Not near the boat right now, but next time I'll get the trouble light and make marks on the hull. Awhile ago we lightly sprayed some dark grey laquer primer over the topsides. sanded it with a flexible long board, and came up with a depressing number dark areas. They've faded.
Dave sys his V-berth stringers on his Commander show up outside.
338, just below the sheer, has two 3' long (1/4" deep in the center) lozenge-shaped hollows in front of where the companionway bulkhead is. Last week I sighted an earlier hull (#175) that was perfectly fair in that area. 'Course it was relaxed in the water - I may have developed these hollows while sitting in the jacks. ??
So what I will look for are the vertical imprints, I really don't think they are there - but I will find out.
Trying to imagine the schedule for putting these boats together, the stringers would have to go in after the bulkheads, but befor the tabbing. So I don't see how the hull could not be cured. You have to be working inside without the wax coat on. And the deck mold wouldn't be on yet. So the hull had to be out of the mold? and free standing? No. Had to be in the mold because the deck had to meet the hull 1/8" tto 1/8" all the way around! So you'ld have to really slap all the fundamentals in like fast. Maybe I can't imagine how fast. Maybe the boat was still hot when they rolled it out into the sun, ready to launch!
Some boats have these horizontal imprint anomalies, some don't. Some have these hollows, like 338. So maybe on another post we can figure out the best way to take care of the problem, if it is a problem? Leave it and love it? Or fill, fair and fiddle?
The imprinting is caused by the shelf "working" against the hull. In all likelihood, one or more of the partial bulkheads (to which the shelf is attached) have come loose. The interior of the boat is being pulled against the exterior.
I had this problem on my boat. I had an "innie" imprint on one side and an "outie" imprint on the other. I re-tabbed the loose bulkheads. Pictures of that repair are on the first page of the Deck Joint thread.
Tony is going to solve the problem during his clean sweep and reconstruction. Nice work, by the way. I feel your pain.
As for other boats with this problem, I wouldn't panic. If your boat gets normal usage, I doesn't require immediate repair. It may get worse, albeit slowly. Still, it will have to be addressed. Movement is never a good thing.
On the outside, I faired the hull with microlight and painted the hull. Thats strictly cosmetic.
C'pete sir,
We have an digression of opinion, based on personal observation.
The shelves in 338 took an act of congress to deconstruct, What had a chance to move were the stubby pieces that held the forward and aft chainplates - they hadn't moved because of the thickness of mat tabbing holding them to the hull - tho there was some rot on the tops. They hadn't moved even tho they were being steadily pulled from the top by the chainplates. The bottom of the forward chainplates were glassed to the shelf!
So all 4 sets of shelves helped the stringers to keep the hull from flexing - or from working. On 338. As I observed, the hull topside on the exact opposite side of the stringer shows a (faint) double imprint of the stringer construction inside. I think the mark comes from extra hot tabbing that was probably used to fix the stringers in place DURING CONSTRUCTION of our boats.
The polyester is hard as a rock. Something would have to be forced against the hull inside to have any effect outside and it would be in the form of a big bow or billow. Even a relatively sharp 3/4" line of ply. The stringer is a 1 1/2" square piece of mahogany that is fairly massively pasted to the hull, 2" wide minimum. I don't think the polyester is gummy enough to imprint the stringers locally as we observe.
The topsides are thinner the closer you get to the sheer, BUT how thin and how flexible would they have to be to make an exact picture of the stringer inside?
The marks had to have occured in the soft early stage of construction when the whole boat was new. That's the only time that something added to the inside would be able to suck a localized area of the hull into an imprint. Kind of like a love bite.
Seems like a very important issue.
Don't have to be persuaded by opioions,
we can lean with our prevailing prejudices.
I'm not a lawyer, just an observer and an
Ariel owner with no axe to grind, doing
the best I can for #338.
Somebody once told me, a poet needs
only a 500 word vocabulary to write the
greatest poems. I know I'm too windy
and use too much color. Still a working
stiff, still dreaming, still trying to get it
straight. Blah de blah
If we ain't having fun yet, I will shut up!
Look, there certainly isn't anything structurally wrong putting in the bulkhead with the wide spread you got there. Let's see how it turns out. That's your gut feeling and it's innovative. My problem is with the assumptions. Are you going to be consistant and put your horizontals in with styro? All the rest of your tabbed in stuff?
Good glassing!
I've shot my 2-part wad on this subject.
Ebb,
We'll have the weird science thing going on in 113. Running our own experiment that is. The lower aft chainplate knees were bonded directly to the hull and when I get to laying tabbing I'm just going to follow the same schedule as I'm putting down elsewhere. So, only in the end will we know if the styro will make a difference on the main bh.
When we were busy cutting things apart I noticed that the wood components of the knees, bulkheads and berths were not bonded directly to or riding on the hull except for some ares where the funky, blue colored 'bondo' wads were here and there. I'd have to say the bulk of the strength/ rigidity/ integrity whatever we want to call it came from the tabbing. Somewhere here I have a pic I snapped just after removing one side of the main bh and you can kind of make out the 3/8" to 1/2" high ridges of tabbing sticking up and when I cut through I was cutting under the plywood.
