LadyInBed
Well-Known Member
This is some info that I have stored away over the years.
Do you have any other technical Formula, Ratios and Rigging info or links?
Maximum Speed
1.4 x sq root of waterline length (ft)
2.43 x sq root of waterline length (mtrs)
Ave speed / day
20 x sq root of waterline length (ft)
Wave Length
5.12 x (time in secs between crests) squared
Wave Speed
3.03 x time in secs between crests
Volume below waterline (in cu ft)
Wt in Tons x 35
[35 (34.973) cu ft of Seawater weighs 1 Ton]
[1 cu ft of Seawater weighs 64 lbs]
USYRC's 'Capsize Risk Factor'
Max Beam devided by the cube root of the Displacement in cu ft
(the Displacement in cu ft can be found by deviding the Displacement in pounds by 64)
Beam / ( Disp / (0.9 x 64)) ^.333
(Values less than 2 are good).
From Ted Brewer (http://www.tedbrewer.com/yachtdesign.html)
PPI immersion and Moment to trim 1 inch
POUNDS PER INCH IMMERSION (PPI):
The weight required to sink the yacht one inch.
It is calculated by multiplying the LWL area by 5.333 for sea water or 5.2 for fresh.
The PPI usually increases as the hull sinks into the water as the LWL area is also increasing
due to the shape of the hull above water.
MOMENT TO TRIM 1 INCH (MTI):
The MTI is the moment, expressed in foot-pounds,
that will change the fore and aft trim of the yacht one inch.
For a displacement hull, the MTI is, roughly (but close enough for all practical purposes),
0.35 times the square of the waterline area divided by the WL beam,
or: 0.35 x WL Area (squared) / Beam WL
For example; a boat has a LWL Area of 165 sq ft and a Beam WL of 8 feet.
The MTI is 0.35 x 165 x 165 /8 = 1191 ft-lbs., say 1200 for rough figuring.
Now you hang a 100 pound dink 18 feet abaft the CB. You've added 1800 ft-lbs of aft moment
so the boat will trim 1800/1200 = 1.5 inches down by the stern.
However, the boat does trim about its CF and, as that is usually abaft amidships,
the stern will move less than the bow. You might find that she trims 5/8" down by the stern,
and 7/8" up by the bow, making a total trim change of 1.5 inches.
Obviously on a cat things are slightly different.
once the new waterline area is calculated you can apply the figures to SA/D
(taking into account the new displacement with the gear onboard)..
this gives a reasonable view of the potential change.. mainly monohull formula though..
DISPLACEMENT/LENGTH RATIO:
The D/L ratio is a non-dimensional figure derived from the displacement in tons (of 2240 lbs)
divided by 0.01 LWL cubed, or Dt/(.01 LWL)3.
It allows us to compare the displacement of boats of widely different LWLs.
Some examples of various D/L ratios follow, but are generalities only,
as there is often a wide range within each type.
BOAT TYPE D/L RATIO:
Light racing multihull 40-50
Ultra light ocean racer 60-100
Very light ocean racer 100-150
Light cruiser/racer 150-200
Light cruising auxiliary 200-250
Average cruising auxiliary 250-300
Heavy cruising auxiliary 300-350
Very heavy cruising auxiliary 350-400
STORM, a wonderful 27' LWL sloop on which I raced with Bill Luders many years ago,
had a D/L ratio of 386 so she would be considered very heavy by today's standards.
However STORM was 39' LOA and when she heeled to a breeze her long ends would
increase her sailing LWL, thus reducing her D/L ratio to a more reasonable figure
when we were beating to windward. If she picked up 3 feet of WL her D/L ratio dropped to about
281, a significant change, and one that made her a very competitive racer in the 1960s.
SAIL AREA/DISPLACEMENT RATIO:
The SA/D ratio is the sail area in sq ft. divided by the displacement in cubic ft to the 2/3 power,
or SA/D x 0.667
Ratios below 14 are suited for motor sailers,
from 14-17 for ocean cruisers
from 16-18 for typical coastal cruisers.
Ratios over 18-20 are seen on racing dinghies, inshore racers and ocean racing yachts.
The more extreme screamers can have very high SA/D ratios indeed; My 60 foot design, WILD THING, had a SA/D ratio, based on 100% foretriangle, of well over 30, depending on her displacement at the moment.
Her displacement varied widely as she could carry 8,000 pounds of water ballast in tanks
on the windward side
Also see
http://www.altendorff.co.uk/search/ratios/
Sail info
http://www.kempsails.com/component/docman/cat_view/5-technical-data.html?Itemid=28
http://www.seldenmast.com/resources/hints_and_advices.html
and modestly from my site
http://montymariner.co.uk/downloads/ (plus Tide Stream Charts and Tide Tables)
Do you have any other technical Formula, Ratios and Rigging info or links?
