steel and alu hull

At 90' max you're right on the cusp of whether steel or composite is best. Both will hold up. Steel is stronger, but is heavier and subject to rust and corrosion. Aluminum is better suited for fresh water as a general rule. What you will very often find is steel hull with aluminum superstructure to reduce weight.

kingping,

Welcome to the forum.

There are many aluminum yachts in salt water, all Burgers and Browards for example.

The are many arguments for all materials, but my favorite is comparing them by shear strength (think of hitting a container) and maintenance. Steel will bend/flex/stretch a lot before it tears, aluminum less and fiberglass less further. Steel rusts, aluminum oxidizes, fiberglass can get water intrusion, especially when used with coring. When steel rusts you remove the rust, treat the metal, prime and paint, when aluminum blisters you remove the oxidation, treat the metal and prime and paint. Fiberglass doesnt blister too often anymore. Any port in the world will have a welder that can handle steel, not as many will have one for alluminum, and fiberglass repair can be even trickier. There are many arguments in support of all three materials, and i think it has been discussed on the forums before so you might want to try a search. I have never worked on a steel hulled boat before, but between fiberglass and aluminum, fiberglass is cheaper to maintain because of less blister repair and they use less zincs.

They have built a number of world class expedition yachts in the pacific northwest out of solid fiberglass, so don't count fiberglass out of your search yet.

For a long range cruiser you do not want a semi displacement hull, full displacement with a deeper draft will ride much better and be more fuel efficient.

nas

Steel or Aluminum or Fiberglass

I have a 70ft Stephens in the PNW since 1991 and sailed her from Ft Lauderdale to Vancouver in heavy seas etc, done Alaska and Mexixo, great boat, great scantlings really make the difference, the teak is a pain on the Aluminum and does cause blistering where in direct contact, modern welding techniques have helped to reduce the gapping between welds thus helping to reduced oxidization and also the application of Myler sheet as a barrier between the Alu and teak also helps.

I also have a F/G 43 ft here in Ft Lauderdale and they leak around the windows which the Alu do not. I prefer drilling and tapping to just drilling and screwing.

It's a all a trade off and well designed Steel, Alu or F/G vessel should give years of good recreational enjoyment provided not overstessed beyond design criteria

Just my 2c

There is no substitute for the strength of steel, but maintanence is higher, between sanding and painting, maybe even replacing the occassional plate. It's also easily repairable. They build commercial ships out of steel, not aluminum or fiberglass.

Fiberglass can be plenty strong and when done right is the least amount of maintanence on a 90'. This would probably be my first choice in most 90', although with a long range cruiser steel would be right there with it.

Aluminum would be my last choice. Between worrying about dissimilar metals, even dropping coins in the bilge by accident. I've seen an adjustable wrench someone dropped under a generator eat it's way through the bottom of a hull. Dealing with painting it every 5 years or so because of all of the paint blisters that pop up. Albeit there are lots of Aluminum yachts running around in saltwater............

Dashew don't paint their aluminium exteriors- the oxide that forms over is tougher than the aluminium metal so the oxide protects the metal.

Theoretically, fiberglass will last forever where metals corrode, but the words "maintenance free" and boats don't belong in the same sentence. Leave any boat in the water for 2 years without a haul, diver or moving and good luck. Your bottom and running gear will be supporting it's own ecosystem. Also, if that's the care you expect to give you don't belong on a boat.
There is a separate thread on Pirates & weapons on board. You should explore that. It will answer any questions you have on that subject.
18-20Kt cruise speed is fairly fast (although certainly not heard of) for a 90 yacht. Remember, the faster you go, the more fuel you burn. Of course, the lighter your boat (F/G, Alum. vs steel) the cheaper it is to go faster if all other factors are equal.

real life experience

I have a 95 feet semi displacement aluminum boat that can go up to 27 knots. She has a range of 2800 miles when you cruise at 10 knots and she only burns 60 liters per hour if I cruise at 11 knots.

To put things into context, displacement steel hulls will most probably burn more at the same speed and 11 knots is the cruising speed for a displacement boat of this size. I usually cruise around 11-14 knots, but can comfortably cruise through out the range from 8/9 knots to 20/22 knots. If you choose a boat from a prime yard and install necessary equipment to detect electrolysis you should not have any serious problems.

I have owned several fiberglass boats previously. Fiberglass is porous and sea water will definitely find its way into the hull. Although osmosis is not a major issue any longer, the thread about Bertram boats in this forum is a good example what can happen to fiberglass hulls under demanding conditions.

Aluminum hulls are lighter than steel, so most probably will need less power to move through the water. Yes aluminum will tear easier than steel, but will not deform as easily as steel. There is no comparison with fiberglass, which will burst open in case of an impact with a hard material.