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  Topic Review (Newest First)
09-10-2002 04:18 PM
What is the difference between a coastal crusier and a bay b

There''s proof.All you have to do is go hang around boat yards.You''ll see it.

09-09-2002 07:39 AM
What is the difference between a coastal crusier and a bay b

Thanks for reinforcing my point that there is probably no conclusive experemental nor empirical proof of either type keel being superior.
Thank you for illustrating my point about jumping to unsupported conclusions, though doubtless you didn''t intend to.
09-09-2002 04:06 AM
What is the difference between a coastal crusier and a bay b

A couple more points, while you are right "If you want the best hull for a grounding, it won''t be wood or fiberglass." but on a pound for pound basis, it would be a composite. On a pound for pound basis a kevlar sheathed, cold molded wood core would be right up there as one of the best materials for impact and abrasion (which is why kevlar is being used for bullet proofing).

To me, two of the most interesting sets of testing done to date have been done in Europe. The first dealt with fairly large steel hulled boat that was sunk a few years back due to wave action. The boat was recovered and the bow sections on one side were found to have been crushed inward by the impact. The boat was donated for research purposes and an experiment was performed in which the other side of the bow was mounted so that a controlled water pressure could be exerted and recorded. The pressure was increased until the bow section crumpled to the same shape as the side wrecked by the sea. Until that time it was pretty much assumed that the greatest load that a boat might encounter would be the concentrated loads of a small area impact with a fixed object at speed (i.e. shipping container or a rock). These are pretty easy loads to calculate and design for. The experiement with the crushed bow, completely altered the way the structural design of bow sections by showing that simply de to wave action there can be are extremely high loads that can be imparted over a large area and that merely designing for a point impact is not enough.

The second set of experiments deal with instrumenting full sized vessels. Probably the most interesting uses a specially constructed boat in which the hull and rig have a certain amount of flexibility built in. Within the hull is a very rigid but comparatively light weight frame that is tied to the hull and rig with are a series of precise instruments. As the boat is being sailed detailed measurements of loads on and movement of the hull are being read and recorded along with precise measurements of wind and boat speeds as well as the wind and water pressure felt at a buch of locations. This data is being compared with computer generated finite element calculations to improve the ability to mathmatically predict the actual loads that a boat will experience in a wide range of conditions. While these kinds of measurements are beyond the rhelm of most small boat builders, the kind of data that is coming out of this type of work has allowed designers to purchase comparatively simple structural design software that provides more reasonable empirical design imput.

09-08-2002 09:14 PM
What is the difference between a coastal crusier and a bay b

NautTwilight,if your statement is entirely correct,we all might as well ''pack up & go home''.
im learning a lot from this messege board,the info ive gathered will greatly help me to weigh up the options,then decide for myself & make my own decisions .(ie on a boat purchase).

it sounds a little like your suggesting no-one say anything,or offer any observations or opinions,in fear of being sued,
your not a lawyer are you? =0)
09-08-2002 07:55 PM
What is the difference between a coastal crusier and a bay b

I agree that we can throw around anecdotal info all day long and not prove anything. BUT there actually has been a tremendous amount of work done on composites and the loadings imparted into various parts of a boats hull. This research has been performed for a wide range of reasons from military, to EU and Insurance standards, to various racing campaigns. With the ability to instrument full size boats and measure real loads there is an enormous amount of data becoming available. I disagree that" Only an extensive statistical analysis, or full-scale, carefully controlled tests will conclusively prove which underbody type is inherently safer, and then only for the exact configuration actually tested." As research is providing more precise information on strengths of materials and loadings felt by individual components of a vessel, it is not all that hard to actually calculate the loads imparted into a keel. Byond that there is a large sampling of boats out there of both types of construction. In talking to a fairly large number yacht designers and surveyors who see alot of both kinds of keels after the extreme impacts I''ve concluded this about encapslated vs external ballast:
What seems obvious is that properly engineered and constructed either encapsolated ballast or external ballast can work adequately in most grounding situations. Both can in fact be designed to withstand very extreme groundings. The problem is that few production boats are engineered as well as they should be if one of the prime design criteria is to withstand an extreme grounding and survive. Usually the prime design criteria includes a lot of issues such as budget, performance, ease of construction and so extreme grounding resistance becomes a bit more secondary.

