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Can anyone please confirm my Pythagorus workings ?


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8 minutes ago, RLWP said:

And of course it does. You can measure the height of the real above water bit and scale the under water bit off the photo

 

Richard

I had thought of doing that, but the picture is 15 years old and it has been repainted several times, I have no idea to within 6 inches either way where the water line would be.

I have 2500 litres (2 tonnes +) of fuel in her at the moment so todays waterline will not necessarily be the same as previous waterlines.

 

The overall height (which now includes radar & a radar mast - that folds) obviously will not change, but, the 'split' between air & water drafts could be /- 6 inches.

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The photo shows skin fittings, have these been moved, or are they still in the same places?

These will provide reference points to the current waterline.

Scale off with a known measurement that has not changed since the photo was taken.

 

Bod

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3 hours ago, Mike the Boilerman said:

 

There is 12. How does that help? :giggles:

I reckon the draught is six rungs deep.

Seriousness to one side, how do the twin rudders do their job when they are tiny and fitted alongside (almost behind) the prosperellors?

Shouldn't they be at least a rung further behind and in line with them?

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26 minutes ago, zenataomm said:

I reckon the draught is six rungs deep.

Seriousness to one side, how do the twin rudders do their job when they are tiny and fitted alongside (almost behind) the prosperellors?

Shouldn't they be at least a rung further behind and in line with them?

 

Single rudder, but with 2-engines you don't need a rudder anyway.

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5 hours ago, Alan de Enfield said:

 

Versatility-35-31.jpg

If you know the air height you can work out the scale off a print of the photograph and therefore measure the overall height.

You can check the scale also by measuring the length.

Or perhaps the ladder helps.

It will not be far out and probably  better than your triganometry approach.

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6 hours ago, Alan de Enfield said:

 

 

So √ B = √ (C² - A²)

 

I estimate / measure the draft as 1.9m

Deduct 50mm for the width of the keel (approx.100mm) gives a draft of 1.85m (6 feet ish)

 

Anyone see any errors ?

I(f it is correct - its maybe another lesson to learn about brokers).

 

Largely correct.  But √ B = √ (C² - A²) should be √ B² = √ (C² - A²) although you have the maths right. 

And, if I understand you correctly, the 50mm half width of the keel effectively reduces the half-beam (A) and thus increases rather than decreases B (the draft) so I make it 1.96m

 

 

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5 hours ago, Alan de Enfield said:

 

The boat tapers in at the stern. I did consider this point to measure the draught because the platform was nearer to the water and easier to measure the beam - but had the Props and Rudder to contend with. 

 

The widest part is roughly just astern of the ladder.

This is where I did all of the measurements (to avoid getting the rope caught around the prop or rudder).

Can I suggest a rather less theoretical approach?  How about three long sticks with the ends tied to form a U shape. Plunge the "crossbar" under the boat at the stern  and mark the waterline on both vertical sticks where they emerge from the water. The draft will then be the average of both wet lines on the vertical sticks?  All very practical but it should work to the tolerances you need for the task.

 

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6 hours ago, Mike the Boilerman said:

 

There is 12. How does that help? :giggles:

Yes there are 12. 

 

Not counting the first rung to allow/compensate for the angle of the ladder there are five rungs to the water line. Each rung will most likely be 10” apart, so it’s approximately 4’2”.

which is somewhere between 4’ and 4’ 6”, as originally stated in Alan’s paper work. QID

 

Edited by Goliath
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11 hours ago, TheBiscuits said:

Just use the picture.  Measure the cabin window for scale,  and work it out from there.

I was going to suggest to measure the railings for scale but TheBiscuits method will be scaling from closer to the center line so should be more accurate. The ladder is at a slight angle so not the best but close.

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Where is Bizzard when you need him? 

13 hours ago, Alan de Enfield said:

In theory yes - in practice it is currently in pieces being stripped and painted.

You've really got me confused.  Is the boat floating in the water or is it ashore?  If the latter, just go and measure it directly.  

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15 minutes ago, Murflynn said:

Where is Bizzard when you need him? 

You've really got me confused.  Is the boat floating in the water or is it ashore?  If the latter, just go and measure it directly.  

In the water.

It was booked in with a painter (for painting indoors) in March, he quoted we accepted we took the boat but then de decided he 'was too busy'

 

We then looked at having it 'teak-decked' took the boat, got a quote. Accepted the quote, took the boat and left it, went home.

Got a call a couple of days later, The price has gone up to £11,000 for the decking and £7,000 for the rest painted. Said OK.

Got another call - can you come and get your boat. The guy who was actually to do the work said the boat shape was too complicated to do it.

 

We had another quote from a painter (to do it on its mooring), he quoted, we accepted, the date came and he didn't turn up, "he had changed his mind"

 

The economy must be good when they can walk away from a £10,000+ paint job.

 

So, now we are doing it ourselves with help from ' a friend who is a bit of a man of all trades' (to do the 'grunt-work').

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44 minutes ago, Murflynn said:

Where is Bizzard when you need him? 

You've really got me confused.  Is the boat floating in the water or is it ashore?  If the latter, just go and measure it directly.  

If it's afloat, is there anywhere you can gently put it aground, then measure the water depth at a number of points around the hull. 

Having already measured your air draught you will be able to calculate the total height of the boat.

