Hull material? Pros and Cons please.

Are icebreakers made out of anything other than steel?

A double hull wall sounds good. But does any yacht builder practice this? For serious impact events I would think that number of frames and bilge pumping capacity would be more practical considerations than hull material?

Can't wait to hear from Lars

rambling Kelly

So what are the yards that do the double hulls? That can't be a cheap option!

To be on the safe side, I think that steel is still a better material to withstand impacts from floating containers or grounding. Aluminium can be dimensioned to the same strength but is usually selected for lightweight construction and the same goes for composites. What I am saying is that all materials can be strong enough but at a cost, price and weight.

The expression "double bottom" is often used when tanks are integrated in the hull structure, making the tank top the second bottom.

The classification societies have rules for collision bulkheads with watertight doors and there should be little risk of sinking after hitting a container with a modern yacht, whatever the material.

I might expect this on an expedition yacht. But how common are collision bulkheads and watertight doors on "regular" motoryachts? Of course you can design this into any custom yacht. I'm just wondering how often it's actually done?

Thanks Lars ,
Kelly

Kelly,
I do not remember all the rules without looking it up, but in general I think all yachts over 24 m/80 feet is built to rules having these requirements. Maybe some of the big "opens" don´t comply?

Safety rules to avoid sinking and preventing fire to spread are pretty strict today, especially if you would charter with the yacht. Big open staircases running through all decks is not possible any longer and all areas should have two escape routes.

Cognac,
On steel and repairs, yes it can be done in many places, but so can aluminium and fibreglass. I think the latter is even easier since you can always do a temporary repair yourself if needed.

Codger,
Anemone as a 20-knot cruising yacht, should probably be built in aluminium. With Alustar there are very strong dimensions available that you can use in the bow to prevent major damage from collisions with ice or containers. But this yacht will also have at least seven watertight bulkheads to keep it afloat after a water intrusion, wherever it occurs.

Thanks for the info Lars, very interesting topic

i am building a boat at 94 feet with a dutch yard. she is built in aluminium. the reason is, i wanted speed alongside good sea keeping ability. she will have 25+ knots top speed and 19 knots fast cruising speed with a semidisplacement hull. she has a round bilge hull, so should be quite capable in high seas as well. her range in slow cruising will be around 2500 miles. as lars indicated, she has her tanks integrated to the bilge and will be double bottom. although i do not intend to charter, she is being built to MCA standards and according to safety calculations she will have a collision bulk head with a sliding watertight door between the VIP and other cabins and there will be 2 more watertight bulk heads at the fore and aft of engine room. initially another bulk head was planned between the guest cabins and the master, but calculations at a later stage did not require this. i have made some investigations in terms of material strength for aluminium and steel. i understand that aluminium has better elasticity, meaning will keep its form better when you hit something; especially when you consider the weight factor. however, it is more expensive than steel. on the other hand aluminium is easier to work with during production, but need more technical expertise for welding. steel has better tensile strength, meaning it will withstand more loads before it is torn. so there is always a compromise, but if you want to go fast, even with a semidisplacement boat, you need to save on the weight, thus steel is not a good alternative.

well, i should state that corrosion was not a crucial point in my decision base. however, i have tried to study best possible pros and cons of aluminium in respect to steel. aluminium bonds very easily with other metals, so both during the production and during the life span of the boat one should be careful abt properly taking necessary measures to avoid bonding. i also found out that there are systems which detact electrolisys activity of the hull, so one can take precautions at an earlier stage if your anodes are not functioning properly or there is a contact with other metals. in terms of corrosion it is much more difficult to maintain steel, because oxidation is very effective with steel and painting and maintanance of steel is much more important. you do not need to paint the upper sides of an aluminium boat for reasons other than esthetics.

I know this is purely a cosmetic consideration. But I wonder which usually requires more filler material to achieve a "yacht finish", aluminum or steel?

Kelly

With NC cutting of the plates and also more modern welding methods, there are not so much filler needed on any metal boat any longer. This is thanks to the new 3D -modelling, by those who know how to use the programs...

Yachts do not have to be built to MCA, or any other classification society reguardless of size if they are going to be private only.
If a yacht is going to charter or be commercial use then she should be classed.
Delta is most likely the best US yard right now, yet many of their boats are not built to class, Westport does not build to class (although the new 164 will be classed).
Building to class will insure a high standard of engineer and safety including watertight bulkheads and automatic doors on larger yachts. Current class status also helps resale value when you decide to move to another yacht.
Good luck with your build
Dave

I've been doing a little bit of reading about different hull materials lately, and have come across some interesting info.

The first is from a company called Trekker Yachts, they build small explorer style yachts out of aluminium and don't paint them at all.....

http://www.trekkeryachts.com/frtrekconst.html

The next two links are to the site of a marine designer who appears to have put a lot of thought into hull material.

http://www.kastenmarine.com/alumVSsteel.htm

http://www.kastenmarine.com/metalboats.htm

Has anyone heard of "Monel"?


Thanks for the SPS link Codger, very interesting.

The more I read about the Sandwitch Plate System (SPS) system, the more impressed I become.

This report from the Lloyd's website has some interesting aditional info.
The report starts about halfway down (pg 5), and is a pdf, about 380kb.

http://www.lr.org/news/downloads/marine_bulletin_00-3.pdf