C17 hardtop support

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OneWayTraffic
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C17 hardtop support

Post by OneWayTraffic »

I’m after feedback on my plan to support the hardtop I’m putting on my C17. More photos are in my build thread. The most convenient place to attach it would be by bolting to the consoles on either side, at frame C.

The consoles are made of 9mm ply and all sides are taped in with at least 200g. Some seams are biax, especially those to the sides. If I grab a console and shake the whole boat moves. I’m not much concerned that they will pull loose.
The gap between the consoles is 600mm (about 2’) and the top would be supported on uprights bolted to either side of that gap. The sides would cantilever out past this 2’.

The top will weigh about 15kg total, dimensions 1800mm by 1100mm and will be a little less than a metre (3’4”) above the top of the console. No plans to add any more weight to the top, though I’m sure someone will use the uprights as grab bars.

I have wooden dowel 35mm (1.25”) in diameter which I can wrap with glass and carbon fibre sock. I have enough for one of these per side, and can get more or bigger if needed.
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OlivierP
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Re: C17 hardtop support

Post by OlivierP »

Do you plan to use 2 uprights only at frame C ? Might be flimsy in waves and wind ? I would use 4 legs for stronger support, maybe the back ones at the back of your pilot seat?
Built C17 (app.php/gallery/album/262), GF14, Devlin Bella 16. Sails a 30ft Biloup 89 sailboat.

OneWayTraffic
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Re: C17 hardtop support

Post by OneWayTraffic »

Yeah I was planning on two per side. I'd like them both to be bolted to the console, allowing me to lower the top if needed for storage. 250mm apart bow to stern, 600mm side to side. I'm not sure if that will be enough, or if 35mm wrapped in glass will be thick enough. Commercial t-tops use 2" Aluminium tube, but then any flex at all can lead to welds popping. I'm not worried about that as much with wood.

fallguy1000
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Re: C17 hardtop support

Post by fallguy1000 »

Four standing posts will be shaky.

There needs to be a span support and gusseting. The span and gusset joints cannot move at all.
2202B33B-FEE2-423F-B0AC-A68A6B95A53C.png
My boat build is here -------->

viewtopic.php?f=12&t=62495

fallguy1000
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Re: C17 hardtop support

Post by fallguy1000 »

You can avoid head banging on the gusset by making it shorter or by making the top of the post interlock with another span support.

Use neoprene between any fastenings to avoid noise at low rpm.

The span supports either must saddle or be built as a whole unit.

This is mine in 1.5" aluminum; still needed span support. The top has a saddle vs a gusset. My top has an aluminum frame. Front is bolted to the welded windshield and overhangs it for glare or rain..

Zoom in and see the span helper just below the seat.
AC765184-DD80-4ACE-8D78-843C09D98996.jpeg
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My boat build is here -------->

viewtopic.php?f=12&t=62495

OneWayTraffic
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Re: C17 hardtop support

Post by OneWayTraffic »

I can see how the span support at the back locks the two back posts together, but you still seem to have a fair bit of unsupported pole above, maybe over 4 feet? Would you be able to tell me how thick the wall is in your tube?

I was thinking that I could easily lock the supports together bow to stern with plywood beams but port to starboard I want to be able to step through without ducking. Maybe if I’m careful with the gusset height.

OneWayTraffic
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Re: C17 hardtop support

Post by OneWayTraffic »

In terms of saddles at the top I was planning on having the uprights epoxied into wooden beds under the top. I can drill a hole to take the dowel and get a lot of contact area. Shouldn’t be any play there.

fallguy1000
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Re: C17 hardtop support

Post by fallguy1000 »

The tubing is 1/8 afaik.
My boat build is here -------->

viewtopic.php?f=12&t=62495

OneWayTraffic
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Re: C17 hardtop support

Post by OneWayTraffic »

Roughly equivalent to a plain 2” wooden dowel. Or my 35mm with a fair bit of glass and carbon wrapped.

Stiffness is proportional to the fourth power of diameter for a circular beam. For a tube it’s similar except you need to subtract the innards as they are empty. Hard to calculate how much impact the carbon and glass have as it depends on fibre orientation and workmanship.

I’ll look into adding some supports or get some bigger dowels. Or both.

fallguy1000
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Re: C17 hardtop support

Post by fallguy1000 »

Vibration is the other thing...

Mine is all demountable and screwed into giant rubber spacers at all points of contact.
My boat build is here -------->

viewtopic.php?f=12&t=62495

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