Breaking All the Rules ...

[Snowpetrel]

Originally Posted by a64pilot

An untrasound that is used to test for internal corrosion of aircraft tubing is not that expensive. The age old method of testing was with an ice pick, actually an awl, but the ultrasound is far better. It's operating principle is exactly the same as a depth sounder, thicker substrate takes longer for the reflected sound wave to return.
The machine is very easy to use and does not require a lot of training, assuming you can't find someone to do it for you.


Sent from my iPad using Cruisers Sailing Forum

Ultrasounding a metal boat is unlikely to find all the corroded spots. Its good for getting a general feel for the thickness, but it is only used in limited spots, and will likely miss a small isolated patch of corrosion. It certainly has it's uses in a survey, but can't be relied on.

I think homeless has the right approach at the moment, inspect and look for dampness inside and out. Blasting (with whatever eg grit, glass, soda etc) is the ideal but still won't show up thin spots, only the holes. It's expensive and if the paint is otherwise in good condition it would be unnecessary. Maybe a spot blast on any suspect areas inside and out could be useful. Every Time you blast you loose a small amount of metal over the whole surface, so it's best to limit the number of times you do it.

The one small corrosion hole I found in the aluminium hull of Snow Petrel II was very small and just looked like a pit. it was only by digging into it and then spot blasting that a small neat 3mm hole through the 5mm plate was found, with bog outside it. I guess a bit of copper fell into the engine bilge and caused the hole. I wouldn't have found it without a very good visual inspection and spotblast (or maybe a good water blast inside?). And I doubt it would have given me any problems at sea as the corrosion salts where very solid, with good epoxy bog outside.

[homeless]

I spent the morning using the hole saw on the back and floor of my rather nice shower to try to find the hole in the hull underneath. There must have been a layer of glass on the surface as after two showers I still have that prickly feeling. I still haven't found the hole, but did find lots of water saturated foam with some corrosion underneath that I am in the process of removing, , so the effort was worth it and I am close. If you build an aluminium boat don't spray foam beneath the waterline. Went to the hardware store this afternoon to get a jig saw to speed up the destruction.

I also managed to remove the inspection hatch on the top of the starboard fuel tank with a pry bar and the BIG hammer. I bailed out the remaining diesel and gunk in the bottom and washed the tank out with a water hose, and since I removed handfuls of old welding residue the tank is now the cleanest it has ever been in 27 years. The hole in the tank is the result of minor corrosion on a thin seam weld, and there is no other corrosion obvious inside the tank which is a relief.

Yesterday I got a recommendation for a welder, and he turned up today to have a look at the work. He will be back on Thursday morning, so I have 2 days to prep the holes. Unfortunately he called me back at the end of the day to say he spoke to his insurance company and they would not cover him to weld on a diesel tank as the residue may be explosive (the previous owner of the company died in a gas explosion when welding on a boat). I believe there should be safe options to weld the tank including washing, steam cleaning, using a blower, or filling with water, so I am still hopeful I can get him to do the tank welding, otherwise I may try to talk him into setting up the gear before going to lunch.

I had planned to do the antifouling myself, but am asking around for quotes, and if they are low enough I will hand that work off to allow me to focus on other projects. I also had a rigger on the boat today to quote on replacing standing rigging, which may well be original, and therefore would not be insurable as it is over 10 years old, and may be an impediment to selling the boat. Will also be good to get the mast out of the boat to check the corrosion at the mast base and repair it then isolate it. If I do get the mast pulled, I will remove the old radar and HF radio from the boat, as they have pretty much been made redundant by electronic charts, AIS, and satellite phones.

I went into the chandlers at the boat yard to check the price on replacement through-hulls, but they only had bronze fittings, and no aluminium, stainless, or plastic. I asked about plastic fittings, and was told by the shop owner that he does not approve of plastic through-hulls, so I should use bronze on my aluminium boat. I did feel like asking him to come to the boat and guess which one of the 6 round holes in the boat was the only one that used a stainless fitting (hint, the only one that was corroded).

[downunder]

If the old radar is still working I would not remove it.

Can be very useful fixing position as a check on chartplotter GPS particually sailing north through coastal Qld and GBR.

Certainly if not working not worth fixing.

cheers

[Wotname]

Could you get the welder to to weld in thick wall Al tubes (pipe) instead of discrete through hulls, perhaps plated with a backing plate on the inside of the hull.

As for welding fuel tanks, I always understood that one filled the tank with an inert gas (argon or similar) before welding. This might be wrong but check it out anyway!

