Question: Making twin-rig yacht ("Bug: Main Sail object has no attribute IG")

[G0rocks]

When I ran my code then I got this error:

runVPP.py 73 <module>
vpp.run(verbose=False)

VPPMod.py 237 run
sol = root(

_root.py 255 root
sol = _root_leastsq(_wrapped_fun, x0, args=args, jac=jac, **options)

_root.py 323 _root_leastsq
x, cov_x, info, msg, ier = leastsq(_wrapped_fun, x0, args=args,

_minpack_py.py 425 leastsq
shape, dtype = _check_func('leastsq', 'func', func, x0, args, n)

_minpack_py.py 23 _check_func
res = atleast_1d(thefunc(*((x0[:numinputs],) + args)))

return fun(*fargs)

_root.py 215 _wrapped_fun
return fun(*fargs)

VPPMod.py 301 resid
Fxa, Fya, Mxa = self.aero.update(vb0, phi0, tws, twa, flat, 2.0)

AeroMod.py 91 update
self._compute_forces()

AeroMod.py 117 _compute_forces
self.Mx = self.Fy * self._vce()

AeroMod.py 205 _vce
deltaCH = 0 if self.sails[1].up!=True else (1-self.ftj)*0.05*self.sails[1].IG

AttributeError:
'Main' object has no attribute 'IG'
PS C:\Users\Huldar\Reykjavik University\Meistaraverkefni - Huldar - General\Model and calculators\VPPs\Python-VPP> python .\runVPP.py

Which comes from line 205 in AeroMod.py which is:
deltaCH = 0 if self.sails[1].up!=True else (1-self.ftj)*0.05*self.sails[1].IG

In the Vectical centre of effort lift/drag weigted function.

But looking at the Main Sail object it defined in line 58 in SailMod.py and is defined as:

class Main(Sail):
    def __init__(self, name, P, E, Roach, BAD):
        """
        Initialize mainsail
    
        This function initializes an object of class Main which inherits the class Sail. 
        It calculates the area, the Vertical Center of Effort (vce), 
        sets CE = 1 and calls the super class constructor. 
    
        Parameters
        ----------
        name : string
            Of the sail
            
        P : Float
            Height of the Mainsail  in meters
            
        E: Float
            Length (Foot) of the Mainsail  in meters
            
        Roach: Float
            Percentage by which the triangular area is increased in order to obtain the mainsail area. 
            This is area behind the line from clew to head. 
            To get this number you have to calculate  Mainsail_area / (P*E/2) -1
            
        BAD: Float
            Boom Above Deck: Distance between boom and Deck  in meters
        
        Returns
        -------
        Main
            Object of type Main( Sail )
    
        See Also
        --------
        Jib( Sail )
    
        Examples
        --------
        >>> Main("MN1", P=16.60, E=5.60, Roach=0.1, BAD=1.0)
        <src.SailMod.Main object at 0xFFFFFFFFF>
        """
        self.name = name
        self.type = "main"
        self.P = P
        self.E = E
        self.roach = Roach
        self.BAD = BAD
        self.area0 = 0.5 * P * E * (1 + self.roach)
        self.vce = P / 3.0 * (1 + self.roach) + self.BAD
        super().__init__(self.name, self.type, self.area0, self.vce)
        self.measure()
    
    def measure(self, rfm=1, ftj=1):
        self.P_r = self.P*rfm
        self.vce = self.P_r / 3.0 * (1 + self.roach) + self.BAD
        self.area = self.area0*rfm**2
        self.CE = 1.

Where there is no IG parameter. I've tried adding it anyway when I make the mainsail but it just crashed also and said it was not expecting the parameter. Understandable. Now I'm unsure what this IG parameter is supposed to be but this is resulting in zero polar plots for the vessel I've inputted. What can we do to fix this?

[G0rocks]

According to https://orc.org/measurements/rig then "IG is defined as the height of the foretriangle and is the vertical distance from the mast datum point (at the sheerline at the mast) to the forestay attachment to the mast."

This can be computed since the height above deck is known and the height of the mainsail is also known.
Modifying the mainsail init function worked for me. I changed it to:

class Main(Sail):
    def __init__(self, name, P, E, Roach, BAD):
        """
        Initialize mainsail
    
        This function initializes an object of class Main which inherits the class Sail. 
        It calculates the area, the Vertical Center of Effort (vce), 
        sets CE = 1 and calls the super class constructor. 
    
