Keel-stepped vs deck-stepped masts - pros & cons

[prv]

Generally, size also comes into it. Bigger boats, more rig tension, more beef needed in deck section if deck-stepped = more weight where it is unhelpful.

?

Only on very small boats where a central post would divide the accommodation too much do you find the mast being supported by a beefy deck. Everyone else (above mid-20-foot at the most) has a compression post directly supporting the mast step. No need for any special strengthening of the deck; perhaps a keel-stepped mast would actually need more in order for the partners to offer meaningful support.

From totally unscientific observation, looks like about 32-34 feet is the upper limit for deck-stepped, maybe unless it's not a very powerful rig.

??

I've been on lots of charter boats up to mid-40s, and none of them had keel stepped masts. It seems like quite an unusual feature on modern boats, except perhaps very racy ones.

Another advantage of keel-stepped is that all the wiring emerges below decks and you don't need possibly dodgy cable glands or connectors to get the electrickery below.

Just one damn great gland (which nobody manufactures as a single part so you have to build it yourself[1]) to get the mast below!

Pete

[1] Admittedly there are now some good products for making less-leaky mast boots.

 

[prv]

I have a 1950s reprint of a 1930s book by Uffa Fox. It's interesting to see what the state-of-the-art thinking was back then - the changeover from gaff to bermudan (bermudan still being considered less reliable) and the novel idea on some yachts of an "all-amateur crew" instead of carrying paid hands in the fo'c'sle.

At that time, all masts in seagoing yachts were keel-stepped, but based on ideas in small boats, Fox predicts that in time the radical idea of deck-stepping would become the norm, as he considered it far superior.

I'll have to dig the book out tonight and remind myself why he thought that.

Pete

 

[Tanqueray]

Most people would regard Sparkman & Stephens as being worthy of an opinion.

Here it is;

The strength of a mast relates to the strength (measured as stiffness) of the mast section and the length of unsupported mast sections. Having 2 sets of spreaders reduces these section lengths and means that for the same strength the mast does not need to be as large or heavy. This translates into less heeling, less pitching and more speed. The disadvantage is the added cost of the extra set of shrouds and spreaders. As more spreaders are added there is a diminishing return and for the S&S 34 two pairs are optimal. The strength of the twin spreader and original single spreader rig is about the same, both have ample strength. Having the mast keel stepped adds about 35% to its structural strength, and therefore reserves of safety. Although it is possible to step the mast on the deck, this is not recommended and requires an extra heavy mast section to give the same safety margins as a keel stepped mast..

I would like to humbly associate myself with the above opinion (if I am allowed to that is).

 

[Seajet]

Yes but S&S probably said that a long time ago ?

Writing off all deck stepped boats as inshore motorsailors is possibly unwise...

 

[Tanqueray]

Yes but S&S probably said that a long time ago ?

Writing off all deck stepped boats as inshore motorsailors is possibly unwise...

As always, I respect your stated opinion

 

[30boat]

I had an experience that strongly reinforced my trust in deck stepped masts.My boat was hit by a ship in 2010 and the deck stepped mast was heavily struck by the stern corner of the ship.The boat was capsized by the blow and the port spreader was dislodged.Still the mast stayed upright albeit with loose shrouds.Despite moving alarmingly from side to side it stayed put for the 20 hours that took me to motor back to harbour.It's a 3/4 backswept rig.

 

[doug748]

Most people would regard Sparkman & Stephens as being worthy of an opinion.

Here it is;

The strength of a mast relates to the strength (measured as stiffness) of the mast section and the length of unsupported mast sections. Having 2 sets of spreaders reduces these section lengths and means that for the same strength the mast does not need to be as large or heavy. This translates into less heeling, less pitching and more speed. The disadvantage is the added cost of the extra set of shrouds and spreaders. As more spreaders are added there is a diminishing return and for the S&S 34 two pairs are optimal. The strength of the twin spreader and original single spreader rig is about the same, both have ample strength. Having the mast keel stepped adds about 35% to its structural strength, and therefore reserves of safety. Although it is possible to step the mast on the deck, this is not recommended and requires an extra heavy mast section to give the same safety margins as a keel stepped mast..

Quite so.

Nice someone else is injecting some thought into the debate before it falls into another silly row about who has got - best mast.

