Re: June Bug sail rig
I am very skeptical of this method. The lift vs. angle of attack
behavior varies a lot depending on shape. Aspect ratio of hull is very
different from that of a centerboard. Might sort of work for a Colin
Archer type where the keel is very long.
behavior varies a lot depending on shape. Aspect ratio of hull is very
different from that of a centerboard. Might sort of work for a Colin
Archer type where the keel is very long.
--- In bolger@y..., "nasplundh" <nasplundh@y...> wrote:
snip but the idea is to trace or loft the underwater profile of
> a hull and appendages (CB, LB, and make sure you include the rudder)
> onto a piece of stiff paper or cardboard. snip
> Using the needle, you then find the fore-and-aft balance point along
> the fold. Theoretically, that point identifies the center of lateral
> resistance, and from there you can calculate the "appropriate" CE
for
> the sail area based on "necessary" lead from CLP to COE. snip
Actually, there is an engineering "trick" that could be performed
with pencil and paper, as well as scissors and a sewing needle.
Can't remember the book or magazine (maybe WoodenBoat?) in which I
saw this, but the idea is to trace or loft the underwater profile of
a hull and appendages (CB, LB, and make sure you include the rudder)
onto a piece of stiff paper or cardboard. Also include a bit of the
topsides, how much may not be all that important, as you will be
folding it over at the DWL.
Using the needle, you then find the fore-and-aft balance point along
the fold. Theoretically, that point identifies the center of lateral
resistance, and from there you can calculate the "appropriate" CE for
the sail area based on "necessary" lead from CLP to COE. (I caveat
the above comment based on seeing different designer's opinions of
how much lead is needed).
Change the cardboard profile, find the new balance point. "Go nuts"
as they say.
(Having said all this, I'm betraying something of an ingrained bias
from nearly 30 years experience in two-dimensional design and desktop
publishing. After I've built three small Bolger boats, 10 years ago,
I'm now working on a scale paperboard-and-balsa of a Michalak design.
Gotta tell ya that when you finally get into the third dimension,
either in scale or full-size, it's a whole different world).
with pencil and paper, as well as scissors and a sewing needle.
Can't remember the book or magazine (maybe WoodenBoat?) in which I
saw this, but the idea is to trace or loft the underwater profile of
a hull and appendages (CB, LB, and make sure you include the rudder)
onto a piece of stiff paper or cardboard. Also include a bit of the
topsides, how much may not be all that important, as you will be
folding it over at the DWL.
Using the needle, you then find the fore-and-aft balance point along
the fold. Theoretically, that point identifies the center of lateral
resistance, and from there you can calculate the "appropriate" CE for
the sail area based on "necessary" lead from CLP to COE. (I caveat
the above comment based on seeing different designer's opinions of
how much lead is needed).
Change the cardboard profile, find the new balance point. "Go nuts"
as they say.
(Having said all this, I'm betraying something of an ingrained bias
from nearly 30 years experience in two-dimensional design and desktop
publishing. After I've built three small Bolger boats, 10 years ago,
I'm now working on a scale paperboard-and-balsa of a Michalak design.
Gotta tell ya that when you finally get into the third dimension,
either in scale or full-size, it's a whole different world).
--- In bolger@y..., "petehodges" <petehodges@y...> wrote:
> Leeboard and sail location is important.
>
<snip> Few of us are
> equipped with the engineering skill to sit down and figure it out
> with a pencil and paper.
>
> Modeling can be fun and very instructive.
Leeboard and sail location is important.
When a boat bottom has rocker the lee board is typically at the
deepest point of the rocker. It is supplying a pivot point for the
boat to turn on.
The sail has a center of effort as does the underwater hull shape.
These things need to be close to lining up.
I suppose you could get the idea of what might happen if you were on
a yawl and tried sailing with just a jib or just the mizzen under
normal conditions. The boat will be more difficult to maneuver and
will end up in irons more often when you tack.
The relationship of the leeboard, sail and hull location and will
also greatly effect whether you normally experience lee helm or
weather helm or balanced helm.
Have a constant lee helm is down right dangereous. If you fall out
of the boat or get knocked out by the boom on a jibe, the boat will
just keep right on sailing. With slight weather helm the boat will
round up into the wind and wait for you.
The best way to figure this stuff out is with a model. Few of us are
equipped with the engineering skill to sit down and figure it out
with a pencil and paper.
