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-   -   Draft minus keel depth on Cape Dory 28? (http://www.sailnet.com/forums/boat-review-purchase-forum/17586-draft-minus-keel-depth-cape-dory-28-a.html)

Nonkjo 06-23-2006 01:52 PM

Draft minus keel depth on Cape Dory 28?
 
I'm interested in a Cape Dory 28. I am interested in this boat because it appears that it can do it all, even long distance cruising when I get to that point.
I was wondering if anyone out there can tell me the draft of this boat minut keel depth. I was doing some research and as I understand, a boat with an angle of vanishing stability less than 140* might not right itself if capsized. The reviews say thet the CD 28' is a rugged and seaworthy full keel boat capable of making blue water passages so I was curious as to what this number would be for it.

Thanks,
James

Jeff_H 06-23-2006 09:15 PM

The Cape Dory 28's are nice little boats. I actually like the Cape Dory 28 more than most of all of the Cape Dory line. For their day they were wholesome designs with a reasonable amount of waterline length and a nicely modeled underbody.

To me they are complex boats to classsify in a lot of ways.

I don't think of them as good daysailers or good boats to learn to sail on. I think that ideal daysailors and boats to learn to sail on are responsive so that you can feel the full richness of the sailing experience, the subtle clues to the impact of wind and water or response to small sail trim or steering changes.

I don't think of them as being very good coastal cruisers. Their excessively high weight and small sail plan do not make them very handy in the changeable conditions and lighter air typical in coastal cruising. I think that this is a personal preference thing, but I think that coastal cruisers need to accel in a wider range of conditions, and offer good enough performance to run for cover or beat off of the more frequent hazzards found inshore. In my mind, on that basis boats like the Cape Dory 28 fail my sense of a what a good coastal cruiser should be.

By the same token, my opinion of them is complex when I think about them as offshore cruisers. These are good boats in a lot of ways for offshore use. If you start out saying that you want to go offshore in a 28 footer, these boats have reasonably good tankage and a reasonably good layout for a boat that size, but small for any serious cruising. If I remember the interior correctly, it would be pretty easy to adapt the main cabin settees to good seaberth. It would take some pretty serious alterations to the interior to install more than a single burner gimballed stove or a proper navigation area. Most have an engine that is way too small for a Cape Dory that is fully loaded for cruising. But the price of the large tankage is that most of the other storage is quite high above the waterline.

While I would hate to re-ignite the discussion of the definition of a fin keel vs Full keel, which has taken place on this site many times before, I would like to touch on the comment that the Cape Dory 28 is a "full keel" boat. It is not. As I have pointed out, that the past, histroically the defintion of a fin keel was a "A keel whose length on it bottom is 50% or less of the LOA or length of sail plan which ever is longer". By that definition the Cape Dory 28 would be a fin keeled boat with an attached rudder.

As has been pointed out in prior discussions, this definition has dropped out of popular use, and to most people who have started sailing in recent decades, these boat are not fin keelers. I think that the general consensus was that boats like these were moderately long length keels. Whatever you call them, they certainly are not Full Keeled boats (I suggest that you look at the Bristol Channel Cutter or the Westsail 32 if you wish to see what a full keel actually looks like.)

In any event, whatever you call the keel on the Cape Dory 28, they have a sharply cut away forefoot, and a rudder post that is quite far forward in the boat, and an attached rudder. This results in boat that does not tarck all that well and which can develop quite a weather helm. What is nice about the Cape Dory is that you can reduce sail area and help balance the helm. But that occurs at windspeeds that would further slow the Cape Dory below newer offshore cruisers (Take a look at the Southern Cross for example) or boats with hulls and rigs that can benefit from better sail handling gear.

This brings us back to your original question. In waves large enough to roll a boat, it is generally thought that a limit of positive stability as loaded in the range of 125 degrees should be adequate. Which is not to say that there this is the only LPS that you see recommended. I have seen recommendations as high as 145 degrees, but these high limits of positive stability generally refer to LPS based on a 'dry' loading. In big boats there is comparatively little difference between an LPS based on the dry loading vs fully loaded. But in smaller boats, like most of us around here seem to sail, the vertical center of gravity rises pretty sharply when the boat is fully loaded for offshore cruising. This is especially true boats like the Cape Dory where a lot of the bulk storage is above the waterline.

