View Full Version : Checks in Steamed Oak Frames

10-31-2004, 09:52 PM
I'm used to breaking steamed frames. I understand, to some extent, the compression forces involved in a tight radius bend. In the severe bend, twist areas of my Buzzards Bay 14, I'm batting a little better than 500. (Sorry for the baseball reference...I'm still celebrating the Red Sox!) Anyway, much to my dismay, I've found a couple of the 1" x 1" frames which had set well, now show checks in the region of the frames which were not subject to bending at all. The following photo doesn't help much, but you can see that some checks have developed which actually run roughly perpendicular to the fore and aft direction of where the frame would be bent in the boat.



This is a shot of the construction set up:


First, I'm wondering why this is developing. I haven't seen this happen before, and I'm somewhat relieved that it's only a couple of frames so far. Second, I'm wondering whether to fill the checks with epoxy and move on, or whether I should replace those affected frames. I bet I know the answwer to the second question, but I'd be curious to see if there are any other thoughts. Thanks.


[ 10-31-2004, 10:18 PM: Message edited by: DanO ]

Disco Bay
10-31-2004, 09:55 PM
Your picture didn't show. Glad you asked, I'm in the same boat!

10-31-2004, 10:02 PM
If you're in the same boat, let's hope we get this thing figured out, or we may be sinking! (kidding). I'm just really surprised with this, because I've successfully bent this frame into a pretty tight radius two or three feet away from where this checking situation is going on. In addition, if you can tell from the photo, the annual rings are going roughly fore and aft, which is usually the best way to bend the frame.

Bob Smalser
11-01-2004, 01:19 AM
I'm afraid you have a much larger problem....the grain on the one in your pic isn't straight by a huge margin. You have a shortgrain problem with those that may have caused the checking all by itself with kilning (if kiln dried), steaming or both.

That's also probably why you are breaking so many.

Every single one that looks like that one needs to be replaced. If the design specs call for a 1 X 1 scantling, the stick in your pic only has the strength of a 1/2 X 1/2 scantling....if even that.

Even a board that looks like the one below...which is significantly better than the one in your pic....needs to be ripped/jointed to align the grain with all 4 board surfaces for it to be used in a structural application:


[ 11-01-2004, 12:40 PM: Message edited by: Bob Smalser ]

11-01-2004, 09:03 AM
What Bob said. smile.gif

Also, there was an excellent article in WB,(go figure), a few issues back that told all about picking and sawing white oak for steam bending. It explained wood grain and how to saw a plank into frame stock, thus avoiding your problem.

Steve Lansdowne
11-01-2004, 06:14 PM
Is this what is referred to as "grain run out"?

landlocked sailor
11-01-2004, 06:29 PM
Yep, Rick

Jack Heinlen
11-01-2004, 10:09 PM
Every single one that looks like that one needs to be replaced. If the design specs call for a 1 X 1 scantling, the stick in your pic only has the strength of a 1/2 X 1/2 scantling....if even that.
Hold the panic button Batman. I'm not sure that's true. Granted, perfectly straight-grained stock is desirable, but from what I can see the run out is in the sided dimension. Is that really going to decrease the strength by 50 percent? Seat of the pants, I don't think so.

I'm just asking. A lot of less than perfect stock goes into even very well made boats. In production boats of thirty years ago... well. I'd want to learn more before I started ripping out framing.

Where's Fleming? Who knows what the books say? I may have known once, but have forgotten: what slope of grain run out is acceptable in the sided dimension according to Skenes, or Chapelle?

11-01-2004, 10:28 PM
Once again, the expertise on this Forum is invaluable. I hate to confess that I thought the grain orientation might be a problem on this piece when I saw the problem developing. The problem is that the rough sawn, nearly vertical cut pieces of butt oak were tough to read. Most of the 2 planks I used had what appeared to be fairly straight grain. Once cut and planed, however, I could see that the rays were angled on some of the pieces (fortunately only a few that I could see...I don't think the majority of my frames have this problem. I'll know more when I inspect all sides closely.)

Bob, I now understand your point about ensuring that the grain and rays are aligned on all 4 sides of the stick.

Tonight I found the article in WB #172 which discusses reading the slope of the grain. The author concedes it may be difficult to read on vertically sawn pieces (I know what he means). In any event, he suggests only using stock with grain which slopes no more than 1:12. Otherwise, you'd likely end up with broken frames when trying to bend. OK, point well taken. But if the angled grain (say somewhere around 1:8 or so) isn't in the orientation of the bend, is the grain run out that much of a problem? As usual, I'm scratching my head again on this one and really appreciate the feedback!


