Under Skinning

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mr geets

mr geets

Petty Officer 3rd Class
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I looked at my 21 foot Princecraft in my storage shed tonight and those cross bars just scream to be covered. Last summer I lay down on the front deck and looked underneath to a mess of churned up water beating off the crossmembers.

Any tips on what to do or not do? I am thinking 1/16 inch aluminum sheet underneath attached to the crossmembers with aluminum rivets.

Thanks for any input.
 
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bav/270w

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Re: Under Skinning

I added sheets of aluminum to my toon last summer. Made a huge difference in the ride. Highly recommended. I would use stainless steel self tapping screws instead of aluminum rivets. Start from the rear and overlap the panels with the one that is in front of the other on the bottom. Only need to overlap and inch or so.
 
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MaPaHa

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Re: Under Skinning

Yes this is a "must do" for any pontoon boat.
If you have round toons I would turn a flange down to cover the risers from the toon to the bottom of the joist and bend a 1 inch hem at the bottom to make the bottom edge rigid. On mine this was about a 6-8 inch turn down. You may want to get a sheetmetal shop to do the bends to make them neet. They would do the 1 inch hem first and then the turn down. Just need to measure accurately. This will keep water from squirting out the side between the joist. I think I used .030 aluminum on mine but you could go thicker. I also ran a bead of butal metal roof caulk down the edge of the aluminum and the toon.

Yes, start at the back and overlap to keep the water flowing over the seams. I used 1/8" aluminum rivits.
 
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gpfishingdude

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Re: Under Skinning

Where do you guys get the metal for doing this underskinning? I would like to use that .030 aluminum and the stainless self tapping screws. Also how wide do you get the aluminum sheet metal in? Just don't know where to look for supplies. Thanks!
 
WaterDR

WaterDR

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Re: Under Skinning

I have owned toons without and now with skin. I would never have one without again. But if you have a small powered motor, I would not worry about it.
 
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Todd4

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Re: Under Skinning

gpfishingdude said:
Where do you guys get the metal for doing this underskinning? I would like to use that .030 aluminum and the stainless self tapping screws. Also how wide do you get the aluminum sheet metal in? Just don't know where to look for supplies. Thanks!
Click to expand...

Look at how the manufacturers underskin their boats (at boat dealers). Overlapping is not 'required'. IMHO (I'm not saying NOT to do it.) Where do you buy it? LOL Well, SSS (Triple S) in Houston is the only place I whole heartedly recommend - locally. Really, it depends on where you live. Shop around - many places really don't want to sell you a "few" sheets and will waaaaaaaaaaaaaay overcharge you for the priveledge of buying a small order from them. They want to order a large enough 'lot' directly from their supplier to make a tidy profit. (You'll only be able to buy from the mill if you order an entire 'mill run' - not going to happen.) Also, there are good sellers on the Internet, but you have pay for shipping. Sooooooo.............LOOK AROUND! You'll need to know the grade of aluminum and temper, also (read the pontoon boat dealer's websites.) WE sell "aluminum" is not neccessarily the aluminum you want (I work with steel so I'd have to research corroson resistant aluminum grades - or I'd make a recommendation, here.) It's common knowledge, though.

Todd
 
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MaPaHa

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Re: Under Skinning

It's harder to find than regular sheetmetal but an HVAC supply house that’s known for specialty metals is where I got mine. Also a supplier that deals in metals such as angle iron, channel iron etc will sometimes have flat sheet stock. I would look up any commercial supplier that handles iron and aluminum metals. You might also get a welding shop to find it for you and they will usually mark it up but they are buying it less than a walk-in customer. If you need it bent you might find a custom sheetmetal shop or maybe an HVAC shop that does a lot of metal work that you could buy it from and bend it to your specs. You can get the screws at a commercial bolt supplier if you can’t find them at Lowes or a big box hardware store. The aluminum sizes are available in standard sizes such as: 3x8, 4x8, 4x10 and 5x10. If you run it crossways the 4x8 works but you have some leftover on each sheet. If you run it long ways you can go to the 4x10 foot sheet but they will overlap in the middle but that’s not a bad thing.
 
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gpfishingdude

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Re: Under Skinning

I found a .063 sheet and some smaller pieces at a salvage yard in Kankakee Il. They sell new material and it cost me $182 for one 4x8 sheet and three 22 1/2" x 53" pieces. The #12 x 1" SS sheet metal screws cost $34 per hundred. They are the ones with the washers and the rubber seals on them. This .063 metal is easy to cut with a 14 TPI jig saw blade and it doesn't do too bad of a job, so I'm saving some money from having to find somebody to shear it for me. Right now I'm figuring on $250- $300 for the job on the 18' boat with a couple of inches open on the sides. I will try it out and see if I need to do the sides or if this will be enough to stop the water from flexing the decking like it did last year
 
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TurboM700

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Re: Under Skinning

This is what i'm doing. I had 6 of these bent up at my local sheet metal shop and they will run the long way starting at the back then moving to the front.

Not 100% sure how I'm going to fasten them but I'm kind of thinking some marine grade adheisve will work the best.

You can see by the drawing that is only .040 thick but by the time its bent and glued/screwed in place it will have plenty of strength.

I tested with some wood last yr and was able to get it 100% sealed up but it seemed to gain me a little over 5mph with the skinning I also notived a huge improvement another 5pmh by doing lifting strakes on the inside of the toones.



