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DougC DougC is offline
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First recorded activity by BoatBanter: Jun 2010
Posts: 33
Default the pancake skiff - episode 1

On 7/30/2010 7:33 PM, Bruce in Bangkok wrote:
On Fri, 30 Jul 2010 11:50:17 -0500,
wrote:

I have made a Freeship model of the hull I am interested in.

page with file link-
http://www.norcom2000.com/users/dcim...oat_makin.html

-or Tiny-
http://tinyurl.com/2g8h8f8

This is not the 100% final version, just a close approximation. The idea
is basically a extra-wide rowboat hull with a very flat bottom. There
will be a flat sealed floor set 6" above the hull bottom on frames
spaced every foot.

This is a inland/fla****er boat only.

Your URL links to a site that provides a ZIP file which expands to be
a FBM file. My system doesn't read fbm files.


Sure it does. Just go download and install Freeship, and you'll be all
set. (at times it is spelled FREE!ship)

http://sourceforge.net/projects/freeship/

Freeship is rather dated but downloading it does not require
registration, as the Delft program seems to.

I would get it rated for a small motor, 5 HP I think. Not very fast, but
as light & broad as the hull is, it's just not going to be safe going
fast anyway. Other 14" boats seem to be running 20-30 HP regularly. 10
MPH is okay for this, I just need a motor that's "faster than rowing"
while being and "less effort than rowing".


Why do you want to "get it rated" for a motor? Are you going to
manufacture it commercially?


I thought that (assuming US laws of course) any given powerboat had a
rated horsepower limit. Stated on the HIN plate.

As I said, this part of the USCG "homebuilder's handbook" is not real
clear. They have an "outboard example" that says how to figure out the
displaement, persons and gear capacity, then they just say the boat's
HIN plate would say it was rated for X people, X lbs of gear and "100
horsepower"..... they never say how they arrived at the 100 HP figure as
safe or allowable.

One 14" commercially-made boat I found used 2mm (~.078") for the hull, I
dunno what alloy. I have no idea how thick to go for the floor. I think
the usual sheet the local metals supplier has on hand is 5052.

You can't equate length and skin thickness. You need to first develop
the actual structure of the boat and then decide the force which must
be opposed by the skin. To exaggerate - a boat with no formers or
stringers depending solely on the skin for strength, i.e., monocoque
construction, would require a totally different material then one
that used a "egg crate" type of structure..


Yea but if I was using metal half as thick (-or twice as thick-) as
comparably-sized commercial boats usually use, that would seem to
indicate something rather odd.

I have found a couple companies that use 1/8" plate for the decking. On
boats about 15'.

I know (in rough terms) what finite element modeling /is/ , but I have
no access to software that can do it. Nor (I would bet) do most of the
people on Earth who build small low-speed boats they've designed
themselves.

~