Maximum Speed
1.4 x sq root of waterline length (ft)
2.43 x sq root of waterline length (mtrs)
Ave speed / day
20 x sq root of waterline length (ft)
Wave Length
5.12 x (time in secs between crests) squared
Wave Speed
3.03 x time in secs between crests
Volume below waterline (in cu ft)
Wt in Tons x 35
[35 (34.973) cu ft of Seawater weighs 1 Ton]
[1 cu ft of Seawater weighs 64 lbs]
USYRC's 'Capsize Risk Factor'
Max Beam devided by the cube root of the Displacement in cu ft
(the Displacement in cu ft can be found by deviding the Displacement in pounds by 64)
Beam / ( Disp / (0.9 x 64)) ^.333
(Values less than 2 are good).
From Ted Brewer (http://www.tedbrewer.com/yachtdesign.html)
PPI immersion and Moment to trim 1 inch
POUNDS PER INCH IMMERSION (PPI):
The weight required to sink the yacht one inch.
It is calculated by multiplying the LWL area by 5.333 for sea water or 5.2 for fresh.
The PPI usually increases as the hull sinks into the water as the LWL area is also increasing
due to the shape of the hull above water.
MOMENT TO TRIM 1 INCH (MTI):
The MTI is the moment, expressed in foot-pounds,
that will change the fore and aft trim of the yacht one inch.
For a displacement hull, the MTI is, roughly (but close enough for all practical purposes),
0.35 times the square of the waterline area divided by the WL beam,
or: 0.35 x WL Area (squared) / Beam WL
For example; a boat has a LWL Area of 165 sq ft and a Beam WL of 8 feet.
The MTI is 0.35 x 165 x 165 /8 = 1191 ft-lbs., say 1200 for rough figuring.
Now you hang a 100 pound dink 18 feet abaft the CB. You've added 1800 ft-lbs of aft moment
so the boat will trim 1800/1200 = 1.5 inches down by the stern.
However, the boat does trim about its CF and, as that is usually abaft amidships,
the stern will move less than the bow. You might find that she trims 5/8" down by the stern,
and 7/8" up by the bow, making a total trim change of 1.5 inches.
Obviously on a cat things are slightly different.
once the new waterline area is calculated you can apply the figures to SA/D
(taking into account the new displacement with the gear onboard)..
this gives a reasonable view of the potential change.. mainly monohull formula though..
DISPLACEMENT/LENGTH RATIO:
The D/L ratio is a non-dimensional figure derived from the displacement in tons (of 2240 lbs)
divided by 0.01 LWL cubed, or Dt/(.01 LWL)3.
It allows us to compare the displacement of boats of widely different LWLs.
Some examples of various D/L ratios follow, but are generalities only,
as there is often a wide range within each type.
BOAT TYPE D/L RATIO:
Light racing multihull 40-50
Ultra light ocean racer 60-100
Very light ocean racer 100-150
Light cruiser/racer 150-200
Light cruising auxiliary 200-250
Average cruising auxiliary 250-300
Heavy cruising auxiliary 300-350
Very heavy cruising auxiliary 350-400
STORM, a wonderful 27' LWL sloop on which I raced with Bill Luders many years ago,
had a D/L ratio of 386 so she would be considered very heavy by today's standards.
However STORM was 39' LOA and when she heeled to a breeze her long ends would
increase her sailing LWL, thus reducing her D/L ratio to a more reasonable figure
when we were beating to windward. If she picked up 3 feet of WL her D/L ratio dropped to about
281, a significant change, and one that made her a very competitive racer in the 1960s.
SAIL AREA/DISPLACEMENT RATIO:
The SA/D ratio is the sail area in sq ft. divided by the displacement in cubic ft to the 2/3 power,
or SA/D x 0.667
Ratios below 14 are suited for motor sailers,
from 14-17 for ocean cruisers
from 16-18 for typical coastal cruisers.
Ratios over 18-20 are seen on racing dinghies, inshore racers and ocean racing yachts.
The more extreme screamers can have very high SA/D ratios indeed; My 60 foot design, WILD THING, had a SA/D ratio, based on 100% foretriangle, of well over 30, depending on her displacement at the moment.
Her displacement varied widely as she could carry 8,000 pounds of water ballast in tanks
on the windward side
Also see
http://www.altendorff.co.uk/search/ratios/
Sail info
http://www.kempsails.com/component/docman/cat_view/5-technical-data.html?Itemid=28
http://www.seldenmast.com/resources/hints_and_advices.html
and modestly from my site
http://montymariner.co.uk/downloads/ (plus Tide Stream Charts and Tide Tables)
