Steel frames & ply cladding anyone

[jehardiman]

Originally Posted by SeaSpark

Most modern designs do not require any steaming of timber. The frames are flat and the skin is designed so that the curvature in the ply can be achieved by just bending it. Steaming ply would debond (not sure about my english here) the ply layers.

The ply can also make a smaller radius bend if you make many parallel cuts in it to about 1/2 its thickness and later fiberglassing over it to strengthen it.

You are correct if the design was for developed plywood skin construction. Otherwise, to touch back to the original topic question of steel backbone and ply planking, steaming of frames is most closely follows that construction technique and opens the door to all sorts of different hull forms that cannot be made with developed ply skins.

[SamSam]

Originally Posted by jehardiman

You are correct if the design was for developed plywood skin construction. Otherwise, to touch back to the original topic question of steel backbone and ply planking, steaming of frames is most closely follows that construction technique and opens the door to all sorts of different hull forms that cannot be made with developed ply skins.

Planking was never mentioned by the original poster as far as I can tell. He talks about replacing panels if they become bad which seems to me to be plywood skin. In another post it was mentioned about heating metal up and beating to shape like a blacksmith. He is talking a small dingy with lightweight tubuler framing. That sort of stuff could be bent cold with simple benders. In another forum someone asked about using metal beams instead of wood in replacing his stringers in a fiberglass boat. I ventured that the different expansion/contraction rates between the two materials might cause problems,etc. It turns out there are actually metal framed fiberglass boats around and it apparently works well. A metal framed, plywood skinned boat would seem to me that it would work. There might be issues of decay but what's new there. The parameters of the boat that I remember are small, cheap, quick and DISPOSABLE. I think the idea was for the frame to maybe last through 2 or 3 changes of very cheap skins. I think another part of the idea was to fart around with some surplus materials that happen to be laying around. Sam

[SeaSpark]

It turns out there are actually metal framed fiberglass boats around and it apparently works well.

Steel frames were mentioned in this thread:

http://boatdesign.net/forums/showthread.php?t=12322&

It is made clear in this thread that the proper way to use steel frame parts in a fiberglass structure is to galvanize them before laminating them in, to prevent untreatable rust.

From Milan in this thread:

Some quality production boat builders use galvanized steel girder which takes all the loads from the keel, mast and rig.

From me:

In all boats i have seen or heard of the steel was galvanized to prevent corrosion.

From Danishbagger:

Yup, galvanised seems to be the deal here. Especially if encapsulating.

From SamSam quoting a thread from another forum:

I once owned a 1960s Cheoy Lee Frisco Flyer sloop and it had galvanized steel pipe for stringers and frames. The pipe was glassed in just like any other material. Designed by Art Robb...an architect of highest regard, these were certified by Lloyds of London and bullet proof ocean crossing sailboats. I owned the boat when it was 12 yrs old and there were no problems.

I have my doubts if it really were pipes in this design.

Galvanized steel floor parts supporting the keel and engine foundation in a fiberglass boats are very common in sailboat design. Complete steel frames are not.

[ted655]

Everything erodes, even SS if it doesn't get oxygen. ACQ treated ply would solve rot issues. A bigger question is the fasteners & joints. I've seen water wheels with steel angle frames & wood paddles. After a couple years the holes around the fasteners wear out & the boards rattle. Would the joints spread or compress as the 2 dissimilar materials each moved at their own molecular rate?

[Thin water]

ACQ Ply is awesome stuff for building houses with but ted655 is correct to question the fasteners as this treated wood dissolves brass, bronse and aluminum and non stainless steels. Glass and resin won't stick to it either. I would just paint the plywood and metal with paints made for each before assembly and keep the boat dry when not in use. I built two little hydroplanes out of exterior plywood (see my gallery pictures) and just dry them off after use and put them in my shop.
Good luck with the project and post any results.

[bertho]

gents,
i just post a thread on the forum woodenboat construction, regarding "composite wood aluminium", i look for people who already experience aluminium for structural frame instead of steel ? bolting or glue with elastomere ? and so

[bertho]

did some one have already experience using aluminium frame instead of steel for those "composite wooden boat" ??

[ted655]

Actually the new stuff hasn't been out there long enough to know what sticks to it. All the various companies I've contacted say they have no rekiable data one way or another. They think sanding or wire roughing the surface is all that's needed for a bond. None of them want to stick their neck out first on this though.The doubt stems from the wax used in the mix. ACQ is corossive to most metals though. It eats aluminium like candy. SS & hot dipped galvinized being the 2 that will work. I now see claimes that a new elctro plated process is suitable.
I have been using Titebond 2 to glue it and have no problems. I have destroyed a few joints to test & they all have failed in the material & not the joint.
I still wouldn't build a big boat out of it but a small skiff would be worth the effort.

Sorry, didn't mean to steal the thread.

Originally Posted by Thin water

ACQ Ply is awesome stuff for building houses with but ted655 is correct to question the fasteners as this treated wood dissolves brass, bronse and aluminum and non stainless steels. Glass and resin won't stick to it either. I would just paint the plywood and metal with paints made for each before assembly and keep the boat dry when not in use. I built two little hydroplanes out of exterior plywood (see my gallery pictures) and just dry them off after use and put them in my shop.
Good luck with the project and post any results.

[sandpiper]

Originally Posted by SamSam

Planking was never mentioned by the original poster as far cheap, quick and DISPOSABLE. I think the idea was for the frame to maybe last through 2 or 3 changes of very cheap skins. I think another part of the idea was to fart around with some surplus materials that happen to be laying around. Sam

Hi, Imagine for the sake of it, a square frame, made up of 1" sq hollow section stainless, ali, or steel. As you look at the square frame, it has a lip running inside of it, to which you fit a ply panel ' like a picture in a frame', now imagine, quarter of an orange ( same principal ) so , imagine two quarter oranges, bolt them up & there you go, Yes I know, half an orange. That the best I can do to explain whats on my mind, & yes it is based on whats kicking about at the time.

[jehardiman]

Ahhh, sandpiper, do you want a "fair" shape or not? The difficulty in forming a steel shape (such as square tube or Z-bar or I-beam) to lie along a "fair" hull surface should not be underestimated. It is very difficult to get an exact bend and twist into the shape at the same time.

If the hull and framing is limited to multiple chines with single curvature (necessary for both ease of forming and use of large ply panels) then it is most likely better to go with either stich-and-glue plywood or orgami steel, both of which would be lighter, easier and cheaper than composite framing. Which pulls us around to the reason that it was abandoned in the first place.

[sandpiper]

Hello jehardiman, I am coming to this conclusion also. However I needed constructive debate to put my mind at rest ' if you know what I mean'. The idea was that the inner lip of the framework ' added later' would take up the twist, & allow for fair shape. Maybe as you say stitch & glue is the proven quick & cheap route to take ?.

[roeslerjd]

I am new and don't have much experience in building boats... but I work as an Architectural Technologist and have some knowledge about characteristics of building materials. And I know in buildings that we try to stay clear of mixing materials with such different properties (with some exceptions), Steel with expand and contract but to hear way more then the wood will... and wood will expand more due to moisture. So it is possible that it could cause cracking or other damage. Although it might be possible with Marine plywood... I don't know its properties.

[ted655]

Many new coatings are avaialable.
http://news.thomasnet.com/news/paints_coatings/140