Sailing: Newsletter Challenge (06/01/10)

Your interpretation may be correct, but I think by "a tacking strategy, sailing back and forth across the river's width" the writer meant sailing back and forth at the angle that would best cause you to win the race (about 45 degrees to the banks and the induced wind). It is, after all, a sailing race, in which the sailors are expected to sail the course that will cause them to win. Sailing a "proper course" (a term used in the rule book) would mean that you would arrive at the finish line in significantly less than 2 hours.

I have to agree with you fully.

GA

What many have forgotten is that the boat that tacks, but just for example at this moment does not gain any speed over a boat just going down river, WILL ARRIVE AT EXACTLY THE SAME TIME AS THE RIVER MOVES BOTH BOATS AT THE SAME SPEED!!!! (All other points being equal!)

Stupid statements that losing momentum at the point of going about is simply not understanding the situation. The boat STILL moves downstream at the speed of the river, even while going about!!!

Assuming that you have a large well cut Genny and your boat can sail at 45° to the wind, then it is HIGHLY likely that you will make up and actually add a tiny bit of speed to the boat that is tacking, therefore the tacking boat will win....it does not have to be much, even 1 cm in front is a win situation.

For the opponent it would be better to have less free board and you would want maximum hull drag and minimum air drag to maximise the speed down the river. The air drag will slow you down you would end up say 4.9 or 4.8 km/hr.

The tacking manouvoure is better as the sail will act like an aero foil and drives the boat forward while the current is still pushing at less than 4.8 km/hr but you would be gaining by 2 - 3 km/hr by the action of the apperent wind giving you a total VMG of 0.7 (cos 45 Deg) of the 2- 3 km/hr gained ( so 1.4 to 2.1 km/hr ) in total of 6.9 km/hr

So the opponent will finish at 2.08 hours while you will finish at 1.44 hours

1.) 5km/h is nearly 3 miles/hour!

2.) the induced windspeed of 3 knots creates a sailing speed of 3 knots rectangular to the rivers flow direction, a total sail speed of ~4.2 knots (45° cruising, square root of 18)

3.) the distance for the diagonal speed line is more than 40% (factor square root of 2) higher than the shortest line for the drifting sailor.

4.) result: the higher speed for the longer distance results in the same race time for the sailor as for the slower drifter

fixed and closed

LOL!!!

A person with a strong sense of humour and a manager's intellect!!!

I think you are forgetting that regardless of the wind all boats move downstream at the same speed. So I think that instead of considering on one case JUST the flow of the stream and on the other case JUST the induced wind, on the second case the induced wind should add to the stream effect, thus giving the tacking boat an advantage.

Hum... I believe the achievement is not to "gain" on the wind (there is really no wind) but not to be slowed down downriver by that immobile mass of air while tacking madly across the river. While it might not have been entirely his intention, Randall illustrated very clearly the movement of two boats starting in precisely the same position in his diagram in post #21.

Again, failing to see a geometric illustration of a tacking boat advantage, I am forced to maintain that the passive sailboat wins for the keel of the tacking sailboat cannot be perfectly efficient (that is, discounting the gains that could be attributed to that madly tacking boating while "rolling from one tack to the next ;-)

I still believe adding the river flow to an imaginary wind, as you (and many others) are suggesting, amounts to counting the river flow twice.

Now, to really mess things up, I confess to having come up with the "ice boat on a drifting ice slab" analogy in a previous discussion on the very same subject. If someone is willing to rationalize this - you are very welcomed...

I had to give you a GA.

Not just because of your (fully correct) sailing knowledge, but also because you held back like a true Gentleman (or Lady?)....well done.

I am not well renowned (as you now are by the way) for such good manners in such cases of blissful ignorance!!!

Also your English is really excellent too (assuming it is not your first language!), better than many here with it as a first language!!

As you requested and very LOUDLY:- "PHUKET!!" (Was that "LOUD" enough?)

Sounds not so good in English though!!!

(I hope everyone understands why I said it so LOUDLY!!)

Also I hope to see you more often on CR4 as well......you are most welcome.

"I still believe adding the river flow to an imaginary wind, as you (and many others) are suggesting, amounts to counting the river flow twice."

If I may, I'll try to counter this statement:

. set a reference frame solidary with the body of water

. on the initial moment you have, on this reference frame:

. Vboat relative to the air = 5 km/h

. Vboat relative to the water = 0

(this is obviously a simplification, but the drag effect of the air at this speed can be safely neglected, on bare poles etc.)

