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  #21  
Old 09-11-2007
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Dont count out the Allied Seawind II. A great sea boat with better stats than the SC31!
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  #22  
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That does sound a bit optimistic doesn't it Sorry...my kids are shouting at me in the background. It opens up to about 50-60 ft to turn around. But the docks are perpendicular to the current and there is only about 20-30 ft to back out. I've been hanging out with the yard guys all year and at the end of the day they sit and drink beer for an hour and watch everone's mistakes....laugh about people finding new rocks to hit at low tide. I was so paranoid because i had heard such bad things about how the prop/rudder/keel setup of the SC would be horrible. It is actually very easy to manuver. I have a new F-16 anchor on the bowsprit and all i could imagine was twisting up someones rigging etc... After my last sail though, i set the boat right on the dock in a 1.5knt current and stepped down casually with both lines in my hand, tied her up and killed the motor. They were all sitting there drinking, watching but in usual new england demeanor they said not a word....they only comment on the mistakes
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  #23  
Old 09-11-2007
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LOL... a little optimistic, and a bit unrealistic... 50–60' makes more sense.
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You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.

—Cpt. Mal Reynolds, Serenity (edited)

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  #24  
Old 09-11-2007
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southerncross - thanks for the post - maybe you (or anyone else) can answer my question #254: after length & draft, I had on my list: a keel stepped mast as a requirement for blue water capability.. then i stumbled over the SC31! What gives? Why wouldnt a CE Ryder build without? Seems like a no brainer

btw, I just rec'd in the mail John Vigors "Twenty Small Sailboats to Take You Anywhere" and it has a chapter on the SC31.. he comments about the cored hull (he summizes its not his 1st choice) and gives the boat the following ratings:
Seaworthyness: 7 (out of 10) - surprising for a boat that gets a 1.55 capsize ratio!
Speed rating: "No sluggard"
Ocean Comfort level: 2 persons, maybe 3 max

Overall, I think he likes the boat, but questions the lack of a keel stepped mast as well..

Dave in NC
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DB-

There are many bluewater capable boats that have deck-stepped masts. The preference of a deck-stepped or keel-stepped mast is mostly personal at this point. What makes you think a deck-stepped mast is less seaworthy than a keel-stepped mast??
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You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.

—Cpt. Mal Reynolds, Serenity (edited)

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  #26  
Old 09-11-2007
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Dave,

One thing you need to realize is that the capsize screen ratio (or the motion comfort index) tells you absolutely nothing about how likely a boat is to capsize or how comfortable its motion is likely to be. I know that I have explained this on this forum before but here it is again, both of the capsize screen formula and motion comfort index 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 are very similar but are totally useless and misleading in most cases.

Neither formula contains almost any of the real factors that control motion comfort or stability. 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. In other words these formulas lack all of the major factors that actually control motion comfort or likelihood of capsize. Weight in and of itself has next to no bearing on motion comfort or stability; nor does max beam, which in this formula is measured at a single point on the deck.

An example that illustrates this might be two boats of equal length, equal max beam, and displacement, but one had a longer waterline and a 1000 lbs of lead in a deep draft keel, while the other had a shallow draft keel with a 1000 lbs less ballast, a hard turn of the bilge, and a 1000 lb heavier interior and deck.

Obviously the boat with the deeper draft, lower ballast and longer waterline would be the less likely to capsize and offer a slower motion through a smaller roll angle, yet their capsize ratio and motion comfort index would be identical.

That is why I see these formulas as being worse than useless.


Jeff
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  #27  
Old 09-12-2007
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DB27513 asked: <>

There are many, many, solid blue-water boats in this size range that have deck-stepped masts. There will always be debate about what is the better approach, but properly executed there is nothing inherantly wrong with a deck-stepped mast on a boat of this size. There are eve some advantages to deck-stepped, and it is a fairly straightforward process to design sufficient support via a compression post that transfers the loads to the keel.

As boats get larger, it eventually becomes easier to just step the mast on the keel. So speaking very generally you will often see boats in the sub-35 foot range with deck-stepped masts, in the mid-upper 30's it can go either way, and above 40 usually it's keel-stepped (again - generally speaking). In the realm of "blue-water" boats, a good example that I'm familiar with is the Pacific Seacraft line, where all their models under 40 feet (Flicka 20, PSC 25, Dana 24, Orion 27, Mariah 31, Crealock 31 & PH32, Crealock 34, Crealock 37) all have deck-stepped masts. The Crealock 40 & PH40, as well as the Crealock 44, have keel-stepped masts. All were built to be blue-water boats (even if many are considered small for that purpose by today's standards).

I wouldn't lose sleep over the deck-stepped mast. But, someone pointed out that some of these boats were kit or home-built, so be sure that the compression post arrangement was properly designed and executed.
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  #28  
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JeffH - thanks for the detail on the capsize figures.. am aware that it doesnt deal with weight placement, or depth of ballast.. but what else is there?? Im an engineer and want just the facts .. not anecdotal data! sigh

JohnR - with respect to KS masts, I think its my conservative sailing nature that likes that one more level of safety. A KSM provides that. Sure a deck stepped can be strung up tight and strong, but a failure of any one of those shrouds or stays and your in deep doo doo.. the same failure with a KSM, presents a problem, but having that solid member bolted to the keel is at least reassuring, if not more..

and there are some smaller bluewaterish boats that go with them.. Bayfield 29, Tarton 30, Bristol 29.9, so there must be some design factors that play into it.. but your right - been chatting with an SC31 owner and he said for sure to look hard at the stepping plate area and the base of the compression post for deterioration..

