SS vs ALUM hard top / B28

[Yannis]

You all who have those towers and extras, can you please explain to the idiot if an SS or Alum hard top is preferable, and why?
It has to be extra light, extra flexible and extra strong, because it will be carrying two 70 X 100 solar panels. Not that they are heavy, but they catch air (they have to, so as to keep cool at standstill, but at winds and speeds they should be anchored sturdily).
Thank you.

[Carl]

Yannis,

I can't say I've ever seen a SS hardtop.

Aluminum I have seen when combined as floor for Tower.

Mostly what I am familiar with are Fiberglass hardtops and fiberglass/canvas over alum pipe structure hardtops.


As to being sturdy...all three can be.

Flexible...not sure what you mean as all flex to a degree...

And going sturdier in design kind of reduces amount of flexibility to my thinking.


Lightweight...Alum then fiberglass followed by SS. Although highly dependent on design and needs.


Design...Fiberglass can be curved and contoured, molded to follow boats lines better then the other two choices.

Price--

If I had to mount large panels on top of boat...
Alum pipe structure with integral Alum plates and mounts, topped with aesthetically pleasing Fiberglass top.
Panels sit on fiberglass but secured to Alum plates.

If appearance was not a factor, and was not looking for cover I'd forgo the fiberglass aspect.

My.02

[Navatech]

First, an idiot would have bought a floating chlorox bottle of some kind or other... Definitely not a Bertram!...

Second, SS or Stainless Steel is really only StainLESS... It's definitely not Rostfrei (Rustfree) as the Germans put it...

For that reason I would go with Aluminum... Aluminum is also lighter in weight... Even though you'll need slightly thicker Aluminum...

As for catching air, either would catch the same amount of air due to having the same area... I wonder, could you get louvered sheets?!... Something like this:



Having said that, I think I would go for some lightweight honeycomb or foam core with fiberglass covering...

[Yannis]

Nav,
I dont give a flying damn if it rusts. It will stay in that condition till a tree blossoms on my remains.
The alum has to be thick and I dont like.
The Ss may be heavier, but with the difference in thickness the weight dif is perhaps negligible.
Your ever inventive talent has not perhaps thought that a metallic louvre, even under the shade of the pannels of our summer sun, will reach 100 C easy. A new stove top !

[Joseph Fikentscher]

Stainless will flex more. But, it will be shiny. I had no rust at all after 10 years.

Stainless with Sunbrella top. Note the braces.

[Yannis]

Thanks Joe,
I was thinking of the same principle, only with a hard top instead of Sunbrella.
Sunbrella I have now and I want out because, finally, it costs more.

[Carl]

For that reason I would go with Aluminum... Aluminum is also lighter in weight... Even though you'll need slightly thicker Aluminum...


Having said that, I think I would go for some lightweight honeycomb or foam core with fiberglass covering...

Pound for Pound Alum and SS weigh the same...


It's kind of a trade off...for same strength you can go thinner with SS and weights become similar.


Yannis- Now...If you really want light and sturdy you need to look into adding Ribs, Folds and Ridge forms to a panel. That is why you can sit on a very sturdy feeling folding chair made from paper thin Sheet metal. Those contours and ribs give tremendous support to a flimsy piece of sheet metal.

Panels on your car...same thing. Those shapes add structure to a flimsy panel.

Piece of paper stood on edge can't support its own weight, now Roll that sheet into a tube and push down on top. Bet you could place a reem of paper on top before it fails

[Yannis]

Carl,
I wish I had pics to show you of the dream top a local guy made for another 28 last year. The guy, just because that boat was away, took measurements on MY boat! So, if I ask him to duplicate, at first he has the mold = cheaper for me, and the measurements are there already.
The structure is what bothers me. At first, ss vs alum and then, how to make sturdy without double pillars, flat surfaces etc, it has to be thin and sturdy.
Also, while I'm at it, I want to convert the fb seating completely. I want to put two helm seats and a setee facing aft. This will dismantle completely the already existing SS structure all around, which is where the actual sunbrella bimini + solars stand on and also are bonded to. Tough sh$$t man...

[Yannis]

Like this:

[Tony Meola]

Yannis

watch how much weight you stick above your head. It will make the boat roll more since you are increasing the length of the Fulcrum. If you go stainless, maybe don't go with a solid top. How about just a frame work the panels can sit on. It will help cut down the weight.

By the way, what type of tree would you like us to plant.

[Yannis]

By the way, what type of tree would you like us to plant.

Very good one !! LOL

Yes Tony, like I said, only the frame will be in metal. The top will be foam cored glass. The solars dont weigh much anyway. I think 3-4 kilos each.
I would avoid the top altogether, and have just the solars do the shade, if they were not so ugly underneath, plus the cables etc.

[Navatech]

like I said, only the frame will be in metal. The top will be foam cored glass.

OK, I now have to confess that I misunderstood your question... I understood that when you were talking about Aluminum vs Stainless you were talking about the actual top... Now I understand that you were talking about the framework for the top... In that case IMHO it's six of one and half a dozen of the other... The biggest issue with either is that the fabricator only use the proper (marine) grade of the material... For the construction and for the welding...

As for the top itself, my cover is a kind of plasticized "canvas" and though it gets hammered by the Caribbean sun (no less destructive then the Mediterranean sun if not more so) and it's holding up very well...