These conditions are mechanically equivalent in all aspects to a boat sitting still in a body of still water (suchs as a lake) with a 5km/h breeze coming from the finish line.

Now, as MoronicBumble (#53) has explained perfectly, there is a way to start sailing upwind under these conditions.

So you end up, on your mobile reference frame, with Vboat relative to the air > 5 km/h and Vboat relative to the water > 0.

Now, if you revert back to "earth" coordinates, if you are to determine Vboat you have to sum the velocity of the boat relative to the moving reference frame with the velocity of the reference frame itself (the velocity of the flow).

I think you will agree that this doesn't amount to accounting for the flow twice.

(Thanks to Randall for his help on how to insert pictures - a picture is worth a thousand words :) )

Really well put (even I understood it fully, well done, So surely some of the "non" sailing types will also? or am I hoping too much for that?).

I would just like to add for anyone who understood what you just wrote, please remember that on lakes around the world, many boats sail on completely still water, but with a 5MPH breeze (Zephyr?) and get about, even directly into wind (tacking and reaching).

That is the same as wind still and a 5 MPH current of the river water......

Under such conditions on the lake, some special boats will achieve as much as 10 MPH or more, but of course the are on still water and are sailing longer distances (tacking/reaching), BUT THEY ARE STILL MAKING HEADWAY DIRECTLY INTO WIND!!!! (Also called "Course Made Good", which is also the "ACTUAL" speed "DOWN" the river, parallel to the banks, which may only be say 2 or 3MPH!!!! )

But then add this headway speed made to the speed of the river in the case in question AND THAT WILL BE THE SPEED THAT THE BOAT WILL ACHIEVE DIRECTLY DOWN THE RIVER. Maybe in total 8MPH or so..... (depending upon boat type/quality of skipper etc..!).

I wonder if the sceptics now understand full?

(But I somehow doubt it, they are too well entrenched!!) Let us wait and see!!

If it was me. I would throw in a drouge anchor, lean back and open a frosty

The time is 2 hours (5km/hr for a 10km race). There is no wind on land so there should be no wind on the river. The boat sails were taken down to reduce the wind resistance produced from the 5km/hr movement with the river current. Without wind tacking would not be possible.

I have to disagree: I have never sailed; several posters who claim they do still don't "get it". Everyone, whether they are a sailor themselves or not, knows that it is possible to make headway against the prevailing wind by tacking. What the people who still don't "get it" are struggling with is the change of frame of reference. This is despite the fact that Tornado explained it perfectly in posts #2 and #4; someone even voted against post #30 from Usbport, which explained it perfectly in a very intuitive and non mathematical way.

No, those of us who have sailed, especially those who have sailed home on an incoming tide and against the wind do understand it. Yes, it is possible to make headway against a prevailing wind by tacking, otherwise sailors could never complete a triangle course, or any round trip in a prevailing wind for that matter. One needs to remember that in addition to the prevailing wind, you also have a 5 knot current (that is creating that wind). The question comes down to this: Will the tacking boat be able to use the apparent wind to make good over and above the current. I agree with those who say that it can, but only in an ideal theoretical world. My earlier post was based on real world conditions. Of course, in this exercise, I should have realized that only a theoretical ideal can be considered, so, I will change my earlier answer and agree with those who say that the tacking boat wins.

"Will the tacking boat be able to use the apparent wind to make good over and above the current"

BMW, you are not trying to "make good over the current", it's already carrying you in the direction you want to go, you are using the apparent wind to add to it, thereby making significantly greater progress towards the finish line than the fellow that just lets the boat be carried by the current.

Right, that is what "over and above means", adding to it.

Exactly. You're making baxterm and Randall's points for them. Assuming the boat is capable of making any progress upwind in still water in a 5-km/h headwind, it will add that progress to the 5 km/h current and therefore win the race against the boat that is travelling marginally slower than the current.

I have only sailed a handful of times, so can't speak from great experience, but are you seriously suggesting that the effects of slip angles under sail and drift during tacking are such that a typical real-life boat and crew cannot make any upwind progress in a 5-km/h wind?

