Confessional: admit to boat-related things you've never quite understood...

Good grief! I've been off the air for 36 hours since late morning yesterday, and I return to find the confessional has become a forum for limericks and rude jokes!

Got any more?
 
AntarcticPilot said:
If you have a big enough map (or better, a globe!) the Position Line is always a small circle (i.e. a circle defined by the intersection of a plane through the surface of the earth but NOT passing through the centre of the Earth) centred on the nadir point. The DR position is used to determine the azimuth of the nadir point, and hence the local azimuth of the position line.

It nearly always helps if you visualize these problems with a globe. The problem is three-dimensional, and diagrams on flat paper can be misleading.

As you say, in theory you could measure the azimuth of the body being used and hence get a fix. However, it wouldn't be very accurate a) because the bodies move quite quickly, as you say, and b) because you couldn't measure the azimuth with enough accuracy. An error of one degree in Azimuth would give errors of 0-60 miles (depending on how far from the nadir point you were), and I'd be surprised if you could measure the azimuth of a celestial body with anything like that accuracy from a moving boat! I reckon I'm doing quite well to measure the bearing of something at sea-level to a couple of degrees with a hand-bearing compass; measuring the bearing of a body at (say) 45 degrees elevation would be much harder.

I'm trying to get my head around whether you could use a method of successive approximations, as the post about Moitessier suggested, but I can't get it clear in my mind at the moment. I suspect that it would work some of the time, but that there might be pathological situations where the solution could diverge, or converge on the wrong point.
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Theoretically you can use any position as an assumed position or DR. including one 600 miles away.
You wont be able to plot the 600 mile intercept.
You could calculate the intercept terminal point through which your true position line passes using a Mercator sailing calculation.
 
Never understood lightning, people say 'turn off everything, others say, leave everything on, some people say we are happy you arrived as you have the tallest mast, others say don't worry now that catamarans in they have the biggest grousing footprint so
They will get struck
And not you.

So yes Lightning. Never understood it and it appears no one else does either.
 
Here's my question... on secondary port calculations, why does the time of high tide for the secondary port depend on whether it's Springs or Neaps?
 
One thing I understood about lightning this year is that it seems to have been following me... closely.

In the end I resigned myself to the fact that if we got struck, we got struck, and just enjoyed the show.
 
dancrane said:
Good grief! I've been off the air for 36 hours since late morning yesterday, and I return to find the confessional has become a forum for limericks and rude jokes!

Got any more?
Click to expand...

A Yachtmaster (Ocean) from Sanquhar
Obsessed over choosing an anchor
At last got his hands on
A stainless steel Manson
It cost him a bomb - what a​

Sorry, can't think of an ending for that one. Let's try again.

Fed up with his old Volvo Pentaur
A chap made a well for a Centaur
He sold her next year
At a West Scottish pier
It might have been cheaper to rentaur​
 
JumbleDuck said:
A Yachtmaster (Ocean) from Sanquhar
Obsessed over choosing an anchor
At last got his hands on
A stainless steel Manson
It cost him a bomb - what a​

Sorry, can't think of an ending for that one. Let's try again.

Fed up with his old Volvo Pentaur
A chap made a well for a Centaur
He sold her next year
At a West Scottish pier
It might have been cheaper to rentaur​
Click to expand...

Bravo!

Pete
 
reeac said:
A very experienced dinghy sailor once told me that the only time that she tightened the Cunningham was when she saw someone about to photograph her boat.
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I do like a nice tight Cunningham.

I used one for a while when my main sail had stretched.

Jamesuk said:
Never understood lightning...
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Two important things to note: put electronics in the oven if there is a thunderstorm. Lightning doesn't always come downwards.
 
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john_morris_uk said:
Instinct says that halyard tension has already sorted out luff tension but cunningham tension works for counter intuitive reasons.
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Having had some very baggy sails I can confirm that a taut main halyard will only work up until the point at which the leech tightens. Unless you can move the gooseneck down and the kicking strap (vang) will continue to pull the leech tight you can still have a belly above the foot of the sail. It may still be there despite these compensations.
Then the cunningham will remove the flappy powering bits of the sail (but leave some flappy, unproductive folds above the boom)
This is still true in a full-cut newer sail, but the control is more delicate, and less obvious.
I had a brand new main made for my Foxcub which would only set really well with a touch of cunningham. It may have been that I was strangling the fullness of the sail, but each to their own.

See that crease from the clew up to the first slider on the luff. The cunningham is hanging loose. If I tweaked it that crease went.

Slippy.jpg
 
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JumbleDuck said:
A Yachtmaster (Ocean) from Sanquhar
Obsessed over choosing an anchor
At last got his hands on
A stainless steel Manson
It cost him a bomb - what a​

Sorry, can't think of an ending for that one. Let's try again.

Fed up with his old Volvo Pentaur
A chap made a well for a Centaur
He sold her next year
At a West Scottish pier
It might have been cheaper to rentaur​
Click to expand...

Nice. I'm wary of what line of humour might emerge next, hereabouts...

An Osprey sailor known to you...
Couldn't distinguish a self-tapping screw...
He set up a thread...
To see what folk said...
And woke to a hundred or two.

I felt like Brian the Messiah. When SWMBO saw the number of replies here, she said "There's a MULTITUDE of 'em!" :calm:

By the way, what new hell is this weird alternative selection of smiley faces? Each time we're offered new ones, they're somehow much worse than before. Can it be deliberate?
 
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RobF said:
Here's my question... on secondary port calculations, why does the time of high tide for the secondary port depend on whether it's Springs or Neaps?
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As nobody's offered, here's my explanation - and I'm assuming you refer to the tabulated time differences of HW at the Secondary and Standard ports being dependent on whether it’s Springs or Neaps.

At every location, the tidal curve varies with the Spring/Neap cycle, as one clearly sees with the published curves for Standard Ports. But the relationship between the tidal curves for different locations also varies with the Spring/Neap cycle, such that the time differences of HW (for example) between Standard and Secondary Ports vary between Springs and Neaps.

Now that’s not a mechanistic explanation I appreciate. For that, one needs to ask why the relationship varies. The basic answer is that tidal curves are complex functions of the interaction between tidal forcings and local topography, and there is therefore no reason why the tidal curves for the Secondary and Standard Ports should necessarily keep in lockstep through the Spring/Neap cycle.
 
vyv_cox said:
How does the thermostat control the temperature in a raw-water cooled Volvo? I have aired this one several times, last time only yesterday, but nobody seems to know. I was previously put in contact with several Volvo repairers/servicers but they had no idea either.
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Typical thermostats have a flap in the centre that opens as the water temperature rised and closes as it cools down.

This made possible by the use of a bi-metal spring or strip that expands or curves with heat and pushes the flap open allowing more flow as it heats up and less flow as it cools down.

so the temperature is regulated by the amount water flowing through the system.

Good luck and fair winds. :)
 
oldsaltoz said:
Typical thermostats have a flap in the centre that opens as the water temperature rised and closes as it cools down.

This made possible by the use of a bi-metal spring or strip that expands or curves with heat and pushes the flap open allowing more flow as it heats up and less flow as it cools down.
Click to expand...

The only bimetallic cooling thermostat I have ever seen was the bellows type used to regulate airflow round a VW Beetle or Campervan cylinders. All the car-type thermostats I have seen, including the one on my Yanmar 1GM10, use expansion and contraction of wax as the driver.
 
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