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Old 06-04-2009, 10:32 AM
brian eiland's Avatar
brian eiland brian eiland is offline
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Join Date: Jun 2002
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Location: St Augustine Fl, Thailand
Summary thus far, & New Stock Design

Hello Kimosadler,
I believe you have received some interesting advice on this subject tread you started, and hopefully more will be forthcoming. I am not an alum expert at all, so I will make only a few observations about it as a building material for a catamaran..

In order to end up with the most rigid vessel in aluminum, I think Simon expressed it well:
Originally Posted by simon View Post
I think the advantage of strongall is that you have hull-skin that is very resistant to localized impacts. I am not sure about more global stresses, as the properly designed thin plate construction with stringers and frames may be overall stronger.
Global stresses in a multihull are important both in being able to maintain a rigid base for the rig, and a rigid structure athwartships. And this is an important factor for longevity, as the vessels flexes over its lifetime. The homogeneous sheet aluminum material lacks the rigidity of the steel and sandwich composite. I believe web- reinforced alum sheet is considerable better in this respect. I might also question the true puncture resistance of the 12mm plate over the 10mm plate. Is it really that much superior that its worth building in the heavier material?

Originally Posted by kimosadler View Post
I have my shop built, have 25 years of welding/fitting experience and am ready to make it happen. Of course I will need all the help and advice that I can get, and would appreciate conferring with other builders.
You appear to have the expertise to construct a nice aluminum vessel, so I might think you would spend the little extra time required to build the slightly more sophisticated version of the alum vessel. Particularly since light-weight is an important factor in the performance and weight carrying capabilities of multihulls. Besides the lighter weight vessel just might make her less susceptible to impact damage by virtue of carrying less momentum into the impact incident.
Originally Posted by BlueWaterMarine View Post
I have a 65 ft strongall-type monohull under construction. It is fast to build & ice-ready.....and....30-40% lighter than a steel hull.

You are most probably familiar w/pros & cons of cats. One of the biggest problems is weight. Not a sure a strongall cat would make a seaworthy & good performing vessel. As my last project, we built a 53 ft AL cat. The sister ship made it across the Great Barrier Reef---literally---ran aground, no hole. We sailed ours around the world & had several instances where a foam sandwich cat would have gone down. The cat was built on bulkheads with T-bar stringers. Underwater she was built in the lobster tail system & had double floors for safety. This boat was also fast built.

What can I say, I am an AL convert after years of professionally building steel vessels! For cats, I would strongly consider the weight of the strongall system. For a 40fter would not go strongall.
Originally Posted by simon View Post
I took my thin plated aluminum monohull to Antartica and thought that it withstood quite well the ice.

Originally Posted by kimosadler View Post
Insulation will be 'blown-in' polyurethane foam 20 to 60 mm finished with easy to clean vinyl like Manta Cats have.
I would give serious considerations to investigating this idea further. I once saw a beautiful newly constructed 53 foot French cat down in Lauderdale that had had foam sprayed the inner surfaces of her alum hull. There was some sort of defect in the welding job that was going to have to be corrected, and the huge job of getting all that foam and its residue unstuck and washed, and etched from that alum structure was going to be so costly and intrusive to the cosmetic interior installed already, that the boat was declared a total lost and sold for salvage value.

Most quality aluminum boats I’ve seen utilize an insulation material that is cut into sections to fit between the ribs and stringers and adhesively bonded to the inner hull alum sheet. This allows for different qualities of insulation materials, spot repairs, and far less mess. Any welding heat around polyurethane residues could create poisonous gases.

I might add there was another 59 foot alum cat I inspected in Fl that had really done things proper with respect to the proper adhesion of the insulation material. We all know of the difficulties of keeping paint adhered to alum….requires a proper etching job. This boat’s inner alum structure had been painted with an etching primer prior to adhesion of the insulation material. I think I still have some photos of that vessel…very nice home fit-out.


Originally Posted by whoosh View Post advice, choose a pretty yacht.... she will be worth much more
MARKETABILITY. I just don’t think enough emphasis is put on this appearance aspect sometimes. For instance, have a look at the photos I found of that alum cat I spoke of as being put together marvelously with lots of attention to detail. I would not refer to this vessel as pretty…its clunky looking!! I believe I have detected that you (kimosalder) are not concerned with the looks that much…just a good tough vessel??

At some point in your life I will place a bet that you will want to try and salvage some of your investment out of this vessel….either to get out of boating and on to something else, or to build another dream vessel, It’s not really that much more difficult to build a nice looking design than a poor looking one. And that nice looking vessel will be much more marketable than a clunky one,….even if its just the overall structure’s looks verses the quality of fit-out. On the other hand you may have invested a considerable amount in quality gear and fit-out of engines, electronics, sailing rig, etc, etc, and hope to recover some of these monies. If these quality items are on a clunky vessel it might prove to be much more difficult to recover your investments. Remember the cost of the hull and deck structure of a vessel is probably only 20-25% of the total cost of building a vessel.