You are probably correct that any craft should be able to make some progress versus drifting in the current. In a real world scenario, how much truly depends on the boat as well as the skipper and crew. I have sailed all my life, including a regatta winning career in FJ's and dinghies as a youth. I have also sailed catboats, catamarans and windsurfers. Some can make a 45 degree angle of attack, some definitely cannot. When I say that the tacking boat has to make good over and above the current, I am saying that the lift and speed generated with a 5 knot breeze will need to more than compensate for the effects of increased drag and the change in the angle of attack of the apparent wind (the faster you go, the more the apparent wind forces you to bear off as it changes direction relative to the boat). There are times when sailing a windsurfer in light air, 10-12 knots for example, that you are doing well to hold position on a plane; it is usually possible to pinch upwind at a very slow pace and sailing as a displacement hull (non-planing) in these conditions. In reality, we generally "pump" to get back to the beach when confronted with less wind and are happy to have made it back to the cooler.

Nonetheless, my initial error in this was to think too much like a sailor and not stay in the theoretical realm; as I said earlier, I have changed my answer.

(His name is BWW I believe!)

He agrees with us now as well, so do forgive him please!!

Why is everyone leaving out the fact that the hypotenuse is always shorter than the sum of the other two sides of the triangle and that the efficiency of the sailing/tacking boat must be sufficient to overcome the additional distance it must travel?

is the air mass above the river moving with the river? Consider adiabatic process. Does it not change day to night on a river, especially a river with head waters at high altitude?

"The river is infinitely wide, it is moving at 5k, the air is still. So you in your boat can't tell whether the water is moving or the air is moving. Given that, you do the logical thing and sail. Good God almighty this is so simple!!"

The perfect answer!!! (Except for the units)
Now, on to thngs that matter.

Why bother????

If the boat just drifts with the current, it does 5MPH downstream.

A tacking boat STILL DRIFTS DOWNSTREAM AT 5MPH WHILE SAILING! So at that point both are still equal!!!

So its final speed will be 5MPH PLUS what it makes good tacking........that is the sum of both tacks going directly into wind.......

So a tacking boat, only actually has to make a tiny bit of extra speed in the direction of downriver to win....even quite unhandy boats with little ability to "point high" will still get there first!!!

Also, as I and several others have pointed out, if you take a lake with still water, with a 5MPH breeze over it, many boats will be able to "sail" around the lake quite easily........as some boats can actually sail to windward (sum of both tacks in the direction of directly into wind) at a speed approaching twice the wind speed.......the better the boat design, the faster it can "make up" under such circumstances.....

No tricks needed. Nor Pythagoras either!!!

Your loss, not mine!!!

sail down wind at night and you would win by a mile, although everybody would do it.

katabatic drain

you are right, we win because the captain did his math and positioned his boat properly for this race. He put in and sculled to the center, or was towed, (before 5 minutes any thing goes) so he crossed the start line just after the gun, going at max speed. the other boats start drifting downstream as soon as they put in and they are also at the mercy of the current, so how does one time the start? in the real world the one who does best at this gains a big advantage. ( in theory, all boats start equal and drifting parallel so any tack would make you bump into another boat, and is this really a sailing race? we would be the only boat in it )

You are right, indeed. Reality is harder.

Thanks.

You are not thinking "out of the box"....

Read some of the other good posts here that will demonstrate in a far easier manner, that the tacking boat will always win.......no matter HOW bad its tacking angle is as long as its 89° or better........

At 90° it will take the same amount of time as the boat just riding the current!!

Its a really simple problem........you are thinking at too high a level........its simply not working for you!! Sorry!

Assume that the tacking does not bring any positive (or negative) effect on boat speed for a second. Then both boats will arrive together. That is tacking with a 90° angle........anything better than that (easily achieved) will mean that the tacking boat (which has a consistent 5 MPH, as has the non tacking boat) will add to that 5 MPH a small measure of extra speed.....OK?

So the tacking boat will win.

Take a high perforance hull, that tacks at near to 40°, it will streak away......

Was just curious to know the approximate winning time.

Thanks, buddy.

"Sometimes you get the bear. Sometimes the bear gets you!''

If I am in this sailing race , I am the only boat that is sailing, thus the race is canceled due to lack of competitors. In this theoretical race , how could every one start equal? There can not be any racing among drifters, who dangle their toes and have brewskis.

You can look at this as a relitivity problem. Change your point of view and say you are in open water with a wind of 5 km/hr and you can see that the best your opponents can do is stay in the same place and not drift back. Finding the time is just an estimation at best. You have to make a lot of assumptions about conditions.

