Savitsky Power Prediction

[guest12020101217]

Hi all

I am writing a savitsky planing power prediction porgram in Mircosoft excel at the moment. Well in fact l am writing two! One using the thoery in principles of yacht design and the other from copies of savitsky's and others papers.

Can anybody tell me how l can get Excel to solve equations like the one below. I need to solve for CLo.

CLb = CLo - 0.0065*B*CLo^0.6

CLb = Deadrise Lift Coefficient
CLo = Flat Plate lift Coefficient
B = deadrise angle.

I can do it by getting excel to plots graphs and me having to pick the value off and enter it in, but l really want excel to solve it.

I want to do the same when solving for the wetted length/wetted beam ratio (L).

CLo =t^1.1 x {0.012L^0.5 + (0.0055L^(5/2))/Cv^2}

t=running trim
L=wetted length/wetted beam ratio
Cv= Speed coefficient

Plan to develop the programs over time and use Maxsurf's Hullspeed as base data. May but the program on net when happy with it.

Any help or comments are very welcome.

[Dim]

all input data - "from my mind". Check formulas, please.

[guest12020101217]

To Dim

Thanks for your help, but think l didn't explain what l needed help on clearly. Need excel to find CLo from a inputted value of CLb, in the first equation and then use that value to solve for the wetted length/wetted beam ration "L" in the second equation.
But, once again thanks for the reply.

[Dim]

on first to yours post, I have understood (not correctly has understood), that the help on job with Excel is simply necessary.
:)
Dim.

[BrettM]

Use solver... May be easier to rewrite the eqn to equal zero so you don't have to think next time.... Can also set up a macro button to automate it. Good Luck.

[nevd]

Hello,

As a new member, I think your project will be very useful to myself and many other members.

Please advise how the programme is progressing.

nevd

[nico]

Hi,

When u think that all the formular are right,etc.. If i have the file, i could program a bit and add some macros using the solver from excel (I am already using it for a VPP). I think it is easy to understand VB language so it ll be easy to change.

Nico

[guest12020101217]

Thank you for the offer. It been on the back bench as l am still waiting for copies of the papers by savitsky from SNAME. Want included pre planing prediction. I will be making the program free on the WEB but not until l am 100% happy with it. Plan to learn VB myself as there is other plans for programs l want to follow up.

[tspeer]

Did you ever get a real answer to your Excel question?

There are a couple of ways to solve the equation. One is go to the Tools menu and using Goal Seek. Tell it to set Clb to the value you want by varying Clo.

If you have several sets of equations to solve for, you can have a column of desired values for Clb, a column of Clo values (loaded with initial guesses), a column of Clb's calculated from the formulae, and a column of squared errors. Sum the squared errors in one cell, and use Tools/Solver to minimize the sum of the squared errors using the Clo cells as the parameters to vary.

You can also do it by intentionally setting up an implicit loop and going to manual calculation. Hit F9 repeatedly to iterate to the solution once you have your starting guesses entered.

[Guest]

Congratulations for taking the time to do learn Savitsky by doing this instead of just using available programs.

However, if you want to have a benchmark to check your answers, search on "fishmeal" and "kamen". His site has a free Savitsky program for download.

[guest12020101217]

To Guest

Thank you for your support and links. They where very useful

[Humberto Rodrìg]

Hi all

I am writing a savitsky planing power prediction porgram in Mircosoft excel at the moment. Well in fact l am writing two! One using the thoery in principles of yacht design and the other from copies of savitsky's and others papers.

Can anybody tell me how l can get Excel to solve equations like the one below. I need to solve for CLo.

CLb = CLo - 0.0065*B*CLo^0.6

CLb = Deadrise Lift Coefficient
CLo = Flat Plate lift Coefficient
B = deadrise angle.

I can do it by getting excel to plots graphs and me having to pick the value off and enter it in, but l really want excel to solve it.

I want to do the same when solving for the wetted length/wetted beam ratio (L).

CLo =t^1.1 x {0.012L^0.5 + (0.0055L^(5/2))/Cv^2}

t=running trim
L=wetted length/wetted beam ratio
Cv= Speed coefficient

Plan to develop the programs over time and use Maxsurf's Hullspeed as base data. May but the program on net when happy with it.

Any help or comments are very welcome.


I´d like to have more info on your program. Please contactme at HumbertoR92@hotmail.com

[Guest]

I have already written an Excel spreadsheet to solve Savitsky's planing hulls. Give me your e-mail and I will send it to you. You can either use it, or see how I get Excel to solve Clo by itself.

[gonzo]

Would you post it?

[Dingo]

Here is my spreadsheet on Savitsky and other methods. It contains various allowances for trim-tabs and shafts etc. Unfortunately, it was written by me in Dutch and Afrikaans, but the symbols and references should pose no problem. Any translation problems just e-mail me at: dingo at postmark dot net.

[guest12020101217]

Thank you for posting your spreadsheet. Hope to have mine finished after new year and will post it here. It's been on back burn abit.

[Dingo]

Glad I could help. If anyone out there finds an error, let me know please.
Regarding the use of the spreadsheet, fill the boxes that are coloured yellow with your input; this includes the LCG's (LSP in the program), and velocities, as well as the various parameters regarding the vessel. Click on the 'Voortgaan' putton (proceed), and sit back and wait. The values of resistance and thrust will be calculated. Further on down are calculations for rollstability etc. using various theories from Lewandowski etc.
I am currently updating this spreadsheet to include planing catamarans based on the theory of Lee (republished by Insel) who builds upon the theory formulated by Savitsky and which takes into account the distance between hulls. If anyone out there has empirical formulas for cats that are as 'easy' to use as Savitsky (without going into triple integral formulas etc.!!) please let me know, otherwise I shall proceed with this one.

[Guest]

Hi Dingo much apreciated your spreadsheet, congratulation for the excellent work.

[Humberto Rodrìg]

for Colin, I have already written an Excel spreadsheet to solve Savitsky's planing hulls. Give me your e-mail and I will send it to you. You can either use it, or see how I get Excel to solve Clo by itself.


Here is one: HumbertoR92@hotmail.com
I will appreciate your help

[Brent]

Dear Sir;

I was wondering if you were willing to divulge the Password for your resistance spreadsheet posted on boatdesign.net(Prestasie.xls). I want to unlock the remainder of spreadsheet for translation and use if for my senior design project at school(working on a high speed sportfish concept).

Thanks,

Brent

Email: wyy551@yahoo.com


Here is my spreadsheet on Savitsky and other methods. It contains various allowances for trim-tabs and shafts etc. Unfortunately, it was written by me in Dutch and Afrikaans, but the symbols and references should pose no problem. Any translation problems just e-mail me at: dingo at postmark dot net.

[Dingo]

Brent, I have written another spreadsheet for Savitsky/Hadler/Blount etc. (in English) that is cleaned up and easier to use. I will sent that to you if you desire. The calculations are hidden but I can give you the details to unlock it if you need to translate any Dutch/Afrikaans that I made notes or references in (old habit I picked up studying in South Africa).

Dear Sir;

I was wondering if you were willing to divulge the Password for your resistance spreadsheet posted on boatdesign.net(Prestasie.xls). I want to unlock the remainder of spreadsheet for translation and use if for my senior design project at school(working on a high speed sportfish concept).

Thanks,

Brent

Email: wyy551@yahoo.com

[Humberto Rodrìg]

Please send a copy of your spreadsheet to HumbertoR92@hotmail.com

[stillgar]

Dingo:

Could you please email me a copy of your translated spreadsheet?

stillgar_@hotmail.com

Regards,

[albresco]

Please send me a copy of your English spread sheet as well.
Thank you
albresco@shaw.ca

[cgorton]

I'd love a copy of your English translation spreadsheet- thanks!

Craig

cg@zurnyachts.com

[Dingo]

Here is my spreadsheet. I've made it easier to use, translated it into English with a help file and hidden the calculations (password is Dingo to view it on a separate sheet). I've still yet to add catamaran resistance results, but will do so as soon as I have time. Any problems or errors, let me know please. By the way, be careful when predicting drag around the hump speed; there are other methods that can be used, but this is good for estimating.

Dingo

[albresco]

Thank you for the sreadsheet post. Looks great!!

[Dingo]

This reply is for Nev, but I will republish it here in case others have the same questions:
If you go to the Help tab in the spreadsheet, most of the definitions that you wrote in red are explained with diagrams. Regarding the sheet 'Berekenings' (Dutch for Calculations): the sheet is hidden but can be turned on and inspected (password is Dingo). All the background calculations are there. You ask why the thrust is more than the drag: it is because the drag is in the direction of motion (ie. horizontal), but the thrust acts at an angle slightly downward, so it has to be slightly higher in order to get the equal amount of horizontal force to counteract the drag. Regarding the Go button: press the button once you change a value. The trim will change to almost zero on the first run, then increment upwards until it reaches the equilbrium value for zero moment. If #VALUE appears, it means that the resistance can't be predicted for those particular given parameters.

[ars-technica]

Make 2 column
clo clb
0.1 value obtained with =clo-....
0.2 value obtained with =clo-....
make this for all number of clo you need
then use the function search to discover the value you need in that moment.
warning taht search function give you the value incorect if you do not impost an interpolation before...



