Converting wooden boat designs to aluminum construction

The majority of boat plans on the internet are geared to wooden costruction,which is understandable,due to the required skills ,these methods
appeal to a broader audience.My preferred method is welded aluminum,not only because I have made my living as a metal fabricator / alloy welder for 20years, but for me, the net result is faster construction times and low maintenence.That being said, the majority of boat designs that appeal to me are wooden boat designs.Currently, my interest is building a low powered pocket cruiser in the 25-30 ft. range.The Mark v 28 is definitely the front runner ,I also like nexus marines Salty 29,and spira internationals La paz
[all wooden boats]These boats all share that salty look whereas Most alloy boats in this class lack that style.I would like to borrow from both disciplines
to produce a boat that appeals to the eye [employ paint finishes and wood accents]with the superior aspects of aluminum construction. Any comments
or suggestions are appreciated...

 

No problem! Just start with any nice design for plywood, read up on aluminum fabrication and scantlings (Pollard's book, and Gerr's "Boat Strength" are great resources), then go for it!

I am partial to Bolger's designs, and am now in the middle of an aluminum W Atkin "Rescue Minor".

What dsigns are you thinking about?

Sal's Dad

 

Here is a builder of a Didi 26,
http://www.mbyachts.com/start.html

Designed for plywood with a radius chine, built in aluminium.

 

Converting wooden boat plans...

I am looking at the Mark v 28 houseboat cruiser. The website has a construction section and therein lies the problem. The boat is built upside down from a series of frames set at stations and then sheathed with plywood and then glassed.The plans section says no lofting required as all frames and molds are dimensioned ,which leads me to believe the bottom ,sides,and transom panels arent developed.From my experience building aluminum boats [a 16 ft vee bottom center console,and a 15ft 6" flat bottom outboard jet which were both my own design,{read limited experience}] I have always started with bottom,sides, and transom and then installed longitudinal stringers
transverse frames which was the way I was taught by local long time aluminum boat builder Darcy Kellehan. I would like to avoid spending a lot of time and effort building wooden frames to layout sheets so they can be battened to the correct shape.

 

Aluminum (as you know) shapes pretty easily, so the developed panel layout isn't as important as it is with other sheet goods, like ply or steel. Building with your preferred methods shouldn't be a problem, though you may have to use different techniques to get the same results. This can be done on the fly or you could have it worked out for you.

I have a few low power cruisers that could make the aluminum conversion from ply, in this size range. If you drop me an email (click on my name) I can send you a few sketches. The tricks with this particular conversion are to get a stiff enough structure (compared to the weight and stiffness of the original), isolating dissimilar metals and of course, controlling weld distortion. A substantially experienced aluminum boat builder, could make a reasonable go of this conversion, the amateur should get some assistance. Dave Geer's formulas ("Elements of Boat Strength") will produce a nice healthy craft, but it will be heavier and less economical then in has to be. Typical low power applications, usually have a considerable effort in governing weight at the design level.

 

I'm pretty sure I saw this boat (in Gibsons, BC). I was intrigued with it, because so few performance sailboats, especially small ones, are built of aluminum anymore. This boat had an articulating bowsprit like an Antrim 27. It's silver but I think it's actually painted over the bare aluminum. It looks great. I was hoping the owner would show up while I was still there so I could talk to him! I wonder how it comes out, weight-wise, compared to plywood or foam and glass.

 

Aluminum boat off plywood plans.

Hi, I just rolled over the hull on a 25' dory skiff in aluminum which is also desgned for plywood. I believe that most plans for small plywood boats could be translated directly to Al. I wouldn't attempt to build any hull designed for sheet goods that wasn't conically developed. I'm guessing that as aluminum boats become more popular in the recreational boatbuilding market more designers will offer this service as a matter of routine. Becouse of the investment involved and the greater complexity relating to power, tankage, and stability issues it would be money well spent to consult with a naval architect for any boat larger than say 30' or with a lot of superstructure. good luck rusty

 

Regarding the weight issue,Renn Tolmans book states "Plywood weighs about 35 pounds per cubic foot,adding a couple of pounds for fiberglass and epoxy,whereas aluminum weighs 168." This being said, aluminum is 5 times as heavy as plywood.A boat with two layers of half inch plywood on its bottom could be built with 3/16" plate aluminum and be very close in weight. Paying carefull attention to keep scantlings very close using this simple formula the aluminum hull will be slightly more heavy but not to a fault.I would love to see pictures of the "rescue minor" and "dory skiff" in aluminum ...

 

I suppose you need more framing with a thinner aluminium skin.

 

more framing?

Is this a "bait" question ?

 

Can you explain "bait question"?

 

definition of " bait" question

A question created to draw a response purely for the entertainment of the questioner. The reason I asked is becouse I noted that you are a naval architect/boat designer and thought you might have been toying with me. Forgive me if my assumptions were wrong. Rusty

 

OK, I see, it as probably an obvious statement? "More framing". Sorry for that, but it was not my first post in this thread, and I think sometimes people forget the obvious when they compare materials. For small boats local stiffness is the dimensioning factor, not global stiffness.

 

Global stiffness in boat design

Hi, Reggi, Getting back to your original question. I just happened to have a set of plans from the same designer that depicts an almost identical boat in plywood to the one I'm building in aluminum. The boat in plywood has frames drawn on 18" centers as opposed to the 36" centers for the aluminum boat. I have to admit I would have guessed the framing schedule would have been the same. I see boats today in both plywood and aluminum constructed as " frameless" with only a minimum of transverse bulkheads, I realize this is shape dependent but would like to hear your thoughts on this. regards, rusty

 

This is a common misconception and generally based in the differing framing methods employed in metal boats. Most metal boats are longitudinally framed, where wooden are typically athwartship. Often you'll see a combination in metal, with athwartship in the hold or accommodations areas, for maximum interior volume and longitudinal everywhere else.

Frameless metal is "shaped" metal, where the metal is formed (lapstrake aluminum skin for example) at near right angles, which provides much of the longitudinal requirements.