Narrow or Widebeam, Used or New?

[Amicus]

I quote;

Steven D. Tripp

University of Aizu

Aizu-Wakamatsu, Japan

 

 

I don't believe education/ID has ever really had any theories worthy of the name "scientific." I am told that astronomers say that they have no theory of Pluto. Now from the point of view of us education people it seems they have a theory: It goes around the sun (we'd be thrilled if we a theory as predictive as that). But they mean that they cannot predict with precision where Pluto will be a year from now. They have to look. Naval architects say they have no theory of a hull's wave making. Of course they have oodles of data drawn from real ships, but if you alter that ship's hull slightly, they cannot predict, with precision, what the resulting wave-making characteristics will be. They need to do tank testing. Why do aeronautical engineers use wind tunnels? Because they have no theory of the behavior of airframes. If they did there would be no need for wind tunnels. The performance would follow directly from the formulas. (Maybe they are getting close to this now.)

<ducks> <ducks/>

[Big COL]

You see Maffi I told you there is no easy answer to this. Could it be that the Earth is flat and not round.

[maffi mushkila]

You see Maffi I told you there is no easy answer to this. Could it be that the Earth is flat and not round. 

 

'Eeee by 'ecky thump, thar could be reet the'er Col me ol' mate.

Edited August 26, 2005 by maffi mushkila

[DHutch]

Is it me, or did this thread go majorly off topic over a page ago!

[maffi mushkila]

Is it me, or did this thread go majorly off topic over a page ago!

So sue!

[bottle]

So sue!

29141[/snapback]

 

Suewho!

[maffi mushkila]

Sue who!

 

Outline plans are free as are typographical corrections.

 

If you want the whole shebang that comes at a cost.

[stoner]

Thanks Maffi, I only wanted a sensible answer to my questions

[Jamie]

Hi there stoner,

Just add my thoughts on the 'ol narrow vs widebeam. i have a 60ft narrowboat and I sailed part of the ouse a few months ago. Salters Lode lock which brings you onto the middle levels will only take narrowboats. If your happy not going past there then thats ok as the ouse and around are really pretty to cruise.

 

As far as I'm aware widebeams pay the same mooring fee's as narrowboats as they are priced at ft per year. However you may have problems finding space in marina's finger/pontoon moorings as they often just have room for 2 narrowboats between the fingers - I don't think that a widebeam and a narrowboat would fit, at least not in the ones I have been to.

 

A wide beam might also have more room for generator, larger water/diesil/toliet tanks. I don't know anything about re-sale values or anything. I like wide beams and on the ones I have been on they feel so much roomier when you are inside even if they are a smaller lengh.

[Carrie]

I just like the 'humbleness' of a narrowbeam. Personal taste of course, but I think the widebeams are more housey.

 

As a fairly inexperienced boat driver, I still get a flutter of nerves when passing moored boats and a Chunky Monkey in a narrow part of the canal.

[ChrisPy]

Erm? Whaddah yah mean? Limiting hull speed is proportional to factor1 x length raised to a factor2! The factors are determined by hull design and displacement.  My 18' (1 tonne?) sea-going trad clinker boat would never make more than 4 knots!  My 35', 6 tonne canal boat might make 8 knots maximum were the engine twice as big whereas my 70' 25 tonner could do 11.7 knots maximum

28709[/snapback]

sorry to be pedantic, but the factor is proportional to the square root of the hull length. It might appear that you were saying the square of the hull length.

 

a 72ft boat has a 'natural hull speed' twice that of an 18ft boat, if the shape factors are the same.

[Amicus]

sorry to be pedantic, but the factor is proportional to the square root of the hull length.

30961[/snapback]

Sorry to be pedantic but it is the square root of the water-line length and then times a factor which I seem to remember is sommick to do with the block coefficient 1.4 seem to be rattling about in the bottom of me memory unit.

Square root of W/L in feet x yada, yada, gives the hull speed in knots.

Edited September 14, 2005 by Amicus

[Amicus]

On tother and;

http://www.sailingusa.info/cal__hull_speed.htm

 

Edit Isnt the Internet wunnerful;

http://en.wikipedia.org/wiki/Hull_speed

Edited September 14, 2005 by Amicus

[bottle]

Just did that for 59ft and it works out to over 10knots. Now where did I leave those

 

water skis

[Amicus]

Reasons and details here;

http://www.sailnet.com/collections/article...cleid=colgat006

[John Orentas]

Very interesting that but I notice there are a few approximately's in there, ship designers still spend millions of pounds building test tanks and other facilities so I suspect hull design is still as much an art as a science.

[ChrisPy]

Very interesting that but I notice there are a few approximately's in there, ship designers still spend millions of pounds building test tanks and other facilities so I suspect hull design is still as much an art as a science.

31065[/snapback]

and one thing that the test tank proved is that a bulbous bow can kid the water into thinking the boat is much longer than it really is. With a bulbous bow, the bow wave starts well ahead of the bow. With a fine bow like the old Queen Mary the bow wave built up to a peak over the front 50 feet of the water line.

 

where hull length is the limiting factor for the intended service, then a bulbous bow is useful. With canal boats of say 50 to 60 ft, the speed is well below the natural hull speed. In such a case the hull form becomes much more critical to economy (and the rate of use of energy can largely be measured by the amount of wash created).

 

Most analyses provide the same result : if you double the speed you quadruple the power consumed. This includes considerations of skin friction and hull form.

 

Of course once you reach the hull speed the relationship between speed and power changes again. A true displacement hull will never plane, no matter how much power you apply. But it will sink down by the stern with the risk of swamping if you slow down quickly and the stern wave overtakes you.

 

So be happy cruising along consuming 20hp at 4 knots, 'cos at 8 knots you'd need 80hp. Double the consumption per mile, and 4 times the consumption per hour.

Edited September 15, 2005 by chris polley