Hi all

I am writing a savitsky planing power prediction porgram in Mircosoft excel at the moment. Well in fact l am writing two! One using the thoery in principles of yacht design and the other from copies of savitsky's and others papers.

Can anybody tell me how l can get Excel to solve equations like the one below. I need to solve for CLo.

CLb = CLo - 0.0065*B*CLo^0.6

CLb = Deadrise Lift Coefficient
CLo = Flat Plate lift Coefficient
B = deadrise angle.

I can do it by getting excel to plots graphs and me having to pick the value off and enter it in, but l really want excel to solve it.

I want to do the same when solving for the wetted length/wetted beam ratio (L).

CLo =t^1.1 x {0.012L^0.5 + (0.0055L^(5/2))/Cv^2}

t=running trim
L=wetted length/wetted beam ratio
Cv= Speed coefficient

Plan to develop the programs over time and use Maxsurf's Hullspeed as base data. May but the program on net when happy with it.

Any help or comments are very welcome.

[Danielsan]

Hi,
I did use the last version (English) of Dingos spreadsheet

Any one thinks this can be a correct result? I should need 160HP to get my boat planning at 50kts

http://www.boatdesign.net/forums/showthread.php?t=4610 (my boat)

THX in advance,

Daniel Peeters

Inputs

Hull Beam B 9.18 feet
VCG VCG 1.02 feet = 0.311 metres
Displacement D 6,800 lbf = 3,084 kg
Deadrise @ Transom b T 27 °
Deadrise @ Amidships b )0( 27 °
Distance to Amidships L )0( 12.160 feet = 3.706 metres
f 1.00 feet = 0.305 metres
e 15.00 °
q 0.000 °

Minimum Speed Vmin 6.1 kn = 10.3 feet/s This is the minimum speed valid for this analysis
Maximum Speed Vmax 132.4 kn = 223.4 feet/s This is the maximum speed valid for this analysis

Number Number of Propellers N 1

Trim Tab Chord cF 1 feet = 0.305 metres
Span Ratio s 0.333 ( <= 1 )
Deflection Angle d 0 °

Rudder Chord crudder 0.00 feet = 0.000 metres
Thickness t 0.00 feet = 0.000 metres
Area Arudder 3.60 feet2 = 0.334 m2
Centrepoint xc -0.80 feet from transom = -0.243 metres (+ve fwd)
yc -0.60 feet from baseline = -0.183 metres (+ve up)

Shaft Diameter of Shaft Fshaft 0.00 feet = 0.000 metres
Length of Shaft & Hub l 0.00 feet = 0.000 metres
Centrepoint xc 5.50 feet from transom = 1.676 metres (+ve fwd)
yc 0.00 feet from baseline = 0.000 metres (+ve up)

Strut Chord cstrut 0.00 feet = 0.000 metres
Thickness t 8.00 feet = 2.438 metres
Area Astrut 0.75 feet2 = 0.070 m2 ****
Centrepoint xc 3.50 feet from transom = 1.067 metres (+ve fwd)
yc 2.00 feet from baseline = 0.610 metres (+ve up)

Output V LCG t D T Peffective h
[kn] [ft] [metres] [°] [lbf] [kN] [lbf] [kN] [ehp] [ekW] [ft] [metres]
6 10.5 3.2 10.3662 595 2.6 659 2.9 11 8 3.51 1.070
7.5 10.5 3.2 11.5474 1,087 4.8 1,215 5.4 25 19 3.51 1.070
10 10.5 3.2 14.2537 1,665 7.4 1,909 8.5 51 38 3.29 1.003
12.5 10.5 3.2 > 15° #VALUE! #VALUE! #VALUE! #VALUE! #VALUE! #VALUE! #VALUE! #VALUE!
13 10.5 3.2 > 15° #VALUE! #VALUE! #VALUE! #VALUE! #VALUE! #VALUE! #VALUE! #VALUE!
14 10.5 3.2 > 15° #VALUE! #VALUE! #VALUE! #VALUE! #VALUE! #VALUE! #VALUE! #VALUE!
15 10.5 3.2 > 15° #VALUE! #VALUE! #VALUE! #VALUE! #VALUE! #VALUE! #VALUE! #VALUE!
17.5 10.5 3.2 > 15° #VALUE! #VALUE! #VALUE! #VALUE! #VALUE! #VALUE! #VALUE! #VALUE!
20 10.5 3.2 14.0987 1,583 7.0 1,812 8.1 97 73 1.38 0.421
25 10.5 3.2 11.0293 1,318 5.9 1,467 6.5 101 75 1.18 0.360
30 10.5 3.2 8.7581 1,151 5.1 1,257 5.6 106 79 1.09 0.332
35 10.5 3.2 7.1278 1,065 4.7 1,149 5.1 114 85 1.04 0.317
40 10.5 3.2 5.9385 1,045 4.6 1,118 5.0 128 96 1.01 0.308
45 10.5 3.2 5.0493 1,081 4.8 1,151 5.1 149 111 0.99 0.302
50 10.5 3.2 4.368 1,169 5.2 1,239 5.5 179 134 0.97 0.296

[Dingo]

Danialsan, Hoe gaat 't?

I entered the numbers that you gave and I obtained different results. I noticed that you are using a trim tab of 1 ft chord and no rudder (?). The top speed that Savitsky will predict for this boat is 45 kts (trim > 15 deg at 50 kts) and will require 262 effective kW (or 352 ehp). This is the power required to tow the boat, not what the engine power is. The actual brake power depends on the propeller and transmission losses, which as a basic rule is 60% and 97% efficient respectively.

Also, you used an LCG of 10.5 ft which is very far forward for a planing craft. I re-ran it for an LCG of 8 ft (2.438 metres) and got a lower effective power of 207 ekW (277 ehp) for 50 kts, or a brake power of 355 ekW (476 bhp). Note that your deadrise is 27 degrees; high for a fast planing boat. I would suggest lowering it to 16 degrees unless you are going to use it in rough open seas.

For the others, and yourself, here is an updated version of my planing spreadsheet. It includes an addition for wind resistance due to superstructures and above water hull; the theory for the rest remains unchanged.

Dingo

[Danielsan]

Hi Dingo, Met mij goed en met U?

Thx for the reply

Did some more precise measurements, as I didn't have the drawings on my other PC

and came to the next results:
(I am a bit disapointed, as I want to build that boat from scratch and for the lowest budget possible, but now I would need a high power engine? So I can't fall back on my 6l +150HP Perkins long block)

How do I have to translate this to prop size/pitch rpm, any idea?

Length of Waterline LWL 24.34 feet
Beam B 9.180 feet
VCG VCG 1.02 feet = 0.311 metres
Displacement D 6,700 lbf = 3,039 kg
Deadrise @ Transom b T 16.61 °
Deadrise @ Amidships b )0( 19.89 °
Distance to Amidships L )0( 12.172 feet = 3.710 metres
q 1.372 °
Angle of Thrust Line e 9.25 °
f 3.32 feet = 1.012 metres

Minimum Speed Vmin 6.1 kn = 10.3 feet/s This is the minimum speed valid for this analysis
Maximum Speed Vmax 132.4 kn = 223.4 feet/s This is the maximum speed valid for this analysis

Length Overall LOA 24.34 feet = 7.420 metres
Maximum Beam Bmax 9.81 feet = 2.990 metres
Moulded Depth of Hull Z 4.95 feet = 1.509 metres
Height of House HSS 1.30 feet = 0.396 metres
Breadth of House BSS 8.00 feet = 2.438 metres
Frontal Area of House ASS 10.4 feet2 = 0.966 m2

Number of Propellers N 1

Chord cF 1.2 feet = 0.366 metres
Span Ratio s 0 ( <= 1 )
Deflection Angle d 5 °

Chord crudder 1.60 feet = 0.488 metres
Thickness t 0.10 feet = 0.030 metres
Area Arudder 2.59 feet2 = 0.241 m2
Centrepoint xc -0.20 feet from transom = -0.061 metres (+ve fwd)
yc 0.24 feet from baseline = 0.073 metres (+ve up)

Diameter of Shaft Fshaft 0.10 feet = 0.030 metres
Length of Shaft & Hub l 3.00 feet = 0.914 metres
Centrepoint xc 0.20 feet from transom = 0.061 metres (+ve fwd)
yc 0.80 feet from baseline = 0.244 metres (+ve up)

Chord cstrut 0.00 feet = 0.000 metres
Thickness t 8.00 feet = > 15° metres
Area Astrut 0.75 feet2 = > 15° m2 ****
Centrepoint xc 3.50 feet from transom = 1.067 metres (+ve fwd)
yc 2.00 feet from baseline = 0.610 metres (+ve up)

