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

[lw395]

Rest assured, I would have pounced if such sails were available 2nd hand, there. The lovely new sails I saw were for Int14s and 49ers. Mine is the only Osprey at my club.

I saw a complete set of Osprey sails available online, in good condition according to the seller, at a reasonable-sounding £200. But the ad was long out of date, so I didn't enquire.

Have you looked for the Class Association website?

http://ospreysailing.org/index.php?...and-pab&catid=22:equipment-for-sale&Itemid=33
Try a 'wanted' ad.

 

[dancrane]

I might well do that. Really depends how busy I am until March...very busy means cash for stuff. The more time I spend writing nonsense here, the sadder my sails will set next year!

 

[Seajet]

Dan,

when I crewed on a ' state of the art ' Int 14 in the 1990's with the hi-tech sails stowed ( stupidly in my view ) at the owners' club sail loft, - pretty much a ' help yourself ' deal - the jib, a good £500 even in those days, no numbers of course, was stolen; so beware of stuff on t' internet and boat jumbles; the boat owner was built like a Rugby Forward, and as far as I know is still looking & rather upset !

 

[dancrane]

Thanks mate. Well, if he ever finds the rat who swiped his jib, the rat won't have my sympathy. I found a Harken block in the grass equidistant between dinghies on Saturday. I handed it to a member who thought it had been dropped by an I14 crew. I'm not sure if there's a lost & found box at the club - there should be, there's always a lot lying about.

I like to imagine that the Osprey class doesn't attract thieves in the way bigger classes do - there can't be a very broad market for stolen kit, and word of mouth about instances of loss must discourage opportunists. The thief would almost have to steal-to-order, because advertising rare sails on the internet would quickly attract the attention of the victim.

Is it possible to mark sails more permanently than with the adhesive numbering? Having said that, I have sails from two different Ospreys, so indelible marking may not be desirable.

 

[dancrane]

Quote (me): Self-tappers are straight?

Taking care of yourself, being immaculately dressed and a great dancer didn't have the same implications in mid 20th-century america

I only just got that one...

 

[alant]

Yeah but, no but ... there must be at least a broad consistency in the differences between the HW times at the Standard and Secondary Ports, both at Springs and at Neaps, for the tables to work at all. As to 'it's just so', I suppose my last sentence ('The basic answer is that tidal curves are complex functions of the interaction between tidal forcings and local topography ...') is almost saying that - for most of us at any rate! No doubt with detailed hydrodynamic modelling of the situation at a pair of Standard and Secondary ports, one could get an understanding of why the HW time differences varied between Springs and Neaps - "The sandbanks at the mouth of Y (Secondary Port) affect the inrush of the tide differently at Springs and at Neaps, an effect absent at X (Standard Port)" sort of thing.

My thanks to NormanS for his compliment on my original answer. As to his follow-up question "... when the tide goes out, where does it go?", I cannot better the accuracy of John Morris's "somewhere else", but will offer the more specific - and thus far more helpful - "Ultimately, to where it came from when it came in".

Don't know if this helps.
Some time ago, I asked Christopher Jones, head of Tides @ UK Hydrographic Office, why the differences for a secondary port went from +0015 to -0010, at 0600/1200. His reply (unfortunately couldn't copy the tables, are below.

Explanation of the Time and Height Differences published in Part II of Admiralty Tide Tables
Extract from Admiralty Tide Tables Volume 1, NP201

The time differences shown have been derived originally from a non-harmonic analysis of tidal observations at both the Standard Port and the Secondary Port.

