STRONGBACK DISCUSSION etc.

[carl291]

Sometimes I wonder if making one area super stiff (strong back area) is wise in a vessel that is constantly flexing and subject to so many outside forces.
My judgment is based on a tractor trailer truck that I had lenghtened the frame 30 " to install a larger sleeper. The frame rails cross members were C shaped steel, in my wisdom for improvement I used square tubing for extra support. This move stiffened the frame but after a period the truck suffered from cracked frame rails before and after the square cross members. After two attempts at repair that failed, I decided to go back and use the C shaped crossmembers, at this point I never had another frame fracture. What I learned from this was every componet has to work (move) together. Granted frame rails are parallell and the curvature of a hull and deck by nature spreads out a loading force
After 50 years of sailing, these boats are still floating, I don't thnk there has been any reports of a mast pushing through the deck on an Ariel or a Commander mast pushing through the keel.
I may be ignorant on boat construction but I would think short of total interior reconstruction (ie. Ebb) repairing water damage and worker screw ups and short cuts, the Alberg design is pretty sound, even when confronting bridges.
Hey, I'm just saying

[ebb]

Carl, this is a great point for discussion.
On boats I think naval architects and engineers are still out to lunch on the subject. Look at the constant breakdowns of the sleds in the Volvo Ocean Race and the repairs modern frp boats have to their hulls and decks.

I think FLEX came down to us from wooden boats, which are but bundles of mechanically connected pieces. Might say that the massively built clipper ships were very flexible - and while that may have saved them in heavy going - it may also have numbered their days.

I see the mighty oak vs the flexible sapling metaphor - but not sure how that relates to our A/Cs. Anything I propose comes from observation and reading, no formal training.

BUT, I think our boats have survived BECAUSE they were overbuilt and because they are STIFF.
We have exceptionally full and fair curves in the hull with no flats. The deck/cockpit mold also has curves in the flat appearing sections. As you know Ariels and Commanders have a pasted together BUTT JOINED DECK TO HULL SEAM. I don't know about other Pearson's of the time, but we might be the only class of boat that was put together this way. Lighter buillt engineered (chinsy) boats have serious problems with their hull to deck join - even if flanged, glued and screwed together.

And yet this seam which was pierced with screws from the s.s half round trim has never had an issue of actually coming apart. And I think that is because the boat AS A TORSION BEAM does not twist much. Given imco the seemingly casual way the bulkheads were put in this is pretty amazing.
I could be very wrong obviously. Somebody with a sailing Ariel can check this out by tying two lengths of string in an X from corner to corner in the cabin. If the tension is about even you might test any twist to the boat when close hauled by observing if one string or the other sags on a point sail.

Assuming this is a valid test, right? The boat might get more bent punching through heavy seas.


Because our four decade old boats began life in the beginning of the FIBERGLASS revolution Pearson got away with things modern boats have learned not to do. Engineers still push the envelope - usually for speed, and they don't ever think longevity.
While modern boats still manage to forget: stringers should never just stop but continue to the bow and stern. (Not done in the Ariel.)
Bulkheads (which are what helps keep a glass boat from twisting) should be attached to the hull and deck top-bottom-sides. (Not done in the Ariel.)
Bulkheads should not bear on the hull or deck without spreading the point load with wide fillets and tabbing. Thinner hulled modern boats float bulkheads
and attach them only from the sides - like a C-channel.

Carl, is your arguement that the funky way our boats were put together actually is the reason they lasted so long?

Even the A/C "over-built" hull showed the stress points. I know I found them when I faired the topsides prior to painting. The brown fairing compound in minor depressions on the old white gelcoat made a topo map of interior structures influencing the hull laminate.


I believe it is the nature of monocque construction to attain its integrity from having a stiff skin. Except maybe for ferro and steel the concept in fiberglass has its problems. Maybe a talented designer like C.A. takes that into account so that flex is factored into a plastic sailboat. The interior structure would take that into account.
But for the tabbing in of the accommodation settees and berths, I don't see that either the designer or manufacturer paid particular attention to hull-flex in my Ariel.

Ebb is certainly on record here concerning the support system under the mast.
I believe any flex here was due to corner-cutting and selling price. There cannot be flex here!

Don't know really to what extent the pros went to inside Scott's Ariel to tie the compression beam to the deck and to the bulkhead. In my mind's eye I see what I would have done. I believe the mast foundation should not move, ever. Any flex should certainly be in the rig. And setting up tensions in the rig would benefit hugely from an immovable base. We are talking about this single bulkhead. To spread the mast point load the cabin arch it stands on cannot be compromised. So arguably preserving that arch by almost any means is the right thing to do.


Now, Ebb, doing what he did: taking out most of this extremely important bearing and anti-torsion bulkhead, may be really asking for trouble. I'm depending on the overbuilt hull (which turns out in this later built hull, A338, is not so over-built) to stay out of trouble. Taking out the bulkhead and introducing FLEX could be my monkey. I'm tabbing in ALL my furniture, and call these panels: web frames. I feel that enough of them will nearly cancel out the torsion flex of the hull. Could be wrong. Like you say, Carl, trying to cancel out the natural flex of a fiberglass boat could be not only wrong but impossible.

On this score, I believe the lead ballast should be immobilized in the keel. That amount of weight concentrated in that one area in a relatively thin skinned vessel could out flex the innate stiffness of the monoque concept.


I've witnessed a couple earthquakes here in California.
I sat through one with a cup of tea in hand, actually enjoying the time of day and the landscape. I saw EVERYTHING in or on the landscape turn into waves: the solid ground, the porch I was sitting on, the house, the trees. Everything became plastic or liquid. Can't recall if the cup in my hand had the wave going through it.

Why couldn't a similar thing happen to a sailboat. Who's to say unknown vibrations can't happen to a vessel in water? So engineering gibberish and web frames will mean nothing when the boat turns to rubber. And it all becomes a wave form, including the skipper.

[carl291]

Carl, is your argument that the funky way our boats were put together actually is the reason they lasted so long?

I hadn't thought of it in that manner, but, yes to a degree. In my introductory work on 259, I find no part of the boat where the workmanship stands out as skilled joinery. The balsa under the mast step was a mistake but look how long that lasted! The cabin door is missing on 259 ,may have started to drag and was removed. When I check the squareness of the opening, it was still square.
Creating a super stiff section with no flex I don't think lessens the force, I would think it transfers the force and maybe even multiplys it to the weaker non-reinforced area, at least in the case of the truck frame.
Not having bulkheads fit perfectly to the hull and glued solidly helped to eliminate hard spots in the hull.
To look at any part of the construction of these great boats and say not done good enough really has been proved wrong by time. IMHO
Can you think of anything built in the 60's that has been used, abused and neglected and still be brought back to as good or better than new for less than the original purchase without adjusting for inflation?