, you need some very accurate calculations and measurements to get the correct angle and position for the stern tube. It may be better to leave it until you’ve completed the plating and turned the hull. In hulls built upright, it’s easier to figure out where the engine beds are located and where you should install the stern tube.
Just a note on stern bars. If your plans call for a stern bar that is, say, 2 to 4 inches (50 to 100 mm) wide, then you may be better served by using a flat bar placed in the fore-and-aft plane and cutting it to take the tube. When you plate the hull, the plating will have a half-oval shape around the stern tube, and the water flow to the propeller will be much cleaner and less turbulent than it would be with a wide stern bar.
