Re: Fair and Square: Anhinga Flared
POSTED 070321 Anhinga Flare Reply 2
Forgot some Gloucester Yawl group links:
Scanned lines from Small Boats
http://groups.yahoo.com/group/Bolger2/files/Gloucester%20Yawl/
Scanned photo from the later Bolger Boats (A later book combining
Folding Schooner & Small Boats, with some additional ~10pp of
material)
http://groups.yahoo.com/group/bolger4photos/files/Gloucester%20Yawl/
Some comments additional to PCB's caption to the above photo
http://groups.yahoo.com/group/bolger/message/38952?threaded=1&p=8
Interesting to consider the dog leg with banks dory stability in
mind - though of course the metatarsus of the motorboats is shorter
http://groups.yahoo.com/group/bolger/message/7063
Any lines of a Light Dory about?
http://groups.yahoo.com/group/bolger_study_plans_only/files/Glouceste
r%20Yawl/
http://tinyurl.com/yvkw88
Graeme
Forgot some Gloucester Yawl group links:
Scanned lines from Small Boats
http://groups.yahoo.com/group/Bolger2/files/Gloucester%20Yawl/
Scanned photo from the later Bolger Boats (A later book combining
Folding Schooner & Small Boats, with some additional ~10pp of
material)
http://groups.yahoo.com/group/bolger4photos/files/Gloucester%20Yawl/
Some comments additional to PCB's caption to the above photo
http://groups.yahoo.com/group/bolger/message/38952?threaded=1&p=8
Interesting to consider the dog leg with banks dory stability in
mind - though of course the metatarsus of the motorboats is shorter
http://groups.yahoo.com/group/bolger/message/7063
Any lines of a Light Dory about?
http://groups.yahoo.com/group/bolger_study_plans_only/files/Glouceste
r%20Yawl/
http://tinyurl.com/yvkw88
Graeme
Of course, Bolger has done this before!
The difference to final stability performance? He got a Banks dory
in the square, I propose a Swampscott. He used massed live ballast
to extend the righting arm, I propose using the increase between the
lifted windward ballast and the leeside knuckle (and... maybe a
sponson?).
Bolger agreed with an old observation "that sharpies suffer from
being wide for their length, and from having flaring sides." He
wrote "My flow theory accounts for this, but I've long thought that
a sponson sharpie would produce the benefits of a flaring side
without the drawbacks, or most of them." He designed the step
sharpie "Gloucester Yawl" At the time this boat alarmed a lot of
people, but IIRC eventually one was built and proved a good sailer;
if wet.
In Gloucester Yawl,when heeled to the gunnels though the lee sponson
provides approx. 3cuft of offset bouyancy this is offset by the lack
of bouyancy of the step in between the bottom side and sponson
bottom. The cancelling effect delivers stability performance akin to
the flare of a *BANKS* dory. Bolger has often remarked that a banks
dory is a poor sailer and he would no longer be involved in
designing a sailplan for the type! G Y stands up to its relatively
large amount of sail because the sailplan is low, she has a big crew
of 5, and flat decks for them to scramble out on. She rows well on
the narrow bottom at 1" wider than a June Bug. She has chine
curvature in accord with Bolgers sharpie bow water flow theory.
What a surprise to see proportional numbers for SoP Gloucester Yawl
sharpie that closely match Gloucester Gull dory!
Gloucester Yawl Light Dory Type V
Length bottom 21' 3600mm
LOA 21' 4740
BOA Bottom 3'4" 572
BOA Gunnel 5'6" 1190 +30
Sponson side height 9"
Bottom side height 11-4/8" Side height 419
Bottom L/B 6.3 6.29
Gunnel L/B 3.8 3.88
LOA/Overhang total length 4.66 (21'/4'6" & 4740/1140) 4.15
Beams/Heights
Bottom side top 4.44 NA
Upper side bottom 6.66 NA
Gunnel 3.21 2.91
SA
218sq' (EeeK! see below... 24sq')
They may look different, but will perform similarly in almost every
way!
Moving on to Anhinga.