If I had to guess, based on stability plots that I have seen for similar boats, I would expect the Cape Dory to have a limity of positive stability somewhere in the 120 degree range. In the CD 28's favor when it comes to LPS is a reasonablely deep draft, and high freeboard and cabin structure for a 28 footer. The ballast to weight ratio is also reasonably good for a boat of this era but would be be absolutely dismal when fully loaded for offshore use. Another negative re LPS is the Cape Dory 28's rig which is very heavy for a 28 footer and while pretty sturdy, makes a good ballast keel when inverted.

The other component of inverted stability is how stable they are inverted and the CD 28 is quite beamy and the beam is carried quite far towards the ends of the boat giving the boat a bit more inverted form stability than one might expect. This is partially offset by the large volume of the cabin structure.

Regards,
Jeff

hellosailor 06-24-2006 12:56 PM

http://www.toolworks.com/cdsoa/cdinfo.html has specs on the Cape Dory boats, and points to

http://www.image-ination.com/sailcalc.html which lists the Cape Dory 28 specs for stability, etc.

Questions of seaworthy or bluewater capable...I don't know the boat but those are areas where experience, rather than numbers, will mean more to you. Figure whatever boat you start with, you may want to change at least once before taking off around the globe. Personal decisions about sail balance, seakindly motion, proper layouts and such.

Jeff_H 06-24-2006 04:33 PM

I am afraid that there is nothing on Carl's Calculator http://www.image-ination.com/sailcalc.html that actually tells you anything meaningful about stability, or motion comfort.

Carl’s calculators provides a useful service but the Capsize Screen Formula and the Motion Comfort provide no useful information in evaluating a boat for either motion or stability. I know that I have explained this on this forum before but here it is again, both of these formulas were developed at a time when boats were a lot more similar to each other than they are today. These formulas have limited utility in comparing boats that otherwise are very similar.

Neither formula contains almost any of the real factors that control motion comfort or seaworthiness. Neither formula contains such factors as the vertical center of gravity or buoyancy, neither contains weight or buoyancy distribution, and neither contains any data on dampening all of which really are the major factors that control motion comfort or the likelihood of capsize. Weight alone has no bearing on motion comfort and stability.

I typically give this extreme example to explain just how useless and dangerously misleading these formulas can be. If we had two boats that were virtually identical except that one had a 500 pound weight at the top of the mast. (Yes, I know that no one would install a 500 lb weight at the top of the mast but if we compare a boat with teak decks, heavy decks, wooden or steel spars to the opposite extreme at the other end, a boat with a deep bulb keel those differences can easily have that kind of impact.) The boat with the weight up its mast would appear to be less prone to capsize under the capsize screen formula, and would appear to be more comfortable under the Motion Comfort ratio. Nothing would be further than the truth. That is why I see these formulas as being worse than useless.

Jeff

chknlips 03-09-2007 05:59 PM

Cape Dory 28
 
I am not sure but I may have more sea miles on a Cape Dory 28 than anyone I have ever chatted with... My wife and I cruised the Pacific from Astoria Oregon to Hawaii and then the South Pacific (Marquesas) and back on our Cape Dory 28.

I can't say enough good about the boat's sea kindliness.

If there are drawbacks, it is the interior size ( I am 6' 4" tall) and possibly my opinion that has formed over the years of sailing in the ocean that fiberglass is just not the medium I would choose unless you are staying in what is referred to as the 20-20 regions of the ocean. (20 degrees north to 20 degrees south latitude).

However, again, I have never sailed a production boat with such a combination of stability and agility than the Cape Dory 28. The only other boat in the line that retains the perspective of the 28 is the 36 and though I have not sailed one, I would expect it to be very similar if not better in the ocean due to sheer physical size.

The hull was stout and the rig was sufficient to survive some pretty severe weather.

Be sure if you get one to acquire a heavy weather 130 genoa and a healthy boom vang.

