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Old 17-12-2012, 16:18   #16
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Re: Aluminum floor beams in a steel hull?

Well, certainly some things to think about. Given the amount of material needed, in terms of linear feet, I might actually be kidding myself in terms of weight saved.

However, Sabre Dance is a heavy old lady and I've been putting her on a diet as much as I can. While 60-80 lbs is isn't much in the grand scheme, its still 60-80 lbs of water or stores.

While wood would the easiest, I find that metal will give me more space, with similar or slightly less weight per foot depending on section. I am planning on building all the furniture framed in aluminum, and I do have the steel to do the floors.

My frames are 33 inches apart so the fore and aft frames for the floor have to span that much. I could put a vertical in at mid span, welded to the skin but I'd prefer not to. I currently weigh some 300lbs and figure that 1 or 1.5 inch angle will do as I use 3/4 ply floor plates. Very stiff, no flex at all.

I'll ponder the question some more over the next few weeks. For now the old wood frames have been reinforced with angle clips and are holding. But they will eventually have to go as the floors are currently made of bits and pieces cut to fit around the old furniture and as mentioned are rotting.

Thanks for the input. S'what I love about this place. Instant knowledge.
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Old 17-12-2012, 16:30   #17
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Re: Aluminum floor beams in a steel hull?

Just as a note . . . you can get structural fiberglass L beams. I used them inside an aluminum boat for cabinetry framing (they glue quite well unlike aluminum). But they are likely rather more expensive than steel L's.
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Old 17-12-2012, 16:31   #18
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Re: Aluminum floor beams in a steel hull?

The hive-mind knows all.
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Old 17-12-2012, 16:47   #19
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Re: Aluminum floor beams in a steel hull?

"My frames are 33 inches apart so the fore and aft frames for the floor have to span that much. I could put a vertical in at mid span, welded to the skin but I'd prefer not to. I currently weigh some 300lbs and figure that 1 or 1.5 inch angle will do as I use 3/4 ply floor plates. Very stiff, no flex at all."

just a question: wouldn't it make more sense to span port to starboard in line with the ribs - increasing the hull stiffness at the same time?
and then "truss" it to the ribs as needed.
no worries about lateral bracing.
then you would just have to check the plywood spans are adequate.
you will likely need intermediate members fore and aft (along the plywood seams at min.)
if available using a tongue and groove plywood will help greatly.
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Old 17-12-2012, 18:01   #20
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Re: Aluminum floor beams in a steel hull?

I should have mentioned that Boracay could do with a bit more hull stiffness.

When the wind blows the wrong way the mast seems to get a vortex going and the entire boat resonates.

Stiffer floors and soles help!
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Old 17-12-2012, 18:27   #21
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Re: Aluminum floor beams in a steel hull?

I should clarify: i'm not a boat builder or naval architect.....just know a thing or two about structure and it seems to me the sole could be a critical/integral component of the hull structure if designed correctly.
the question was also for my own curiosity!
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Old 17-12-2012, 20:03   #22
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Re: Aluminum floor beams in a steel hull?

Quote:
Originally Posted by smaarch View Post
I should clarify: i'm not a boat builder or naval architect.....just know a thing or two about structure and it seems to me the sole could be a critical/integral component of the hull structure if designed correctly.
the question was also for my own curiosity!
cheers
Usually in metal boat building it is not. Its usually just tacked on to the ring frames and NOT part of the 'designed structure'.

I have never been sure why because they could certainly be part of the design structure. I guess the metal boat is so stiff/strong for other reasons already that it not necessary/useful to make it 'more sophisticated'.

My aluminum hull was originally designed as a racing boat, and the framing is moderately 'sophisticated', but the sole and interior are not part of the structure. Even the bulkheads are not.

This does contrast with glass boats where the interior is often used to stiffen the hull.
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Old 22-12-2012, 15:24   #23
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Re: Aluminum floor beams in a steel hull?

Quote:
Originally Posted by smaarch View Post
just a question: wouldn't it make more sense to span port to starboard in line with the ribs - increasing the hull stiffness at the same time?
and then "truss" it to the ribs as needed.
no worries about lateral bracing.
then you would just have to check the plywood spans are adequate.
you will likely need intermediate members fore and aft (along the plywood seams at min.)
if available using a tongue and groove plywood will help greatly.
I'm not sure just what you mean by spanning in line with the ribs. Each rib has a doubled beam going from side to side except for the one at the back and the front of the floor area. Those are bolted then welded in place or bolted if aluminum. The 33 inch sections run fore and aft between thos main beams and are spaced to allow an accessable center bay plus one bay on either side that is also accessable. The two outside sections of sole are permanently bolted to the main frames and the fore and aft stringers. At the bow end, it ends up with one center bay and two bolted down sides, then finally one section bolted down.

To put another main beam set across between the ribs would shorten the fore and aft bits by half, but add complication and more weight.
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Old 23-12-2012, 02:47   #24
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Aluminum & steel = bad idea

Electrical insulation will delay the inevitable. Humidity alone with allow galvanic cell to develop. I would glass any area (bilge) that may hold water to prevent mic corrosion.
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