Use of bevel board for frame angles

[D Gobby]

I could use some help on the proper use of bevel boards for frame angles and plank thickness.
I understand using the board from two different frames forward and aft to get the proper angle and to reduce thickness for planking if the station distance is the same but what do you do when the frame spacing changes eg. frame 1 from stem to frame, and frame 1 to frame 2? Since the frame spacing is of different distances fore and aft. Do I loft in a frame forward of frame 1 the same distance as the spacing between frame 1 and 2 and take one reading from this false frame? The same situation occurs and the stern as well.
Do I need to make two angle readings fore and aft for each frame and average the two or will only one reading be ok. Any help would be Great!!!
I really would like to do this right.

[Bob Cleek]

Take the angles off of your lofting of EVERY frame and make up a bevel board for each frame. You may find two or three amidships are nearly the same and be able to fudge those, but as few (decent) designs are completely symetrical on either side of the middle station, you need to take the bevels for each frame. This is particularly important at the bow (and stern of a double ender) where the bevels increase dramatically. The bevel will affect the plank thickness deduction and you have to develop the plank thickness accurately or your hull won't come out right. Console yourself with the reality that the more time you spend doing this, the less time you'll spend fairing frames and planking will be much, much easier. If you take the bevels off the FRAME, rather than the station, (as you should) you won't have any issue with frame spacing. Your frames are lofted, aren't they?

[ 08-18-2002, 02:07 PM: Message edited by: Bob Cleek ]

[D Gobby]

Thanks Bob

Maybe I worded my question wrong. How bout the proper use of degree sticks for frame bevels. In Wooden Boat (March/April 2000) #153 pg 64. It shows how to make and use a degree stick for frame bevels. The Design I'm working on has 3 different frame spacings. I understand the concept of measuring the frames which are lofted when the frames are of equal spacing. eg. frames #2,3,4 are all the same distance apart. Make a degree stick for that spacing and take readings from both sides. Works great for frame #3 as the two frames on either side are equal distant. But what do I do at frame #1 where the distance fore and aft of frame #1 are not the same eg.from stem to frame #1 is 40" and from frame #1 to frame #2 is 30" the same occurs at the stern between the last frame and the transom. Or should I just measure from frame to frame using a degree stick of that spacing eg. check frame #1 from frame #2 using a degree stick made using the 30" spacing. In (Boat Building In Your Own Backyard) by S.S.Rabl He also explains using a bevel stick but only measuring forward frames forward and aft frame aft. Checking the frames from both forward and aft seems to be more accurate and also determines how much to reduce for plank thickness. I understand how important this and want to do it right!!!

Thanks for any help.

[D Gobby]

Not quite ready to let that cat out of the bag just yet. I need to get frames built and plywooded then I'll let you know. It is a very sweet 15' day sailor and to my knowledge this design has never been built.Any help with my confusion on this bevel stick thing would be a help.

[Paul Scheuer]

Let me take a shot at misunderstanding this.
If you look at three frames (from the top), the angle of the bevel of the center one will be parallel to the line between the first and third one, if, and only if, they are equally spaced. If that's the question, I personally don't think the difference for reasonably unequal frame spacing would matter, if the spacing is within 10% or so. If you really want it to be exact, the false frame would be the easiest way, or you could do the geometry. You're going to true up the frames with a batten when you plank, right ?

[On Vacation]

Ask questions and expect answers of a mystery. The moon must be in a bad angle this week.

[Tar Devil]

Any help would be Great!!!
I really would like to do this right. Not quite ready to let that cat out of the bag just yet. I need to get frames built and plywooded then I'll let you know. As Spock would say, "Is not logical!"

Later,

Phil

[A. Mason]

D Gobby, I think you better fess up to what you are building. These guys are real inquisitive and really do need to know the specifics in order to be able to really help you. They're a good bunch ;D and ought to be more forthcoming if they know what you are working on. - Anita

[Ross Faneuf]

I had to deal with variable frame spacing when I lofted Ceol Mor; frame spacing varies from 14" to 22". I went through that (very) satisfying process a whole long time ago, and so I may not remember the entire process I used; but it was something like:

Make up a bevel board like the book says. Lay out all your different frame spacings on it (so the board has to be big enough for that). Now make up a degree stick for each of the spacings (I seem to remember I had about 8).

I assume you have done a complete lofting, faired and all, or you have the equivalent. That you have faired and verified the body plan. And that, most importantly, you have lofted the frames (full size) and faired them (on the gain side, naturally).

I also assume your goal is to end up with an accurate, fair frame plan with the planking thickness removed (otherwise, the whole exericise with degree sticks and all is a waste of time).

For each frame where the frames on either side are evenly spaced, grab the correct degree stick and read your bevels off the lofted frame plan. You read the degree stick to each adjacent frame, and average if you don't get the same angle each way.

For each frame where the spacing is irregular, grab the two degree sticks for the spacings to each side. Making sure you are using the correct degree stick (DONT mix them up), read the bevel to each side, and average if they don't agree. I found they didn't disagree all that much, but Ceol Mor has a nice fair shape with no surprises.

The aftmost and foremost frames will be a bit more approximate, as you can only read bevels to one side. Don't worry about it.

Then, (and this is what I did) you can make up a planking stick which allows you to lay out the projected planking thickness directly on your lofting. This is how you do it (this is probably in some book someplace, but I don't remember and so can't give proper credit).

Go through the step above of figuring out your frame bevels - say, every six inches along each frame (depending on your boat size; I used about 6", and Ceol Mor is lofted 31' on the water line). Anyway, measure the bevel in enough places on each frame so you can do a good job of lofting each frame with the planking thickness removed. I ran the frame lines out past the sheer line to get fairer curves. Now make up a single thickness stick. I used a piece of 1/8" pine. The width of this stick is the molded planking thickness (for C.M, 1 1/8"). Now draw successive lines across this stick at 1 degree increments, spaced far enough apart so each is distinct - say, 1" apart. You will draw a line for each bevel you found on the frame plan (nearest degree, don't bother with fractions). I did this by laying it across the bevel board at a convenient point and tracing the bevel lines. Label the lines, of course. Each line represents the thickness of planking projected at that bevel.

Go back to your frame plan. At each spot you've labeled with a bevel (in degrees), find the corresponding line on your thickness stick. Lay the stick with one edge (at that line) on the frame so the line is perpendicular to the frame at that point (much easier to do than describe). The other edge of the stick projects your plank thickness quite precisely; mark the spot (an awl does so quickly and accurately). Do this at every point, connect and fair the dots (or punch marks or whatever you did. VOILA. A frame plan with the projected plank thickness subtracted. Once you've done all the bevels, using a thickness stick to subtract planking thickness goes quickly. If it looks like you could use more points, simply put them in; you can always add another bevel point.

I did this with Ceol Mor. I used the faired frame plan to laminate all the frames, and I then built to these lofted frames without molds (carefully set up, of course). When I finally had the backbond and frames set up, my maximum error was about 1/16" in 2 frames, and I got rid of most of that by re-bracing the frames.

[D Gobby]

Ross
Thank you very much. That was what I needed. You answered all my questions for now. The boat as well as the frames are lofted. I'm getting ready for frame construction. Thanks again for the explanation.

Anita
I'm not trying to keep this a secret. I would just like to have something to show before I tell the world what it is I'm up to. I know that everyone here will be supportive. I would feel better once I'm further along.