Aluminium or Fiberglass HULL good and bad of both??

T Dunn

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May 23, 2018
16
Allied Princess Southwest Harbor
There are lots of different aluminum alloys. Some have good corrosion resistance and some don't. If the right alloy is used and care is taken to avoid galvanic corrosion, then aluminum is a very good material for boat building. As noted above many large yachts are built in aluminum. There are several aluminum boats locally that have sailed extensively for years without problems. For example Palawan VI is at the marina in Southwest Harbor right now. It is aluminum, 34 years old and in as new condition. Another aluminum yacht that summers here is the 140' ketch Rebecca. I also have friends who have a 40 aluminum boat named Grendel that has sailed the north Atlantic for years with no corrosion problems despite not being painted above the waterline.

As far as weight goes, an aluminum boat will generally be lighter than fiberglass for equal strength in contrast to steel (particularly for boats under 50').
 
Jan 11, 2014
11,323
Sabre 362 113 Fair Haven, NY
Dave, you're in NY so you've seen salted winter roads. Ever see aluminum that has been attacked by salt? It starts to display a layered effect. Soon you can peel it like mica. My understanding is that this is what basically happened with the 47'er. Pinhole leaks developed and progressed .
I'm not saying that Aluminum can't or won't corrode in a salt water environment, I think there are some other factors involved in addition to the saltwater. The cause could be poor quality or wrong alloy aluminum (It wouldn't be the first time defense contractors cut corners), poor building techniques (i.e., welding errors), failed electrical system, damage to the hull coating, and so on.

You might find this link interesting: https://www.totalmateria.com/page.aspx?ID=CheckArticle&site=ktn&NM=187 which describes various types of aluminum corrosion.

Everett Collier's The Boat Owner's Guide to Corrosion is a good resource on the subject.

I believe that fiberglass is better for a sailing yacht, as it can be built lighter for the same amount of strength.
I'm not sure I entirely agree with this. Certainly modern composites with carbon fiber and other exotic fibers can be lighter than aluminum. Most of the current crop of high end (IMOCA 60s, VOR 65s, America Cup etc.) are made of exotics, however, the expedition yachts, designed for high latitude sailing tend to be of aluminum. Although this couple (https://www.youtube.com/channel/UCxUG_7A_tUT8SrYKgC6FB0A) did a northwest passage in a wooden boat, but then they are Australian. :biggrin:

The other part of the equation is cost and how easy it is to build the boat. I haven't priced the cost of a newly constructed Aluminum or CF boat lately (or ever), my guess it that an aluminum boat, especially a one off, is cheaper to build than a similar boat built with exotic fibers or even traditional glass and resin.
 
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Oct 19, 2017
7,733
O'Day 19 Littleton, NH
I once read a Cruising World article about steel boats. I was especially impressed with the story of a guy in a steel cruiser of about 45' who suffered damage from being pinned between two tugboats at a marina in Europe during a storm. He was sailing home to NY to get repairs. Not something a fiberglass boat could do. Thus, I did a little research into building steel boats which led me to aluminum. It is my understanding that aluminum is a more expensive material but easier to build with. The difference in cost tends to equal out. Aluminum doesn't need paint to preserve it from corrosion like steel, although there are steels that also don't corrode (oxidize). They are expensive.
As far as other comparisons to fiberglass: every yard knows glass. Aluminum requires skill and equipment that may not be accessible.

-Will (Dragonfly)
 
Oct 22, 2014
20,995
CAL 35 Cruiser #21 moored EVERETT WA
@videorov Being a confessed YouTuber... it is a wonder you have not shared this vlog on a boat owner who went from fiberglass to Aluminum and then decided not to paint their boat...:yikes:
 
Jan 11, 2014
11,323
Sabre 362 113 Fair Haven, NY
Aluminum doesn't need paint to preserve it from corrosion like steel, although there are steels that also don't corrode (oxidize). They are expensive.
As I mentioned earlier I am involved with a NFP that has acquired a steel boat needing a lot of work, thus, my delving into metallurgy and corrosion.

We often use corrosion and oxidation interchangeably, apparently in the technical world they are different. Oxidation occurs when electrons exchange with oxygen and the metal. This typically forms a hard protective coating over the metal. A lot of road bridges and metal power lines are designed this way, that's why they are rusty looking. Stainless Steel works this way, a thin coating of oxidation forms and protects the steel, it needs a constant flow of oxygen to keep the SS from corroding.