V LCG t D T Peffective h tcr Comments
[kn] [ft] [metres] [°] [lbf] [kN] [lbf] [kN] [ehp] [ekW] [ft] [metres] Lew.[°] Angeli [°]
6 7.45 2.271 7.8498 509 2.3 535 2.4 9 7 2.66 0.811 > 15° > 15°
7.5 7.45 2.271 9.6101 959 4.3 1,017 4.5 22 16 2.75 0.838 > 15° > 15°
10 7.45 2.271 10.8676 1,370 6.1 1,466 6.5 42 31 2.52 0.768 14.97 > 15°
12.5 7.45 2.271 9.6235 1,346 6.0 1,428 6.4 52 39 2.10 0.640 10.33 11.44
13 7.45 2.271 9.2981 1,325 5.9 1,403 6.2 53 39 2.02 0.616 9.70 10.85
14 7.45 2.271 8.6521 1,281 5.7 1,352 6.0 55 41 1.88 0.573 8.62 9.81
15 7.45 2.271 8.0358 1,240 5.5 1,303 5.8 57 43 1.76 0.536 7.74 8.94
17.5 7.45 2.271 6.6964 1,163 5.2 1,214 5.4 62 47 1.51 0.460 6.14 7.28
20 7.45 2.271 5.6434 1,130 5.0 1,173 5.2 69 52 1.32 0.402 5.08 6.11
25 7.45 2.271 4.1786 1,171 5.2 1,207 5.4 90 67 1.07 0.326 3.78 4.59
30 7.45 2.271 3.2527 1,312 5.8 1,348 6.0 121 90 0.91 0.277 3.04 3.66
35 7.45 2.271 2.6356 1,522 6.8 1,559 6.9 163 122 0.80 0.244 2.58 3.04
40 7.45 2.271 2.2053 1,782 7.9 1,823 8.1 219 163 0.73 0.223 2.26 2.60
45 7.45 2.271 1.8939 2,081 9.3 2,127 9.5 287 215 0.68 0.207 2.04 2.27
50 7.45 2.271 1.6621 2,412 10.7 2,462 11.0 370 276 0.64 0.195 1.87 2.03

[ABoatGuy]

You may also want to search SNAME for Donald Blounts papers. He has a few which apply a correction to the hump area for a better fit to reality.

aboatguy

[gonzo]

Without doing the numbers, I am sure there must be some error. The HP seems too low. Also, how are you going to build a boat of such low displacement to be structurally adequate for 50 Knots?

[Danielsan]

Without doing the numbers, I am sure there must be some error. The HP seems too low. Also, how are you going to build a boat of such low displacement to be structurally adequate for 50 Knots?


Good Question.

I do find it has low dispacement or maybe not low displacement, but more low draft? the one goes with the other I know...

On the other hand I did find some (fast)planning boats that where 10% bigger, with around 3600 Kg of displacement

On the other hand (damn I only have two of them) it does not have to do 50kt, if it goes by 30kt and it keeps a float I will be verry happy.

I am also a bit concerned about the low draft, displacement as if I would go out on our North sea, it can be kind of rough.

Anu sugestions, all welcome...

Daniel Peeters

[RThompson]

Dingo,
Thanks a lot for making the spreadsheet available. Its superb.

Rob

[Ilan Voyager]

I have just downloaded the excell sheet by Dingo (nice work!) The FP does not seems to be too low; it seems that it's the HP at the PROPELLER (I have bot looked in detail in the sheet cells) which about 50 %

Efficiency gear box: 95 % (new, when old ...oooh)
Efficiency shaft, bearings, joints: 95 % if everything turns round.
Efficiency of the propeller; that hurts badly:
9.6m diameter propeller 79 tons of bronze 85 to 90 % efficiency at 105 RPM, but this propeller is not common on small power boats for evident reasons.
Common 13 to 15 inches propeller turning at 2000 RPM...in the very best case 65 % efficiency. 45% of the HP is used to make foam in the water.

So 0.65x0.95x0.95: 0.58 or 58 % of efficiency.

Take the given HP and multiply by 1/0.58 or 1.724 and I think you'll have the true horses. I'll compare the excell sheet with some empiric formulae I have and I'll give you the results.

[Danielsan]

Thx for the comments,

So in the best case I will need to have around 300 Hp to get my boat at 30-35kt?

Do I get this right? What is the influence of torque, there is a diff. between Diesel and Gas engines. Won't I need to have less Hp because using a dieselengine?

Greetings,

Daniel Peeters

[martok13]

When i apply this excel sheet to my catamaran..... i get all #VALUE!

Length of Waterline LWL 66.48 feet
Beam B 14.000 feet
VCG VCG 6 feet = 1.829 metres 95396.64 210311.4325
Displacement D 210,311 lbf = 95,397 kg
Deadrise @ Transom b T 17 °
Deadrise @ Amidships b )0( 21.5 °
Distance to Amidships L )0( 33.239 feet = 10.131 metres
q 1.064 °
Angle of Thrust Line e 3.00 °
f 3.00 feet = 0.914 metres

Minimum Speed Vmin 6.0 kn = 12.7 feet/s This is the minimum speed valid for this analysis
Maximum Speed Vmax 132.4 kn = 275.9 feet/s This is the maximum speed valid for this analysis

Length Overall LOA 78.00 feet = 23.774 metres
Maximum Beam Bmax 27.50 feet = 8.382 metres
Moulded Depth of Hull Z 12.00 feet = 3.658 metres
Height of House HSS 14.00 feet = 4.267 metres
Breadth of House BSS 27.50 feet = 8.382 metres
Frontal Area of House ASS 385 feet2 = 35.768 m2

Number of Propellers N 1

Chord cF 0 feet = 0.000 metres
Span Ratio s 0 ( <= 1 )
Deflection Angle d 0 °

Chord crudder 0.00 feet = 0.000 metres
Thickness t 0.00 feet = 0.000 metres
Area Arudder 0.00 feet2 = 0.000 m2
Centrepoint xc 0.00 feet from transom = 0.000 metres (+ve fwd)
yc 0.00 feet from baseline = 0.000 metres (+ve up)

Diameter of Shaft Fshaft 0.00 feet = 0.000 metres
Length of Shaft & Hub l 15.00 feet = 4.572 metres
Centrepoint xc 5.50 feet from transom = 1.676 metres (+ve fwd)
yc 0.00 feet from baseline = 0.000 metres (+ve up)

Chord cstrut 0.00 feet = 0.000 metres
Thickness t 8.00 feet = > 15° metres
Area Astrut 0.75 feet2 = > 15° m2 ****
Centrepoint xc 3.50 feet from transom = 1.067 metres (+ve fwd)
yc 2.00 feet from baseline = 0.610 metres (+ve up)

[Dingo]

Marktok13, The reason that you have VALUE in all the boxes is because the trim is above 15 degrees at all speeds. This theory is valid only for trim angles below 15 degrees.

[RThompson]

Hi there,
I am most interested in learning a bit more about the "Sea Keeping" and "Roll stability" aspects of Dingo's spreadsheet. ie what the numbers really mean .

So, my questions:

Are the following papers possibly available on-line anywhere:

Lewandowski, Edward M., "Prediction of the Dynamic Roll Stability of Hard-Chine Planing Craft", Journal of Ship Research, juni 1996

Savitsky & Brown, "Procedures for Hydrodynamic Evaluation of Planing Hulls in Smooth and Rough Water", Marine Technology, Okt. 1976


Dingo, you suggested e-mailing you for translation issues, I figured you have already given your time in the spreadsheet, I could get off my bum and translate it myself. :)
So, can anyone direct me to a suitable on-line Afrikaans/English translator?
(I'v had a look and there's not to much out there)

Thanks again for the spreadsheet,

Rob

[nevd]

Rob,

Lewandowski, Edward M., "Prediction of the Dynamic Roll Stability of Hard-Chine Planing Craft", Journal of Ship Research, juni 1996 is on the SNAME CD. It is highly mathematical.

Let me know if you find somewhere to get the Savitsky paper as I am also interested.

nevd

[mistral]

for Dingo

i've put savitsky calculus routine into a mathcad spreadsheet as you've done with excel;the surprise came when i saw that given the same input parameters, outputs are dramatically different in terms of power required, although similar in terms of trim angle. How could it be possibile?? i used savitsky formulations as they're explained in Larsson & Eliasson text,
other question: i don't find any parameters in your spreadsheet involving propeller efficiency. Am i wrong??
If you're interested i may post you the mathcad file to understand differencies between them;
other few questions:
have you compared your results with some commercial software like hullspeed???
have you tested them with any real boat??

thanx
Mistral

[Dingo]

Mistral, Please note that the calculations from Planing.xls give the effective power, not the required engine power. Hence there are no propeller efficiency results used since I am only interested in the actual drag (or thrust vector). Regarding propeller efficiency, I use another program that I wrote based to the B-series to determine the efficiencies of the prop for a given diameter, pitch etc. and then use the various losses for the final installed power included. The trim is worked out using mostly Savitsky's theory based on equilbrium of force vectors. I am not familiar with the Larsson & Eliasson text. Also, I do not have MathCad so unless you can post the calculations in a text format, I would not be able to debug them.
I have compared my results with other programs that other engineers use and they compare favourably. One that I have directly compared with is NavCad, and the results corresponded well with thenm, as well as various waterjet manufacturer's curves for hull resistance.