Sail safe,

BillOfCapeCod 04-08-2009 03:48 PM

Cape Dory 28
 
I have had limited experience with the Cape Dory 28, just one year ownership compare to 7 years with my previous boat, a Westsail 32. However, I am really impressed with the sea-kindliness of the Cape Dory 28, and consider her a better windward sailor than our Westsail.

Ericb 07-14-2009 07:49 PM

A little knowledge
 
Nonkjo

I think you are referring to what is called the fairbody line and it - by itself - will tell you almost nothing about a boat...

Jeff H

I have no doubt that you have the best of intentions, as well as more experience sailing than I do. I also have no doubt that you are wrong on so many points it is scary.

In my mis-spent youth I designed a couple dozen boats - power boats. The market for sailboats having bottomed out in the early 1980's. But I do know how to design a sailboat. Yacht design is a fascinating subject. A lot of things in life are a blend of different aspects of science and art, are subject to differing opinions and subject to the uninformed jumping to the wrong conclusions about what makes something tick. But none more so than boat design.

Yes, the Cape Dory 28 is a full keel. I don't know where this "A keel whose length on it bottom is 50% or less of the LOA or length of sail plan which ever is longer" came from but it is nonsense. If you want to see a real full keel ship look a couple hundred years ago - and look at the clipper ships as an intermediate stage with more lateral plane at the bow and stern than was usual for hundreds of years before. Yes the Bristol Channel Cutter and Westsail 32 are full keel boats, but they too are modified full keel boats derived from the ships/boats that preceded them. And yes the Cape Dory (and even the Southern Cross) could be said to be another modification of full keels compared to them - but full keel boats they most certainly are.

A fin keel is by definition a keel separated from the rudder. The Contessa 32 with a skeg mounted rudder is still a fin keel design. Any and all proportions of fin keel with a separate rudder is still a fin keel.

A rudder on the end of the keel - however short - is still a full keel.

As far as stability and motion comfort calculators are concerned it is widely acknowledged that they are to be taken with a grain of salt. I do not know how you calculated your example with "...a 500 pound weight at the top of the mast" but stability is a far more complex subject than a layman can understand from just being in a boat. And indeed - simplistically - raising the centre of gravity could make a problem boat more seaworthy, more comfortable - as long as it did not lose too much range of stability so as to be dangerous.

Stability has two components - initial stability and the range of stability - both are important. Both need to be 'balanced' shall we say for the type of boat and what it is going to be used for. It is generally accepted that the more the boat is 'in' the water rather than 'on' it, the more it has a little less initial stability combined with a larger range of stability the better it is - the safer it is - for an ocean going sailboat.

The Contessa 32, Alberg 30 - among others - are perfect examples of this.

Why then are so many modern sailboats like a big flat dinghy with a lot of their beam extending all the way aft and large sail plans combined with a low centre of gravity? Because they sail fast and they have room to be floating cottages. They accomplish with brute force and a hull strong enough to take the punishment what used to be accomplished by subtler and slightly slower means and ways. The higher initial stability that lets these boats carry more sail and go faster is also what makes them less safe than something like the Contessa 32, Alberg 30 or even the Cape Dory 28. Higher initial stability is pretty much always combined with a smaller range of stability. On the ocean these boats want as much as possible to be 'upright' on the water, 'upright' on the face of a wave. Even if that means that they have to turn turtle to do it. Boats with a little less initial stability/higher range of stability just keep going...

As I said - you mean well - but you are spreading what amounts to gossip as if it were fact...

Sometimes a little knowledge is a dangerous thing.

Jeff_H 07-31-2009 05:19 PM

Eric;

I am not sure why you feel the need to dig up old threads and attempt try to nitpick my postings but I will attempt to respond to a couple of the points raised in your post above and perhaps correct some of your misunderstandings.

When you say," A fin keel is by definition a keel separated from the rudder. The Contessa 32 with a skeg mounted rudder is still a fin keel design. Any and all proportions of fin keel with a separate rudder is still a fin keel." You are citing but one currently popular definition of fin keel but not a totally accurate one either in contemporary colloquial use or historically speaking as I will explain below.

You obviously came to the sport later than I did because when I began sailing in the early 1960's what distinguished a fin keel from other keel types was souly the length of the keel on its bottom relative to the length of the boat. Obviously that definition has changed in common usage.

