Michlet

How work Michlet?

We introduce a table of offsets in in.mlt. There, the maximum half beams is 0.079, however in the Michlet window appears B = 0.168 m instead 0.158 m.

Consequently the coefficients and physical characteristics are not from my hull.

Michlet is a family of hulls, like propellers Troost series, that approach my hull to one of the hulls of the serie?

 

Michlet manual:
http://www.cyberiad.net/library/pdf/michman_090110.pdf

Or, in spanish:
http://www.cyberiad.net/library/pdf/Michlet_805_Manual_Spanish.pdf

Or ask Leo Lazauskas, he is a member of this site.

 

The manual do not explain how Michlet works.

Leo is invited.

 

Yes, you are right. The theory behind Michlet was published by J. H. Michell, and you can find what appears to be a transcript of the original paper in this site:
http://www.science.sakhalin.ru/Ship/JHM.html

A brief summary of the theory is also given in this paper, co-written by the author of the software, L. Lazauskas, and others:
http://www.scullen.com.au/DSc/Publications/tuck_scullen_lazauskas_00e.pdf

If it is not what you are looking for, and you are trying to understand how a particular aspect of software programming was done, then you could contact L. Lazauskas. He is a nice guy, and usually replies to quests if he has time.

 

Fred
Michlet is not a family of hulls.

The viscous drag is determined by either the ITTC1957 friction line or Grigson friction line, depending on what you select. The default form factor is 1 but there is provision to alter it. Using 1 is satisfactory unless you have a large included angle at the bow and stern.

The wave drag is determined from the fundamental physics using Mitchell's thin ship theory. This has been validated with L/B as small as 4.5.

The transom drag, if one is present, is determined by the reduced water pressure acting on it as the immersion reduces.

Note: You have a printing error in your question with half beam at 0.79. You should have 0.079.

The difference is due to the resolution of the displacement. The Delftship to Michlet export file has only 3 decimal places. I believe Michlet is proportioning the beam values to get the correct displacement. If you adjust the volume value to the correct 4 decimal places in the Michlet in.mlt file you should be able to get the beam value in the window to agree with the half beams in the offset table. This is only a problem if you are working with small hulls. Normally 3 decimal places is satisfactory.

Rick W

 

Fred
Delftship only provides volume to 3 decimal places. So in metric the resolution is to the nearest litre.

One way to determine the correct volume value to more places is to scale hull 10 times in all dimensions. This will give you 1000 times the volume so you will have an accurate figure from Delftship to manually place in the Michlet in.mlt file.

The block coefficient in the Delftship file is also accurate enough to get more decimal places on the volume. So you can use the block dimensions in combination with the coefficient to determine volume to more decimal places then manually load into the Michlet in.mlt file.

Rick

 

Rick

Thanks more one time for your reply.

In all calculation concerned frictional resistance we need use one of these methods that you appoint because the frictional resistance is attached to Reynolds number that is not relationed with direct informations from tank tests results because the model velocity , unlike residuary resistance that we can have direct information from tank tests results.
So, we can do a family of boats that if we have some hulls tested in tank. We can form a family that we can extrapolated the results. Like propellers families, series 60 and others boat series.
The great problem for me is accept that I furnish a table of offsets for a hull that have maximum beam 0,158 m and Michlet give to me a result for a hull that have B = 0.168 m a wrong Cp and a wrong wetted area.
Is not my hull!
My hull have maximum waterline beam = 0,158 m, Cp = 0,58 and wetted area = 0,142 m² and the hull that Michlet work have Bmax =0,168 m; wetted area = 0,155 m² and Cp = 0,62.
Is not my hull!
I think that is not a problem "The difference is due to the resolution of the displacement."
When I do the drawing my hidrostatics values from Freeship are for 1 mm increase waterlines.
That offsets that I give for Michlet is for a hull with Volume = 0.00400 t.
If we calculate that areas from that offsets and integrated them we have a Volume = 0.004 t.
Sorry, but I think that is not a resolution problem.
Yes, we can change the scale for 1 to 10 but the problem do not modify.
All is scaled.

Sorry Rick but I do not have yet a good response.

 

daiquiri

Thanks very much, I will study them.
I am waiting for Leo, really he is a nice guy.