To all, I have received some e-mails stating that they have trouble running the spreadsheet Planing.xls. Note that macros must be turned on. It is not password protected, but be sure that the Visual Basic editor can display the macros, otherwise you will get wrong results or #VALUE in various cells. Check also that anti-virus software will allow the running of the macros, or that your firewall allows them through when downloading. (Note, if the trim is greater than 15 degrees, the theory will not be valid). Also be careful when using it for catamarans since I have not yet adapted it for cat use yet (I've just moved house and jobs, so I've been busy).

Dingo

[rxcomposite]

Sorry but you are reinventing the wheel.I've seen a savitsky based program by arneson drive.Its tailored to arneson but it is a simple filling in the data program. if you want the complete series of formula, a publication (i dont know if it is still current) by SNAME about prediction of performance on planing craft.Yes, it can be programmed into excell but it is not simple.
Rxcomposite

[Chris Krumm]

I have a copy of the Savitsky method applet published by Arneson (somewhere) . If I remember correctly, it is a very "short form" and simplified Savitsky power prediction method - assumes thrust line passes through CG, etc. Dingos' work in Exel exposes the calculations and formulas, which is really cool for gaining an underdstanding of what is behind "the answer."

Chris Krumm

[rxcomposite]

Yes, the program was very simple. Keep up the good work chris. We are all in search of "what happens if?". Dingos work is great. I have to find my copy of SNAME's publication on planing craft to decipher the formulas.

[DBDMarine]

Hi all
We make a new stern drive leg and are looking for a application that we can use to not only predict vessel speeds, gearing prop diameter and pitch.
Since the leg doesnt contain a gearbox, the drive uses a ZF 8 degree downangle box, which attaches to the drive.
Now what way would I do this is there no strut, rudder, shaft etc but planing hull?
Im trying to figure this out, looks like this is very close
Can you give me any hints please
Regards
Darren Finch
DBD Marine
www.dbdmarine.com

[atahawaii]

There is a Savitsky spreadsheet available on the web at www.hawaii-marine.com/templates. It does not use Excel's Solver or macros or Visual Basic. It does the iterations automatically and evaluates several speeds. It does both the Short and Long Forms of Savitsky's methods.

[micheler]

Hi all,
I am a new member of the forum. I found the spreadsheet of Dingo really interesting. I'm interested in making a slight modification on it in order to input manually the resistance forces that I obtain from a CFD planing computation.
The procedure may be the following:
1. determine the position of the boat with the Dingo's spreadsheet
2. compute the drag and lift forces acting on the hull via a CFD free-surface computation (with sink&trim from step 1.)
3. insert the CFD-computed drag estimates at the various speeds in the spreadsheet and re-run the computation uptating sink&trim
4. return to step 2. until convergence...

I have to say that I want to make CFD computations only of the hydrodynamic part computing viscous and wave resistance, but without simulating spray formation (almost impossible to get reliable spray-induced-drag up to date). So the results I get are only a part of the total drag/lift.
Dingo could you suggest me where I should input my CFD drag/lift forces? I think the "Berekenings" sheet, but where? How the spray formation and aerodynamic forces are taken into account?

Thanks
Michele.

[Dingo]

Micheler,

I will look into where putting the CFD results should go.

Lines 78 to 83 is where the input for the air drag due to superstructure is placed. This can be modified for lift also but then the total moments must then be recalculated (add lift due to s/str in line 13).

Please note that my e-mail address has changed.

It has also come to my attention that the calculations when using a trim-tab might be slightly off. I will look into it and re-post the spreadsheet if incorrect and as soon as I have time. Sorry for any problems.

[Tim B]

Be careful using CFD, there may be a lot of instances with multi-phase flow. You also have a trim question to get right.

Dingo, you don't have a copy of the SNAME Savitsky paper do you?

Tim B.

[Dingo]

Tim B,

I do have a copy of Savitsky's 1964 paper at SNAME, but it is not the only paper that I used for my spreadsheet. All references are quoted in the spreadsheet in the 'Berekenings' section.

[Tim B]

Ok, I'll have a look at it sometime, I'd really like to add a Savitsky method to LMH at some point, but it will need to be written in C/C++. It also infers that LMH should be finished... yeah, Christmas perhaps.

Cheers,

Tim B.

[micheler]

Thanks for your replies.
I'm trying to understand the "Berekenings" section. But I haven't the Savitsky paper so I have some questions.
I'm especially interested in the first part of the section, where the Savitsky method is applied for computing the planing hull resistance (up to row #43).
For computing the resistance, it seems that the Schoenherr '32 + the ATTC Ca of 0.0004 are applied on the Sf area.
What does the Sf (=lambda * B^2 / cos (beta_e) ) area exactly represents?
Why the Df force is computed with the 0.97 factor instead of the more usual 0.5? What it accounts for? Is it a correction for spray formation? Or is it merely a units conversion factor?

After computing all force components, it is applied an M-factor. What does this correction stands for?

Thanks
Michele.

[subbu]

Hi,

Its great to hear from u that "Dingos' work in Exel exposes the calculations and formulas, which is really cool for gaining an underdstanding of what is behind "the answer." ".

I would like to have that copy, can u send it to me

Subbu

[patrik111]

Hello All,

Is the planing equations applicable to rounded bilged hulls? (i.e. modern round bottomed beach-cats).

The question could also be read:
Are the equations valid for long, skinny and rounded hulls?
If not, at what are the input limits for the equations?

Best Regards

Patrik

Best Regards

[patrik111]

Could deadrise for instance be approximated as some sort of average over the curved surfaces?

Anyone have some sort of hint??

[rxcomposite]

Could deadrise for instance be approximated as some sort of average over the curved surfaces?

Anyone have some sort of hint??

Yes. The rulebook says that if it is a "S" curve deadrise should be measured from the keel intersection to the centerline to the outer edge of the chine.

If the keel has a fairly rounded section, it should be measured from the point tangent to the radius to the edge of the chine.

If you have a reverse chine, the edge of the chine pointing downward is still the edge.

[Willallison]

I've run Dingo's program on a number of occaisions since he 1st (very kindly) made it available to us all.
I don't doubt the validity of the calculations, but perhaps someone might be able to give me a definitive means of interpereting them....
For instance, I ran the numbers thru for a 40 footer powered by a single duoprop sterndive (hence the zero entries for rudder, strut etc...) with the following results:

Inputs

Hull Beam B 10.53 feet
VCG VCG 3.31 feet = 1.009 metres
Displacement D 14,265 lbf = 6,471 kg
Deadrise @ Transom b T 9.3 °
Deadrise @ Amidships b )0( 15 °
Distance to Amidships L )0( 14.400 feet = 4.389 metres
f 3.60 feet = 1.097 metres
e 0.00 °
q 2.182 °

Minimum Speed Vmin 6.5 kn = 11.0 feet/s This is the minimum speed valid for this analysis
Maximum Speed Vmax 141.8 kn = 239.3 feet/s This is the maximum speed valid for this analysis

Number Number of Propellers N 1

Trim Tab Chord cF 1 feet = 0.305 metres
Span Ratio s 0.32 ( <= 1 )
Deflection Angle d 0 °

Rudder Chord crudder 0.00 feet = 0.000 metres
Thickness t 0.00 feet = 0.000 metres
Area Arudder 0.00 feet2 = 0.000 m2
Centrepoint xc 0.00 feet from transom = 0.000 metres (+ve fwd)
yc 0.00 feet from baseline = 0.000 metres (+ve up)

Shaft Diameter of Shaft Fshaft 0.00 feet = 0.000 metres
Length of Shaft & Hub l 0.00 feet = 0.000 metres
Centrepoint xc 0.00 feet from transom = 0.000 metres (+ve fwd)
yc 0.00 feet from baseline = 0.000 metres (+ve up)

Strut Chord cstrut 0.00 feet = 0.000 metres
Thickness t 0.00 feet = 0.000 metres
Area Astrut 0.00 feet2 = 0.000 m2 ****
Centrepoint xc 0.00 feet from transom = 0.000 metres (+ve fwd)
yc 0.00 feet from baseline = 0.000 metres (+ve up)

Output V LCG t D T Peffective h
[kn] [ft] [metres] [°] [lbf] [kN] [lbf] [kN] [ehp] [ekW] [ft] [metres]
6 10.5 3.2 4.9135 786 3.5 790 3.5 14 11 2.71 0.826
7.5 10.5 3.2 5.4956 1,061 4.7 1,069 4.8 24 18 2.80 0.853
10 10.5 3.2 6.7204 2,011 8.9 2,029 9.0 62 46 2.90 0.884
12.5 10.5 3.2 7.4953 2,437 10.8 2,465 11.0 93 70 2.77 0.844
13 10.5 3.2 7.518 2,465 11.0 2,493 11.1 98 73 2.72 0.829
14 10.5 3.2 7.4427 2,478 11.0 2,505 11.1 106 79 2.59 0.789
15 10.5 3.2 7.2444 2,451 10.9 2,477 11.0 113 84 2.45 0.747
17.5 10.5 3.2 6.4822 2,313 10.3 2,333 10.4 124 93 2.11 0.643
20 10.5 3.2 5.6434 2,175 9.7 2,190 9.7 133 100 1.82 0.555
25 10.5 3.2 4.2328 2,034 9.1 2,043 9.1 156 116 1.40 0.427
30 10.5 3.2 3.2351 2,067 9.2 2,073 9.2 190 142 1.13 0.344
35 10.5 3.2 2.5363 2,227 9.9 2,232 9.9 239 179 0.94 0.287
40 10.5 3.2 2.0349 2,483 11.0 2,487 11.1 305 227 0.82 0.250
45 10.5 3.2 1.6647 2,815 12.5 2,818 12.5 389 290 0.72 0.219
50 10.5 3.2 1.384 3,210 14.3 3,213 14.3 493 368 0.65 0.198

...hmmm I see that the table doesn't line up all that well, but the long and the short of it is that at my target max speed of 25 knots, the spreadsheet gives a required effective hp of 156hp.
So, the question - how to relate this to SHP or even better, a published engine / propeller curve....?

