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Modal wave period Article rated 3.0/5.0
Why does the resistance not change when I change the modal wave period? The likely reason is that not all of the methods to predict the added resistance in seas use the modal wave period. The planing...
Different outboard-inboard engines Article rated 3.0/5.0
I have an application with four engines of two types, and of course, two each of the two different propellers. The mission is to operate the principal engines while conducting surveys and to kick in a...
Effect of the “Trim by stern” field Article rated 3.0/5.0
When entering data for the “Trim by stern” field for a resistance prediction in NavCad, is it appropriate to enter hull coefficients in the trimmed condition and include the trim angle, or...
Bottom loading of planing hulls Article rated 2.9/5.0
We are working on a small planing vessel with a large deadweight requirement, and are able to get NavCad resistance results for all speeds. However, the jet drive vendor feels that our bottom loading ...
NavCad and Windows 7 Article rated 3.0/5.0
Can you tell me if NavCad is compatible with Windows 7? The quick answer is yes. We have two Windows 7 computers (one each of 32-bit and 64-bit) in-house for testing. NavCad 2009 (and prior) works a...
Wind resistance methods Article rated 3.0/5.0
We are conducting a study for a research ship (with a very high superstructure) that includes an evaluation of wind resistance. The two methods that we are using – “Taylor head wind”...
Planing hull drag affected by chine length (LCH) Article rated 3.0/5.0
I have noticed that my planing hull resistance prediction results change when I change chine length (LCH). My understanding was that LCH was a data check parameter only and did not affect drag. Is thi...
Transom interceptors Article rated 3.0/5.0
Is there any plan to incorporate the ability to evaluate interceptors for planing hulls? We seem to be putting them on more and more craft these days. Interceptors are indeed “on our radar&rdqu...
Form factors and expansion results Article rated 3.0/5.0
When using a 3D form factor, total resistance is computed to be less than without the use of a form factor.  How can this be possible? This is indeed the correct behavior. Your confusion may be ...
Printing KT-KQ curve Article rated 2.9/5.0
Can I generate the propeller coefficients KT, KQ and ETA for a given geometry without entering ship data? Yes you can, but you do this without actually running a Propulsion calculation (which would n...
Resistance-weight ratio Article rated 3.0/5.0
I’m working on a problem where I need to separate the components of resistance and look at each individually. I like to use displacement to normalize, but when I take Rr, Rw, or Rbare (kN) and d...
CPP pitch and relative-rotative efficiency prediction Article rated 3.0/5.0
I am performing a preliminary propulsion analysis and am sizing a CPP.  I am unclear on the “Pitch” input under “Project data – Propulsor” because I am using the Com...
Entering custom resistance data Article rated 3.0/5.0
I am working on the design of a boat that will be used to push a small train of barges. The client gave us the resistance of the barges. How can I add this barge resistance into my NavCad prediction? ...
Engine files Article rated 2.9/5.0
Why don’t you provide a library of engine files, at least for the most common manufacturers? There are a number of reasons why we do not provide engine files. 1. We try to deliver the greatest...
Effect of LCB shift on drag Article rated 3.0/5.0
I have been working on power predictions for a containership hull form. The parent hull had an LCB forward of midship, but the new vessel’s weight distribution would allow me to move the LCB aft...
Stern shape terminology Article rated 3.0/5.0
The Help text indicates that a vertical section slope is “U shape” and a flat section slope is “V shape”. This seems counter-intuitive to me. If I have a stern shape that has v...
Outboard vs inboard turning propellers Article rated 3.0/5.0
Which is better – propellers that turn inboard or outboard? The typical orientation is for propellers to turn “outboard” (at the top) as viewed from the stern. (For example, a starb...
Evaluating skewed propellers Article rated 3.1/5.0
Skew is the “sweeping back” of a propeller blade, as shown in the image below. These two propeller blades are identical, except for skew.
Acceleration analysis with a towed body Article rated 3.0/5.0
I need to conduct an acceleration analysis for a ship towing another ship. I can predict the drag of the towed ship separately, and add it as an additional resistance. But, how can I account for the &...
Design of entrance angle Article rated 3.0/5.0
I am working on a motor yacht hull design. I have looked at various publications that show half angle of entrance for a number of vessel types, but hull parameters for motor yachts seem relatively sca...
Transport efficiency (or effectiveness) Article rated 3.0/5.0
I found your paper “Sea Trial Analysis: The Value In the Data” very interesting, especially about transport efficiency. Is there a way to plot this in NavCad? If not, could you please writ...
Waterjet solution warning Article rated 3.0/5.0
I am running a propulsion analysis for a boat with a waterjet. Why would I get a “Calculation interrupt” warning stating that it “Cannot reach solution”? The most likely reaso...
