Ship calculations

I don't know if anyone else has been interested in designing their own 1905-1927 era warships, but I have been interested in doing that for a very long time. All that is really needed is to do the general design. That involves doing a layout, weights analysis, and power calculations. The last is the most time consuming of the design process (at least the way I do it). I am just going to outline the process, for this post.

The weights analysis can be done, with some work, using an Excel spreadsheet. I have been using an Excel spreadsheet for the power calculations as well. I mechanized a process for doing the calculations that I learned from Frank Fox (he is interested in more than just 17th Century ships).

I use the weights spreadsheet to do the displacement calculations, as well, so that I define the fundamental dimensions there. Then, I do a scale drawing. I have found that a 1-inch = 100 feet drawing is adequate. For greater accuracy, you can always do a larger scale drawing, but there are so many approximations involved, that I only do a larger scale drawing for smaller vessels.

I actually clone an existing spreadsheet, to start the process. However, the basic outline is that I have the dimensions and summary weights on the left. On the lower right, I do the hull armor calculations. On the upper right, I do the turret and gun weight calculations.

To do decent estimates of turret and gun shield weights, you need to do some larger scale drawings that you can measure. It is also helpful to refer to real ship data for which there are weight noted. I have use both R.A. Burt's book, British Battleships of World War One and John Roberts' Battlecruisers book. The book that got me started on doing general design was William Hovgaard's classic book, The General Design of Warships. I was amazed that I was actually able to buy a copy at a reasonable price. Another source is paying some fairly big bucks to get the Library of Congress to make a good photocopy for you. I did that first, before I knew that the book might be available.

The propulsion calculations require determining the wave-making resistance and the surface friction resistance. There are more modern methods available that seem to depend on interpolating from a database of ship characteristics. The classic method uses graphs from Speed and Power of Ships and Schoenherr coefficients from Morton Gertler's A Reanalysis of the Original Test Data For the Taylor Standard Series. This book occasionally comes on the market. I found a copy a few days after Frank Fox had recommended the book to me. Explaining the method will have to wait for later, as it is quite involved. Essentially, for a range of speeds, the residual resistance and frictional resistance are calculated and summed. From this "effective horsepower", then we can estimate the actual horsepower needed, given some assumed efficiency. I have some example spreadsheets that illustrate the method (sadly, I lost a lot of this sort of work in October 2002 when I had a hard disk failure that wasn't adequately backed up).