        Parameters
        ----------
        name : string
            Of the sail
            
        P : Float
            Height of the Mainsail  in meters
            
        E: Float
            Length (Foot) of the Mainsail  in meters
            
        Roach: Float
            Percentage by which the triangular area is increased in order to obtain the mainsail area. 
            This is area behind the line from clew to head. 
            To get this number you have to calculate  Mainsail_area / (P*E/2) -1
            
        BAD: Float
            Boom Above Deck: Distance between boom and Deck  in meters
        
        Returns
        -------
        Main
            Object of type Main( Sail )
    
        See Also
        --------
        Jib( Sail )
    
        Examples
        --------
        >>> Main("MN1", P=16.60, E=5.60, Roach=0.1, BAD=1.0)
        <src.SailMod.Main object at 0xFFFFFFFFF>
        """
        self.name = name
        self.type = "main"
        self.P = P
        self.E = E
        self.roach = Roach
        self.BAD = BAD
        self.area0 = 0.5 * P * E * (1 + self.roach)
        self.vce = P / 3.0 * (1 + self.roach) + self.BAD
        super().__init__(self.name, self.type, self.area0, self.vce)
        self.IG = self.P + self.BAD
        self.measure()    

What do you think?

[marinlauber]

@G0rocks what are you trying to do to get such an error?

We have tested the VPP on a lot of cases and it never happened. If I am not mistaken IG does not relate to the mainsail, but the Jib.

Please describe what you are trying to do and send a Minimal Working Example (MWE) to replicate the issue, see https://share.google/azJ217GP5OSgnfnau

Just an error message and no context can be a lot of different things, a bug, user error, etc. Just pasing an erro like this does not allow us to isolate what type of problem you are having.

Please make clear request next time you open an issue.

[G0rocks]

I just input the vessel I'm examining or some approximate values and tried to run runVPP.py
Here is the file:

runVPP.py

[marinlauber]

This is not a bug. This is going to work since we assume there is only a single mainsail on the yacht.

You will have to change part of the source to make it work for your double-masted yacht.

[G0rocks]

Ok. I imagine this to be quite a bit of work and am not sure I can afford to start this endavour. Will confer with my supervisor next week.

For context I'm making a polar speed plot for the Towt Artemis ship:
https://www.voilier-cargo.towt.eu/en/suivi/2nd-vessel/

Looks like this:

[marinlauber]

@G0rocks I think it's not impossible to do. In essence, what you have to do is write the runVPP straight into your script and add the force and moment contribution from the second rig.

I'm happy to guide you if you need.

[marinlauber]

@G0rocks, here is an example of how you would do that.

The main idea is to explicitly write the run(vpp) and resid() functions in your main script. You can make another dummy VPP object that has a yacht with zero dimensions (to make sure you don't add windage twice in the aerodynamic forces), but the rig you want to have.

You can then add the contribution of this new rig onto the force balance in resid_new(), which you then have to pass to the root function.

Below is a MWE example of this. I've just added a very small rig on top of the existing one. Since we only resolve surge sway and roll, you don't need to add it at the correct longitudinal position -- the yaw equilibrium is not solved for here.

I your case, I suppose the two rigs would be identical, so you can just copy-paste the first rig onto an empty yacht.

#!/opt/miniconda3/bin/python
# -*- coding: utf-8 -*-
import numpy as np

import logging

logging.basicConfig(level=logging.INFO)

from src.SailMod import Jib, Kite, Main
from src.VPPMod import VPP
from src.YachtMod import Keel, Rudder, Yacht

