Sheet material for rigid bimini

[Kelpie]

We're adding a bimini this year. It will comprise three panels- rigid solar panels port and starboard, and a middle section made of some sort of rigid sheet. The middle panel will be slightly trapezoidal so I can't just use a third solar panel- and anyway it would get too much shade from the boom, and add more weight to an already quite heavy construction.

The middle panel needs to either be strong enough to stand on, or be easily slid, folded, opened etc, because I expect to need access to the boom for working on the sail cover or sorting any snags with reefing lines etc.

Another consideration is waterproofing. I'd like the three areas of the bimini to act as a decent rain canopy, probably with water harvesting. So really the central part needs to slightly overlap the panels, which points to a thin rigid material being best.

I could simplify life and have one big sheet, with the panels sitting on top. But that sounds heavy, and means I can't dismantle and stow away the whole thing in case of extreme weather or for winter storage.



Anyway... what are my options for the sheet material?
-5mm ply. Cheap, readily sourced and easy to work with. Will need support to make it strong enough to stand on, limited lifespan.
- GRP sheet. I have a source for this in the form of a scrapped dinghy. Will need more work than ply, but could last forever. Fairly easy to stiffen up with foam core stringers. Probably heavier than ply.
- thin (single skin) plastic. Not sure how easy this would be to source. Depending on type, may have good lifespan. Should be fairly light. Might be very floppy and need a lot of support.
- DiBond aluminium composite. Lasts forever, similar stiffness and weight to ply but much thinner. Smaller sizes so might need joins, harder to work with.
- Corrugated plastic. Very very light. Not sure where to buy. Will probably disintegrate in the UV. Not really tough enough to be stood on.

Anything I'm overlooking?

Any clever ideas about how to make a panel open up? I'd really prefer that option, rather than having to climb on top of the thing.

 

[penfold]

Composite sandwich sheet, either honeycomb if you have deep pockets or plain vanilla foam. Both would bear a human being readily. As you want it to collect water making up a tray with a rim and an orifice for a drain fitting would be a relatively simple bit of laminating, you could even vacuum bag it or do resin infusion for greater bragging rights.

 

[Kelpie]

Composite sandwich sheet, either honeycomb if you have deep pockets or plain vanilla foam. Both would bear a human being readily. As you want it to collect water making up a tray with a rim and an orifice for a drain fitting would be a relatively simple bit of laminating, you could even vacuum bag it or do resin infusion for greater bragging rights.

Could be a very good option. I saw Sailing Atticus on Youtube build something similar, quite impressed with that. Light but solid.
That sort of work would be a bit out of my comfort zone, but you don't know until you try. I did a lot of ply/epoxy work earlier this year building a dinghy and have a fair amount of resin left over, so it is tempting.

 

[Neeves]

As Penfold said - Foam and glass, both sides. You can curve the foam a lot, but you might like a slight curve, then glass the curve and when set off it will hold the curve, then glass the other side. The thickness and type of foam and the area to be built will determine the weight of the glass (ask the supplier of the foam and glass - they will advise what you need to allow you to stand. As mentioned if you are harvesting water you can have a lip all round.

If you wanted you could also build a window into the panel to allow you to view the main. If its solid foam and glass with 2 solar panels either side your sail trim ability will be, roughly, zero.

Its all very easy - all you need is the space in the dry to do it.

Jonathan

 

[savageseadog]

Carbon fibre

 

[dunedin]

Are you sure you want such a solid permanent structure? If so great. But for me I would fit a conventional “canvas” bimini, with semi flex solar panels attached with 5cm “Velcro”.
Does the job when needed but removable when not wanted. We found it disconcerting not being able to see the rig in the dark so stowed the Bimini overnight doing an Atlantic crossing. And in moderate climates we’re keen to be able to open to get more warmth from less harsh sun.
(Also can stow to reduce wind age when get caught at anchor or at sea in severe storm / hurricane, and without all the extra weight and wind age up high..)

