Alwest Superstructure Rebuild
Posted: Sat Jan 17, 2009 11:14 am
This is an attempt to move the discussion from the general topic of Winter projects to the more specific topic of the superstructure rebuild.
Recap of the thread. In a response to the question "What projects are you thinking about ?" I indicated a desire to reskin the superstructure on Buster. I typed:
"Not unlike the job on Catherine Ann, except I would do it all in Aluminum. I am relatively certain that there is nothing good to find under the superstructure skin. I am thinking of ripping it all off and building a welded aluminum replacement. Not a trivial task, but I have some ideas. Having seen Catherine Ann, it is hard to argue with Rob's selection of materials, but I think I can lighten Buster a little bit by using aluminum. I really need to think about this one, because it could be an expensive mistake if I am wrong."
To which Rob Farrow responded:
"Completely replacing the superstructure would be a huge (but intriguing) project. We have talked about this before. This would essentially eliminate the "achilles heel" of the Alwest construction methods. This would mean also having to replace the interior walls because they are attached to the inside of this same wooden structure. I think you would end up pretty much gutting the boat and starting fresh. . . . If one could acquire an empty Alwest hull . . . one could begin this journey at the right place. Just imagine a properly insulated and heated boat that would be comfortable from early Spring to late Fall Eventually you could transfer over all the pieces that you want to keep and ultimately again have an empty Alwest hull to sell to the next adventuresome soul. The size of a project like this is daunting . . . . but people build whole boats all the time. Case Vandenbelt would be a good resource to talk to. He has already done this very thing . . .. more than once."
Then I said:
"I am actually thinking of keeping the original superstructure intact as much as possible, including the interior paneling. What I would like to do is replace the outer skin with a welded aluminum version with as little as possible change in position. This would allow me to re-use the windows and everything elese without major re-build of the structure. I am thinking of angle-section aluminum attached to the wood frames and sheeting welded to the aluminum to make it happen. I hope it is lighter, stonger and higher integrity that the aluminum over ply original skin."
Rob:
"I can see how this method could work.
Fastening aluminum angle to the sides of the superstructure frames, positioned to carry the new skin at exactly the original wall thickness would make re-installation of the original windows (and door) quite easy.
Fastening the new skin to this new support structure would take a little thought.
One idea would be drill holes through the skin where it contacts the frame. Pressing the skin tightly to the frame and welding the hole closed, would create a solid attachment. This could then be ground flush on the ouside to create a seamless exterior without visible fastenings to the underneath structure."
Me:
"I had been thinking of using screws, but I like the idea of drilling holes in the skin and then filling them with weld material. It is a little more obvious when joining two pieces of sheet together. I am thinking of making sure all the sheets join at an angle piece. That way I can leave a small gap between the sheets of metal and fill the gap with weld material. This would join the pieces together and attach the whole thing to the angle. My biggest concern is how to do this without setting the boat on fire."
Rob:
"Not setting the whole works on fire is an important consideration !
I would not be too worried about the heat generated by small plug welds. Continuous seam welds would be another matter.
Epoxy fillers bond very well to properly prepared aluminum. You might want to think about skin seams plug welded (to minimize heat) to a support angle
and the seam faired with epoxy filler."
Me:
"My other thought was to join the sheets together before installing them on the boat. Then just use the plug weld everywhere. This could work everywhere except the corners."
Rob:
"What thickness were you thinking of for the skin ?
The side panels in particular are going to be big floppy pieces of aluminum to handle in one piece, but it could likely be done with many hands to bring them into position. The holes drilled for the plug welds would really help with assembly because you could see that the skin was tight to the structure before each weld."
Me:
"I haven't determined what thickness to use yet. I recall Case saying something about 1/8" for Cadoruca, so that will probably be my starting point for calculations. I just took a look at the brochure for the Alcan 370 and it indicates that the "side sheets" (I assume that means the superstructure) were 9/64" thick, so 1/8" will probably do. I hadn't thought too much about handling the sheets. My research says that 1/8" aluminum is about 1.8lb per sq. ft. My rough math puts the sides at about 130 sq. ft. for a weight of 234lb. So... three or four people should be able to handle it.
