Sawn frames.

I just read the book Wooden Boats (I can't remember the author's name off hand though) and it mentioned having sawn frames. What is the process for making these, and is there any bending and/or steaming involved? Just one of my many curiosities about wooden boatbuilding.

 

A sawn frame is made up of one or more pieces of wood that are sawn to the shape desired. Like this.

 

There are only a few types of frame construction used and one is sawn frames. As has been said, they are frames (loaf of bread slices through the boat on mostly even spacing) built up of flat stock. The stock may be lumber or plywood. They're used when frames of steam bending would be too large to handle or on lower cost applications and seen in chine boats.

Materials can be of lesser quality, because of the over lapping joints sharing the loading, but can take longer to build and install. It's a tried and true technique, though I'm glad I'm working on a bent frame project now. I cut the oak to size, cook it in the steam box for an hour or so and slap it on the hull, clamp it in place and I'm done. No measuring, very little cutting, no making the same pieces two or more times and fast.

All framing techniques have their pros and cons. The boat I'm working on has 42 steam bent frames on 8" centers. 27 of them are cracked or broken after 40 years of service. Had the boat been of sawn frame construction I'd have not near as many frames to fix nor would quite as many broken. On the other hand I'd have lost a bit of interior volume as sawn framing takes up a lot more room in a hull, and doesn't look as nice, to my eyes at least . . .

 

Cool. I never would have guessed that. But don't those joints (unless you have very strong cleats) weaken the frames themselves?

 

On a wooden boat individual structural members by themselves may appear weak. When they are properly joined together as a complete hull they become strong.

Gary

 

I understand now. One last question and I'm done. (I'm quite new to the boat building and design realm, but so far I love it!) Are they slightly bent pieces that are connected with cleats cut to shape, or bend by steam, or another method?

 

In a perfect world it would be nice to find wood where the grain followed the curve. In reality you use straight grain wood and put in as few joints as is necessary. You start with wide stock apply the curve to it than saw it out.

Gary

There are no last questions.

 

I see. You guys know quite a lot! Thanks for all your help.

 

The structure you've described sounds like a built knee. The curved piece may be steamed to shape, bent dry or one of a number of ways to talk wood into doing as we wish.

 

As always Paul, very informative and very good explanation of the pro and con of the different systems.
Perousing the forum for old thread is fun and interresting.
I think a thread do not have to die because its old. Some still very good.

Daniel

 

...may I respectfully suggest that laminated frames are far superior to any sawn frame, they are very easy to make, have maximum strength for size and cost bugger all.
...sawn frames are the weakest and heaviest frames there are.....

 

in times gone by they would bend tree saplings to grow in shapes like stems,
I was in Turkey, there were piles of such shapes in a corner of a traditional yard , where in places they still build that aways

 

Some early uses of Sawed Frames

Hi,
I live in South Florida, and have traveled to the Bahama Islands dozens of times in my life. What I saw there, and I don't know where their techology came from, was Sawn frames in the Bahamian Boats. When they needed a particular shape for a frame, they found a tree branch that had something near that shape, shaped it to their desired shape, then sawed it down the centerline to make 2 similar frames. I must assume that that is the most Nature Intended shape for a piece of wood as it is in it's Natural Shape. I don't disagree that Modern Laminated frames can be quite strong, but the simplicity here seems quite appropriate, and I have seen these boats last for decades with little maintenance and no cracked ribs. The case for Laminated ribs might be in High Stress, High Speed, Modern Boat Design. Maybe we can still learn from some of this old but useful technology?
Regards,
John Vitsur

 

...yes of course the grown frames are the right shape, but grown frames are not sawn frames as such, even though they do get thicknessed.

...sawn frames are from straight stock that is sawn to shape, and they do have their failings

...grown frames are off the tree shapes and used very often as knees, we use mulga wood here for such, and they do tend to fracture along the grain whereas laminated frames (and knees) will not generally do this if glued correctly.

...laminated work is very easy to do once you start doing them, you will wonder why you would bother digging roots out of the ground or driving hundreds of miles to get suitable wood....

 

Lubs, nobody is questioning lam frames, in fact our new boat has lam beams in wood I posted that just as point of interst for those who do not know
if you want some wonderful timber I have source spruce to 12m length Germany and sizes to 300 deep. 200 wide