 

Fred
Can you provide the following values from your Delftship model:
Bwl
Lwl
Draft
Block Coefficient
Volume

Rick W

 

Rick

I sent to you some informations by e-mail.

If you need something else, please say me.

Thanks

Fred

 

Fred
The FreeShip Hydrostatic values from the file you sent are:
Bwl 0.157
Lwl 0.936
Draft 0.055
Block Coefficient 0.4405

This gives a displaced volume of 0.00356Cu.m. However it shows a rounded displacement volume of 0.004Cu.m.

When FreeShip exports the data the exported volume is also rounded to 0.004Cu.m.

Michlet determines that the data is inconsistent and scales the offsets to produce the correct displacement.

The way to correct this is to set the displacement value in the Michlet export file manually to 0.00356. You will then get closer agreement with the other derived hull coefficients.

The wetted area then works out correctly but there is still a small discrepancy with the coefficients and Bwl. I have not yet got to the bottom of this.

Rick W

 

Rick

You see these data in the Design Hydrostatics if you go to Hydrostatics you see that data that I sent.

If you see the table of offsets that Freeship export you see that the maximum half beam is 0.079. This is the value that is furnished to Michlet and signifies Bmax = 0.158 m. This is the value that Michlet have. B= 0.158 m.

I do not know how you have a volume = 0.00356 m³, if you use datas like Cb, L, B, H, I alert you that these values have more digits than displayed in the report that will change your result. Certainly this value is wrong.

If Michlet use the volume furnished in the data to change offsets, for me, is a great mistake, because when the offsets change they are not more the hull searched.

And more, if some changes is accepted in the table of offsets by one scale, that for me is inadmissible, the Cp do not could change. Wetted area yes.

And, I do not understand if a software have a table of offsets why it need the volume.

The volume is there in the offsets. Is only do the calculations. Is a minimum that we can expect, not a given volume change the offsets.

For me, this is crazy.

 

Fred
The volume of your hull is not 0.00400Cu.m it is 0.00356Cu.m. That is 11% different.

You are exporting inconsistent data to Michlet. It makes the data consistent and the chosen method is to adjust the beam. It retains the length, draft and volume you provided. If you do not want it to change the beam then you need to provide consistent values of length, draft, beam and volume.

The easy way to test the data consistency in FreeShip is to scale your hull 10-fold. You then get a volume of 3.568Cu.m. Certainly not 4Cu.m.


The FreeShip software is not really suitable to working with such small scale as it rounds displacement to 3 decimal points. To get your hull to sit on its line it will need to be 3.56kg, not 4kg. If you built the boat to 4kg then it will sit below its lines.

You will need to take up the reason for keeping the volume inviolate with Leo. To me that makes sense as displacement is usually difficult to change as a design objective.

Rick

 

Rick

We are oysters between rock and sea waves? Between Freeship and Michlet?

I am not exporting nothing to Michlet. Who is exporting data is Freeship.

Freeship gives data that Michlet do not see. The importance is not values given. Is the table of offsets. If the data give by Freeship is not according with table of offsets Michlet should reject all the input.

The table of offsetts is the real boat. Not the volume or draft or other else gived.

How you do to scale 10 the boat? You scale the boat? Or you only affirm this?

You say some things that I do not understand.

Ok Rick, unhappy I do not agree with you.

The minimum that Michlet need do, if you are right, is alert that the table of offsets is not according with the data given.

By other way Freeship or Delftship need learn to export data or to alert to the validity for appropriates lengths to use the software?

For me, I do not have problems with Freeship or Delftship. When I design a one meter hull, paint a waterline mark and put the boat in water, the marks of waterline are correct for my displacement of 4 kg.

If the mark was for 3,56 kg I do not understand not more.

 

Fred
The attached data is for you hull scaled 10X from your hull. If the displacement of the original hull was .004Cu.m then the 10X hull would be exactly 4Cu.m. It is not. It is actually 3.568Cu.m.

The volume data you are getting from FreeShip is rounded to 3 decimal places, which is only 1 significant figure for your design. It is not very accurate. The FreeShip software really does not have the precision for such small hulls unless you are happy to tolerate large errors.


Rick W