Corrosion proofing inside of Tinny

[brisvegasjack]

Hi All
I am in the process of rebuilding a 20 yo Stacer Tinny. Does anybody have ideas on what to coat the floor with inside to help seal or prevent deterioration. It has been painted inside at factory but the paint is peeling and I do not want to repaint the floor inside unless I have to. It also has a false plywood floor. The floor is sound with no major corrosion or perforations. Just normal white deposits on aluminum in patches. I was told to coat with diesel or Lanoline as a way of helping to slow the oxidisation process. Are there any other ideas out there. Appreciate any feedback. Incidentally the water police were launching their two new Kawasaki jet skis at Wello Pt this morning. They are weapons. Probably out to frighten a few people doing the wrong thing.

Jack

[CHRIS_aka_GWH]

jack,

Nature has given you the most durable coating available. Aluminium like gold, silver etc prevents further corosion with its own layer of airtight oxidised material. No air = no further oxidation.

Aluminium oxide is incredibly durable almost diamond like in hardnesss & often used for sanding belts etc. Anodizing (have you heard of that) is using deliberate impurities to colour the aluminium oxide.

Smearing oil etc on it will make for a dangerous tinny once wet. They usually paint the inside of tinnies to cut reflection not stop corrosion.

Be sure there is no electolysis going on with old wires (cracking plastic), lights that are no longer insulated - installing new wiring thru bilge tubing is good & make sure the battery is isolated etc

chris

ps a useless unrelated fact - When Aluminium was first isolated as metal it was so rare that it was more expensive than gold, silver or platinum so Napoleon had a cutlery set of aluminium made to show off to dignitaries he was dining.

[wayneoro]

mate detergent & a hose down beats it my clarke abalone is 25 yrs has sm patchers of orig paint no worries cheers wayneoro

[brisvegasjack]

Thankyou for your replies. The area concerned is under a plywood suspended floor anyway so you normally cannot see it. It was more of a preventative question to see what other members have done before as inside the keel is out of sight, and at the moment the boat is getting a total going over. The boat is washed inside and out regularly with soap and fresh water. I have only owned if for a few months and guess I want to give it the best chance of longevity. If any other ideas come forward please post them. 8-)

Regards Jack

[dnej]

Jack ,
In the 80's, Stessl built 18 cuddy cabs for the navy, all with ply floors.
They developed deep pok marks on the aluminium, under the floor.

Navy thought battery acid, but CSIRO built the same conditions, to experiment, and found that in humid conditions, salt water evaporated, and formed concentrated drops under the ply, which fell onto the aluminium, and caused corrosion.

Today , epoxy paint is used to combat that issue.
However you can use Lanolin grease instead. This self heals if scratched, and protects the aluminium marvellously. I have done my boat. Works a treat.
Hope this helps
David

[FNQCairns]

I have owned this 14 foot tinny for 15 years I am sure it was at least 10years old when I bought it. Was bought freshly painted, paint is in flakes now, once a year it may see some detergent but mostly it just gets hosed out, no corrosion problems except for one around the transducer screws.
Dont think you have anything to worry about, but be carefull of lost sinkers etc over time.

cheers fnq

[Louis]

You can buy a sacrificial anode from boating stores etc which you can attach to your hull just beneath the waterline which will certainly help to stop electrolosis



Louis

[Chris-Coffs]

[quote author=CHRIS_aka_GWH link=1132364422/0#1 date=1132430223]jack,

Nature has given you the most durable coating available. Aluminium like gold, silver etc prevents further corosion with its own layer of airtight oxidised material. No air = no further oxidation.

Aluminium oxide is incredibly durable almost diamond like in hardnesss & often used for sanding belts etc. Anodizing (have you heard of that) is using deliberate impurities to colour the aluminium oxide.



Well this is true to a point, the aluminium oxide layer that forms is not 100% impervious to oxygen which is what makes the alloy (aluminium is not a "metal") so hard to weld, especially the older, and therefore thicker, the oxide layer. This is because firstly any metal or alloy oxide cannot be welded due to it's exposure to oxygen and secondly the base alloy melts at 660 degrees Celcius and the oxide layer does not melt until 3,000 odd degrees. In smaller pieces this can be like working with a balloon full of water, the inside alloy is molten while the oxide layer is still solid. Also the oxide layer induces informities into the molten weld pool.

This is why Aluminium does deteriorate in the long term and is not the main stay in exposed marine environments like Stainless Steel is, the same process happens but the oxide layer on Stainless Steel is 100% impervious to oxygen and is very wear resistant. It is important not to confuse hardness and wear resistance. To help prevent this Marine Grade Aluminium as extra additives to help with the composition of the oxide formed and to give it better corrosion resistance but the downside of these additives is brittleness and the tendancy to work harden. It is the work hardening that causes the biggest problem, especially when using this material to build boats as to get from the simple flat plate to the many contours in your average hull introduces many stresses, these stresses are only multiplied when all the edges are then welded. Add many years of being pounded by waves and you have the reason for the majority of the cracking that occurs in Aluminium hulls and the difficulty in having them repaired. Realistically, once the stress cracks start to appear the base material is too fatigued to be rescued and is past it's use by date.

To dribble on a bit, this is why you should never work on Aluminium or Stainless Steel with grinding disks, sand papers, files, etc. that have been used on mild steels. Tiny particles of the mild steel can become trapped in the disk (for example) and be then transfered to be trapped in your Aluminium or Stainless causing a straw like effect tunnelling the oxygen through it as it corrodes, seriously pitting the base Aluminium or Stainless it is trapped in.

Sorry to drone on, best to be fully informed than only partly.......

[88fishframe]

Chris-Coffs,

Thanks mate. That's helped me and I have certainly learned from it. Good stuff !!! David