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Discussion Starter · #1 ·
Hello. I'm looking at several boats in the 35 to 40 foot range for Caribbean cruising. I've seen boats with both deck and keel stepped masts and am curious to hear opinions on the merits/deficits of each. Vigor states in his book that one should avoid deck stepped masts and gives a number of reasons.
 

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I think you will find that there is no clear right or wrong way to do it. Keel stepped will let it more water. I think you will find that almost all keel stepped masts leak water into the bilge.
They are tricky to remove and reset with more risk to the interior during the process.
They limit cabin layout options.
They can provide a stub to attach a jury rig after a dis-masting.
It is possible that a failure can cause deck damage that can lead to sinking.

A deck stepped mast can be strong too it just has to be designed properly.

What specifically did vigor say he didn't like, which book?
 

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Bristol 45.5 - AiniA
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I agree that it is more a matter of sound engineering that anything. I prefer a keel-stepped mast, but that is likely just because I have had several boats that had them and am more comfortable with them - probably someone who had had deck-stepped masts would like them better.
 

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As mentioned by davidpm, this is an ongoing debate with both having their pros and cons, along with all the other you decisions you'll need to make when buying a new boat.

I have had both deck and keel stepped with de-masting annually. When I was looking for my current boat deck/keel step mast was lower on the priority list, below speed, comfort, sound structure, ease of sailing, and med - low maintenance.

Whatever way you go I do suggest you make sure the deck around the step is sound with absolutely no moisture or else repairs could be very costly. For the keel step, similar advise if ply it is supporting the step - but repairs may be easier and less costly replacing this with a more solid material, perhaps stainless plate.
 

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I prefer deck stepped

Hello,

I have had both. I prefer deck step. This is because:
  • Deck stepped is drier. I am constantly trying to adjust the boot on my keel stepped mast. It always leaks some water in when it rains and I hate that because I work hard to keep the bilge dry
  • Deck stepped mast is shorter (and cheaper) - my boat gets hauled each year, the rig taken down, and stored during the winter. I pay one price for the boat and another for the mast. A deck stepped mast is longer and that costs more $ (not much but you know how cheap sailors are).
  • Deck stepped is easier to step and unstep. Every spring and fall I worry abut the mast being stepped / unstepped. The mast wires need to get fished around and connected, etc. On my deck stepped boat there were simple plugs that made connecting easy. Also, there are no wedges to play around with.

Just my $02

Barry
 

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Discussion Starter · #6 ·
Thanks! In Vigor's book "The Seaworthy Offshore Sailboat", Chapter Two, point 44; he gives two points to a deck stepped mast which is less offshore worthy than keel stepped but no further explanation that I could find. I'm re-reading the book now to re-find his discussion on this. I do appreciate all the help!
 

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Deck-stepped for me.
Easier to lift the mast, methinks.
I have never had a keel-stepped mast.
I should miss that beautiful stainless sampson post dominating the cabin if i did.
As for leaks. My ship has always leaked so it doesn't make any difference, really.
 

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Farr 11.6 (Farr 38)
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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 opinion 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 and design approaches.

I would like to start this discussion with the structural 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). But because of the continuous attachment of mainsails and the point loadings of intermediate control lines like vangs, pole lifts and the like, 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.

One of the goals in designing a mast is to create a configuration that, within reason, reduces the size of the bending moments within a mast. In a general sense, the greater the number of panels (segments between shrouds and other supports) the smaller the moments within the mast would 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 (adding more panels above the deck) and to a lesser extent as moment connections at the deck are being employed on 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 the deck is not engineered for side loads it 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 superimposing 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 with 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 (they must if they are going to reduce the moments in the mast as mentioned above). This added side load when combined with the multiple panels above deck greatly 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 big ‘if’!

