Passage Plan Advice from Chi to Gosport!

[prv]

the optional 20 Yanmar with a 3 blade prop is definitely worth having over the 10 Yanmar in a Crabber 24 I still havn't had it at full whack yet.

Ah ha - the secret weapon! Yep, that'll carry you over all but the most severe misjudged tidal streams. Or in my case on the 2012 Scuttlebutt trip, streams which you can judge perfectly well but decided to punch anyway in order to make time for a big fryup ashore with Colin and Chrissie

I think sometimes you can over think all this, which anchor, which GPS, which shroud material etc etc. I recently sailed with a lovely old guy who has years of professional skippering experience especialy abroad. He has now downsized to a lovely little Shrimper which he bombs about in with a big grin on his face.
[...]
He reminded me that sailing was meant to be fun

Good. Dave said the other day that he thought some of the forum kit-and-techniques pedantry could be worrying for beginners, and I think he's right. People (myself included) can debate endlessly the absolute best way of doing something, but this doesn't mean you'll instantly come a cropper if you do it any other way. Good enough is good enough, especially for coastal pottering in good conditions.

Pete

 

[lustyd]

Yes I only mention it because Portsmouth entrance in full flow can be a bugger if something goes wrong. Your engine may be able to punch through it, but if (like happenned to me) your engine stops when doing 0.5kt OTG but 5.5kt TTW and the continental cat is coming in you'll want to have a second plan. The reason being that you'll very shortly be travelling at 5kt OTG toward a very large ferry who is travelling at 10kt towards what to them looks like a sailing dinghy!

 

[lustyd]

Eh? Care to elaborate?

Yes, in your almanac you'll see lots of tables like:

times


[table="width: 500, class: grid, align: center"]
[tr]
[td]High [/td]
[td]Water[/td]
[td]Low [/td]
[td]Water[/td]
[/tr]
[tr]
[td]0000[/td]
[td]0600[/td]
[td]0500[/td]
[td]1100[/td]
[/tr]
[tr]
[td]1200[/td]
[td]1800[/td]
[td]1700[/td]
[td]2300[/td]
[/tr]
[/table]
Oh FFS the forum lost all my text explaining this
Under the table will be differences, for instance Ryde is 10 minutes early if HW is noon or 10 minutes late is HW is at 1800. This is due to the angle of the sun at those times acting differently on the water and causing the movement to be different (original text explained better, sorry I don't have time as working!).

As Pete rightly said, this is not all that useful to a beginner (or even to an experienced skipper), just added as a warning to say that being OK on one weekend with Springs may not mean the next will be as good. Chris clearly knows this but future beginners taking this thread literally may not be aware and might find themselves in front of a ferry making no progress! Also the high pressure this weekend would have limited the flow a bit and resulted in a lower tide - certainly I was 40 minutes late getting out of the marina for this reason!

 

[jac]

Wasn't there an epic thread about differences at secondary ports a couple of months ago that really went detail on why the difference is different at different times of the day. (Feel free to reword that)

Fwiw, differences at secondary ports, especially when extrapolating can become a bit finger in the air anyway. Add to the inaccuracies created by the original prediction at the standard port plus the impact of wind, pressure, rainfall upriver etc and the one thing you can certain of is that HW won't agree to the minute with the calculation.

 

[Zagato]

Bring it on!

Lol... Anyday but maybe not on a downwind run

 

[lustyd]

Wasn't there an epic thread about differences at secondary ports a couple of months ago that really went detail on why the difference is different at different times of the day. (Feel free to reword that)

Fwiw, differences at secondary ports, especially when extrapolating can become a bit finger in the air anyway. Add to the inaccuracies created by the original prediction at the standard port plus the impact of wind, pressure, rainfall upriver etc and the one thing you can certain of is that HW won't agree to the minute with the calculation.

Ah good then someone has said it better than me! I would never do the calcs when sailing, don't get me wrong. My point was more that even when you've seen it "at springs" there are various things in nature which may have conspired to make it less springy than it could be. In the case of Portsmouth entrance I have seen 5kt tides and heard of worse where many yachts bigger than mine turned back rather than press ahead against nature. I'd never advocate a beginner or otherwise trying to understand all the extra stuff that can be learned if one is OCD enough. In my mind it's sufficient to know that nature can always surprise you and to have a plan B. Zagato obviously understood this so I only mentioned it in case someone read this thread in the future and took it to mean that Portsmouth would always be an easy entrance therefore no need to plan. My earlier post did say these things before it was killed by internet daemons...

