Underpinning question (or underskinning, underskirting)

[TDJ2591]

My local metal dealer carries .063 aluminum in 3003 grade but not in 5052 which is what all the forum postings recommend. Does anyone know if the 3003 will work just as well or not? He can special order the 5052 but it will likely be much more expensive that way. I understand that 5052 is designed for marine use but I know nothing about aluminum grades.

What is the best way to cut the .063? Or, can it be scored and snapped like thinner material?

Thanks! I hope to start the underpinning later this month.

[HandymanHerb]

Has to be cut

Aluminum sheet is used in a wide variety of applications for its light weight, corrosion resistance and good formability. Two of the most popular grades for commercial applications are 3003 and 5052.

3003 H14 is relatively low in cost and widely available, making it a common choice. It is a non-heat treatable aluminum alloy with moderate strength, excellent formability and good corrosion resistance. H14 signifies the temper. The “H1” portion of the “H14” designating the material was strain hardened (cold worked) and the “4” designates it is half-hard. The main alloying ingredient is manganese which makes it a good choice for spun, formed or stamped parts. It can be easily welded and typical applications for 3003 H14 include:

• Electrical Component Cabinets
• Marine Parts
• Truck, Trailer and Transport Parts
• Storage Tanks
• Doors, Window Frames, Siding and Trim
• Mailboxes
• Fan Blades

5052 H32 is also a non-heat treatable grade with good corrosion, forming and considerably higher strength than 3003 H14. The addition of magnesium makes it an ideal solution for saltwater applications. The “H3” portion of “H32” temper designates that the material is strain hardened (cold worked) and stabilized, while the “2” designates its quarter-hard temper. It can be easily welded and typical applications for 5052 H32 include:

• Trucks, Trailers and Transport Parts
• Marine Parts, Boats, Pontoons and Docks
• Tanks and Pressure Vessels
• Electronic Chassis

[teecro]

My local metal dealer carries .063 aluminum in 3003 grade but not in 5052 which is what all the forum postings recommend. Does anyone know if the 3003 will work just as well or not? He can special order the 5052 but it will likely be much more expensive that way. I understand that 5052 is designed for marine use but I know nothing about aluminum grades.

What is the best way to cut the .063? Or, can it be scored and snapped like thinner material?

Thanks! I hope to start the underpinning later this month.

You will not score & snap 1/16" it will need to be cut either with tinners shears or a jig-saw....

I would not think twice about using 3003 for underskinning or pinning...

I plan on skinning my boat with 1/8" HDPE Plastic sheeting next month... HDPE is the same plastic used in making cutting boards and is very tough and very low cost so I'm going to be odd man out and try this stuff.....

[Soonertoon]

My local metal dealer carries .063 aluminum in 3003 grade but not in 5052 which is what all the forum postings recommend. Does anyone know if the 3003 will work just as well or not? He can special order the 5052 but it will likely be much more expensive that way. I understand that 5052 is designed for marine use but I know nothing about aluminum grades.

What is the best way to cut the .063? Or, can it be scored and snapped like thinner material?

Thanks! I hope to start the underpinning later this month.

What does he sell each sheet for and I assume they are 4 x8?

[Liquid Asset]

Use it. My lifting strakes are made out of 3003. It was the go to alloy before 5052. The psi rating is only a few pounds lower. My fabricator friend who did my welding said it was great to work with. I cut my 1/8" with a MK metal devil blade and Milwaukee circular saw. Worked great and made nice clean cuts. My friends 8' brake couldn't handle the 1/8" so I cut the sheet down and had a shop with a hydrolic brake do the bending.

[TDJ2591]

Thanks all for the great information. 4'x10' sheet of .063' is $107.70. Another dealer in a nearby state quoted $179 for same size 5052. Local guy is getting me a quote on the 5052 but it sounds like I should accept the 3003 which he has in stock. I'm hoping that I can bend it on a 10' manual brake!

I plan to cut each sheet in 1/2 and install perpendicular to the toons, which will leave about a 2" gap on each end. I'll then cut and bend approx. 8" wide x 10' strips to fill in the gap with some overlap and extend down to the toons on each side.

