table of offsets. Math Help!! Any gurus in here? long post

[pyrofly73]

Hello Everyone,

I have decided on building an enlarged version of the "Ranger".
The reasons in case your wondering...

1. When increased proportionately in all directions to the same length as a "Prospector" It has way more capacity, a higher free board and much higher stems. (I also plan on spacing my 10% enlarged molds out to 17.5' further increasing capacity.)

2. The aspect of having a big part in drawing, designing, and number crunching my own unique boat is something that I'm finding very rewarding. Having zero back ground in lofting has made this little aspect of the project an awesome learning experience.

3. In the end I hope to have a very high load carrying canoe that will perform at least as good as an "old town- tripper" but will look a million times better and probably be 15lbs lighter.

I sent an email to Steve Killing seeking guidance and he suggested I do the math to increase the table of offsets and then loft out full size the new design.

I spent a few hours last night crunching numbers, but I'm almost sure I did something wrong.

I lofted the station 0 with the original numbers and everything works out, I then tried to loft the 10% increased points and it just doesn't work for the sheer , Butt 16", WL 22", and WL 24"? canoe has grown to now have a W.L.26"..

what i did is change the fraction to a decimal. Multiply by 1.10 and then convert the decimal back to a loft point. rounding up or down to the nearest 1/16" as necessary.

Here is the math.

station 0 decimal +10%
sheer 0-11-5+ 11.6875 12.85625 1-0-7 no good!!!
butt 2" 2-00-5+ 24.6875 27.15625 2-03-1+
butt 4" 2-00-5 24.625 27.0875 2-03-0+
butt 6" 2-00-4 24.5 26.95 2-03-0
butt 8" 2-00-2+ 24.3125 26.74375 2-02-6
butt 10" 2-00-0+ 24.0625 26.46875 2-02-4
butt 12 1-11-5 23.625 25.9875 2-02-0
butt 14" 1-11-0 23 25.3 2-01-2+
butt 16" 1-09-5+ 21.6875 23.85625 1-11-7 no good!!!
profile 2-00-6 24.75 27.225 2-03-2

Table of Half-Breadths
sheer 1-04-3 16.375 18.0125 1-06-0 no good!!!
WL 2"
WL 4"
WL 6"
WL 8"
WL 10"
WL 12" 1-04-3+ 16.4375 18.08125 1-06-0+
WL 14" 1-04-6+ 16.8125 18.49375 1-06-4
WL 16" 1-05-1 17.125 18.8375 1-06-6+
WL 18" 1-05-2+ 17.3125 19.04375 1-07-0+
WL 20" 1-05-0+ 17.0625 18.76875 1-06-6
WL 22" 1-03-5 15.625 17.1875 1-05-1 no good!!!
WL 24" 0-10-3 10.375 11.4125 0-11-3+

what's up? Is there special math I should be doing?

I'm about to give up... :-(

I could just loft the original table and then take it to a copy place and blow it up 10%. I dont see why that wouldn't work...

Help!!!!!

thank you.

[Rick]

I have no idea why your conversions aren't working... the way I was going to do it was to convert all the values to metric then multipy by 1.10.

[pyrofly73]

I have no idea why it doesnt work either. In principle it seems ok. I would love to get the real answer. I know it's lurking in here somewhere

[Patricks Dad]

sheer 0-11-5+ 11.6875 12.85625 1-0-7 no good!!!

I'm sure this is a dumb question but why do you think the math doesn't work? What is wrong with your 1-0-7 answer above?

[pyrofly73]

well the Sheer point ends up bellow WL 12" and out of the smooth radius of the curve when i try to loft it. I would expect my sheer to be above my smallest waterline??

I only lofted one station and then stopped because it looked so weird, The points just don't seem to fit maybe I'm lofting wrong ,but if i am i don't know how i am able to do it right with the original numbers...

I think if anyone checked the math and tried to do it they would understand... I could take a picture of this and post it somewhere if you think a visual might help.

Xavier
305-801-6979

[pyrofly73]

i used different color markers so it would come out well in the picture.

little black dots is the original lofting unchanged by any percentage.

Big orange dots are points that look good.

The red ones are all screwy...

I made notes with arrows to them.

http://farm3.static.flickr.com/2590/415 ... 4d54_b.jpg

[Glen Smith]

Xavier, see this post: http://www.bearmountainboats.com/phpbb2 ... 2131#22131

[purple otter]

doesen't the 2"grid have to be multiplied by 10% too? Idk,just a thought.

