Aluminum or Fiberglass?

Hi Steve, I think the answer in all four variables you gave, is who built it and how is it maintained. There are good and bad boats as well as owners. And this is the same if you should look at brand new boats. The only real difference is that a painted aluminium boat needs a little more attention to keep blisters away...

I have owned a 70 ft Aluminum MY built by Stephens Bros. in ca. 1974..owned it since 1991, Have cruised ZFlorida, Bahamas, Mexico, Alaska and the PNW.
Biggest issue was too much teak trim, paint blisters where the teak joins the aluminum and in some areas where the welds were not continous. The paint blisters would take at least 5 yrs to show up.
Given the choice of this vessell Vs identical F/G vessell I would opt for the Aluminum construction, also, construction methods today are superior to those in the 70's and most of the blistering can be avoided.

I feel the aluminum is much more maintanence. The aluminum vessel needs to be painted more often, every once in a while a plate needs to be changed on the hull due to electrolyses .If any metal tools are dropped anywhere in the bilge of an aluminum boat (especially copper) it is a disaster. Also you have to be careful what metals if any are used throughout the boat when it comes to piping and water lines (when doing repairs and such).

Fiberglass you don't have these issues. It IS harder to do a repair on fiberglass if damaged, but not that much more difficult in most cases unless the damage is severe.

Might be helpful

These articles may provide some insight from Michael Kasten of Kasten Marine Design.

How Do Composites Compare with Steel & Aluminum for Boat Structure...?
http://www.kastenmarine.com/composites.htm

Aluminum For Boats
http://www.kastenmarine.com/aluminum.htm

Metal boats are generally constructed with tankage integral with their hull bottoms. Especially in the area of blackwater tanks, the plating can be prone to wasteage on the inside.

There is no substitute for an audiogage periodically.

Good question. You might want to contact, say, Palmer Johnson in Sturgeon Bay, WI to see what they do with their Al hulls/tankage.
I know freshwater tanks in steel boats receive 'job-specific' paint jobs.
As regards sailboats changing the dynamics, I don't think oxidation knows if it's going fast or slow.

Hi,

In addition to the FW the Black, Grey, Ballast and Bilge Water Tanks also get "job specific" paint jobs on metal hulled motor yachts.

Hi,

IMO Bladders are not any use at all for anything longer term, they do not fill easily and tend to suffer failures from chafe in a short period of time, this can be very short of they are installed and filled on anything that sticks up even as slight as weld splatter

Hi,

I agree that Bladders are very good in aircraft, Air craft and yachts are two completely different beasts.

I am also aware from my limited experience with Helicopters of the ability of aircraft bladders to be self sealing in event of someone shooting holes in one, These type baldders are quite different in construction from what you will find in use on boats which is what I was referring to with my post above yours, not aircraft ones.

Interesting thread. Could you narrow down the 'fibreglass' option ?
Cored or monolithic hull shell ?
If cored, foam or balsa ?
Internal liner mouldings used as hull structure or transverse / longitudinal bulkheads and stiffening ?
Filled + faired + painted hull or gel finish ?

Well built with collision bulkheads, whatever. But i would rather have a carbon fibre mast than aluminium if I am hitting a container...

Kanter

Don't know if you need a builder, but Kanter Yachts has quite a bit of experience in building some great aluminum yachts, both power and sail, while working with well known designers such as Chuck Paine, Ron Holland, Dave Gerr and Greg Marshall.

http://www.kanteryachts.com