THE HULL
The hull of any boat is, without a doubt, its single most important part. It supplies flotation and without flotation, nothing else really matters. However, a hull does much more than supply flotation. It also plays a major role in how a vessel handles both going ahead and backing and determines its stability. It must withstand navigational hazards such as rocks, banks, logs, jet skis and debris plus survive in a corrosive environment. A shortcoming in any of the above can mean disaster or, at the very least, result in a less than adequate vessel. Therefore, much planning and consideration should go into the design and construction of the hull.
I cannot go into great detail here due to space limitations and the complexity of the subject but we will look at the main areas of concern.
These are
1. SHAPE
2. SIZE
3. MATERIAL
4. CONSTRUCTION
SHAPE
Let's look at the hull as three parts...the bow...the body...and the stern.
The bow can be either 'model' (pointed) or 'scow' (sloped). There are advantages and dis-advantages to both. A model bow does move through the water more easily than a scow bow. However, there is some question as to whether the extra complexity and expense is justified. Sternwheel vessels, of the size we are concerned with, utilize a 'displacement hull'. That is, each time the vessel moves one length of itself, it displaces its equivalent weight in water. Compare this to a 'planing hull' which, with enough power and speed, comes to the top of the water when running. A vessel such as a ski boat, that is designed to plane, will definitely benefit from a model bow. There is another drawback to a model bow besides expense, especially when running in rivers. If you park a model bow boat against the bank overnight and the river drops, the next morning you will probably be stuck. Flanking the stern from side to side while backing is usually to no avail because the vessel will just pivot around the bow. Where as, with a scow bow, you can 'crab craw' the boat back off the shore. There's even more to the argument of model verses scow bow, however, the discussion is too involved for this site. I'll just say that I prefer a scow bow with a low angle of entry to the water for boats used on inland waterways. I also suggest using heavy (1/4 or 3/8 inch) plate for the bow and having it wrap under the bottom three or four feet to protect against rocks, ice, banks and debris.
For the body, a flat bottom with sides sloping outward a few degrees works well. Rounding the intersection of side to bottom (chine) will improve the hulls' response to the rudders. Provisions should be made in this section of the hull for fresh water tanks, fuel tanks, a waste holding tank and probably the hot water tank. This section is also normally used for storage of items which aren't frequently used.
The stern is where I see mistakes made most often. A 'rake' or slope must be applied to the stern for three important reasons. One is to allow water to 'feed' the paddlewheel when going ahead. Two is to allow water from the wheel to be pushed under the hull when backing instead of piling up on the back of the boat. Three is to create an area to position the main steering rudders where they are both in a good flow of water and also up out of the way. Thus, they are protected from debris and other navigational hazards. I strongly urge that nothing project below the flat bottom of the hull!
SIZE
The size of a hull is, of course, dictated by your needs. I trust that you have studied and refined those needs after reading the section on "Planning For Your Needs". There are, however, a couple items to keep in mind regardless of the hull size that you choose. First is the 'water line ratio'. This is a ratio created by dividing the vessels water line length by its beam at the water line. In yachting circles, this is referred to as the 'slenderness ratio'. Those of you who are quite astute will ask, how can I determine these dimensions when one and possibly both ends of the hull slope up and the sides slope out? Good question. The answer is, you can't, not without knowing the exact draft of the vessel. The best you can do without complete design specifications, is pick a 'reasonable draft' and look at that ratio. The number that you arrive at should not be less than three. The higher the ratio the more efficiently the hull will perform. It's kind of like pushing a car up hill. If the tires are fully inflated (a ratio of four plus), the car pushes fairly easily. If the tires are a little low on pressure (a ratio just under four), the car pushes a little harder. If the ratio is under three, it's like the tires are completely flat. This ratio is very important so, do your best to get it right!
A second size criteria that you should consider is the hull depth for this will ultimately determine your vessels 'freeboard'. This is the distance from the deck to the water. I know of no situation where a hull depth of less than three feet should be considered. Whatever the depth, it should produce a freeboard of at least twelve inches. A little more is better, but to much is not good either because it raises the center of gravity and increases the vessels 'sail area'.
MATERIALS
All things considered, there is only one logical choice of material to use in constructing a Sternwheel riverboat hull, and that is steel. Most hulls can be constructed of 3/16 or 1/4 inch plate. Larger vessels, of course, require a greater thickness. A good quality plate should be used. One that is ductile, has good welding properties and is free of impurities. Steel plate designated A-36 is quite good. The hull framing or 'scantlings' must be selected based on the size and proportions of the hull. Structural items with lower thickness dimensions and larger leg dimensions are more desirable. For instance, 2 x 3 x 3/16 angle is usually a better choice than 2 x 2 x 1/4 yet the weight is essentially the same.
CONSTRUCTION
There can be chapters written on the subject of hull construction, so here, I can only touch on a few key items. One is, don't forget to install bulkheads. Spacing them equally on eight to ten foot centers is okay. However, closer spacing at the ends of the hull with more distance between them at the center is better. The goal is to keep the vessel afloat even if a compartment on either end is ruptured. Items passing through the bulkheads, like water and fuel lines, should be installed with 'packing glands' and not welded to the bulkhead. Do not install 'through the hull' fittings below the water line! Sooner or later, these could spell disaster. Locate all liquid holding tanks as close as possible to the vessels center line both forward-to-aft and side-to-side. Last and certainly not least, give the hull a good paint job. On the inside, either sandblast or mechanically clean and coat with a good rust inhibiting paint. This should be white or a light color to permit this area to be used for storage. On the outside, I recommend using "coal tar epoxy" applied over a well sandblasted surface. Apply it generously....it's a lot cheaper than repairs!
I realize that this is very little information on a very complex subject. However, as I stated earlier, if you want to know more, contact me through my E-mail address.
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