[Yannis]

As for the top itself, my cover is a kind of plasticized "canvas"

Thank you Nav.

How strong is this plasticized canvas?
Can it hold two panels at 9 Beauforts?
I was thinking of a similar thing to Joe's, only instead of canvas a glassed foam, WITH braces underneath that will act as backplates to the panels' screws and will make the structure more rigid.
Finally which is heavier; thick alum (with necessary redundancies) or thinner SS ?

[Navatech]

How strong is this plasticized canvas?

Not sure... Fajardo, PR where my boat is located had one glancing blow from a hurricane last year... Nothing bad happened but then again, it was far from a full hit...

Can it hold two panels at 9 Beauforts?

My radar has it's own Aluminum plate which is part of the frame... There's another similar plate which once held a marine TV antenna... I wouldn't expect the canvas itself to hold anything...

WITH braces underneath that will act as backplates to the panels' screws and will make the structure more rigid.

I think that would look ugly... A better idea might be to incorporate hard points IN the foam core BEFORE it's glassed in...

Finally which is heavier; thick alum (with necessary redundancies) or thinner SS ?

If actually designed for the same strength there would be a VERY slight weight advantage to an Aluminum structure... Having said that, go with what your fabricator is experienced in... If he usually works with Aluminum go with that and if he usually works with Stainless go with that...

[Carl]

OK, I now have to confess that I misunderstood your question... I understood that when you were talking about Aluminum vs Stainless you were talking about the actual top... Now I understand that you were talking about the framework for the top...

Nav,
Yup, I understood the question the same way.

Yannis,
The top panel in a hardtop, whatever material chosen, is not the structure you mount items to. The top panel, fiberglass, canvas or plasticized canvas is sandwiched between the mounted item and a mounting plate that is incorporated into the frame. Gaskets and/or silicone to seal and all thru bolted with washers, lockwasher and nut...or locknut.

The frame is usually made from tube/pipe as it is quite string for its weight. However thin walls of tube do not hold screws very well, and thru bolting tubes it is hard to tighten as tube crushes, pounding, vibration, wind rocking can allow bolts to rock back and forth opening holes in tube, so mounting plates are usually welded into spots you intend to install equipment. A plate fitting flush with top of tube, welded between tubes is incredible strong and you can crank down on thru bolts so nothing moves and breaks free.

SS or Alum...Either can be a good choice, mostly dictated by your fabricator. SS will more then likely be heavier then alum.

[Yannis]

If you both understood it that way, then its my fault...anyway, now we all talk the same thing.

A better idea might be to incorporate hard points IN the foam core BEFORE it's glassed in...

I thought someone would bring this up. I wanted to avoid putting wood inside the top, in between the foam. Not only because it might eventually soak in water if badly pierced for the mounting holes; also because this will necessitate a thorough measuring of distances where panels screw holes will eventually fall, and....what if one day I have to change the panels with new ones whose new holes are out of the wooden "hard" points.

PS I dont know why Nav's quote above appears as my own quote to myself !

[Navatech]

I thought someone would bring this up. I wanted to avoid putting wood inside the top, in between the foam. Not only because it might eventually soak in water if badly pierced for the mounting holes; also because this will necessitate a thorough measuring of distances where panels screw holes will eventually fall, and....what if one day I have to change the panels with new ones whose new holes are out of the wooden "hard" points.

First, nobody said anything about wood... Second, not all wood will rot before that tree goes up... Third, there are non wood alternatives... Talk it over with your fiberglass guy... He's done this before...

As for thorough measuring of distances and future proofing, if you put in wide supports (say 10cm) and run them almost full length you don't have to be that accurate and you'll have some future proofing... Again, consult with your fiberglass guy... He's done this before...

I dont know why Nav's quote above appears as my own quote to myself !

One day I'll have to try and teach an old dog (you) some new tricks... But, we'll have to meet for that... I'm not going to even try it through a textual medium...

[Joseph Fikentscher]

If you already have a bimini top, check this out.
http://hardtotop.com/

I'm thinking Azek sheet could be used with aluminum extrusions for support, or Varnished mahohany for the custom look.

[Navatech]

If you already have a bimini top, check this out.
http://hardtotop.com/

I saw that stuff at one of the boat shows (Miami or Ft. Lauderdale)... I liked what I saw... Lightweight and opaque... No idea how well it holds up in sunlight though...

[Carl]

If you already have a bimini top, check this out.
http://hardtotop.com/

I'm thinking Azek sheet could be used with aluminum extrusions for support, or Varnished mahohany for the custom look.

Those light Bimini railing aren't meant to hold any kind of load.

[Yannis]

Thank you Joe, i'll keep busy looking at the various alternatives.
Looks like those huge polycarbonate panels they carry in hardware stores, only more refined and with a frame.


Nav,
I told you so many times to stop over for a weekend ; plenty of time to teach me things...
We could also discuss that tree!

[Navatech]

Looks like those huge polycarbonate panels they carry in hardware stores, only more refined and with a frame.

Just make sure it's UV stabilized (i.e. for outdoor use)...

I told you so many times to stop over for a weekend

Maybe one day soon...

plenty of time to teach me things

I would have thought we would have better things to do...

We could also discuss that tree!

That's one thing I'm NEVER going to discuss with you (or anybody else)!...