[NSboatman]

Wotname has it right - fill the tank with Argon, or whatever shielding gas the welder is using anyway (should be argon I think... but I'm a steel guy not an AL guy so I haven't done it). it'll make for a better weld too. concur on the thru hulls as well - you shouldn't bother with typical thru-hull fittings - especially NOT bronze (unless you're going to fully isolate with sleeves and backing pads on both sides of the hull plate...which is doable if you absolutely want bronze).

Like Wotname sez, weld short sections of heavy wall pipe for thru hulls, then use marelon seacocks. no fuss no muss. Only thing to be wary of is to match the threads between the pipe and the seacock properly - some are straight, some are tapered. don't mix the two.

There's a guy on here- I think his handle is Panope - who is a master with Aluminum. search for his threads and read his experience. he's documented things well on here, and was very creative with his solutions.

you're doin it right...

bg

[Terra Nova]

Originally Posted by homeless

...The hole in the tank is the result of minor corrosion on a thin seam weld, and there is no other corrosion obvious inside the tank...

I am still hopeful I can get him to do the tank welding, otherwise I may try to talk him into setting up the gear before going to lunch...

I will remove the old radar and HF radio from the boat, as they have pretty much been made redundant...

I went into the chandlers at the boat yard to check the price on replacement through-hulls, but they only had bronze fittings...

Pressure test the tank.

Unless you are a welder skilled in the use of tig or mig welding, leave this to a pro.

Radar is NOT redundant.

Do not use bronze thru-hulls or sea cocks. Use Marelon.

[NSboatman]

...have to agree with others radar is not- and likely will never be- redundant.

You may not need it where you cruise now, but sooner or later you'll want it.

Bg

[Cadence]

I must agree with TERRA NOVA, radar is not redundant.

[hpeer]

As to fuel tank repair, perhaps look to the aircraft industry for a solution.

As I understqnd it, small aircraft use wing voids as fuel tanks. They ar not welded but sealed with a two part polysulfide sealant. It comes in a couple of different thickness variants. One is "flow able" and can work into cracks. A stiffer version is for "vertical" applications. It will fill 1/4" cracks.

Others here have used it and had good success over long periods. I used it last year when converting a keel area to a fuel tank and it seems to be working fine.

It can be bought through Boatlife, the polysulfide sealant folks. But I found it much cheaper through an aircraft distributor.

Boat Caulk | Boat Sealant | Sealant Remover

Look for Type H heavy and Type P pourable.

[a64pilot]

Aircraft fuel tank sealant is usually classed as A or B, with B being the thicker stuff, then there is a number behind that like B-2 or B-1/2. The number corresponds to pot life or working time, with B-2 being almost universally what is used. The B is similar in thickness to silicone caulk and the A is similar in thickness to 5200. And like 5200, one little tiny spec can and will get all over everything. Acetone will clean it up before it cures and nothing will after it cures. You can also get painters wipes at a home improvement store, comes in a plastic dispenser like baby wipes that will clean it up without all the issues acetone has.

Oh the 2 is a 2 hour pot life, 1/2 of course 1/2 hour

[homeless]

The old Furuno green screen radar on the boat does not work, so choices are remove it or replace it ... so it will be removed.

The fuel tank is integral to the hull, and the hole is through the hull, so no, I will not fix a hole in the aluminium hull under the waterline with polysulphide sealant.

[Cadence]

Originally Posted by homeless

The old Furuno green screen radar on the boat does not work, so choices are remove it or replace it ... so it will be removed.

The fuel tank is integral to the hull, and the hole is through the hull, so no, I will not fix a hole in the aluminium hull under the waterline with polysulphide sealant.

I hope you do not have to replated the entire hull. I would replace the radar with a 15 mi. job. They are cheap, not everything is AIS. Re: radar the horizon is 15mi.+/- at your elevation.

[Terra Nova]

Originally Posted by homeless

The old Furuno green screen radar on the boat does not work, so choices are remove it or replace it...

...or repair it, if the repair is cheap.

An OLD radar is better than NO radar.

[Cadence]

Originally Posted by Terra Nova

...or repair it, if the repair is cheap.

An OLD radar is better than NO radar.

We live in a throw away world. Labor is so expensive a new unit made in China would be cheaper and probably better.

[JPA Cate]

Terra Nova,

We had one of those old Furunos, and it died twice. Once it was fixable, not twice. The first time, in Noumea, the tech said it would be a temporary fix. The second time, it became a challenge for the radar expert, and he finally couldn't put any more time on it.

I'm thinking that if homeless says it's kaput, it is, those units are quite old now. While someone here might have parts for it, getting the manuals needed to DIY at this point would be pretty hard.

Just my 2 Cents.

My understanding is that homeless bought this boat to re-sell. Why not let the new owner pick the radar?
A.