11-01-2004, 10:40 PM
The twist in the grain is very severe.I don't work with hardwoods all that often but a twisted log is to be avoided whenever you saw small lumber out of it.Any wood that is going to be bent and under any load or stress needs to be straight grained.

Any twisted wood that you put into a boat is going to have to be replaced very soon.We've had that experience with the broad,lapstrake fir planks on MUNIN.The planks with twist looked allright at first but in the last three years we've been replacing 3-6 sections of split, twisted planking each winter.Without exception they have had some moderate twist in the grain.Some of our large,sawn frames have a bit of twist in them but they don't have grain run-out and they're not stressed like planking or steam-bent frames.

(edited for spelling and punctuation :rolleyes: )

[ 11-01-2004, 11:08 PM: Message edited by: yorgie ]

Bob Smalser
11-02-2004, 10:57 AM
Originally posted by Jack Heinlen:
I'm not sure that's true. I am, Jack.

My Bureau of Ships Wood Manuals don't have grain runout data like lumber grading manuals do...perhaps somebody else has a more complete set...but the 1:6 slope in the pic doesn't meet grade for a Select or No. 1, 5" structural member in house construction, let alone a 1" bending stock frame.

Slope of Grain 1 in 15 in middle 1/3 of length,
balance of piece may be 1 in 12. The "fiber stress in bending" and "modulus of elasticity" adjustment values for differing degrees of grain runout in the lumber grading tables don't equate to smaller boat frames, as the bigger the timber, the more crossgrain you generally can get away with. In a relatively small streambent frame, even 1:12 is questionable....I'd consider that a minimum.

Remember that the difference between a "Select" member with 1:15 grain runout and a "No. 2" member with 1:7 grain runout can easily mean being required by the engineers to go from a 2X8 to a 2X10 or 2X12 for the application....all of this being much less critical than bent boat frames.

Sorry about all this, but better to replace them now than later...that stock can be used elsewhere in non-structural applications, especially if it's laid up to wider widths, alternating the cups.


[ 11-02-2004, 11:06 AM: Message edited by: Bob Smalser ]

Jack Heinlen
11-02-2004, 11:03 AM
My Bureau of Ships Wood Manuals don't have grain runout data like lumber grading manuals do, but the 1:6 slope in the pic doesn't meet grade for a Select or No. 1, 5" structural member in house construction, Not to be a PIA about this, and you may well be correct Bob, but a bent frame in a boat is not the same as a structural member in a building. The forces of tension and compression are very much shortened in a steamed frame, constrained as it is by the plank fastenings.

What does Skenes say about this, anyone?

[ 11-02-2004, 11:16 AM: Message edited by: Jack Heinlen ]

Bob Smalser
11-02-2004, 11:15 AM
Originally posted by Jack Heinlen:
... but a bent frame in a boat is not the same as a structural member in a building.No argument there....boat framing and small scantlings in general require significantly higher standards in many areas.

Jack Heinlen
11-02-2004, 03:44 PM
I've been told, by brother Bill who has a copy, that Skene's isn't the place to look for this. But someplace has to have it. Bud Mackintosh? One of the Harr'shoffs?

It's interesting, maybe, but when I was twenty five and learning this stuff 'old timey' we didn't pay much attention to it. If the frame bent without breaking you were one to the good. But someone has to have studied it in more detail. I'm curious.

[ 11-02-2004, 03:47 PM: Message edited by: Jack Heinlen ]

11-02-2004, 05:20 PM
A couple of comments- Bob is defintely giving you the straight dope on grain run out, I was flabbergassed to see the grain run out in your first picture, it looks like the grain is running out in about 6 or 8 inches. I was thinking how in the world is this guy getting this stuff bent with out it blowing apart left and right. You may not want to hear this, but with that kind of pressure you probably will see as time goes by, more frames cracking or twisting.Bad grain orientation can cause a lot of pressure, not only now but in the future. Didn't see where you mentioned whether or not it was kilned or air dried. I am all in favor of kiln dried lumber -( BUT )- large pieces of bent would be much better being aired dried, higher moisture content with more flexibility. You also may give some thought to soaking the wood down a couple of times before steaming, kinda loosen up the grain and not put the piece in such a state of shock. I also remembering reading years ago that guys that made the little round oak mast hoops, didn't steam the oak at all, but rather boiled them in water along with some ivory liquid dish washing soap. They said the soap aided in helping the grain to slip by itself. Something to think about.