The boat tacking back and forth. Less water will slip past the hull and keel crossing the current than one inline with it.

The current is moving the boat and the apparent wind is creating resistance to the motion. The winner (in a little more than 2 hours) will use his sail to keep his hull 90 deg. to the current to get maximun exposure and little resistance to the air.

Assuming the boat can sail upwind at the wind speed (5 kph), and can sail at an angle of 45° to the wind, the boat speed downriver through the water will be 3.54 kph. Over the ground, the speed will be 8.54 kph, and so the boat will reach the finish line 10 km downstream in 1 hour, 10 minutes, 17.7 seconds. The boat that drifts downwind at the speed of the current will reach the finish line in 2 hours. The tacking boat will win handily.

I win in the time of one hour.

The river current carries me at 5 Km/Hr.
I tack at approximately 45 degrees.
Assuming zero wind and water resistance,
the still air advances my boat at an additional 5 Km/Hr.

ASSUMING that I can either complete the course on a single tack,
or change tack instantaneously, the total speed = 10 KM/Hr.
Therefore, I travel the 10 Km course in one (1) Hr.

The other boat takes two (2) Hr, assuming zero wind resistance.

You win! Your boat is positioned perpendicular to the direction of water flow all the time which results in overall largest momentum. Never mind the tacking - there is no wind. The winning time is somewhat larger than 2 hours.

Actually, using the 5Km/hr current it is possible to create an apparent wind, airflow over the sails, this would allow the boat to tack downstream at 6-7-8km/hr Therefore the tack boat (if tacked efficiently) would be quicker

The drifting boat takes 2hours the tacking boat would take less than 2hours - if it was a catamaran or trimaran it would be even quicker

No wind on the land usually means no wind on rivers. So tacking and using the wind is a no-go anyway.

Boats going downstream direct at 5km means two hours for 10 kms.

Tacking with no (stated) wind loses - distance is longer anyway.

The direct approach wins and takes 2 hours.(Though they could have rowed or paddled and travelled faster)

Just read the thread ...

Total rubbish.

"Though they could have rowed or paddled and travelled faster"

If you hold to that, how can you not understand the wind issue?

Rubbish.

Let's make it simple. Consider the water as stationary, and the air, land, and finish line as in motion relative to the water and boats. Since the drifting boat remains at the starting point in the water, the finish line will reach that boat in 2 hours. The tacking boat will make some progress away from the starting point in the water, in the direction of the finish line, so the finish line will reach it in less than 2 hours.

Bends in the river make no difference because, in this case, the relative wind is always blowing upstream.

As far as cheating in a drifting (light-air) race by blowing on the sails is concerned, that doesn't work (trust me); just face the stern, pucker up your lips and blow.

Assuming the river is deep enough, I would suggest that you put up all sails, capsize your boat i.e. turn turtle. climb on top of the hull and drift downstream with the current.

Upside down vessel will be very stable and totally maxing out the engagement with the water flow, upside-down hull will offer least drag resistence to the relative air flow.

You should get there sooner than other rafts, but maybe slightly wet. Time to finish - less than 2 hours.

There are a couple of other points that are being neglected.

1) The time it takes to decelerate and accelerate at the end of each tack. How wide is the very wide river. I consider a minimum of 5 Km to be very wide.

2) The resistance that is being applied to the hull from the 5 Km/hr river current pushing against the 5 Km/hr wind of the tacking boat.

Your point 1) is totally irrelevant provided the tacking boat tacks "better" than 90° (which is a broad reach and not a tack anyway...!!).

The current does not slow down (like the other boat being just carried by the current) just because the boat is tacking!

The boat, even if it went into "Irons" would still be moving downriver at 5MPH.....as is a stationary (I mean not sailing or tacking, just letting the current carry it) boat....The slowest speed relative to the land will always be 5MPH.....never a "minus" speed!!

Most sailing boats can tack at around 50° or better, some (Rotor Sails) can even get to within 20 - 30° of the wind.......(for a normal mono hull sailor thats almost as good as "tacking directly into wind" for him......incredible....)