 

[Neeves]

OP mentioned he wanted to stand on the structure (and harvest rain)

Jonathan

 

[Kelpie]

Are you sure you want such a solid permanent structure? If so great. But for me I would fit a conventional “canvas” bimini, with semi flex solar panels attached with 5cm “Velcro”.
Does the job when needed but removable when not wanted. We found it disconcerting not being able to see the rig in the dark so stowed the Bimini overnight doing an Atlantic crossing. And in moderate climates we’re keen to be able to open to get more warmth from less harsh sun.
(Also can stow to reduce wind age when get caught at anchor or at sea in severe storm / hurricane, and without all the extra weight and wind age up high..)

A few things put me off semi-flex panels. They are much, much higher cost. They don't appear to last as long especially when used in that way, as the flexing leads to delamination. I've heard a pretty scary first hand account of a failing semi-flex panel setting the sunbrella underneath on fire. And I already own the rigid panels so I'm pretty much committed to going that path. At the time I bought them, I thought it would be easier and lower cost to build a rigid structure, especially as I don't have anybody local who could visit the boat to make a canvas bimini. In hindsight I think I may well miss the ability to see and access the rig, which is why I'm now wondering about either a slightly complex opening design, or a really solid one that I can stand on.

 

[Kelpie]

OP mentioned he wanted to stand on the structure (and harvest rain)

Jonathan

I might be asking too much. I want to be able to access the aft end of the boom, so either standing on the bimini or having a part of it that opens up. A solid design would be simpler.
Rainwater collection would be very helpful, but I know it complicates everything. Would be a shame to give up on it though.

 

[cherod]

quite a few u tube vids on the subject ,, i think Tulas is one of the best , also Zingaro . bit complex building the frame etc but simple fibre glass work . on a solid one collecting rain is a simple addition .

 

[Neeves]

Don't give up your idea - if for the only reason the posts cost you nothing. Later you can revise your dream - if you so wish (and start a new thread. I think everyone here is happy to throw ideas at you.

You can have a frame made from stainless tube, they are commonplace, they are not rocket science. You can have the frame made to accomodate anything you want. If you go for a solid and load bearing centre section, so that you can stand on it, it can contain an acrylic window, easy to build a recess and cement the acrylic with Sika, or whatever is recommended. If you are really flush you can have an opening hatch in the solid, load bearing section, that you can open (a yacht near us has this option). If you have any pride in your sailing and know how to trim a main - you need to be able to see the main (but you know this if you have pride in your sailing.

The advantage of the frame, apart from it being simple, you can obviously extend the coverage and make the frame part of an enclosure to enlarge your living space when at anchor (you spend more time stationary than sailing). You can add half height dodgers to make the cockpit a bit drier - without removing the vista.

If you envisage standing on the centre panel at sea it needs to be both robust and comfortable - if you need to balance on stainless tube, or the side panels you will feel most insecure. Standing on a Bimini in rough weather with a less than stable boom engenders insecurity alone - without you not feeling surefooted.

Stick to the dream - amend when it appears too much like hard work.

Take care, stay safe

Jonathan

 

[dunedin]

A few things put me off semi-flex panels. They are much, much higher cost. They don't appear to last as long especially when used in that way, as the flexing leads to delamination.

Our semi flexible panels from Photonic Universe weren’t expensive, and only issue so far after 5 years on the spray hood hasn’t been with the panels but a Bulgin connector which corroded. And panels have survived 5 sets of Scottish winter gales.

A lot does depend on the size of the boat. I need to stand on the solid cockpit table to zip up the sail cover. That is fine, as spray hood gives safety handles. But I would not want to stand up on top of a rigid bimini, to stow sail (or fix tangled reef lines, for example)

 

[Benzerello]

Hi there.. Im new here and thinking of 40kg of solar on a purpose built bimini on a macwester 27....i do weld and am good with electrics... I have 2 celltower batteries each weighing around 50kg... I was going to put them iether side of the cockpit mounted on the lockers on the inner cockpit walls.... I would appreciate any ideas for bimini construction and whether or not the overall weight which would be around 140kg would be too much for the boat... I am in construction on land so am well aquainted with load bearing materials.. However boats are new to me.. Thanks in advace P

 

[sarabande]

Welcome to the forum Benzerello.