Corrosion occurs when the metal atoms leave the metal, as in galvanic corrosion where the zinc, aluminum or magnesium atoms leave the anode and plate on some other metal.

One form of corrosion, crevice corrosion, occurs when metal is left in stagnant water and the oxygen is depleted. The oxide stops forming and the metals in the alloy start reacting and corroding. This apparently can happen with SS and aluminum.

So bear with me as I ramble through some of this as it helps me to understand the issues. Maybe I'll grow up to be a metallurgist some day...
 
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Sep 20, 2014
1,320
Rob Legg RL24 Chain O'Lakes
If Aluminum is so bad as a tool to use why would the someone invest so much money.
https://yachtharbour.com/news/world-s-largest-aluminium-yacht-in-build-at-royal-huisman-1829
View attachment 158073
This is a boat due to be completed in 2020

They just flipped the 81 meter hull.
https://www.royalhuisman.com/royal-huisman-turns-largest-hull-ever/
Quite a trick.
Because it is much cheaper for a non-production boat. Fiberglass needs to be built in a mold. Building a mold for a single one off boat adds to the cost. You end up building the boat 3 times instead of once. The process of fiberglass means you build a plug, then build a mold, and then build a boat. If you can't spread that cost out over multiple hulls, it gets really expensive.
 
Oct 19, 2017
7,733
O'Day 19 Littleton, NH
Because it is much cheaper for a non-production boat. Fiberglass needs to be built in a mold. Building a mold for a single one off boat adds to the cost. You end up building the boat 3 times instead of once. The process of fiberglass means you build a plug, then build a mold, and then build a boat. If you can't spread that cost out over multiple hulls, it gets really expensive.
For one offs, there are other approaches to fiberglass. You can build a plug to build a mold to build the hull or you can build the core and sandwich it in glass. Of course, then you have all the problems of cored glass construction. Done right and cared for, it can last as long as any boat.

-Will (Dragonfly)
 

DArcy

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Feb 11, 2017
1,691
Islander Freeport 36 Ottawa
For one offs, there are other approaches to fiberglass. You can build a plug to build a mold to build the hull or you can build the core and sandwich it in glass. Of course, then you have all the problems of cored glass construction. Done right and cared for, it can last as long as any boat.

-Will (Dragonfly)
It's still cheaper to build with metal than fiberglass for a one off, even if you build a frame, core, laminate structure.
In production building, fiberglass is cheaper. One offs, metal is cheaper. Steel rusts and is 3 times as dense as aluminum so a lot of customs are aluminum. Carbon fiber is stronger and stiffer than any of the above (fiberglass, aluminum and even steel) so is a better material for boats but is also more expensive.
A friend of mine has an aluminum boat. A few years ago the crane screwed up and dropped his boat on a jackstand that had slipped, the pad came off and the jackstand went through the hull. It was a few square inches so should have been easy to fix. The insurance company insisted on selecting the welder (probably on price) but the welder screwed up and the welds were junk. I inspected it myself and it was definitely not water tight. My friend then told the insurance company he was going to select the welder and we found someone that had much more experience in large aluminum structures. The problem was the weld area was now bigger and up against a frame and some cabinetry so more work was involved. In the end it was repaired properly.
This long story just reinforces the comment above about it being easier to find someone to repair fiberglass than aluminum.
 

dLj

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Mar 23, 2017
3,373
Belliure 41 Sailing back to the Chesapeake
Aluminium or Fiberglass HULL good and bad of both??

I've seen people with both on Youtube sailing the world.
You'll also see people sailing boats around the world made from steel, epoxy composite, carbon fiber, wood, ferrocement, etc. That is to say, every material that boats are made from are all sailing around the world, or have at one time or another.

They all work, they all have advantages and disadvantages, a lot of "good and bad" lies with where and how will you be sailing and what your personal preferences are.

dj
 

dLj

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Mar 23, 2017
3,373
Belliure 41 Sailing back to the Chesapeake
We often use corrosion and oxidation interchangeably, apparently in the technical world they are different. Oxidation occurs when electrons exchange with oxygen and the metal. This typically forms a hard protective coating over the metal. A lot of road bridges and metal power lines are designed this way, that's why they are rusty looking. Stainless Steel works this way, a thin coating of oxidation forms and protects the steel, it needs a constant flow of oxygen to keep the SS from corroding.
The definitions of corrosion and oxidation, taken from H.H Uhlig's "Corrosion Handbook":

Corrosion: Destruction of a metal by chemical or electrochemical reaction with its environment.
Oxidation: Loss of electrons by a constituent of a chemical reaction.

