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brazilnut 11-11-2004 07:56 AM

What can you tell from the numbers?
 
I have been looking for a 28-32 ft yacht for a while. I think I''ve found something that meets most of my basic criteria (headroom for tall person is one of them). Can one of the experts here tell me what the numbers of this boat might mean in terms of sailing ability, seaworthiness and perhaps comfort in big seas. The boat has a full keel, fairly low freeboard and is from the early 70''s.
LOA: 28ft
LWL: 22ft
beam: 8,10
draft: 4,9
displacement: 7716
ballast: 3858

It has a very low CSF and a high motion comfort rating for a boat of this size. The ballast to displacement ratio is very high (50%) compared to all the other boats I''ve been looking at. What does this high ratio do for the boat? I realize these numbers in isolation don''t mean much, but some pointers would be appreciated.

thorJ30 11-11-2004 01:53 PM

What can you tell from the numbers?
 
lol
whats the brand and model...

it almost looks slow and heavy to me ...

motion comfort seems to be over rated a bit, than again if you are stuck with a slow boat you need all the comfort to hang on until port comes into sight ...

Thorsten

brazilnut 11-14-2004 12:26 AM

What can you tell from the numbers?
 
Re-reading my post I realize I was pretty vague, so let me try again. I''ve been looking at boats in the 28-32ft range for a while. I''m not looking to race the boat- just use it to overnight and spend a few months a year cruising in southeast Brazil (which is a terrific cruising ground, BTW). I''m not terribly interested in speed, but I do like the idea of having a boat that is safe in a blow. I may never cross an ocean, but deep down, I think everyone would like to know their boat is up to it if they should suddenly get the inkling to do so. Now comes my doubt. It seems that half of what I''ve read would look favourably on the boat I described above for it''s narrow beam, high ballast ratio (and even high displacement). It has a low center of gravity and low freeboard (though at the cost of a high wetted surface). When I compare this boat to a modern 28ft. production boat made here in Brazil (the Aruba 28) it seems as though they were made on different planets. The Aruba 28 looks like a Volvo Ocean racer with it''s wedge-shaped hull, long waterline wide, flat stern and fine entry. It also has a low ballast ratio. So, here is what I would like to understand a little better.
1) What are the advantages (if any) from a high ballast ratio, and how does this affect the way the boat sails? What are the trade-offs?
2) Are there advantages to a narrow beam? (I keep thinking of thoses images of Volvo Ocean racers upsidedown with the crew sitting on the overturned hull waiting for their rescuers).


WHOOSH 11-14-2004 02:51 AM

What can you tell from the numbers?
 
BN, I think we need Jeff, our resident naval architect, to wade in here and give you his answer...but let me mention a few things that may be helpful.

First, I think you are trying to zero in on a one or two discrete characteristics (of a boat''s design) in order to determine qualities that are shaped by a variety of variables. E.g. you are asking about the value of a high B/D ratio when in reality your issue is probably the boat''s ultimate stability at sea, which in turn is going to be determined by a variety of things (form stability, beam, rig, keel type & shape, and how the boat is managed, among others). When we see a modern production boat (several French & U.S. mfgrs. come to my mind...) with a shallow draft keel, a tall rig and a real-world, fully provisioned 30% B/D ratio, I think we all are a bit worried about its capsize potential out in Big Water. But that doesn''t necessarily mean that more ballast is always better. Shopping for a boat for offshore sailing is better done by using a mix of information, including but not limited to numerical design parameters. (So in response to your title for this thread, I would answer: "Some things but not a lot..."

Second, I think you would benefit by doing some selective reading on boat design. It won''t necessarily produce a list of ''good boats'' which will suit your purposes but it will get you to reflect on a wider range of issues and better discern ''good'' from ''bad'' designs. Everyone has their favorites references but here are a few sources I''d encourage you to read:
1. Dave Gerr''s The Nature of Boats; Dave strikes me not only as a knowledgeable sailor & designer, but an artist with the written word.
2. John Neal''s web-based discussion on the characteristics of a good offshore sailing boat, found at www.mahina.com/cruise.html John has sailed over 300,000 offshore miles now and has provided cruising instruction to sailors in the SoPac, Antarctic and Atlantic for several decades and his discussion is about the real-world design and build features of a boat being taken offshore.
3. I would also recommend one of the cruising boat references that integrates a discussion of sailing and cruising with a discussion about boat design and boat features. One good choice IMO is Nigel Calder''s Cruising Handbook, specifically the first few chapters.