Modeling can be fun and very instructive. If modeling does not float
your boat ( pun intended ), the make your self something like the
$200 sailboat. Something cheap that has an exterior leeboard that
you can move the location of and room to have multiple mast steps so
you can move the sail foward and back.
You will learn alot about sail rig design and have fun while you are
doing it.
When a boat bottom has rocker the lee board is typically at the
deepest point of the rocker. It is supplying a pivot point for the
boat to turn on.
The sail has a center of effort as does the underwater hull shape.
These things need to be close to lining up.
I suppose you could get the idea of what might happen if you were on
a yawl and tried sailing with just a jib or just the mizzen under
normal conditions. The boat will be more difficult to maneuver and
will end up in irons more often when you tack.
The relationship of the leeboard, sail and hull location and will
also greatly effect whether you normally experience lee helm or
weather helm or balanced helm.
Have a constant lee helm is down right dangereous. If you fall out
of the boat or get knocked out by the boom on a jibe, the boat will
just keep right on sailing. With slight weather helm the boat will
round up into the wind and wait for you.
The best way to figure this stuff out is with a model. Few of us are
equipped with the engineering skill to sit down and figure it out
with a pencil and paper.
Modeling can be fun and very instructive. If modeling does not float
your boat ( pun intended ), the make your self something like the
$200 sailboat. Something cheap that has an exterior leeboard that
you can move the location of and room to have multiple mast steps so
you can move the sail foward and back.
You will learn alot about sail rig design and have fun while you are
doing it.
--- In bolger@y..., "reyburgh2002" <reyburgh@s...> wrote:
> With respect to the June Bug sailing rig, is the mast location
simply
> a function of having to have the leeboard back where the boat's
beam
> is at its maximum? In other words could the rig be moved forward
> without harming performance if one were to convert the leeboard to
a
> more forward positioned centreboard, keeping in mind the
relationship
> between the centre of the sail and the centreboard? The question
> arises out of personal preferance, I think that the boat might look
> better with the rig right up against the front deck.
>
> Cheers
>
> Peter Reynolds
> reyburgh@s...
--- In bolger@y..., "reyburgh2002" <reyburgh@s...> wrote:
You've got it. You could move the board forward with the rig a bit
and stay in balance. Any radical move might cause a problem from a
couple of aspects. First the center of lateral resistance is derived
in part from the hull and the rudder in addition to the leeboard. On
small boats, though, you can get away with some sloppiness in the
relationship between the COE and CLR as long as you don't wind up
with lee helm in strong winds. Secondly a leeboard is a lot harder
to support from anywhere else on the hull. It would take a structure
capable of holding it solid and holding it parallel to the centerline.
Of course I always play with what the designer put on paper and Phil
B. sees that tendency as a natural instinct...have fun.
Reed
> With respect to the June Bug sailing rig, is the mast locationsimply
> a function of having to have the leeboard back where the boat'sbeam
> is at its maximum? >Hi Peter,
> Peter Reynolds
You've got it. You could move the board forward with the rig a bit
and stay in balance. Any radical move might cause a problem from a
couple of aspects. First the center of lateral resistance is derived
in part from the hull and the rudder in addition to the leeboard. On
small boats, though, you can get away with some sloppiness in the
relationship between the COE and CLR as long as you don't wind up
with lee helm in strong winds. Secondly a leeboard is a lot harder
to support from anywhere else on the hull. It would take a structure
capable of holding it solid and holding it parallel to the centerline.
Of course I always play with what the designer put on paper and Phil
B. sees that tendency as a natural instinct...have fun.
Reed
With respect to the June Bug sailing rig, is the mast location simply
a function of having to have the leeboard back where the boat's beam
is at its maximum? In other words could the rig be moved forward
without harming performance if one were to convert the leeboard to a
more forward positioned centreboard, keeping in mind the relationship
between the centre of the sail and the centreboard? The question
arises out of personal preferance, I think that the boat might look
better with the rig right up against the front deck.
Cheers
Peter Reynolds
reyburgh@...
a function of having to have the leeboard back where the boat's beam
is at its maximum? In other words could the rig be moved forward
without harming performance if one were to convert the leeboard to a
more forward positioned centreboard, keeping in mind the relationship
between the centre of the sail and the centreboard? The question
arises out of personal preferance, I think that the boat might look
better with the rig right up against the front deck.
Cheers
Peter Reynolds
reyburgh@...