YD41 = Yacht(
    Name="YD41",
    Lwl=11.90,
    Vol=6.05,
    Bwl=3.18,
    Tc=0.4,
    WSA=28.20,
    Tmax=2.30,
    Amax=1.051,
    Mass=6500,
    Ff=1.5,
    Fa=1.5,
    Boa=4.2,
    Loa=12.5,
    App=[Keel(Cu=1.00, Cl=0.78, Span=1.90), Rudder(Cu=0.48, Cl=0.22, Span=1.15)],
    Sails=[
        Main("MN1", P=16.60, E=5.60, Roach=0.1, BAD=1.0),
        Jib("J1", I=16.20, J=5.10, LPG=5.40, HBI=1.8),
        Kite("A2", area=150.0, vce=9.55),
        Kite("A5", area=75.0, vce=2.75),
    ],
)

vpp = VPP(Yacht=YD41)

vpp.set_analysis(
    tws_range=np.arange(4.0, 22.0, 2.0), twa_range=np.linspace(30.0, 180.0, 31)
)


# make a dummy aeroMod using a yacht with no dimensions
Rig2 = Yacht(
    Name="Rig2",
    Lwl=0.0,
    Vol=1.0,
    Bwl=0.0,
    Tc=1.0,
    WSA=0.0,
    Tmax=0.0,
    Amax=0.0,
    Mass=0.0,
    Ff=0.0,
    Fa=0.0,
    Boa=0.0,
    Loa=0.0,
    Sails=[ # very small sails for now
        Main("MN2", P=1.60, E=1.60, Roach=0.1, BAD=1.0),
        Jib("J2", I=1.20, J=1.20, LPG=1.20, HBI=1.8),
    ],
)
from src.AeroMod import AeroMod
rig_2_aero = AeroMod(Rig2)
# make sure windage from hull will be zero
rig_2_aero.fbav = 0.0

def resid_new(x0, twa, tws):
    """
    Custom residuals function for the VPP optimization, to be used with scipy.optimize.root
    """

    vb0 = x0[0]
    phi0 = x0[1]
    leeway = x0[2]
    flat = 1.0  # x0[3]
    red = 1.0  # x0[4]

    # the first rig
    Fxh, Fyh, Mxh = vpp.hydro.update(vb0, phi0, leeway)
    Fxa, Fya, Mxa = vpp.aero.update(vb0, phi0, tws, twa, flat, 2.0)

    # add the second rig here
    Fxa2, Fya2, Mxa2 = rig_2_aero.update(vb0, phi0, tws, twa, flat, 2.0)
    #check that windage is really zero
    assert rig_2_aero._get_Rw(rig_2_aero.awa / 180.0 * np.pi) == 0.0

    # add the second rig forces to the first rig forces
    Fxa += Fxa2
    Fya += Fya2
    Mxa += Mxa2

    return [(Fxh - Fxa) ** 2, (Mxh - Mxa) ** 2, (Fyh - Fya) ** 2]

KNOTS_TO_MPS = 0.514444
from scipy.optimize import root
for i, tws in enumerate(vpp.tws_range):
    logging.info("Sailing in TWS : %.1f" % (tws / KNOTS_TO_MPS))

    for n in range(vpp.Nsails):
        vpp.aero.sails[1] = vpp.yacht.sails[n + 1]

        logging.info(
            "Sail Config : " + vpp.aero.sails[0].name + " + " + vpp.aero.sails[1].name
        )

        vpp.aero.up = vpp.aero.sails[1].up

        for j in range(len(vpp.twa_range)):
            twa = vpp.twa_range[j]

            vpp.vb0 = 0.8 * tws
            vpp.phi0 = 0
            vpp.leeway0 = ( 100.0 / twa if (twa > 1.0 and 100.0 / twa < 2 * tws) else 2 * tws)
            vpp.flat = 1.0
            vpp.red = 2.0

            # don't do low twa with downwind sails
            if (vpp.aero.up == True) and (twa >= vpp.lim_dn):
                continue
            if (vpp.aero.up == False) and (twa <= vpp.lim_up):
                continue

            # the new resid is here
            sol = root(resid_new, [vpp.vb0, vpp.phi0, vpp.leeway0],
                       args=(twa, tws), method="lm")

            # get sol
            vpp.vb0, vpp.phi0, vpp.leeway0 = res = sol.x

            if not sol.success:
                logger.debug(sol.message)

            vpp.store[i, j, n, : len(res)] = (
                res[:] * np.array([1.0 / KNOTS_TO_MPS, 1, 1, 1, 1])[: len(res)]
            )

logging.info("Optimization successful.")



vpp.write("results")
vpp.polar(3, True)
vpp.SailChart(True)