The bottom length and breadth measurements of the light dories are
almost exactly the same as those of Eeek, the ESC type cruising
canoe. Does sail carrying capacity diminish proportionally to the
cube of LOA? If so, then the reduction from 218sqft carried on
Gloucester Yawl to 24sqft carried on Eeek is about right; a slightly
greater reduction needed for the taller proportioned sailplan. This
sailplan should work well for the Light Dory if sailed like the Eeek
with supine crew lying all but prone on the floor. The addition of
side decks may see her self righting from beam ends with dry crew
aboard.
Side deck a Gull? Well, why not? PCB sponsoned a bigger open
row/sail sharpie of similar proportion - that at bottom is much
like an EeeK! of lower freeboard.
So much for banks dories not sailing. Ha! Is it a joke?
Nevertheless, a banks type dory is not able to stand up to sail as
well as one with a knuckle to the sides. How to get the benefits of
flare without the drawbacks and keep the water bent to theory?
Changing the water ballast geometry in Anhinga to that giving the
appearance of a two chined dory having moveable ballast might square
things up a bit.
GG - GY - ESC it's always water.
Graeme
--- Inbolger@yahoogroups.com, "graeme19121984" <graeme19121984@...>
wrote:
The difference to final stability performance? He got a Banks dory
in the square, I propose a Swampscott. He used massed live ballast
to extend the righting arm, I propose using the increase between the
lifted windward ballast and the leeside knuckle (and... maybe a
sponson?).
Bolger agreed with an old observation "that sharpies suffer from
being wide for their length, and from having flaring sides." He
wrote "My flow theory accounts for this, but I've long thought that
a sponson sharpie would produce the benefits of a flaring side
without the drawbacks, or most of them." He designed the step
sharpie "Gloucester Yawl" At the time this boat alarmed a lot of
people, but IIRC eventually one was built and proved a good sailer;
if wet.
In Gloucester Yawl,when heeled to the gunnels though the lee sponson
provides approx. 3cuft of offset bouyancy this is offset by the lack
of bouyancy of the step in between the bottom side and sponson
bottom. The cancelling effect delivers stability performance akin to
the flare of a *BANKS* dory. Bolger has often remarked that a banks
dory is a poor sailer and he would no longer be involved in
designing a sailplan for the type! G Y stands up to its relatively
large amount of sail because the sailplan is low, she has a big crew
of 5, and flat decks for them to scramble out on. She rows well on
the narrow bottom at 1" wider than a June Bug. She has chine
curvature in accord with Bolgers sharpie bow water flow theory.
What a surprise to see proportional numbers for SoP Gloucester Yawl
sharpie that closely match Gloucester Gull dory!
Gloucester Yawl Light Dory Type V
Length bottom 21' 3600mm
LOA 21' 4740
BOA Bottom 3'4" 572
BOA Gunnel 5'6" 1190 +30
Sponson side height 9"
Bottom side height 11-4/8" Side height 419
Bottom L/B 6.3 6.29
Gunnel L/B 3.8 3.88
LOA/Overhang total length 4.66 (21'/4'6" & 4740/1140) 4.15
Beams/Heights
Bottom side top 4.44 NA
Upper side bottom 6.66 NA
Gunnel 3.21 2.91
SA
218sq' (EeeK! see below... 24sq')
They may look different, but will perform similarly in almost every
way!
Moving on to Anhinga.
The bottom length and breadth measurements of the light dories are
almost exactly the same as those of Eeek, the ESC type cruising
canoe. Does sail carrying capacity diminish proportionally to the
cube of LOA? If so, then the reduction from 218sqft carried on
Gloucester Yawl to 24sqft carried on Eeek is about right; a slightly
greater reduction needed for the taller proportioned sailplan. This
sailplan should work well for the Light Dory if sailed like the Eeek
with supine crew lying all but prone on the floor. The addition of
side decks may see her self righting from beam ends with dry crew
aboard.
Side deck a Gull? Well, why not? PCB sponsoned a bigger open
row/sail sharpie of similar proportion - that at bottom is much
like an EeeK! of lower freeboard.
So much for banks dories not sailing. Ha! Is it a joke?
Nevertheless, a banks type dory is not able to stand up to sail as
well as one with a knuckle to the sides. How to get the benefits of
flare without the drawbacks and keep the water bent to theory?
Changing the water ballast geometry in Anhinga to that giving the
appearance of a two chined dory having moveable ballast might square
things up a bit.