[Tad]

Will,

Excelent question, what you are after here is "Pe", Propulsive Efficiency or Propulsive Coefficient.

This really rates it's own thread but I'll give you a couple of short notes.

Reference L&E Principals 2nd Ed. pp191-193, 199-204
Professional Boatbuilder #59, Alan Gilbert, Speed Predictions, pp60-62
Skene's Elements, 8th Ed, pp86

L&R say use the propeller efficiency figure from the prop charts, but then later they mention fudging that for a water jet which is their example boat. (from 65% down to 50%) The highest Pe I have found is with surface drives at high speed, (40+ knts) up to almost 70%. The lowest I have found is waterjets at low speed, about 42%. The usual figure used to be 50%, so double your ehp for required. Modern twin inclined shafts with 4 bladed wheels are about 60%, outdrives 60-65%. Kinney mentions 10% for folding 2 blade props!

The only way to predict this accurately is to measure boats and compare them with your predictions.

All the best, Tad

[Willallison]

Thanks Tad - and I think you're right... it probably does deserve its own thread....
You're response leads me to another - very broad-reaching, rather off-topic, and definitely worth its own thread - question.... Just how did you drag up those references so quickly? I've been battling with a decent way to archive all the info I gather for ages - time spent studying means that I've not had the time to come up with a decent system yet.....:confused:

[Willallison]

Another point... what we really need is a prediction spreadsheet that includes input for the drive system being used - apart from the Arneson calculator, I don't think I've come across one that allows for the use of anything but traditional shafts & props....

[Tad]

Will,

Here's an urban myth attributed to Einstein. During an interview someone asked Albert his phone number, he replied "I don't know it, but I know where to look it up!".

A long time ago, around 30 years, I started writing all the useful tidbits in a little notebook. These are small, 3" by 5", the first one was ring bound and filled long ago, some of it's penciled entries are unreadable now, and I've moved on to several more. But I still have and use the first one, minus a few pages that have fallen out of the front, just wear and tear. The newer ones are still expanding. Most people I've worked with have copied everything out of these books into their own notebooks.

These booklets start off with the really useful stuff, address and phone number of the current place of business! Then we have decimal equivalents for feet and inches, Planimeter scale correction factors(not used in a while), then a number of pages of conversion factors, then reams of form factors and ratios, SAE bell housing sizes, block coefficients, steel plate weight, chain weights, engine cooling areas, weight estimations coefficients, things like capsize screening formulas, sheeting angles and loads, mast rake for various boats, rig dimensions, construction scantlings, d/l ratios real and guesstimated, various dimensions used by certain builders. Lots of good stuff.

This simple reference is supplemented with files in the filing cabinet. My main reference is called "Design", below this are " Preliminary Design, Sailboat Design, High-Speed Powerboats, Lobsterboats, Sportfishermen, Long-Range Powerboats, etc" These are supplemented with files like "Rudders, Keels, Steering, Engines (a bunch of these), Specifications, Appliances, Gas Turbines, Noise Reduction, etc." In addition I have files full of drawings and brochures of various boats, mostly by size or type, and equipment and hardware files. That plus a file for each job I've done.

Beyond that there are about 400 dedicated books and something upwards of 6000 periodicals in here. I now lose things more often than I find them!

Tad

On your second note, BHP or installed power would just be another column in the spreadsheet with a Pe input up top. Go to it!

[rxcomposite]

There is a Savitsky spreadsheet available on the web at www.hawaii-marine.com/templates. It does not use Excel's Solver or macros or Visual Basic. It does the iterations automatically and evaluates several speeds. It does both the Short and Long Forms of Savitsky's methods.

Atahawaii,
I have heard about this excel solver before but could not access it. I do a lot of excell programming and this will certainly help. How do i access it?

Thanks in advance

[Willallison]

Rx - you pays your money, they send you the stuff......

[Leo Lazauskas]

Those who want something a little more physics-based than Savitsky's method can consult Prof. Ernie Tuck's latest contribution to "Slender Planing Theory" at:

http://internal.maths.adelaide.edu.au/people/etuck/index.html

See the paper towards the bottom of the page.

I look forward to seeing a spreadsheet version ;)

Incidentally, many people here seem to be "stretching" Savitsky's formula in a variety of directions. Has anyone done any experiments on these variants to see whether they are even in the ballpark?

Leo.

[atahawaii]

Incidentally, many people here seem to be "stretching" Savitsky's formula in a variety of directions. Has anyone done any experiments on these variants to see whether they are even in the ballpark?

Leo.

The Savitsky calculations at www.hawaii-marine.com/templates were checked with great scrutiny for validity with Savitsky's sample calculations provided in his original paper. The calculations provided in the template are slightly more accurate than Savitsky's because parabolic instead of linear interpolation was implimented for determining the equilibrium conditions. At the time Savitsky wrote his paper powerful spreadsheet programs were not available. If he wrote it at a later date he might have also incorporated a parobolic interpolation method. I have not checked the other variants available, so I cannot speak for them.

[atahawaii]

Atahawaii,
I have heard about this excel solver before but could not access it. I do a lot of excell programming and this will certainly help. How do i access it?

Thanks in advance

If I recall correctly Solver is in an older version of Excel. But I may be mistaken. There are new tools like "Goal Seek" and "Scenario" in the tools menu of the newer Excel versions. The problem with these alternatives is that you need to directly interact with them to get the answer each time you do the calculations. I was looking for an automatic method that did not involve this personal interaction with these functions for each set of calculations.

The main problem with automating the Savitsky Method is that two formulas need to be iteratively worked out backwards. One good method, for solving this numerical analysis problem, is the Newton Raphson Method. But this method requires programing that uses iterative do loops. So as far as I can tell a macro should be able to do this. But a recent problem I have experienced with macros is that Microsoft is now requiring security certificates for them in the newer versions of Excel. I wanted to completely avoid this hassle and the extra expense, so a propriatary was method was developed in the Savitsky Spreadsheet located at www.hawaii-marine.com/templates. This proprietary method does not involve programming with do loops or use macros or involve time consuming interactions with functions like "Goal Seek" and "Scenario." The goal of automatically generating results is met in the product at this website.

[Leo Lazauskas]

If I recall correctly Solver is in an older version of Excel. But I may be mistaken. There are new tools like "Goal Seek" and "Scenario" in the tools menu of the newer Excel versions. The problem with these alternatives is that you need to directly interact with them to get the answer each time you do the calculations. I was looking for an automatic method that did not involve this personal interaction with these functions for each set of calculations.

The main problem with automating the Savitsky Method is that two formulas need to be iteratively worked out backwards. One good method, for solving this numerical analysis problem, is the Newton Raphson Method. But this method requires programing that uses iterative do loops. So as far as I can tell a macro should be able to do this. But a recent problem I have experienced with macros is that Microsoft is now requiring security certificates for them in the newer versions of Excel. I wanted to completely avoid this hassle and the extra expense, so a propriatary was method was developed in the Savitsky Spreadsheet located at www.hawaii-marine.com/templates. This proprietary method does not involve programming with do loops or use macros or involve time consuming interactions with functions like "Goal Seek" and "Scenario." The goal of automatically generating results is met in the product at this website.

Sorry, I wasn't clear enough about what I meant. I am more concerned whether Savitsky's formula captures the physics of the problem accurately (if at all), especially when it is applied to slightly curved shapes and other variations.

Cheers,
Leo.

[rxcomposite]

Atahawaii,
Thanks.What they have mentioned is a solver that will create a formula based on a graph. manually, i can do this but not all the time. or the more complex formulas. I understand that it is the reverse of a graph. the graph goes in first, then the formula is created.

Rx

[Humberto Rodrìg]

A couple of years ago i asked for a sample of this method and a copy of Savitsky´s paper. I understand you have information about this matter. Would you be so kind as to share it with me.
I have this mail address: humbertor92@hotmail.com
and hrra2004@yahoo.com.mx
thanks in advance

--------------------------------------------------------------------------
Micheler,

I will look into where putting the CFD results should go.

Lines 78 to 83 is where the input for the air drag due to superstructure is placed. This can be modified for lift also but then the total moments must then be recalculated (add lift due to s/str in line 13).

Please note that my e-mail address has changed.