You can read more on tacking here:-

http://en.wikipedia.org/wiki/Tacking_%28sailing%29

If you think for a moment of a river that is completely still (I know, thats a long lake not a river!!), eg. no current and a steady 5MPH wind is blowing along it, you will find literally thousands of different types ofsailing boat that can "tack" or "beat" to windward in such a breeze.....moving (at an angle to it) in the direction that the wind is coming from. Its a normal sailing procedure.......Thats how boats get from "A" to "B" when the wind is against them.....for many thousands of years!

If you then work out that "speed made good" directly to windward on a still river, and add it to the one moving at 5MPH only, you will have the speed of the tacking boat on the river....

It would not surprise me if certain types of boat are able to make at least another 5MPH made good (travelling on a 45° tack at say10MPH or so "MORE" than the river current!) on top of the river current, though most will make probably between 6 to 8 MPH in total (River current + speed made good along the river)....

As far as I am aware, the original poster ignored wind resistance, hull resistance etc etc.....so it is really only a theoretical question......though in practise it will be quite easy for a tacking boat to still make far, far better time down river than one just floating, in such conditions as set.....

I mentioned before (in an earlier post) that for similar reasons, certain fast mono and multi - Hull boats, even "Tack" (Jibing!) downwind and still make a far better pace downwind than boats who just run before it.....it also makes for a steadier boat, whereas a mono hull running before the wind will tend to "wallow" to port and starboard, a motion that I personally detest of all the sailing and boating "motions!"

Yes I have puked my guts up a few times over the last over half a century or so....one forgets just how bad it feels when one steps on the boat at the start of the voyage.

If its any consolation, there are many others here that simply have even less of a clue about sailing than you do.....

PS. If I have used any sailing terminology that is not understood by anyone, either look it up on the web or ask me, I will explain further!!

I live on a sailboat on a very wide river. (St. Johns) This condition exists all the time. I just start the engine and get on with life.

I can honestly say after a couple of years on CR4, that I have never seen a Blog that provoked so many idiotic posts from guests!!! But as guests of course we cannot see who they really were.

So guessing a bit, they knew they were not up to the question in some way.....

It really has driven the worms from the woodwork.......

Andy,

Based on a response I got last year, it appears that most "guests" are active members of this forum but, when out of town or some such and on a different computer, they cannot log on with their normal forum ID.

I really cannot vouch for this, as I never have any trouble logging on with my active CR4 ID, no matter where in the world I am or whose computer I am using.

I agree in all respects except one, they are actually posting Anonymously.....because they have decided to.

No more, no less!!

Gosh Andy, you are sooooo clever....

Why thankyou, but actually its not true, I do understand simple math and physics (because that is all thats needed to understand this problem). Thats all.....

You certainly do not need to be very "clued up"!

I stiil say that it still astonishes me that so many DO NOT UNDERSTAND THIS SIMPLE PROBLEM/CONCEPT....as even I understood it!!! WOW!

I'd put my crew members in the water telling them, kick baby! kick!

It seems to me that tacking is the correct way to approach this problem.

Without going into the math and all, when your boat presents a wider (longer) surface for the current to act upon, it is going to increase your speed slightly, thereby putting you ahead of your opponent at the finish line.

Ken Leigh

yes going down steam creating a 5 klm head wind on your sail, I don't mean to be a smart ass but as you say some people don't or can't grasp the whole picture pls think ?

Ok not an engineer or physicist, but a sailor. By drifting, the boat will eventually reach 5km/hr. At this speed the boat has no way on (speed relative to the current)and thus cannot steer (ie. tack). Prior to reaching that speed, the boat speed will not exceed the speed of the river either. The winenr will be the most aerodynamically streamlined boat in a little over 2 hrs. The displacement of the boat will be a factor as well (length of time to accelerate to current speed)

Oops.

Now we are getting WAY out there in magic land. Neither the displacement nor the orientation have anything to do with it! Except as regard the orientation of the vessel and its sails in the effective wind.

Plus, if there is any wind; real, apparent, or otherwise, there will be relative movement between the vessel and the water, which will allow the rudder to perform its intended duty. Therefore, the boat that is sailing (rather than just floundering) absolutely will cross the finish line first.

Think of it another way -- consider the boat trying to sail UPRIVER. Here the sail definitely affects the response of the vessel because it reacts to the apparent wind, providing resistance to the downstream motion of the vessel. Therefore, why should the sail not affect the response of the vessel sailing down river?

Complete and utter twaddle.....

Evidentally you have not sailed in a current or in a river. There are also pilots who have no clear concept of how a plane flies, so you needn't feel bad.

