Aluminium SailBoats VS Fiberglass SailBoats

[redneckrob]

Originally Posted by noelex 77

Aluminium has very different properties depending on what other metals are added to the pure alumnium . For aircraft manufacture typically the highest strength aluminium alloys are selected to reduce weight as much as possible. Unfortunately the trade off with these is that they have very poor corrosion resistance (especially the 7 series such as 7075). Aluminium boats are are constructed from one of the five series such as 5083.

Certainly true, same as with different stainless alloys. But even 7 series can be tuned for corrosion resistance, for example the C-130s used 7075-T73 which was a substantial improvement over 7075-T6 and isn't that far off 5083. Bottom line is that all aluminum
corrodes in a salt water environment, some just slower than others. There's also a bit of a survivor bias happening in reports here about aluminum boats that didn't suffer corrosion; those who did probably don't have an aluminum boat anymore!

[Sailingwithgil]

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Aluminum Sailboats VS Fiberglass Sailboats
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[capn_billl]

I use aluminum anodes, don't do that with an aluminum boat.

I'm thinking of buying an aluminum dinghy. It's half the weight (twice the cost), of an frp rib. And has conplete boat furniture.

Seat, integral fuel tank locker, helm.

My only concern is aluminum is soluble in salt water, but since it spends half its time on davits.

[ftamburrano]

I saw the answers and agree with most of them. For a program implying long cruises in far seas for a long time navigation, there is no doubt that ALUMINUM ALLOY is the best material. As a former importer of sailboats to Italy and doctor in chem. engineering, I would definitely choose ALU for the above navigation program, but always remembering that just a hidden copper coin could destroy the toy, and the galvanic issue must be kept in mind every second of the boat life, everywhere.

[edlepera]

Best to obtain an vinyl patch kit and learn aluminum welding

[noelex 77]

Originally Posted by redneckrob

Certainly true, same as with different stainless alloys. But even 7 series can be tuned for corrosion resistance, for example the C-130s used 7075-T73 which was a substantial improvement over 7075-T6 and isn't that far off 5083.

7075-T73 is less strong than the more common 7075-T6 temper. It does have slightly better corrosion resistance, but this aspect is still very poor compared to the 5 series alloys used for boat construction.

If you mad enough to have an aluminium boat made with 7075 there is no need to drop copper coins into the bilge. 7075 (irrespective of temper) has 1.2 - 2% copper included in its composition .

[noelex 77]

Originally Posted by capn_billl

I use aluminum anodes, don't do that with an aluminum boat.

Aluminium anodes are used quite commonly to protect aluminium boats and aluminium components such as sail drives.

Aluminium anodes are formulated to corrode easily and have quite a different composition to marine aluminium.

[Leighpilot]

Actually ferro isn’t a bad idea if done properly. Buy a well made second hand boat , they’re dirt cheap. Get the cruising done and then sell it on, still dirt cheap.

[Mike Burch]

Aluminium yachts are generally lighter than steel, but not as much as you might conclude if you only considered their relative densities. Steel weighs around 7.2 tonnes to the cubic metre, aluminium 2.7.
But steel retains all its strength when welded, whereas aluminium loses up to 50% of its strength in way of the weld, meaning the frames and plating all have to be thicker (heavier) than would be required if they were not welded. Also, flexing aluminium, even within its elastic limits, weakens it. And let's face it, all yachts flex repeatedly.
Because aluminium is a very active metal chemically, pretty well everything that it comes in contact with will rot it to some extent. Plastics are usually OK, but even wood can cause problems. And the comments above about the dangers of electrolysis are spot on.
Nevertheless, if you are meticulous to the point of obsession, aluminium is no worse than anything else as a material from which to build a yacht.

Incidentally, integral tanks sound attractive, but are really a nightmare. It's usually impossible to repair even the tiniest leak. AVOID!

[goboatingnow]

Incidentally, integral tanks sound attractive, but are really a nightmare. It's usually impossible to repair even the tiniest leak. AVOID!

wot I said upthread

[Harmen]

Originally Posted by noelex 77

7075-T73 is less strong than the more common 7075-T6 temper. It does have slightly better corrosion resistance, but this aspect is still very poor compared to the 5 series alloys used for boat construction.

If you mad enough to have an aluminium boat made with 7075 there is no need to drop copper coins into the bilge. 7075 (irrespective of temper) has 1.2 - 2% copper included in its composition .

