Additional notes as of early 2006 - : Recently, Hornby have released a new tooled version Seacow wagon. It should be noted that these represent the batch constructed from 1981, which are of welded construction, all coded YGB, and are not therefore totally suitable for this conversion. Bachmann however announced in January 2006 that they intend to release their own version and their website shows photographs of the older 1971 version (being as per the Lima model), which is of riveted construction. Therefore this may provide a better base for the conversion as described below.

Prototype notes:
Bogie 40 ton hopper wagons were first introduced by the LSWR in 1903/4, built by G & R Turner of Nottingham. This led to a number of versions prior to the introduction of the SR dia 1774 which, along with SR dia 1775, were the forerunner of the later BR built Walrus, Sealion and Seacow hoppers.
Twenty two hoppers to SR dia 1774 were introduced in 1935/6, built by the Metropolitan-Cammell Carriage and Wagon Co. These were an improvement on previous designs in three respects: the door controls were split so that each side of the hopper (it had a transverse central partition) could be discharged independently, the side discharge shoots were extended by a few inches to prevent the stones falling on the conductor rail and the angle of the hopper slope was increased.
In 1947 a further 20 hoppers were introduced to SR dia 1775, which differed from dia 1774 by virtue of a further increase in hopper angle, and the fitting of the American AAR Cast Steel bogie which gave improved high speed running and reliability over the diamond frame bogies previously used.
The Walrus hoppers built in 1954 were a poor version of the Southern wagons with an inferior plate bogie design and retrograde door control mechanism. Eventually all were transferred away from the Southern.
The 1970s built BR 'YGH' Sealion and 'YGB' Seacow hoppers are similar to each except that the sealion was fitted with the earlier AFI vacuum brake equipment. A number of 'Sealions' were in fact converted to 'Seacows' - these had either the riveted Gloucester type bogie or the newer welded Y25C or Y27C bogies.

Southern Livery notes:
As these hopper wagons were allocated to the Engineers Department they were painted in red oxide with black under frames. As some of the SR dia 1774 hoppers were introduced in 1935 some examples were seen with the pre-1936 style large 18" SR initials. Eventually these were replaced by the post 1936 smaller 4" style lettering in the bottom right hand corner. In common with all Engineers Department wagons the prefix E D to the wagon number was used.

The Lima Model:
Lima has marketed this model as both a Sealion and Seacow although it is closer to former as the latter does not have the large vacuum cylinders. The bogies on the Lima model are in fact based on a continental bogie and therefore incorrect for representation of any of the bogies fitted to the UK prototypes. The correct type bogies are available from either Cambrian Models or Appleby Model Engineering for anyone interested.

Notes on the conversion:
I used Diamond bogies available from Ratio for these models along with Keen Maygib disc wheels. I followed the Ratio instructions for the bogie itself but removed the long extension to the pivot plate as this is there to enable tension lock couplings to be fitted which I did not require.
These ratio bogies provide a reasonable representation of the type fitted to the SR dia 1774, I am not aware if cast steel AAR bogies are available, maybe in the USA which could, perhaps, be used to model the SR dia 1775.
The Lima bogies simply unclip to remove them. I glued M2 brass nuts, from above, into the hole left once the Lima bogies had been unclipped to enable the nRatio bogies to be held in place by a M2 screw. I use a small amount of Loctite® 603 bolt retainer on the screw to prevent it vibrating loose. The use of a proper bolt retainer means that the bond can be easily broken to enable maintenance whilst at the same time will not work loose.
I carefully removed the two vacuum cylinders and associated mouldings and repositioned then centrally at each end between the stanchions supporting the door operating hand wheels.
I added an additional horizontal cross member, made from microstrip, between the central two hand rail posts at each end which provided the top fixing point for the vacuum hose (white metal castings from ABS).
Cast white metal buffers from ABS (SR Brake Van Buffers) were used to replace the later BR style.
The handrails and control hand wheels supplied by Lima were used, suitably toned down in colour.
I painted using an aerosol of Halfords red oxide plastic primer which is, of course, the correct final colour. HMRS 'Pressfix' transfers were used to produce models in both Pre and Post 1936 lettering style. Weathering was applied with rust highlights, stone dust colour spray from the top and track colour from the base, to give the finish I required. I made removable load inserts covered with 'N' scale ballast as I find that that ballast sold as 'OO' is too coarse.