Brief description of non-harmonic analysis
In order to derive the time and height differences at the Secondary Port with respect to the times and heights of High (and Low) waters at the Standard Port, the differences need to be calculated by comparing the available tidal data at each location, as follows:-

4 plots are then required as follows:-

· High Water Times at the Standard Port vs. High Water Time Differences at the Secondary Port
· Low Water Times at the Standard Port vs. Low Water Time Differences at the Secondary Port
· High Water Heights at the Standard Port vs. High Water Height Differences at the Secondary Port
· Low Water Heights at the Standard Port vs. Low Water Height Differences at the Secondary Port

Examples of these plots are shown as follows:-

Time Differences:-

Height Differences:-

Time Differences
On looking at the Time Difference curve diagrams it can be seen that there is one ‘peak’ and one ‘trough’ along their length, which effectively refer to the maximum and minimum time differences tabulated for the Secondary Port in the Admiralty Tide Tables. The times at which these maxima and minima occur at the Standard Port being the headers used in bold in the Standard Port header information (e.g. 0000 & 1200, 0600 & 1800 etc. etc.)

The above explanations of how the time differences have been originally derived at the Secondary Ports also account for the variations seen in the Standard Port header information, for example as follows with Plymouth.

and

Essentially the differences are caused by the specific relationships between the Standard and Secondary Port(s) during the period of observed tides collected at both locations, i.e. the specific turning point of the maxima and minima has shifted slightly along the length of the time difference curve referenced above.

Reference to Spring and Neap Tidal Conditions
The ‘maxima’ and ‘minima’ referred to above could also be thought of in terms of Spring and Neap tidal conditions.

For example, looking at the Plymouth predictions for a Spring High Tide on a Spring gives the following prediction:-

So High Water Springs on this day occur at 06:37 and 18:57, which is relatively close to the columns shown above at 0600 and 1800 (remember this is only one day’s Spring Tide in isolation).

Similarly, Low Water Springs occur at 00:29 and 12:50, again relatively close to the Low Water column of 0000 and 1200 (and the ‘alternative’ column of 0100 and 1300).

The Neap Tide gives similar confirmation:-

High Water Neaps on this day occur at 01:19 and 13:42, which is relatively close to the columns shown above at 0100 and 1300 (and quite close to the ‘alternative’ column of 0000 and 1200).

Similarly, Low Water Neaps occur at 07:21 and 20:04, again relatively close to the Low Water column of 0600 and 1800.

Again this is one Neap tide in isolation. The non-harmonic ‘time stamps’ were derived from a much longer period of tidal observation.

Conclusion
The above information gives a general feel for the way in which the time and height differences have been established initially and how the Secondary Port data relates to the Standard Port data accordingly.

It is not an exact science!"

If you want to contact this very helpful 'Head of Tides', you can e-mail him at Christopher.Jones@UKHO.gov.uk

 

[lw395]

Dan,

when I crewed on a ' state of the art ' Int 14 in the 1990's with the hi-tech sails stowed ( stupidly in my view ) at the owners' club sail loft, - pretty much a ' help yourself ' deal - the jib, a good £500 even in those days, no numbers of course, was stolen; so beware of stuff on t' internet and boat jumbles; the boat owner was built like a Rugby Forward, and as far as I know is still looking & rather upset !

Many sails these days are quite identifiable. For one, they have a measurer's signature and date. Also many manufacturers put serial numbers on.
Sometimes discreetly.
Of course some owners don't bother recording the details.
I think if you buy from an owner in the class you will not have any problems.
The stuff that gets stolen probably ends up outside of the racing fleets, even outside of sailing.
I know someone who found a local scrote walking his dog on the end of a tapered vectran spinnaker sheet.

 

[stevebrassett]

My question is why do so many things boating increase in cost relative to LOA - especially finger pontoons ?

If I park my Rolls Royce in a parking space I pay the same as I would for my mini.

I haven't seen a reply to this, so here goes.

1. Because they can charge more.
2. Some marinas do have different densities in different parts of the marina, so bigger boats do take up more room.

 

[Hydrozoan]

... In order to derive the time and height differences at the Secondary Port with respect to the times and heights of High (and Low) waters at the Standard Port, the differences need to be calculated by comparing the available tidal data at each location ...
Essentially the differences are caused by the specific relationships between the Standard and Secondary Port(s) during the period of observed tides collected at both locations, i.e. the specific turning point of the maxima and minima has shifted slightly along the length of the time difference curve referenced above.
The above information gives a general feel for the way in which the time and height differences have been established initially and how the Secondary Port data relates to the Standard Port data accordingly.