First of all, 7000 series alloys are not weldable but in the proper temper can be as strong as steel. That is why it is a great aerospace material, but normally it is riveted, bolted or bonded. Most other heat treatable aluminum alloys (6000 and 2000 series) will suffer loss of mechanical properties in the heat affected zone when welded, and like the 7000 series have poor corrosion resistance.
The most popular "marine alloy" , Alu 5083, is not a heat treatable alloy, and therefor does not suffer property losses during welding, using 5356 filler material. Similar advantages are available for the "Cast Alloy" A356, used extensively in Navy applications, ex.(Phalanx Gun System}

[Dr.No]

In her previous life, my Alubat Cigale 16 broke loose from her mooring in an unnamed winter storm in Boston Harbor. She eventually ground up and down on a granite wharf for hours, looking a little beat up but intact. I figure that a fiberglass boat would have sunk in the first 15 minutes. The insurance company didn't know what to do with her. You don't throw your Ferrari (or a boat that has done 22 knots) away because you dented a fender. You find the right guy to fix her.
Integral tanks are fine. Mil spec aluminum anodes are recommended in my case, due to the exposed lead bulb. Cheers!

[noelex 77]

Originally Posted by Harmen

First of all, 7000 series alloys are not weldable but in the proper temper can be as strong as steel. That is why it is a great aerospace material, but normally it is riveted, bolted or bonded. Most other heat treatable aluminum alloys (6000 and 2000 series) will suffer loss of mechanical properties in the heat affected zone when welded, and like the 7000 series have poor corrosion resistance.
The most popular "marine alloy" , Alu 5083, is not a heat treatable alloy, and therefor does not suffer property losses during welding, using 5356 filler material. Similar advantages are available for the "Cast Alloy" A356, used extensively in Navy applications, ex.(Phalanx Gun System}

The above post illustrates some of the significant differences in aluminium properties that are achieved. If you are constructing an aircraft where the strength to weight ratio is an overwhelming concern , one of the seven series aluminiums is likely to be the best choice. The poor corrosion resistance of 7075 is less of an issue.

Boat owners are familiar with the practical corrosion resistance differences between different steel compositions. Mild steel is obviously significantly different to stainless steel. Even within these different types of steels, there are other variations. 304 stainless steel is not as corrosion resistant as 316, and then there are compositions such as the duplex stainless steel that are better again.

Like various types of steel, different aluminium alloys exhibit a wide range properties based primarily on their composition and slightly on their temper. Perhaps because the various alloys are given confusing numbers such as 7075-T6 and 5083-H321 rather than names such as steel and stainless steel there is a tendency to wrongly consider them under the general category of aluminium without differentiating the very different properties based on the type of alloy used.

[jannw]

I actually own an older Garcia yacht - so you can PM me if you have specific questions.

Garcia are probably the best production aluminium boat builders around. I like mine and, for what it's worth, Jimmy Cornell, Skip Novac, and Beth Evans all chose alu boats

That said, the specific question is about maintenance cost - an aluminium boat has more expensive maintenance than a comparable fibreglass boat. Alu hulls require special antifoul, bigger and more anodes, and priming /painting them is complicated and difficult and, essentially, temporary. Alu hulls have very specific galvanic corrosion issues, which mean that you can't leave them plugged in at the marina long-term, you need to be careful with electrical work, and you can't drop and forget miscellaneous metal items into the bilge. Aluminium is not very compatible with other metals, so all bolts or other attached metal parts need special attention (much like those that go onto alu masts)

However Alu hulls have many very specific advantages - which mean they a premium product which appeals to a very specific buyer. Garcia's further are also (almost always) a centreboard design, which will never win races, but has advantages in specific situations. Due to their unique nature, resale of Alu hulls is a bit hit-and-miss ... generally they are most appreciated in France, and its neighbours. Finally all alu huls are semi-custom by nature, so no two are quite the same.

[merrydolphin]

I met a boat down in Pacific Mexico. She was an aluminum Catamaran, 50’ .
She had been around the world twice. The name was “Beach House” When I asked him about the penny in the bilge water he laughed. He said “what bilge water?” Everything on the boat is welded. Nothing is through bolted. Any bilge water is very rare.

I talked to the Capt. Of an all aluminum dive boat. It was an old (50 yrs) oil rig crew boat. I asked him about maintenance of the hull. He said that there basically is none. The boat was full of dents from decades of hard commercial use and otherwise the bare aluminum was just fine.


I think that a properly built and designed aluminum boat is the absolute best. Biggest draw back is the cost.