It has also come to my attention that the calculations when using a trim-tab might be slightly off. I will look into it and re-post the spreadsheet if incorrect and as soon as I have time. Sorry for any problems.

[luminary]

Does Savitsky model slamming/wave loads? I see nothing in the model that would suggest it does (eg. sig. wave height). If not, does anyone have anything that does model this phenomena?

thanks

[Davor]

I have programmed Savitsky in program SeaPower. It comprises 28 resistance methods + propellers.

you can download demo program www.sea-power.net

rgds

Davor







If I recall correctly Solver is in an older version of Excel. But I may be mistaken. There are new tools like "Goal Seek" and "Scenario" in the tools menu of the newer Excel versions. The problem with these alternatives is that you need to directly interact with them to get the answer each time you do the calculations. I was looking for an automatic method that did not involve this personal interaction with these functions for each set of calculations.

The main problem with automating the Savitsky Method is that two formulas need to be iteratively worked out backwards. One good method, for solving this numerical analysis problem, is the Newton Raphson Method. But this method requires programing that uses iterative do loops. So as far as I can tell a macro should be able to do this. But a recent problem I have experienced with macros is that Microsoft is now requiring security certificates for them in the newer versions of Excel. I wanted to completely avoid this hassle and the extra expense, so a propriatary was method was developed in the Savitsky Spreadsheet located at www.hawaii-marine.com/templates. This proprietary method does not involve programming with do loops or use macros or involve time consuming interactions with functions like "Goal Seek" and "Scenario." The goal of automatically generating results is met in the product at this website.

[vijay]

i need an excel sheet of savitsy's power prediction can any body please post it and if possible the papers also.

[Dingo]

Here is the Planing spreadsheet with the correction for the trim tabs. Sorry for any inconvienence!

Has anyone looked and used the theory in the paper "A Rational Prismatic Hull Approach for Planing Boat Analysis" by Richard A. Royce, Jan 1994, SNAME local section paper of the Great Lakes (also on the Small Craft CD)?

[Dingo]

I was asked by CGN on another thread what the section by Lewandowski is for on the spreadsheet Planing.xls
This paper set out the dynamic stability for a planing vessel. For a given angle of roll, the restoring moment in ft-lbs is calculated (note: a negative moment means a restoring moment, positive is non-restoring).

[CGN]

Thanks dingo, I much appreciated your help

cheers

[Janamon]

Hi Dingo.

I'm working through your excel spread sheet. Have you a copy in English. I just can't work out some of your symbols. If you could help me that would be great.

Cheers John H
ngaire_john@xtra.co.nz

[vankamal07]

i am new here, and a young naval arc, i want to predict my boat using savitsky method because what i know this method suitable for planning hull.

so i had got all the particular from that formula, but i still confuse with one thing, my boat length overall is 12.0 meter, and LWL is about 10.33 and her draught is 0.53 meter.

what the problem i get, when i calculate the Lk from the savitsky method it give larger than my length's boat. why? and it give the effect for power prediction i getting. here i attached for you the results i get. i just attached the Lk result and speed and power prediction i get only.i just want know, it is what i get is correct or false to compare with my length of boat.

please help me senior and junior :rolleyes:

[Dingo]

vankamal07,
Please give me more details on your vessel especially LCG, displacement, speed etc. I can't analyze any results without knowing more about the vessel. One thing I can tell you is if the LCG has been assumed incorrectly, the value of Lk will vary. Note that Savitsky's method does not take into account the length of the vessel since the beam dimension is what gives it its lift. The length only comes into play to calculate wind resistance etc.
Dingo

[vankamal07]

Thank dingo for your co-operation,

Here i state the particulars of my boat and the results i got.

Boat's particulars:

Weight = 4.5 tonnes,
Estimation LCG = 4.72m from transom,
Beam = 2.76m
Deadrise = 15 degree

Results:
Based on Savitsky's method, i got
at 50 knots,
λω = 2.414,
trim = 1.452,
Lk = 11.31 m
Ds = 0.29
Stotal= 19.03
EHP (hp) = 551.7 hp

So , i hope u can tell me what wrong in my calculation.:idea:

[Dingo]

Vankanal07, I could not get the results exactly that you had since I still do not know your VCG, angle of shaft etc. What I did notice is that under the comments column, it displayed "Note: Not Planing". This method is used only for planing vessels, so Lk could be wrong for your vessel.

[vankamal07]

dingo i appreciate on your help, i am new in this field, so i don't have enough knowledge an experienced, i hope u can guide me...dingo can u give me the methods of your calculation...so that i can study on and find the answer from it...

[Dingo]

If you look inside the tab entitled "Berekenings", you will see all the calculations. On the very right-hand side of the columns I have listed all the references and papers which I used. Hope this helps.

[rxcomposite]

What is the best method to predict the performance of a demi hull planing catamaran? The flat side of the hull is located inboard. Section shape looks like a tunnel boat.

[rahaman]

Dear Dingo Tweedie,

I have found your latest planing spreadsheet. It is very nice work. Thank you very much for sharing your excellent work . Is it possible for you to provide the password of your spreadsheet? I want to do some calculation by using your spreadsheet for my graduate report and I have to submit my report on next Tuesday(2/9/2008). So, if possible please........

Thank you once again.

Rahaman Md. mashiur

[Dingo]

Dear Rahaman,
The spreadsheet should work without needing a password. All calculations and formulas are visable, and the macros work. If the spreadsheet has a problem running, let me know.

[rxcomposite]

Rahaman,
You may try copying the sheet to another spreadsheet. You will lose some macro but the cells can be edited. Dont edit the formulas however.

Dingo,
I tried this to disable the password because I have an officemate who is Dutch Afrikan. He says the words are in Dutch German. He was able to translate closely most of the word anyway. I find your work very complete and I want to know how everything connects so I need to decipher some words.

Rx

[Dingo]

The reason that I lock the spreadsheet is so that no one can tamper with it and re-post it, or submit it as homework by tweaking it and calling it their own. It took me a long time to write it, but, for the purposes for sharing engineering knowledge, I allow the formulas to be seen, and all the macros to be read. Nothing should be hidden; all references are also able to be read (see the right hand side in Berekenings). I am willing to explain my logic and any translations required if asked. I hope that this seems reasonable.

[rahaman]

Dear Mr. Dingo,

Thank you very much for your reply. Your work is really excellent and thank you once again for sharing your knowledge and work with us. I can understand the effort you made for completing your works and I have no intention to do the things you mentioned in your mail because we professionals must have some ethics.I just seek the password only to convert some headings in your calculation that is written not in english. I would like to mentioned here that I have collected all the papers you mentioned in your calculation and I read all of them. So for me now your calculation is understandable and your spreadsheet is running properly.

Thank you very much.


Dear Mr. rxcomposite,

Thank you for your advice but I am not interested to do that.

[Dingo]

Rahaman, what is your e-mail address? I will send you the password.

[Dingo]

Regarding demi-hulls, there is a paper by Mustafa Insel of Turkey that addresses this subject. This is the paper that I was going to use to add to the Planing.xls spreadsheet. My copy is currently in storage since I moved and will take a while to retreive it.

[rahaman]

Dear Mr. Dingo,

My e-mail address is rahaman@triton.naoe.t.u-tokyo.ac.jp

Thank you very much.

Rahaman

[Sercan]

Hi Dingo,

This is an old thread but I still want to reply because I'm confused about the critical trim angle before porpoising. I see the critical angle results from Angeli and from Lewandovski on the excel sheet. And they are different. On the other hand some people uses Savitsky 1964 in order to find the critical angle. Which one is more realistic? And also what to do for warped hulls, because I think all these methods are for prismatic hulls.
If there is anybody out there still interested in the subject Im waiting for some advices.

Thank You very much
Sercan

[Dingo]

Sercan,

Savitsky, from memory, predicted the running trim angle, not the critical trim angle (note, from memory, but please correct me if I am wrong). Angeli and Lewandovski gave different theories on when the porposing angle occurs. My opinion is to use the lesser of these angles to be on the safe side when designing the vessel.
Regarding warped hulls, this spreadsheet takes into account the warped hull. That is why the deadrise at the transom and amidships is required; they do not have to be the same.

Dingo

[Paul Kotzebue]

Hey Dingo,

It's been awhile since the AAA days in Bremerton. Good to know you're still at it.

[Yellowjacket]

While we are on the subject of your most excellent spreadsheet, perhaps you could explain what the limitations are on the maximum valid speed for the analysis.

The maximum speed is calculated as 13 x the square root of (g times the beam) all over 1.688.

I was curious as to what part of the theory this is based on and why it this is so.

Also many thanks for creating this fine piece of work, it obvoiusly took a long time and it has been a huge help in some analysis I was doing.

Thanks,

[Sercan]

Sercan,

Savitsky, from memory, predicted the running trim angle, not the critical trim angle (note, from memory, but please correct me if I am wrong). Angeli and Lewandovski gave different theories on when the porposing angle occurs. My opinion is to use the lesser of these angles to be on the safe side when designing the vessel.
Regarding warped hulls, this spreadsheet takes into account the warped hull. That is why the deadrise at the transom and amidships is required; they do not have to be the same.

