Sail Making - PolySail

[PatrickARiva]

Ok ok, yes I'm making a polysail lol

I'm building my first boat and wanted to also make my first sail. After reading and viewing some video i ended up using SailCut as one youtuber used with success.

I plotted the panels and it was in metric. I scaled up to imperial and started to plot my own points.
When overlayed ontop of each other the panels dont match, specially at the negative "Y" values along the Y axis.

Am i not suppose to interpert the negative values as a negative input? why do these not line up? What am i doing wrong?

if you look below you will see 3 yellow marks as the Y values are -xx numbers they are below the x axis. Am I not suppose to do this?

 

[Tops]

My guess is that you are not accounting for the shape of the individual panels adding draft to the sail along with the curves of the luff, leach, head, and foot.
Would you be able to copy the *.saildef file to *.txt and upload it to the forum?
I did a polytarp sail once and ended up with a dart near the tack to add more shape.

 

[PatrickARiva]

My guess is that you are not accounting for the shape of the individual panels adding draft to the sail along with the curves of the luff, leach, head, and foot.
Would you be able to copy the *.saildef file to *.txt and upload it to the forum?
I did a polytarp sail once and ended up with a dart near the tack to add more shape.

From my understanding the program does take into account the draft as I put it into the program. I just figured it configured that into the line drawing it generated. But when i plotted the numbers on my own on CAD it didnt match the drawing layout for that panel. If i follow the logic of -17 means below the x axis then i get something different. and if i follow the wrong logic and just use postitive numbers i get something different too. So im not too sure where to go about his. The youtube video seemed very straight forward.

I've copied the program parameters in case anyone has used this program before.

Moulds Window

Dimensions Window;

side profile

straight profile showing draft

Let me know if any of this makes sense. I'm still trying to piece it all together. Been reading the sailmakers apprentice while making this. Essentially a copy of the 51sqft Jim Michalak sail for his small dinghy boats.

Patrick

 

[Tops]

The panels of your sail are not 'straight' so to speak. Your first picture, the small panel, is the most affected.
To affect this shape in a poly tarp sail (one piece) you would need darts to remove material to add belly to the sail between a- a' and b-b'
The darts would start on the outer edge and taper to nothing just short of the middle of the theoretical seam.
Similar concept to broad seaming except a poly tarp sail does not have such seams...
Your outer/other seam allowances seem narrow for typical poly tarp construction to have enough room for carpet tape, bolt ropes, grommets, etc.
When I sewed mine, I took the longest straight side and made it the x datum line and took measurements from there. If you lay out the whole sail at a time you can use your rounding dimensions and positions to draw on the tarp.

 

[PatrickARiva]

Thanks Tops,


my sail program does not take into account darts. it focuses on panels.
I attached my panel "0" showing the luff side. and after a bit of research i found my own answer. the issue i had was with the curve sections of the draft depth. That line is not to be taken from x/y 0/0 but from a second dx/dy axis point. Which is taken for each end of said line. See below i found in the instructions of the program.

 

[Tops]

Patrick, is this the video you are using as a guide?

You are building a paneled sail from polytarp materials rather than a sail cut from a single polytarp.
My comments about darts and seams apply to the latter instead of the former. Sorry for any confusion from my side.

Below link is an overview of single sheet 'polysail' construction:
Duckworks Magazine https://www.duckworksmagazine.com/06/howto/polysails/index.htm

Carry on, all the best, glad the conversation led you to your answers.

PS I find the software SailCut CAD fun to use, but do not have the know-how to adjust the foils or twist for a given sailplan.

 

[PatrickARiva]

Yes thats the video i was referencing!

I like that he took a few extra measures to ensure his polysail last a longer time.

I prefer to do this method as suppose to the single sheet, i don't know maybe the complexity of it entice me i guess lol

With that said do you still feel my seams and hems are small? i'm following the instructions from the plan of the Piccup pram from Jim Michalak. Should I increase the seams and hem?

 

[Tops]

I think the seam/hem dimensions are probably OK, seeing how TrevC folded them over and taped and such.
His video of the sail while sailing looks great.
I did mine to accommodate a 2" (25mm) double-faced carpet tape, folding over the polytarp to one side, and to be stitched.
The only external tape I used were on the corners and a strip to take the place of a patch or webbing.
Here are a couple pics. The leech is the long straight dimension, the tack (closest to deck) has the dart.
The boat I used this on had a Jim Michalak designed rudder check/blade combination. The boat and sail are gone but I still have the rudder.

 

[montero]

Poly Tarps - Lowest Price - TarpsPlus.com https://www.tarpsplus.com/collections/poly-tarps
Is average tarp made of polyethylene ?

 

[PatrickARiva]

I think the seam/hem dimensions are probably OK, seeing how TrevC folded them over and taped and such.
His video of the sail while sailing looks great.
I did mine to accommodate a 2" (25mm) double-faced carpet tape, folding over the polytarp to one side, and to be stitched.
The only external tape I used were on the corners and a strip to take the place of a patch or webbing.
Here are a couple pics. The leech is the long straight dimension, the tack (closest to deck) has the dart.
The boat I used this on had a Jim Michalak designed rudder check/blade combination. The boat and sail are gone but I still have the rudder.


Thanks, yeah i thought the same thing. And then when he posted the video of him sailing with the new sail i was convinced this would be a good experiment for myself. The only local sailmakers here in Southern Ontario seem to cater to high end large sailboats so i rather save some funds and do it myself. Thats my moto on most things really lol. I entended to stitch parts of it as well but when I messaged TrevC on YT he mentioned there is no point to stitch with the tape as it will hold up and the needles will get all gunked up he mentioned. He has done both and he says its the same result.

I went along with what JM stated on his plans for the seams but i didnt consider the size of grommets needed, the plans call for a no.3 grommet. What outside diameter do those come in. My seams are to be 1inch so I would assume i would need 3/4" outside dimension grommets to make this work but is that enough for the line that I need to wrap the sail? (newbie question)


thanks for the photos of the dart. I'm understand now and will add that to my sail. My SailCut program (version 1.36) doesnt have a dart element. What program did you use?

 

[PatrickARiva]

I have a 10x12 tarp i got. and im planning to layout the panels like this.....

I did this as i was told its best to keep the leech and luff parallel to the edges as that is the strongest section of the tarp. If that makes any sense.

I will enough leftover material to make the reinforcement panels for the corners and reef points.

 

[Tops]

Poly Tarps - Lowest Price - TarpsPlus.com https://www.tarpsplus.com/collections/poly-tarps
Is average tarp made of polyethylene ?

In my case, yes. We also have very thin ones here, so-called 3 mil. I would start thicker at 6 mil for a sail.

thanks for the photos of the dart. I'm understand now and will add that to my sail. My SailCut program (version 1.36) doesnt have a dart element. What program did you use?

Patrick, you will not need the dart since you have panels. The dart came from an internet article with a polytarp version of that sail (no panels). I took that original plan and added my wider hem allowances via AutoCAD and rotated the straight edge into the x datum as mentioned before and dimensioned the drawing in a way that made sense for me. The curves were done with splines and weights similar to the video.

I used grommets from the local fabric store. It looks like your example has added reinforcement for each grommet, see the video preview picture above.

I am using the same Sailcut CAD program but version 1.3.902.