Author: Carl Douglas
Last saved by: J S Blockley
Company: Carl Douglas Racing Shells

Amateur Rowing Association,
The Priory,
6 Lower Mall,
London  W6 9DJ.							8 January, 2001

Attention:  W.C. Thomson, ARA National Water Safety Advisor

Rowing & Sculling Boat Buoyancy

Dear Sirs,

	Thankyou for your letter of 5 January, which arrived this morning as I was preparing a letter to yourselves on the same subject.  I assume that it arises, as does my concern, out of the OULRC accident in Spain which claimed the life of Leo Blockley?

	I have researched the OULRC tragedy, including an exchange of correspondence with Jeremy Fagan who was involved in the event, and believe I have a reasonably clear view of the circumstances.  I have also witnessed several swampings on the Tideway and discussed swamping experiences with other rowers .  And almost 20 years ago I received witness reports following the death of a friend of mine in the French National Squad in a swamping of an eight in Bulgaria which occurred in very similar circumstances to the OULRC accident.

	I will, under the circumstances, restrict consideration to the swamping/sinking problem.  Our response is subdivided in a way which, I trust, makes problem & solutions the most clear:

1. Swamping effects in different classes of shell
1.1. All racing shells can be "swamped" - when waves force water over their saxboards to completely fill the open interior.  But the consequences of swamping are very different for different boat classes.
1.2. Single & double sculls have small open volume (the footwells), the large enclosed volumes (the decks) and usually enclose the space beneath one or both of crew.  Thus the ratio of the boat's residual buoyancy (its load carrying limit when swamped) to the all-up weight of crew, boat, etc. is so high that it retains sufficient freeboard both to support its crew within the boat and to allow it to be rowed to a safer place.
1.3. Most quads & fours, particularly coxed and especially bow-loaders, when full of water settle so low as to become difficult or impossible to row.  Due to their lower residual buoyancy (large open volume & relatively small deck volumes) they may even sink so low as to be driven under by the total weight of crew & boat, thus obliging their crew to enter the water.
1.4. Most eights cannot provide that minimum level of flotation which would allow the crew to remain aboard a swamped shell.  While the eight remains inherently buoyant (it will not sink), nonetheless it is easily swamped and has insufficient residual buoyancy to carry the crew, who then have to enter the water.

	In view of item 1.2 above I will now restrict discussion to boats for four or more crew.

2. How swamping occurs
2.1. If the waves are of sufficient height, water inevitably overtops the saxboards of even a stationary eight or four.  If the boat is moving, water generally comes in more quickly.
2.2. If any water is taken aboard, the boat sits lower in the water than before, making the waves relatively higher and increasing the inflow.  If the water is rough enough for the initial inflow to be fairly fast, the boat will settle rapidly in the water and quickly become unrowable.
2.3. To illustrate the scale of the inflow problem, I will first note that the perimeter length of the saxboards of an eight is close to 25 metres.  So now please consider the following analysis:
Where in long (not crested) waves the water surface goes just 15mm above the edge of the sax, the rate of inflow will be 0.0032 cubic metres/second (3.2kg/second) for every metre length of saxboard.
With waves just 15mm above the sax for 30% of its length, this will cause an inflow into an eight of about 24kg/second.
The volume inside an eight is around 1.8 cubic metres, and the weight of water corresponding to this volume is 1800kg.
So, at the indicated rate of inflow, this entire volume would fill in 75 seconds.
2.4. But that inflow would, of course, increase swiftly as the boat settles under the weight of incoming water, and sinking would be likely within 25 seconds.  This is very consistent with rates of swamping seen on the Tideway.
2.5. Once there is an appreciable volume of water within the boat, in the absence of bulkheads or other "dams" at stations across the boat that water sloshes to one or other end of the boat.  As it does so it depresses that end further into the water.  This greatly increases the overall rate of inflow (inflow at any point is proportional to the 3/2 power of sax depth below the water surface, and the percentage of saxboard length overtopped by waves also increases with immersion).  So the boat then swamps even faster!
2.6. The OULRC case highlights the problem:  2 eights went out in calm conditions but were both swamped when the water later became rough.  One was later bailed out but swamped again.  At each swamping the crew were forced into the water.

3. Consequences of immersion for the crew
3.1. If a crew can stay in a swamped boat - which, since the boat will sink under their weight once the water reaches the sax top, demands maintaining some degree of freeboard - then they avoid the risks of swimming (albeit holding onto the boat).  They also have some ability to propel the boat to a safer place.
3.2. If forced into the water the crew have lost all means of moving the boat to safety and now face the added risks of immersion - including hypothermia, thermal shock, miscalculated actions, panic reaction and being swept onto or under obstacles.
3.3. The OULRC case highlights the risks:  Despite swamping in relatively warm water, some of an intellectually elite crew did jointly decide to swim for the shore and one of them drowned.  Others say they felt themselves lucky to survive.