There are several things that I consider critical to engineering a deck stepped mast properly. Primary is having a properly engineered jack post below the mast to take the vertical loads of 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. My preference would also be to design the jack post, mast foot and mast step to create a moment connection between the base of the mast and the top of the jack post, so that the jack post could still act as an extra mast panel. Then the deck and interior structure need to be designed to distribute 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. These elements are obviously more complex to engineer and build properly than simply having a fat spot on the keel for the mast step to land on.


My biggest objections to keel stepped masts are to the purely practical. Keel stepped masts with internal halyards mean that there is always water in the bilge. This water comes in at halyard boxes and other openings in the mast and there really is nothing you can do will stop that. Second, it is way harder to step and un-step 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 for offshore use advocates point out that if you lose a keel stepped mast you are more likely to end up with a bigger stump after the mast fails. I am not sure that that is always the case. For example with a deck stepped mast there are cases where you are able to tow the rig as a drogue 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 mast that has buckled 20 feet off the deck at the spreaders. .

As mentioned above, 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. If the mast buckles it can be unbolted and jettisoned, or kept up partially by the moment connection at its base. 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 offshore with her.
 

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Thanks! In Vigor's book "The Seaworthy Offshore Sailboat", Chapter Two, point 44; he gives two points to a deck stepped mast which is less offshore worthy than keel stepped but no further explanation that I could find. I'm re-reading the book now to re-find his discussion on this. I do appreciate all the help!
As others have said, with proper design, either should be fine. There may be some benefits for each, but either, cared for properly should get you around.

As far as Vigor, this boat cirlced the earth 3 times non-stop. Holds the worlds record- and a deck stepped mast:
About Project Endeavour: Refitting the Parry Endeavour
 

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Jeff_H,

"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."

Are you saying that the jack posts has a top flange plate located (height) to the underside of the fiberglass cabin deck and then you have another flange plate with a step for the mast to seat in on the cabin deck, provide a solid spacer within the existing hole where the mast use to go through the cabin deck (not fiberglassing the opening but a solid metal spacer and sandwich the two plates via throughbolt. That's what I am planning to do within the next two years but not sure if that is what you are referring to. I am dealing with a engineer and there is some concern about lateral - horizontal load or movement at the flange and possible reinforcing the fiberglass around this area but I can't see that much movement, while not any more then what you would have with a keel step mast.

Any additional thoughts on this?
 

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Farr 11.6 (Farr 38)
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That is basically what I had in mind. My intent was to build up the strength of the deck below the mast and insert and glass in an aluminum spacer between the king post and the above deack bearing plate.
 

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Jeff.. do you think you would be as easily able to induce the required prebend with a deck stepped set up (esp on your style of boat?)

Otherwise I too prefer the deckstep primarily for the potentially dry bilge..
 

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"Do you think you would be as easily able to induce the required prebend with a deck stepped set up (esp on your style of boat?)"

Ron,

I do think so. The key is getting a moment connection at the deck between the base of the mast and the king post. That was how the Laser 28's were built which has a very similar rig to my boat.

Jeff
 

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Do you really want the fiberglass around the mast to be stronger? Not more flexible? It sounds to me like this bolted-together mast is really just a keel-stepped mast with slots cut in it that a sheet of material goes through in order to keep water out of the boat.

I'm (obviously) not a nautical engineer, but it seems to me that you want the fiberglass right around the mast to be more flexible - like the boot around the keel-stepped mast -- to prevent any horizontal movement of the mast from damaging the "real" deck.
 

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Having had both, I prefer deck stepped masts, for the reasons given. I use a heavy plate arch connected to the chines to prevent the mast support from intruding into the interior design. This arch is far stronger than any extension of the mast would be.
When I bury the side decks, the lee shrouds don't even slacken , in the least.
Those who build my boats with a keel stepped mast, eventually go for a deck stepped mast, when re-rigging.
 

