Aftmast rigs???

Brian,

Does this mean that I could go faster in my old Tornado catamaran with a raked mast?

Marc

 

NO, I would not recommend this rig for a vessel like that....not in style, nor size vessel. Besides what I am speaking to is a 'cruising rig' for easy handling....it's a single masted ketch...not a hi-aspect performace sloop...

 

Brian There is an aft mast cat about 40' long that has been anchored of the beech near my windsurfing club in Na Jontiem Thailand for the last six months or so. Is it one of your designs?

 

Hi Timothy,... none of my specific designs have been built. However I'm guessing it might be one of these from a Thai builder??

http://tinyurl.com/catamaran-power-sailing-HK40

...or posting #425
http://www.boatdesign.net/forums/sailboats/aftmast-rigs-623-29.html#post426517

 

Thats the one

 

Brian: I'm not new to this thread but I have not posted before.

There is an interesting sailboat concept called the Universal Hull that uses an aft-mast rig and a single staysail. I wonder if you have seen it. This site has a reprint of an article the July issue of the British magazine, "Seahorse" (alas, without the referenced diagrams), but the YouTube video shows good performance from a small rig.

<http://woodenboat.com/boat/?paged=2>

 

Thought Provoking Discussions (& some videos)

That was an interesting posting. I had not seen it. I've made a copy and reread it several times. It has more to do with hull design, but it was interesting that he used that mast-aft rig with the single foresail as a beginning,....and maybe more interesting once he experiments with a more std rig, as he mentions doing.

Fanie should find that quite interesting.

By the way, if you wish to include a web link in your posting there is a little icon at the top that looks like a 'globe' with a link symbol.

Your link:
http://woodenboat.com/boat/?paged=2

I also enjoyed this little quote from the article,
"For the purposes of the article, I submit that the best type of research science has no fear of being wrong, because we often learn as much from a theory which is proved wrong as from one which is proved to be right. Instead, we make progress when we make bold and clear predictions which are sufficiently explicit to be tested to destruction."

Youtube videos of aft mast sailing
http://www.youtube.com/watch?v=OUQHQmmdSZc

http://www.youtube.com/watch?v=R_TEDjFCKJM
Even though the breeze was light, you can also see a little of the explosive acceleration when the boat heels and the chine touches the water....towards end of video

 

Lyra's Rig

I was just recently sent a link to this aft-mast article that appeared in an Australian publication called “The Coastal Passage”. Here is the PDF article (see pages 36,37) they made available on-line, but seeing as how the print size is very small (for us older guys), I've reproduced some of the 'rig related' portion of the article in a larger print style for this forum discussion.

I've included this material here as it is another aft-mast vessel that exist in real life, and that is the subject matter of this forum thread. The gentleman has some interesting observations about the sailing capabilities, particularly with reference to its basic single-sail configuration. I can't help but think that even his rig's capabilities could be improved with just a few modifications I'll outline in this posting. Meantime here is his observations:

By Ian Campbell, SC Lyra
I see quite a few cats using the “staysail sloop” rig now, and in a recent Multihull Magazine there were two new designs using a mainsail-less rig. Lyra has been in the water for a year and a half now and has 7000 miles under her keel including a Coral Sea crossing so we have had quite a lot of experience travelling without a mainsail and I think it may be time to give an honest evaluation of it.

The rig is not perfect; if it was every boat would have one. It does have a flaw that is inherent in the concept and it comes about this way. In order to get good balance the mast has to be stepped right aft and to have a rake aft. In order to get a similar sail area as a conventional rig the mast has to be higher. And the big staysails have to be made from heavier cloth. We wind up with a tall mast stepped far aft with two long foresails and with a short rigging base aft it is the very devil to get enough tension into the cap shrouds to stop luff sag. You wind on shroud tension until the hull starts to flex and still there is more sag than you would like.

Those two heavy sails on the sagging foresails flog from side to side in a big seaway so much that the masthead can sometimes flex forward as much as 5 inches. One reason for doing away with the mainsail was to get away from the annoying boom slatting to and fro – that drives me mad in a seaway, and here we have our own boomless equivalent. It's not dangerous or noisy, just annoying.

The cure is to rake the mast much further aft to open up the rigging angles at the masthead, and to build a stiffer glass beam athwartships under the mast compression post. From the point of view of performance I don't think this rig can be beaten for a cruising cat. The contention that the rig won't go to windward is codswallop. We travel at a hull speed equal to the true wind speed at 30 degrees apparent under auto pilot and down to 28 degrees hand steering, and the rig still pulls well down to 23 degrees when motor sailing.

