Pram Plans Question

[Dave R]

I've been looking at plans for a little pram. I have come up with a question I figure should be right up somone's alley so here goes.

The drawings for both bow and stern transom bear the note: "Projected Stern/Bow Transom Take Bevels From Work" The bevels part seems pretty straight forward but what's this about "projected"? Does this refer to a geometric projection? Or are these dimensions actually the ones used to layout these pieces?

[Dave R]

Thanks for your reply. I might be misunderstanding this but are you saying that the dimensions and shape are developed from the ends of the side and bottom pieces?

My expectation was that the bow and stern transoms would be mounted at the ends of the strongback at their final angles and the bottom and side panels would be trimmed back to them.

BTW this is Sabot, a boat plan sent to me by the nice folks at Classic Boatworks of Maine. Similar to a D4.

[Dave R]

The plan consists of a single sheet. It was e-mailed to me as a JPEG and I have it printed on a standard size sheet of paper. The transoms are given in half-breadths. I don't know if the dimensions are inside or outside.

I discvered that I had a copy of this plan on a disk and uploaded it to http://www.imagestation.com/picture/sraid18/pb54ee5fde5a49ecd95c84bd48594c05e/fdcdef2b.jpg.orig.jpg

Hopefully you can view it.

Thanks for the help.

[Dave R]

I guess I'm dense. I looked at the pictures and it seems logical to let the sides and bottom run beyond the transom and then to trim them back.

The picture showing the boat prior to attaching the bottom seems to show that.

Am I correct then that the given dimensions of the transoms are what should be actually laid out?

[Paul Scheuer]

It seems that there have gotten to be three items in this discussion: These are my understandings. More expert advice may follow.

Projected - I believe that the "projected" shape of the transoms are the images as seen from perpendicular to the surface of the transoms. Easy for me to say, it's your lumber. The concept could be checked with a rough scale drawing.

Bevels from the work - The bevels are cut as the joining pieces are fit, not as the transoms are cut out. (The projected shape above is the requried maximum shape to accomodate the bevels).

Running by - The pieces that can be fitted and joined with extra length and trimmed later, should be.

[Thad]

Paul's answer is clear and correct, not necessarily solving all your problems, but it should help.

[Paul Scheuer]

Not so fast. I am finally able to open the drawing file. My first shot at a scale drawing from the available information didn't give a result that agrees with either assumption. I'll try again, with a sharper pencil.

What I see from the drawing is that he gives a 17 inch dimension in the "bottom view" from the cl to the chine at the stern transom.

The "projected" stern transom dimension is given as 17 11/16 inch. I believe that the 17 inch cl to chine dimension includes the planking. So the actual transom wood showing outside (not including the planks and the bevel which is hidden inside) is 16 3/4 (1/4 inch planking).

The 17 11/16 projected stern transom dimension seems to include enough to cut the bevels. A good scale drawing still might be the ticket.

If nothing else, make all of your curves fair and do the same thing on both sides (i.e. make neat, symetrical mistakes). It has worked for me.

Also: See Norm's pram story about fitting a cheaper piece on the building form before cutting the expensive stuff.

[Paul Scheuer]

A good scale drawing doesn't yield a conclusive answer. It doesn't look like there is enough to do the bevels if you use the given projected dimensions as cut dimensions of the transoms. There must be someone here who knows the conventions. My skiff plans gave the dimensions to the outsides (points) of the bevels, and the bevel angles, but the drawings were not called projections.

[Dave R]

http://www.imagestation.com/album/?id=4292389405

Well, thanks Paul. I need to digest what you said and I'm beat right now so it'll wait until morning.

If anyone else is interested the link above should get you to the album with the plans. There's only a few pictures so it should be easy enough to find. Should be right after the airplane shots.

[PugetSound]

Dave,
I think that you are being overwhelmed with too much info of too detailed a nature, so let me back up to your original question:

The term "Projected View" is intended to tell the reader that the view is the real shape and not a fore-shortened shape such as what you might get if you had just drawn the end view of the boat (because of the slant of the transom). In other words, the projected view is basically the pattern you want the transom piece to be cut out to.

Follow Custom Skiff's advice and leave some extra on the transom so that you can template the bevels from the planks. You can still cutout and mount the transoms on the strongback since the top or shear edge of the transom will be your final shape (i.e. you can measure to the center of the top edge).

[ 04-16-2002, 01:49 AM: Message edited by: PugetSound ]

[Dave R]

Thanks to all for the info.

I was thinking that a "projected" view would be that as seen on a vertical surface and not perpendicular to the surface of the transom. It makes more sense to give the actual dimensions.

Paul, in your opinion, are the offset dimensions to the outside of the planks? Is that SOP for offsets?

Thanks loads to all for your help.

[Paul Scheuer]

PugetSound is correct. The "projected" shapes are the "flat views" of the transoms. A third projection, not shown on the Sabot plan drawing, would be the "end view" of the boat. In my world this would be called an orthogonal projection, and is not a true shape unless the transom surface is vertical.
Yes, the offsets are to the outside of the planking. Where he shows what looks like a bottom view of the boat, in the upper half of the center image on the drawing. The lower half is the top view, without dimensions showing the interior details.
My problem is whether the "projected" transom shapes/ dimensions include the bevels and/or the planking. Surely there must be some Sabot builders out there that could give you some measurements.
At any rate, I'd leave both transoms larger than you think you will need, and do the final fitting when you get to planking.
By all means, don't cut the arch in the transom tops until you get it all put together and right side up. You'll want a sweet curve with a bevel on top that relates to the sheer, and harmonizes with the angle of the knees. I get the most compliments on the transom-knee-sheer combination on my Yankee Tender.