Dingo

Thank you very much for your reply
If you check Savitsky 64 , page 92 you will see that there is a graph showing purpoising limits for prismatic planing hulls ( for 0,10 and 20 degrees of deadrise angle). I think you are right , Its a good idea to use the lesser of these angles.

[Victor T]

Thank you very much for your reply
If you check Savitsky 64 , page 92 you will see that there is a graph showing purpoising limits for prismatic planing hulls ( for 0,10 and 20 degrees of deadrise angle). I think you are right , Its a good idea to use the lesser of these angles.

Porpoising regime of planing (by Savitsky 64) is calcs in Free!ship Plus v3.07+.

[Dingo]

Yellowjacket,
From memory, Savitsky tested a few models and obtained parametric formulas for their performance. Any theory is only valid for the particular set of models, speeds etc. that were tested. In this case, I assume that Savitsky concluded that his theory was only valid within given parametric boundaries, hence the speeds were valid from 0.6 x sqrt(gB) up to 13 x sqrt(gB). Beyond these speeds, the theory may or may not be valid.

[Yellowjacket]

Yellowjacket,
From memory, Savitsky tested a few models and obtained parametric formulas for their performance. Any theory is only valid for the particular set of models, speeds etc. that were tested. In this case, I assume that Savitsky concluded that his theory was only valid within given parametric boundaries, hence the speeds were valid from 0.6 x sqrt(gB) up to 13 x sqrt(gB). Beyond these speeds, the theory may or may not be valid.

Dingo,

Thanks,

I was looking at some analysis for high speed small monohulls with zero deadrise, and the analysis showed improvements for narrower planing surfaces. As you go to higher speeds, the trim angles are getting very small, so it is not suprising that a narrower surface will provide lower drag since you can't get the CG far enough aft to make the planing surface efficient.

The problem was that I was quickly getting below the minimum beam and was wondering why the analysis was limited at this higher speed. As we look at very high speed hulls, such as padded v hulls, you can easily exceed the recommended speed limits for Savitski so perhaps I should look at the work that Jim Russel has done in this area as this may be more appropriate.

Not sure myself as to why there should be an upper speed limit for the analysis based on beam. I can see a lower speed limit, since the edge effects become pronounced and you are falling off a plane. But at higher speeds, the trim angles become lower and the effects of edge losses are not as pronounced. What I'm saying is that I can understand an upper limit for the analysis, but I had trouble understanding why it would be based on the width of the planing surface.

[sandmanclose]

Dear Mr. Dingo
may be I late to read this forum, but I really interst with your spreadshet, I really want convert your program in matlab language, can you give me your password sheet protection
please send to sandmanclose@yahoo.com

[Adis]

Dear Mr. Dingo,

I would like to thank you for giving in public such a wonderful spreadsheet. It is an amazing piece of work, and I appreciate your kindness to allow all of us to have such a valuable tool in our hands!!!

Thank you very much again!!!;) ;) ;)

[XXL]

Dear Dingo,

I programmed Savitsky equations using Basic HP on a workstation, then with HTBASIC on a PC years ago., for my studies.
I would like to program it now under Excel and to have a basis for a transverse step planing hull calc. using modified Savitsky equations.
Would it be possible to have the password of your file in order to have a sound basis for my new program of hulls with steps?
Thanks a lot for your answer and for your help.

kind regards
Michel

[peterraymond]

I have compared probably the simplest Savitsky equation to the high aspect ratio calculation in Fluid-Dynamic Drag by S. F. Hoener. I found that somewhere before an aspect ratio of 5 the Savitsky calculation gave a higher lift coefficient than airfoil theory would give for even an infinite aspect ratio.

With a stepped hull the pitch angle is controlled by the geometry of the step and you typically can have higher aspect ratios, at least at higher speeds. The higher aspect ratios have better lift to drag too. I'd just suggest being a little careful and confirm with some reasonable reference that you are in a regime were Savitsky is valid.

Savitsky is I think also simplified compared to many real boat hulls. Ocean racing deep-V hulls all have strakes that are spaced and optimized, including ones that control trim angles by not going all the way to the transom. Maybe for this case Savitski would over estimate drag.

Many high speed boats also use air pressure to produce lift and isn't this outside Savitsky too?

[Dingo]

XXL,

Please give me your e-mail address?

[u4ea32]

XXL,

Will you provide us all with the enhancement to support steps?

Dingo,

Can you provide a version without macros? The visual basic macros don't work on Macs.

[Dingo]

u4ea32,

Sorry, but without macros it would be a tedious process to do. I would suggest running the spreadsheet on Windows, print out the macro code, and rewrite the code in whatever language you desire.

XXL, I agree with u4ea32; will you provide us all with the step mods?

[Ed Glowacki]

Go to this web page to get the code I wrote in 1981 for the old programmable HP-41C. The search technique I describe on page 3 to solve for those terms may be helpful to you. Frankly I don't know if Excel can search for solutions (within a given tolerance) but it may be worth a look.

http://www.boatdesign.net/forums/design-software/planing-boat-power-prediction-22579.html#post203228

Good luck!

[Paul Kotzebue]

Frankly I don't know if Excel can search for solutions (within a given tolerance) but it may be worth a look.


I use the "Goal Seek" tool in Excel to find solutions in my Savitsky short form spreadsheet. It's easier than writing macros for me.

[Mat-C]

1st of all Dingo, congrats and thanks for providing such a wonderful resource... don't suppose you have one for scantling calcs too do you!?!;)

I was wondering if you could tell me what some of the correct entries would be if using the spreadsheet for outboard or sterndrive installations...ie I presume the inputs for all the rudder shaft and strut entries ought to be set to zero..?

[Dingo]

Mat-C,
A outboard or sterndrive can still have a angle of thrust, and added resistance due to the leg. In my opinion (note, this is my opinion, so by definition I can't be wrong!) I would add a factor for the extra resistance (drag) to the final results. This would be the best practically; a CFD model will give better results.
Note that this theory (and especially the spreadsheet) is only a basic estimate of the resistance; model testing will give better results.

[Willallison]

Mat,
Dingo's right - there's absolutely no question that there is drag created by the 'leg' of an o/b or sterndrive. In practice, however, I've found that the results are very close with the inputs that you mentioned set to zero even though this is technically not correct. This is probably down to the choice of factor one chooses in converting from effective horsepower (EHP) to the actual required shaft horsepower.
Depending on the type, I've found good correlation using a factor of between 0.6 and 0.65

There's at least one scantling spreadsheet (using Gerr's rules) in the spreadsheet library....If you come across any others, be sure and let me know!;)

[rxcomposite]

Dear Dingo,

I programmed Savitsky equations using Basic HP on a workstation, then with HTBASIC on a PC years ago., for my studies.
I would like to program it now under Excel and to have a basis for a transverse step planing hull calc. using modified Savitsky equations.
Would it be possible to have the password of your file in order to have a sound basis for my new program of hulls with steps?
Thanks a lot for your answer and for your help.

kind regards
Michel

I was also planning to do this but if you beat me to it, good. Please send me a copy.

A planing boat is like an airplane that is cruising. Similarly, a kite (flat plate) is in a perpetual stall condition with the speed of the wind as velocity and the pull (tug) on the string as thrust. A program was written in Java about this, Search Aerodynamics/NASA about kite design.

I plan to write the code in excel but I have to figure out a way to present the integration of finding the Center of Pressure at varying angle of attack. The projected area would be similar to a series of triangles, one on top of the other. Any ideas?

If I can present varying areas at varying angle of attack, maybe I can integrate it into Dingo's work to balance it with the other forces (thrust, drag, vector quantities, lift, ect). I intend to work only on the projected areas of the hull.

Rx

[dustycrockett]

...
I was wondering if you could tell me what some of the correct entries would be if using the spreadsheet for outboard or sterndrive installations...ie I presume the inputs for all the rudder shaft and strut entries ought to be set to zero..?

Mat, For my outboard, I used the dimensions of the lower unit below the keel for "Rudder", and set "Shaft" and "Strut" to zero. I/O stern drive should work the same. I'm getting very close to observed results (depending on how you evaluate the efficiency of the drive train).

dingo, I really admire your spreadsheet work.
just a couple things I'm unsure about --
Angle of thrust line -- I'm entering as a negative value as my propshaft is pointing down (as opposed to the shaft in your illustration), does that sound right?
Lwl -- not sure -- is the waterline at rest, or the waterline on plane?

thanks!!

[Dingo]

Waterline is static waterline.

It seems that using a negative value for the angle of thrust line is a no-no. I looked at the formulas and using a negative angle would give a negative drag (!) and a positive "lift" force, whereas in fact it should be positive drag (acting aftwards) and negative "lift" (since, if a shaft, a normal force acting downwards would be experienced).

I will have to tweak the spreadsheet and re-submit it.

Dingo

[dustycrockett]

I'm getting barely 1% difference between -5º and +5º, with +5º being favorable (reduces hp requirement).

