ZEUS, THE TAMAR, TIDES AND OTHER MYSTERIES
by Gill Mannings Cox
All have things in common: we love them and they command ultimate respect for they are unforgiving. There is no romance without an edge of danger. They all have many volumes written about them but I’ve limited this to what we need to know plus a few bits of interest.It is aimed at rowers who love what they do but who would like to satisfy their wonder at the amazing boats and the mighty forces they were built to work together with.
At the end there is a glossary of words you may not be familiar with and a brief bibliography.
I hope you will forgive the places where it becomes personal but it would have been dry as dust to write - and probably impossible to analyse our boat on our river otherwise.
ZEUS
All wooden boats are at the same time tough and fragile, on the eggshell or tunnel principle. On the outside surface they’re strong structures. On the inside they’re weak. A wooden boat resiststhousands of lbs of water pressure on the outside of its hull, but press down on the structure from the inside, or press on a part of the boat which is not its frame and it will be damaged.
So –
it can’t be tied down too tight onto a trailernamely the seats, the strake the seats sit on, and failing them the gunwale preferably above the seat.
Don’t stand on the seat unless you have no choice
Don’t run and jump in the boat
If you find you have responsibility for a gig on a shore at a regatta, ensure the keel is supported all the way along its length. Boats are lined up facing down the beach to the sea and when there are banks of sand or shingle, the keel is resting on ridges. Daylight in the middle = support at either end, danger of breaking its back. Daylight either end = supported in the middle, danger of hogging. Gigs are disproportionately long, so these things happen much more easily. `normal’ boat proportion for a 5ft beam would be 17 0r 18 ft length. Zeus is 32ft!
Slow down well before you think you need to: the boat will usually drift softly in( see `tides’). You can always dab her up a stroke or two – it’s easier than trying to hold water hard enough to come to a sudden halt.
Zeus is a finer build than most gigs. She’s a racing boat. Most training boats are clunkers. Think thoroughbred compared to cob, saluki to Labrador.
In practice this means that Zeus’s planks are thin – I look at my little finger nail and think half of that -and they’re shaved very fine where they go into the stempost and transom. The timbers ( ribs ) are thin but close together. The planks don’t overlap by more than they have to. The wood of the gunwale is pared right down to minimum weight. We don’t have a training boat, just an aristocrat so . . . Zeus – maximum respect! Gig design has a straight stem or cutwater, then hollows behind the bow to allow the displaced water to run on past. There is a lovely shear from the bow to stern.
Flare amidships then a sharp tuck up to a little wine – glass transom, the tuck is what allows following seas to run under not swamp the boat. All this plus the length of the boat is what sends the boat cutting across a lumpy sea. They have been honed over hundreds of years for the task. When I get into the boat the thrill of that history is always there, I am always aware of the privilege of rowing in a gig and especially such an outstandingly fine one.
THE TAMAR- (Not the pub)
Often beautiful and serene on the surface, full of danger beneath. We may envy sea – going gig clubs for their familiarity with chop and swell, but they don’t get a seal, kingfishers, egrets, and early mornings with water like satin.
It should be mandatory ( but it’s difficult to arrange ) for everyone to row up to Morwellham and down to say Cargreen at low water Spring Tides. Most of what I say next wouldn’t be needed. You would see trees like giant spiders all down the river. You’d know where the main channel runs, usually on the outside of bends. The channel splits into two up the wide reach from the monument on the Devon bank to Roger Lovejoy’s galleon. And you’d know where old quays have collapsed leaving dressed stone just under the surface where it looks ok to pull in, or an old boat suspended to keep wet.There are two back – eddies that at certain half – tides turn into whirlpools. The one just up from the galleon is the bigger. A 32’ boat wouldn’t be affected, just get a bumpy ride and it’d be hard to keep in the stream. I rowed a 12ft dinghy into it to see what would happen – it just spun a couple of times and was spat out. The other one is just up from Butspill. There is also a place where a depth – finder goes briefly off the clock, up from Okeltor, probably a collapsed adit. And downstream of the Danescombe bend the depth goes bout 40ft plus; it can be checked on the Admiralty chart.Also between Holes Hole and Cargreen.
