How to measure a bimini for backstays

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Snowdog2
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How to measure a bimini for backstays

Postby Snowdog2 » Tue Jun 12, 2018 6:23 pm

I ordered a new bimini for my Chrysler 26 today. Once it gets here, I am going to need to figure out how to accurately measure where to put two holes in the fabric for the backstays (I'll use some sort of grommets). I just am a little stumped at this point how to make an accurate measurement before I make any cuts. I have been researching and have seen a variety of methods for accommodating the backstays, including zippers from the back and zippers from the sides. My feeling is that if I can just have two small holes, it will be simpler and less costly (I would need to hire out sewing), though the side zippers do look like a good method. I looked at the back stays and believe that I can fit the attachments through a 3/4" hole.

A few FYI's: I plan to mount the bimini next to the toe rails and to keep the whole bimini just behind the boom, so I don't need to be concerned about any chafing.

Has anyone here done this successfully? If so, how did you do it? What process did you use to measure where the holes in the canvas will go.

BTW, I searched this site and found some broken links, but nothing was available that answers this question.

Thanks.
Last edited by Snowdog2 on Fri Jun 15, 2018 6:53 pm, edited 1 time in total.

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EmergencyExit
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Re: How to measure a bimini for backstays

Postby EmergencyExit » Wed Jun 13, 2018 5:38 am

Mine is probably one of those broken links, it had a lovely color diagram too; I just measured how high the bimini would be once mounted by assembling the bimini, standing it up, etc (for an example say it will just touch the boom lower edge) , and also measure what is the relation of the leading edge of the bimini to the end of the boom where you want the bimini to go (again for example it just touches the end of the boom). Measure from the point on the boom where the leading edge would be back to the backstays, level and AT the height the bimini will be. Transfer that measurement to the bimini . Now for the final piece of the puzzle, do not fasten the bimini mounts to the hull until after you have successfully ran the backstays thru the bimini top; that way if you are an inch or two off you just fasten the mounts where they land. As long as that doesn't make the bimini hit the boom a bit of leeway shouldn't matter.
EDIT (also you need to measure the distance between the split backstays at the measured height and if you are going to use grommets that measurement has to be tight. Not much room for error. I tried and failed, so I had to cut the grommets out and go with two slits that I re-enforced with cloth tape that matched the bimini. )

If I get a chance later I'll dig up or recreate the old diagram and post it here.

Snowdog2
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Re: How to measure a bimini for backstays

Postby Snowdog2 » Fri Jun 15, 2018 6:45 pm

Thanks EE, I'd love to see your diagram (yes your link was broken - I can't understand why... You only posted it 6 to 10 years ago.) :D Your comment about using the toe rails to mount your bimini was very helpful though! My thinking has evolved since my first posting. I am thinking that I can assemble the bimini at my house, then bring it to the boat and mount it in front of the back stays (using the toe rail for mounting), then measure the distance I need to go back to clear the boom, then measure that same distance on the bimini and put dots on the bimini. As far as the side to side distance between the backstays and the edges of the bimini, that seems simple if I can figure out the exact height (which I think I will know by mounting the unit forward of the backstays first). It does seem that the back straps of the bimini will need to come straight down or possibly even forward a bit rather than the 30 -60 degree back recommended, unless I rig some sort of extension beyond the back of the surface that the toe rails are mounted on.

After I have the dots, I will take bimini to local upholsterer to put in the two grommets. Having someone else put in the grommets is much cheaper than getting the tools I would need. I guess if I mess up there is always the slit method. I am optimistic though.

One question I have is, if I do this on a windless day (boat on the water), can I disconnect the backstays, and just use the mainsheet halyard to prevent it falling forward... or do I even need to do that. Does the toe on bottom the mast and the back two shrouds prevent it from falling forward on its own?