Third, some folks will recommend a book that describes a selection of ''good designs'' or good offshore boats (e.g. John Vigor''s Seaworthy Offshore Sailboat) but of course that means you are relying on someone else''s homework rather than your own. Still, the value of such a reference is that you can pick up info on how a boat was built, which can be very instructive.

You asked about narrow beam. While it is just one more variable, it''s true that in general narrower boats can provide a speed advantage, other parameters being equal. While modern offshore boat design has sometimes led to more beam and initial form stability, another track has produced decidedly narrow (B/L) ratios in order to provide faster passage times for a given displacement and therefore boat cost. That was part of the original rationale for the Sundeer yachts from South Africa.

Jack

Jeff_H 11-14-2004 06:51 AM

What can you tell from the numbers?
 
(I warn all that this is a very long answer to a fairly complicated set of questions)

First of all, I agree with Jack, you need to do a lot more reading. With all due respect comments like the one that you made about seeing "Volvo Ocean racers upsidedown with the crew sitting on the overturned hull waiting for their rescuers" is just plain wrong and suggests very superficial understanding of modern distant racing boats. In the world of offshore monohull distance racing there are two main branches, one that includes boats like the ''Volvo 60''s'' and the other which are based on the ''Open Classes''.

The Volvo based boats tend to be moderately narrow with fine bows and comparatively balanced hulls. They are designed to be good boats on all points of sail and have proven to be quite fast and surprisingly easy to handle. You have never seen a picture of one upside down with the crew waiting to be rescued. That has never happened.

What you may have seen are Open Class boats inverted. Open Class boats go for a very extreme beam and huge sail plans. They are designed to be single handed rather than crewed and they are optimized for reaching and running which is generally what the do most of the way around the world. They tend to be lighter than the Volvo boats, faster on a reach, but the lack the kind of ballast stability that the Volvo boats have. With thier extreme beam the earlier boats were capable of remaining inverted for long periods of time. The newer boats are actually designed to have a self righting ability.

All of that aside, and to try to answer your questions, When you talk about the design of a boat for offshore use there are a lot of desirable features that cumulatively make up a good offshore design. In most cases, moderation is critical as the extremes tend to produce boats that have serious faults.

To talk about the specifics of stability and comfort, both are not just a question of ballast/displacement ratio, or beam to length ratio but a whole range of other factors (such as overall drag, weight and bouyancy distribution) as well.

In a general sense, the core factors that control stability relate to weight distribution and buoyancy distribution, both when the boat is standing essentially upright (Initial stability) and when it is heeled at extreme angles (ultimate stability).

In all cases, a low VCG (vertical center of gravity) is a good thing. There is no such thing as too low a vertical center of gravity for either motion comfort or stability. A low VCG is achieved in a lot of ways such as a high ballast to weight ratio, high density ballast (cast lead) placed low in the water (deep draft and a bulb keel for example), Light weight aloft (light rig, topsides and deck structure, and moderately low freeboard and deck houses), and in a cruising boat storage that occurs low in the boat. So from a VCG standpoint and therefore stability standpoint a high ballast ratio is a good thing.

But ballast ratio alone tells you one small piece of the puzzle. As a boat''s draft becomes shallower, the ballast ratio has to increase to offset the shorter lever arm. As a ballast becomes lower in density (iron, or lead in concrete) it takes up more volume and so ends up being higher in the boat or stretched out longitudinally or both. Modern boats generate enormous stability relative to their ballast to weight ratios, overall drag, and displacement by moving a large percentage of their ballast into a deeply placed bulb at the bottom of their keel.

Then there is the issue of beam. This is a harder topic to explain verbally. Like so many aspects of yacht design, beam is only a one part of the equation that affects motion, and performance. Like weight wide beam is often singled out as having a particularly large affect on sailing performance. While there are broad generalities that can be assumed about the affects of beam on the behavior of a boat, the realities of the affect of beam on any specific design can vary very widely from the assumed generality.

In general, all other things being equal, a boat with a narrow waterline beam will have less initial stability and a motion marked by softer acceleration and de-acceleration. It will be easier to drive through the water meaning that it should have less drag in high winds and low. Narrow boats tend to have an easier time going to windward especially in a chop. Narrow hulls tend to have better directional stability (helping the boat to hold its course better) but all other things being equal having a larger turning circle. They also tend not to develop as much weather helm from heeling because their heeled waterlines are more symmetrical than those of a beamier boat.

