rudder function

[Marangon]

I am new to this forum and actually I design ships from antique texts. I have a problem in designing the stern end and rudder post. Can anyone give me information? I want to know if a hull shape is possible in a rounded V shape....specifically will a rudder function with this flat transom (all the way down to the keel therefore under the water line) or will it create too much turbulence to function well? The hulls I usually see are tapered to about the stern rising line giving a smooth exit

 

[TANSL]

Do you have any paintings from the stern of your boat?

 

[jehardiman]

I second TANSL, tell us what type of historical ship you are looking at. While I do recall some boats having them, historical ships rarely (in fact I only think of one main type and the Chinese/Korean/Japanese box ships even had sweep up, skegs, and underslung rudders) had an absolute flat transom, keel to shear. It is a structural fastening and caulking issue as well as rudder effectiveness.

 

[Blueknarr]

I second TANSL, tell us what type of historical ship you are looking at. While I do recall some boats having them, historical ships rarely (in fact I only think of one main type and the Chinese/Korean/Japanese box ships even had sweep up, skegs, and underslung rudders) had an absolute flat transom, keel to shear. It is a structural fastening and caulking issue as well as rudder effectiveness.

Not to mention DRAG. I can't think of any "historical" plaining craft. Large vertical underwater transoms are simply bad idea all round.

 

[JSL]

drawings would be useful - and How 'old' and what culture.
I have a book (Ships & the Sea)with drawings/sketches from 1500BC to present from various parts of the world. Maybe yours was fitted with a 'steerboard'?

 

[Marangon]

The ship is Venetian 1550s, I know it had a sternpost mounted rudder. The sternpost transom assembly is angled too at 20° distally. I have designed on Autocad, I hope I can send you a screen shot. The top row is having the tangent follow the rising line and floor narrowing...so the exit curves to the stern post under the rising line.
The second row uses a tangent ( this was found in a document...but we don't know how they used it) , this tangent is a theoretical......the exit is straight to the stern post leaving a square tuck all the way to the keel.
I favour the first....to me the second would only create a lot of drag and even impare the rudder function......any thoughts?

 

[philSweet]

By "sternpost mounted rudder" do you mean metal strap pintles and gudgeons? I didn't think those came along until much later (on ships of this size). The bottom of the rudder post probably just fitted into a big hole in the keel.

 

[Marangon]

No Venice had used pintles and gudgeons for many years...

 

[jehardiman]

From the backbone profile, the location, and the time (1550) that looks like either a nao or a nef. Both are types of small carracks and fairly typical of age of exploration ships. In typical construction the lower planking strakes would sweep in a hard curve into the sternpost. Sometimes there was a true flat transom (especially in the larger 'true' carrack or in the similar sized caravel) but this started several strakes above the keel, often close to or at the waterline. In The Evolution of the Wooden Ship By Basil Greenhill, the full construction of a nao from votive models and structural remains is shown on pages 66 through 74.

As for the tangent found in a manuscript, it was likely a section construction line as there where many "geometric rule" methods for laying out a ship's lines published about that time.

Edit: It just struck me re-reading your post...is the tangent line from the manuscript drawn on the profile, or on a section? It could be indicating the deadwood buildup, the sweep of the garboard, or the bearding line.