Jeff H. I stand corrected, that is a valid point.
From what I've seen, plugs taken from older, thicker hulls like the Trident, or Pearon 33, say when installing a through hull, show a lot of thickness, but a lot of dry fiber. I have read a postulation that some of the thickness designed into these hulls was in reaction to the poor layup techniques of the time. Certainly a fiber rich laminate with complete saturation but little excess resin will show less drop in strength and stiffness when cycled below yield and it becomes obvious that vacuume bagging and oven curing will yield the best return in ultimate strength to weight.
There seems to be a mind set that states that thick and heavy equals strong. Conversly, the never ending search to make a profit building boats would lead in the direction of using, or certainly waisting the smallest amount of consumables possible. This could easily lead to a hull that is as close to perfect as possible in construction, but designed with a little less excess than might be desirable when everything goes wrong.
With no intent to offend anyone, I cite the J/24 which though marvelously light and strong does have a habit of some pretty serious hull failures caused by keel strikes.
Regarding the Pearson 33 with a flexed hull, there could be serious damage if the laminate was built resin starved, or if the hull has been flexed to the point of fiber/matrix bond failure, or even fiber failure, and on the other hand, if the laminators were awake at the time they layed up that point there could be nothing more than a minor cold set in the hull, well below the yield point, and a year from now no one will remember where it even was.
Interesting thread though, which shows some wisdom and some lack thereof.
I'm not sure if we have answered the origional question or eased anyones worries though.
I am going to copy, and print these posts, so that later, when the defenders of the OLD SLOW and HEAVY is better than NEW, LIGHTER and FASTER, come here defending the 1450's Valiants and the 1867's Passports can have something to chew on...
Any hull, solid or cored, will dent (oilcan) if the jackstands are placed in the wrong places or too few of them are used, so pressure builds on one.
Fiberglass does flex, but if you flex it too much you break the fibers and structurally damage it. Hard to say without seeing it or having an expert look it over--which is what a good survey can tell you.
You certainly can have some new fiberglass laid up inside the bow to strengthen it, assuming you can access the inside of the hull. Whether it is needed...Can't tell over the internet.
I had an Islander Bahama 24 many years ago. When I bought it, the wood cradle had deteriorated to the point one pad had pushed in the hull on the port quarter by about 4". I spent much time worrying and planning on how to repair the damage, but when we put the boat in a new cradle with no pressure on the area, it popped right back out, There were no interior braces or bulkheads in that area, and no apparant damage. We sailed that old boat for a couple of years, and saw it on the lake several years after I sold it, and while there were issues with this old boat, none were related to the depression in the hull. That being said, check it thoroughly for cracks and damage, but don't let it scare you until you see for sure there is a problem.
DD
If we have not seen hulls failing due to the static (and dynamic) load of the keel on these old Albergs, Pearsons, C&C's, S&S, etc by now; then it probably aint gonna happen. 3-8000 lbs depending on size of boat is a significant concentrated load to put on a fiberglass hull and if there were signs of substandard construction, inadequate strength of construction, or fatigue it would be showing up long before now.
Until I read the report that shows specific sailboats of this era to have compromised strength (below that of what would be a safe design); I'm going to disagree. Bending/impact strength of a fiberglass panel is not what I would consider a proper structural analysis of a sailboat hull. It might be a consideration for collision strength; but you really want to know what the tensile and shear strength is (stresses that are along the direction of the fibers).
I think that Valiant would beg to differ on the strength of their new hulls (1" thick at the toerail) VS those built by their competitors. No; it's not a fast boat, but if you want to sail to the far side of the world it would be near the top of my list.
I agree that I have not seen hulls fail due to the normal service static and dynamic loads. The report seemed to be saying that as well. What the report indicated that areas of the hull were weaken due to the factors mentioned in my post above, and that has contributed to greater damage due to impact than would be expected otherwise.
So while I would agree that I have not heard of a boat "failing due to the static (and dynamic) load of the keel on these old Albergs, Pearsons, C&C's, S&S, etc" what I have observed that does appear to be stress cracking has occured in an area that is roughly a third of the topsides down from the rail near the bow area, an area of the topsides around the main bulkhead and chain plate knees radiating out onto the hull, and area radiating out onto the bottom of the boat near the skeg on skeg hung rudder boats, in the hull above the keel stub, and to a lesser degree sections of the run/counter of the boat.
If the skin is deflecting, it's either a rotted hull and it'll stay caved in, or it's fine and will pop back and be fine. Boats don't sail in labs. Seeing the aftermath from hurricane damage showed newer boats with thinner, lighter hulls, including at least one made with carbon-fiber suffering far more fatal hull damage. Obviously, none are impervious, but even comparing the hull between the C&C 29 I got for salvage and my 32 shows a massive difference in strength and integrity, as well as resilience once damaged. The C&C got holed by pier pilings and the belly ripped out by the fin. Standing on the deck of a Pearson 10M I looked at and then standing on my 32 (solid deck, not cored) is a telling comparison. The 10M was a bit springy. Mine is solid, like a concrete floor. Now, that being said, there's obviously a place for cored components, and thinner hulls with kevlar or other component. Especially in a world built around planned obsolescence. And, how convenient that we don't have an agency out there that tests boats the way the car agency does (testing off-center impacts, etc.....can't think of the name). Anyway, our auto makers had everything showing they made safe cars. Why? They made the tests. When these same vehicles are tested in a more real-world scenario, the results are telling. It's the same where the FDA takes drug companies' data on new drugs. What happens 5 years later? "Hey, why are all these people dropping dead? The drug company said it was safe." Same for boat makers who produce data on how less is suddenly more. Sure, there are improvements in materials, but a Kevlar boat isn't cheaper. It doesn't fatten the profit margin. A thinner boat, using the same materials as previous models, or less fiberglass supplemented with wood fillers is strong enough. It may well be.....in a lab.