Beamier boats tend to have quicker motions, more wetted surface and therefore more drag. They tend to be slowed by wave action. The have more stability when inverted. They have greater initial stability (stability at small angles of heel) but a smaller angle of ultimate stability (the angle at which the stability becomes negative and the boat would rather invert than come up). For normal coastal conditions they require less ballast for a given stability. If coupled with lightweight, they tend to be faster down wind in a moderate to heavy breeze because are more likely to be able to surf or plane. They tend to point upwind better in moderate conditions (a combination of greater stability and more foil length for a given draft). They also tend develop as more weather helm and are more prone to wiping out due to heeling because their heeled waterlines are less symmetrical than those of a narrower boat and wide beam tends to “jack” the rudder and keel out of the water.

Now those were the broad generalities about beam but as I said before boat to boat there are big variations between the normally expected impact of beam and the actual affect of beam. One major reason that there is such a variation is that we tend to talk about the beam of a boat as a single measurement taken at the widest point at the deck. In reality, the actual affects of wide or narrow beam on the performance and comfort of a boat can be altered by a lot of factors. These would include items such as waterline beam, the distribution of beam fore and aft at the waterline and immediately above, the cross-sectional shape of the hull, weight and weight distribution and the amount of free board and height of deck structures.

To really understand the affects of beam you need to understand the affects of form vs. ballast stability. There are three ways that boats develop stability; form (also called stiffness or initial stability), ballast, and dynamic. Of the three, dynamic has the least relevance to displacement boats as they rarely have enough speed to create a useful amount of dynamic stability.

As the name implies, form stability derives from the shape of the hull of the boat. A shallower and wider hull generates more stability than a deeper narrower hull. Visualize a piece of wood lying in the water. On the flat it has a lot of form stability. On edge it has next to none. This is because stability in any floating object comes from the distance between the center of gravity (the balance point for all of the weight in the boat including those things that are part of the boat and those things that can be moved around) and the center of bouyancy (the single point that is the center of all of the volumes under water). In a wider, shallower boat (talking about the part of the boat that is in the water) as the boat heels, the center of bouyancy moves more quickly toward the low side for small increases in heel angle.

Form stability has several problems. First of all at large angles of heel, approaching 90 degrees form stability drops off dramatically. This is the point where it can be needed most. Second form stability tends to give the boat a quicker motion as the boat quickly builds stability and the boat snaps from one hard bilge to another. This is less comfortable for the crew in rough conditions and can be more tiring. Lastly, in the extreme conditions of a blue water passage, a boat that depends on large amounts of form stability also tends to be more stable in an inverted position.

Ballast stability has mostly positives associated with it. All other things being equal, the deeper and heavier the ballast the more stability a boat will have. Ballast that is heavier and deeper also gives the boat a slower, more comfortable motion. Of course like most things in yacht design, there are some tradeoffs in this area as well. If the ballast occurs at the end of a deep keel, the boat cannot get into as shallow water. As you start to shorten the keel length you substantially give up performance for the same stability because you either end up with a low aspect ratio foil or you end up with a big bulb or wings also increasing drag. No mater what the ads say, nothing performs like a deep fin keel in all conditions. They do loose some efficiency in heavy seas but not as much as the long keel proponents like to hypothesize that they loose. Of course deep fins have their own compromises but that is not the point of this discussion.

There was a lot of discussion of the physics of stability. Ignoring dynamic stability for the moment, the stability of a boat simply a product of the weight of the boat times the horizontal distance from the boat’s center of bouyancy and the boat’s center of gravity. To define the terms the center of gravity is the one point (fore and aft, athwartship and vertically) that is the center of all of the weight on the boat. The center of buoyancy is the single point that is the center of all of the weight of the water displaced by the hull.

When the boat is sitting still and not subjected to outside wind or current forces, the center of gravity occurs directly above or below the center of bouyancy. But as the boat heels, the center of buoyancy moves toward lower heeled over side. Discounting for the moment weight being shifted on a boat (such as crew crossing the deck or fluids in a tank seeking the low side of the tank), the center of gravity does not move relative to the hull of the boat as the center of bouyancy does but it does move relative to its previous position. Depending on the shape of the hull and topsides, the hull either “jacks up” or “rolls out” (typically boast with high form stability, and flared topsides) meaning the center of gravity rises, or “sets in” or “rolls down” (typically boast with slab sides, tumblehome and Vee’d or wineglass hull sections) meaning the hull moves lower into the water and the center of gravity lowers at the boat heels.