"positive lift force" seemed reasonable since the downward force on the stern tends to lift the bow. It also seems to reduce drag, as RPMs rise as you trim out. I haven't got a clue how to model it, though. On a boat with power trim you adjust the angle on the fly. Never gave it much thought, but I wonder if direction of thrust aligns with direction of travel....

any rate, in my attempt to validate my understanding of your model by applying it to a boat with known parameters, I'm getting about 3% variance (est 33 knots vs. 32 actual). That's the equivalent of about a 3-inch error in my LCG estimate.

The implication here is that I could increase top speed by 5% just by moving one deepcycle battery about 10 feet aft. ...hmmmmmm...

It's a better prediction than I expected, and especially considering hull & engine both over 30 years old.

Most difficult parameter to measure might well be "actual horsepower". I know I'm losing right at 10% at the prop, and assumed a 15% crankshaft/propshaft difference in rated horsepower. Most would assume some power loss due to age of the engine; RPMs tell a different story though.

[fastpowerboats]

Try software at AeroMarine Research for tunnel hull design/performance (http://www.aeromarineresearch.com/tbdp6.html) and for vee hull design/performance (http://www.aeromarineresearch.com/vbdp.html). I think the algorithms used are modified Savitsky formulae, but seems very accurate. They've got alot of good graphic presentation of results (http://www.aeromarineresearch.com/tbdp6/graphscreen1.html). Their website also has several free papers (http://www.aeromarineresearch.com/articles.html) written on powerboat performance.

[indra.s]

dear mr.dingo

This spreadsheet is very helpful in doing my final project. please send me the english version of this spreadsheet. it would really help me in working on final project. :)



best regards

[Dingo]

Sorry everyone, but I will not be making a translation of the spreadsheet. It will take awhile and my custom with my programs is the user interface is in English, but the background calcs and notes are written in Dutch or Afrikaans. The input parts are in English as well as the information in the "help" tab, but the calculations use Dutch for the names etc. in the calculations. If one has the papers by Savitsky and others that I reference on the right-hand side of the calculations, it would be easy to follow the process. The headings under "Berekenings" (Calculations) are as follows: aanhangsels (appendages), luchtweerstand (air resistance), rolstabiliteit (roll stability), zeewaardigheid (seaworthiness).

[Flev]

Dear Dingo,
is it correct the formula for M-factor in your sheet?

I think the 1/2 factor is wrong....

Flev

[Dingo]

I have somewhere in my papers that the factor 1/2 was added to more closely resemble what actually happens. I could not find where I got this value, but it is not a typo. I have found that it more accurately predict the pre-planing hump resistance. If I can track down where I found this, I will let you know. If anyone else knows of where this factor was referenced from, please let me know so I can add it into the references in the spreadsheet.

[Olav]

Dingo is right. There's a paper called "Design of Propulsion Systems for High-Speed Craft" by Donald L. Blount and Robert J. Bartee in which they feature this particular factor:

[...]

The authors use a variation of the Blount/Fox resistance prediction method (reference [15]) for design studies involving hard chine craft. This method was originally presented in 1976 as an "M" factor multiplier for the Savitsky method [6] as a means to improve hull resistance predictions for semi-planing speeds. Experience since 1976 indicates that this "M" factor tends to favor resistance predictions for heavy, beamy craft. Thus, the following variation of the original "M" factor is now recommended:

M' = [K(M-1)+1] for 0 ≤ K ≤ 1

K is a correlation factor for refining the hull resistance at hump speed. The following indicates the influence of varying K:

K COMMENTS
0.0 Original simplified Savitsky resistance prediction

0.5 Realistic hump speed resistance for craft of normal proportions and loading

1.0 Original Blout/Fox resistance prediction


Wherever practical, hull resistance should be taken from model tests or from vessels currently in service.

[...]

BIBLIOGRAPHY:

[...]

6. Savitsky, D., "Hydrodynamic Design of Planing Hulls", Marine Technology, Vol. 1, No. 1, Oct. 1964

[...]

15. Blount, D. L., and Fox, D. L., "Small Craft Power Predictions", Marine Technology, Jan. 1976

[...]

[Ricardo Rios]

I have the sheet Dingo

"M"-Dingo=SI( 0,98 + 0,5*( 2*(LZP/B)^1,45*EXP(-2*(Fn_v - 0,85)) - 3*(LZP/B)*EXP(-3*(Fn_v - 0,85)) ) >= 0,5; 0,98 + 0,5*( 2*(LZP/B)^1,45*EXP(-2*(Fn_v - 0,85)) - 3*(LZP/B)*EXP(-3*(Fn_v - 0,85)) ); 0,5 )


I have two comments

1. By limiting factor "M"> = 0.5?,
2. the factor "M" original "blount and fox" is:

M=0,98 + 2*( 2*(LZP/B)^1,45*EXP(-2*(Fn_v - 0,85)) - 3*(LZP/B)*EXP(-3*(Fn_v - 0,85)

on this factor "M" can apply that "Olav" says

PD:sorry for my English

[Dingo]

Sorry Ricardo, was there a question?

[Ricardo Rios]

I have the publication "Small-craft power prediction" I read it and said that M:

M= 0.98+2*(LCG/Bpx)^1.45*e^(-2(Fv-0.85))-3(LCG/Bpx)*e^(-3(Fv-0.85))

I have de publication "Design of propulsion systems for high-speed craft" I read it and said:

the following variation of the original "M" factor is now recommended

M'=K(M-1)+1 for 0=< K=<1

K is a correlation facto for refining the hull resistance at hump speed. The following indicates the influence of varying K:

K=0 for original simplified Savitsky resistance prediccion
K=0.5 for realistic hump speed resistance for craft of normal proportions and loading
k=1 for original Blount/Fox resistance prediction

in the spreadsheet "prestasie"is not expressed in this way, but the numerical meaning is the same, good job Dingo I was a little confused.

The coefficient M is multiplied by the bare hull resistance, Why? in "prestasie" appears multiplied by the resistance of the hull with appendages?

PD:Please excuse my bad grammar, do not speak English.

[Dingo]

Ricardo, thank you for that excellent catch. You should play cricket for Australia! I have attached a corrected spreadsheet here (the values did not vary much, but I believe to keep errors down whenever possible). If anyone sees another error, please let me know.

Does anyone know how to update the spreadsheet in the BoatDesign.net library?

[tangi]

Hello , i'm new on the forum
i'm from FRANCE , not very in english..,
i have made my own boat for pleasure, small fast boat : Rib , with aluminium hull, 6,95m, 900kg with engine and fuel, the engine : mercury optimax 250XS ( 270hp at prop shaft ).
actual max speed : 62kt.
constant V hull 24° with 3 raws of strake.
http://pneuboat.com/frames.php?url_frame=/serv-bibl/modules/pages_perso/aff_pp.php&num_pp=1349


Hello Dingo!
so , i've tried your excel savitsky model , to test my hull: it's seem's to be ok = 60kt for 262 effective HP. !! ( but for each speed , comments is :"Note: not planing" , it's stange ? )

i have somme question about the savitsky model :
-
1-the model don't take the influence of stake for the lift force ? important , not important ?

2-in your excel model , i' have test a boat we have at office , 11m, 6000kg, V hull : 21°at transom, 26° at mid lenght, with two 315HP + zdrive ( Nb of prop = 2 ( in motorisation section)
the excel result : 37kt for 328hp effective , the boat run à 37-38kt, so ok!
-> to know how many HP i need if i mount only one engine , i've pass the value " Nb of prop " at 1 ( for one engine ?, right ?) --> calculate --> result effective power would be 325HP !! i ve imagned a single 500HP or something around that !!

could you said me where i've do a mistake?

I hope you could help me.

thank's and best regards

Tangi

[Dingo]

Tangi, what is the LCG of the boat? Also waterline length and beam? Otherwise post the spreadsheet to me at Dingo at Engineer dot com so I see all the parameters.

[Dingo]

Tangi,

Effective power is defined as P[eff] = D x V. It is not the value of the engine power P[eng], but the amount of power required to tow the boat due to its drag. When you enter prop = 1, then the drag decreases since there is only one prop and shaft in the water, and the resistance is lower (what you would expect). To work out the engine power required, P[eng] = P[eff] / propulsive efficiency (due to propeller, shaft and wake losses). If you are using two engines, then each engine would only have to have roughly half of what you worked out for one engine.

Regarding the waterjet in your e-mail, if the waterjet is not matched to the engine or desired speed of the vessel, then it will have more losses compared to a propeller. Waterjets (depends on the model) sometimes are only efficient at higher speeds like +30 knots.

I hope I explained to your satisfaction.

Dingo

[tangi]

hello thank's.

so , if i have understood your explications :

for a calculate total effpower of 328hp ( 2 zdrive )

the power engine needed will be : 328 / 0.65 ( example of total efficiency of transmission, prop included ) = 504hp so 2 engine with around 250hp at crankshaft, It's ok ?.

what is the common efficiency used for a " standard prop "?
----------------------------------------" standard waterjet" ?
on our waterjet boat we have the good motor rpm for the jet + impeller, but with the same motor+Z-drive vs jet we have a différence of 6kt ( around +15% of efficiency loose for waterjet vs prop !!)..

thank's for all.

Tangi