Bimini frame design

[Cpt Mark]

Hi all,

I have a cat that has a canvass Bimini. Bimini came off a sister ship and attached to the side rails/lifelines. Mine are 1" tubing on top. It was located in Seattle area not known for great winds so it actually unfolds over the boom.

I would like to take this down to the deck and through bolt it with backing plates. The Bimini tubing is 1.25 SS with a three bow construction. I can hang off one of the bows and it will hold my weight and not deform. The plan is hard top.

The dimensions will be roughly 14' across and 8' long by 6'2" high.

I could also make it smaller width wise by going to the edge of the cockpit instead of the coaming but would prefer to create as much shade as possible. Am setting off this June.

I do not have a traveller o the main and cannot put one in from of the dodger. I would like to put one on top of the Bimini. The current arrangement hits my head.

2 questions come to mind.

1. Would 1.25" tubing be strong enough to hold the traveller in place

2. What about racking?

I'm thinking I can take the folding bow, lengthening it and welding the two bows together to create a strong structure. Think of a ladder rung with cross pieces every foot or so. The 3rd bow would be at the front with 2-4 pieces connecting to the rear. I wish to put solar up there as well as be able to get up there to deal with the main should it not wish to go in the stack pack.

I appreciate and advice.

[coopec43]

Sorry I can't help you but did you look at these to get ideas?


https://www.google.com.au/search?q=c...w=1069&bih=587

[Cpt Mark]

Originally Posted by coopec43

Sorry I can't help you but did you look at these to get ideas?


https://www.google.com.au/search?q=c...w=1069&bih=587

Thanks. Doesn't answer the questions but does offer some other perspectives

[rgleason]

I don't think one or two bent tubular frames 1.25" dia joined is going to be adequate for new traveler loads. I believe will need to find another way to take the mainsheet loads, perhaps by having two mainsheets from port and starboard, secured to solid locations in the cockpit/deck, preferably somewhat high so it does not impact your bimini, if at all possible.

Perhaps you should get the traveler and frame designed and built for you by someone skilled at this? Then perhaps you install it. While you are at it, inquire about your reuse of the frames for solar pv of the type you identified.

I think the tubes you have are likely adequate for semi flexible solar panels, but not the heavier glass panels, particularly because of your span of 14' and the total number of panels.

[model 10]

I don't think round tubing with such a long arm is going to work with the main sheet loads. Have you thought about composite? There are some really great homemade bimini tops out there.

[rgleason]

I could see a traveler constructed of this system, but I am not sure the fasteners are non-ferrous (you could replace with SS316), and it would look too mechanical I think, but there are larger members available and it is modular.


https://8020.net/

[Suijin]

Hunters have arches on which the traveller, or at least the mainsheet pully, is mounted. That said, I don't think your plan could withstand, as you asked about, horizontal loads of any real force. One good hard gybe and you could find the whole thing bent over to the side, cracked welds, etc. You really need some sort of diagonal support/bracing. If it's formed like a staple it's just going to shear sideways.

How is the mainsheet mounted currently?

[Cpt Mark]

Originally Posted by Suijin

Hunters have arches on which the traveller, or at least the mainsheet pully, is mounted. That said, I don't think your plan could withstand, as you asked about, horizontal loads of any real force. One good hard gybe and you could find the whole thing bent over to the side, cracked welds, etc. You really need some sort of diagonal support/bracing. If it's formed like a staple it's just going to shear sideways.

How is the mainsheet mounted currently?

Currently the mainsheet attaches to a single point just behind the helm seat.

1.5" ss tubing should be fine from what I've been told. 2 tubes welded together for additional support on the sides and then along the top edged with a plate for the traveller.

[Cpt Mark]

Originally Posted by rgleason

I could see a traveler constructed of this system, but I am not sure the fasteners are non-ferrous (you could replace with SS316), and it would look too mechanical I think, but there are larger members available and it is modular.


https://8020.net/

Interesting product. Kind of like Unistrut but in Aluminum.

[rgleason]

Well its your experts. What are the typical loads involved in a jib?

Harken's website has some wizards that will help you determine this. Then start asking the right questions of your experts.

[RaymondR]

My advice, after just going through what you are contemplating, is the find the solar panels you feel you will need for your future cruising needs. Then design the frame to support the panels. Then design the structure you need to hold the frame and panels up.

The boat I have now had a bimini with panels mounted on top. I discovered that the entire structure was being held down by four 1" #8 wood screws and four grub screws which I considered insufficient.

I decided I needed a couple of hundred Watts more of panels and that consequently would need a frame to support both them and the existing panels.
The first image shows the frame mounted on the bimini using the SS panel supports which came with the boat.

One of the problems with the bimini was that it was mounted on the cockpit coamings and I could not sit on them and quiet often when I lunged across to throw a sheet of a winch or dive towards a mooring cleat I would bang my head. Also there was exposed wiring cable tied and taped everywhere. In addition I was looking at hundreds of dollars when the fabric cover needed replacing.

Being a cheap bugger and a self supported retiree and a pragmatic and practical sort of soul who values function above cosmetic I decided to be rid of the SS and fabric bimini and turn the panel frame into a roof.

The second image shows the new roof. The front bow id 50mm x 3mm alloy fastened into the deck with 4 x 1/4" SS bolts each side, the rear supports are pieces of SS cut from the original bows the ends of which retain the original grub screw sockets but which are niw through bolted on with 1/4" SS bolts.

The 50mm tube of the front support now contains all the formerly exposed wiring as well as the two drains for the panel mount "roof".

When I can find someone who can heat bend them I am going to install tinted perspex "spats" on either side along with roll down shades.

I tend to the opinion that if you went this route with the heavier alloy frame at the back end it would provide sufficient strength and lateral stiffness to allow the main sheet to be anchored from it.

I also tend to the opinion that it does not look as ugly as the original bimini even though it might look a bit industrial but at least I no longer have to wear my bicycle helmet when sailing or mooring the boat

[rgleason]

Harken Mainsheet Load Calculator
https://www.harken.com/content.aspx?id=9094