A floatbridge or transfer bridge is a movable structure that connects the shore line with a vessel so that railroad rolling stock may be loaded. In 1997 when it was announced that Walthers was going to do their Waterfront Series, there was a degree of suspense and anticipation among rail-marine enthusiasts as to what design they would choose. As anyone who has purchased the first installment in the series, the book Railroading Along the Waterfront, will observe, Walthers had a very tough choice in selecting a floatbridge because of the wide range of styles employed in ports around the US. Floatbridge styles tended to be somewhat regional , but even within a region, e.g. the Great Lakes, New York, Baltimore, etc., there was variation. Walthers ended up executing a hybrid design with prototype inspiration. Many modelers who are casually interested in having a floatbridge and carf1oat as another "industry" or interchange point will be satisfied with the kit as is. We could fill numerous issues with material on modeling f1oatbridges. However, the following in formation is offered for those who wish to pursue more specific prototypes as well as for those who hunger for more information on floatbridges.
There are at least three categories of floatbridges that have been used on the East Coast of the US: the pontoon style, the mechanically counter-weighted style and the electric style. Walthers chose to represent the electric style. Here the actual movable bridge structure is suspended by cables which are counter weighted. (Walthers refers to the entire float bridge as an "apron." Purists will note that the term "apron" has multiple meanings. One meaning includes the usage made by Walthers. In other designs, the apron is a smaller movable component of the floatbridge itself. The word "apron" in marine context also refers to the portion of the pier deck between a waterside structure and the water's edge.) The cable arrangement has to be very sturdy as it must support the weight of the movable bridge as well as that of rolling stock traveling over it. In some designs, intended for lighter use, the cables alone are used to suspend the bridge and adjust the floatbridge height. In units intended for heavier traffic and much faster loading/unloading cycles, the load is carried by threaded rods extending vertically overhead. Which of these floatbridge designs is selected in a particular situation depends on the amount of traffic, the desired speed of operation and the tidal range.
Close inspection of the Walthers kit will reveal there are numerous and extensive differences between it and the frequently photographed prototypes at Long Island City, Jersey City, Oak Point and Bay Ridge to the point where some modelers claim the Walthers unit is "completely wrong." The Walthers model is intended to represent the lighter-duty unit and is actually very close to its actual prototype in many respects. Personally I feel this is appropriate for the typical model railroad; few of us are modeling the huge transfer operations that took place there. Frankly, given their Great Lakes base, I would not have been surprised to see Walthers choose the "counter-weighted lever arm" style (my nomenclature) employed on the Lakes!
The photos here show Reading float bridges on the Delaware River. According to Bob Gallegos from Walthers, these light duty units were in fact the inspiration for their kit. The kit was intended to be generic rather than as lavish replication of a prototype. Thus it can be used either with modification or simply as a starter set of components to represent other styles. Indeed, the Reading prototypes here which I knew of, but little about, until this research, turnout to be actually supported by pontoons. The overhead structure is used to raise the bridge for maintenance - i.e. it supports the "dead load." The load of the rolling stock is supported by a combination of the pontoon and the linkage, via toggle bars, with the carf1oat itself. The photo captions elaborate on these points. The information in the captions is from interpretation of the photos and my general knowledge of floatbridges - mostly gained from reading articles published by others in Transfer, the publication of the RailMarine Information Group. Consequently, I freely accept the possibility I have misinterpreted something. If you have operated these float bridges and/or can document anything different from my interpretations, please share your insights.