Sensitivity analysis Article rated 3.0/5.0
I did a sensitivity analysis for a container ship and I found some of the conclusions quite surprising. It shows that if you increase LWL, BWL, T and CX, the resistance will decrease. I can see for LW...
Savitsky trim and dynamic lift Article rated 3.0/5.0
I would like to use the Savitsky equations in NavCad to predict Trim and Dynamic Lift.  I see that there is a column predicting trim, but I do not see dynamic lift.  Does NavCad output these...
Design of bulbous bows Article rated 3.0/5.0
I am researching the efficiency of bulbous bows, and am hoping to find a relatively simple way to calculate the optimum size. Can I use the Holtrop (or other) method in NavCad to do this? The answer ...
Contributions of the nozzle in ducted propeller performance Article rated 3.0/5.0
Can you give me an overview of the nozzle’s contribution to the performance of a ducted propeller? Great question – so I wrote the reply as a small article for our latest issue of the Mar...
"Aligned prediction" options Article rated 3.0/5.0
We are preparing a speed/power calculation for a vessel very similar to one of our existing designs. The only difference is that the new design will be about 7% longer.  We want to use model test...
Savitsky dynamic trim Article rated 3.2/5.0
I’m trying to get a better understanding of the Savitsky trim angle results. Are these relative to the given hull geometry or do they include the static trim of the hull as well? The short answ...
Get-Y-from-X utility Article rated 3.0/5.0
I am trying to use the the “Get Y from X” utility (from the “Analysis” menu) to get information from a graph. How should I use this tool? This utility simply allows you to fin...
Temperature correction of water properties Article rated 3.0/5.0
How can I predict the effect of temperature on water density and viscosity for my resistance predictions? As you know, temperature does affect the density and viscosity of water. NavCad (and our othe...
Predicting drag for OSVs Article rated 3.0/5.0
In your experience, what is the best prediction method for Offshore Supply Vessels (OSVs)? I have had good success modeling the bare-hull drag of OSVs with the Holtrop method, even given the very hig...
Under-hull boat drive systems Article rated 3.1/5.0
I read the article about contra-rotating stern-drive propellers. Is this information applicable to under-hull boat drive systems? Almost everything can be applied as written to the recently introduce...
Path/File access error Article rated 3.0/5.0
When we try to create a report after a resistance or powering calculation in NavCad 2008, we receive a “Path/File access” error message, and report is not generated. Please help us in solv...
Propeller tunnels Article rated 3.0/5.0
We are developing a new project for a 30 m yacht. The propulsion is by means of two 5 bladed propellers, and we want to propose a modification of the aft region including some type of tunnel in order ...
Contra-rotating stern-drive propellers Article rated 3.2/5.0
Can you provide any guidance on how to model a stern-drive with contra-rotating propellers in NavCad?   We have never had much success in our efforts to obtain reliable performance and efficien...
Towed barge resistance Article rated 3.1/5.0
We are running NavCad 2004. Is it possible to access the Dai towed barge resistance as the bare-hull resistance calculation, similar to Holtrop, Oortmerssen, etc.?  We are trying to establish the...
NavCad on 64-bit Windows Article rated 3.1/5.0
I am having some difficulty with NavCad on a computer running 64-bit Windows, notably with the security key driver installation and updates. Can you help? NavCad itself functions properly on 64-bit W...
Planing hull geometry definitions Article rated 3.0/5.0
Some time ago, we bought NavCad and it is very useful for us. Now, I would like to clear my mind about some definitions such as “BL”, “Deadrise angle”, and others. Specifically...
Rudder offset position Article rated 3.0/5.0
Do you have any thoughts on whether it is better to offset a rudder outboard or inboard of the propeller shaft (to allow for the removal of the shaft without dismantling the rudder) for twin-screw app...
Simple propeller analysis Article rated 3.0/5.0
Is there any way I can get NavCad to just calculate thrust vs speed for a given propeller independent of any hull or environment information?  (I realize I would need to input some assumptions fo...
NavCad updates Article rated 3.0/5.0
Question – if we want to update a NavCad installation do we need to run each update since their last individual update, or will the latest update do it all? Generally, each update installation ...
Appendage drag multiplier Article rated 3.0/5.0
Quick question for you.  From your experience, what presently do you feel is a good number to use for the Drag Multiplier on the Appendage Data page under Appendage Parameters.  The program&...
Display of catamaran performance results Article rated 3.0/5.0
I am designing a catamaran, and I have a question.  Are the resistance results displayed for one demihull or for both? For Resistance calculations, the results are for the whole system (i.e., t...
Report cache problem Article rated 3.0/5.0
I am having trouble creating reports with NavCad. When I click on any of the report tools, I get “Run-time error 75″.  Please help! When NavCad shows a report, it creates a temporary...