I have a keel stepped mast and would prefer not. If I set off around the world I might be quite grateful for the extra security, but, for the sailing I do, I would prefer a nice parafin heater in the space occupied by the spar. It does look good though.

I have had problems removing the mast by crane, in smaller yards you may find that they struggle to command enough vertical lift. If you plan to transit canals, with the mast lowered on top, the length would also be an embarrassment.

I have never minded the drainpipe effect because it just runs into the bilge. This would be a problem well worth avoiding in a modern boat with minimal bilges. Apart from that a modern lightweight boat could well benefit most from lowering the CoG and windage of the rig in this manner.

 

[prv]

I would prefer a nice parafin heater in the space occupied by the spar.

I did hear of someone who blocked off the inside of the mast just above the table it passed through, and again a couple of feet further up (presumably some arrangement for drainage was made). He then fitted a tap just above the bottom partition, and a filler cap just below the top, and filled the space in between with rum

Pete

 

[Tranona]

Most people would regard Sparkman & Stephens as being worthy of an opinion.

Here it is;

The strength of a mast relates to the strength (measured as stiffness) of the mast section and the length of unsupported mast sections. Having 2 sets of spreaders reduces these section lengths and means that for the same strength the mast does not need to be as large or heavy. This translates into less heeling, less pitching and more speed. The disadvantage is the added cost of the extra set of shrouds and spreaders. As more spreaders are added there is a diminishing return and for the S&S 34 two pairs are optimal. The strength of the twin spreader and original single spreader rig is about the same, both have ample strength. Having the mast keel stepped adds about 35% to its structural strength, and therefore reserves of safety. Although it is possible to step the mast on the deck, this is not recommended and requires an extra heavy mast section to give the same safety margins as a keel stepped mast..

I would like to humbly associate myself with the above opinion (if I am allowed to that is).

However - it was 40 years ago and said in relation to a specific design of boat of a type and method of construction which is no longer used.

It is clear that many other respected designers and builders of cruising boats do not necessarily share that opinion.

The empirical evidence ie the 000's of boats with deck stepped masts that safely sail all over the world would seem to support the opinion that such an arrangement is satisfactory.

 

[Salty John]

I sail an Amel Maramu from time to time and that has deck stepped masts. At nearly 50' it does seem a big boat for such an arrangement, but Mr Amel knows what he's doing and these boats have traveled far and wide.

One issue with keel stepped masts that no-one has mentioned is the requirement for securing the mast foot at the base. Offshore racing rules require that the mast heel be bolted into something structural to avoid damage caused by the below decks portion of the mast thrashing around in the event of the rig failing. I wonder how many boats comply? My 41' ketch didn't.

 

[Tanqueray]

However - it was 40 years ago and said in relation to a specific design of boat of a type and method of construction which is no longer used.

It is clear that many other respected designers and builders of cruising boats do not necessarily share that opinion.

The empirical evidence ie the 000's of boats with deck stepped masts that safely sail all over the world would seem to support the opinion that such an arrangement is satisfactory.

The OP asked for 'pro's and con's' - I gave my input - no more.

You must go with what you feel is right, you could equally argue that it is good (better) practice to hang a rudder on a surface mount gland on the outside (bottom) of the hull with no hull penetration or upper bearing (the reverse of a mast) - You could argue that, you could do that, and you may well survive that - but I wouldn't want to.

I gave an opinion not a diktat - each to their own

 

[BobPrell]

However - it was 40 years ago and said in relation to a specific design of boat of a type and method of construction which is no longer used.

It is clear that many other respected designers and builders of cruising boats do not necessarily share that opinion.

The empirical evidence ie the 000's of boats with deck stepped masts that safely sail all over the world would seem to support the opinion that such an arrangement is satisfactory.

S&S are making a statement of a general principle, and then stating how a particular design complies with it.

I would think the other designers and builders share the opinion, but have elected to compensate for the situation in another way.

Which as you say, has been effective, thousands of examples have shown.

 

[Neil]

Thank you all for your input; I hadn't imagined that there would be so many advantages to a deck-stepped mast, and disadvantages with a keel-stepped mast (even though I had experienced leaks in a school boat).