To touch on some of the other points, for an equal keel shape and equal ballast, an external ballast keel should have a deeper more voluminous bilge than an encapsulated keel because the ballast occupies the volume of the encapsulation. The nice thing about externally ballasted boats is that they can usually be repaired to their original condition. The same cannot be said for encapsulated ballast boats.

In my experience I have not encountered an externally ballasted keel that can''t withstand substantially more than a 4 knot grounding. I have been aboard quite a few boats with externally ballasted keels that have run aground at pretty high speeds (in quite a few cases approaching 6 to 7 knots)and in each case the boats have come through with little more than superficial damage to the ballast (mushroomed lead in the case of rocks). That has not been the case in encapsolted keel boats.

In the most extreme case that I know of an externally ballasted Contessa 33 was dropped from a crane while being offloaded as deck cargo from a ship. While there was clearly damage to the internal framing, it was a pretty straight forward repair that is still intact and invisible after 15 years pretty hard years of useage. But of course that''s just another set of anecdotes.

09-08-2002 02:45 PM
What is the difference between a coastal crusier and a bay b

All this anecdotal "proof" proves absolutely nothing.
Nobody here has seen enough to eliminate the skewing of results caused by uncontrolled factors.
Only an extensive statistical analysis, or full-scale, carefully controlled tests will conclusively prove which underbody type is inherently safer, and then only for the exact configuration actually tested. Is anyone aware of any of the naval architecture institutes conducting any? I didn''t think so. They''re probably too busy to bother with sailboats. And it''s too expensive for recreational boatbuilders, In any case, The ocean is irrestible enough a force and the earth is immovable enough an object that any hull can be breached like an eggshell and any bolt can be broken like a matchstick. If you want the best hull for a grounding, it won''t be wood or fiberglass.
09-07-2002 03:52 AM
What is the difference between a coastal crusier and a bay b

I thought Weepeckett was how Mainers referred to a small Island Packet. :-]
09-06-2002 05:02 PM
What is the difference between a coastal crusier and a bay b

Jeff: you have seen a picture of TPIII''s keeel and daggerboard. On a race around Catalina way back when we had the Dagger board down all the way. Hit a rock which we went over after the dagger board bore the boats entire weight and impact. We hauled as soon as we got back to Long Beach Marina. We drove the board aft 8" in the keel. Had to cut a section out to remove the board. Repaired the cut out section, put the board back in and 30 years later its still going strong. Bye the way the keel has 3200# of lead inside. The box mwmber was built as part of the hull shape the lead was then glassed in a water tank,125gal built on top of it. No Problmo!!
09-06-2002 11:12 AM
What is the difference between a coastal crusier and a bay b