GG - GY - ESC it's always water.
Graeme
--- Inbolger@yahoogroups.com, "graeme19121984" <graeme19121984@...>
wrote:
>from
> On getting out of the box by turning the outside in, or gaining
> flare by cheating on square - while keeping things fair.Ruminations.
On getting out of the box by turning the outside in, or gaining from
flare by cheating on square - while keeping things fair. Ruminations.
First some sharpie hull type behavioural propositions:
Premise 1) "The upright stance is possible because in spite of
being narrow for her length, she's wide for her
depth under water." (Bolger, FS, p81 Rondo ll);
Premise 2) "But regardless of her length, a boat that is deep
bodied for her breadth, and doesn't carry her
ballast on a deep fin, will be tender under sail."
(FS, p69 Blackgauntlet ll)
Premise 3) "Water ballast is effective only when there's enough
bouyancy to lift some of it above the water line as
the boat heels. As long as the neutral-bouyancy
water is submerged, the stabilility of the boat is
whatever it would be if the volumes containing water
were removed entirely. A couple of years ago one of
my water-ballasted designs met with an accident that
completely flooded her... {... Some foam high up in
the hull would have righted her...}" (BWAOM, p244
Whalewatcher)
Premise 4) In the first phase of sharpie hull type heeling the
waterline width diminishes as heeling angle
increases, the immersed cross section becomes
narrower - and deeper.
Consider 1), 2), and 3) above for water ballast placed as a sub-
floor flat slab, or alternatively as paired rectangular sectioned
bilge tanks in a firm bilged boat like a Bolger box.
Ok then, now consider:
Anhinga as a special case of dory, canoe, or sharpie... whatever.
http://groups.yahoo.com/group/BolgerCartoons/files/Anhinga/Her sub-
floor slab of water ballast and deepest draught both lie aft of the
centre-of-bouyancy on a bottom of diminishing width
http://tinyurl.com/2chz8vsuggesting:
For Anhinga the immersed triangulatoid prism of the aft underbody
now slopes descending aft, it's centroid sinks (In the case of the
usual sharpie the relative overall hull c-o-g has not moved, but c-o-
b has, and not only out but downwards.
http://www.boatdesign.com/postings/pages/knockdown.htm), also for
Anhinga, this ESC (Economy Seagoing Cruiser) hull type, the overall
effective c-o-g has moved relatively aft as more neutral-bouyancy
water is lifted upon heeling away from level trim, and c-o-b
initially moves not only down and out, but also aft.
Dynamically, an effect noted in 3) of activating ballast sinks the
aft sections further. Uhh, ohh. A positive gravitational feedback
energised by heeling force occurs between the tenderness of 2)
exacerbated by 4), and the rising potential of 3).
Then a crossover occurs and she trips and capsises just like any
sharpie, and nothing will prevent her, for according to 3) with her
sub-floor slab of ballast removed she is but a plain sharpie of less
depth for her width as per 1). The tipping point may occur too
quickly for confidence in the design.
Foam, high up, should stop her turtling then [3)]. Yet...
One reason slab sided dories are considered seaworthy boats results
from the flare increasing secondary through to higher ultimate
stability on heeling (GM increasing with heel as the c-o-b moves
more outboard), but the low initial stability makes them very tender
under sail.. As Bolger says, it's easy to dip the gunnels of a
Banks dory to the water to haul in a fish, for there is not the same
initially increasing stiff stability as for the sharpie. But in the
sharpie it's followed by a capsise tipping point - and in a high
sided sharpie this may be well before there's any warnings sloshing
over the lee gunnel. However, dories with a knuckle to the sides,
that is with two or more chines like the Swampscott, are able to
stand up to sail quite well after some initail heeling. PCB's done a
few of those.
Now,
what if the water ballast of the box sharpie were in paired bilge
tanks of triangular section? The inboard face of the tanks in
Anhinga would slope inwards under the present cockpit seats from the
sides to the very bottom. In accordance with 3) the lee side of the
hull in way of the tanks would present to the surrounding water for
stability purposes as that of of a two chined dory. The centre-of-
gravity / centre-of-bouyancy over centre box-sharpie Capsise Tipping
Point may be delayed, and may not be so sudden at least. More
relaxed and confident sailing may be a benefit at the sacrifice of
some initial stability.