It occurred to me that you might get most of the advantages of each (excepting the space issue) by having a two-part mast: a stub from keel to a metre or so above deck, and the rest of the mast which fits over the projecting stub. Bolt through and you're sorted? Easier to prevent leaks, the main mast section easy to lift off....or am I bonkers?

 

[Twister_Ken]

or am I bonkers?

Quite possibly.

 

[sailorman]

Thank you all for your input; I hadn't imagined that there would be so many advantages to a deck-stepped mast, and disadvantages with a keel-stepped mast (even though I had experienced leaks in a school boat).

It occurred to me that you might get most of the advantages of each (excepting the space issue) by having a two-part mast: a stub from keel to a metre or so above deck, and the rest of the mast which fits over the projecting stub. Bolt through and you're sorted? Easier to prevent leaks, the main mast section easy to lift off....or am I bonkers?

yes

 

[30boat]

Thank you all for your input; I hadn't imagined that there would be so many advantages to a deck-stepped mast, and disadvantages with a keel-stepped mast (even though I had experienced leaks in a school boat).

It occurred to me that you might get most of the advantages of each (excepting the space issue) by having a two-part mast: a stub from keel to a metre or so above deck, and the rest of the mast which fits over the projecting stub. Bolt through and you're sorted? Easier to prevent leaks, the main mast section easy to lift off....or am I bonkers?

mmmm,yes.

 

[Tanqueray]

Thank you all for your input; I hadn't imagined that there would be so many advantages to a deck-stepped mast, and disadvantages with a keel-stepped mast (even though I had experienced leaks in a school boat).

It occurred to me that you might get most of the advantages of each (excepting the space issue) by having a two-part mast: a stub from keel to a metre or so above deck, and the rest of the mast which fits over the projecting stub. Bolt through and you're sorted? Easier to prevent leaks, the main mast section easy to lift off....or am I bonkers?

Oh how I wish I had known this at 0935 today

 

[prv]

It occurred to me that you might get most of the advantages of each (excepting the space issue) by having a two-part mast: a stub from keel to a metre or so above deck, and the rest of the mast which fits over the projecting stub. Bolt through and you're sorted? Easier to prevent leaks, the main mast section easy to lift off....or am I bonkers?

Not hugely bonkers - it's exactly how TS Pelican's masts are made (except with a bolted flange rather than sliding profiles over each other) and is apparently the currently recommended approach for vessels with large steel masts.

Not sure it's directly transferable to yacht masts though.

Pete

 

[Tranona]

It occurred to me that you might get most of the advantages of each (excepting the space issue) by having a two-part mast: a stub from keel to a metre or so above deck, and the rest of the mast which fits over the projecting stub. Bolt through and you're sorted? Easier to prevent leaks, the main mast section easy to lift off....or am I bonkers?

Not entirely. That is how the unstayed masts on a junk rigged Coromandel were made.

However, what is missing from this "debate" is any recognition that a mast is only one component of a system and its safety and security is not just a function of whether it is keel stepped or deckstepped, it is how the loads from the sails are transmitted to the hull. Keel stepped masts date from the time when the keel was the major structural member of the boat, so loads were transmitted direct to the keel as the rest of the structure wa not capable of sharing any of that load. You only have to look at the elaborate mast steps of performance wooden boats to see how difficult it was to deal with those loads.

Once it became possible to build structures that could spread the loads more accurately the need for basing the mast directly on the keel became less important - helped by all sorts of other changes such as lighter dispalcement, better mast sections, more efficient rigging etc that have come from developments in designs and materials.

Like many aspects of yacht design and construction, things have moved on in the last 40 or 50 years, and many of the old "truths" are no longer relevant to today's designs, even though they were (and still are) perfectly valid for the designs of the time.

BTW this is not knocking design thinking of the past. The very people who were expressing an opinion about the merits of keel stepped masts were also challenging the orthodoxy of the day in other areas, and you can be sure that if they had the materials and technology available to them that are available now they would have been exploiting them.

 

[Marakei]

Thanks Tranona, I thought of the Coromandel when I saw the OP's two part mast idea, but couldn't remember exactly how it worked.

Talking of junk rig, junk masts were traditionally always keel stepped because they were unstayed, but there is discussion about this now, bringing in some of the points you mention.