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Re: How to measure a bimini for backstays

Postby EmergencyExit » Sat Jun 16, 2018 1:59 pm

Not sure how far forward the mast would go before something stopped it, and I wouldn't want to find out ! I did use a halyard as a backup, then loosened the backstay enough to take one side of the split off, put the bimini in place at an angle, work that one side thru, hook it back up, then remove the other split, swing the bimini around and slip that one thru, and then hook it back up and retighten the backstay. Then I mounted the bimini feet where it landed.

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Re: How to measure a bimini for backstays

Postby Snowdog2 » Sun Jun 17, 2018 6:16 am

Sounds like a good method.... of course, as you said it didn't end up being right the first time till you did the slits. I guess I will see. Right now I still have about a week or so before the bimini arrives and I get to start playing.

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Re: How to measure a bimini for backstays

Postby Snowdog2 » Wed Jun 27, 2018 9:16 am

Emergency Exit, do you remember what size grommets the back stay ends needed to fit through?

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Re: How to measure a bimini for backstays

Postby EmergencyExit » Wed Jun 27, 2018 9:43 am

No, sorry, was maybe 1/2" tho since that's all I see at the blue home store web site and that's where they came from - I'd say get as big as you can - leaves you room for error and if you center the backstay in them you won't have any chafe of either the stay or the grommets.

Snowdog2
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Re: How to measure a bimini for backstays

Postby Snowdog2 » Wed Jun 27, 2018 5:44 pm

Well, I had 5/8" grommets put in (I wanted larger but that was all I could get from a local boat builder - they said that any larger requires a machine that would press them together). I also had them put in some common sense latches (like you would see on a ladies pocket book where the tab slips through an oblong hole and one twists to vertical position it to close it) onto the boot so I can close it on the side the zipper won't get to. I guess the cover will remain on top of the bimini (I had grommets put on that too).

Tomorrow is windy and rainy. Friday looks like a good installation day. I get to find out how good my measuring was then. I think the greatest difficulty was marking the left to right distances . What I did was measured the cloth from edge to edge, then, knowing the distance between the stays from measuring on the boat, I just measured out from the center of the fabric half the distance. I found it really hard to find those points when I had the bimini mounted in front of the stays on the boat.

Emergency Exit, I found your ideas of (a) using the toe rails to mount it, and (b) mounting it in front of the stays just to take measurements really really helpful. Thank you.

On Friday, I am planning to loosen up the front and rear stays so that the rear ones are slack, then do what you did, one stay at a time. It could be challenging, I will see. I'll give a report and maybe take pictures if I think of it.

Snowdog2
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Re: How to measure a bimini for backstays

Postby Snowdog2 » Mon Jul 02, 2018 11:42 am

Ok, I'm not sure if even 3/4ths would have been large enough. Since the ends of the back stays are two prong, they don't fit down the middle. In any event, I think I measured where the holes in the bimini go correctly, but the backstays ends didn't fit through the grommets, so I had to remove the grommets. Then I used matches and melted the edges of the holes, then I put a small square of Gorilla tape on each side with an asterisk cut into the center so that I could fold each prong back of the tape to make the hole.
Next, I went to the hardware store and bought some 1" threaded plumbing pieces and some rubber gaskets that fit tightly around them and plugged the whole resulting in a hard plastic guide where the back stays go through.See pictures I may put some glue on to make sure they don't slip. They are pretty tight though.

When measuring, I found that I could not measure the side to side distance with the bimini in place, so instead, after I got home I measured the width of the bimini, found the center, and measured out 1/2 the distance between the stays, at the height I determined earlier in the process. That worked out well. I also put common sense clasps on one side of the bimini boot to close it, since the zipper would not go past the first back stay.

Since the boat ends a bit short of where I would want to attach the back strap. I put extensions on with some rectangular aluminum tubes I had kicking around. I may replace them with some ipe wood pieces if the aluminum proves not strong enough.

That is the end of this adventure.... I hope. I haven't been out sailing with it yet.
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EmergencyExit
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Re: How to measure a bimini for backstays

Postby EmergencyExit » Mon Jul 02, 2018 1:07 pm

Good save ! Glad it worked out.


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