Aluminum Hulls
Bob La Londe
say the main hull should be 3/16 and yet .100 is used in a heck of a lot of
commercially available small boats. .125 is considered heavy duty. Is it
just CYA?
Steve Lusardi
FAST, but ultimately the scantlings of any boat is a product of size and hull design. Your comment of .125" as heavy duty, that
true if the boat doesn't exceed 18'.
Steve
"Bob La Londe" <nos...@nospam.no> wrote in message news:hev73g$9lb$1...@news.eternal-september.org...
Bob La Londe
news:hf1iaf$7at$02$1...@news.t-online.com...
I've been looking at some of the smallest boats, and there are some with
hulls as thin as .043. Holy cow. No wonder they are riveted. When I was
first practicing aluminum welding I discovered that was below the threshold
for my skills and/or machine. I could make two piece of .043 tube stick
together, but it wasn't pretty.
http://www.trackerboats.com/boat/specs.cfm?boat=3257
Holy cow. Its like tissue paper.
Bruce In Bangkok
wrote:
I suspect that it is mainly a matter of cost, or how their particular
shop is set up to work. Certainly there isn't much of a trick to
welding 1 mm stuff and that is thinner then .043" stuff so I doubt
that it is the wielding itself that is a problem. My guess is that it
is warping that makes them rivet it as welding seams in flat aluminum
can result in some very exotic shapes if considerable effort isn't
taken to prevent it.
Cheers,
Bruce
(bruceinbangkokatgmaildotcom)
Bob La Londe
news:6799h5l4h5p38660j...@4ax.com...
Well, of course its "possible" to weld. I imagine if I went to a smaller
(maybe .23) diameter wire and got feed rollers for my spool gun to handle it
I might even be able to do it with my big MIG rig. Might have to go to a
helium mix instead of straight argon so I could reduce material removal
during cleaning, and then of course I would have to lock stitch and then
back fill. It's a big pain though, and that's why:
"No wonder they are riveted."
Its just not worth the effort of welding for a low price "throw away" boat.
A small TIG torch could handle it easily enough, but it would be
slooooooooowww.
P.S. You do the lock stitch and back fill method on thicker material too.
Bruce In Bangkok
wrote:
I know...
Cheers,
Bruce
(bruceinbangkokatgmaildotcom)
Bob La Londe
Anyway, getting back to my original point. A lot of commercially
available boats seem to be made out of a lot light sheet than the
designers are reccomending in the boat plans they are selling.
http://www.seaarkboats.com/boat.php?measure=Standard&boat=Big+Easy
For example: The link above is to a medium V design 24 footer. The
specs says .125 thick sheet. I can't buy a plan to build a boat that
size designed for .125 sheet. Most of the ones I have seen want to
spec .1875 which basically means .190. Now why is that? Is it just
the typical over building to cover your dearie aere, or are all those
commercial boat builders building inadequate boats and damn the
liability?
Bruce In Bangkok
I wonder whether you are comparing designs that could be in one case
simply a covering attached to a structural frame where the skin only
keeps the water out while the structure provides the strength versus a
design where the skin provides some of the total structure strength?
Think of the original kayak design versus a stitch and glue dinghy
with no internal frames for exaggerations of this concept.
I remember reading that some of the British Steel 70-footers found
dented plating around the bow after leaving the Southern Ocean. the
answer was to add frames to the bow section for the next year's race,
not increase the thickness of the plating. In other words the
thickness of the plating was not considered a factor in the strength
of the bow portions. The frames provided the strength while the
plating kept the water out.
Cheers,
Bruce
(bruceinbangkokatgmaildotcom)
Bob La Londe
Well, it seems except for S&G conversions most of the aluminum plans I have
seen call for building a frame. Atleast in the 20 foot size range. Here is
an example from the Glen-L design catalog. 230 Max HP. The Sea Ark in my
previous post is rated at 225 so similar in stresses.
http://glen-l.com/designs/hankinson/slither-snakeshtr.html
SNAKE SHOOTER VEE between 17-1/2' and nearly 23'
Plating
1/8" 250 sq. ft.