Would not the box sharpie Anhinga hull with neutral-ballast so
arranged behave like Sweet Pea with the lee bilge, lacking in
bouyancy easily heeled under at first, but only as if the other side
bilge had to drag more and more weight above the waterline, and so
give much increasing stability and stiffness for the increasing
heel? (Anhinga is a bit more complex as in this consideration the
half of the hull immersed forward of the main bulkhead remains an
unballasted square box! (*~*)
The reduction in, or doing away all together of the underseat
ventilation ducts may be a disbenefit, but then it is possible that
in some events these are condusive to main cabin flooding. Another
method could be easily used to ventilate the cabin, and a benefit of
the phantom-dory bilge ballast would be some extra leg-stretching
room in the cockpit without the double bottom.
A boon when heeled would be that, although appearing to behave with
the stability characteristics of a two-chined dory, the hull would
cleave the on-rushing water with a single turbulence reducing chine
derived from Bolger's sharpie bow water flow theory. An aside about
that cleaving here:
As I have said before and shall undoubtedly repeat again there
Is a lot to be said for the flat bottom model. For sailing it
is a better form than the V bottom, and so much simpler to
build. When a V bottom boat is heeled down the draft is
decreased and the flat of the V is presented to the surface of
the water; consequently there is much slapping and shaking wind
from the sails. The flat bottom model when heeled down
increases in draft and sails on the sharp corner of the chine
which is obviously an easier form against a head sea.(William
Atkin)http://www.boat-links.com/Atkinco/Sail/DavyJonesToo.html
Any sleeping live ballast in the forwad cabin may be less disturbed
than in other box sharpies by bow wave slap as the neutrally bouyant
ballast aft of the c-o-b in level trim may allow the bow to dip more
deeply when overnighting at anchor.
Gunna have to test it.... after testing for error here in
Bolgerspace...
Here's a pic of a Sweet Pea trimmed down by the stern
http://ph.groups.yahoo.com/group/Bolger2/photos/browse/4f88Are
there any similar of a Surf, or Windsprint etc? Any ever tested for
capsise performance with a loaded stern, or comparison tested a
multi-chine double ended dory like Sweet Pea and Surf, or similar?
and keep the foam up high ;-)
Graeme
flare by cheating on square - while keeping things fair. Ruminations.
First some sharpie hull type behavioural propositions:
Premise 1) "The upright stance is possible because in spite of
being narrow for her length, she's wide for her
depth under water." (Bolger, FS, p81 Rondo ll);
Premise 2) "But regardless of her length, a boat that is deep
bodied for her breadth, and doesn't carry her
ballast on a deep fin, will be tender under sail."
(FS, p69 Blackgauntlet ll)
Premise 3) "Water ballast is effective only when there's enough
bouyancy to lift some of it above the water line as
the boat heels. As long as the neutral-bouyancy
water is submerged, the stabilility of the boat is
whatever it would be if the volumes containing water
were removed entirely. A couple of years ago one of
my water-ballasted designs met with an accident that
completely flooded her... {... Some foam high up in
the hull would have righted her...}" (BWAOM, p244
Whalewatcher)
Premise 4) In the first phase of sharpie hull type heeling the
waterline width diminishes as heeling angle
increases, the immersed cross section becomes
narrower - and deeper.
Consider 1), 2), and 3) above for water ballast placed as a sub-
floor flat slab, or alternatively as paired rectangular sectioned
bilge tanks in a firm bilged boat like a Bolger box.
Ok then, now consider:
Anhinga as a special case of dory, canoe, or sharpie... whatever.
http://groups.yahoo.com/group/BolgerCartoons/files/Anhinga/Her sub-
floor slab of water ballast and deepest draught both lie aft of the
centre-of-bouyancy on a bottom of diminishing width
http://tinyurl.com/2chz8vsuggesting:
For Anhinga the immersed triangulatoid prism of the aft underbody
now slopes descending aft, it's centroid sinks (In the case of the
usual sharpie the relative overall hull c-o-g has not moved, but c-o-
b has, and not only out but downwards.
http://www.boatdesign.com/postings/pages/knockdown.htm), also for
Anhinga, this ESC (Economy Seagoing Cruiser) hull type, the overall
effective c-o-g has moved relatively aft as more neutral-bouyancy
water is lifted upon heeling away from level trim, and c-o-b
initially moves not only down and out, but also aft.
