Here is a list of all the postings Sam Longley 1 has made in our forums. Click on a thread name to jump to the thread.
|Thread: Aldi bargain laser level|
I did try to delet the last post when i realised it was totally out of context but the edit was stopped
I am beginning to recall the method now. One doubles the angle & forms a triangle with 2 equal angles at the base & the top angle is the observed sextant angle- (or is it twice the observed angle, or was the base angles each half the observed angle- cannot recall?). The base being the line between the 2 observed points. From that top point one strikes a circle through the 2 stations. But i seem to recall that one had to know which side of the stations one placed the triangles. Trial & error based on dead reckoning. Or obvious from the position of the land I think !!
Now I am going to have to find a b..y book & read it up for no other practical purpose other than reminding myself how !!!
Trouble is that reading a sextant horizontally through 2 points is almost impossibly on any small yacht in any sort of sea. The method possibly stemmed from the days of square riggers with a stable platform. There was also a special protractor for setting out the triangles. Forget the name. Will have to sleep on that one.
Edited By Sam Longley 1 on 15/07/2019 22:46:41
You have just said something that conflicts-- that you have to get 2 points to coincide. Of course it matters if they are jiggling about. have you never tried tossing about in a swell aiming a sextant at a target. I have enough trouble aiming binoculars in a 2 metre chop, let alone aiming my sextant at 2 shore targets at once. I have to admit that my sextant does not lend itself to horizontal use, I have had it 40 years & it does not have wheel adjustment. I certainly have tried( just testing really) & given up as a bad job. Easy vertically. Lack of use in the last 20 years makes it difficult to pick up now
My Sestral compass is about as good as they get & i can get fairly good top hats depending on boat motion.I use it regularly in places like Channel Islands
To each his own- we are not going to agree- but does that matter- Of course not
I would back the accuracy of my Sestral Handbearing compass aimed at a single point up against my sextant held horizontally, whilst trying to fix on 2 points any day.
With the greatest respect, Are you sure about that?
Somehow I do not think that would give a reliable fix.The RYA method uses 3 compass bearings not a sextant angle If one has a sextant one has to work from a point towards the targets
One would have to lay the compass bearing line first then set the angle with a protractor or similar tool & slide it along the bearing line until it met the target. Repeat for the third point. The whole fix would be totally reliant on the first bearing, thus making the fix very unreliable. If one had a compass to take the bearing in the first place then one would continue to take bearings.
If you think about it, there is no advantage in using a sextant which is not only difficult but would produce an inconsistent fix.
Edited By Sam Longley 1 on 15/07/2019 19:27:30
My first "foreign trip" from Burnham on Crouch to Ostend was in 1969 & I missed Ostend by 9 miles (no lessons for me) I hadn't a clue where I was.
I have just returned from 6 weeks single handed cruise to the Channel islands (picking up the June 06 D day landings on the way) & just as I left, my chart plotter failed. The best part of the trip was having to manage the navigation conventionally. Especially 2 legs of approx 100 miles - part over night,out of sight of land-, wondering where on earth I would end up. The rocks around Channel Islands tend to focus the mind .
Spot on every time- So what I learned all those years ago still worked.
Edited By Sam Longley 1 on 15/07/2019 19:07:07
A Horizontal angle on its own will not give you distance off because it will subtend an arc which could be any distance from the shore dependent on the length of either leg. You need a compass to determine the direction of the legs. In which case the sextant is not required. Without the compass bearing you would not know where to draw the lines.
However, Charts show the height of light houses which gives the third dimension of your triangle for distance off if you take the angle vertically. You need to be able to see the base & know the height of tide then you can calculate the distance to the object That is unless you know the dipping distance, in which case the vertical angle is irrelevant. But you still need to know the bearing from the light to get a position fix within a reasonable estimate.
The "dipping distance" is the distance at which the light appears to drop below the horizon.Add to that, the dipping distance of the observers eye above the waterline & you have an approx distance off.
Better still if you have GPS & it is not being jammed
Edited By Sam Longley 1 on 15/07/2019 16:47:42
But a laser level, which is a very common use for them, could be pointing up in the air (or down)
Edited By Sam Longley 1 on 15/07/2019 08:05:45
Of course they are antiques now & consigned to the bin.(mine is not, I used it last year) But when Paul used a laser to align his fence & drains he could possibly have used a set of boning rods to far greater effect.