So oxidation is a term used in chemical reactions, which may be (usually are) occurring during corrosion. Corrosion is the term used when you have a detrimental effect on your metal.

What you are talking about with the "hard protective coating" are what are often called passive oxide layers. Aluminum actually oxidizes way faster than steels. If you take a piece of aluminum and scratch it revealing the underlying metal, which is shinny, you can watch the oxidation take place as you are looking at it.

When aluminum is oxidizing, it is forming an inert, impervious oxide layer that then protects the underlying aluminum metal from further oxidation (or corroding) as that oxide layer prevents oxygen from passing through it to further oxidize the underlying metal. One of the implications of this is that you need to keep abrasion from occurring on your aluminum or that will remove the protective oxide layer and the underlying metal will corrode essentially instantaneously.

Stainless steels are similar although there is a much greater resistance to corrosion in the base metal than aluminum. The passive oxide layer in stainless steels is much thinner than the oxide layer on aluminum. Stainless steels are also rather complex in their corrosion behavior. Stress corrosion cracking is a complex subject in itself. But I think an in-depth discussion of both are a bit beyond the conversation level of a forum like this.

dj
 
Oct 10, 2011
619
Tartan 34C Toms River, New Jersey
For one offs, there are other approaches to fiberglass. You can build a plug to build a mold to build the hull or you can build the core and sandwich it in glass. Of course, then you have all the problems of cored glass construction. Done right and cared for, it can last as long as any boat.

-Will (Dragonfly)
I had a friend who built a Bruce Roberts Design 54' using the core method. It came out great that was back in the late 80s.
I can remember the biggest pain was getting the hull faired.
As far as I know he is still chartering in the Caribbean, although I have not been in touch with him for awhile. His last name is Romano if anyone ever ran into him.
 
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genec

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Dec 30, 2010
188
Pacific Seacraft Orion27 HP: San Diego, M: Anacortes
If you are referring to the Stratton, it was repaired and is in service. https://www.marinelog.com/index.php...ifies-causes-of-stratton-corrosion&Itemid=257

Aluminum is a perfectly fine boat building material if it is done correctly, if there well designed cathodic protection and if it is maintained well. It seems to be the building material of choice for sailors exploring high latitudes, like Skip Novak, Evans Starzinger and Beth Leonard, and John Harries among others.

While fiberglass hulls are not subject to corrosion, stray current and galvanic corrosion can sink a fiberglass boat just as quick as an aluminum boat, because the corrosion will attack the underwater metals like rudder posts, prop shafts, and through hulls.

The which is better question is really the which material is better for which purpose.
Hmmm, that got me to thinking that since it is the metals that are generally the issue when looking at problems with an FRP boat... perhaps the solution is to avoid thru hulls, go engineless, and use externally mounted gudgeons for the rudder... by doing so, one eliminates all the potential thru hulls, and thus the possibility of the failure of such.

Now I realize that in a practical way, things like gudgeons, shrouds and stays need to have backing plates... which will support bolts that do actually go through the hull... but these are very small holes, vice the typical thru hull.

Just a thought.

I know Lin and Larry went engineless and vastly enjoyed the space otherwise allocated for the engine and components.
 

T Dunn

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May 23, 2018
16
Allied Princess Southwest Harbor
The incidence of thru hull failure is vanishingly small. If you are really concerned about it go with marelon (fiber reinforced plastic), which will eliminate galvanic corrosion. As far as your prop and rudder shaft penetrations are concerned I would recommend traditional stuffing boxes which do not fail catastrophically like dripless seals do.
 
Aug 13, 2012
533
Catalina 270 Ottawa
traditional stuffing boxes which do not fail catastrophically like dripless seals do.
Traditional stuffing boxes can fail catastrophically if not maintained properly and the dripless seals don't fail, if maintained properly. In the meantime, if you have a dripless seal, you have a dry bilge.
 
Jan 11, 2014
11,323
Sabre 362 113 Fair Haven, NY
Traditional stuffing boxes can fail catastrophically if not maintained properly and the dripless seals don't fail, if maintained properly. In the meantime, if you have a dripless seal, you have a dry bilge.
Both seals rely on a section of rubber tubing, both can fail. The exception being those stuffing boxes that are glassed into the hull.