Obtaining heeled waterlines in Freeship

Yep... It would be nice if Martjin could think it over too, because Delftship is most probably behaving in a same manner. They appear to run on the same graphics and a similar math engine.

 

dont really know what bugged him out but if Martijn say's hello here again i'll pay my last but long overdue 50.- share for the program rite now

 

Oh...he's around...just not every day or in every thread. I think he checks in once a week or so.

 

Hi Guys,

To jump in straight away, the orginal FREE!ship code was not setup for asymmetrical hulls, (or symmetrical hulls in a heeled condition). As some of you might remember the project was heavily under development. Still, this work around is quite ingenius and should work, even in FREE!ship. The longitudinal center of buoyancy is displayed along with the VCB. TCB is also calculated if I remember correctly. I'm sure Victor would be willing enough to include it in the output.

If you send me the file Lewis, I can run it through DELFTship as a benchmark.

 

By the way Steve,

You design reminded me of Bolger. I just found out about him the other day. Really, really sad.......
But then again, he wasn't really a conventional type of guy....

 

Morning...after doing a bit of research into my books to look up for the correct formula...determining the righting arm from the available data appears to be relatively easy. Hopefully my math is up to the task.

First...heeled displacement is a factor of draft...and is given in the displacement portion of the data. To adjust the displacement at heel (which should match the displacement at rest...just 'cause it leans over doesn't mean it gets any fatter) you will need to play with the draft until you get the correct displacement. I recommend you save many iterations of the hull at different angles of heel and with corrected drafts to get an overall picture at the same displacement.

To determine the righting arm at a specific angle of heel take the Transverse Metacentric height and multiply it by the Sin of the angle in degrees. This should give the length of the righting arm. Then multiply that result by the displacement. To get foot lbs (for working with smaller boats) multiply this by the number of lbs in the selected displacement unit (2240 lbs/ton in the imperial measure) to get foot/lbs. If you want Newton/metres or something else you are on your own .

 

Cross post!

Sure...no problem. You know...I just noticed I have been spelling your log in wrong for....ever...sorry 'bout that

First name is Martin right?

Steve Lewis

PS: TCB is not included but If I got things right is easily calculated using the GM, the angle of heel and the displacement.

PPS: Check your PMs

 

Actually it's Martijn, but don't worry, I listen to a lot of names, most of which are meant in a good way.

Anyway, GM can only be used up to a small (say 8 degrees) heeling angle. The exact measure for transverse stability, the righting arm, is simply the horizontal distance between the center of gravity and transverse center of buoyancy. So not GM but TCB is what you really need.

 

Aha! I found a paper which gave the formula GZ=GM (sin X) where X is the degrees of heel. They did mention that up to about 10 deg you could sub (X/57,3) for (Sin X) so this is what I used for the above. Guess I'll only build boats that heel to 8 deg then LOL

Steve

 

Steve,

I had to move the boat up a bit so the lowest point coincides with the base plane. I hope the draught and displacement are still correct.

Here's what DELFTship came up with:
(Notice also the small difference in upright and heeled sectional area curves of the 3rd image, the design is very close to trim neutral at this angle of inclination)

 

Actually the draft listed in the file you got should be .75 ft or 9 inches and displacement of .882 tons. I forgot to save the last iteration where I had corrected the draft and disp to match the unmirrored original hull. I will re-upload the file in a moment so if you hit the link it will give you the correct file. Give me about 2 minutes

 

File uploaded. It should have a draft of .531 and a displacement of .494 tons which is the design displacement for the hull

Steve

 

I take it that that is a GOOD thing? I assume that it means the hull shape at this angle of heel is still fairly balanced and the helm won't be very affected.

Steve

Edited to add: no...sounds like the boat hasn't pitched any significant amount as it heeled to that angle.

 

Yep.
Have a look at the stability report.
You can see that up to 15 degrees of heel there's almost nu change in trim.
Most yachts with a a large beam (and wide transom modern yachts too) tend to dive down with the bow, and lifting the rudder out of the water.
Yours seems just fine.

I only have a displacement of 0.526 tons at .75 foot of draft though.....

 

It seems that you keep your feet dry until 59 degrees of heel.
After that it's over.....