The only one of those that is need – to – know is the Danescombe one – proof that there’s more water on an outside bend. The opposite bank is made of fearsome mud banks just below the surface for some way out into the river. After Pentilly, you should be even more aware of mudbanks. Much of what looks like a wide river is actually only 4 – 12 inches deep. You can tell where it’s very shallow: the water has a different look. At half tide it’s actually shiny mud. Shallow water rows easier than deep ( the man – made International competition lake at Windsor park is a minimum of I think 6ft deep all over, even the practice and return lanes ) but it’d be a brave coxswain who might hope to raise speed by crossing the Tamar mudflats. Round the bend to about Weir Quay you can expect a headwind. Also between cotehele chapel and the Quay, and as you head round the corner to Scrattons and Marsh Haye. You will almost always meet a sharp gust in several places near home: by Butspill Cottages, on the wide reach up to the galleon, and between Gawton mine and the first bit of the Morwellham railway.
The surface of the water gives you a lot of useful information; the water is brackish, yet the salt does not mix with the fresh stream. Unless there’s a ruffled surface, you will notice a double line of bubbles and scummy bits, sometimes only a few feet apart, sometimes spreading wider. That’s the tide pushing up through the stream and you can utilise this knowledge. As you’ve already seen, the tide will go mostly down the centre where the course of the river runs straight and will take the outside curve of any bend. Head your boat up between the lines to get a free lift on the tide. On the way back stay out of it, taking advantage of the freshwater stream that is always there going downriver, till the tide turns again. Beware though when we have big spring tides, or a lot of rain on the moor the day before as there will be big stuff going down the same current you want.
The midstream depth at Cotehele on a high Spring isabout 24ft. Boatyard about 21ft, Calstock about 18ft, Gawton still about 16ft but very narrow channel by then. At Morwellham only about 12ft. this is not This is not Admiralty info, but notes made from a Garmin fish/depth finder when bringing an 82ft lugger up for repairs. Ifyou’re not a confident swimmer, remember it’s only a few feet to the bank. ( Recommend swimming to the Cornish side)and at low water you could walk out.( apart from the mud)
WEATHER
We’re sheltered on the middle reaches of the Tamar but not unaffected. Mainly it’s cross - winds; a long narrow boat can cut accurately into a head – wind but where the estuary widens out a gig is vulnerable to a wind on the beam. As you can imagine, that’s the weakest point in this structure. A famous sea rescue many miles west of Bishop Rock, Scilly, was carried out in sea so rough that turning was impossible and the gig was brought home backwards. We’ll never go out in that but I have once been in a gig off Kingsmill lake when the turn was so dodgy I was nearly scared. Heavy weather at sea: we have a pump and a bucket but regatta organisers would cancel by force 4.
TIDES
By the time the tide reaches us 16 miles up the estuary it’s a different animal from what coastal clubs contend with. They can launch and recover at any stage unless they have rocks or big surf. If the club is on a lee shore they will have the constant concern about drift onto rocks. They also have tide - races close inshore and recurrent rips. Later when we all want to expand our racing skills we’d do well to learn about tide – races and prevailing coastal tides. Incorporating them into race strategy can give a boat a huge advantage as we have enviously noted on Scilly. Rips are too unpredictable to be useful to us but I suspect may have affected us in the course of one race on Scilly. When coastguarding on the North Coast I was astounded at the strength of the Northeastern flow, which meant good things like plankton being washed up into a certain cove and staying there, closely followed by a reliable number of basking sharks and bad things like the cars from the Boscastle flood ending up at Hartland Point and even south Wales.
I’m starting at the very basic level just in case. Whether on the coast or up the Tamar, we have high tides and low tides twice a day almost 6 hours flow and 6 hours ebb. Tide tables are only pennies over £1 and are fascinating reading. The times of high water get later all the way up the coast. At Penzance it may be at 1.26pm, at Plymouth 2.31 and up by Teignmouth well past 3 o’clock. Same on the North coast: St. Ives is earlier than Tintagel. We don’t have much slack water at Calstock. At the seaside you will have an hour or two slack water at the bottom and at the top end of the tide. Here, by the time it’s pushed all the way up from Plymouth it only has time to dally about 10 minutes ( springs ) and maybe 20
( neaps ) then turn round and go back. Spring tides come twice a month. The highest, all other factors being equal, falls the day after the new moon and the day after the full moon. Springs mean that the top of the tide is very high and the bottom very low. Halfway between the two Spring tides a month come neaps, pronounced round here`nips’. They are the opposite, in that the moon is not affecting the sea much, and the water doesn’t rise much or drop much. If you stood in a boat opposite the quay wall next to the Riverside, during neaps the water level wouldn’t alter much. Springs, the water would reach near the top and then go right down and expose several yards of mud. Regattas and courses on how to sail or handle power boats on tidal rivers tend to be planned for neaps so that you don’t run out of water when the tide goes out.