Over 200 posts, I'm amazed how many folks voted for the drifters even though they acknowledged that there are "effects" of moving through still air.

I think the puzzle would be more interesting if there was another race for powerboats going upstream at the same time, *and* if the question was how far the hawk would travel if it was chasing pigeons from sailboat to powerboat back and forth until the race ended... Then we'd have the infinite series dilemna to confound and create even more humorous responses :^)

I assume that since there is no wind on land there would be no wind on the river. Your speed whether tacking or going straight down river would 5 km/hr, the same as the current. Therefore a tie, with a total time of 2 hours.

Wow, I don't blame you FJD. For all of you doubters of apparent wind: Picture this: it is a still day (no wind); you get on your bicycle and pedal in a straight line at 5 km/hour; do you feel the wind on your face?; what is the velocity of this apparent wind?; 5 km/hour.

Clueless twaddle.

you create the wind by drifting down stream ! do most of you just like to type on the pc or are you realy as ?? as you sound (without problem solveing skills )??? I thought this was a place for engineer's . Oh well ! I find it hard to remain in these discusions as so many ( with a few exceptions ) do not seam to let logic enter their minds ,maybe these are very young people ?

Marjer,, it is hard to believe that these people have never had the wits to notice that when walking in still air there is an "apparent" wind on ones face,, and then extrapolate that one simple, stunningly obvious fact to this problem...

The fastest cataraman I've ever sailed alone was a NACRA 18, a single class boat that reliably could sail to windward at 27 knots in a 15 knot wind, or 1.8 times faster than the wind.

Assuming optimum tack is at 45 degrees, the distance it would have to travel relative to the drifting boat would be 1.43 times farther than the boat drifting, regardless of how many times it tacked.

This would give it an advantage of .37 mph down river over the drifting boat.

I win the race. My opponents are just floating down the river, so their max speed will be 5 km/h. In the other hand I have an apparent wind of 5 km/h to start with. If I use it to maximize my sail power, I will make a little more speed than my opponents.

But this is with "all equal" conditions. In a real situation we have to consider in which part of the river they are floating, weather it is in the middle or closer to shore, type of boats we are using and so on.

As for the winning time... just under 2 hours.

I'm not actually a sail type person, but fluid dynamics wins. The first boat sitting in the middle with the pointy end downstream is going to be dead last. Turn it 90 degrees and see what happens.

Considering a middle of the range dinghy

Tacking Option - Max boat speed say 4km/hr at 45 deg to apparent wind: velocity made good = 2.8 km/hr: so for total of 10 km = 3.57 hrs

Drifting Option - Minimise your windage, point down current, say 4 km/hr achieved, given air resistance on rig and minimal hull hydro resitance: so for total of 10 km = 2.5 hrs

Now this is a race, so my 3rd option is to tighten & cleat the sheets, capsize the dinghy, and point it across the river. We now have min air resistance, max hydro resistance (via the sails acting as sea anchors), so we will achieve a speed of say 4.8 km/hr: so for a total of 10 km = 2.08 hrs

So the answer is Option #3 !!!!

You are making a mistake when changing reference frames: see post #143 for explanation.

No, I'm not buddy...

If the boat is static relative to the water - then there is a 5Km/hr relative breeze upstream ( and the opposite, if the boat is static relative to the air, then there is a pure 5 km/hr current downstream) .

The boat will find an equilibrium vector where the aero force(aka drag) = the hydro force (aka drag). Due to density difference between air and water, that equilibrium vector will be such that the boat's frame of reference will be nearer to static relative to the water endof that spectrum, than to the static relative to the 5 km/hr wind end.

What's more if you are a sailor, you will know this is true.

I stand by my argument...

Geoff

OK, that's true on the "water" frame of reference ... but the race is 10 km as measured between two points on the river bank (they usually are ...) so the speed you calculated relative to a body of moving water will have to be converted to "river bank speed" by adding the velocity of the flow to whatever speed you determine relative to the moving water ... basic frame of reference change maths! I stand by my argument ... :)

You are fully correct. GA.

You are fully correct. GA.

He is correct in everything except the part where he says he stands by his argument (which was presented in post 233). His argument there is not correct, putting the drifters ahead of the sailors.

Some of these people have the bow wave forming at the stern of the boat.

I thought I understood it correctly, now you make me unsure, but thanks anyway....