 

[lustyd]

Dave said the other day that he thought some of the forum kit-and-techniques pedantry could be worrying for beginners, and I think he's right. People (myself included) can debate endlessly the absolute best way of doing something, but this doesn't mean you'll instantly come a cropper if you do it any other way. Good enough is good enough, especially for coastal pottering in good conditions.

Well said by the way, debating is fun as long as we're careful to point out most of it isn't necessary

 

[jac]

Well said by the way, debating is fun as long as we're careful to point out most of it isn't necessary

As long as we don't take that last bit to heart. Would kill the forum if we only put on what was necessary

 

[erbster]

Unless depth over Chi Bar is critical you could leave Chi on the last of the ebb, and enter Pompey on the early flood. Stay close to Hampshire, go through the gap in the submarine barrier, and you'll stay out of the stronger east-going that'll be further out towards the deeper water.

That's what we did last Saturday. Nice jaunt.

 

[prv]

Anyday but maybe not on a downwind run

Yep, gaff rig much better than bermudan off the wind - big barn door of a sail . Skinny pointy ones have to hang a big colourful balloon off the front to make up for it, and I suspect that's a little outside your repertoire for the moment

Pete

 

[Twister_Ken]

Yes, in your almanac you'll see lots of tables like:

times


[table="width: 500, class: grid, align: center"]
[tr]
[td]High [/td]
[td]Water[/td]
[td]Low [/td]
[td]Water[/td]
[/tr]
[tr]
[td]0000[/td]
[td]0600[/td]
[td]0500[/td]
[td]1100[/td]
[/tr]
[tr]
[td]1200[/td]
[td]1800[/td]
[td]1700[/td]
[td]2300[/td]
[/tr]
[/table]
Oh FFS the forum lost all my text explaining this
Under the table will be differences, for instance Ryde is 10 minutes early if HW is noon or 10 minutes late is HW is at 1800. This is due to the angle of the sun at those times acting differently on the water and causing the movement to be different (original text explained better, sorry I don't have time as working!).

As Pete rightly said, this is not all that useful to a beginner (or even to an experienced skipper), just added as a warning to say that being OK on one weekend with Springs may not mean the next will be as good. Chris clearly knows this but future beginners taking this thread literally may not be aware and might find themselves in front of a ferry making no progress! Also the high pressure this weekend would have limited the flow a bit and resulted in a lower tide - certainly I was 40 minutes late getting out of the marina for this reason!

Still don't get what 'sun angle' has to do with it. Sun angle changes day-by-day. It's in a very different place at 0900 in June than it is in December, for eg. Yet your table doesn't mention months. Plus Sun is the minor gravitational influence on tidal heights (and thus flows), Moon is much more important, being a lot closer.

What effects the height and flow (above or below prediction) is much more prosaic - atmospheric pressure, high or low flows coming down estuaries, prolonged periods with wind blowing from one direction.

It's true that, for eg, HW Springs at Portsmouth are generally close to 0600 and 1800 GMT, but those times in winter can see the sun already below the horizon, well to the South and in summer well above the horizon and close to due E or W.

It may be that you're thinking of the Sun's (and, more importantly, the Moon's) inclination which do define how big a spring is (and conversely how weak a neap is) but inclination is not shown on the tidal pages of any almanac I've seen, and in any case is calculated into tidal predictions.

However, I'm ready to be enlightened if you've more info on sun angle.

 

[lustyd]

Still don't get what 'sun angle' has to do with it. Sun angle changes day-by-day. It's in a very different place at 0900 in June than it is in December, for eg. Yet your table doesn't mention months. Plus Sun is the minor gravitational influence on tidal heights (and thus flows), Moon is much more important, being a lot closer.

What effects the height and flow (above or below prediction) is much more prosaic - atmospheric pressure, high or low flows coming down estuaries, prolonged periods with wind blowing from one direction.

