Diagonals on a line plan

[vinceUK]

Dear all,

this may seem as a stupid question but even after a few articles/chapters of books read on this, I am still a bit confused about how to draw diagonals on a lines plan.

They seem of primary importance but I don't know what they reprensent and how to draw them.

If anyone can help me on this, this would be very useful.

Sorry again if it looks stupid to you. Thanks by advance

[Wynand N]

They are useful in fairing hull lines. There are no hard rules as how many or how to draw them through the section lines from centre line....

My 2 cents worth

[alidesigner]

You start will an offset from centreline, say 200mm intervals, and then draw the lines at whatever angle suits. They were mainly used to get offset points for drawing full size lofts by hand. If using CAD you might not even need to bother with them. I havent bothered with them for about 15 years now.

[jehardiman]

Diagonals are used for fairing the aft run or the heeled waterline, and as you surmise, are one of the primary lines of importance. I usually put a diagonal in as the 5th or 6th line (after the profile, waterline, and stations at bow, stern, and midships).

Diagonals should be placed approximately perpendicular to the shell in the area you want them to control. And because they are of such importance, they shouldn't be too close to each other or have any funky kinks in them, especially in modern transom sterns. In lofting, I generally recommend fairing to the diagonal in cases of conflict as this will give a more fair line.