I ain't no lawyer neither, Ebb. I like to think we're among friends here Actually, I have lawyers, Feds and spooks in my family, we don't understand each other very well Tony G
This isn't the exact picture I was looking for, sometimes I get a little delete happy. But if you squint your eyes just right in low light you can make out the depth. From now on I won't erase anything until the dust settles-uh, so to speak.
Yeah, you're probably right. What I'm looking at more than likely happened during construction. Pete's innie and outie may very well have come from movement. But now I've got twenty minutes tied up into cutting these stinking styro pads and damn it I'm gonna use 'em
Ahh, Minnesota. Where else can you go from cooling fans to heaters inside a week? No kidding, the last sanding I did to smooth things out, well, as smooth as you can get with 80 grit, was just bearable with a fan blowing down on me from the forward hatch. A few days later as soon as the last layer of matting went on I started digging around for a small space heater to keep the temp inside in the seventies.
About nine hours to install beam, cut patterns and fiberglass, mix epoxy, roll, etc.. Judging from all of the work Ebb has done he must be a machine!
What I like especially is the tabbing you did on the bulkhead to get that beautyful line! It takes time to make patterns. It takes time to do it right.
Very impressed!!! Happy boat!!!
That beam is a real sunbeam!
[ from Fiberglass Boats by Hugo du Plessis (Adlard Coles, 1966)
Pg 57 in the section titled, "Hard Spots and Stress Concentrations:
"Many hard spots do not appear until several months after the boat has been moulded, not until the moulding has cured, contracted and settled down. Some moulders would probably be surprised to see how noticeable the hard spots have become six months later, and there is no doubt that some, particularly the hard spots associated with bulkheads, are due to contraction during cure.
Most stress concentrations will give no trouble in normal service because a good design will have an adequate factor of safety. But these hard spots are in fact eating into the factor of safety, so that when the overload comes, an impact or a sudden squall, the factor of safety is not there. The moulding will fail, whereas one without hard spots would not,
1. Round off all sharp corners...
2. Broaden and taper off the root of all bulkheads and shelves. Keep bulkheads and incompressible members from direct contact with the skin, so that the strain is taken on the broad-based angle fillets, or use a soft padding between the bulkhead and the hull.
3. End one structural member at another, or fade it into the skin...
4. Make all changes in thickness gradually....
5. Radius all corners...
6. Bolt or fasten all stressed fittings through blocks....
7. Make or pad fittings or woodwork to fit...
Distribute all loading and stress.
Visuallize how the moulding will deflect.
How can any stress concentrations be avoided."
Tho we go to him for his experience, the trouble, as we know, with any expert is that we have his predjudices or opinions to weed thru, as well as the heat level of his persuasion. His saying that the skin will fail at a point load (the boat twisting probably in "a sudden squall") is unsupported by any examples or fotos. Not to say that I doubt it. However, what you are doing IS substantiated by the guy who IMCO wrote the first (and best) manual on the subject.]
I took a close look at 376 this weekend, and you can clearly see the horizontal line made by the port main cabin shelf on the outside of the hull. Nothin on the stbrd side, though. When I first noticed this a few years back, I thought maybe my dad hit something 20 or 30 years ago, got a crappy fix-it job, and maybe he was too embarrassed to tell me about it! He took off part of the rudder one year at Johnson Island near Cedar Point on Lake Erie--- I didn't know till I recently found the repair invoice in an old file. But it definitely is the shelf imprint as opposed to poor seamanship of yesteryear. And the imperfection has so many dips and bobs in it that it could only have happend during the curing process. I'll photo it if I think about it.
Capt Kent,
No problem upgrading yer Dad's seamanship, eh?
What's interesting with these long imprints on Commanders & Ariels(rather than vertical) is that they are not by definition 'hard spots.' Are they?
They are cosmetic, not structural. And they occured at the birthing, not later as the supposed 'working' of the hull.
So that is why I call du Plessis on his unsubstantiated assumption that these hard spots are somehow dangerous. No doubt they are on ultra-light over engineered racing machines. And some boatshow sailboats and powerboats.
I can see perhaps that if you hit a piling on an unsupported section of the hull it could deflect and return to shape with minimal delamination and damage. While if the hull was hit where a bulkhead was you might get some crunching or a hole, depending on whether it was gasketed or not. I don't know. I would really like to hear what an engineer has to say on this, who has direct experience with frp hulls. Or some credible survey of damage to boats after an Isabel.
For what it's worth: On our hard relatively thick skinned old hulls it is ok to paste on edges of plywood and cleats if the join is filleted and tabbed.
Since that is what I'm doing to 338,
I'm seriously open to any call on my practice.
It is possible that an old fiberglass hull can be thought of as more BRITTLE. Has any expert spoken to this? Haven't seen it. The 5 or 6 points of du Plessis' are the way to go.
[I meant to add: Last weekend I did some filling and fairing. Between spurts of damn longboarding I did a lot of eyeballing from the stern up the sides.
It became clear that C'pete's observation that one side of his babe was out - t'other side in.... could be seen on 338, as well. Not exactly the same, but one side of 338 is more fair than the other going forward. Must be why I've almost anthropomorphosized the Ariel whose left and right symetries are a little off. Each one of our boats has its own special character!] ,,,,,,,yea!........
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Tony G