11-02-2004, 05:38 PM
You're building a neat boat! Always liked that H model, myself. And as for frames that break, my rule of thumb is that if you break two in a row in the same vicinity, go to the laminating table. It's not much trouble to pick up a pattern, and the bevels can be cut after the frame is glued up.
What's more, you wn't have to worry about frames popping later on. We just did a refastening on our 40' yawl, age 35, and found several steam bent frames had snapped, while the laminated frames, molded and sided to the same dimensions, were all rock solid.

Steve Lansdowne
11-02-2004, 06:18 PM
I have read from a builder that adding fabric softener to the steamer water helps keep the frames from breaking, much as you suggested was the case with liquid detergent in the water. Adds a clean, fresh scent to the wood also. Is there a scent called "ocean breeze" or something similar that we should use? tongue.gif

Bob Adams
11-02-2004, 06:55 PM
Use Snuggle, keep me employed.....my plant makes it! ;)

11-02-2004, 07:51 PM
I just skimmed my Chappelle's "Boatbuilding" and there's no specific reference to grain slope. However, he did talk about the annual rings orientation. The concern he raised was not to have the vertical grain running in the same face as the frame screws (or else you might split the frame when screwing). I also read through Bud McIntosh's book awhile back, but I don't recall this issue of grain slope being mentioned. The gist I got from most reference books was that with proper scantlings, (don't oversize) reasonably straight grain and proper steaming, the frames which survive the process should be ok. Anyway, from a quick inspection, the frame in the above photo represented the worst of the lot. But, the two indicated below, which survived the most radical torture (tight radius and twist) surrived without a hitch. The stock is all air-dried white oak from trees I cut down last year.


I'll pick through the stock I have left with an eye toward proper grain slope, among other things. In the meantime, I figure I'll take a 12" batten and run it along the installed frames to see which ones have grain run out inside of a 1:12 ratio. I guess for now, that might be reasonable sleep insurance.


11-02-2004, 10:01 PM
Dan- in Chapelle's boatbuilding look at page 358, in Bud Mcintosh's book how to build a wooden boat,look at pages 140 and 141. Your picture above shows the grain running diagonally instead of flat. Harder to bend and a lot weaker frame.

Carlsboats really has a good idea in laminating frames like these for those that just can't find good bending stock with proper grain orientation.

You would almost have to have a small sawyer that understood what you wanted, to saw the lumber as to achieve a lot of flat grain bending stock, or pick through a ton of lumber.
I am sure bob can exsplain this better then me.

11-03-2004, 08:00 PM
I've been thinking.... (not again!)

It looks like I've got about 6 frames where the grain slopes too much for my comfort. Maybe 1:10 in some spots. Kind of amazing, really, because those tortured and twisted frames look perfectly sound otherwise. Nevertheless, based on the expert advice here, I'll never sleep at night unless I do something with them.

I could outright replace them, but my remaining stock is not much of an improvement.

On the other hand, would ripping these frames into thirds on my bandsaw and gluing/laminating say two 1/16" battens between each be a better solution? I did read McIntosh's book about laminating, and he makes the case that even though gluing and laminating is a "space age" solution to an old problem, it nevertheless is a viable option.

Incidentally, neither McIntosh (at p 140) nor Chappelle (at p. 358) actually addresses grain slope in structural members that I can find. There is, of course a reference in all the books I've read to getting the best (i.e. straight grained) stock available, but I haven't seen the warnings I've gotten here. Still, I do get the picture that the frames with grain run out would be weaker, and after all this work on this hopefully classic boat, I'm not about to jeopardize safety and workmanship. That's why I'm thinking that ripping and laminating the already bent frames might actually be a strength improvement here. Note from the above photo that this is a planked-down design with tremendous curves (and probably tremendous forces on framing and planking as well). Of course, if I laminate, I'd then be worried about the whole epoxy and oak controversy too. Arrgh, imagine delamination after this?

What d'ya think...is this approach advisable?


11-03-2004, 09:10 PM
Try finding some straight grained stock for the frames.Laminated or steamed I wouldn't even think of framing with oak with 1/4 the twist that you've shown us.If you want to mill your own stock try contacting a forum member named 'Windfall'.I believe he's in Vermont and he chainsaw mills fallen pepperwood,locust etc.He might be able to set you up with a supply of non twisted wood.