Before you go shooting your mouth off with speculations about what "plastic" is, whether FRP has elastic properties, or if a fiberglass hull will or will not flex or elastically deform; you might consider the fact that other people on this forum have brains also and quite possibly more knowledge and/or experience on a particular subject than you with the help of google or wikipedia. FWIW I majored in both Mechanical & Mat Sci Engineering; we studied plastics and their chemical, physical and mechanical properties up the wazoo so I think I'm qualified to make some generalizations on them...
Well whatever you studied in college/university/wherever, I think we can reasonably infer it wasn't civil discourse
If you read the posts you'll be able to determine that the 'not a plastic' was in reference to a person's usage of the term as an idication of flexibility - his inference was that because the material is referred to as a member of the plastic family - it should bend easily.
Whatever your personal opinion is as to the suitability or seaworthiness of dented hulls is....
Fibreglass boats were not meant to deflect, acquire dents, change shape on stands or otherwise transform themselves.
There is a possibility that permanent damage has occurred to the boat.
In the original post, the question posed was whether or not there is reason for concern when dents like this are noted.
I believe that these dents are a cause for concern, and would advise anyone looking for a boat to avoid hulls that have them.
There are thousands out there whose opinions differ, and they have every right to their opinion and to share that opinion with others.
I encourage all of you who feel that the dents are not an issue to get right out there and buy boats that are sitting on jackstands that protrude into the cabin space. Two or three of them if you have the wherewithal. Load them up, grab the family and get out there and do some serious sailing.
Anyone know much about how Islander was constructing hulls in the early eighties? I just purchased an 81 Islander 30 Bahama for under 10k. The hull deck and rig were in solid shape. I know that the lead ballast is sealed in the keel which is all fiberglass on the outside. It did have one crack in the gelcoat right in line with the starboard chain plate, looks like it bounced off of a dock at one time. Mine has been sitting on stands for about 7months and I had no dimples in the hull from the stands. It also had no blisters. The only thing I did notice with the hull was a piss poor bottom job that wasnt prepped at all before applying paint. My dads friend owns an 84 bahama 30 and told me that the hull is over an inch thick pretty much everywhere below the water line. Does anyone know how correct that is? As for buying that Pearson what do you plan to do with it? any worldly cruising or long distance? I wouldn't worry about the dimples to much its an old boat there could be lots of other things wrong that you won't see cause you might be too focused on the dimples....the boat is over 30 years old.
Happy Sailing
Jeff
Well whatever you studied in college/university/wherever, I think we can reasonably infer it wasn't civil discourse
Hey; you are the one that asked for it. IIRC you were previously telling me to "check my chemistry" with misc. irrelevent footnotes. When you insult someone's intelligence with a meaningless response you should expect a flaming reply. I was trying to be civil in my OP to this thread correcting your first post. At some point the civility has to give way to being more direct.
Quote:
If you read the posts you'll be able to determine that the 'not a plastic' was in reference to a person's usage of the term as an idication of flexibility - his inference was that because the material is referred to as a member of the plastic family - it should bend easily.
Whatever your personal opinion is as to the suitability or seaworthiness of dented hulls is....
Fibreglass boats were not meant to deflect, acquire dents, change shape on stands or otherwise transform themselves.
I don't think you are understanding my point. So here's a more scientific explaination. Almost all plastics are low-modulus and therefore are very "stretchy". Fiber reinforcement will reduce the ability to deform and of course if you build a hull that is mostly fiberglass with minimal resin it will be stiffer and less flexible. But the matrix material is still plastic; and will respond as a plastic does especially when under constant load. When you place a plastic under constant load generally it will slowly deform until the plastic has minimized the stress load. Think of a rubber band. If you stretch it and keep it stretched; at some point the rubber band gets longer semi-permanently and the strain in the band gets lower. The same thing can happen with a fiber reinforced plastic. It's a good reason why you should not over-tension your shrouds and leave them taught; the boat will deform to minimize the stress.
Under normal circumstances the hull is stiff enough to withstand short term bending stresses and bounce back to it's original shape. When subjected to long term stresses the plastic will undergo what is known as stress-relaxation (explained in laymans terms in the previous paragraph); where the polymer bonds actually stretch and change shape to reduce the strain on them. When this happens the fiberglass will slowly become loaded and also stretch enough to elastically deform and the result is a shape change in the hull. It might not be permanent; remember these deformations are largely elastic in nature. Some polymers can stretch up to 50% in length elastically due mainly to stress-relaxation. When the force is removed it will shrink back to it's original length. If you stretch the same plastic more quickly it will yield (plastically deform) and break with the same amount of strain. The rate of strain is a critical factor in the deformation of plastics.
Quote:
There is a possibility that permanent damage has occurred to the boat.
It's also possible that there has been no damage whatsoever. Any hull that sits out of the water on stands for more than a few days will change shape on the stands. You might not be able to see it; but it has changed shape. Since most of the weight is resting on the keel; the bottom of the hull around the keel will flatten first and then the stands will start taking more weight. A boat in long term storage should probably have the stands moved now and then; but you still are going to flatten the hull bottom while sitting on the keel. I think this deformation is probably larger than you would see at a single stand; but it's not visible to the eye since it is not so much of a point load as a single stand pushing in on the side of the hull. The recovery goes unseen because the keel and bottom are submerged when the boat is re-launched.
So despite the visual "uglyness" of a tight stand; it's entirely possible that no damage has occurred. As I said before a surveyor should be able to tell by sounding the hull.
I was trying to be civil in my OP to this thread correcting your first post. At some point the civility has to give way to being more direct.
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