The center of gravity also rotates about the instantaneous axis of rotation. (I say instantaneous because this axis does not remain fixed but shifts as the boat rolls due to the change in shape of the hull as it heels.) If the center of gravity is above this axis of rotation (Lightly or un-ballasted boats, old IOR boats, and some steel boats and some heavy cruisers with heavy rigs, interiors, topsides and decks and low ballast ratios), it will rotate to leeward to leeward the boat heels reducing the potential righting moment of the boat. On boats with the center of gravity below this axis of rotation (first generation IMS race boats, boats based on IMS type hulls and traditional heavily ballasted deep draft cruisers) the center of gravity shifts away from the center of buoyancy increasing the center of gravity aspect of stability. The reason that a deeper or heavier keel helps stability is that it simply lowers the center of gravity of the boat, which results in a larger separation between the center of buoyancy and the center of gravity for any angle of heel.

Of course moving weight to one windward, moves the center of gravity to windward, and so helps spread the distance between the center of gravity and center of buoyancy, which increases stability. So much so that even on a boat as large as a Volvo 60 (nee Whitbread 60) the crew moves every piece of gear and every crew member (who is not doing a task to leeward) to the windward side of the boat and use hinged stanchions so that the crew can lean out further.

So lets go back and look at the exceptions to the rules above. Normally, beamy boats are assumed to have a quick motion. That is because for a given displacement they are assumed to have a lot more form stability. If you visualize to rectangles of equal area one nearly square and one much wider and shallower obviously the flat rectangle will have more surface area and will rock more quickly from chine to chine. BUT, in the newer wider designs, careful modeling has allowed wider boats with less form stability and more symmetrical heeled waterlines. If you visualize a boat that had a cross-section that looked like a section of a cylinder as it heeled it would not develop as much form stability and so would have a slower motion and the waterline shape would always remain the same shape. Through computer modeling, the portion of the new beamier boats that are in the water act more like the cylinder model and therefore often develop less form stability as they heel than their beam would suggest and therefore have a more comfortable motion. The center of bouyancy still shifts relative to the center of gravity as they heel and with their moderately wider beam relative to the depth of the canoe body (hull in the water without appendages) they are still more effective at increasing the distance between the center of gravity and the center of buoyancy and therefore increasing stability.

Another exception to the generalities about the affects comes from the difference between waterline beam and the beam at the deck, as well as, the distribution of beam fore and aft at the waterline and immediately above the water line. As I said above, we almost always look at beam as the number published in the literature about the boat. That beam has absolutely nothing to do with the behavior of a boat in most conditions because the waterline beam can be substantially different than the beam on deck. Because of that a comparatively beamy boat at the deck level can actually have a narrow waterline and behave like a narrower boat in terms of motion and sailing performance. This is often the case with IOR era boats and Open class boats.

The shape of the topsides affects how quickly a boat becomes beamy as it heels so a narrow beam boat with highly buoyant topsides can behave like a substantially beamier boat as it heels, rolling out quickly developing form stability and a quick snappy motion. Another factor, which is totally ignored, is the distribution of beam along the waterline. If you visualize two boats with the same displacement, waterline length, general cross sectional shape, and waterline beam, but one has a diamond shaped water line plane and the other is a simple rectangle, the boat with the rectangular shape would have more form stability than the boat with the diamond shaped water plane. The rectangle would tend to have a snappier motion as well. Because of that phenomenon a narrow boat that carries its waterline beam to its ends would tend to have more form stability than a beamier boat with more diamond shaped or triangular shaped waterlines. Modern hull forms tend to resemble the diamond model more than the rectangular model and so can have a wider waterline maximum beam than its more traditional models, which tend to push the buoyancy more toward the ends of the boat.

We touched on the affects of the cross-sectional shape of the hull. Basically flat rectangular sections give a lot of initial form stability but with the negative affect of promoting quicker motion. Boats with cylindrical, and deeper Vee’d sections have less form stability and softer accelerations than the flat box model. A beamier boat with cylindrical and deeper Vee’d may actually have a more comfortable motion than a hard chine narrower boat. (That is the principle behind Island Packets and IMS type boats alike)

The weight of a boat comes into play here as well. For a given weight, cross section shape and waterline beam there will be a certain depth of the canoe body. The deeper the canoe body, the lower the form stability. With more weight comes a deeper canoe body and a slower motion for the waterline beam. We also discussed the impact of weight distribution above but in general the lower the vertical center of gravity, the more stability. As a result a light narrow boat can have a lot of stability even if the center of gravity is very low (modern race boats for example) and wide boats can lack stability (some lightly ballasted IOR type boats or shoal draft traditional cruisers for example).


