The Steamboating Forum

My personal prejudice is that traditional carvel construction is, by definition, overweight.

I understand that it's the way boats were built and for good reasons. I find them esthetically pleasing but I find a lot of things from the past pleasing. It doesn't mean that I will choose to duplicate the shape without using modern, light construction techniques to save weight. The Wright brothers would have loved to have modern materials. And the 1903 flyer would have weighed less. Or maybe not.

If I'm going to build a hull out of vegetables, I will at least use them for the center part of a sandwich panel
(strip building) or do a bunch of laminating such as plywood or cold molding..

Every pound that goes into the hull comes out of the fuel, supplies and accommodations budget. I find it all too easy to get a boat 'down on its lines'. When I returned from several years of wandering in my 36' sailboat and emptied it out for casual cruising, it rose over five inches. Startling!

Today, however, I am cutting brush away from my driveway. I wonder if there is a way to use this stuff structurally? Like a high quality OSB panel. Horrible thought but they said some pretty withering things about plywood not that many years ago.

If I decide to build a hull that cannot be constructed with simple curves (plywood) I will certainly consider the Culler designs. Beautiful hull shapes. But with strip construction.

I was looking at the former Newport News Shipbuilding tug HUNTINGTON, 103 ft. LOA, 29 ft. beam, approximately 12 ft. draft. This tug has a lot of information available on line and in print (in the textbook Introduction to Steel Shipbuilding). The original was built with an 800 Hp steam plant (later converted to 1300 Hp D****l plant), made 10 knots, and displaced 489 tons. Scaling this down to a 30 ft. version: 103 ft / 30 ft = 3.43. 3.43 cubed = 40.47. 800 hp / 40.47 = 19.76 Hp. 489 ton displacement divided by 40.47 = 12.1 tons!! (as a launch, of course, the forward draft could be diminished considerably to reduce displacement).

My copy of Propcalc indicated the following for the original tug, based on 96 ft length at the waterline:
Recommended propeller: 94 inch diameter and 103 inch pitch.

For a 30 ft. version, with 28 ft. waterline length, the scaled power would be 19 hp.
At 19 hp, 300 rpm, and 24000 lbs displacement, Propcalc indicated a maximum speed of 5.2 knots (versus max hull speed of 7.19 kts).
To make hull speed, it indicated that 49 hp would be required. It also suggested a 37 inch diameter propeller producing 969 lbs of bollard pull.


Interesting, but too heavy and slow to be practical -- back to the drawing board!

Lopez Mike wrote:My personal prejudice is that traditional carvel construction is, by definition, overweight.

I understand that it's the way boats were built and for good reasons. I find them esthetically pleasing but I find a lot of things from the past pleasing. It doesn't mean that I will choose to duplicate the shape without using modern, light construction techniques to save weight. The Wright brothers would have loved to have modern materials. And the 1903 flyer would have weighed less. Or maybe not.

If I'm going to build a hull out of vegetables, I will at least use them for the center part of a sandwich panel
(strip building) or do a bunch of laminating such as plywood or cold molding..

Every pound that goes into the hull comes out of the fuel, supplies and accommodations budget. I find it all too easy to get a boat 'down on its lines'. When I returned from several years of wandering in my 36' sailboat and emptied it out for casual cruising, it rose over five inches. Startling!

Today, however, I am cutting brush away from my driveway. I wonder if there is a way to use this stuff structurally? Like a high quality OSB panel. Horrible thought but they said some pretty withering things about plywood not that many years ago.

If I decide to build a hull that cannot be constructed with simple curves (plywood) I will certainly consider the Culler designs. Beautiful hull shapes. But with strip construction.

Oh, I'm sure we could go on all day weighing the relative merits of traditional wood boat construction vs. various other options, but, let's just say that there is no free lunch. The principles of thermodynamics apply equally to methods of boatbuilding: what you gain in one area, you're bound to lose in another. Anyway, I agree that heavy traditional construction isn't what you want in a steam hull. Lighter is better. Take a look at Nat Herreshoff's Vapor which was double, if not triple planked with shellacked muslin between the plank layers. Amazingly fast as a result of hull form and light weight construction. There are many ways to build strong and light at the same time with traditional grown wood construction. For my money, it's been my experience that by the time one finishes with plywood (usually heavier than grown wood) and all the fabric and googe, you're equal to, if not heavier than with traditional lightweight construction methods and materials. As for strip planking... wasteful of material (all those kerfs), much more labor intensive (unless you enjoy sanding epoxy), costly, considering the epoxy and fabric and sheathing, and very difficult to repair. If you want light and plan to dry store and trailer a boat, you'd probably not find a better way to go than cold molding. As for plywood, in addition to its myriad other limitations (ever try to plane the edge of that stuff?) it only bends one way (no matter how you might "torture" it), thereby imposing severe design limitations: no compound curves. Those "old timey" designs that "look good" look good because they are good. There's a lot to be gained from a well designed fairly shaped hull. (They could easily have built hulls without compound curves in "olden times" and for limited purposes did, but for fast steam launch hulls, they all pretty much came out round bottomed because that shape moved faster and easier through the water.. but everybody's mileage varies. )



Vapor in 1902.



And during her restoration recently. Note the lightweight construction evident. I'd guess one would be hard put to build a similarly sized hull from epoxy sheathed plywood that weighed less.

The Scaled down HUNTINGTON 30 ft tug sounds almost like mine. but a bit heavier.

I don't know a great deal about cold molding. The only jobs I've seen used strips of (guess what!) plywood. Thin stuff but still ply. I'll do some reading.

I recently helped unload a car topper 18' rowing boat that had been strip built of 1/2"(?) by 1" material and I was very impressed by the stiffness and light weight. It had been built with a new technique that allowed the hull to be stripped out in a week of evenings. The wood was ordinary cedar, home milled from box store fence lumber. No bead and cove work. Stuck together temporarily with dabs of hot glue and then faired with epoxy filled light weight filler. Then brought to its lines with electric tools followed by cloth in and out. The original frames were temporary and the keel was attached after the outside cloth was installed.

There are few rivals for stiffness to weight ratio that come close to sandwich panels. Perhaps none. And a nice thing about wood based sandwich building is that the significant loads are in sheer where soft and low density woods like cedar and even balsa do fine.

That would do it. I show up at an event with a balsa cored boat. No one would speak to me! It won't happen. No balsa at my local Home Depot.

Really interesting reading about the hull side of boats, its something I have not really done any off but would like to with the time/money/space all of which I very nearly have if I wanted to move things around to make them.

In terms of the short answer of 'can I make a 30ft steamboat or is that too big' then the obvious answer is that of cause you can make a 30ft steam boat, there are lots, and plenty larger. If you want to be able to trail it as well then thats an extra consideration, but while my knowledge of towing limits in the US is limited from what I have seen you guys and tow almost anything if you want to... steam plant will take more space and weigh more than an IC engine, be more effort all the time and cost more, but your on a steamboat forum so I expect you already know that.

One of my favourite steam moments ever is being on Consuta on the Thames when the opened up the regulator briefly, my god that ship goes! But then, shes about the same length beam as out 58x7ft 22ton steam narrowboat, but weight about a 1/5th of the weight and has a larger engine and boiler!


Daniel