Alan Gilbert
New member
- Joined
- Mar 23, 2022
- Messages
- 3
The transverse of curve of a yacht’s deck is traditionally laid out on the boatyard’s floor as follows:

Draw XY the length of half the maximum beam.
Draw XZ normal to XY the height of the desired crown.
With the compass centred on X sweep an arc from Z to touch XY at W.
Divide XY into four equal parts, XA, AB, BC and CY.
Divide XW into four equal parts, Xa, ab, bc and cW.
Divide the arc ZW into four equal parts, Zd, de,ef and fW.
Join ad, be and cf.
Draw AD normal to XY and the same length as ad.
Draw BE normal to XY and the same length as be.
Draw CF normal to XY and the same length as cf.
Sweep a fair curve through Z, D, E, F and Y—that is your half-deck curve. (The other half is obviously just a mirror-image, so make sure the curve at Z is exactly parallel to XY.)
I would love to know exactly just WHAT (if anything) is that curve? I have seen a claim that it’s merely an arc of a circle, another that it’s a hyperbola. I’ve seen no proof of either claim, and though I did once study maths at university it was many decades ago, and developing such a proof is way beyond me. Can anyone help, please?

Draw XY the length of half the maximum beam.
Draw XZ normal to XY the height of the desired crown.
With the compass centred on X sweep an arc from Z to touch XY at W.
Divide XY into four equal parts, XA, AB, BC and CY.
Divide XW into four equal parts, Xa, ab, bc and cW.
Divide the arc ZW into four equal parts, Zd, de,ef and fW.
Join ad, be and cf.
Draw AD normal to XY and the same length as ad.
Draw BE normal to XY and the same length as be.
Draw CF normal to XY and the same length as cf.
Sweep a fair curve through Z, D, E, F and Y—that is your half-deck curve. (The other half is obviously just a mirror-image, so make sure the curve at Z is exactly parallel to XY.)
I would love to know exactly just WHAT (if anything) is that curve? I have seen a claim that it’s merely an arc of a circle, another that it’s a hyperbola. I’ve seen no proof of either claim, and though I did once study maths at university it was many decades ago, and developing such a proof is way beyond me. Can anyone help, please?