Futuristic Mast Aft Design

[windward]

This is a gorgeous conception. I especially like the idea of the gimbal-mounted cabin. Very slick.

While the technology doesn't yet exist to build such a boat, I believe the mast-aft rigged boat is being built by at least one company today. Of course, the design isn't nearly as radical. The mast is canted about 10deg. forward and set at the front of the cockpit. Note that the mast can be up to 25% shorter and still carry the same sail area as a comparable sloop rig. One of its big advantages is the lower center of effort.

Years ago I saw a similar design from a boat builder in Australia. He called it a Caravel, after the renaissance-era trading vessel. All the sails were stay-mounted and roller furled so that the 18 meter boat could be single-handed from the cockpit.

I think the mast-aft design is both practical and a significant improvement over the standard Bermuda rig. I won't be surprised to see these appearing everywhere in the next few years.

Some links:
http://boatdesign.net/articles/mast-aft-sailing-rig/
http://www.runningtideyachts.com/monohull/
http://www.barefootsworld.net/windwa...ilingcalc.html

[sharpii2]

Originally Posted by windward

This is a gorgeous conception. I especially like the idea of the gimbal-mounted cabin. Very slick.


...Note that the mast can be up to 25% shorter and still carry the same sail area as a comparable sloop rig. One of its big advantages is the lower center of effort.

How can this be? The rig occurs inside a triangle. And the area inside a triangle is dtermined by the length of its base times half of its height. If you are including over laps, I think you will find that a mast head cutter can actually carry more sail. George Buehler once lamented that he could get more sail on one mast than three. Due to the lack of sail behind the mast and the need for massive trussing structure to hold it up, the base of the triangle will have to be shorter.

Years ago I saw a similar design from a boat builder in Australia. He called it a Caravel, after the renaissance-era trading vessel. All the sails were stay-mounted and roller furled so that the 18 meter boat could be single-handed from the cockpit.

I remember that boat. Were any built? And wasn't that really a staysail schooner without a sail aft the main mast? It seemed that it was designed to imitate a lateen rig, hence its name.

I think the mast-aft design is both practical and a significant improvement over the standard Bermuda rig. I won't be surprised to see these appearing everywhere in the next few years.

I doubt it.

The rig has too many inherent short commings. The biggest of which is inordinately high backstay tensions. After that, there is the problem of the Center of Area (CA) moving forward as the jib(s) are reefed. Having two or more jibs helps this out measurably because the forward jib can be reefed more than the aft one and therefore maintain the same Horrizontal CA. loose footed jibs are also harder to sheet correctly for optimum efficiency. The sheet lead as well as the sheet length must be changed with any change of course or wind direction.

A useful variant of this idea would be to set up a mast head cutter with the mast about one length station further back than it usually goes. That way there is plenty of room for decent backstay geometry and the stresses should be much less. The sail aft the mast could easily ballance the shortened down jibs in a blow.

This rig was infrequently seen on some scows, IOR boats, and some '60's catamaran designs. The intent was probably to get a virtical lift component, due to the more pronounced slope of the jib's luff, out of the drive of the rig in high winds. This was to help keep the bow from burrying.

There may be some extremely practical uses for the mast aft rig. Fishing over the transome is the one that has already been succesfully tried. So I would expect at least some will be built. I just wouldn't expect all, most, or even many future sailboats to look like this.

Some links:
http://boatdesign.net/articles/mast-aft-sailing-rig/
http://www.runningtideyachts.com/monohull/
http://www.barefootsworld.net/windwa...ilingcalc.html

do da ding

[windward]

There is a related discussion going on in another thread -
Mast aft rig - discussing the practical applications of the mast-aft rig. I have posted my reply to some of the excellent points you raise there, as it wasn't my intention to defend the rather fanciful Gaudier design, but rather to comment on the possible advantages and practical applications of the concept to today's boat builders.

[J.D.Hogg]

Replaceable bow cap?

[sharpii2]

Here is a possible example of a 'mast aft' design that is a little less extreme and deals with most of my objections with the design concept which I stated in earlier posts.

This boat is designed for a class I invented where the sail area, Length, and draft are limited. The class is also supposed to be able to carry a 1,000 lb payload.

Here the jib does not hank onto the forestay, but rides on a pivoting boom that is attached to the deck by a stay and a swivel. This jib will sheet just like a mainsail will. Only the sheetline length will need to be changed to trim this sail.

The main acts mostly as a 'spanker' to ballance off the big jib. It will be last to be reefed. Because it has no spar in front of it, It should even provide some drive of its own.

The ladder like bipod mast eliminates shrouds and just steps on the deck, but is attached to the deck solidly. With clever enough design, the mast will be relatively easy to raise and lower. Only its extra weight might hamper that goal.

