Newbie needs a clue ot two...

Question (can't wait for the book to arive)...
From PAR: "Consider epoxy bonding all fasteners and hardware, especially under the LWL." and "assuming the frames are perpendicular to the LWL"
What exactly is the "LWL" ?

Didn't find much on Yarecraft using google.... but will keep looking

 

LWL is literally the "length at waterline", but people seem to often write "lwl" instead of "waterline".

 

One benefit of a good book on boat building or restoration will be a chapter or a glossary with the definition of common terms. It's very helpful to become familiar with the language of the profession.

LWL has two similar meanings. Most commonly it means "length at the water line", as opposed to LOA, "length overall". It is also used, as I think PAR meant it, to mean "load waterine", or the waterline itself. "load" because the waterline is meant to show how deep the boat sits in the water in its loaded condition, with engine, full tank of fuel, and maximum number of people.

If frames are perpendicular to the LWL, measurements taken along the length of the strongback (to the top of a frame when the boat is upside down) will be the same as if you crawled under and measured the length to the same frame at some point inside the hull.

Fasteners below the LWL then, are fasteners that are always underwater when the boat is in use or moored.

If you want a head start on nautical terms, there are good glossaries here:
http://www.taylormarine.com/glossary/L.html

and here: http://www.modelshipbuilder.com/resources/glossary.html

 

I wonder if I spelled Yarecraft correctly.

 

Charlie and Danish Bagger have covered it. I usually think in terms of load when I mention LWL, unless I'm discussing length (if that makes any sense at all). An example would be increasing LWL for better speed in a displacement vessel (Length) or height of the mast off the LWL (Load). In the instances quoted above, I meant Load Water Line.

 

Not sure this will be covered in the book I'm waiting for so I'll ask... can the LWL, (loaded or unloaded) be calculated "as she sits'"? Another one that I'm curious about, does the tumblehome aft have any significance to the boat's stability? Not sure if that's the correct term, but it's used in canoe lingo and I believe it's a feature that's designed in to provide initial and secondary stability. The reason I'm curious about how this relates to this specific boat is that a 79" beam on a 15' boat suggests an already stable boat, at least when stopped. I can imagine being able to walk around in her without any tippiness at all. The more I think about this boat, the more I think about this boat....

Have a great weekend folks, and thanks again for the education!
Ben

 

You have caught the boating bug. There is no cure. You must let it run its course.

Tumblehome (means the same thing here as in a canoe- gunwales are farther inboard than the outermost point of the hull sides at a particular station), in a boat like that is more for style than anything, as such a craft should never roll or bank far enough for the topsides to actually meet the water surface.

 

Tumblehome was originally incorporated into large ships, hundreds of years ago. You must realize, they stacked very heavy cannons next to each other, along the rails which tended to make them less stable, so tumblehome moved the weight closer to the centerline.

In a rolling ship, tumblehome can increase the initial stability by presenting a "harder" bilge turn to the sea as she rolls.

Ships of these eras had very high D/L ratios and low ballast/displacement ratios, which generally means they'll roll around a fair amount. The only options open to them, which also afforded the required interior volume necessary, were very fat bellied craft with the beam taken well into the ends of the boat. These shapes, some nearly square in section, have the least movement in rolling conditions, though not particularly efficient.

As materials qualities got better, so did manufacturing process and huge gains where made, especially during the golden age of sail in the later half of the 19th century. Hulls became more refined, sharpened entries, decreased wetted area, external ballast more commonly used, heavy guns placed in turrets on the ship's centerline, etc. These refinements increased the ballast/displacement ratios and lowered the D/L which improved efficiency.

Tumblehome became less a necessity and more a styling exercise.

Some fishing craft used tumblehome to permit the fisherman feet a good purchase on the deck, but brought the rail close to their body so net handling would be easier.

In modern craft, tumblehome is purely aesthetic in value, though a few, typically reasonably unstable craft still can benefit from it.

In your powerboat, it's all looks, though some can argue it saves weight in racing craft.