Your estimated weight is roughly equivalent to 2 persons, so will be OK for the boat.

Perhaps a bit of a think about where to place the batteries ? There are reasons why batteries tend to be below the waterline, yet above the lowest point in the cabin. Are these batteries additional to the existing domestic ones, or replacement, and what is their purpose ? At 50kg each that looks like a lot of Ahr. They will for certain need a lot of strong strapping to hold them securely.


A permanent bimini with 40kg of panels sounds as if it is going to raise the CofG a bit, and also look a bit overwhelming on the boat. There's lots of comment in the forums on adding panels to a stern gantry or to the lifelines. 40kg is a lot; again how many panels of what output and size ?

 

[Benzerello]

2 panels of 375w output... Batteries are 175ah ( ex celltower batteries... I do see the c of g being effected a little but if the batteries are below as you say the waterline will this not cancel the effect of the bimini.. Inly summising as i said i know little about boats.oh and the other batteriey will be gone . I reall do appreciate you responding.. What you reckon?

 

[sarabande]

Hi Benzerello

It seems you have just 1 battery at present ? That's unusual, as the normal is to have 1 for the engine, and 1 or more for domestic use. Again, for the MacWester (nice boat BTW) , in general terms a dedicated engine battery of about 80Ahr (and good CCA) is enough, and domestics of about 110Ahr each. Lots of more precise advice on battery sizes and types on the forum.

And FWIW, I am in the process of putting in 2 batteries of 210Ahr each for domestic use (quite a lot of gadgets....) with an engine battery of 110Ahr, on a boat of 32ft. Present plans are for 4 gantry-mounted panels of 40W each, though that is likely to change.

What do you need /want from your boat's domestic electrics ? Have you made a check list of all the electrical kit and its likely power consumption over 24 hours with the boat in normal usage patterns ?

At the risk of grandmother and eggs, here's a sample list

Boat Electrics; How to Calculate Your Daily Amp Requirement (sailboat-cruising.com)

You say 2 panels of 375W. Is that each or total ? If total, that seems to be a lot, and again I would expect, in very general terms, a good installation of 180W-ish, optimised for Alt and Az (pointing towards the sun ) to be sufficient for normal UK use. If you are cooking via an induction hob and an inverter, or using a freezer, those figures need a rethink.

Last thought. If you put a lot (relatively) of mass above and below the CofG, you will increase the moments of polar inertia, and the boat's motion will change. People can get very excited about metacentric height, but your figures are roughly acceptable. My concern about 2 big solar panels on a permanent bimini are windage and appearance. (BTW I am using bimini for a structure over the cockpit, in contrast with a gantry which sits aft of the cockpit.

 

[Benzerello]

Thanks again.. There are two batteries.. One in port storage cockpit and one center next to prop shaft... Both are dead.. Been standing for 2 years or so... Putting it on a rack at high tide tues to defoul and antifoul weather permitting so thats first job... I intend to get a fridge and yes an induction hob... Gantry is probably the correct term for what im doing... I was thinking i could then use gantry to create a larger cockpit tent type of thing when moored to give a bit more headroom so its extra living space? I have one of them brains that never stops cosidxering improvement ( problematic mainly tbh)

 

[sarabande]

Hmm, that is beginning to look like over electrification.. If your sole cooking is an induction hob, you will need those monster panels, and the new batteries will get a thrashing through the inverter.

I would certainly look at a more conventional solution, and go for a spirit stove (or gas if you like risks )

The gantry as a base for a cockpit tent is fine, but those panels are truly enormous.

With a lot of weight on the stern, plus some people sitting in the cockpit, you may find that the cockpit drains are below water level.

 

[Benzerello]

Maybe centrally placed then the batteries?
And maybe 1 panel for now?

 

[LadyInBed]

If you want to stand on the bimini, it's not just the strength of the roof that you need to consider but also the strength and geometry of the support struts.
I would use a hinged access flap.