I'm thinking about attaching with #10 SS self-tapping screws with sealing washers like used by others on the forum. The challenge may be to drill holes in the panels to align with the 1/4" deck bolts that extend down 1" below the cross members. I' may need to make a template from HDF then use it to drill the holes in each aluminum panel.

How's all this sound?

Reading this forum can get expensive. I keep finding improvements I want to make. Although my wife agreed to the underskinning when we bought the boat, she says I have to stop pouring so much $ into the "hole in the water" (at least for now).

[rockhound]

we pulled our toon on a loger trip this last week, about 800 miles round trip. the underskinning on the boat was installed using self tapping screws. I did not do the install. I have gone through and replaced a few here and there over the last month, reset a few that missed the cross members etc.

I discovered after arriving at our destination that the frost heaves in the roads we traveled have rattled several, like 15 or more of the self tapping screws out of the holes. they were nicely snug upon departure.


I wound up using a rivet gun to reattach them. You might consider using rivets instead of the screws. They held better and are not affected by a rough road.

[Cycleman07]

Every manufacturer i have ever seen uses rivets for attaching the underskinning... probably for good reason.

[fergusmj]

My local metal dealer carries .063 aluminum in 3003 grade but not in 5052 which is what all the forum postings recommend. Does anyone know if the 3003 will work just as well or not? He can special order the 5052 but it will likely be much more expensive that way. I understand that 5052 is designed for marine use but I know nothing about aluminum grades.

What is the best way to cut the .063? Or, can it be scored and snapped like thinner material?

Thanks! I hope to start the underpinning later this month.

You will not score & snap 1/16" it will need to be cut either with tinners shears or a jig-saw....

I would not think twice about using 3003 for underskinning or pinning...

I plan on skinning my boat with 1/8" HDPE Plastic sheeting next month... HDPE is the same plastic used in making cutting boards and is very tough and very low cost so I'm going to be odd man out and try this stuff.....

I was planning on going this route until I got a good deal on aluminum sheet. Please take pics and post so I can see. Good luck!

[Soonertoon]

A word of wisdom for using tek screws from someone in the aluminum business. When using tek screws, you are relying on maybe one or two threads to be in contact with whatever you are screwing them thru. Alum does not offer the same holding power for threaded items like a steel or polycarbonate does. I have seen numerous applications where Teks back out from vibration, expansion and contraction of the alum base material. You can also strip alum VERY EASILY with too much torque.
I would HIGHLY recommend from 23 yrs experience NOT to use Teks. You will be replacing them and remember...once the thread has cut its groove, replacing the same side Tek in the hole, WILL NOT provide the same holding capacity as it did the first time.
I would use an aircraft grade aluminum rivet. Stay away from stainless as over time you will experience galvanic corrosion from the mix of two materials....steel mated to alum.

Just trying to steer a brother right......

[Tallykenj]

You should consider using structural alum rivets. Check out http://www.rivetsonline.com/rivets-en/b ... ivets.html.

[TDJ2591]

Thanks for the advice on the rivets, guys. i'll take your advice and use them instead of screws. I need to make at least one of the side panels (from the top of the toons to the horizontal under-deck panels) removable in order to access wiring or to run additional wiring. What would you recommend using to attach the side panels so that they may be removable?

For those asking about prices, the local metals dealer called with a quote of $125 each for the 4'x10' 5052 panels. Plus he will cut them to size for free.

This forum is a great source of information and advice.

[teecro]

I plan on skinning my boat with 1/8" HDPE Plastic sheeting next month... HDPE is the same plastic used in making cutting boards and is very tough and very low cost so I'm going to be odd man out and try this stuff.....

I was planning on going this route until I got a good deal on aluminum sheet. Please take pics and post so I can see. Good luck! [/quote]

At 31.00 for a sheet of.125" x 48" x 96" black HDPE plastic the price is too good to not try out..

[TDJ2591]

I agree. Please post pics of the HDPE installation.

[TDJ2591]

Is there a standard thickness for C channel cross members? Are mine 3/16" or 1/4" (or some other size)? I can't get to my boat for a couple of weeks, which is when I want to install the underpinning, so I can't go measure the cross members before I order the rivets. Here are some photos I took a while back. I hope I was successful resizing the pics.