For those who want a model of other types of f1oatbridges. the Walthers kit offers a good beginning point for kitbashing. There are a number of directions you can go. First of all, if you wanted to be more precise in replicating the actual Reading units, you would augment the Walthers kit with a block of smoothed 1x stock - say, a 1x3 - to simulate a pontoon. Embellish it with some Plastruct tubing and electric motor to represent the pump motor and outlet manifold. Another aspect is that you may find the bridge structure itself too short for your tidal range, too. I do not know the dimensions of the actual Reading bridges, but Walthers has obviously tried to keep things as compact as possible in response to our almost universal space challenges. Consequently, the bridge certainly appears to be shortened to the point of caricature. From a practical standpoint, remember that the shorter the bridge, the steeper the grade leading to the carfloat under extreme tidal conditions. You may wish to splice several kits together to make a longer bridge structure and redo the trackage and add the center girder to be more prototypically accurate. The width of the bridge, 4 1/2", with track center-to-center spacing of about 2 15/32" appears to allow satisfactory clearance for a center girder. Some modelers have also lamented the execution of the bridge deck with "cast-in" planking, but apparently the additional complexity required for removable decking, ala Walthers' GSC flatcar, created problems. In any event, many modelers will end up redoing the bridge deck because of this; if you chose to do so you can also rearrange the trackage and add the center girder. A comment on the center-to-center track spacing which comes out to about 18 scale feet may also be fitting here. While this is somewhat wider than the "standard" in New York Harbor of 16'9", this additional width is preferable from a modeling standpoint because of our big fingers, and there was in no way a universal standard outside of New York Harbor anyway. (Transfer No. 19 published the "standard" New York carfloat interface.)
Moving in other directions, the Walthers kit offers great potential for the kitbasher who wants to replicate the heavy-duty-style "French Design" (for the engineer James B. French) that many modelers are familiar with from New York Harbor. See, for example, Railroading Along The Waterfront, p. 19 (Erie) and p. 21 (Lehigh Valley). Other roads in New York Harbor also used this style. The most distinctive feature of these - even if you fudge on some of the other features I will mention - was four bridge lifting screws that protruded vertically like smoke stacks in pipe housings from the roof of the machinery housing. Secondly, the rigging was also significantly more substantial (heavy, multiple sheaves and a heavier bridge structure). A third feature is that the bridge itself was two separate spans with internal complexities too involved to describe here, not a single span as in the kit. A small drawing of this style appears on p. 121 of Paul Mallery's Bridge and Trestle Handbook, 4th Edition (Carstens). It is my understanding that this drawing actually shows not the A. H. Mallery patent. but instead the heavier French design that was adopted when the Mallery design proved too light (the drawing for the A. H. Mallery patent was published in Transfer No. 20).
Another variation, which would describe as a "medium duty" unit was a design employed by the B&O in Baltimore Harbor. This design, shown on p. 25 and mislabeled as the "Western Maryland carfloat apron" was replicated in at least two other locations in the harbor. It lacks lifting screws, the entire live and dead load being carried by counter-weighted cables; however, it introduces another wrinkle in the form of a "pick-up" counterweight system. This system is characterized by paired - fore and aft - towers on each side - one for the primary counterweight, the other for the pick up counter weight, as a careful study of that photo will reveal. Also notice the twin spans with the two girders visible in the middle. I will need at least one of these in my caricature model representation of Locust Pt. so will be using the Walthers kit as a source. I will also be looking for derelict Athearn wrecking crane parts at train shows for the rigging.
Going further and depending on your prototype and locale, you could replace the kit's overhead machinery housing and solid girder with either an open truss or a light girder and larger visible counter weight sheaves. Page 34 shows the former, Milwaukee's installation at Pier 27, Seattle, although the towers are of timber, not steel construction on this unit. In both cases, the float bridge itself is a single span like Walthers, not twin spans, although the track arrangements vary. The latter was represented by Santa Fe in San Francisco Bay; page 13 shows their China Basin unit. The West India Fruit and Steamship Company used a style similar to this on their Florida Havana service.
Another variation is to replace the steel plate girder float bridge in the kit with wooden Howe trusses - yes, in some modern floatbridges of the B&O, CNJ, Reading and PRR in some places, the wooden truss was found to be more flexible and durable than the steel plate girder.
Finally, one could cut down the towers to support the Great Lakes style lever counter weight arm (many of these used an A-frame, but there were some that used the fabricated tower to support the lever), or eliminate the towers entirely and just use the bridge structure with a wooden or plastic box underneath the outer end for a pontoon.
For more about floatbridges in general, and New York - style ones in particular, a comprehensive series entitled "The Transfer Bridge at the Port of New York" appeared in issues No. 12-15 and 23 of Transfer. These articles discussed and profusely illustrated with photos and reproductions of drawings the various design alternatives that have been used. For back-issue information, send a SSAE to RMIG, 12107 Mt. Albert Rd., Ellicott City, MD 21042.