Death of a 4 Week-Old Boat

[maxingout]

Originally Posted by paradix

Since cat owners love to boast about how they might flip but they never sink, what about a cat that sails just as well regardless of which way up it is? Like those monster truck toys with huge wheels which flip over and keep driving...

You'd need symmetric hulls, a big centreboard which would double as a wing sail when the cat is flipped over, and carpet on the ceiling... Oh and your giant domestic fridge/freezer would become a freezer/fridge in one orientation...

I'm off to the patents office.

That's a great concept. All you would need is a gimbaled interior to complete the design. You are a genius!

[s/v 'Faith']

Originally Posted by paradix

....EDIT: darn, looks like SV Faith has beaten me to it. Hope I can run faster...

Naw... no rush on my part. It is still gonna look like something from 'revenge of Mothra'..... I gotta have "the belle of the ball" waiting for me when I return in the dingy...

[hellosailor]

"point is WHY does it comes off? "
Tear on the dotted line? Maybe those boats have been "dropped" on the keel, during yard storage, subjecting the hull to hard vertical shocks from the keel, which would crack glass fibers and invisibly create a "dotted line" to tear out after enough shock? Or maybe, simply improperly blocking boats at the yard is leaving a similar stress form the hull sitting on the keel when it isn't designed to the load?

Dave-
What you need is a "boat ball". Enter through a hatch like a B17 belly turret, and just have the whole rig rotate around it. Pointy hulls are SO passe. (VBG)

[Seahunter]

Originally Posted by bewitched

I don't disagree - whether the keel rips off, leaving the bolts, the bolts stay in the keel and are ripped from the hull, or a section of hull is pulled out with the keel - it still has the same result - the keel comes off.

The point is WHY does it comes off? I would like to argue that in the vast majority of cases it comes off because the keel is being put through something that was never in the designed to experience or accommodate in the first place (grounding, poor maintainance, modification)

Of the examples you had in your previous post, the only conclusion I could find of why the keels failed was for the Cynthia Wood, where USCG stated that the failure was due in large part to repeated groundings and improper repair.

Let's face it the reason a hull fails is abuse and stress to the hull itself, regardless of the reasons. We've been talking about keel lose through hull failure of sailboats, however, powerboat hulls fail for the same reason. There's a very distinctive "crack" when a powerboat's hull gets overstressed from repeatedly pounding it hard through heavy seas. I experienced this myself and it's very unnerving hearing your hull shrudder. In a sailboat when you hear it, it's all over.
Getting on with the "why"; here are a number.

Fiberglass fatigue and moisture: (from National Fisherman)

One report that is available is a six-year study of fiberglass laminate fatigue on hulls carried out under the direction of Paul Miller, assistant professor of Naval Architecture and Ocean Engineering at the U.S. Naval Academy. The academy and the University of California at Berkeley jointly did the work and were supported by the American Bureau of Shipping, the fiberglass boatbuilder TPI Composites (formerly Tillotson-Pearson) and Maricomp (a California marine structural analysis company).

The study depended on locating one or more fiberglass boats that had been in service for a significant period of time and whose service history could be documented in detail for the hours on the water, and wind, weather and sea conditions the hull was subject to. From these figures, the number and magnitude of strain cycles or wave impacts could be estimated with reasonable accuracy.

Then the boats' manufacturer had to be able to supply test samples and panels fabricated to the original specifications to represent the laminate's original strength. Calibrated strain gauges went on the boats to measure the effects of fatigue on stiffness and strength.

The boats that met the criteria were two J/24 one-design racing sailboats, which had been built by Tillotson-Pearson (now TPI Composites) of polyester resin and E-glass. Both boats were used at a sailing instruction and charter company in the San Francisco Bay area and detailed records of usage were available. Typical sailing conditions were 1-foot seas, 10- to 12-knot winds and boat speeds in the 5- to 6-knot range.

One boat, the "high-mileage" J/24, entered the charter fleet in 1984 and had 11,300 hours of sailing, and 10.2-million wave encounters. The "low-mileage" boat began service in 1999 and had 740 hours of sailing and 600,000 wave encounters. The stiffness, or strength, loss in the high-mileage boat was 18 percent, and that for the low-mileage boat was 4 percent.

