# Freeship trim problem

Discussion in 'Software' started by mattr87, Aug 27, 2011.

1. Joined: Aug 2011
Posts: 3
Likes: 0, Points: 0, Legacy Rep: 10
Location: Italy

### mattr87New Member

Hello everyone,
I'm an italian student of Politecnico (Milan). I have to project a new flyingboat with the tecnology of 1935 for a course of mine. One of most difficult threads is for me the definition of the hull. I'm trying to make some tests with Freeship to determine the planing resistance for the boat but the trim angle is driving me crazy because is too low... in addition I get an issue for lambda in the results windows:

Lambda is outside valid domain 2,0 ... 5,0

I'm not sure of the value of LCG but I think that should be the entire boat center of gravity value.
Thanks for the help!!!

I forgot the results log:

Final calculations of resistance and power for planing ships

Project :
Designer :
Filename : C:\Documents and Settings\Mattia\Documenti\Dropbox polimi\Dropbox\Scafo\scafo catia-freeship\scafomesh3.fbm

Design length : 22.000 m
Design beam : 3.760 m
Design draft : 1.200 m
Midship location : 11.000 m
Water density : 1.025 t/m^3
Appendage coefficient : 1.0000

Date : 27/08/2011
Time : 19.21.43

----------------------------------------------------------------------------------

Input variables

Hull
Effective waterline length : 19.618 m
Beam on waterline : 3.304 m
Draft hull : 1.131 m
Wetted surface area : 59.37 m^2
Prismatic coefficient : 0.5242
Displacement : 29.12 t
X of CoG : 12.185 m
Midship area above waterline : 0.00 m^2
Roughness coefficient *10^3 : 0.000
Maximal speed : 30.00 knots
Angle between Thrust and Keel lines : 4.00 degr
Distance between Thrust line and CoG : 0.150 m

----------------------------------------------------------------------------

Final calculations of resistance and power for planing ships by D.Savitsky

+-------+-------+-------+---------+---------+---------+---------+
| Vs | FrB | Tau | R_f | R_p | R_t | Pe |
| [kn] | - | [degr]| [kN] | [kN] | [kN] | [kW] |
+-------+-------+-------+---------+---------+---------+---------+
Lambda is outside valid domain 2,0 ... 5,0
| 18.81 | 1.70 | 1.30 | 10.594 | 6.564 | 17.158 | 166.038 |
Lambda is outside valid domain 2,0 ... 5,0
| 19.93 | 1.80 | 1.31 | 11.716 | 6.640 | 18.356 | 188.198 |
Lambda is outside valid domain 2,0 ... 5,0
| 21.05 | 1.90 | 1.33 | 12.871 | 6.721 | 19.592 | 212.147 |
Lambda is outside valid domain 2,0 ... 5,0
| 22.17 | 2.00 | 1.34 | 14.062 | 6.802 | 20.864 | 237.926 |
Lambda is outside valid domain 2,0 ... 5,0
| 23.29 | 2.10 | 1.36 | 15.278 | 6.889 | 22.166 | 265.538 |
Lambda is outside valid domain 2,0 ... 5,0
| 24.41 | 2.21 | 1.38 | 16.516 | 6.980 | 23.495 | 294.983 |
Lambda is outside valid domain 2,0 ... 5,0
| 25.52 | 2.31 | 1.40 | 17.779 | 7.071 | 24.850 | 326.298 |
Lambda is outside valid domain 2,0 ... 5,0
| 26.64 | 2.41 | 1.41 | 19.066 | 7.162 | 26.228 | 359.493 |
Lambda is outside valid domain 2,0 ... 5,0
| 27.76 | 2.51 | 1.43 | 20.355 | 7.264 | 27.619 | 394.446 |
Lambda is outside valid domain 2,0 ... 5,0
| 28.88 | 2.61 | 1.45 | 21.670 | 7.360 | 29.030 | 431.313 |
Lambda is outside valid domain 2,0 ... 5,0
| 30.00 | 2.71 | 1.47 | 22.979 | 7.466 | 30.445 | 469.866 |
+-------+-------+-------+---------+---------+---------+---------+