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The arguments against a deck stepped mast that I have heard primarily go to a deck stepped mast with no support post, IE arch, or thickened deck to support the downforce of the mast. In these water intrusion of core material, or arch can weaken mast base to dangerous levels. Second more of a stub to rig makeshift mast, I'm not sure I follow that one, with a wooden mast maybe.

Not having tried to rig a makeshift mast on either types of boats, I'm not sure how it would work, but IF I had to I would start with using my cordless drill to drill holes in the base of whichever is longer, remains of mast, or boom, then attaching stainless screws to el brackets. With a keel stepped mast assuming you still have a cabin top, the mast will remain upright while you rig shrouds, but you will have a large hole left from the diameter change of original mast to makeshift mast.

With a deck stepped mast you would prerig shrouds first, then screw el-brackets to old plate on deck leaving your boat in original configuration with a shorter mast.

I my opinion is lashing a mast fragment to a stub of a mast would be an excercise in futility, try lashing two sticks together and then put a side load on them.

Generally speaking a keel stepped mast might be less vulnerable to dismasting, but a deck stepped mast would be easier to repair at sea, in both cases raising a mast in a rolling sea in a single masted vessel is going to be problematic.

I would say even in calm seas raising a mast of any size would be not only impossible, but extremely dangerous.

It may not be very seaman like for me, but if dismasted, and engine failed I would call for help, if dismasted and engine working, (or fixable), I would motor to nearest landmass.
 

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Not having tried to rig a makeshift mast on either types of boats, I'm not sure how it would work, but IF I had to I would start with using my cordless drill to drill holes in the base of whichever is longer, remains of mast, or boom, then attaching stainless screws to el brackets. With a keel stepped mast assuming you still have a cabin top, the mast will remain upright while you rig shrouds, but you will have a large hole left from the diameter change of original mast to makeshift mast.

With a deck stepped mast you would prerig shrouds first, then screw el-brackets to old plate on deck leaving your boat in original configuration with a shorter mast.

I my opinion is lashing a mast fragment to a stub of a mast would be an excercise in futility, try lashing two sticks together and then put a side load on them.

Generally speaking a keel stepped mast might be less vulnerable to dismasting, but a deck stepped mast would be easier to repair at sea, in both cases raising a mast in a rolling sea in a single masted vessel is going to be problematic.

I would say even in calm seas raising a mast of any size would be not only impossible, but extremely dangerous.

It may not be very seaman like for me, but if dismasted, and engine failed I would call for help, if dismasted and engine working, (or fixable), I would motor to nearest landmass.
here's how

 

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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.
I mainly quoted the above to give the link back, I deleted most of Jeff's post.

Jeff_H, I want to state that I greatly admire your posts, and make a point to read all that I see. You personify the old saying of "he's forgotten more than I'll ever know". You also write well, express yourself clearly, and don't try to talk over our heads. You are interested in imparting knowledge, not showing off. Thank you for taking the time to educate us and share some of your insights.

I'm a novice in comparison to many, but I have had both types of mast steps. I will never own another keel stepped mast. The amount of water that streams down a mast during wind and rain is incredible, lots of it goes into the bilge with a keel stepped mast no matter how you try to keep it out. I've had one dismasting with a keel step, and it tore the cabin top as it came down. I was able to limp home under sail, using the boom to "sort of" hold up the main.

Raising and lowering a deck stepped mast is so much easier and safer that there is no comparison.
 

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I have had both and like the deck stepped for being less wet as others have stated.

Some people feel the keel stepped is stronger, but I doubt it being im portant even if it is.

This is just another thing people spend too much time thinking about because they somehow think they know more than the boat builder.
 

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+ 1 that it's a matter of opinion. I certainly wouldn't shy away from another deck-stepped mast (I have had both).

I was dismasted in the deck-stepped mast, which had nothing to do with the way the mast was engineered. In that case, it probably wouldn't have mattered which method of "attachment" I had.

Having said that, though, if a rig failure is something less than catastrophic, you're probably better off with the keel-stepped mast.
 
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