Where exactly is the waterline, or should it be?

[Rushdie]

Hi, it's Paul again, still collecting pore filler, paint, etc... before continuing on my "Lady Nelson".  I did prepare the normally submerged part of the hull for application of color by putting masking tape just about where I've observed others having done.  I've seen various, different, "waterlines" and I tried to search the subject, but not found anything really.

So ...where is that elusive "waterline" located?  It should be easy, right?  And, of course, the waterline varies with the deadweight, the hull's immersion increasing with the gross weight of stores, fresh water, crew and belongings, as well as the salinity of the water...

What, from a viewpoint of, say, 1800, is a proper approach?

...thanks once again for your much appreciated comments.  I'm really curious, too!

Safe sailing!

Paul

 

[Roger Pellett]

Paul,  From a Naval Architect’s perspective, you are exactly right.  Determining the waterline at which a vessel will float requires knowing two things:

 

1.  The weight of water displaced with the vessel assumed to be floating at several waterlines shown on the lines drawing.  The results of this calculation can be plotted as a curve displacement vs waterline height.

 

2.  The weight of the ship in different load conditions.

 

With this information, the draft of the vessel can be picked off for any load condition.  In 1800 there were several methods for calculating displacement from the shape of the hull.  These ranged from numerical approximations calculated manually, but based on techniques similar to the computer algorithms used today to actually measuring the quantity of water displayed by immersing a model in a tub of water.

 

The big unknown for ships built in the wooden ship era was the weight of the ship itself.  Shipbuilding management systems were simply not capable of accurately predicting how much of the timber allocated for a particular ship would actually wind up in the finished vessel.  Iron and steel construction would eventually change this.

 

The answer to all of this would come when the vessel was launched, and the draft of the floating vessel known. With this they could pick off the weight in the as launched condition from the curve. Adding  the weight to be added to complete the ship, the armament, stores, etc. they could get a realistic estimate of the draft of the vessel in various loaded conditions.

 

My suggestion:  Coppered vessels- Follow whatever drawings you are using.  Vessels not coppered-  White or back stuff up to the bottom of the Wales.  The stuff was cheap.

 

Roger

[Rushdie]

Thankee Roger!  Brilliant reply, which I tend to understand from previous experience and developed primitive Excel predictions of modern vessels' cargo capacity under circumstances of departure and arrival port limitations.  At best, these were approximations, with ships more resembling cubic boxes than my ... elegant British cutter's sleek hull shape.  And, in terms of "ancient" wooden sailing vessels, I feel it's very much a matter of appearance, if not outright copycat behavior.  And I suppose, as (and to the degree that) my modelbuilding progresses, I assume I may not necessarily continue in a completely "correct" manner.  Such as leaving out the cannon altogether, saving (fickle) future time.  And I'm deeply worried about how on earth I'll manage the rigging.  But that's a motivation to continue!

Paul

 

[wefalck]

On a real ship the waterline may have looked really awfu, hand-applied bottom paint just by eye ...

 

I gather for many ships a good approximation would be that the bottom paint goes up to below the wales (as Roger already pointed out) at it's deepest point. From there it would follow a horizontal line forward and backward to the stem and stern respectively. Well not exactly: in most cases the waterline was given a slight(!) curve upward towards the stem and stern. This has two psychological/aesthetic reasons: for one the hull looks more dynamic and the ship faster in that way and then, particularly larger wooden ships tend to 'hog' with time, meaning that the ends begin to hang down, because of the stresses on the hull in the sea; an upward curve of the painted 'waterline' compensates for this.

 

Edited March 7 by wefalck

[Rushdie]

Hoi...very reasonable, in fact, you appear to be saying that the actual line of immersion was ... somewhat "beautified" by the (shipowner) which, eventually, was authenticated by poop sag.  

I assume there are many factors, not in the least that deeper bow immersion slows a ship down, and the visual indication by way of a painted waterline would be considered an easy guideline.

Awaiting consolidation of the acquired (assumed) knowledge, I've just realized I forgot to order the white Vallejo acrylic 😵‍💫 but that's been meanwhile rectified.

Paul

[allanyed]

Wherever you decide to paint the bottom, the line would usually be parallel with the earth.   Your photo appears to have a curve to the tape.  There are hundreds of photos you can check out of contemporary models on the RMG Collections site, including the one at https://www.rmg.co.uk/collections/objects/rmgc-object-66510

 In any case, if you want a very clean line, before painting, spray a couple clear coats which will seal the tape at the edge.   Afterwards, after you paint the color and it has dried peel off the tape it will be a very straight line.

Allan

[Rushdie]

Now, Allan, that's the reply I will base myself upon, the pictures in the link are perfect for my purposes, as well as the concise "clean line" recommendation. Cheers!!!

Paul