Thanks for all the insight..
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<>

Like I said, the pros and cons are open to debate, and I am not claiming that one approach is markedly superior to the other. But the corollary to your argument above is that there have been instances where keel stepped masts have torn massive, gaping holes in the coachroof during a rollover. And the smaller the boat, the more susceptible to rollovers in extreme conditions. All things considered, I'd rather have a well-designed deck-stepped mast in this size range. I think the primary reason you see some keel stepped masts in this size range is that it is simply cheaper to build them that way.
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This is from another venue but it reflects some of the thinking on keel vs deck stepped masts:

I personally strongly prefer a deck-stepped mast over a keel stepped mast but once again this is an area where opinions can differ widely. There is no right answer here. There is a contingent that thinks that the only proper way to step a mast is on the keel. There is a logic to that but it is a logic that can be engineered around and which comes out of a historical context that is less relevant with modern materials.

To start with the basics, the base of a mast has a vertical and horizontal thrust to it that tries to push it down through the bottom of the boat and also sideward off of the mast step. In normal conditions the down load is several times greater than the side load. Beyond the loads imparted to the boat, there is also the issue of the loads that happen internally in a mast. When you look at the structure of a mast it is really a truss standing on end but it does not completely act as truss because the components of a truss are not supposed to have bending loads on them. Ideally the loads in the mast are primarily axial (acting along the length of the mast) rather than in bending (acting perpendicular to the long axis of the mast). Of course masts do have fairly large bending loads imparted into them. The two most often cited reasons for keel stepped masts being considered stronger is the way that the bending loads (moments) are distributed within the mast itself and the way that the mast imparts its loads into the boat.

If the goal of designing a mast is to reduce bending moments within a mast, the greater the number of panels (segments between shrouds and other supports) the smaller the moments tend to be. In the days when single spreader rigs were most common a keel-stepped mast added one extra panel, the segment between the mast partners at the deck and the keel. This has become less significant as bigger boats have routinely gone to multiple spreader rigs and moment connections at the deck mounted mast steps.


In terms of the way that the mast imparts its loads into the boat, masts are generally located in the area of the cabin trunk and because of the shape of the cabin (i.e. the deck folds up at the cabin side and horizontal again at the coach roof) this area, if not engineered for side loads is more prone to lateral flexing than would be the keel. One idea behind a keel-stepped mast being stronger is that with a keel stepped the mast is not supposed loads are put loads into the deck.

In reality, this ideal is rarely accomplished for a number of reasons. First of all, if the mast is not tied to the deck or the deck tied to the keel near the mast, either with a tie rod or a tie from the mast to the deck and a connection from the mast to the keel, the downward force of the mast working in opposition to the upward loads of the shrouds can pull the hull together like a bow and arrow lifting the deck and separating the joint between bulkheads and the deck. You sometimes see this type of separated bulkheads on inexpensive or early fiberglass boats with keel stepped masts.

Not only do keel stepped masts impart vertical loads into the deck (through the ties mentioned above) but they also typically end up imparting side loads as well (if they must if they are going to reduce the moments in the mast as mentioned above). This somewhat reduces the structural advantages of a keel-stepped mast to next to zero assuming that a deck-stepped mast is properly engineered, and of course that is a moderately big if!

There are several things that I consider critical to engineering a deck stepped mast properly. Primary is having a jack post below the mast. A jack post is a vertical member that carries the vertical loads of the mast to the keel. My preference is to have an aluminum jack post rather than a wooden one but a wooden post can work as well. The other issue is the distribution of the side loads. Ideally there should be a bulkhead or ring frame adjacent to the mast that can take the side loads and distribute them into the hull. Done right these are obviously more complex to do than simply having a fat spot on the keel for the mast step to land on.


My objections to keel stepped masts are to the mostly practical. Keel stepped masts mean that there is always water in the bilge. This water comes in at halyard boxes and other openings in the mast and there is nothing that you can do will stop that. Second, it is way harder to step and unstep a keel-stepped mast making the boat more subject to damage in the process.

Beyond that if you loose a mast (I have lost two in my life) it is better in my opinion to loose a deck stepped mast because a keel-stepped mast is more likely to damage the deck when it fails and a deck-stepped mast is easier to clear away. The keel stepped mast advocates point out that you are more likely to end up with a bigger stump after the mast fails. I am not sure that that is the case if you are able to tow the rig as a drougue until things quiet down enough to rig a jury rig. I am not sure what you do when the boat is being beaten to death by the upper portion of a keel stepped mast that has buckled 20 feet off the deck at the spreaders. .

My preferred set up is a deck stepped mast that has a welded flange on its bottom that is through bolted through the deck into the top flange of a structural aluminum jack post in such a way that there is a moment connection and yet the mast stub can be unbolted and jetisonned if it risked sinking the boat. My current boat has a keel stepped mast. It is my intent to pull this mast and have it modified to that arrangement if I ever go intend offshore with her.
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