C.W.F.Hamilton & Co. type of waterjet calculation, according to [1,2]:

Vs = 30.00 kn = 15.433 m/s

Nwj = 1
Ct = 7.045
Cp = 18.444
EtaW = 0.382
Power (P) = 1230.03 kW = 1671.24 BHP
ATTENTION !!! Power is out valid domain 30 ... 400 BHP per unit for used diagram.
Impeller Type: 9 11 12 13 14 15
RPS (n) = 85.4 82.4 78.7 75.8 74.5 73.1
RPM (n) = 5121 4941 4721 4550 4473 4386

Nwj = 2
Ct = 3.523
Cp = 7.566
EtaW = 0.466
Power (P) = 504.57 kW = 685.56 BHP
ATTENTION !!! Power is out valid domain 30 ... 400 BHP per unit for used diagram.
Impeller Type: 9 11 12 13 14 15
RPS (n) = 63.4 61.2 58.5 56.3 55.4 54.3
RPM (n) = 3805 3672 3508 3381 3323 3259
Power*Nwj = 1009.15 kW = 1371.12 BHP

Nwj = 3
Ct = 2.348
Cp = 4.639
EtaW = 0.506
Power (P) = 309.36 kW = 420.33 BHP
Impeller Type: 9 11 12 13 14 15
RPS (n) = 53.9 52.0 49.7 47.9 47.1 46.1
RPM (n) = 3233 3119 2980 2872 2823 2768
Power*Nwj = 928.08 kW = 1260.98 BHP

Nwj = 4
Ct = 1.761
Cp = 3.332
EtaW = 0.529
Power (P) = 222.24 kW = 301.95 BHP
Impeller Type: 9 11 12 13 14 15
RPS (n) = 48.3 46.6 44.5 42.9 42.1 41.3
RPM (n) = 2895 2794 2669 2572 2529 2479
Power*Nwj = 888.94 kW = 1207.81 BHP

REFERENCES:

1. Donald M. MacPherson.- A Universal Parametric Model for Waterjet Performance,
HydroComp, Inc., Presented at FAST-99, Aug 1999.
2. HydroComp, Inc., "Waterjet Data Files for NavCad", HCI Report No. 119,
December 1997.

2. Joined: Feb 2007
Posts: 127
Likes: 6, Points: 0, Legacy Rep: 58
Location: Ukraine

### Victor TSenior Member

LCG/Lwl must be < 0,4. Optimal is 0.3...0.4

Regards

1 person likes this.
3. Joined: Feb 2007
Posts: 127
Likes: 6, Points: 0, Legacy Rep: 58
Location: Ukraine

### Victor TSenior Member

Displacement : 29.12 t
X of CoG : 7.185 m
Midship area above waterline : 10.00 m^2
Roughness coefficient *10^3 : 0.400
Maximal speed : 30.00 knots
Angle between Thrust and Keel lines : 4.00 degr
Distance between Thrust line and CoG : 0.150 m

----------------------------------------------------------------------------

Final calculations of resistance and power for planing ships by D.Savitsky

| Vs | FrB | Tau | R_f | R_p | R_t | Pe |
| [kn] | - | [degr]| [kN] | [kN] | [kN] | [kW] |
Lambda is outside valid domain 2,0 ... 5,0
| 18.81 | 1.70 | 4.01 | 7.116 | 20.342 | 27.458 | 265.701 |
Lambda is outside valid domain 2,0 ... 5,0
| 19.93 | 1.80 | 4.16 | 7.744 | 21.100 | 28.845 | 295.725 |
Lambda is outside valid domain 2,0 ... 5,0
| 21.05 | 1.90 | 4.36 | 8.366 | 22.134 | 30.500 | 330.251 |
| 22.17 | 2.00 | 4.55 | 8.982 | 23.077 | 32.059 | 365.590 |
| 23.29 | 2.10 | 4.72 | 9.592 | 23.943 | 33.535 | 401.732 |
| 24.41 | 2.21 | 4.87 | 10.198 | 24.723 | 34.921 | 438.432 |
| 25.52 | 2.31 | 5.00 | 10.804 | 25.397 | 36.201 | 475.336 |
| 26.64 | 2.41 | 5.11 | 11.411 | 25.969 | 37.380 | 512.335 |
| 27.76 | 2.51 | 5.20 | 12.027 | 26.418 | 38.445 | 549.071 |
| 28.88 | 2.61 | 5.27 | 12.656 | 26.745 | 39.401 | 585.403 |
| 30.00 | 2.71 | 5.31 | 13.301 | 26.954 | 40.255 | 621.263 |