I have a 19' strip built sailboat similar to a Buzzard's bay and some of the laminated frames were sloppily made.Replacing them would involve removing deckbeam shelves,working under decks and in cramped quarters.I know it's not a pleasent prospect to remove the framing that you've put all that effort into but when they start failing after you've finished the boat you'll regret not having done so.

Good luck I really like that design! Chris.

[ 11-03-2004, 09:14 PM: Message edited by: yorgie ]

11-04-2004, 07:40 AM
From my experience, white oak epoxies fine if the wood surface is rough and not polished or burnished. Some planers and sharp drills can leave the wood too smooth, etc... Cutting out on a bandsaw or table saw will leave plenty for the epoxy to key into.
Laminations are better for ribs anyway. I would do it and saturate the whole rib in epoxy. Has anyone diluted epoxy with MEK solvent for better penetration into wood?
For me I tend to heat up epoxy with a heat gun and let it soak into the wood cracks. I pretty much use DOW 331 resin with versamid hardener. It can get quite hot and still take a long time to set up.

11-04-2004, 12:39 PM
Originally posted by sdowney717:
Has anyone diluted epoxy with MEK solvent for better penetration into wood?
For me I tend to heat up epoxy with a heat gun and let it soak into the wood cracks.
You can thin epoxy with alcohol, but your approach of heaqting works better.
Or start with a thinner epoxy.


Bob Smalser
11-04-2004, 04:17 PM
Here's the Technical Data.

Navships Wood Manual Volume III Jul 1962.

Strength of Wood Members With Various Combined Slopes of Grain

Percentage of the Strength of Straight-Grained Members:

Impact Bending Strength By Slope of Grain (ability of the member to take a blow)

1:25 - 95%
1:20 - 90%
1:15 - 81%
1:10 - 62%
1:5 - 36%

The framing stock displayed is 1:7 or so....less than 50% as strong as straight stock.

11-04-2004, 07:25 PM
As usual, some great pointers. Bob, you're a wealth of knowledge. Based on those stats, which no doubt are as valid today as they were in 1962 (tree evolution probably hasn't gone too far) I'm definitely going to do something with the affected frames. I'll be able to replace a few with some straight grain stock, but I'm seriously considering laminating. Some more work, but it might be worth it.

I'm wondering whether it's worth it to rip and glue even the straight-grained stock so as to improve strength and rule out the possibility of failure down the road? In other words, if I had stock which had grain slope of 1:15, would I improve strength by ripping the stock into thirds and then regluing?


11-04-2004, 08:42 PM
Dan- I personally wouldn't mix steamed bent frames with laminated frames. Just replace the ones you need to, even if you have to find and buy more stock. Even though laminating might be perfect for something like this,by mixing the two together, I think you are going to find a difference in flexibility and stiffness between the two. You want all the ribs to have the same stiffness or flexibility, so the boat flexes uniformly. Thats my opinion, think you are going to have a nice boat, hope you enjoy it, good luck.

Bob Smalser
11-04-2004, 08:46 PM
...which no doubt are as valid today as they were in 1962... Nope.

May not apply to you, but most of the western softwoods were reevaluated when the oldgrowth dried up a bit later than 1962.

No new strength figures for slope that I'm aware of...but modern wood isn't generally rated as high. But if your softwood stock is 8 rings/inch or tighter, you'll be ok. The inferior stock I speak of is 4 rings/inch.

Bending oak is just the opposite....you want new fast growth from the outer part of the log (but no sapwood) and wide rings.

[ 11-05-2004, 02:08 AM: Message edited by: Bob Smalser ]

11-05-2004, 12:19 AM
I've heard that new grown oak and hickory may actually be stronger than old growth.I can't explain why. New softwoods, unfortunately,are vastly inferior to the old growth.

Jack Heinlen
11-05-2004, 07:54 AM
Thanks for the stats Bob. They bear out your contention of a 50% loss in strength, at least in impact loads delivered in the sided dimension.

I haven't been arguing that grain runout isn't a factor to be considered. I am suprised that we haven't been able to come up with a figure that is considered acceptable in light yacht construction. It would also be interesting to know how the tests cited were conducted. Subjecting a beam supported by its ends to blows isn't the best way to look at how the complex fabric of a bent frame boat actually reacts in the world. Throw in the issue of scantlings and the picture becomes more complex. Some boats are designed right to the edge of the material's engineering qualities, and some are designed overbuilt(or under).

Obviously, perfectly straight is desirable, but what is acceptable? Given the issue of scantlings there probably isn't a correct answer. Which would explain why no one can find one. ;)

Thanks for the interesting conversation gentlemen.