3/16" 200 sq. ft.
1/4" 40 sq. ft.
3/8" 10 sq. ft.
Based on a once over that looks like 3/16 plating for the hull bottom and
1/8 for the sides to me. I have not looked at just one or two designs.
Bruce In Bangkok
wrote:
I don't think you can tell from the materials list. The plywood boat
for example uses 1/4" for the bottom planking and 3/8" for side
planking. Looking at the aluminum list it appears that 1/8" is for
bottom and 3/16" for side, which assumes that the two versions are at
least similar in design.
Given that Glenn-L makes a meal of saying that anyone that can weld
can build one of these boats I would suggest that thickness of plating
may well be selected from sizes that the designer expects that
"everyone" can have some hope of welding successfully.
Again assuming that the basic design is at least similar the aluminum
thickness doesn't seem to relate to the plywood sizes given that
aluminum has an ultimate tensile strength of somewhere around 90 MPa
while plywood is in the region of 30. If it were simply strength
bottom aluminum plating would be in the region of 0.083, based on
plywood strength.
Cheers,
Bruce
(bruceinbangkokatgmaildotcom)
cavelamb
If they are using 1/4" ply for the bottom, it must be double layered.
In plywood construction I would expect the bottom planking to always be heavier
than the sides.
That's where the heaviest stresses would be imposed.
Bob La Londe
news:DLOdnaUR__E9SL3W...@earthlink.com...
I have found similar over design criteria in Pollards book on aluminum boat
building as well. That was just one example. Anyway, it looks like most of
the purchased designs want you to over build.
As to selecting a thickness based on ease of weld I can understand that.
Although why use any 3/8 then? 1/8 is easy with a little care. 3/16 and
1/4 are ok too. when you get up to 3/8 it can be a real trick for an
amateur welder. Especially when tying it into thinner sheets. It has its
own problems just like welding really thin stuff.
Now for a new thread on a technique that will no doubt raise tons of
controversy.
I am Tosk
59055f...@g22g2000prf.googlegroups.com>, alarm_...@hotmail.com
says...
>
> On Nov 29, 6:28ï¿œpm, "Bob La Londe" <nos...@nospam.no> wrote:
> > I find it interesting that a lot of the small boat aluminum designs seem to
> > say the main hull should be 3/16 and yet .100 is used in a heck of a lot of
> > just CYA?
>
> Anyway, getting back to my original point. A lot of commercially
> available boats seem to be made out of a lot light sheet than the
> designers are reccomending in the boat plans they are selling.
>
> http://www.seaarkboats.com/boat.php?measure=Standard&boat=Big+Easy
>
> For example: The link above is to a medium V design 24 footer. The
> specs says .125 thick sheet. I can't buy a plan to build a boat that
> size designed for .125 sheet. Most of the ones I have seen want to
> spec .1875 which basically means .190. Now why is that? Is it just
> the typical over building to cover your dearie aere, or are all those
> commercial boat builders building inadequate boats and damn the
> liability?
I think the latter is the answer. I have seen a lot of large
manufacturers with design and limit stickers that small home builders
would never get away with. Look at the HP ratings for inflatables for
starters. They can put a frekin' 40 horse on a boat and a wooden one the
same size and shape will only hold a 3-5??
Scotty from SmallBoats.com
Justin C
Could it be something to do with the ability of a professional to make a
good weld in that thickness, where an amateur might just be left with a
big hole? Maybe the plans are expected to be completed by self-builders
without the skill of the pro, and a margin for error is built in.
Justin.
--
Justin C, by the sea.
Bruce In Bangkok
wrote:
I'm going only by the materials list that Glenn-L supplies which
doesn't go into detail and simply says something like Plywood, 1/4", X
sheets,bottom planking.