On very low Spring tides when there hasn’t been much rain we can get a phenomenon called a `bore’, like the Severn but small, about 6 inches at Morwellham. Around Calstock you might feel it as an unexplained small heave under your boat. The first time I felt it I had a scared passenger in a small sailing boat and I was sure a seal had huffed up under us, so I kept stum. You won’t feel it in the gig but you might feel your oar lift up.
If high water is in the morning and evening it will be spring tides here. If it’s in the middle of the day it’ll be neaps. If you watch local weather forecasts you will see that the times of high water vary progressively around the coast. Between Springs and Neaps the time of high water will move on just under an hour a day and the height of the tide will drop a little every day until you’re back at neaps. For instance the Spring tide might be 5.3 m and next day 5.1 m, then 4.8 m and so on. Then it will start to increase again after neaps until we’re back at Springs.
Standing at the boatyard slip or the pontoon on a neap tide coming in you may well see clearly defined the current of the tide moving up the middle and the stream moving down at the same time.
The speed of the tide alters during its ebb and flow. You’ll hear people say `it’s a very fast tide today’. Well that’s not possible. The tide certainly does increase speed on Springs because the huge volume of water pushes with more weight behind it up the channel. But what they are usually seeing is the difference between the speed of the water at very roughly half – tide. As the tide approaches the top it gradually loses momentum, till it finally reaches slack water. Same at the bottom. There is a mariner’s gauge called the rule of twelfths, which tends to be thrown out of true on a tidal river so I have adapted it down to fit our nees. We divide the 6 hours into thirds: the first third being slow and getting gradually faster over the next hour or two, then two hours where it races followed by two where it slows down and stops ready to turn again. You can see how prudent it is to boat out just as it slows down towards the top of the tide, especially on Springs, returning any time up to an hour or so after it turns, just before it speeds up. Although the increase and decrease in speed is gradual, it will seem crucial during launch or recovery to aim as accurately as possible at the best time when you’re dealing with a long, comparatively lightweight boat With the above knowledge there is no need to be hit or miss.
Rule for all boats, if you’re approaching your destination with the current, carry on past then turn and come in to land against the flow.
On the wider estuary, If you’re coxing down at Saltash or off Weir Quay, aim behind an obstacle such as a moored yacht so that the current won’t carry you sideways onto it. You smash your planks and swim and the yachtsman complains you scratched his paint.
If you’re aiming at a point across on the other bank, aim a good way upstream to compensate for the push of the current.
These are all applications for our own specific needs of the boating rule: `course made good’.
It is possible to calculate by how much but the above will get you there safely. You may not need to be in charge of these or any of the manoeuvres dealt with in this article for some time yet, but if you know about them and observe what’s happening when someone else does them it will help you when it’s your turn.
Appearances are deceptive on this river. After the surface seems to have stopped moving, you’d think the tide’s about to turn. Actually it will go on getting higher for another 40 minutes or so, half an hour at Morwellham. I call it filling up from the bottom and always guessed that it was something to do with difference of temperature between salt and fresh, but I don’t know why it does that and I’m sure it has a proper name somewhere.
Sometimes the tide tables seem way out. There are good reasons for this. I don’t know how much astronomical calculations predict tide times which are then affected by how much a ria has silted up, but this river has choked up a lot over even 10 years, and lots more over the last 30.
Then there is atmospheric pressure which affects tide times and heights. As I understand a very simple version of it, if there is low pressure the tide will rise higher and turn earlier than expected. High pressure will mean lower high water.
Much more exciting to a rower is the third phenomenon, when there is so much rain coming down this river in spate that it becomes unrecognisable from the lovely sun – dappled green tunnel going up to Weirhead. Difficult to believe that two Octobers ago we had no up tide here for about 3 days – it simply made no headway against that frighteningly turbulent force. Cautionary tale: I did once go out for a blast with a friend on a day when between Cotehele and Danescombe the water was like boiling milky cocoa and when the forecast gale came in early it hit the sails and knocked the little boat flat, several times. The old boy could have drowned, my fault for going out. I never sailed there again and the boat was sold. Next day I tried to row another boat home ( same size as the 42 ) and was thrown about like a cork – long oars with big scoops but they might just as well have been matches. All that rather shaming personal story is to prove several things: we will never take the gig out in that; if you get your own rowing boats, which I think is a great thing, please don’t go out in that; and where flashboats are concerned, best not.
USEFUL TERMS, not in any particular order.
Pieces of rope are called lines. The one you tie off from bow to pontoon is the painter. Pointy end, the bow. On the beam, sideways on to the middle of the hull. On the quarter – between the bow and the beam, ie at about 2 o’clock on a diagram. On the aft quarter, over the cox’s shoulder on either side. Usually talking about wind direction, an upcoming obstacle, an overtaking boat or a landmark when out at sea.