Calculated FrV=2.810
+------------------------------------------------+
| Parameter | Calculated | Optimal |
+------------------+---------------+------------+
| L/B | 5.938 | 5.750 |
|Cg=D/(Rho*g*B^3)| 0.807 | 0.487 |
| Beta | 25.000° | 15.707° |
| Xg=LCG/L | 0.366 | 0.404 |
+------------------------------------------------+

As can be seen from the table, we must reduce the L / B Deadrise amidships (Beta) and D.
And use a newer version Freeship Plus 3.24 +

4. Joined: Aug 2011
Posts: 3
Likes: 0, Points: 0, Legacy Rep: 10
Location: Italy

### mattr87New Member

Thank you very much for the fast answer. I'm going to try right now

5. Joined: Aug 2011
Posts: 3
Likes: 0, Points: 0, Legacy Rep: 10
Location: Italy

### mattr87New Member

I'm sorry if I bother you again but I have some questions:
Why did you put 7.185 m as LCG? Is it the center of gravity of all the flying boat, isn't it? In fact if I take LCG =12.185 that is the CG of the seaplane the trim is quite low (around 1.4).
Unfortunately I cannot touch the values of the total lenght and of the beam that are fixed in order to project constraints to B=3.76 and L=22m ...
How can I reduce lambda (that is LCG/Lwl isn't it?) without modifying these parameters?
Last question: how is Cg calculated? Because I cannot find the value of D that returns me the same result of the program.
Thank you again for your patience.

PS. I downloaded the new version of freeship... that's quite better and a little faster, thank you!

6. Joined: Jun 2011
Posts: 119
Likes: 8, Points: 0, Legacy Rep: 120
Location: somewhereonearth

### CmbtntDzgnrSenior Member

Hi,

Hydronship... err, umm, FREE!ship Plus 3.24+ TEST is out. Not sure if it will have more than what is listed here or help you get calcs you're after:

http://hydronship.net/stati/idnews/59

I'm excited and will be checking it out on my lunch break!

Cheers

Last edited: Aug 29, 2011

7. Joined: Jun 2011
Posts: 119
Likes: 8, Points: 0, Legacy Rep: 120
Location: somewhereonearth

### CmbtntDzgnrSenior Member

Well, I'm happy that Fung-Leibman resistance for naval vessels calculation engine works. My one problem that I need to resolve is correcting my Ie (bow entrance angle) to 2.7 deg from the current 89.x degrees.

(When checking the box "extract data from current hull", that value appears, and when I deselect it and alter it to become 2.7 (higher than the 2.6, but lower than the 31.73 domain range), the resistance and power values change to a Pe kW 38141 and RT kN of 2247, from a Pe kW of 1,300,000 and RT kN of 80790.). I'll just adjust the bow area to get that value to correct so the calcs become favorable without my manually adjusting the input variables.

By the way, my hull is around 166.9x18.35x7.8 m. The Cp is 0.6011. The Cb is 0.3318. Cwp is 0.7678. When i change the resistance calc engine to planing hulls, and set speed higher than 44, say, to 44.5 kts, I get some results to appear. Setting the speed to 54 knots generates "Lambda is outside valid domain 2,0 to 5,0." But, interestingly, the Rt is around 5158 kN and Pe is 143302 kW. To get the value of 143000 kW in Fung-Leibman, I would need to set the speed to 43 knots. the Rt pretty much corresponds.

This is an incredible, generaous, great program, even though I'm not an engineer and not capable of fully appreciating the really hard work programmers and architects go through to arrive at or rationalize useable output from software.

Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.