Wednesday, July 30, 2014
Shallow water skiff shapes, ideas
Here are some of my old musings of developing skiff shapes to bring to reality. As I described earlier in my blog of how I like to make a half hull of my vision - idea . I do this after I have done all my weight calculations in advance. Shown are a few past ideas in their growth stages. Sorry but I would love to be able to do this all properly but all I have is the iPad that I got for Christmas this year from my daughters. With out this contraption I probably would not take the time to do all this. Right now it is flat calm with lots of light rain about so I'm inside with a fan on doing something. The iPad is great as I can do this stuff with a simple inverter on our sailboat as we move about and post it later. No TV time in my life so have extra time to fiddle here.
So look at the wood half hull against the mirror. The sections are glued to a 1/4" piece of wood,without this it would sit flush against the mirror with the thickness of the mirror being the center line. This is how it was done before 3 D programs . It does make you feel like a peeping Tom though as you stretch around trying to see the whole thing. Each section is drawn out from the center line to scale. Here you can calculate how many cubic inches are in each section. I do not have the side views showing which would tell and show you the distance between each section. It would not show up here very well.
What I will do this summer is draw up 3-4 new skiff shapes from past knowledge with all dimensions easy to draw up to full size hull sections. These you will be able to cut out and install on a simple building jig and from there you will be able to plank up in light cedar strips, Baltec balsa core strips or Core Cell brand planking strips. From this you fair and then glass the outside. When fair, flip over,
remove the forms and glass the insides. Then you finish the inside. To build a deck I will explain all the ways it can be done simply later. I will put this here for free. In the mean time anyone planning on building a skiff needs to read up a bit on strip plank boat building. This is the same as building a canoe; just a little more odd shape and it has a transom. I will get a list of books or pamphlets to look up.
In looking at these shapes it is easy to start to see how many ways and directions you could now reshape and go. Ha, it can be daunting if you do not have a weight list and a clue as to what the finished hull will weigh. Here I come back to having the vision, idea, whatever. Details.
Of course if you are going to start a new company and you want to follow in the foot steps of something that is already well proven and established then all you really have to do is make a facsimile of it as all the thinking has already been done for you. If you do make it better, and at a better price good for you.
Now with all the shapes here you still have to decide on which side of the half section line you will put your hull thickness. Makes a difference . Take your numbers from the center line out wards and up to the LWL. This is the quickest way. This method shown here has been used for centuries with the creations of some of the most beautiful boats in the world. Go to see the Herreshoff museum in New port RI. He did all his boats this way. There is not a Yankee boat builder up north that does not know this system nor a Carolina one either. The computer today is the way to go though if you have one.
Another idea; this shows how you can take an existing boat today and measure or take its lines sections. Without knowing its length between perpendiculars you could stretch this boat out to ......
In this shape here I wanted a good sea boat at rest that would not be as they say here too "cranky" .
It has good freeboard and was a good all round skiff. I lowered the spray rail on this a bit in the bow area when built. Today I would change the stern section aft so this is obsolete in my mind.
You can see the half sections above and the half hull below.
Cheap 3 - D rendering
You can see here how I'm drawing in a bit of crown. I like crown a lot. It adds tremendous strength over a flat surface. Also you can gain some Disp. But then you have to be careful where it's going to direct the water flow. I do not want crown in my skiff decks as it is a pain in the butt to fit the hatches so the will not squeak and lay flush.
On this sheet you can see the displacement calculation that I wrote down from a simple lines program that I found on the Internet at the time. I put in all my half section numbers and in a second it spit out all these numbers. I had already done it my old way and every thing was pretty close. In the upper left corner you can see the displacement numbers for three different water lines. This you have to think about a lot as the guys, people that will be in the boat, are most likely going to weigh over 200 lbs.
The rest of the numbers there are just adding up Disp. If I posted all my calculation sheets it would be so boring. But I keep em for reference. This is a heavy skiff at close to 2,000 lbs with all the sports in it.