Lastly there is a tendency to think of beamy boats as having great stability in the inverted position. Today manufacturer’s (Hunter and Island Packet for example) are getting around that issue by increasing the height of the boat’s freeboard and deck structures. This increases the angle of the limit of positive stability and makes the boat more unstable in the inverted position by raising the center of gravity higher above the inverted center of buoyancy. Of course high freeboard brings with it a whole range of negatives, such as raising the vertical center of gravity and greater windage, that are outside the scope of this already too long discussion.

There are a few other factors at play here as well. Research suggests that it only takes a breaking wave equal to twice the beam of boat to roll a boat over. In theory this makes a narrow boat more prone to being rolled. In reality there is also the problem that a beamy boat is more likely to dip a piece of its deck into the water and “trip” which somewhat offsets the argument about wave height to beam ratios. A good thing about a very narrow boat is that it less likely to be stable upside down.

These of course are only a piece of the puzzle. Drag comes into play as well. A boat that comparatively has a lot of weight for its sailing length or which has a lot of keel area (long or full length keels) need to carry more sail area. This can become a real problem when slugging it out in heavy conditions. A boat with lower drag can disburse some of the force of the wind by accelerating where as a higher drag boat can only heel. Again at the far extremes of lightweight, a boat will have less inertia and so will be more prone to heave at a higher rate.

In the end the best solution is moderation. Boats like the Saga are too narrow to develop enough initial stability. Boats that are too beamy like Island Packets and the like, also give up a lot for their beam.

I hope this answers your question.

Respectfully
Jeff




PhilMraz 11-14-2004 03:52 PM

What can you tell from the numbers?
 
You said a mouthful, Jeff. I think that was about the most concise explanation of sailboat design dynamics I have ever read. Did you put that together today, or is it an excerpt from that new text book you’re writing?

There is one issue regarding ultimate stability when beam to a wave that I have not heard discussed before. It has also to do with the dynamics of the wave motion itself. Any surfer knows that he can easily dive beneath a wave to let it pass over since the depth of the wave action is relative to wave height and rapidly declines beneath the surface. Given two boats with similar vertical centers of gravity, one having a deep draft and the other a shallower draft, would the deeper lying keel plane not induce greater roll tendency due to the differential of the fluid motion within the wave? Might this not be one scenario where deeper draft actually contributes to “tripping” the vessel?

Got to re-read that analysis once again. More questions will arise!

Regards,
Phil

Jeff_H 11-14-2004 06:30 PM

What can you tell from the numbers?
 
Thanks for the kind words.

You have asked a question that I had avoided discussing because there is not one cut and dried answer to this issue and it would make an already long answer much longer and I wanted to get out sailing for the day. There has been a lot of study of the issue of draft and wave surface speed and like so many sailing dynamics issues thewre are a lot of factors at work beyond the simple draft and the results of testing suggest that there is a lot at play here.

To begin with, the phenomina that you mention is related to the fact that the surface of a wave can be moving at a substantially greater speed than the center of the wave which can be moving at nearly a zero speed. I have seen this described as ''surface sheer'' and ''gradient surface sheer''.

In theory the deeper a vessel extends into a wave the greater the difference in speed will be experienced between speed of the water at the tip of the keel and speed at the waterline.In principle that difference in speed can and does induce a roll moment (We can see wave driven roll even in passing power boat wake or lying cross wise to a chop.)

The current thinking is that it takes a wave at least twice the height of the beam of the boat to induce sufficient force to be considered to be a contributing factor in a capsize or roll over. To some extent that minimum height is related to fact that greater surface speeds are experienced as a wave gets taller. But that is not the whole story because open ocean waves that are twice the beam of the boat are rarely steep enough to cause a roll over. A wave of twice the beam of a boat needs to be at or near breaking for a wave to capsize or roll over a boat.

This is because a wave near breaking is as steep as it can be before the shape of the wave fails due to gravity and the top of the wave simply falls off (breaks). The steepness of the wave also affects its surface speed with a steep wave having a greater surface speed relative to the center than a flatter wave. That relative speed comes from the fact that waves get steeper when they encounter friction. When a wave train encounters friction, the spacing of the waves get closer together and the waves get steeper. Friction comes in the form of a current running in opposition to the wind direction or the bottom of the wave dragging on the ocean bottom in shallow water. It can also occur when a strong wind builds suddenly. To understand this it should be understood that normally when there is a strong wind blowing for a period of time, the wind creates a surface current of water that is moved along with the wind. When a strong wind comes up suddenly there is no surface current so the waves that form experience friction between the wind at the very surface and the still water below making a very steep chop. As the water below begins to move with the wave trains the friction decreases and the wave steepness will flatten.

