Fly-by-wire?

[stuartw]

Re: There is light at the end of the tunnel!

Sorry, I wasn't rubbing your nose in it so to speak. At a risk of repeating myself, I can accept the sinewave crossing method in IDEAL conditions is probably the fastest. We can all accept that the zero XTE is the more precise. All I am saying is that in bad conditions, or rather, non ideal conditions, then engaging the AP + XTE can take the strain out of sailing.

Now I know that there are those yotties who go out in all weathers, and for them beating the elements is what it's all about. I take my hat off to them. But not for me, and I suspect a good many others. There are a good many "leisure sailors" who like getting from A - B in a nice peacefull manner. I suspect not many of those are on the forum.

By the way, I too would feel unsafe in a single engined boat without sails, and probably if it had sails as well. That's why I rely on two.
Happy sailing

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[Skyva_2]

Re: There is light at the end of the tunnel!

There is another reason for the sine wave approach. Its probably my most important reason:

If you are on the rhumb line after a 15 hour passage, your distance from Cherbourg is 3 miles with a 3 knot cross tide, its dark and raining, wind against tide, etc, etc, then the last leg into Cherbourg takes twice as long (it seems more!) and the navigator's popularity with the crew gets lower by the minute.

The worse the conditions, the more you need to be up tide of the entrance.


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[AlanPound]

Re: There is light at the end of the tunnel!

Having read all this with increasing bewilderment, I finally spotted the clue.... You're a stinky rather than a raggie....

... not wanting to start a war, I should explain what I mean....

A great big part of sailing a sailing boat, is getting the best (speed, typically) out of whatever is available in terms of boat, conditions, and available crew energy.

Any fool can sit there and dither along at 2kts in a F4.... But the great fun, and pride, is in coaxing an extra 1/2 kt, 1/4 kt etc... and optimising the trip. And that extends to best possible nagivation (or even navigation).... and a single heading all the way across it the optimal method.

This mindset is *fundamental* to sailing.... (may not be to mobos - I wouldn't know...)


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[goupil]

Re: There is light at the end of the tunnel!

You summarize the thread very well :
XTE method is good in some kind of TUNNEL !
But for a crossing, under sail or power, ideal or bad conditions, race or cruising, you plan your passage to finish a bit up wind and tide for boat and crew comfort: except if you are a masochist !
No one said XTE + AP "doesnt work" but it's for "piloting" the coast not open sea with a cross tide.
Try one day: time is money, you'll be happy to spare some fuel.

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[stuartw]

Is myopia a yottie affliction?

Well done. I did in fact announce the fact on my first post, mainly because of the question.
Also, I have said in later post, further down the thread, that I admire yotties who go out in all weathers to try and achieve the buzz of beating the elements. However there are those, and clearly not on this forum, who I would class as "Leisure yotties" who just want a quiet life. I sincerely hope you would not decry their motives. Every one to his own.

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[stuartw]

Re: There is light at the end of the tunnel!

I'm sorry. If I was 3 miles from Cherbourg aft 15 hours and the crew were fed up, then I would but the bloody engine on. Or can't you afford a 1/2 a pint of diesel? I think there is a limit to bravado.

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[stuartw]

Re: Rubbish - NOT!

I am sorry, I don't want to prolong this part of the thread, but your assessment that an AP using XTE only using one waypoint is wrong. I have never said that. In fact I personally prefer additional ones, which I have already stated ad nauseum. There is nothing to stop you putting waypoints which would be near fit with your intended sinewave track.

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[RupertW]

Re: There is light at the end of the tunnel!

In strong winds the sails are a lot more powerful than the engine in a small sailing boat, so I'd use them as long as I could, but I'm completely with Stuart on looking at the state of the crew. If they are fed up then I'd take the tack that got me as close as possible to the harbour, preferably slightly up-tide, then roll away the jib and gun the motor to get there.

On the larger point, I don't think the sine-wave approach has any more likelihood of getting you up-tide than the Zero-XTE approach. In both cases your target is the harbour entrance, unless you deliberately choose (using either system) to have a waypoint up-tide for your likely arrival time.

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[stuartw]

A nice answer- Where is DeeGee?

I like your synopsis which I accept, but I am not sure everybody will agree.
So will this satisfy DeeGee's original question? He has been very quite after lighting the blue touchpaper.

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[bedouin]

Re: There is light at the end of the tunnel!

The advantage of the "sine wave" approach is that it naturally tends to keep you up-tide of the rhumb line as you approach the destination; which makes making an adjustment a hour or so out much easier.

What is difficult of course is if you plan to arrive near slack water

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[AlanPound]

Re: There is light at the end of the tunnel!

... and considering a purely hypothetical situation where there is 6 hours of 6 kts tide one way, and 6 hours of 6 kts the other way, a boat cruising at 6 kts and trying to stick to the rhumb line would not make a lot of progress, whereas a boat keeping a constant heading would make a perfectly satisfactory (and optimal) crossing.

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[stuartw]

There are some nice yotties after all!

