aluminum procurement

Steel and aluminum boatbuilding. See: "Boatbuilding Methods", in left-hand column of the Home page, for information about alloys.

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mdweber
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aluminum procurement

Postby mdweber » Tue Sep 02, 2014 7:53 pm

Hello,

I'm looking to get a 12"x12" aluminum plate to fit between my transom and motor. What type of aluminum should I get, and where can I buy it?

Thanks,
Mike

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Bill Edmundson
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Re: aluminum procurement

Postby Bill Edmundson » Tue Sep 02, 2014 8:23 pm

Mike

http://www.metalsdepot.com/index.php

Kevin Moran can tell which type.

Bill
Mini -Tug, KH Tahoe 19 & Bartender 24 - There can be no miracle recoveries without first screwing up.
Tahoe 19 Build

Kevin Morin
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Re: aluminum procurement

Postby Kevin Morin » Tue Sep 02, 2014 11:18 pm

mdweber, not sure what you're using the aluminum for? exactly that is, and details like that would help me understand the material thickness somewhat better.

The primary marine alloys are 5052, 5086 and 5083, I'd avoid 60 series or 30 series even though they may hold up OK, the 50series are better for boat work.
Now, if the transom happens to be wood then you'll need to take some precautions, the same types of precautions for plastic to aluminum mounting.
Let me know what the transom is (material) and I'll try to suggest a way to install the metal to avoid corrosion.

Looking to help.

Cheers,
Kevin Morin
Kevin Morin

lakeracer69
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Re: aluminum procurement

Postby lakeracer69 » Wed Sep 03, 2014 4:46 am

What thickness are you looking for? Usually up to about .100" is "sheet" and over that is called plate.

Powder coating it for corrosion resistance is probably the cheapest route.
As Conan the Barbarian says, " It's not how hard you can hit, it's how hard you can get hit and remain standing".

jcallends
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Location: Coldwater Michigan

Re: aluminum procurement

Postby jcallends » Wed Sep 03, 2014 6:05 am

I have had great success with this site; OnlineMetals.com

mdweber
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Re: aluminum procurement

Postby mdweber » Wed Sep 03, 2014 6:18 am

Thanks for the help, guys!

I'm building the squirt. My transom is 3/4" marine ply with a 1/4" okoume veneer. When I mounted the 20 hp (115lb) engine, the motor bracket left indentations on the transom. I'm worried that over time the bracket will pierce the fiberglass and epoxy, leaving the plywood vulnerable to water intrusion.

I want to use the aluminum plate to prevent the motor bracket from digging into the transom. Of course, I will also bold the motor to the transom.

I think 12"x12" will be sufficient, but don't know what thickness is acceptable.

Kevin Morin
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Re: aluminum procurement

Postby Kevin Morin » Wed Sep 03, 2014 10:02 am

mdweber,
I'll discuss both sides of the transom. First the stern side where there are no clamp pads but there are two rails of cast and painted aluminum of the outboard engine frame. This side could be covered easily with a 0.080" thick piece of 5052 the size of the outboard's contact with the wooden transom.

The forward upper transom has the two screw clamp pads about 1-1/2" dia. that do dig in if tightened well and run around for a while. So another pieced of aluminum can be put on the wooden transom in this location to stop the metal clamp pads from digging in. In this case the are to be covered is pretty small so a strip of metal just 2" tall and the width of the transom will do the work of keeping the two clamps from digging into the ply transom. Here a strip of 1/8" x 2" (maybe taller- 3" if the clamp pads are lower than my recollection) will be adequate to protect the wood.

There is another aspect of wear potential; that's the top of the transom.

So what many builders do is to make a "J" of 1/8" aluminum- to protect all three sides ; forward the leg of the inverted J is only 2-3" then the top is the width of the transom top's thickness and the stern end or long leg of the J is the length of the full engine mounts hull rails.

This 'full metal jacket' approach can be bent of one piece or made of cut pieces and welded- or of an angle extrusion for the forward piece and top (and L for the short sides of the J's legs and horizontal) then a flat plate for the stern piece all bolted and glued to the transom.

Bedding aluminum should be done with 5200 or equivalent sealant/calk/glue so there entire surface of the wood to metal surface is completely and thoroughly sealed from water intrusion. Water that is allowed inside the close space between wood and metal will become acidic and initiate crevice corrosion (also called poultice corrosion in this application with wood) so the sealant is pretty important.

If you through bolt galvanized fasteners are longer lasting than SS and if you use screws (counter sunk into the metal) then wetting them with 5200 or TefGel are the accept methods of bedding between the two different metals.

hope this helps, if there is a welding shop near you that does aluminum welding you can make with carpentry and wood working tools all the metal parts and have the welded in a very few minutes at minimal cost. By adding sides to the J I've described above, you'd end up with a 2-3" deep box with a long 'tail' aft and that entire assembly could glue to the transom as a cap.

Cheers,
Kevin Morin
Kenai, AK
Kevin Morin

mdweber
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Re: aluminum procurement

Postby mdweber » Wed Sep 03, 2014 10:58 am

Wow, Kevin you answered all my questions! Thanks!

Kevin Morin
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Re: aluminum procurement

Postby Kevin Morin » Wed Sep 03, 2014 5:21 pm

mdweber, I'm glad that you found the info needed.

What did your friend Brinkley do to deserve the 'cone of death'?

Cheers,
Kevin Morin
Kevin Morin

mdweber
Posts: 119
Joined: Fri Feb 14, 2014 5:56 pm

Re: aluminum procurement

Postby mdweber » Thu Sep 04, 2014 4:46 pm

Haha, we have always had golden retrievers, and they sometimes get hotspots on their skin. We found one on his tail after getting him groomed, so he was in the cone for a week. He was pretty depressed that week.


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