Bending tests showed, as might be expected, that hull stiffness declined with wave impact loads, though the stress damage was cumulative. For instance, with wave impacts at 12.5 percent of the laminate's ultimate strength there was no loss of stiffness, even out to one million stress cycles or wave impacts but after that point, damage did take place. And at 25 percent stress there was no appreciable stiffness loss below 200,000 wave impacts.

Microcrack fatigue growth is the reason the hull loses its stiffness. You can't see that damage, but it is there. Eventually, stress cracks will begin to appear, first on the hull or deck exterior but also on the interior. If the impacts are severe enough, and they continue long enough they will weaken the hull and cause structural failure. Stress also increases permeability and moisture penetration into the laminate, which introduces a whole new set of problems.

Add to this stress related to partial groundings or "smacking" the bottom and you've just added a whole new factor to the bigger picture.

The long and the short of it is that all the data says Endurance limits were found to be near 25% of static failure load, indicating that a fatigue design factor of four is required for infinite service with this material; the Coast Guard requirement is only three. A standard boat laminate of polyester will have a SF = four. An epoxy laminate designed using FEA for a competitive race boat could have a SF as low as:three x (1-0.3)x(1-0.15) = 1.8 .
If you want to read the report, here's the link below...you'll have to pay like I did if you want more info.

ScienceDirect - Composite Structures : Fatigue response of thick section fiberglass/epoxy composites

Here are some good links on the subject:
Composites Engineering Basics
An Overview of Boatbuilding Materials and Methods

[bewitched]

I can go with that - Fibreglass hulls fatigue over time.

But the boat in the OP was 4 weeks old.

There was mention in earlier posts that there was somehow a design flaw with this boat. My contention is that there is no design flaw, but that the boat has been subject to forces that it is not reasonable for a designer to consider for this type of boat.

I would suggest that if a boat buyer required that their boat should be capable of grounding at speed without structural failure, then they should be looking at the steel hull, encapsulated keel end of the market. If they want a competitive racer / cruiser, I see nothing wrong with this boat.

[Seahunter]

Originally Posted by bewitched

I can go with that - Fibreglass hulls fatigue over time.
But the boat in the OP was 4 weeks old.

Yes but it may have had a lower than normal static failure quotient, which has more to do with harmonics of the hull than fatigue, especially in a new boat. The hull just failed.

[Randyonr3]

You guys bring up some interesting ideas for the age of a fiberglass boat.. Like anything else, as time goes on the item is weakened and stressed and going to fail.
Why is it then that most of the older boats are stoughter than hell after years of use..
Is it the construction of the glass or does glass become stronger with age as it cures.. and I say this as it would be in a controled area.. as we all know that glass breaks down with UV contact.
The reason I ask is that as a licenced inspector of concrete, We see that it gains its major strength over a 56 day period but will not fully cure for some 90 years, and all the time it becomes stronger.. I guess thats a plus for ferrow cement boats, as they get stronger with age..

[Seahunter]

Like concrete, fiberglass, epoxy and cf, there is an optimal recipe in the mix of the base components. There has always been an argument regarding hand laid fiberglass as opposed to chop spray, however if the ratios of resin to glass are not correct then the argument is mute. As for glass getting harder with age, the answer is "no"; if anything, it gets softer. The fact that ferro-cement gets harder with age is actually a problem. It loses it's flexibility as it gets older, resulting in catastrophic failure. There is a whole set of calculations in designing hulls based on load distribution, from the effects of ocean dynamics to the addition of (in this context) sail loads.

[hellosailor]

"Why is it then that most of the older boats are stoughter than hell after years of use.."
Because in the prehistoric days before the 1980's, fiberglass and resin were relatively cheap and the MBAs hadn't quite overruled the engineers and architects on the concept of "Let's make it thicker just in case."

Lots of old boats have hulls that we recognize as too thick, too heavy, too slow, too expensive compared to newer boats. Built too conservatively--which turns out to be good thing sometimes for the long run.

[Cyrus Safdari]

I guess this is what's called "keeled over"

[paradix]

Originally Posted by bewitched

I can go with that - Fibreglass hulls fatigue over time.

But the boat in the OP was 4 weeks old.

