broken frames from swelling planks

[forstaysl]

hey there -

We're working on a 1949 30' cutter that has been re-framed and re-planked by someone else (who has since dissapeared). We've read there is a possibility of a boat planked too tightly in mahogony breaking frames in tension as it swells up. The boat was planked in Phillipine, and the frames that were replaced (bent white oak) were slightly smaller than the original.

We'd appreciate any information or experience anyone has had with this... We're working on the interior, but are planning to put the boat in the water very soon to make sure nothing drastic happens.

Thanks!
forstaysl@yahoo.com

[Jagermeister]

As one who is looking at replacing something like 28 sets of steam-bent white oak frames, may I ask what were and are the dimensions of the frames in your boat?

My boat, a 32 foot day sailer/racer, built in 1947, with 3/4 inch Honduran Mahogany on white oak frames has 1 inch x 1 inch frames on 8 inch centers, and I consider them considerably understrength.

I will be reframing with 5-layer laminated white oak frames in at least 1-1/8 x 1 1-1/8 and possibly 1-1/4 x 1-1/4. I consider the improvement both with lamination and larger dimensions to be adequate for light use.

The reason for my curiosity is that I am just amazed that someone would reduce the frame size when reframing, but perhaps your particular boat was overframed? That hasn't been my (limited) experience, but the world is a big place.

[ 10-24-2005, 09:00 PM: Message edited by: Jagermeister ]

[Bruce Hooke]

forstaysl , let's start right off with a first, key question, which is what kind of mahogany? There's African Mahogany, Hondoras (Central American) Mahogany, and Phillipine Mahogany. All three have been used to build boats and they are quite different woods. In the boatbuilding world the generic term Mahogany most often probably means Hondoras Mohogany, but it is wise to be certain, especially when you talk of the previous work having been done in the Phillipines.

Second, How much smaller are the new frames than the old ones? This does seem somewhat odd to me, but if we are only talking a tiny amount then it may not matter that much.

[George Roberts]

If the planks are too tight, something has to give.

Hard to say what the correct sizes for frames or planks are without knowing about the use of the boat.

[forstaysl]

We're a small boat shop, and this is a customer's boat we've been doing a lot of work on. The planking is Phillipine mahogony, 1 1/8", with frames 1 3/16 square on 9" centers. The new frames are a little under 1/4" smaller than original, which may not be too drastic, but it is a noticable difference. Nearly all of the original frames were broken at the bilge clamp (fairly typical) so the former carpenter must have figured the frames were a little too big and the clamp made a hard spot. The boat was designed by George Stadel, and built by Joel Johnson.

The boat hasn't been in the water since the planking and frames have been replaced.

[Don Z.]

Um... it depends. Normally, if the planks swell too much, they can break the frames, but...

My old King's Ametyst was built of African Mahogany over Polish Oak frames. It was tightly planked, to the point that it was not caulked at all... the only broken frames were from when a previous owner ran aground. Other than that things were fine.

If I had to guess, I would say it has a LOT to do with the moisture content when the planks were hung.

[Frank Wentzel]

Forstaysl

Assumimg your measurements are accurate, that is replacing 1 7/16" frames with 1 3/16" frames, you will have reduced the volume of wood in your frames to 68% of the originals. In addition, if the frames were replaced because they were broken, it would seem to indicate that the original frames were already not up to the job. If I were doing that job I would consider adding laminations to the frames in place to increase their thickness by no less than 1/2".

As to the possibility of problems with the plank-fit, I have to say I can't understand how many european boats that have been tight-planked, as Don Z's "Kings Amethyst" was, work well and then others fail. Possibly it is a matter of sufficient frame thickness and fastener spacing that forces the plank edges to yield rather than the frames. Note that this would argue for further increasing frame thickness.

/// Frank ///

[ 10-25-2005, 09:08 AM: Message edited by: Frank Wentzel ]

[J. Labaree]

Read the articles currently running in Woodenboat about sailboat restoration by Ed McClave. Then, consider giving him a call at McClave, Philbrick, and Giblin over in Groton. If you're in that part of CT, it might even be worth a visit. They deal with this sort of thing ALL THE TIME and have given a lot of thought to correcting it. I don't have their number at hand, but you'll find their ad in the back of Woodenboat in the boatbuilder's section.

[emichaels]

I wonder if the Concordia 39/41's have this problem as they are tight seem construction. No caulking originally. Though they were Honduran Mahagony.