It's true that, for eg, HW Springs at Portsmouth are generally close to 0600 and 1800 GMT, but those times in winter can see the sun already below the horizon, well to the South and in summer well above the horizon and close to due E or W.

It may be that you're thinking of the Sun's (and, more importantly, the Moon's) inclination which do define how big a spring is (and conversely how weak a neap is) but inclination is not shown on the tidal pages of any almanac I've seen, and in any case is calculated into tidal predictions.

However, I'm ready to be enlightened if you've more info on sun angle.

At noon the sun is directly overhead. At 6pm it's directly west. Not rocket science...

 

[Twister_Ken]

At noon the sun is directly overhead. Yes, but only if you're underneath of it. In the UK it is never overhead, although it is due South at local noon .At 6pm it's directly west. No. The earth tilts as the year progresses. Not rocket science... Actually, it is

 

[Twister_Ken]

That's what we did last Saturday. Nice jaunt.

Glad it worked for you! Won't work if you draw too much for Chi Bar towards low water, but you've got to be pretty big for that in smooth conditions. And if you are that big, you can probably power through any contra-tide you'll find on the S Coast!

 

[lustyd]

The 23 degree tilt of the earth is nothing compared to the 90 degree change from noon to 6pm which is the cause of differences based on time of day. Try and sound clever if you like but the explanation is incredibly straightforward.

 

[Seajet]

It depends on what you mean by ' sun overhead at mid day ' - ever tried a sextant ?!

Chichester entrance is better dredged now but if in any doubt it's a good idea to look at www.chimet.co.uk or call the Conservancy on VHF 14 or 01243 512301.

Along with the minimum depth consider the swell highs and lows, I know a couple of chancers in a fin keel 26' who ended up bouncing on the seabed, watching the bilges flex and crack visibly, they only just got away with it by luck more than judgement.

Chichester entrance can be a killer, but 99 times out 100 it's a doddle if treated with respect.

 

[lustyd]

It depends on what you mean by ' sun overhead at mid day ' - ever tried a sextant ?!

No need. Luckily I'm smart enough to realise that tide works at the planetary scale, not at river scales. When I said directly overhead, I meant the sun is on the same longitude and therefore offering a different pull on the water than it would be if it were aligned with the longitude 90 degrees to the west at 6pm.

 

[Twister_Ken]

Lustyd, m'dear.

You might want to do a course in astronav, for fun. One thing you'd find is that only on two days a year in our latitudes is the sun due west at 6pm*. And that should be local 6pm, not Greenwich, by the way.

And swat up on tides - the Sun has a minimal effect compared with the Moon.

As for planetary scales - yes, generally, but the shape and volume of the coastline modifies them locally quite considerably. How else would you explain double high-waters, for example? Or a five hour flood and a seven hour ebb? Also, that there hardly any rise of tide mid-ocean, compared to in coastal waters?

*Think I'm right, but I don't have ephemeris tables to hand.

 

[lustyd]

Lustyd, m'dear.

You might want to do a course in astronav, for fun. One thing you'd find is that only on two days a year in our latitudes is the sun due west at 6pm*. And that should be local 6pm, not Greenwich, by the way.

And swat up on tides - the Sun has a minimal effect compared with the Moon.

As for planetary scales - yes, generally, but the shape and volume of the coastline modifies them locally quite considerably. How else would you explain double high-waters, for example? Or a five hour flood and a seven hour ebb? Also, that there hardly any rise of tide mid-ocean, compared to in coastal waters?

*Think I'm right, but I don't have ephemeris tables to hand.

Ken, perhaps you can explain what else happens at noon every day to change the tide times and heights so drastically? This has literally nothing to do with astronav although I will concede that you're a very clever little boy for knowing astronav (if indeed you do have a better grasp on that than on this...).

As for due west, every single day of the year the sun is in the west at 6pm. This isn't something I made up it's a fact. The sun will be at 90 degrees west at 1800 UTC, 180degrees at 0000 UTC and 90 degrees east at 0600 UTC (in the land of the rising sun). That's just how the planet spins, and yes it's tilted by a couple of degrees but at the scale we're talking about the fact that it'd due west is the important bit.

 

[lustyd]

Another way to put it, which you ought to have picked up on your astronav course, is that it is always local noon at 1800 UTC at 90 degrees west, everywhere on the line.