Swing Keel on a Cruising Boat

[Leither]

Since no one seems to have covered it so far, I thought a bit of chemistry might be interesting at this point (though if you feel a tendency for your eyes to glaze over at the very mention, then please move on!).

Aluminium is actually a relatively reactive metal. It is higher than zinc or iron in the reactivity series of metals, for example, and only slightly below magnesium. In contact with any metal below it in the series, it will corrode "preferentially" (and, in the process, actually protect the other metal from corrosion ie act as an anode) hence the concerns mentioned about stray currents and contact with other metals.

Aluminium's built in trick is that the oxide which forms on its surface, when in contact with air or water, is waterproof and protects the metal below. This is in contrast to iron, where the oxide (rust) allows water through and the whole damn thing evtually crumbles away (as we all know to our cost!).

If the aluminium oxide layer is damaged, then a new layer forms and maintains protection (assuming no other metals in contact etc).

One of the problems about this oxide layer is that it is relatively soft and easily damaged, so where the metal is exposed to regular abrasion then there could be an erosion problem. This can be overcome to an extent by "hard anodising" which process essentially thickens up the oxide layer and makes it more resistant to abrasion (commonly done in domestic appliances and industrial applications).

As people have mentioned, the quality of the aluminium being used is important. Lower quality metal contains more impurities which set up localised electrolytic "cells" which can cause pinholes and eventual failure.

If you feel over-stimulated as a result of reading this, then I recommend deep breathing and relaxation!

Stuart

[OsmundL]

Jim H, I am sorry to get away from your main question: keels. It is not only in Barbados that shallow draft can be a blessing. This photo is from my boat in July this year, in Lofoten (Norway). Yes the colour is odd - because it was well past midnight. More important, I am sitting in 80cm of water here, and you could wade to shore. And yes, Lofoten has many sandy beaches. I don't know how many stops I have made in shoal bays at the spur of the moment when a marina was full, the weather dismal, or the schedule gezumpt.
Extra fun at these latitudes is the reaction from sturdy locals who know all about the sea but have not seen too many centreboards. At this particular spot a young man came rowing out to say "You must get outta here; you'll soon stand on the dry." My broad smile confused him no end, especially when I said "Yes, I was hoping for that."
Anyway, I wish my boat would point just-a-little higher - though isn't that how every sailor feels at times? Mostly, it keeps height with other cruisers and sometimes better, but very light winds are no great shakes.

[OsmundL]

Originally Posted by noelex77

The corrosion risk above the waterline is not zero. If any stainless steel fitting is not isolated properly you will get electrolysis even above the waterline.

Noelex77, I was trying not to be pedantic. Yes, on *any* boat *any* proximity of two metals causes electrolysis, given moisture (electrolyte). But this applies to fittings in general - bronze, brass, aluminium and steel on masts, shackles, bolts and accessories. The good news is that exposed aluminium above water does not "rust" like steel, does not absorb moisture and bloat/delaminate like some fibres - indeed it forms a protective layer on its own.

Originally Posted by noelex77

I may be wrong but I think you are misunderstanding the purpose of the paint underneath the antifouling below the waterline. Its main purpose is to simply isolate the metallic antifouling from the hull

Well, it does both, though the choice of antifouling is a topic of its own, and metallic antifouling is a no-no; e.g. common copper-based paints are not used on aluminium.
I have spoken to a few owners, and the corrosion problem that concerns them is the propeller area - like on most boats.

Anyhow, here are photos of my boat, with the hard coat, then antifouled (blue). Finally, run ashore for a show in Oslo; as you can see, getting to the hull for maintenance can be pretty easy.

[noelex77]

Originally Posted by Leither

One of the problems about this oxide layer is that it is relatively soft and easily damaged, so where the metal is exposed to regular abrasion then there could be an erosion problem.

Thanks for the chemistry lesson. I agree with everything, but I would point out that That an aluminium boat is less prone to abrasion problems than a fiberglass one. Many owners have commented how they have rubbed against a pier etc in a storm and done no damage in conditions that would have damaged a fiberglass boat. I guess the abrasion resistance of aluminium oxide might be low compared to other metals, but not gelcoat.
The oxide also reforms almost instantly. One trick when tring to glue aluminim is to sand off the oxide under a layer of glue to stop air reaching the aluminium and reforming the oxide layer. If you sand then apply the glue the oxide will have reformed.
I also have never heard of a practical problem with aluminium corroding in areas of high abrasion. There can be significant problems with both aluminium and ss coroding if air does not reach the surface. This "crevice corrosion" has caused many a problem with aluminium and ss water tanks, but that is a seperate issue. If boatbuilder would stop using aluminium for unsuitable applictions such as water and fuel tanks aluminium boats would have a much better reputation.