And finally, remember the cost of the architect is WELL WORTH the fee he charges in the theme of things. That advanced planning and guidance could well save you more than his fee of 10-12%.(sometimes much less with ‘stock plans’)


Originally Posted by kimosadler View Post
I've been searching for plans for a strongall process aluminum sailing catamaran in the 40' to 50' range.
Originally Posted by simon View Post
..please keep me updated on your progress. I am planning to build a aluminum catamaran soon. Simon
Simon, it’s interesting that you brought up the design site of David deVilliers I consider that 62’ ketch rigged alum cat of his to be a really excellent design. In fact I have been in some talks with him about representing that particular design for, and with him. Here is a portion of that proposal:
So now I come back to the idea of developing primarily ‘two stock designs’ that could satisfy the great majority of my inquiries. I’m defining these two as a 65-ish & a 50/55-ish. I believe these two sizes can fulfill the desires of many clients who might consider a ‘good size private vessel’. If they want something smaller, send them to the production vessels…for something larger, it will involve a custom design.

I really like your 62’ ketch design…so much so that I would be interested in channeling my inquiries for this size vessel to your design. It would become the larger of the two ‘stock designs’ that I’m seeking to establish…the 65-ish one. I presently have two fellows looking at 55 and 56 respectively; that I believe could be talked up to the 62’ (and leave the extra ends of the vessel empty, or lightly loaded). I also have quite a mailing list I would like to go back thru and present this alternative.

I found it interesting that you were also working on a 50 plan. A 50-footer & a 62-footer could well fit into my ‘two stock design concept’. I’m assuming you might make this 50 footer a stock plan as well??

David has considerable experience with aluminum boat design. In fact he was brought in to help with Steve Dashews challenging development of his FPB vessels. He also has computer cut-files for this 62 vessel, and could have them for the 50 footer. These files can save considerable time in construction as well as avoid costly mistakes in cutting all the alum pieces.

What’s not to like about this??

So do you think you two fellows could agree on a 'stock design' that would have appeal to the market as a whole? Or would you both go separate ways and have a custom design done?? That 62' design is MOST appealing in its class.

Some photos of that 59 footer with superb building details
Attached Thumbnails
Aluminum Strongall Sailing Catamaran Plans?-59-cat1.jpg  Aluminum Strongall Sailing Catamaran Plans?-59-cat2.jpg  Aluminum Strongall Sailing Catamaran Plans?-59-cat3.jpg  

Distinctive Expedition Yachts
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Old 06-04-2009, 11:13 AM
brian eiland's Avatar
brian eiland brian eiland is offline
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Join Date: Jun 2002
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Location: St Augustine Fl, Thailand
62 foot deVilliers Catamaran

And finally, I would think you fellows have seen the interesting aluminum material construction discussions occuring over on this other subject thread, "Interesting Alum Design", that deVilliers 62 Ketch
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Old 01-15-2010, 08:10 AM
pato90V8 pato90V8 is offline
Join Date: Jan 2010
Rep: 10 Posts: 1
Location: France


I am French and I live, let's say, 4 hrs driving from META boat builder.

Just to add some news , Prometa boat system has closed on July 2009.

And it was META which built Antoine Boat and not Prometa.

It seems that Prometa has never built boat in Strongall. Just thick alloy + stringer !!.

I am looking on Thick alloy boat for a while now and I will participate in a monthly open event on META workshop. But I don't know when in jan. or feb.

I was also looking for plans and I have called an architect who drawn CATFLOTTER (Antoine Boat) but He was not willing to deal with an "amateur" builder for only one unit. R&D plans need to be done one more time cause legal law has changed in France and to meet those new specifications some CAD calculations need to be added. (reverse torque, ...)

Last thing : META is able to deliver Strongall cut metal sheet to weld by your own in France at least.

Till now only Land Rover alloy have got my heart.
But time brings new dreams.

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Old 12-14-2011, 05:33 AM
adn adn is offline
Join Date: Dec 2011
Rep: 10 Posts: 1
Location: france
Hi Kimosadler
I am a french naval architect, my study office is AND (
I am contacting you because I was very interested by your project . “Banana Split” is a symbol of the cruising catamaran. But it is a little old now. So we design a catamarans in the same spirit, that is to say strong, simply and ready to brave all conditions in all seas but with all modern innovations.
We already designed and built the Galiléo 41 and now we want to design a bigger Galiléo, combining performance, comfort, solidity again. It could be built in strongall (or sealium like the Galiléo 41). And we can work with META.
Feel free to contact us for more informations, plans, and drawings.

Best regards

Guilhèm ANDRE
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