Off Sets

[john]

Hi can anyone give me some info please, on how to loft off ofsets i have some idea but need a little more info on wether you take the BUTT Lines form base line up or down, and if its the same with the WL lines do you mark them from base line up or down

[Port-Na-Storm]

Hi John,
Is there a Lines Plan to go with your table of Off Sets? if so it should give you a clue where the base line is in relation to everything else.  Do You know who the designer is, that might help.

Normally the various water lines are measured up from the base line (Boat right way up ).

Also by Butt lines do you mean buttocks? In which case they should be measured either side of the centre line.  
Hope that helps.
Graham

[simplesimon]

Hi John
It might be an idea if you posted some of the data here so we can see what you're looking at. You can write a book on lofting, and several people have!

Waterlines are slices through the boat parallel to the base plane, at a specified distance above the base plane, and the waterline offsets are the width of the waterline (measured as said) from the centreline.

Buttocks (and bow lines) are vertical slices legthways, parallel to the centreline at a specified distance from it. As said, the buttock offset is the distance of the buttock line above the base plane.

Sections are vertical transverse slices through the hull, like the slices in a loaf. Typically 10, sometimes 12, they normally divide th hull evenly (but watch out at bow and stern where designers sometimes slip in a couple extra to make sure you get the ends right!)

Simplesimon

"Three inches of ice at the edge of the Broad is enough to stop a sailing boat, but not enough to be sure an ice yacht can go from one side to the other without breaking through!"

[Timmo]

Hi John.

Not sure if this will solve your problem, but I learned almost all I know about lofting from following the graphics and voice over on Ron Linton's web page:

http://facstaff.colstate.edu/linton_ronald/

If you click on 'lofting' (fairly intuitive!) and then on each stage he goes through it on screen. 

I certainly found it easier to follow than some of the written descriptions I've seen.

Hope it helps.

Tim.

[Paul H (admin)]

One trick I learned is to mark the "baseline", or something parallel to the baseline, at each end of the shapes to be scarfed.

Then you can run a string line between the shapes and align the string exactly with the baseline marks - this is more accurate than simply butting the two shapes together. A slight twist of a few mm along the LOD length of a panel is easily detected and corrected.

If that doesn't make sense I can draw a diagram to explain it better.

cheers
Paul

[simplesimon]

One warning - check before cutting anything whether the lines are to the inside or outside of the planking! It makes a difference - and designers vary in their practice!

[john]

i have got the table of offsets from the canoe craft book it redbird i want to biuld would it help if i put some of the offsets in for you to look at

[john]

this how it is in the book
Table of heights
Station            0
Sheer            0-10-02
Butt2"           1-02-7
Butt4"           1-09-5+
Butt6"           1-09-4
Butt8"           1-09-1+
Butt10"         1-08-06
Butt12"         1-08-1
Butt14"         1-07-1+
Butt16"         0-10-7
Profile           1-10-0

Table of Half Breaths
 Station            0
Sheer            1-03-6+
WL2"          
WL4"          
WL6"          
WL8"          
WL10"        
WL12"         1-04-1+
WL14"         1-04-3+
WL16"         1-04-2+
WL18"         1-03-3
WL20"         1-00-3+

The Butt measurments i'm measuring from base line down and the WL measurments i'm measuring from the profile line or centre line horizontal am i right in thinking that from WL 10" you read these as being below the water line in the book from the body plan the base line is at the top
           

[Port-Na-Storm]

I think I may be about to reveal how sad I am.............



I hope you've all been playing this at home!

This is very approximately what I think it should look like.

The deliberate mistake is on Butt 2" which I think should read 1-09-7.  

I'm guessing its a Candian canoe, about 32" beam, and that station 0 as shown is actually amidships, the canoe being symmetrical fore and aft.

To be built Strip Plank.

Could be a new game, "What's My Line".

Graham