[noelex77]

Originally Posted by OsmundL

Well, it does both, though the choice of antifouling is a topic of its own, and metallic antifouling is a no-no; e.g. common copper-based paints are not used on aluminium.
I have spoken to a few owners, and the corrosion problem that concerns them is the propeller area - like on most boats.

Thanks for the photos she looks in great condittion.
Antifoulings used on alumium boats are still metal based mostly tin or a special type of inert copper, but as you say don't ever use ordinary copper based antifoulings.
My antifouling needs redoing have you any recommendations ? I used Trilux last time, but the performance has not been fantastic. I guess your swing keel gives the advantage you can dry out and give it a scrub.

[OsmundL]

Originally Posted by noelex77

My antifouling needs redoing have you any recommendations ? I used Trilux last time, but the performance has not been fantastic. I guess your swing keel gives the advantage you can dry out and give it a scrub.

May I do a Palin and say "I'll get back to you on that"?
Honestly, scrubbing has been the saviour and helps a lot. In Europe the state of antifouling paints generally is in flux and not easy to navigate. New environmental restrictions limit the use of metals etc. in the paint, but different countries have not adopted the same standards. In France I believe it is strict, so an Ovni from the factory has a merely so-so paint applied. Sweden differs from Norway and so forth, and I am sure the manufacturers consume copious bottles of valium trying to cope with the diversity. I hear advice on new wonder cures from time to time, but none long-lasting. Last year the gospel was "nanotechnology" but I suspect that so far it's right up there with "Whiter than white" laundry powders.

In short, I wish like you that the sonic system could work. Alternatively, that more marinas would install the system I saw in Sweden - they sweep the boat underneath not unlike going to your local autowash. When it is so easy to sweep frequently, the need for antifouling reduces considerably.

[Leither]

Originally Posted by noelex77

Thanks for the chemistry lesson. I agree with everything, but I would point out that That an aluminium boat is less prone to abrasion problems than a fiberglass one. Many owners have commented how they have rubbed against a pier etc in a storm and done no damage in conditions that would have damaged a fiberglass boat. I guess the abrasion resistance of aluminium oxide might be low compared to other metals, but not gelcoat.

I agree entirely. I guess I was just speculating as to the reasons for using "hard anodising" in certain applications. It probably doesn't apply in a marine environment.......

Stuart

[Jim H]

Thanks to all for the detailed posts.

The Jimmy Cornell presentation was very enjoyable this evening. My son and I attended, and picked up another signed copy of his latest book (given that I left my first copy at JFK airport this year).

He decided to keep his Ovni and currently has her in the Ionian. He noted that he has 70,000 miles on the boat now, and feels that he has her figured out in terms of sailing (even if he doesn't consider himself the best sailor). He noted that the manufacturer disagrees with some of his recommendations, but he makes them anyway.

As far as sailing downwind, he likes the centerboard all the way up. He sometimes flies two spinnakers, and he feels the flat bottom can't broach because there's no pivot point with the keel up.

He keeps her flat going into the wind, because the boat can have a lot of leeway. He's not the best at going to weather, but he had a racing friend do a brilliant job with his boat going close to the wind, so he admits his techniques may not be the best.

His boat, a 43 foot, does have a hydraulic pump that lifts both the board and the rudder, and it can be left in "open" position when using the center board as a sounding board. In closed position, there is a sacrificial copper disc that blows if the board hits something, and he admits he's replaced the disk about ten times after doing that (it's easy to replace).

His boat is only about nine tonnes, so it handles lighter winds well. It was well insulated for the arctic trips, and the insulation also helped in the tropics.

It was fun to hear Jimmy talk again, and my son really enjoyed the stories and the pictures. The talk was mostly about his sailing life and experiences that he most cherished, instead of a specific trip or sea-going advice.

Anyway, that's the report so far. I need to read his book again. I did receive a current price list for new Ovnis, and there will be a 395 owners version at the London boat show next month that we plan to visit.

Now, a few questions for OsmundL:

1) Does your 395 have one or two cabins in back? We have two growing kids, and the idea of separate cabins is appealing, but if the two aft cabins eliminated needed storage space then we're concerned.