Cavitation breakdown Article rated 3.0/5.0
We recently built and delivered propellers for 12m planing hull. We made an estimate of 29-30 kts top speed (for the installed engine power), which was also predicted by the boatbuilder’s naval ...
Sea trial prediction techniques Article rated 3.0/5.0
The shipyard I work for just completed speed trials at a lower draft than the model was tested at.  The speed trials were conducted with 3.5 m aft draft and 3.0 m forward draft, while the model t...
Sizing tunnel thrusters Article rated 3.0/5.0
Do you have a info on using NavCad to size bow thrusters propellers? Predicting performance of propellers in a pipe tunnel (e.g., bow thrusters) can be done in NavCad, but you need to use a suitable ...
Aertssen seas drag Article rated 3.0/5.0
I want to run a containership hull form in a sea state and was trying to use the “Modified Aertssen” method for the added resistance component, however when I use that algorithm, I get zer...
Fixing WMF file name extension Article rated 3.0/5.0
There appears to be some odd file naming behavior with the export of WMF plots in NavCad. In certain circumstances, the export function appends “WMF” to the file name extension (e.g., &l...
Barge resistance prediction Article rated 3.0/5.0
I’ve been trying to predict the resistance for a single 400 ft x 130 ft barge. However, I haven’t been able to come up with what seems to be an “appropriate” number. I’ve...
Load sharing Article rated 3.0/5.0
he vessel I am evaluating has three propulsion units, two outboard and one on centerline. If the centerline shaft has a different engine of less power, can you explain how to handle that within NavCad...
File path errors Article rated 3.0/5.0
I have not used NavCad for a while, and now the attached message is generated when opening up an existing project (.nc5) and trying to re-calculate Resistance Analysis.      Erro...
Where to measure the max chine Article rated 3.0/5.0
I have a quick question considering the “Max Chine Beam”. If there is a chine flat, which chine do you measure beam and projected bottom to? Is this to the inside chine, where the deadrise...
Entering propulsion coefficients from a model test Article rated 3.0/5.0
I want use the wake fraction and thrust deduction data from a model test.  I can select [User] on the window of “Propulsion analysis”, but I can not find the window for data input. Y...
CPP off-design pitch variations Article rated 3.0/5.0
I would like to provide some additional comments to a previous NavCad Tech Support Group email about CPP off-design pitch variation. In particular, a review of one set of CPP model tests provides som...
CPP off-design correction Article rated 3.0/5.0
I have a question about the off-design prediction for CPP analysis. Is the efficiency interpolated from the various fixed-pitch series (such as the B-series) for the different pitch settings? If you r...
Evaluation of catamaran demihulls Article rated 3.0/5.0
We are building a 24 meter sailing catamaran. We want to evaluate the speed and performance but we have many doubts about what method to use. The dimensions of the vessel are: LWL/B-demihull = 7.1; B-...
Interpreting the "Method Expert" listings Article rated 3.0/5.0
I am running a resistance prediction for a tug using the “Hamburg LBS” method, which is ranked first according to the “Method Expert”. Why are all the speeds in the performance...
Importing IDF files Article rated 3.0/5.0
We are running NavCad 2007 and are having problems importing the IDF files produced by GHS v10.5. We are following the instructions on the manual and find the file format the same as the one published...
Wavemaking curve shape Article rated 3.0/5.0
I am working on power predictions for a 20m tug.  In the Vel vs Rbare curve, there is a big depression at 8 knots. Can you help me understand this? Actually, it is the wavemaking hump just beyon...
Catamaran data Article rated 3.0/5.0
Could NavCad be updated so that you can enter the total displacement of a catamaran? Right now I need to type in half the displacement. This is confusing for the people reading the report. For comple...
Definition of chine beam with spray rails Article rated 3.0/5.0
I have a question how to define breadth at chine for two of our designs, as shown in the attached drawing. Both models have spray rails at the chine, either external (model B) or integrated (model A)....
Gawn series number of blades Article rated 3.1/5.0
We have noticed that in NavCad there are two Gawn series. The Gawn AEW can handle 2-7 blades and Gawn KCA only 3 blades.We thought the original Gawn series only had the data for 3 blades, so we a
NavCad vessel "Scope" field Article rated 3.0/5.0
Which vessel "Scope" should I choose from the options - Undefined, ITTC-78 (CT), or Planing - when I don't know much about the subject yacht? Or for different vessels, such as twin-hull craft, speedbo...
Propeller KT-KQ file scale basis Article rated 3.2/5.0
When using NavCad's reference propeller (for" Aligned series" or "KTKQ data"), should I be using one of the Rn basis options or setting it to "Unknown"?   Let's start by considering why we need...
 

 
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