My grandfather was using water levels as did his grandfather before him & mine is hanging in the shed. But ask someone how to fill one (they do not work if they have air bubbles in them) -- there is another question for you
But should they assume that because it is a " laser" the instrument supplied is adjusted for accuracy in the first place? & just because it is modern it does not always make it the best tool for the job
Edited By Sam Longley 1 on 15/07/2019 07:38:49
That brings back memories.
When I was 10 years old my fathers foreman ganger used to let me sight down the boning rods when drain laying.
Salt glazed drains with cement joints..
Datums were set with a Cowley level.
Still would not mess about with a laser if there was 2 of us.
Still got the dumpy level & staff he let me buy for my own use when I was 16. An antique now I suspect.
If a building surveyor told me that i had to have a "certified surveyor" to check my drains I would have told him to get stuffed- (Regardless of the fact I am qualified anyway, it would not matter)
One of the questions I used to ask site foremen when interviewing them was, "Can you use a dumpy level" Answer " yes" - OK
Do you know how to check it for accuracy? That used to stump some of them & I suspect that lasers, when hired, borrowed etc. would not necessarily be accurate. Most would just assume they are. But hired equipment gets abused.
I have never used one in anger; but if i did I would know how to check it.
I wonder if others have had the problem- is it an issue with lasers?
So here is a question for you.
How would one check a "hired in" laser for accuracy prior to use?
Edited By Sam Longley 1 on 14/07/2019 07:30:33
|Thread: Rudder Bushes on Boat|
Before beginning to make rudder bearings it may be worth looking on this site. Jefa make roller bearings for a wide range of craft & by the time one has invested in the material one could have bought a ready made bearing
But in any event do NOT use nylon. I use tufnol in my rope cutter bearings, but in rod form, can be very expensive-- depending on diameter, of course
Edited By Sam Longley 1 on 15/05/2019 07:25:32
|Thread: Anglepoise Lamps & CFL/LED lamps|
Keep it for a few more years. You will find that after a while, you will tend to drift down with it as the day goes on.
|Thread: "Screwing" a car round a corner!|
Perhaps they should have watched John Rodes cornering the works Cooper S at Druids (Brands Hatch) when he used to sling the back of his mini out wide by flicking the hand brake then squirting the throttle to get it to head down the hill towards South Bank
|Thread: Dol starter or just a plug is it really worth it?|
What? worse? you mean as in damage a couple of days work??
Edited By Sam Longley 1 on 26/04/2019 08:06:23
|Thread: Black Holes|
Spot on. Space has been a big subject in our house for some time.
I have been trying to get my wife to let me build another 3 feet onto the end of my shed for ages
It is all relative really
|Thread: Problem with penetrating oil can|
Are we now going to guess which supermarket garage forecourt you will buy the diesel from?
I will start it off-- "a well known one that sell own brand beans that taste awful"
There you are . Now we all know
Edited By Sam Longley 1 on 12/04/2019 20:44:45
I hate quizzes
|Thread: Recommended base flashing for an external wall|
A cheap option is to stick Flashband down - but use the proper primer first & apply it properly on a warm day. ( or warm it a bit with a heat gun helps to make it sticky) Obtainable from any builders merchant & miles cheaper than lead.
Otherwise there are loads of firms that will pre form coated steel flashings if you send them a sketch of what you want
But provided the floor is higher than the surrounding ground & the cladding comes down just past the floor level so that the water is shed down past the concrete floor, you should not need anything. Just laying a flashing on the ground will not stop water coming under it . It has to follow the principle of water flowing down hill all the time..
If the cladding stops above the floor level & you want to shed the water over the edge of the slab( & may be behind the face of the slab) then you would need a flashing to direct the water over the edge, presumably a "Z" shape. That could be lead, zinc, flashband, or a preformed steel flashing. But the slab must be higher than the immediate surrounding ground level otherwise you are wasting your time
Edited By Sam Longley 1 on 21/03/2019 07:33:47
|Thread: How do you make a lifting eye|
size "0"---so they are obtainable. Dunno how many 1000's you have to buy though & not so much fun as making one
But finding a supplier in the UK ???
Edited By Sam Longley 1 on 08/03/2019 07:36:52
|Thread: Plastic Balls in Bearings?|
Most of the pullies on my yacht have delrin balls in the roller bearings in them. The furling gear , which takes considerable load applied by a winch, has delrin balls in the swivels
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