2) If you were considering a used Ovni, what would you look for and look out for? Cornell noted that the Ovnis were improved as the years passsed, in part because the hulls weren't tied to a fiberglass plug that was difficult to modify. That could suggest there are features/design elements of newer Ovnis that are preferable to older ones.

3) When the paint starts to go on the decks or bilge area, is it going to be a major project to prep and repaint again? I saw that caution on the aluminum boats page.

4) If the bare aluminum on the topsides goes milky, do you worry about it, or leave it alone? I know it's protective oxidation, but it sounds like some Ovnis are polished as they age to improve appearances.

Thanks!

[OsmundL]

Originally Posted by Jim H

Thanks to all for the detailed posts.
Now, a few questions for OsmundL:

1) Does your 395 have one or two cabins in back? We have two growing kids, and the idea of separate cabins is appealing, but if the two aft cabins eliminated needed storage space then we're concerned.

2) If you were considering a used Ovni, what would you look for and look out for? Cornell noted that the Ovnis were improved as the years passsed, in part because the hulls weren't tied to a fiberglass plug that was difficult to modify. That could suggest there are features/design elements of newer Ovnis that are preferable to older ones.

3) When the paint starts to go on the decks or bilge area, is it going to be a major project to prep and repaint again? I saw that caution on the aluminum boats page.

4) If the bare aluminum on the topsides goes milky, do you worry about it, or leave it alone? I know it's protective oxidation, but it sounds like some Ovnis are polished as they age to improve appearances.

Thanks!

Thanks, Jim H. I hope you treat my opinions just like Cornells, not as factory bible. Indeed, I suspect Alubat would be slightly annoyed as more people pick up on our options (more work for them). That said, they have been very accommodating, no complaints there. But to be naughty: the factory would give you a list of perhaps 20 common options, but national dealers are aware of so many more. I ended up creating my own database of every option spotted or heard of, mostly with photos. It blew out to a list over 300, admittedly including electronics and safety gear. If you should be very keen one day, I could mail you a list concerning the actual build. It is too long to bore people with here, but I can give examples of small-ticket items: additional welded cleats and handrails, welded dorades, granny bars, bosun’s locker, all the welded ears and loops you can think of for fixing flags, lifting a dinghy in the targa, and more. In the end, you’ll never need a bolt to attach anything.

A particular feature in my and at least one other boat is 2 welded roofbars in the cabin, instead of teak. Alubat don’t like them, every visitor loves them. Another late add-on, not from the factory, is a fixed wind deflector in fibreglass and Lexan, slightly Hallberg-Rassy like.

All that said, I suspect you’ll find greater variations in equipment levels, and in the end that could matter more when buying used.

1) One or two aft cabins? I have one because I am selfish and wanted a washing machine to starboard. Also, the bathroom is larger on that version. Your needs are different, but do note this: the aft port cabin has an enormously wide bed, I’d call it a 3-seater, so if your kids can get along, why waste even more space for sleeping?

2) At the time (2006), the 395 was their newest model and best compromise between performance and comfort. Shortly after the 365 came, also a good performer. Now there is an all-new 445 replacing 435, also with more modern lines and supposedly performance. That said, many people swear by the now older 435, a roomy and safe model. Others may disagree, but I would say the greatest steps forward were made from about year 2000; very old Ovnis certainly were no fashion statements. As far as I know, the models beginning with the 435 sail better. But practically all Ovni buyers are experienced and have had several boats before, so solutions are usually very well planned (if quirky, in some cases). Only a tiny number were chartered.

3) Repaint, yes, I’d call that a big job. The white deck paint is supposed to have an extraordinarily long life – it is after all 2-component and practically a gel coat. Alubat recommends the outside hull to be “sandblasted” and repainted from scratch every five years – I have never heard anyone do that, most grin when I ask.

4) Bare aluminium going milky: I have not worried, though I shall reapply some oil – one day… Something must have changed at the factory along the way, because some very old (20 years and more) Ovnis look rather dull and sad, like old tin cans. It is quite easy to keep the shine, rather like polishing a car, but in some ways one (I?) gets a kick out of knowing it can sit there unattended, no harm done. I had an all-aluminium pilot ship before, all painted, and made the mistake of starting to strip it bare to re-paint. Never again! Remember that folks who paint their hull tend to also add filler to make it perfect. Start stripping back, and all manner of sins come to light.

This was meant to be a brief reply…

[Jim H]

Quick update: we're off to the London Boat Show today to take a close look at an Ovni 395. Should be fun.