[Thad]

The Concordia yawls and the Atlantic Class sloops are two lines of A&R production that had this problem. They are African mahogany (Khaya) planked tight and broke ribs as soon as they were put in the water. Concordia sistered lower ends before delivering many of the boats. The Atlantic owners sistered or replaced ribs similarly.

[ishmael]

Um, what are your options at this point but to charge ahead? I'd make the customer aware of the potential problem, pointing out that if the boat pops some frames it's not from the work you've done, but unless they want to take some drastic remedial action, without knowing what will actually happen, what choice do you have but go for it?

Why did the previous carpenter put in lighter frames? Odd decision. As you said, the old breaks are fairly typical, and may not have been related to the problem now worrying you, at all.

Conundrums, dilemmas, don't ya just hate them!? LOL. There will be no good answer 'til the boat goes over, seems to me.

[Bruce Hooke]

I do have to wonder if this boat should be considered safe to use without doing something fairly drastic to address the issue of the smaller frames, or at least get some pretty solid confirmation from someone competant to make such a determination that the reduction in frame size is not a problem. As Frank noted, the reduction that was made in the frame size was pretty substantial. I would definitely not call the new frames "slightly smaller" than the old ones.

[werner]

took a look at the table of minimum dimensions of bent frames for metre yachts most of them where build closed seamed and often in mahogany : 6 M:
bent frames 1 1/8 siding 1 5/16 moulding at 6"centre to centre plank thickness 5/8"

8M : siding 1 5/8 moulding 1 3/8 spacing 7"

only in combination with steel or grown frames (two bent frames in between) the dimension are reduced with 1/4

[Jagermeister]

Werner:

Are those lengths waterline lengths or overall lengths. I somehow have the impression that 6M and 8M classes refer to waterline lengths, but I might be wrong.

[Nicholas Carey]

Originally posted by Jagermeister:
Werner:

Are those lengths waterline lengths or overall lengths. I somehow have the impression that 6M and 8M classes refer to waterline lengths, but I might be wrong.Under the International Rule, rule that created the 6m/8m/10m classes, the designation doesn't pertain to any particular measurement on the boat.

You plug a bunch of number into a formula (waterline length, LOA, chain girth, skin girth, sail area, etc) and turn the crank. The number that comes out is in meters, but it just represents the rating. Any boat that measures in at "not greater than 6m" can race as an International 6m. And any boat that measures in at "not greater than 8m" can race as an International 8m. Conceptually, a 6m could race in the 8m class, but it would be unlikely to do well.

[Jagermeister]

How are the frame dimensions given for the 6M and 8M yachts, as provided by Werner, related to forstaysl's 30' cutter, or my 32' sloop?

I guess it might help to know the cutter's displacement. (My sloop is 5000 pounds).

In my case, I looked at the frames and said, "hmmm, lost of breaking. Not good. Should do something about it." I can't say I was able to apply any scientific formula. It would feel more reassuring to be able to relay on an authority.

[werner]

the scantlings I gave date from pre 1918 , these were LLoyd's aproved; I am not sure they will aply to your boat but as a reference usefull, a six metre will be around 10.5 m LOA but with a waterline of only 6.5m
displacement of a six was around the 4000 or less with a very heavy keel (so a lot off stresses). plank thickness was minimum 5/8".these boats were racers but the scantlings were on the heavy side.
(and as mentioned the six metre is just the result of a formula.length, beam girth, girth difference, sail area and freeboard )

[Nicholas Carey]

Originally posted by werner:
displacement of a six was around the 4000 or less with a very heavy keel (so a lot off stresses). plank thickness was minimum 5/8".these boats were racers but the scantlings were on the heavy side.6ms weigh in at something like 10,000 lbs displacement with a ballast ratio of perhaps 60%.

A 6m is a veritable lead mine.

[Jagermeister]

I think you both said the same thing, if Werner is posting in Kilos.

[werner]

the six meter from the first rating rule pre 1919 were a lot lighter less displacement minimum displacement for a six was 1200 kg (a seven 1800kg) but generaly they were heavier with a tremendous amount of lead (had to be with a sail area of around 40sq m )

[forstaysl]

thanks for all the info!

We did in fact talk to Ed McClave. He talked about the Concordia problems (a lot of them broke as soon as they put the boats in the first time, then just sistered them). Looking at the construction drawing, the original frames were 2" by 1 1/2", so these are considerably smaller. The customer wants to put the boat in, and we will early next week, for about three or four weeks. Ed's consensus was to see what happens; replacing a few planks with cedar would probably be more trouble than its worth. He also seemed to think that Phillipine was a little less of a problem than African.

So it all comes down to seeing what happens. We're all hoping nothing..