Here is the build of my boat.
http://forums.iboats.com/completed-boat-projects/pontoon-conversion-inboard-outboard-573089.html
 
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gpfishingdude

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Re: Under Skinning

I have worked far enough forward now that I have the biggest sheet fastened on the back end. I decided to go another cross member forward just to be sure that the wake that curls up will have something to splash against besides the cross members. I only needed one more piece of 22 1/4" by 53" so now my total is around $255 on materials. That is without flanging the sides down and without covering an inch or to on each side. Just thought I would give you an idea what it costs to underskin the 18' boat the way I'm doing it. I'm thinking it is going to figure out at about $16 a foot to do the job and I am real happy if that works out for me.
 
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TurboM700

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Re: Under Skinning

gpfishingdude said:
I have worked far enough forward now that I have the biggest sheet fastened on the back end. I decided to go another cross member forward just to be sure that the wake that curls up will have something to splash against besides the cross members. I only needed one more piece of 22 1/4" by 53" so now my total is around $255 on materials. That is without flanging the sides down and without covering an inch or to on each side. Just thought I would give you an idea what it costs to underskin the 18' boat the way I'm doing it. I'm think it is going to figure out at about $16 a foot to do the job and I am real happy if that works out for me.
Click to expand...

Price seems about right. I have 438 dollars into my 24 foor boat. That with the drawing from the above post.

Mike
 
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gpfishingdude

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Re: Under Skinning

Mike, I looked at your shop drawing and I can tell by the 96 that you are using inches-meaning 8'. I can't tell what the dimension of the width is, maybe as needed. Those are pretty tight tolerances for working with sheet metal, they look like tolerances that are suited more for precision machining. Pretty neat what you can do with cad nowadays, we used to have to make those drawings by hand on drawing boards with T-squares Tom
 
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TurboM700

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Re: Under Skinning

gpfishingdude said:
Mike, I looked at your shop drawing and I can tell by the 96 that you are using inches-meaning 8'. I can't tell what the dimension of the width is, maybe as needed. Those are pretty tight tolerances for working with sheet metal, they look like tolerances that are suited more for precision machining. Pretty neat what you can do with cad nowadays, we used to have to make those drawings by hand on drawing boards with T-squares Tom
Click to expand...


Ha yes CAD has sure made things easier and often take things for granted.


We have a basic understand with out sheet metal guys on tolerance. I like to carry them out to 3 places as it makes it easier for them when doing complex parts with radius in them. When we start drop decimals it starts rounding up or down and some computer programs that they use to laser cut out the metal wont figure the difference out.

As a ME I must understand that sheet metal tolerance are very loose and keep that in mind during the design phase.

I ended up getting them bent out of 12' piece there for i only need 4 of them saved me about 85 dollars overall.

Mike
 
dls322

dls322

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Re: Under Skinning

I have been considering doing this but have been worried about possible premature floor rot...seeing that the bottom of the wood cannot breathe. Incase the boat would get caught int he rain and floor soaked, in theory the moisture would just against the aluminum. Does anyone have any opinion on this?
 
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The Woo Woo Kid

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Re: Under Skinning

dls322 said:
I have been considering doing this but have been worried about possible premature floor rot...seeing that the bottom of the wood cannot breathe. Incase the boat would get caught int he rain and floor soaked, in theory the moisture would just against the aluminum. Does anyone have any opinion on this?
Click to expand...

I wondered the same thing.

Anyway, seems another benefit would be a savings in fuel. the one poster here stated a 5 mph gain from underskinning. Surely that would translate into an across the board fuel savings that would also pay for the underskinning before long.
 
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Triphammer

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Jan 22, 2010
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Re: Under Skinning

Doesn't HAVE to be alum or even metal. I bought some large sheets of what might be 1/8" PVC or ABS & used that. Cost $20 for the four sheets I needed. Working great but I believe the lap IS mandatory.
 
rickdb1boat

rickdb1boat

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Re: Under Skinning

The crossmembers go all the way to the outside skirting. There is plenty of airflow over the underside of the plywood. It is not a "sealed system"..
 
mippel

mippel

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Re: Under Skinning

Triphammer said:
Doesn't HAVE to be alum or even metal. I bought some large sheets of what might be 1/8" PVC or ABS & used that. Cost $20 for the four sheets I needed. Working great but I believe the lap IS mandatory.
Click to expand...

Do you have a link to what you used? That sounds like a great idea.
 
Okieboatguy

Okieboatguy

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Re: Under Skinning

I wonder if FRP (Fiberglass Reinforced Plastic) is what he means, if it is, it is available most any hardware store that sells interior paneling. It is mainly used to cover the wall of commercial kitchens. It has a smooth side and a "Bubble side" and I have heard of some people using it as skinning by using the smooth side out and painting.
 
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Triphammer

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Re: Under Skinning

I ran across this in a used materials yard. I don't kow for sure what it is but doesn't have the fibers like FRP. All the FRP I've seen is 1/16th, this is 1/8th. If you could find some heavier FRP or use some flat string fore to aft, I don't se why it wouldn't work. There's no reason a number of different items coundn't be pressed into service. Corragated roofing springs to mind. Twenty feet long & 30 inches wide @ $30 dollars a sheet for galvanized would last for years. Fiberglass roof panels should last but can be brittle.
 
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