Can somebody pro/con a full vs. fin keel for a newbie (will learn to sail on said boat) and taking it thru the Caribbean? All I can seem to come up with so far is fin keel is better to the wind, and a full keel will protect your rudder.
There are two reasons to be fat. First is to get more interior room. Second is to create more righting moment. It is the easiest way to get righting moment. And of course more stiffness.Fin keel or full keel, a boat doesn't have to be fat
True enough, but I'd think the premise would be to avoid such encounters.. I know accidents happen but I'd hate to think that ramming a rock would be a frequent enough occurrence to dissuade me from a particular boat type......... If you haven't seen what happens when a fin keel hits a reef at 6 knots you should come to the Pacific North West and visit any boatyard, its pretty scary. Just a few thoughts
What do you mean by that "kill" thing? You mean if you manage to ram the light boat you can sink it?.. I sail a very small, heavy 22' full keeler that can kill a standard 30' fin on any point of sail in light winds. ...
Jeff, don't misunderstand me, I'd love to be mistaken on this. I have a fin keel boat which is perfectly safe I guess for where I sail it.I would suggest that, in the first quote, Pvajko is in part misinterpreting what was being said, but in both cases, these conclusions were based on the type-forms and limited testing available at the time that the book was written.
I'd really be interested to learn what these tools are. Could you give more information on that, or at least point out where to look?Today, seaworthiness is no longer forgotten. Designers have long since learned how to design around the concerns raised in 'Seaworthiness' and have the tools to make both of the quoted statements inaccurate.
There really is nothing wrong with what he says, but it is incomplete. It has been well documented in 100 year old yacht design books that full keels have the advantage in big water because the rotation of the water in the wave causes the full keel boat to heel toward the wave rather than heel with the wave as with other keel designs.I would respectfully suggest that that Pvajko is mistaken when he says:
"The most important reason is that a full keel with its bigger surface area damps the rolling motion better."
"While a fin keel performs much better in ideal conditions (flat water), stormy weather with big seas is a whole different story.
Strictly speaking that is not always or even usually correct as it is written. While it is easier to keep the weight lower in a longer keel of an equal draft. But modern fin keels generally are deeper and have a bulb which makes it easier for them to carry their ballast with its vertical center lower than most full keels. But also there are a lot of factors that make a boat 'forgiving'. A modern fin keel boats relatively greater stability, lighter helm loads, more forgiving rig and sail handling gear, and more easily driven hull form might work in its favor 'forgivingness' wise. The typically better directional stability and lower vertical center of effort work in the favor of a typical full keel boats 'forgivingness'.BreakAwayFL said:I was under the impression that a full keel also puts more weight lower in the water, which would make it more forgiving if you happen to have too much sail out...
BTW Jeff, doesn't this imply that Paolo's argument with full keel boats "tripping over the keel" vs. fin keels moving easily sideways is incorrect?it is easy to see that a modern fin keel boat could easily develop much higher dampening moments and so have better dampening than a full keel boat, making Pvajko statement incorrect that "The most important reason is that a full keel with its bigger surface area damps the rolling motion better."
But at the beginning of the day, I wish for more understanding, so I don't have to buy too many boats that are 'wrong' for me at the end of the day.At the end of the day, it really only matters "IF" the boat design works for the type of sailing you wish to do, where you wish to do it etc. Be it a fin, full or something in between.
marty
Hello Jeff, I pretty much stopped reading after this paragraph. Damping has nothing to do with inertia. Inertia is related to the square of the distance and the force is a function of acceleration. Damping is related to area and the moment is proportional to distance. The force is a function of velocity.Here is the problem with that statement, dampening (the ability of a boat to dynamically to resist rotational motion) is directly proportional to a moment of inertia the amount of which results from the resistive force of the rotation and the distance that resistive force is from the instanteous rotational axis. In calculating a dampening moment, the force is a linear factor, but distance from the center of that force to the instanteous rotational axis is to the third power.
Why to pay or wait for it? As I have said it is an old book and has many old books it can be downloaded for free:To use water analogies: things are "getting deep" in this discussion, and I find more and more that it's "over my head"!
My copy of the book "Seaworthiness" has been shipped, perhaps if I can digest some of that, I'll at least have a handle on the 30 yr. old side of the discussion.
I completely agree with what you are saying if we compare boats based solely on length on deck. If the comparison is two equal length boats that are equally loaded, one a traditional long waterline relative to LOA, heavy L/D boat, whether full keel or some partially cut away keel form, and the other a more modern equal length boat, the newer boat will not be able carry as much weight in gear and consumables without seriously compromising performance and seaworthiness. But also, since design loads on the hull and rig are proportionate to the displacement of the boat, when equally loading these two boats a lighter modern design will be loaded proportionately more as compared to its design displacement and so would end up being a comparatively less robust boat when loaded to the max loading of the equal length heavy d/l cruiser.I certainly understand the theoretical advantages of the modern design but I question whether those advantages apply in at least one very common scenario. If this boat is 32 feet and used for very long distance cruising, ie a dinghy or two, 3 or 4 anchors and rodes, 40 days of food for 2, etc.etc, is it still going to be just as stable and fast as when it was test sailed by the owner? Personally, in my opinion, this modern design is going to prove to be slower and MUCH less stable than had it been designed a little heavier in the first place and with a little more boat in the water.
Anecdotally I can imagine how this would be true more often than not. Similar to the discussion above, a heavier (D/L) displacement boat will typically offer a slower roll rate, which can be a very good thing in a comparative short chop or in long wave length ocean conditions.I once counted the rolls of 2 very different designs as they were sailing DW off Baja. One, a full keel 32, the other a modern 36. The full keel 32 rolled exactly 30% less than the 36. That is, the 36 rolled 100 times during the 32's 70 times. Both boats rolled at what seemed the same angle. The 32 was sailing about 1/4k faster. Are future cruisers going to have to give up comfort for the modern design or go much longer in WL to get reasonable comfort?