Thanks Alan - I had seen your post containing this on another thread as I was preparing a response to Rob.

Your answer from Mr Jones describes in some detail how the UKHO derives the HW time differences in the tide tables, by comparing tidal data from the Standard and Secondary ports. But despite the reference to ‘causes’, it does not explain why those HW time differences vary between Springs and Neaps - i.e. it does not describe the natural causes (the hydrodynamic mechanisms) which give rise to such variation, which is what I believe Rob wanted to understand. I postulated an example of local sandbanks potentially having such an effect, and I believe local topography will explain many cases. However, I'm sure if Rob wrote to Mr Jones he could give him more information on the typical hydrodynamic reasons for the differences.

 

[RobF]

Thanks, Hydrozoan, you've understood my position very well. It's interesting that the UKHO themselves derive the secondary port time differences solely through observation (i.e. it's possible that they don't know the exact reason for the differences but do understand what the differences are).

Your point about local topography is pertinent and I've recently found a slightly expanded description from BlowingOldBoots, who notes that "The shape of the land, seabed and relative position to the direction of flow from the standard port. With the same geographical area the tide doesn't just go up and down the water also flows in and out. The ratio is not linear because drag/friction is involved which conforms to a power law, so time differences vary as the rate of water flow varies through the monthly tide cycle. Or something like that." This is on the same thread that I think you've previously referred to as it also contains the informative email from Christopher Jones.

I'm also aware that the times and heights of tides at the primary ports are an approximation (due to barometric pressure, wind speed and direction etc), so I therefore deduce that secondary ports are even more of an approximation (or more accurately, an approximation of an approximation).

 

[Hydrozoan]

Thanks, Hydrozoan, you've understood my position very well ...

Thanks Rob - from your earlier reply I hoped I had. UKHO may, as you suggest, not know the detailed reasons, for every Standard/Secondary port pair, why HW time differences vary between Springs and Neaps. But I imagine they do know at least the general reasons for many of them - especially if, as I suspect, the variations display geographical or other patterns.

I invoked sandbanks as my topographical example, but the estuaries themselves introduce higher harmonics of the forcing period, and thus assymetrical tidal curves. Both are manifestations of BlowingOldBoots’s point (which I had not seen) about the water not just going ‘up and down’. There are also S/N differences (other than just ‘stronger/weaker’) in the tidal forcings themselves – e.g. the periodic near disappearance of semi-diurnal tides at Courtown in Eire is attributed to S/N excursions of the semidiurnal D2 amphidrome in the southern entrance to the Irish Sea. To the extent that differences, between Standard and Secondary ports, in these topographical or forcing effects (or in the interactions between forcing and topography) vary over the S/N cycle, they may cause S/N variation in HW time differences.

PS Regarding your 'approximation of an approximation', I find it quite a struggle to write about 'differences in differences' ... :nightmare:

 

[dancrane]

I only just realised, after decades of hearing both names, that Haslar and Hasler weren't essentially connected. I thought the difference was a mere trick of pronounciation.

 

[ProMariner]

I'm glad you said that, because I have no idea what opening and closing the leech actually means (I know what a leech is, obviously). It is often quoted in magazines without further comment.

Set your sail till it looks right, going upwind. Stand under boom, and look up at the top batten, the straight part near the aft end of the sail. If the back of the batten sags off to leeward, compared to the boom, your leech is open. Good for sailing in waves, but otherwise, you are losing power. Try more main sheet. If the batten is parallel to the boom, you have the sail trimmed as the sail designer intended. If the back of the batten is converging with the boom, your leech is hooked. Good in moderation, for sailing in flat water, but easy to overdo, and can just act as a handbreak. Ease main sheet.

When reaching, same process, but adjust the kicker instead of the main sheet.

When the wind drops, easing the sheet/kicker is required, to stop the stretch of the sail from hooking the leach. When the wind builds, more sheet/kicker, to bring the batten parallel again, as it will have blown open.

