I’ve had a go at estimating buoyancy and space in the Titanic lifeboats, together with a suggestion of how the extra passengers might have been accommodated without significantly compromising stability. Sorry for mixing imperial with metric, this is only to identify where the original data came from.
Working on the figures supplied in the earlier posts, and based on the nominal values of 160lbs per person and 64 people per lifeboat, the passenger loading amounts to 10240 lbs. or 4.655 metric tonnes. So if the laden lifeboat weighed 5.5 tonnes, the lifeboat would weigh 5.5-4.655=0.845 tonne. This would be reasonably consistent with a 1” thick yellow pine/elm hull.
The 14 main lifeboats each had an estimated capacity of 655 ft3; this is equivalent to a displacement of 19.05 metric tonnes of seawater leaving a theoretical 18.28 tonnes to support passengers. The gunwale of the lifeboat is lower in the middle than the ends, so the useful volume and capacity for the purposes of buoyancy calculations may be slightly less than the following calculation suggests.
I have assumed the likely average weight of persons in the lifeboats would be around 70 kg (154 1bs)*. Multiplying this by the theoretical capacity per lifeboat of 64 people brings the total weight of people, if filled to design capacity, to 4.55 tonnes. Therefore, the buoyancy safety factor to allow for waves and instability is 4.06 (18.209/4.48) or to put it another way, only one quarter of the available volume is submerged.
Would it have been possible to increase the number of passengers based on buoyancy alone? Lets initially take a target overload value of 12% or 7-8 people per boat, since this would have been enough to ensure all 1316 passengers could have been accommodated. This would bring the buoyancy safety factor down to 3.63 so there seems plenty of spare capacity on these grounds.
Regarding space, I have guessed how the seating arrangement would be, and assuming that some of the passengers have to stand in front of the rowers to achieve the design capacity of 64 (see plan view) although perhaps they could crouch, if not sit. There also seems to be about 2’ 3” of space (about the height of a table) below the rower’s seats, which probably wasn’t intended to be used. Adults could be accommodated below these seats by lying two people on the deck in opposite directions with the legs bent at the knees. (See side view). This would provide 8 extra places per main lifeboat totalling 112. Alternately, children below 4’6” height could sit in the same space, sitting 5-6 abreast, providing up to 22 extra places in each main lifeboat. This arrangement allows the extra weight to lower the centre of gravity and raise the centre of buoyancy, thereby generally improving the resistance to capsize.+
If this was how the 109 children were positioned, there would be space for 72 additional adults, totalling 1359 which makes room for all the passengers plus 43 staff leaving 853 back on the ship, ignoring similar arrangements for the smaller lifeboats. The buoyancy safety factor is in theory reduced down to 3.33 for this larger loading if we stick to the weight assumption of 70kg per passenger, although it might be nearer 3.63 in practice due to the higher proportion of children.
Is all this academic in view that the lifeboats were not filled anyway? I suspect the main reason for the slow loading of the lifeboats was the reluctance of the women to leave their menfolk and the reluctance of the officers to spell out the urgency of the situation to avoid a panic. However, if there was room and the men and women could be loaded together, this may have speeded up the loading procedure.
*People were lighter in 1912 than today and some of the passengers are women and children. As a guide, the average 19 old American male weighed only 139 lbs (63kg) in the 1900s. (Fat History: Bodies and Beauty in the Modern West - Peter N. Stearns). On the other hand perhaps many of the 1st class passengers were overweight!
+ Sailing boats, such as these should have been designed for greater capsize resistance than vessels powered by engines or rowers, so if the sail was avoided this should add a further factor of safety.