Page 294 - Practical Ship Design

252 Chapter 8

8.6.5 Flared form
In this section attention has so far been focused on the provision of high stability at
the load and worst damage condition drafts, but the high GMs which Ro-Ro ships
usually have at these drafts are provided not for the intact condition but because
they are the corollary of providing the minimum allowable GM after damage.
Flared ship sides provide a way of improving the stability after damage, but in a
ship such as a Ro-Ro the freeboard to the bulkhead deck is usually small thus
limiting the gain from the flare. On the other hand, the height to the upper deck is
usually considerable and if the flare is carried all the way to that deck the increase
in the breadth of the ship at this deck will also be considerable: with corollaries of
more material and cost and a higher ship VCG.
A variety of ways of arranging flare with and without associated tumblehome
are shown on Fig. 8.15. Of the alternatives shown, that in (e) seems to offer most
advantages, but unless the freeboard is increased as shown in (0 the gain from
flared sides hardly seems worthwhile.

BHD
DECK/
MARGIN
LINE
BHD DECK / MARGIN
lfF.?.!)-~ LINE
T
(a) ( b) (c)

Fig. 8.15. Alternative flare/tumblehome configurations.
(a) Existing ship; margin line 76 mm below bulkhead deck.
(b) 15" Flare faired into sections; some loss of displacement made good by filling lines and/or
increasing B and/or T.
(c) 15" Flare with knuckle at LWL; maximum beam at upper deck increased by 3.8 m.
(d) 15" Flare between knuckles at LWL and margin line.
(e) 15" Flare between knuckles at LWL and IO" angle from margin line.
(f) 15" Flare between knuckles at LWL and new bulkhead deck (freeboard increased by 1 m).