There was mention in earlier posts that there was somehow a design flaw with this boat. My contention is that there is no design flaw, but that the boat has been subject to forces that it is not reasonable for a designer to consider for this type of boat.

I would suggest that if a boat buyer required that their boat should be capable of grounding at speed without structural failure, then they should be looking at the steel hull, encapsulated keel end of the market. If they want a competitive racer / cruiser, I see nothing wrong with this boat.

I have to strongly (but respectfully) disagree. This is not some all-or-nothing America's Cup racer where there's no chance of grounding, speed is everything, expected lifetime is short and if the boat breaks we'll just use the spare.

Any boat with "cruiser" in its description, whether cruiser/racer or racer/cruiser or whatever, should be able to withstand grounding at hull speed in moderate to rough seas, in my opinion. The conditions for this happening are certainly a possibility when cruising, and indeed in many races as well (as pointed out by a poster earlier on). Or even if the boat is not ever intended to cruise, just sailing to and from races will also likely incur those risks.

I doubt many, if any, potential owners of this class of boat would be happy to treat it as a disposable item. Would they really accept a little extra speed potential at the risk of knowing they'll be losing the boat should it ever run aground?

[Northeaster]

Paradix - well said!

[bewitched]

Originally Posted by paradix

Any boat with "cruiser" in its description, whether cruiser/racer or racer/cruiser or whatever, should be able to withstand grounding at hull speed in moderate to rough seas, in my opinion. The conditions for this happening are certainly a possibility when cruising, and indeed in many races as well (as pointed out by a poster earlier on). Or even if the boat is not ever intended to cruise, just sailing to and from races will also likely incur those risks.

I appreciate where you are coming from, and I could even go along with the arguement that if a boat is sold with "cruiser" in the title, it does infer a stronger construction.

However, if I were buying a new boat, I think I'd look a bit further than the sales pitch.

If my intended use of the boat was to predominantly cruise and if I thought there was a good posibility that I'd ground the boat hard from time to time, I would not even consider a boat with this type of keel.

However, if I wanted to predominantly race the boat, with occasional weekends away, the requirements for the boat change. This type of keel is certainly an option.

My opinion is:
- I do not believe a keel of this type can be expected to remain structurally sound after such a hard grounding. The loads imposed are simply too high.
- I do not believe that it was ever designed to do so.
- If this is not acceptable to the buyer, then they should not buy boats with keels of this type - it is clearly not suited to their needs.

You pays your money, you takes your choice.

[Randyonr3]

Theres more to the design of the keel on the OP boat than just performance issues.
as this type of boat, designed mostly for racing, is often transported around the US and around the world for races..
Its not an Americas Cup boat but if you were to set out at Andersons Boat Yard in the San Francisco area durring some of the different series you would see a large amount of these "High Performance" boats being shipped into the yard with the keels being hauled in another trailer and preped for races on the bay.
I've seen boat with "home ports" from the land of OZ and NZ in the bunch durring the "Big Boat Series" ...
Much of the equeptment on these boats are bolt on and go racing.. and two weeks later it stripped off and the boat is shipped somewhere else..

[Stillraining]

Originally Posted by Randyonr3

Theres more to the design of the keel on the OP boat than just performance issues.
as this type of boat, designed mostly for racing, is often transported around the US and around the world for races..
Its not an Americas Cup boat but if you were to set out at Andersons Boat Yard in the San Francisco area durring some of the different series you would see a large amount of these "High Performance" boats being shipped into the yard with the keels being hauled in another trailer and preped for races on the bay.
I've seen boat with "home ports" from the land of OZ and NZ in the bunch durring the "Big Boat Series" ...
Much of the equeptment on these boats are bolt on and go racing.. and two weeks later it stripped off and the boat is shipped somewhere else..

Very good point...and like any well funded racing circuit everything is minutely inspected and generally replaced with new ( bolts and such) with each reassembly...something a cruiser is not going to do every 2 weeks.

But were not talking bolt failure in this case.... its stress loads to too small of an area to be structurally sound for bumping into things...plain and simple im afraid.

Id love to sail on a go fast boat someday ..but Ill stick to a bit sturdier keel for crossing the ocean with my family thank you very much.... or general gunkhole cruising in rocky Puget sound for that matter...