Gardner's Clamming Skiff

[Quick Karl]

Par, I would love to see a sketch of the geometry you describe for developing surfaces! Is there a book or article somewhere I could read/see?

I just don't want or need an 18' boat! 15' to 15'-6" would be about max.

As soon as I get the new book and work up a computer model I will see what I can come up and post it for your comments, should you be so inclined.

Thanks to you and David for all of your help!

 

[gdavis]

qcarl-once you decide on a skiff you want to build and get some plans then put the frames together and set up on a strong back it will be very easy to see if they are fair by using a batten.Then the frames can be tweeked here and there if needed. I think you will find that following the plan dimensions for the frames will give you pretty fair curves. (after bevels are cut) Basically,any skiff with flat sides can be built with plywood, you're only bending in one plane.
If you look at some of the ply kayaks out there you'll see just how much thin ply can be tortured into shape. Pretty cool stuff. Ok, hope I made sense to you, sometimes I don't make any sense to me!......................................have fun.............g

 

[PAR]

Actually, there are lots of carvel skiff designs, that can't be done in plywood, unless diagonally planked in thin stuff, but as a rule, most modern designed are fully developed, or close enough you can "talk" to it as you bend the panels around. Many of the Atkins designs, particularly Billy's efforts are like this. They look like you could simply plank them, until you attempt to bend stock around.

 

[Quick Karl]

I'm not questioning Gardner's, or anyone else's hull fairness. All I am interested in is knowing how to prove them out, mathematically, or geometrically as PAR hinted at.

I just want to know how to do it.

 

[DCockey]

What do you mean by "prove them out"? Prove that the sides are developable?

The shape of the sheer and chine of John Gardner's clamming skiffs are such that a sheet of plywood can be wrapped to lie along them. However since the flare of the sides is not constant a developable surface would not have straight side frames, and the sides of the transom would not be straight. But the deviation from straight frames is small and it shouldn't take much to force the plywood to lie against straight frames.

 

[Quick Karl]

OK, I withdraw the question.

However, I know there is an algebraic way to determine offsets for a developed surface, and when I find out what it is, I'll post it.

 

[tdem]

For figuring out the shapes of the stations and hull panels:

SS Rabl: Multiconic development of hull surfaces.

http://www.boatdesign.net/forums/at...low-aluminum-hull-plates-side-plates-rabl.pdf

It's not an algebraic method. I suppose you would need exact equations for your lines plan for that, which you didn't have drawing a skiff by hand.

 

[Quick Karl]

For figuring out the shapes of the stations and hull panels:

SS Rabl: Multiconic development of hull surfaces.

http://www.boatdesign.net/forums/at...low-aluminum-hull-plates-side-plates-rabl.pdf

It's not an algebraic method. I suppose you would need exact equations for your lines plan for that, which you didn't have drawing a skiff by hand.

THAT is Wonderful! Thank you very much! I have seen that before, and had read through it quickly, but it was a looooong time ago and I had totally forgotten about it!

Thank you very much!

Back to my boat - my new book arrived today and sure as heck, that IS Gardner's Clamming Skiff that I have been thinking about for all of these years! I am going to build it exactly as drawn except with a plywood bottom (though Gardner talks about grating if plywood is used for a bottom?), and the center console he refers to at the end of the chapter.

But first, I am going to model the boat in SolidWorks, piece by piece. and create the assembly!

[Edit: Yes flat (no rocker) from midway all the way to the back, as Gardner suggests.]

 

[DCockey]

Which version do you plan to model and build? I did some preliminary "lofting" in Rhino of the revised version. It's probably the least fair set of offsets from Gardner that I've worked with.

 

[Quick Karl]

It doesn't matter - I trust Gardner and I like the boat.

 

[PAR]

Gardner was old school and assumed a builder would loft and fair. In this boat's case this would be an easy thing once the four frames where erected and a batten sprung around the chine and sheer. I wouldn't cut the chine notches before springing this batten. A model of this boat wouldn't be very helpful unless converting to a taped seam build, which would save a good bit in materials and boat pieces to cut and install.

 

[DCockey]

It doesn't matter - I trust Gardner and I like the boat.

You could build to the offsets without any adjustments, and force the chines, rails and planking to conform to the published offsets. The result would have some bumps and hollows.

Adjustments I'd make based on a preliminary look at the offsets of the 18' revised version:

Sheer
Raise Station 3 and/or lower Station 4 a small amount.
Move T1 out slightly; or set T1 and T2 half-breadths equal to Station 5 half-breadth

Chine
Raise Station 3 slightly. Move Station 3 inboard.

 

[PAR]

I pulled out his book and had a look, the lines for both of the revised models are the same, except for station spacing. I see some irregularities, but nothing that wouldn't be fixed once the frames/molds where erected on a strongback.

 

[DCockey]

Station spacing is the same, 2' 4", for both lengths of the revised version. The short version ends at T1. The long version ends at T2 with an extra station added.

 

[DCockey]

Another approach would be a full size lofting of the sheer and chine curves, adjusted as needed. Then pick the points for the frames/molds directly from the lofted curves. No need to measure, just use a tick strip to transfer from the lofting to the frames/molds.