Sailing against a Seawind in the Brisbane to Gladstone race we were pretty much neck and neck he was faster in light wind; we went better when the wind got up. We saw 18 knots a time or two, 12 a lot of the time though I must say we do a lot of traveling stooging along at 7 knots. We have done quite a lot of sailing in winds of 35 knots, gusting to 40 knots with seas to 4 meters and found the boat as rigged handles well with a few turns in the furler and no tendency to slide off a wave. No panic, no heart stopping moments. We only had a bit of water in the back of the cockpit twice from big breaking waves. In light winds the big outer staysail sits well and is always well balanced.

The true benefits are ease of sailing. Up wind in a narrow channel you just steer from side to side and
let the self tacker do its thing while the other boats go by under motor, and downwind with the wind dead aft accidental jibes are a ho-hum event, the sail just goes to the other side. Whatever the angle of sailing If the wind gets too hard you just pull the furling line in on the electric winch and if the wind is light and variable it is no big deal to pull the other string and get a furled sail out. The result of all this is we sail a lot more than we did on any other boat I have owned.

The effect on the fuel bill is lovely. We spent a month traveling from Gladstone to Cairns and used 160 litres of diesel. We motored through the narrows and around the Hinchinbrook creeks to Ramsey Beach landing and through the channel in a dead calm. We used the engines to anchor and to maneuver into the marinas in Townsville and Cairns and we charged the batteries every two or three days. I don't think we could have done that journey over that length of time with a conventional rig and used so little fuel. We just would not have sailed that much.

So for the next boat definitely use the same rig, no contest. Rake the mast further aft and plan to move the shroud chain plates further aft. Spend some of the money saved in not having batten cars, boom, lazy jacks, sail covers, vangs, topping lifts, main halliards, main sheets, battens, reefing winches etc, etc, etc, on light weight headsails. Fatten the hull sections forward. Rake the bow a lot. Lift the run aft a couple of inches at station number 9. Design for a little more displacement...stiffen the main beam......build the bottom step at the transom higher............


Modifications (I would suggest)
I've hi-lighted those portions of his article that caught my attention, both positive and negative.

In general I have to believe that some improvements to his sail shapes would have to improve the wind propulsive efforts. After all the sail is acting like airfoil, and we all know the shape of an airfoils very important for its efficiency. Furling headsails, particularly “sagging” ones can produce awful sail shapes.

1) Modifying the leading edge of these foresails should be a high priority. Something as simple as providing a foam pad insert of varying dimension sewn into the luff of the headsail can flatten that partially furled sail needed for increased wind strengths. Here are relatively simply modifications to the leading edge of these roller furling/reefing headsails presented by noted designer Dick Newick back in 1980 (attached PDF patent).

2) Provide for a better backstaying arrangement. His angled backstays (the cap shrouds) is just not a very good means to provide for good forestay tensioning. He is placing all of the loads onto the windward side of the vessel, and asking this shroud to act as both a shroud and a backstay! Traditional shrouds on 3-point multihull rigs are already coping with big loads from the increased stability of the multihull form....now you want to add backstaying loads to that shroud....and ask it to operate at a much slimmer angle with masthead!!

I believe you have to get a little more creative about providing decent backstaying, that will in turn provide more acceptable forestay sagging, thus better sail shape.

One key to this better aft staying has to be looking at the situation somewhat analogous to what we already do with athwartships staying....the use of some spreader(s) arrangement. I call one of my 'aft spreaders' an 'aft jumper strut' . The arrangement I use on my forward leaning aftmast rig could also be adapted to a straight standing aftmast.

3) Another fault I find with the 'Lyra's Rig' is there appears to be a lack of a proper 'staying base structure' for the rig to attach to. Nothing is stayed back to the primary bulkhead that the mast sets on? There is no athwartships, nor longitudinal rigid frame structures to the vessel. It's an 'open cavern' vessel that depends upon its skins to support its rig....as such there must be a lot of sagging in the rigging as “the hull starts to flex” as he says. A little more attention needs to be paid to the 'hull structure' to properly engineer a boat for an aftmast arrangement.....in fact this could be said for a conventional rig on most multihulls as well.

On a positive note I did find these comments by the owner interesting....quote:
1) the contention that the rig won't go to weather is codswallop.
2) accidental jibes are a ho hum event.
3) the result of all of this is we sail a lot more than we did on any other boat I have owned.
4) I don't think we could have done that journey over that length of time with a conventional rig and used so little fuel. We just would not have sailed that much.

 

How very interesting. The design I am working on is a polycore aft mast design. I believe Lyra is polycore too. I need to share a cup of coffee with Ian!