Dynamically, an effect noted in 3) of activating ballast sinks the
aft sections further. Uhh, ohh. A positive gravitational feedback
energised by heeling force occurs between the tenderness of 2)
exacerbated by 4), and the rising potential of 3).
Then a crossover occurs and she trips and capsises just like any
sharpie, and nothing will prevent her, for according to 3) with her
sub-floor slab of ballast removed she is but a plain sharpie of less
depth for her width as per 1). The tipping point may occur too
quickly for confidence in the design.
Foam, high up, should stop her turtling then [3)]. Yet...
One reason slab sided dories are considered seaworthy boats results
from the flare increasing secondary through to higher ultimate
stability on heeling (GM increasing with heel as the c-o-b moves
more outboard), but the low initial stability makes them very tender
under sail.. As Bolger says, it's easy to dip the gunnels of a
Banks dory to the water to haul in a fish, for there is not the same
initially increasing stiff stability as for the sharpie. But in the
sharpie it's followed by a capsise tipping point - and in a high
sided sharpie this may be well before there's any warnings sloshing
over the lee gunnel. However, dories with a knuckle to the sides,
that is with two or more chines like the Swampscott, are able to
stand up to sail quite well after some initail heeling. PCB's done a
few of those.
Now,
what if the water ballast of the box sharpie were in paired bilge
tanks of triangular section? The inboard face of the tanks in
Anhinga would slope inwards under the present cockpit seats from the
sides to the very bottom. In accordance with 3) the lee side of the
hull in way of the tanks would present to the surrounding water for
stability purposes as that of of a two chined dory. The centre-of-
gravity / centre-of-bouyancy over centre box-sharpie Capsise Tipping
Point may be delayed, and may not be so sudden at least. More
relaxed and confident sailing may be a benefit at the sacrifice of
some initial stability.
Would not the box sharpie Anhinga hull with neutral-ballast so
arranged behave like Sweet Pea with the lee bilge, lacking in
bouyancy easily heeled under at first, but only as if the other side
bilge had to drag more and more weight above the waterline, and so
give much increasing stability and stiffness for the increasing
heel? (Anhinga is a bit more complex as in this consideration the
half of the hull immersed forward of the main bulkhead remains an
unballasted square box! (*~*)
The reduction in, or doing away all together of the underseat
ventilation ducts may be a disbenefit, but then it is possible that
in some events these are condusive to main cabin flooding. Another
method could be easily used to ventilate the cabin, and a benefit of
the phantom-dory bilge ballast would be some extra leg-stretching
room in the cockpit without the double bottom.
A boon when heeled would be that, although appearing to behave with
the stability characteristics of a two-chined dory, the hull would
cleave the on-rushing water with a single turbulence reducing chine
derived from Bolger's sharpie bow water flow theory. An aside about
that cleaving here:
As I have said before and shall undoubtedly repeat again there
Is a lot to be said for the flat bottom model. For sailing it
is a better form than the V bottom, and so much simpler to
build. When a V bottom boat is heeled down the draft is
decreased and the flat of the V is presented to the surface of
the water; consequently there is much slapping and shaking wind
from the sails. The flat bottom model when heeled down
increases in draft and sails on the sharp corner of the chine
which is obviously an easier form against a head sea.(William
Atkin)http://www.boat-links.com/Atkinco/Sail/DavyJonesToo.html
Any sleeping live ballast in the forwad cabin may be less disturbed
than in other box sharpies by bow wave slap as the neutrally bouyant
ballast aft of the c-o-b in level trim may allow the bow to dip more
deeply when overnighting at anchor.
Gunna have to test it.... after testing for error here in
Bolgerspace...
Here's a pic of a Sweet Pea trimmed down by the stern
http://ph.groups.yahoo.com/group/Bolger2/photos/browse/4f88Are
there any similar of a Surf, or Windsprint etc? Any ever tested for
capsise performance with a loaded stern, or comparison tested a
multi-chine double ended dory like Sweet Pea and Surf, or similar?
and keep the foam up high ;-)
Graeme