	I believe the 3 preceding sections amply describe the problem.  I will now make some observations and proposals, implementation of which would very much reduce the risk of swampings causing crews to enter the water.

4. Consideration of how to make crew boats safer
4.1. The fundamental cause of the vulnerability of many eights and fours to the unsafe swamping phenomenon (see Section 2 above) is their lack of adequate residual buoyancy when swamped, due to their large open volumes and quite small enclosed volumes.  Doubles and singles, which have large enclosed volumes precisely because they are readily swamped (often by the abysmal conduct of coaching launch drivers), will remain rowable and survive any swamping which does not break them up.
4.2. There is no significant difference in residual buoyancy (see 1.2.) between traditional wooden shells and contemporary honeycomb or foam cored composite construction.  Indeed, cored composite shells may have a marginally higher residual buoyancy than traditional shells, due to the lower mass per unit volume of the cored skins.
4.3. Contrary to popular belief, the swamping risk to an eight or a four is not increased by having transverse barriers to the longitudinal flow of water within the hull (e.g. section joints, full bulkheads or enclosed compartments).  Lack of transverse barriers allows water, if taken aboard in quantity, to flow or surge unrestrictedly to one end, forcing that end lower into the water, increasing water inflow & thus causing faster swamping.
4.4. Raising saxboards, and removing gaps in the saxboards (e.g. behind the cox's seat), will tend to reduce or delay the onset of swamping.  But it is doubted that saxboards can be higher than at present without hampering the rowing stroke.  Nor would this attack the fundamental problem of inadequate residual buoyancy.
4.5. Thus we believe that the only practical cure for the swamping problem is to increase the shell's residual buoyancy, making it able to carry its crew when swamped.  This can be done in two ways:
4.5.1. Enclose the entire space under each rower's slides, down to the hull, into a sealable compartment.  This would increase the boat's residual buoyancy, depending on its extent, by upwards of 35kg per person but add little or nothing to the weight of the shell.  That should be ample to make the boat unsinkable while carrying its crew through swamping conditions.
Some eights and fours are built that way.  The rest are so built that conversion to enclosed under-seat compartments would involve minimal work or cost.
(N.B. 35kg of buoyancy is enclosed by a cuboid space of only 80cm x 40cm x 11cm.)
4.5.2. Insert additional buoyancy under each seat, either by means of added pieces of low-density rigid foam (with resin-sealed surfaces to prevent water absorption), or by inflatable bags.
This could be done with almost any existing eight or four.
4.6. Either of the above added buoyancy alternatives would further act as barriers to prevent the surging of water to one end of the boat.

5. Summary & Conclusions
•		Swamping is a ever-attendant hazard of rowing, whatever the class of shell from single up to eight.
•		When a boat with insufficient residual buoyancy (i.e. enclosed volume) is swamped it cannot be rowed towards safety and will probably sink, forcing the crew into the water.
•		Swamping will be more rapid if a shell lacks effective barriers to longitudinal internal flow & surge of onboard water.
•		A crew forced into the water is in far greater danger than one which can remain in their boat.  This danger comes from several causes, and fatalities do result.
•		The one sure way to prevent a swamping situation forcing a crew into the water is to ensure that the shell is built with, or has added to it, sufficient enclosed volume to ensure that it retains adequate freeboard to remain afloat with its crew in place and to be rowed (albeit with difficulty) towards safety.
•		The additional buoyancy volume, present or added, should preferably be located at a level below the slides.  The space exists there, in any case, for 35kg or more of buoyancy per crew member (except cox), which should be adequate for the purpose
•		Preferably the buoyancy volume will be as enclosed & sealable compartments, occupying the entire volume between each slide bed and the hull.  This already exists in certain makes of shell (e.g. Janousek) which appear to remain afloat with their crews when swamped.  It also provides surge barriers.
•		For modern products which lack under-seat buoyancy there appear to be no production or structural reasons why the space beneath each slide bed cannot be entirely enclosed as almost all now feature solid slide-beds with almost-complete end closure below.
•		For older shells it would be possible either to insert blocks of solid foam buoyancy (with sealed surfaces) or inflatable bags.  The problem with inserted buoyancy is to ensure that it does not come loose.  The problem with inflated bags is that they require maintenance and could bulge & interfere with the seats.

	I trust that after reading the above you will return to the writer with any queries & comments you may then have.  I look forward to hearing from you very shortly, but meanwhile I am copying this letter to Jeremy Fagan of OULRC for his reactions.

	Yours faithfully,

	_______________
	Carl Douglas   C.Eng.  MSc  MIChemE

Copy:   Jeremy Fagan, OULRC