The straight piece of strong wood down the bow and disappearing under to become the keel is the stem. At the blunt end is the stern, the lovely wine – glass shape flat piece that the rudder sits against is the transom. The tiller is the bit you hold; the rudder the fin that changes direction as you move the tiller. The metal pins that fit the tiller to the rudder are pintles. Gigs have a clinker – built hull. This means that each plank of wood overlaps the next. I think in the USA the word is `lapstrake’. Built in narrow – leaf elm. Strakes as we know them are horizontal strengthening bars such as under the edge of the seat, which by the way is a thwart.
Where you sit numbers from stern to bow cox, 6 - stroke, 5 – bow, 4 – stroke, 3 – bow, 2 – stroke, 1 – bow. 6 sets the rate of strike, Tish calls cadence, 5 transmits that to bow side. 4 and 3 are the engine room. 2 and 1 are directional, hard to explain – the bow oar or sail or motor if it were possible is always in a position to turn the boat the most sharply. Hence why when we’re manoeuvring in or around an obstacle you’ll be told bow only or 2 only pull a stroke. That will pull us round in a sharp turn whereas all 3 rowers that side would be pushing us forward as well, making it a much bigger turn. Ship oars is the command to slide the oars down the length of the boat, the same side as your thole, as you glide up to the slip. We’re not very good at it.
Those fragile looking ribs going from the inwale down to the keel are timbers. The gunwale is the thick piece of wood often oak that runs all the way from bow to stern on the outside, pronounced gunnel. On the inner edge it is an inwale. Round the vulnerable part of the stem is a bow – fender. Along the gunwale are blocks with holes in, called tholes. In those go thole pins. Between them are leather pieces protecting the wood against rubbing, soaked in neatsfoot oil. The oars are usually Sitka spruce often imported from Canada where they grow very tall and slow in the cold climate, producing straight and close grain. The construction is interesting to inspect. They are fragile despite their strength and we shouldn’t really push off with them. A lightweight aluminium boathook is better for our river where you often need to avoid obstacles and free yourself from mud. The straight part is the loom and the spoon part is the blade. There are different shapes and weights of oar. Ours are strictly speaking river and estuary blades, but that isn’t a cause for alarm as most clubs’ blades seem to be not much different, we are not missing out on special sea oars which were always flatter and longer blades.
Port = left(red)
Starboard = right ( green ), as you look forward, pronounced forrard. Back of the boat is aft
If a boat’s keel is hogged, there is a hollow curve in it which will cause drag. Some older boats you’ll see at regattas are hogged and much as it’d be a thrill to row one of the 200 year – old boats they are not competitive; they’re possibly hogged, sodden, spread.
Ria = river valley drowned by the sea
Force 4 refers to the Beaufort scaleForce 2 is a gentle breeze, force 8 a gale.
All of these terms are in common use at regattas or on the estuary. Not among us because we’re new. You don’t have to learn them and use them, it’s your choice.But knowing them can mean you know what everyone else is talking about.
BIBLIOGRAPHY
· If you’re very serious about it and obsessed, take out a subscription to the ARA magazine `Rowing’, which often has an article on general aspects of rowing such as endurance, rehydration why a boat checks and so on. Sometimes there are pieces about coastal and Cornish.
· `Gigs and cutters of the Isles of Scilly’ A.J Jenkins, ISBN 0 954239-0-8
· `Weather- the Ultimate Guide to All the Elements’ contributors, pub Collins ISBN 0-00-220064-3(Lots of good weather books to choose from )
· `The Physics of Sailing Explained’ Bryon D. Anderson. ISBN0-7136-6886-5; excellent on tides. There are lots of good sailing books. They give you useful and interesting information on boats and how best to work WITH the water rather than impose your will on it which will not succeed. The means of propulsion doesn’t matter here. Others are `Sailing – A practical Handbook’ Jeremy Evans, ISBN1-84309-459-2, but it’s often available at Trago or remainder book shops for a fiver. The best is reckoned to be
· `Complete Sailing Manual’ by Steve Sleight, try Amazon because it’s a lot to pay when you only need certain sections of it.
This guide is here to help you as a reference manual. You’ll find that bits of it will come to you as you encounter the real – life situation. If there are any gaps I hope you’ll let me know. I’ll revise it from time to time. My qualifications for taking the job on are best illustrated by the project I was given at the age of 5 - `My Estuary’. On the blue water I painted a trawler and a sail boat and lots of black dots. When Miss asked what they were I said currents of course as if she was a daft landlubber.