So... some additional math
Two sides at ~130 sq. ft. each
The front ~54
The back ~36
~340 sq. ft. of aluminum weighs just over 600lb, Plywood is around 1 to 2lb per sq. ft. depending on the type. so the weight should be similar to the original.
I just priced out aluminum sheet on an online web-site and it would be around $3,000 to $4,000 depending on the alloy, which leads to the question of which alloy to use. Interesting that you can buy aluminum sheet up to 6' x 12' in size. I am used to seeing 4' x 8' sheets of stuff. I guess people build big things out of aluminum."
Rob:
"Anything less than 1/8" would be really difficult to handle without distortion. If the sheet got stretched during handling, it would be tough to get it to lay flat. A very floppy 234 lb sheet of aluminum sounds like a lot to handle for even 3 or 4 people. This sheet could be temporarily "reinforced" with pieces of wood duct taped to the outside surface to prevent accidental distortion until it reaches its final position.
In the overall weight comparison, you also have to add the weight of the angles to be fastened to the existing wooden frame. Additional framework around the windows might also be required to support the wall compression that retains the windows. With reference to what is there today, the current walls likely weigh considerably more than dry plywood because of the water that they have absorbed.
Regarding alloy, I would pay particular attention to the welding characteristics, since this will be most important. Some of the more expensive alloys cost more because of sophisticated heat treating. This tempering will be negated by the welding anyway, so no real point in paying for it in the first place.
BTW, is there a way to gather and move this "superstructure dialogue" to its own tech section title ?
We have kind of buried this under the "what projects" section but I think any Alwest owner should be interested in this discussion. A unique title might attract input from others. This is probably THE MOST IMPORTANT thing for any Alwest owner to solve, in preserving the value of their boat."
Then Wayne jumped in an typed:
"I have been following this and even though I have not anything to add find it very interesting.
Want to know how it turns out"
Recap of the thread. In a response to the question "What projects are you thinking about ?" I indicated a desire to reskin the superstructure on Buster. I typed:
"Not unlike the job on Catherine Ann, except I would do it all in Aluminum. I am relatively certain that there is nothing good to find under the superstructure skin. I am thinking of ripping it all off and building a welded aluminum replacement. Not a trivial task, but I have some ideas. Having seen Catherine Ann, it is hard to argue with Rob's selection of materials, but I think I can lighten Buster a little bit by using aluminum. I really need to think about this one, because it could be an expensive mistake if I am wrong."
To which Rob Farrow responded:
"Completely replacing the superstructure would be a huge (but intriguing) project. We have talked about this before. This would essentially eliminate the "achilles heel" of the Alwest construction methods. This would mean also having to replace the interior walls because they are attached to the inside of this same wooden structure. I think you would end up pretty much gutting the boat and starting fresh. . . . If one could acquire an empty Alwest hull . . . one could begin this journey at the right place. Just imagine a properly insulated and heated boat that would be comfortable from early Spring to late Fall Eventually you could transfer over all the pieces that you want to keep and ultimately again have an empty Alwest hull to sell to the next adventuresome soul. The size of a project like this is daunting . . . . but people build whole boats all the time. Case Vandenbelt would be a good resource to talk to. He has already done this very thing . . .. more than once."
Then I said:
"I am actually thinking of keeping the original superstructure intact as much as possible, including the interior paneling. What I would like to do is replace the outer skin with a welded aluminum version with as little as possible change in position. This would allow me to re-use the windows and everything elese without major re-build of the structure. I am thinking of angle-section aluminum attached to the wood frames and sheeting welded to the aluminum to make it happen. I hope it is lighter, stonger and higher integrity that the aluminum over ply original skin."
Rob:
"I can see how this method could work.