Bob

[kach22i]

Originally Posted by brian eiland

http://danielsimon.net/community/arno/arno_gaudier.html
[/b]

Now that is sexy.

[brian eiland]

Originally Posted by sharpii2

...Here the jib does not hank onto the forestay, but rides on a pivoting boom that is attached to the deck by a stay and a swivel.

I don't understand this explaination. Your 'boom' I assume is along the foot of the sail, not the luff.....what used to be called a 'club footed' jib. So how is the luff of the sail supported ("does not hank onto the forestay")??

The ladder like bipod mast eliminates shrouds and just steps on the deck, but is attached to the deck solidly. With clever enough design, the mast will be relatively easy to raise and lower. Only its extra weight might hamper that goal.

Are you basically talking about this configuration with the bipod mast stepped a little more aft, and the self-tailing jib attached to a club-footed boom??
http://www.boatdesign.net/gallery/showphoto.php/photo/2094/cat/500/ppuser/399

Or maybe a wishbone mast like these two variations with the mast located a little further forward and a main rigged behind it:
http://www.boatdesign.net/gallery/showphoto.php/photo/5630/cat/500/ppuser/399
http://www.boatdesign.net/gallery/showphoto.php/photo/1075/cat/500/ppuser/399

Here both sails are club-footed and self-tacking (and the mast is leaning forward by the way):
http://www.runningtideyachts.com/articles/othermansboat1.html

[sharpii2]

Originally Posted by brian eiland

I don't understand this explaination. Your 'boom' I assume is along the foot of the sail, not the luff.....what used to be called a 'club footed' jib. So how is the luff of the sail supported ("does not hank onto the forestay")??



Are you basically talking about this configuration with the bipod mast stepped a little more aft, and the self-tailing jib attached to a club-footed boom??
http://www.boatdesign.net/gallery/showphoto.php/photo/2094/cat/500/ppuser/399

Or maybe a wishbone mast like these two variations with the mast located a little further forward and a main rigged behind it:
http://www.boatdesign.net/gallery/showphoto.php/photo/5630/cat/500/ppuser/399
http://www.boatdesign.net/gallery/showphoto.php/photo/1075/cat/500/ppuser/399

Here both sails are club-footed and self-tacking (and the mast is leaning forward by the way):
http://www.runningtideyachts.com/articles/othermansboat1.html

Brian:

The luff is unsupported. It might have an internal wire or extra thick luff 'taping'. The boom attaches to the foot of the jib. It is different from most 'club footed' arrangements because the pivot point is aft the luff by a considerable margin. this is to keep the aft end of the boom from cocking up. Most 'club foot' arrangements I have seen have travelers or horses for that purpose.

this is not an original idea. I once had a scow designed by someone else with this rig (except without the bipod mast). I can attest to its effectiveness. Even with crude matterials and (must I admit) crude craftsmanship on my part.

I like the pictures you have shown me. I just don't like the complex staying on some of them.
The bipod sloop is nice and is very close to my concept. But one of the goals of my concept was to have the biggest, most user friendly jib possible while keeping things reasonably simple at the same time.

Maybe bipod sloops should be tried for trailerable boats. If the bipod hinges on the deck, cross winds during mast raising time might lose much of their terror. Going with a straight mast head arrangement and putting up with jib over laps may keep the heavier mast sufficiently short.

Then the only standing rigging that will have to be dealt with would be a fore stay and a back stay. Just two wires. And only one will have to be detached to lower the rig.

Bob

[Redsky]

that thing shure looks pretty, but it dosent have any apparent purpose other than that and it requires a material which is in demand driven short supply world wide and requires a computer to sail, ERRRRRRT! wrong answer! in my book, seawater/eletricial field disturbance + required computer for boat handeling..........nooo thanks...pretty though unless u can find a giant spider to run the rigging for u while u sail then u still need cargo space for carrying the the spider and food for it lest u become a snack yerself...

[FAST FRED]

I have come across an aft mast design that seems to "solve" the structural hassles.

There is a "boom' mounted about half way up the mast that extends beyond the stern by a good bit.

The back stay runs from masthead , to the outer boom end and then to the deck.

A loose footed mainsail of small size was hoisted , and sheeted to the deck.

FAST FRED

[globaldude]

Hi Fast Fred, do you have any links / photo's of said rig / yacht ??, sounds interesting !
Pete.

[MikeJohns]

Here's an aft mast design for sale


http://www.yachtworld.com/core/listi...oat_id=1699447

[brian eiland]

Thanks for that reference Mike. I thought this subject was more in line with this other discussion I had started on 'wishbone shaped mast' configurations, so I did a cross reference between the two discussions:
http://www.boatdesign.net/forums/sho...8&postcount=51