I am just amazed it took some 50 or so posts, to go from XTE sailing is wrong, to one of yes, it has it's place, and it's safe. That's all I ever wanted to say. I think the Yottie-Mobo thing got in the way.

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[Rich_F]

Re: Rubbish - NOT!

That's OK. I've never had a problem with prolonging pointless discussions!

I think that we're (all) agreed that AP using XTE does work for a long crossing, and can be done using single or multiple waypoints.

The point on which we seem to disagree is the extent to which the inefficiency of this approach outweighs the convenience it offers. My view is that it is unacceptably inefficient, while being, at best, only slightly more convenient. And substantially less convenient if it prevents you from crossing in a single reach. You're fully entitled to disagree.

Rich

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[RupertW]

Re: There is light at the end of the tunnel!

Sorry, but I'm not sure that's true about the sine wave method.

If you make no adjustments and go faster than planned then you will end up-tide, and if you go slower you will end up down-tide. If you are going much slower then by the time you are an hour away you may be well down tide.

I think (as I've said in another post), that the desire to arrive up tide is an additional goal of your passage planning, and not relevant to sine wave vs. Zero-XTE.


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[bedouin]

Re: There is light at the end of the tunnel!

What I mean is that if you have got your calculation roughly correct (and you are not aiming to arrive at slack water) you should find yourself uptide of the rhumb line, from where it is easier to correct than if you have already been carried down-tide. Checking your position regularly should give you an early warning of any potential deficit.

In fact I always start off with a couple of spare miles of tide, and then correct that as I get closer to the destination

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[DeeGee]

Re: A nice answer- Where is DeeGee?

My original question was specifically targetted to the use of an AP where the destination, or wp, is to windward, ie you can't sail straight there. I got the answers I expected and went off at a different tangent to yours.

Others have been delightfully well-mannered, but you are completely and utterly wrong about sailing so as to constantly correct for tide. Others have explained the maths, so I won't repeat it. Substitute GPS+CTS for GPS+WP. The first will allow the boat to follow the banana-or-s course, the second will take far longer, wasting some component of the ships speed to counter the tide. Just to elaborate, consider that the boat is gently wafting along at 5kts, and the tide is 2kts. To counter the tide will reduce speed to less than 4.5kts, about 10%reduction in vmg.

This smokescreen about lack of precision is baloney: there is no such thing as precision, "rudder to this way or that...". You simply plan to be a mile or two uptide, and correct when a few miles off. [At that point, GPS+WP becomes de rigeur!!].

All this baloney some have said about safer courses only applies to some straight line course with a big rock off the rhumb line..... what about a straight line course with a big rock dead in the middle? You have to plan your course with tide and leeway effects, or stick to driving your BMW on the motorway.

<hr width=100% size=1>Black Sugar - the sweetest of all

 

[stuartw]

A change of heart?

It would seem I have touched a raw nerve. I am even more perplexed now, as your original reply to my own first post, was, and I copy:-
"Looks like this is what I would like to achieve (I have an old gyro unit at home from model helicopter days)..."

So please tell me what's changed? Also I strongly suspect you know a lot more about the capabilties of an AP, than your initial question led us to believe. Your discussions with Bedouin at the bottom, clearly indicate this. So why ask the question in the first place?
For the umpteenth time, I have never stated that the zero XTE method was the fastest or the most effecient. All I have ever said it works.
If you are such a pureist, then please tell me why are you even considering utilising a more intelligent AP system which will take you to your destination, taking into account, tides, wind etc etc.?
There are several people who have contributed to this thread, which you consider are talking baloney. I think that is a rather disrespectful statement. They are entitled to their opinion as you, and I are.
I, conclusion, all I will say, if you are real sailor, who enjoys the challenge of getting the best out of your boat, no matter what the conditions, then throw you Autopilot overboard, you don't need it.


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[DeeGee]

Re: A change of heart?

Let's forget that argument, eh? My original question is where I started and finish.
Like you suggest, as a sailor, I tend to eschew the AP. I have relegated it to helming only, but believe me, in a rainy, cold, crossing of the North Sea, it is nice to have George's hand on the tiller, and not mine.

QSIV has already addressed my question, but chose not to elaborate. I was interested in the proposition of an AP intelligent enough to steer to windward, making the best course possible. Suppose the next WP was due north, and the wind coming from say 005. The intelligent AP should a) suggest we should be on starboard tack b) whatever tack we are on, should take a default wind angle, say 30deg, and adaptively try tuning WA until best VMG is acquired - just as a human would. Clearly, we have to leave sail-trim out of it for now, at least. If the wind shifts sufficiently, the AP should suggest tacking over to the favoured tack.
Now, as I said, QSIV seemed to indicate that his kit does some or all of this... as a poor man, and blessed with what I have got in the way of instruments, but also having a laptop and some ancient skill with programming, it seemed something that might be worth trying - not to substitute for the fun of sailing, but to add a bif of un to my non-sailing life (unfortunately, too high a proportion).

I suspect this thread is dead, except for our little whimpers, but it was interesting the directions it took. You should try reading threads originating from NigeCh on the subject of lee-bowing....... -))



<hr width=100% size=1>Black Sugar - the sweetest of all