Hi Jeff,
I love these debates on underbodys.To me it''s determines what the boat should be used for.
First of all,I dont think there are many ex. ballasted(lets call them EB and IB ok?) boats that will survive a four or better kt. colision.
Do you consider Sabre a well designed yacht?I would hope you do,because they are.Now my friend has a Sabre thirty-eight with
,of coarse, an EB keel
When he bought the boat in ninety seven I had to repair the stringers in the foward part of the bildge(BTW EB boats don''t have much bildge either).Three out of five of them were broken and the dent in the leading edge of the keel looked like three or four kts.The same friend was lust telling about a C and C forty three or four that had hit something and you could put your hand through the hole/crack at leading edge fillet.That boat came extremely close to being lost.I''ve never seen or heard of this happening with a IB keel.The keel is integral.The shock is more evenly dispersed.
Last June when I hauled out because I was going over the road tracter trailer,the wind was N/E @ fifteen to twenty.I had to load on to the trailer heading west with that wind on my stbd qtr. Down wind there is about thirty more feet of room,so, don''t screw up! The driver did not have the drop down through the trailer holes,he had a straight beam.Well, I hit that beam doing four knots. It stopped my boat dead!After she was on blocks and stands I rushed to survey the dammage.Nothing! Not even a crack in the gelcoat.No shifting of the ballest,no voids(in my boat anyway)
and no broken membrane.So much for the leading edge being thin.Also you make it sound as if IB boats have some kind of inadequacy in design around the keel area,in my years of fiberglass repair I find this not to be true.Anyway, I''ve never seen it.Nor have I seen shifting ballast.And not all of the IB boats have their ballest that low in the bildge. My Endeavour thirty-two draws four ft two inches and benith my two ten inch deep by two ft by two and one half ft floor compartments rests the sealing membrane to the ballast... very easily excessable!I think that if the membrane were to break, the only boats where it would be difficult to repair would be very deep draft IB boats.Anyway that membrane isn''t the only thing that holds the ballast in place.What about the back of the keel?And breaking that membrane won''t cause you to loose your boat.
While it is true that we did find some relitively small voids in some IB keels, this repair is simple.
About the daggerboards?You''ll never convince me of that.I''d have to be on the boat and see the whole thing with my own eyes and do the survey myself.
Well Jeff, as you know I just re-launched this morning(all went well thanks)and now I have a date with an island called Weepeckett.
Looking forward to a response,

09-06-2002 04:03 AM
What is the difference between a coastal crusier and a bay b

Good question. You have to look at how an encapsulated keel is constructed. In most cases that I have encountered, the laminate for the hull of the boat is continued downward into the keel area so that there is a sharp turn in the laminate at the point that the hull turns down into the keel. In properly engineered bolt on keel there are heavy tranverse frames at the top of the keel that distribute the loads outward into the hull. In the case of the daggerboard scabboard the scabboard is glassed in at the hull and deck creating a large lever arm. But in the case of most encapsulated keels there is very little framing involved. The loads are being applied perpendicular to the comparatively thin skin of the hull. This results in more flexure and that flexure can result in fatigue over time. It can also pry the sides of the encapsulation and waterproof membrane at the top of the keel loose from the ballast keel.

In an encapsulated keel, the watertight membrane is below the ballast keel where it can be exposed to the full impact and abrassion of rock or coral. Generally above the ballast keel there is a thin membrane that simply keeps bilge water out of the ballast cavity. In a bolt-on keel the hull passes across the top of the keel so that the watertight membrane is not exposed to the actual impact with coral or rock.

The laminated keel itself is difficult to layup well as the yard crew is forced to work in the narrow confines of the keel cavity. In my experience trying to repair encapsulated keels the glass work at the bottom of the keel is often quite thick but very poorly laminated. Big voids, unwetted out cloth and unreinforced lenses or resin are quite common. Placing the ballast so that it is properly adhered to the sides of the ecapsulation is quite trickly. Last year when this was discussed I believe that we found by walking through boat yards and tapping on keels that somewhere between 25% and something less than 50% of encapsulated keels had voids between the encapsulation and the ballast keels.

What this means in a hard grounding is that the skin is more easily pierced in an encapsulated keel, there is less to resist the ballast keel from being forced upward and once forced upward the boat has damage that is next to imposible to to repair. I have cited as an example my family''s Pearson Vanguard that clipped a rock at 4 knots which was enough to crush the encapsulation and drive the ballast up through the water proof membrane and dislodge the tank above.

With a Daggerboard a well engineered scabboard has a hard rubber crush block that absorbs much of the force of an impact rather than distributing the impact loads into the hull. Again the water tight membrane is not exposed on impact.

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