[Patricks Dad]

If you want to create the same effect of putting the plan in a photocopier, you would have to expand the 2" grid of water lines as well by the same percentage. Also, I would think that the 10% increase in each dimension would produce a >10% increase in overall volume (1.10 * 1.10).

[pyrofly73]

making the grid bigger?... Interesting...javascript:emoticon(':thinking')

so if i was making a 50' canoe I a would need a REALLY big grid.??.. LOL

That was my thought when I initially read your suggestion, and then i thought that the measuring would get really complicated... But wait!! for something as small as a canoe I could take a ruler put it in a copy machine and enlarged it by 10%. If i then used the enlarged ruler copy as a measuring device to make the grid and plot the points in theory it should all come out 10% larger... This might actually work and requires no math.... the ruler would read one inch but in reality it would be 1-1/10"!!!! WOW!!!

Purple Otter your a freaking genius!!!! javascript:emoticon(':applause') Thank you so much this is right up my alley ..

Pat's dad, according to mr. Killing an increase of 10% in loft size does in fact increase greater than 10%in volume except you left out a 10%. remember this is 3D (length width and height). So it's 1.10X1.10X1.10=1.331

a ranger of 375lb displacement suddenly becomes a ranger of 499.125lb displacement....
extend the stations out to 17-1/2' after the 10% enlargement and you have a VERY high volume canoe. This is the cargo ship of the canoe world.

I am running to Kinko's tomorrow and giving this a shot, but i would still love to find out the real way to do this. any naval architects in the house?

Xavier

[pyrofly73]

I photocopied the ruler increasing it by 10%. The photocopy was then laminated in plastic and then the straight edge was cut using a paper cutter. This made a pretty usable ruler. If i put the photocopied ruler next to the real ruler the 5" lines up with th 5-1/2" mark. Exactly 10%

I lofted the whole thing and it came out perfect. This technique will also work for shrinking a boat.

Thanks for the help guys.

[Patricks Dad]

Pat's dad, according to mr. Killing an increase of 10% in loft size does in fact increase greater than 10%in volume except you left out a 10%. remember this is 3D (length width and height). So it's 1.10X1.10X1.10=1.331

You're exactly right. The first two (1.10 X 1.10) come from the station mold changes you are making (larger grid in both directions). The 3rd one will come when you position those station molds an extra 10% apart on your strongback.

Sounds like you are well on your way. Good luck! I'm sure you will enjoy the process from one end to the other.

[purple otter]

Xavier, I am building a 1/4 scale model as a wedding gift for friends of mine who got engaged in my Bob's special.I am doing the same thing in reverse.I just used 1/2 inch graph paper instead of 2" grid.
On my last boat ,a16'6" resolute ,I lofted right onto 1/4"plywood and made 1/2station templates.Then I used these to cut the 3/4 stations with my router and a pattern bit.This way the stations are perfectly symetric.I wonder if you ripped a guide 2.2" and laid out your grid and used the dimensions you calculated earlier ,if this would work?
Good luck,
Steve
'

[Glen Smith]

Xavier, one fellow asked me to post this info for you:

station 0 decimal +10%
sheer 0-11-5+ 11.6875 12.85625 1-0-7 no good!!! (original should read 11.625)
butt 2" 2-00-5+ 24.6875 27.15625 2-03-1+
butt 4" 2-00-5 24.625 27.0875 2-03-0+
butt 6" 2-00-4 24.5 26.95 2-03-0
butt 8" 2-00-2+ 24.3125 26.74375 2-02-6
butt 10" 2-00-0+ 24.0625 26.46875 2-02-4
butt 12 1-11-5 23.625 25.9875 2-02-0
butt 14" 1-11-0 23 25.3 2-01-2+
butt 16" 1-09-5+ 21.6875 23.85625 1-11-7 no good!!! (original should read 21.625)
profile 2-00-6 24.75 27.225 2-03-2





could you post to him that his offsets for 5/8” are incorrect at .6875 and should be .625? That may not solve all his problems, but will help to some degree.



Thanks,

Mick Allen

[Patricks Dad]

I think 5/8" are reflected correctly as .625. The .6875 is 5/8 +1/16(5+), right?