However... The aluminum version doesn't not specify what the various
thickness' they list are used for and there is a noticeable difference
in quantities of say, 1/8th sheet and 1/4" plywood, so I doubt that it
is a case of apples and oranges.
There are no construction drawings and the photographs are mainly
included to show you what a beautiful boat you can build so details
aren't detailed enough to make a reasonable assessment of how the boat
is built, other then a general idea of the frames and stringers.
But you are correct and normally the bottom is stronger.
Cheers,
Bruce
(bruceinbangkokatgmaildotcom)
Bruce In Bangkok
I don't think it is the welding as much as the warping. If you assume
at least minimal skills and reasonably suitable equipment a welder
should be able to weld thinner then 1/8". Perhaps not with stick but
using TIG it is not a difficult feat.
The difference, I believe, is the warping. Thin Aluminum would be all
over the place as soon as you struck an arc and without a really fancy
set of jigs and fixtures I doubt that anyone could get it flat. My own
thoughts are that the thinner thickness' are specified at thickness
that you might get away with without extensive fixtures.
Cheers,
Bruce
(bruceinbangkokatgmaildotcom)
Bob La Londe
That is a good point. I'm not a great aluminum welder and thin aluminum is
a trick for me. The thinnest I have done with a MIG welder is about .043,
and the thinnest I have been able to do a fair job on is about .075.
>> Justin.
>
> I don't think it is the welding as much as the warping. If you assume
> at least minimal skills and reasonably suitable equipment a welder
> should be able to weld thinner then 1/8". Perhaps not with stick but
> using TIG it is not a difficult feat.
>
> The difference, I believe, is the warping. Thin Aluminum would be all
> over the place as soon as you struck an arc and without a really fancy
> set of jigs and fixtures I doubt that anyone could get it flat. My own
> thoughts are that the thinner thickness' are specified at thickness
> that you might get away with without extensive fixtures.
1/8" is actually pretty easy. Fixturing is certainly the way to go.
Warping is certainly a big issue, which in part led me to the idea for the
other thread I started.
Bob La Londe
news:MPG.258af...@eternal-september.org...
> In article <4c685479-5e3d-489a-87e5-
> 59055f...@g22g2000prf.googlegroups.com>, alarm_...@hotmail.com
> says...
>>
>> > I find it interesting that a lot of the small boat aluminum designs
>> > seem to
>> > say the main hull should be 3/16 and yet .100 is used in a heck of a
>> > lot of
>> > just CYA?
>>
>> Anyway, getting back to my original point. A lot of commercially
>> available boats seem to be made out of a lot light sheet than the
>> designers are reccomending in the boat plans they are selling.
>>
>> http://www.seaarkboats.com/boat.php?measure=Standard&boat=Big+Easy
>>
>> For example: The link above is to a medium V design 24 footer. The
>> specs says .125 thick sheet. I can't buy a plan to build a boat that
>> size designed for .125 sheet. Most of the ones I have seen want to
>> spec .1875 which basically means .190. Now why is that? Is it just
>> the typical over building to cover your dearie aere, or are all those
>> commercial boat builders building inadequate boats and damn the
>> liability?
>
> I think the latter is the answer. I have seen a lot of large
> manufacturers with design and limit stickers that small home builders
> would never get away with. Look at the HP ratings for inflatables for
> starters. They can put a frekin' 40 horse on a boat and a wooden one the
> same size and shape will only hold a 3-5??
Yeah, but some designers go the other way to. Lots of designs by glen-l and
bateau are rated by them much lower than if you plug in the USCG formulas
from their backyard boat builder pamphlet for the craft in question.
P.S. I have visited your site before and found a very informative.
I am Tosk
Thanks. It's been a while since I left the shop to move north and take
care of Dad. In case anyone wondered where the heck I went;)
Scotty. I do plan on returning to the shop someday if I can...