I mention the frictional aspects of steep waves to explain why there steep waves have a greater difference in speed between the surface and the center and therefore are more dangerous.

Which brings is back to the original question at hand. In theory your question should have a simple answer. All things being equal a deeper boat, with the same VCG as a shallower boat, should be heeled more and therefore be more likely to trip. The only short coming is that boats rarely have all things equal.

For example, a deeper keeled boat is likely to have less keel length (fore and aft) and keel area than a shallower keeled boat because the deeper keel is more efficient and does not need as much area. Its shorter length means that it is more likely to stall at high incident angle and absorb less energy than the shallower longer keel which is less likely stall and therefore absorbs a lot more energy. A lighter boat is more likely to heel and slide down the wave (in effect surfing sidewards.) A heavier boat is likely to stand its ground be rolled by moment created by the difference in speeds of the surface sheer. A boat with a high roll moment of inertia, is less likely to be rolled. That said, it is far less likely to be rolled if that the high moment of inertia occurs due to weight that is below the instantaneous roll axis. A boat that has a high roll moment of inertia that includes a lot of weight aloft builds up a lot of kinetic energy that would tend to continue the roll of the boat towards a capsize even after the energy of the wave has ceased to propel the boat. In fact as the boat encounters the back flow on the other side of the wave, the inertia of weight aloft can cause the mast to dip into the face of the back of the wave further guarantying the capsize or roll over.

In any event, it is easy to argue either side of this one. Deep is good vs deep is bad, high moment of inertia is good vs high moment of inertia is bad. Fin keel is good, vs fin keel is bad and the reality seems to be that there are situations where each can be good or bad but a deeper VCG is always good.

As to this morning''s post. I wrote most of it this morning but some of it was editted from a draft of something that I was writing for another venue.

Regards
Jeff

WHOOSH 11-15-2004 04:10 AM

What can you tell from the numbers?
 
Phil, I have both an observation and suggestion I''d like to pass along.

First, the observation: As happens in many threads on boat design and boat selection on BBs like this one, I notice we have quickly moved from a general question about a few design measurements for a given boat to its suitability for sailing offshore and now to its keel depth vs. likelihood of capsize. IOW we''re now w-a-y over in one little corner of the general topic of the seakeeping qualities of a boat, which in turn is only one subset of your original question about its sailing qualities.

This is normal because I suppose we''d all feel irresponsible if we chose a boat that had inherently unsafe behavior offshore in a storm...even tho'' 99+% of boats never experience a storm, offshore. Not even once in their many years of use. And I would agree with Jeff''s conclusion: it''s a fool''s errand to attempt to correlate a specific draft with a boat''s inherent ability to avoid a capsize. In fact, I would argue a different perspective altogether: If we''re going to sit over in this one little corner of a boat''s mission - avoiding a capsize in a storm - then I''d suggest the main variable by a wide margin is how the ship is managed by the crew, which in turn should in part be a function of the crew coming to learn about the boat''s behavior and adjusting their practices and gear choices so as to look after the ship despite its vices, whatever they may be.

Which leads me to the suggestion: Given what seems to be your interest, I''d suggest you see if you can locate a copy of VanDorn''s Oceanography & Seamanship. There are two unique qualities of this book that make it a great resource: First, the book is in two separate sections, one discussing how an ocean functions on the surface and therefore how it affects a ship, while the second section then applies this theory when discussing seamanship in its various forms, including storm tactics. The second quality is that VanDorn is (or at least was) both a Professor of Oceanography at UC San Diego AND a seasoned seaman, on a wide range of vessels from sailboats to ocean research vessels...so you get a good blend of the theoretical with the real-world. You might find it very helpful not only in selecting a boat, but then in preparing her for the kind of ultimate conditions about which you are inquiring.

Good luck on the research!

Jack

garyp 11-17-2004 10:11 PM

What can you tell from the numbers?
 
Regarding the tripping issue: would a centerboard boat hove to or lying ahull in heavy weather be less likely to roll with the board raised?

Jeff_H 11-18-2004 02:44 AM

What can you tell from the numbers?
 
It would generally be thought to be better off with the board raised in terms of tripping but worse off in terms of leeway.

Jeff


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