How much stretch on canvas for rigid bimeny cover

[theller]

Prepping to build an enclosure for my boat. I have a non flexible tubing system that is attached to a hard dodger and it has nearly no flexibility in it.

In the tutorials for building a bimeny, they compress the bars to get stretch in the canvas.

In my case, the bars wont move hardly at all, so I need to put an appropriate amount of stretch into it. For the flexible systems, sailrite says 1" of compression on the bars to get the stretch right.

If my bars are rigid, how much smaller should I make my cover to get stretch into it?

[psk125]

If you have a "non-flexible tubing system" attached to a hard dodger that "has nearly no flexibility in it", it has no relation whatsoever to what Sailrite says to do with canvas. You will have to figure out how much your hard dodger moves and use that amount to determine the compression you need.

[theller]

Hard dodger has no perceptible movement. It’s fiberglass and tempered glass through bolted to the hull.

I’m aware that the sailrite input would be we wrong. The tension that needs to be put into it should be expected stretch?

I’ve seen 1% noted.

Anyone built a canvas cockpit cover for a similar arrangement?

[JPA Cate]

I'd suggest that you make the aftermost edge to lace tight, then you can adjust it to suit. If you try to use zips, what will happen is that they will be very hard to start and then zip up tight. When you lace them, you can play with the tension as you go along, so that you can get it really tight if that is what you want.

Did build a cockpit cover, awning, but different purposes: It was an awning at anchor, but converted to a rain water catcher, and the sides were permethrins-treated bed mosquito netting, to keep out flies, mosquitoes and who ever else was around that would bother us. Have built a number of cockpit awnings over the years.



Ann

[wrwakefield]

The amount of stretch [and future shrinkage…] will depend upon the fabric chosen. Some stretch [and shrink…] more in one direction than the other… [warp and woof…]

I concur with Ann re: lacing to be able to adjust tension as needed. Instead of rows of grommets we prefer a product Sailrite carries called EZ Lace. Sew it on the edges you wish to lace together and you are ready to install. [It is the black seam strip running full length along bottom of the weather cloths in the photo, below. The top is bolt rope.]

We made our own dodger and bimini - and center cockpit enclosure.


In this photo our boat cat is load testing the newly installed dodger, and the temporary weather fly is still up…

We made it very tight. Then, after initial install, I added 1/2” thick foam pipe insulation to some of the tubing structure and re-installed the dodger and bimini. That made everything extra tight and padded the tubing to make it more comfortable to fall against...

Have fun with your project!

Cheers, Bill

PS: If you are interested, here is a list of materials we used for our last big canvas project.

PPS: Don’t cheap out on the thread unless you like to resew things every few years…

[Kd9truck]

Hi theller, I have built my Bimini, dodger, lazy Jack sailbag, sunbrella covers for my salon cushions and cockpit cushions, all with the sailrite LZ machine with the heavy duty flywheel.

My Bimini is 11 x 12 with 4 SS frame tubes, I did not get caught up in building stretch but mainly because I built the Bimini to be pulled taught from 4 webbing tensioners, 1 on either side of the Dodger (pulling foward) and one on each side of the transom steps pulling aft. They can be adjusted and retightened when they occasionally get loose. I added a button pocket up the center and that helped with rain runoff as my SS frame is a wee bit too flat.

Side note:
I broke 2 residential machines and then went with sailrites machine, you could find a cheaper alternative to their machine but it comes with a book to tune it and I have found it invaluable.

[JPA Cate]

I'm lazy, and don't like restitching things like dodgers, or even awnings. I use PTFE thread. It will last the life of the cloth. For its first two years, it is not quite as strong as UV resistant dacron; after that, it will be better for over 15 yrs. The dacron, where UV hits it is pretty well used up at 4-5 yrs, and whereas some people only keep their boats short periods, we've kept all of ours a long time. To me the extra cost, and putting up with the learning curve for PTFE thread has been well worth it. If you have really good eyesight, you might like working with the clear, otherwise, choose the contrast that looks preferable to you. I have used the black and the white.



Ann

[Kd9truck]

Originally Posted by JPA Cate

I'm lazy, and don't like restitching things like dodgers, or even awnings. I use PTFE thread. It will last the life of the cloth. For its first two years, it is not quite as strong as UV resistant dacron; after that, it will be better for over 15 yrs. The dacron, where UV hits it is pretty well used up at 4-5 yrs, and whereas some people only keep their boats short periods, we've kept all of ours a long time. To me the extra cost, and putting up with the learning curve for PTFE thread has been well worth it. If you have really good eyesight, you might like working with the clear, otherwise, choose the contrast that looks preferable to you. I have used the black and the white.



Ann

Hi Ann, what did you find different about working with the PTFE ? I have plans to build an off shore cockpit enclosure and I have not sourced materials yet but this would be a good time to upgrade construction components. Ty

[JPA Cate]

Hi, Kd9truck,

My experience was different from many people who take it up. The thread (as you might have guessed) is extraordinarily slippery, and therefore is fiddly to get the tensions right on both the bobbin and for the top thread as well. You have to get them "perfect", the loop captured in the fabric just so. Once you have the machine properly adjusted, it's just sewing, mostly straight seams. Whatever tricks you have learned for helping zips around curves still work, etc. And, if you want, something like the basting stitches one uses in parallel to gather sleeves, can be used also on zips, and if not exposed to UV, can be out of the dacron thread--but when you shift back and forth then you get to play the perfectionist tension adjustment game, as the PTFE thread is not only slipperier, but of smaller diameter. I would find myself using it in places it wasn't really needed, because I wanted to reduce adjusting time and finish up the job.

One of my woman friends, herself an experienced sewer of canvas work and clothing (like me), had difficulty with how the thread comes off the spool, and mounted it horizantally (SailRite sells and item to do this). What I do is have the spool on the floor, near the pedal for the sewing machine's motor, so the thread comes up, over the edge of the fiddle on the saloon table, then up to the machine, and it works for me.

I think anyone who sews can use it, it's just fiddly, and it's way better for longevity.

For your highest stress areas, you can consider double stitching some of those seams.

Having a walking foot sewing machine will also help at times.

If you're going to bind the edges with something, you'll find the alignment between the binding tool and the foot is critical to consistent results. I prefer black to white, because over time, although the black turns dark grey, the white just looks dirty.

Ann

[Kd9truck]

Wow, thank you Ann, i usually have a follow up question but in this case I am at a loss. You have saved me hours of second guessing and frustration, i will take your thoughtful direction to task (agreed with the black thread color preference).

[JPA Cate]

Originally Posted by Kd9truck

Wow, thank you Ann, i usually have a follow up question but in this case I am at a loss. You have saved me hours of second guessing and frustration, i will take your thoughtful direction to task (agreed with the black thread color preference).

Thank you very much for the kind words.

Ann