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Fixing a Marinette Hull? Then ...
 | Check the hull first before you decide to weld.
 | Aluminum hull percussion sounding or ultra-sounding can
cost $20.00 per foot to find flaws, ask a surveyor who knows
this stuff. |
| If it feels deeply pitted, it's too far gone, see below. |
| A small patch is usually just fine. |
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| Alloy : Plate and Sheet Aluminum 5086-H34 or 5086-H116 (GATW or TIG welding). Don't
switch to a "better" alloy and for heaven's sake don't use
non-marine aluminum. A specific welding alloy is recommended for H5086-H34
or H5086-H116,
use it. Aluminum Roamers, I'm told are usually the same metal. (Yes, ABS
American Bureau of Shipping rules
say mixing marine aluminum allows is OK with the right filler metal (weld
wire)).
| Hint, A wrecked Marinette has aluminum for patches. |
| But Marinette hulls can always be fixed. |
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| Thickness :
| Bottom plating - 28' and 32' 5/32 inches 37' and up 3/16 inches |
| Sides and Top - 1/8 (source Aluminum Cruisers Brochures, circa
1977) |
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| Repair Welding is GATW with a ceramic backing strip. Hire only expert
welders for repair. Expect an aluminum welder to make at least $35-$100 hour
depending on location and demand. Fixing a hull with a few plates
should not be an exorbitant amount. A prepped boat can be welded quickly. |
| Hire an expert welding shop with expert aluminum welders.
| An expert won't weld in the wind. |
| Will use a ceramic backing strip. |
| Will know which welding alloy to use. |
| Will know when to Mig or Tig weld. |
| Will not have a "sooty" weld. |
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| Clean the areas which will be welded. Get all the tar out and thoroughly
clean it as a welder would. Be ready to weld. Do not use grinders on
aluminum, they damage the surface with heat. Sandblasting is not generally
required to weld aluminum. Do not use steel or copper brushes to clean
aluminum, stainless brushes are ok to break the oxide layer. (Aluminum melts
at 650 C, but the oxide layer melts at 2000C +. A clean weld area is
essential, and that means that even finger print grease is not
permitted. |
| Do not braze marine aluminum that will be immersed, it's too large
a galvanic (voltage) difference. Aluminum brazing (like Duraweld) is an
above the waterline patch. It's better to use epoxy than this stuff. In fact
I'd just avoid brazing marine aluminum, unless you boat in distilled
water. The brazing metals are high in zinc and will corrode. (ABS does
not state that brazing is permissible for hull construction.)
| Brazing is using a lower melting metal to attach two higher melting
metals together. It's not necessarily weaker than welding. |
| Brazing may be ok for many above the water uses where salt is
not an issue. |
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| Check the welds.
| Good welding and repair makes that part of the boat "new". |
| Expect that welder will know how to check the quality of the welds.
Hull fixes should cost less than you'd think. |
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| After it's done right; clean it, rough it, and paint it. |
| Remember, It's usually cheaper to fix it right, than to try some weird
epoxy fix. A large epoxy patch may fall off as the hull flexes (you
can use it for fairing), but don't put the life of the boat on it. |
| Marinette Hull anode is a aluminum alloy called Sealloy. It's common here
to put zinc and Sealloy zincs on the same hull. I am trying to get the exact
metal
composition of the Sealloy. |
| You can hammer and fair out a dent in a Marinette. It'll stiffen the
aluminum in that spot a little, so I'd replace that area of aluminum after
it's first 10-20 dents. After the first 10 dents, consider replacing
the captain also. |
| Non-Marinette boaters : Inspect the hull of the boat you own often,
because too many companies put out cheap aluminum hulls that end by breaking
up. One of my friends lost two small Jon boats and had it replaced
twice by the company. They considered it normal business. BTW: He had
warning cracks that he ignored, and was happy with his 3rd boat. Go
figure...
| A rivet on an aluminum boat hull is a bad idea. (But you should never
mix rivets and welds on the same boat, the fastening systems are too different.) |
| Tongue and groove boat construction on an aluminum boat hull is a bad idea. |
| Ultra thin hulls on an aluminum boat hull is a bad idea. |
| A real hull is welded and is nearly bulletproof. |
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Aluminum 5086 H-34
Chemistry
Aluminum Balance
Chromium 0.05 - 0.25
Copper 0.1 max
Iron 0.5 max
Magnesium 3.5 - 4.5
Manganese 0.2 - 0.7
Remainder Each 0.05 max
Remainder Total 0.15 max
Silicon 0.4 max
Titanium 0.15 max
Zinc 0.25 max
Machinability in the strain hardened tempers
H34 is relatively good. Use of lubricants is advised when cutting with tools.
This alloy is readily weldable by conventional
methods for Aluminum. Use of
electric arc welding (GTAW) in particular
produces excellent results. Differing chemistries of Marine Aluminum should not
be welded together. Most commonly welded with 5356. Must be clean and oxide free
to weld.
Form Sheet
Condition H34
Temperature 68
Tensile Strength 47
Yield Strength 37
Elongation 10
Sources ATSM and SAE
Fixing Stainless ? Then ...
| You'll replace the stainless shaft and the rudders before the aluminum
hull. |
| Not all stainless is equal, so use only series 300 stainless clamps (316).
(Beware " automotive all stainless" clamps, they rust.) Marine stainless is 300 series
only.
| Double clamp all hoses. |
| Buy the better clamps. |
|
| Stainless shafts
| Stainless welds just fine, but in my opinion brazing should be an
above the waterline fix. Rudders on the Marinettes are probably brazed
(with a nickel alloy) to their shafts. I just don't care for brazing in
the marine environment. |
| Stainless can be filled and fixed, and shafts can be remade, (unless
they look like Swiss cheese). |
| Oxygen starvation or electrolysis corrodes immersed stainless steel.
That's why the area around the cutlass bearings and seals goes first.
(Enclosing stainless under water will chew it up). |
| Check shaft isolation from the engine. |
| A bronze prop and a stainless shaft just need to be zinced correctly
to be together. |
| A shaft zinc too close to the prop will affect performance. |
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Fixing Steel ? Then ...
| Know that steel can almost always be fixed. You can fill holes with
welding and grind the steel down. |
| Rudders that have huge pits can be weld filled or have plates
welded. |
| Steel is the easiest metal to weld, and I'm told it's OK for brazing in
marine applications (when properly zinced). |
Off Site help
Walke
Point
- a discussion of welding aluminum
Aufhauser An aluminum brazing company explains marine alloys and welding. (FYI:
Marinettes are 5086-H34 or 5086-H116 alloys.)
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