Incidentally, this does highlight the advantage of having draught marks on the hull so you don't have to guess the draught.

 

Howard

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43 minutes ago, Alan de Enfield said:

In the water.

It was booked in with a painter (for painting indoors) in March, he quoted we accepted we took the boat but then de decided he 'was too busy'

 

We then looked at having it 'teak-decked' took the boat, got a quote. Accepted the quote, took the boat and left it, went home.

Got a call a couple of days later, The price has gone up to £11,000 for the decking and £7,000 for the rest painted. Said OK.

Got another call - can you come and get your boat. The guy who was actually to do the work said the boat shape was too complicated to do it.

 

We had another quote from a painter (to do it on its mooring), he quoted, we accepted, the date came and he didn't turn up, "he had changed his mind"

 

The economy must be good when they can walk away from a £10,000+ paint job.

 

So, now we are doing it ourselves with help from ' a friend who is a bit of a man of all trades' (to do the 'grunt-work').

 

 

Well given your track record of scaring off tradesmen, I'd say it doesn't matter what the total height of the boat is, as the transport lorry won't turn up anyway! 

 

:giggles:

 

 

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It's a lot of "if's" but if you have a boat-hook and if the bottom of the rudder is about the deepest part of the boat and if the rudder is accessible from the stern then hook the boat-hook under the bottom of the rudder, hold it there for 30 seconds or so (to get the pole wet so that the level is easily read) and then measure the distance from the curve of the hook to the watermark.

 

Whether that is accurate enough is for you to decide!

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12 hours ago, Capt Ahab said:

Can I suggest a rather less theoretical approach?  How about three long sticks with the ends tied to form a U shape. Plunge the "crossbar" under the boat at the stern  and mark the waterline on both vertical sticks where they emerge from the water. The draft will then be the average of both wet lines on the vertical sticks?  All very practical but it should work to the tolerances you need for the task.

 

no .... that's much too practical and simple.  

 

I'm still waiting for Bizzard to come up with a better way.

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14 hours ago, Capt Ahab said:

Can I suggest a rather less theoretical approach?  How about three long sticks with the ends tied to form a U shape. Plunge the "crossbar" under the boat at the stern  and mark the waterline on both vertical sticks where they emerge from the water. The draft will then be the average of both wet lines on the vertical sticks?  All very practical but it should work to the tolerances you need for the task.

 

refinement? on above use a metal bar maybe 1 foot long, that sinks, fastened to two tape measures, lower under the skeg and pull up, two readings one each side and average them, job done.

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28 minutes ago, Detling said:

refinement? on above use a metal bar maybe 1 foot long, that sinks, fastened to two tape measures, lower under the skeg and pull up, two readings one each side and average them, job done.

That is pretty much what I did.

If the 'bar' is only 1' long then the beam of the boat (14') will mean that the tape measures are at an angle as the bottom (keel) is only 4" wide- we get back to Pythagorus.

 

The only way to use the tape measure (as suggested) is to use a 'bar' in excess of 14 feet long. You still need to hang 5 feet over the side (and wedge your feet in the rails) to get down to see the tape measure reading at water level.

 

I'll get back to the boat and measure some 'fixed' points (maybe window sizes, rail-spacings, etc) and apply them to the picture, then subtract the air draft.

Edited by Alan de Enfield
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1 hour ago, Alan de Enfield said:

That is pretty much what I did.

If the 'bar' is only 1' long then the beam of the boat (14') will mean that the tape measures are at an angle as the bottom (keel) is only 4" wide- we get back to Pythagorus.

 

The only way to use the tape measure (as suggested) is to use a 'bar' in excess of 14 feet long. You still need to hang 5 feet over the side (and wedge your feet in the rails) to get down to see the tape measure reading at water level.

 

I'll get back to the boat and measure some 'fixed' points (maybe window sizes, rail-spacings, etc) and apply them to the picture, then subtract the air draft.

use a bar 14 ft long something light and easily available like 2 x 2m lengths of 22mm copper plumbing tube joined in the middle..

 

you don't need to hang over the side......  just use a stick with 1.5m marked on it, lower it so it touches the water, and note the reading on the tape at the 1.5m mark.  

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SORTED - HOPEFULLY

 

Taking 'on-board' the suggestion of using some known measurements and comparing them to a known 'item' on or around the waterline I could work out the draft.

I could then scale it off the photograph.

 

So looking at the photo :

To the left of the ladder (by the blue-stripe) are two- hull openings. The lower on of these is approximately 4" above the water line (as she sits in the water today)

Measure the distance (on the photo) from the keel to 'just below' the bottom hull opening and get 42mm.

 

Now - a couple of fixed items.

The rear Pushpit Rails : The space between the rails is 14" (centre to centre) and the overall height of the top rail from the deck is 27". On the photo these two dimensions equate to about 11mm and 23mm.

 

If I take the waterline level of "42mm" as equating to roughly 4x the rail spacing of 11mm then the water draft equates to a little less than 4 x 14" (56" = 4' 8") so call it 54" or 4' 6" which is closer to the 4' given to me by the broker when we bought her (and bearing in mind she now has 2000kg more fuel in her tanks than she did, it may account for the 6" difference).

 

Total 'trucking height' is now 10' 3" + 4' 6" (14' 9") which is 'doable' on a low loader to get under the UK bridge minimum of 16' 6".

 

Thanks to all that contributed.

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