In responce to your perhaps rhetorical quandry: "I don't know where this "A keel whose length on it bottom is 50% or less of the LOA or length of sail plan which ever is longer"" That was the oft cited popular definition when I was first exposed to sailing in the very early 1960's. It was used or included in sailing primers, yacht design books of the day, and in yacht design courses of that era. (Although earlier references usually referred to the length of the sail plan and later references to the LOA.)

In those days, the hull forms of a fin keel boat were not all that different from the hull forms of a fuller keeled boat, both had slack bilges and wineglass sections and so any other form of distinction was harder to make.

In those days, boats like Allberg 30 were described in their early literature as having 'a modern fin keel' even though we all knew that they had attached rudders, and in the early 1960's, magazines routinely described boats like Dragons and early 'meter' class boats as fin keel boats regardless of whether they had attached rudders or not. It was the definition within Westlawn courses of that era.

Obviously the definition of a fin keel being defined by the length of the bottom of its keel has fallen out of popularity, but it has not really been replaced by as clear a definition today. I respectfully suggest that your definition above "A fin keel is by definition a keel separated from the rudder." or to say, "Any and all proportions of fin keel with a separate rudder is still a fin keel." is not inherrently correct. While your personal definition of a Fin Keel is used by some people today, that definition does not necessarily totally jibe with current usage either. For example, Island Packets have post-hung, spade rudders rather than keel hung rudders and yet they are typically referred to as having a full keel. You also see some more moderate fin keel/skeg hung rudders referred to as 'full keels with a Brewer bite'.

As to the explanation and example that I wrote above regarding Capsize Screen Formula and the Motion Comfort, I have used that before and while I may infact be an amatuer, the respected designer Robert Perry responded to nearly that exact quote with;
"Jeff:
Many thanks for your common sense approach to this subject. I have been harping on the same thing for years."
The Uselessness of the Capsize Screen Formula and the Motion Comfort Index. - Anything Sailing Forums

The one thing that you and I do agree on is "Sometimes a little knowledge is a dangerous thing."

Jeff

Ericb 07-31-2009 07:24 PM

"I am not sure why you feel the need to dig up old threads ..."

Hey I am new here - they are not old to me. And your posts are hard to miss - I have to wonder when you find time to work or to sail....

As far as "Capsize Screen Formula and the Motion Comfort" is concerned we are not so far apart. I said "it is widely acknowledged that they are to be taken with a grain of salt". And a LOT of respected yacht designers feel it is a useful tool.

Yes, there will always be examples that will not fall into easy classification of full keel fin keel etc. Thats life - it is human nature to want to classify/explain everything.

And just because something is in writing/taught/on the INTERNET does not automatically make it correct.

Also as just stated in another post we are just going to have to agree to disagree.

:)

JohnRPollard 07-31-2009 10:56 PM

Quote:

Originally Posted by Ericb (Post 510162)
"I am not sure why you feel the need to dig up old threads ..."

Hey I am new here - they are not old to me. And your posts are hard to miss - I have to wonder when you find time to work or to sail....

As far as "Capsize Screen Formula and the Motion Comfort" is concerned we are not so far apart. I said "it is widely acknowledged that they are to be taken with a grain of salt". And a LOT of respected yacht designers feel it is a useful tool.

Yes, there will always be examples that will not fall into easy classification of full keel fin keel etc. Thats life - it is human nature to want to classify/explain everything.

And just because something is in writing/taught/on the INTERNET does not automatically make it correct.

Also as just stated in another post we are just going to have to agree to disagree.

:)

Eric,

If you spend more time here you'll learn that, while not everyone agrees with every position that Jeff espouses, he is widely respected for the contribution he makes to the Sailnet community. That contribution spans many years and thousands of thoughtful, respectful posts.

By comparison you are new here with a history consisting mostly of personally criticizing a well-respected member. When you come in and precede statements such as "we are just going to have to agree to disagree" with "your posts are hard to miss - I have to wonder when you find time to work or to sail....", that is textbook passive aggressive and you are not doing yourself any favors in so far as building credibility.

If you want to join the debate here and develop credibility, my best suggestion is to focus on the subject matter and avoid personalizing it.


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