Fastening aluminum angle to the sides of the superstructure frames, positioned to carry the new skin at exactly the original wall thickness would make re-installation of the original windows (and door) quite easy.
Fastening the new skin to this new support structure would take a little thought.
One idea would be drill holes through the skin where it contacts the frame. Pressing the skin tightly to the frame and welding the hole closed, would create a solid attachment. This could then be ground flush on the ouside to create a seamless exterior without visible fastenings to the underneath structure."
Me:
"I had been thinking of using screws, but I like the idea of drilling holes in the skin and then filling them with weld material. It is a little more obvious when joining two pieces of sheet together. I am thinking of making sure all the sheets join at an angle piece. That way I can leave a small gap between the sheets of metal and fill the gap with weld material. This would join the pieces together and attach the whole thing to the angle. My biggest concern is how to do this without setting the boat on fire."
Rob:
"Not setting the whole works on fire is an important consideration !
I would not be too worried about the heat generated by small plug welds. Continuous seam welds would be another matter.
Epoxy fillers bond very well to properly prepared aluminum. You might want to think about skin seams plug welded (to minimize heat) to a support angle
and the seam faired with epoxy filler."
Me:
"My other thought was to join the sheets together before installing them on the boat. Then just use the plug weld everywhere. This could work everywhere except the corners."
Rob:
"What thickness were you thinking of for the skin ?
The side panels in particular are going to be big floppy pieces of aluminum to handle in one piece, but it could likely be done with many hands to bring them into position. The holes drilled for the plug welds would really help with assembly because you could see that the skin was tight to the structure before each weld."
Me:
"I haven't determined what thickness to use yet. I recall Case saying something about 1/8" for Cadoruca, so that will probably be my starting point for calculations. I just took a look at the brochure for the Alcan 370 and it indicates that the "side sheets" (I assume that means the superstructure) were 9/64" thick, so 1/8" will probably do. I hadn't thought too much about handling the sheets. My research says that 1/8" aluminum is about 1.8lb per sq. ft. My rough math puts the sides at about 130 sq. ft. for a weight of 234lb. So... three or four people should be able to handle it.
So... some additional math
Two sides at ~130 sq. ft. each
The front ~54
The back ~36
~340 sq. ft. of aluminum weighs just over 600lb, Plywood is around 1 to 2lb per sq. ft. depending on the type. so the weight should be similar to the original.
I just priced out aluminum sheet on an online web-site and it would be around $3,000 to $4,000 depending on the alloy, which leads to the question of which alloy to use. Interesting that you can buy aluminum sheet up to 6' x 12' in size. I am used to seeing 4' x 8' sheets of stuff. I guess people build big things out of aluminum."
Rob:
"Anything less than 1/8" would be really difficult to handle without distortion. If the sheet got stretched during handling, it would be tough to get it to lay flat. A very floppy 234 lb sheet of aluminum sounds like a lot to handle for even 3 or 4 people. This sheet could be temporarily "reinforced" with pieces of wood duct taped to the outside surface to prevent accidental distortion until it reaches its final position.
In the overall weight comparison, you also have to add the weight of the angles to be fastened to the existing wooden frame. Additional framework around the windows might also be required to support the wall compression that retains the windows. With reference to what is there today, the current walls likely weigh considerably more than dry plywood because of the water that they have absorbed.
Regarding alloy, I would pay particular attention to the welding characteristics, since this will be most important. Some of the more expensive alloys cost more because of sophisticated heat treating. This tempering will be negated by the welding anyway, so no real point in paying for it in the first place.
BTW, is there a way to gather and move this "superstructure dialogue" to its own tech section title ?
We have kind of buried this under the "what projects" section but I think any Alwest owner should be interested in this discussion. A unique title might attract input from others. This is probably THE MOST IMPORTANT thing for any Alwest owner to solve, in preserving the value of their boat."
Then Wayne jumped in an typed:
"I have been following this and even though I have not anything to add find it very interesting.
Want to know how it turns out"