Most people don't want to keep moving to the middle to look up from under the boom, so fit telltales to the back edge of the sail, these tell you the same info, but with more accuracy. If the telltale on the top baton is stalled round the sail 80% of the time, the leech is closed, ease sheet/kicker. If the top telltale is stalled 20% of the time, and flying 80% of the time! your leach is open, more sheet/kicker required. 50/50 means your leech is parallel.

I am very sad. I can get hours of entertainment from just looking at one sail. I still don't get the difference between halyard/Cunningham, would like to myth bust that one, one day.

 

[Woodlouse]

On the halyard/cunningham question I was lead to believe it's main purpose was extra luff tension. Since the halyard provides tension to the top of the sail it can provide less tension to the bottom of the sail due to friction from the mast track and cars. The cunningham therefore pulls down on the lower half of the sail whilst the halyard pulls up on the top half.

 

[JumbleDuck]

On the halyard/cunningham question I was lead to believe it's main purpose was extra luff tension. Since the halyard provides tension to the top of the sail it can provide less tension to the bottom of the sail due to friction from the mast track and cars. The cunningham therefore pulls down on the lower half of the sail whilst the halyard pulls up on the top half.

Am I right in thinking that a cunningham pulls a point above the tack down towards the tack, thereby scrunching the sail up a bit in that corner and having a different effect from my undoing the gooseneck clamp and pulling the whole boom down a bit on my wee Hunter?

 

[dancrane]

Am I right in thinking that a cunningham pulls a point above the tack down towards the tack...?

My cunningham does that, because the eyelet is about ten inches above the foot. But on loose-footed sails, I've had a cunningham attached at the very foot of the luff.

I always thought it was just to pull the luff taught when you'd done all you could with heaving on the halyard.

 

[theguerns]

Hi All, Here is my pet hate and one I never understand. I bought some paint the other day and looked at the chemical components of it carefully. Then went to another shop not a marine shop found the exactly the same thing but was 18% of the marine product. I have found this in so many things that being retired and a moaning old sod I now look at everything I buy for the boat and blimy haven't we saved some cash. I have also found that many products not made for the marine trade are also made of the same stuff or better and a lot cheaper. For instance for years I have used Sikaflex and although they say UV safe and never breaks the bond I have found it to be rubbish. I did a joint on our Colvic Watson with Sikaflex and had to do it each year as it broke down in the sun. Three years ago I used a product called CT1, haven't touched it yet and still as good as the dayI used it plus the tube is still usable after opening a year later. Happy sailing and Merry Christmas to you all.

 

[nigelmercier]

... Stand under boom, and look up at the top batten, the straight part near the aft end of the sail. If the back of the batten sags off to leeward, compared to the boom, your leech is open. Good for sailing in waves, but otherwise, you are losing power. Try more main sheet. If the batten is parallel to the boom, you have the sail trimmed as the sail designer intended. If the back of the batten is converging with the boom, your leech is hooked. Good in moderation, for sailing in flat water, but easy to overdo, and can just act as a handbreak. Ease main sheet...

Very clear, thank you. Note to self: fit tell-tales.

 

[boguing]

A reply to a couple of questions.

Admiral WH Smyth (really) wrote 'The Sailor's Word Book' in 1865. (I got mine from British Bookshops). He writes:-

Vang: A rope leading from the end of the gaff to the rail, one on each side, so that the two form guys attached to the outer ends of the gaffs to steady them, and when the sails are not set keep them amidships.

This is from boguing's word book.

Another reason for a Cunningham is that a racing boat will have a black band to mark the full hoist of the main's luff. Using the halyard to take it past that point is a breach of the rules. This means that once the sail is up as far as allowed, a downward tensioner is the only way to tighten the luff. On reflection (because the boom will also have a band) there isn't a horizontal equivalent to the Cunningham. Never thought about that before.

 

[Uricanejack]

Cunninghams are for boats with fixed goose necks. Acting like a down haul on older boats.

Or at least that's what I've always thought.

I just added this to get to 300 not because I know what I'm talking about