The more I look at the aft mast set-up the more sense it makes for a cruiser.

Mick

 

Solaris Sunstream 'Prout type rig'

...just happened across a few comments by this gentleman 'Southern Star' over on another forum.
Brian


Sandy, I agree with your assessment of the earlier Prout 34's. As to what is commonly called the 'Prout' rig (cutter rig with mast stepped well aft by the companionway bulkhead), there have already been discussions of the relative merits of the rig in another thread on this site - I suspect it was in relation to some of the new Broadblue cats where there was a choice of rigs.

My Solaris Sunstream has an identical rig and I firmly believe that, for the following reasons, it has serious merit in an offshore cat:

1. It steps the mast at the strongest point of the bridgedeck - over the companionway bulkhead.

2. All lines are automatically led to the cockpit without various turning blocks for the halyards, reefing lines etc.

3. It allows sail area to be maintained, but breaks it up into smaller, and hence easier to handle sails. This is particularly important with respect to the mainsail, which will not require electric winches etc. to facilitate hoisting.

4. It has a dedicated stay for a staysail/storm jib, which brings the center of effort both down and back in precisely the wind conditions which favour the same (witness the number of offshore monohulls that now have 'solent rigs', with a detachable inner forestay for the staysail/storm jib).

5. The additional stays provide additional strength to the rig.

6. A furling staysail/storm jib permits the use of much heavier weight dacron than would be appropriate for a genoa, and therefore ensures that the lighter genoa is not used (abused) in excessive wind conditions. Furthermore, sail shape is easier to maintain if one is only reefing a furling sail to about 30 percent of its overall size. Finally, it is easier and safer to unfurl/reef a dedicated staysail/stormsail from the comfort of the cockpit than having to go forward to raise a sleeved storm jib ( eg. galerider) over the furled genoa, or to remove the genoa from the slot in the extrusion and raise a dedicated storm sail in its place. (On the negative side, I will agree that higher aspect-ratio sails tend to peform better and, in particular, the new huge mainsails with significant roach and flat-tops provide much more sail area up higher, where the winds tend to be stronger).

7. Since the Prout rig spreads the sail area more fore and aft than the typical fractional sloop rig, it will tend to have a lower mast. This in turn lowers both the center of effort and center of gravity, important in a catamaran in terms of reducing the risk of capsize. Furthermore, the lack of a mainsail with significant roach allows much better sail shape when reefed, and permits the use of backstays - further strengthening the rig.

Although direct comparisons are impossible without sailing the same hull with each type of rig, I have found that the larger foretriangle aids in tacking; I do not, for example, need to depower the main, as is sometimes necessary with huge flat - top mains in order to come about cleanly.

Once again, different horses for different courses - but for offshore sailing with its greater potential of being caught out in heavy conditions, the 'Prout rig' made and continues to make a good deal of sense.

Brad
http://www.cruisersforum.com/forums/f48/affect-of-mast-location-on-a-catamaran-21229.html

*************************************************



Clawing off a lee shore? If what you say is true, one would have expected the seas to be littered with the wreckage of Prouts that were forced onto a lee shore. While they are not demons to windward, the ability to fly a dedicated staysail/storm jib from a proper location (further inboard) and with proper sheeting angles; and, the very low freeboard/windage make them quite capable of sailing off a lee shore.
http://www.cruisersforum.com/forums/f48/opinions-on-a-1983-prout-37-a-61437.html#post697983

 

Scrumble Project

Hi
The Scrumble project is going with a mast further aft than "normal". Have a look on their blog.

Mick

 

Would you happen to have an address for the blog? Somehow I can rarely find things that are jus "on the Internet". This shouldn't take but a minute if you really think people should look at the blog.

 

Here you go... http://scrumbleproject.wordpress.com/

 

another Twin Genoas on Bows Arrangement

Originally Posted by brian eiland
http://www.boatdesign.net/forums/boat-design/wishbone-sailing-rig-1999-12.html#post485560

Somehow I missed ever seeing or knowing of this vessel, but here is a gentleman who is not affraid to experiement:

63' Catbird Suite .... http://www.damsl.com/
"The rig was completed in December, 2006. It works very well, is quite efficient upwind, is especially good reaching and running, and is easy to handle because all sails furl and there are other advantages as well........."

Interesting detail...he can vary the sail's tack (down) positions across the beam of the vessel, and in some instances get a 'heeling effect' on a non-heeling multihull.

 

Solitary Island Catamaran Kit, with Aft-Mast Rig

Hey Mick, would a nice Polycore 40 footer in kit form do you?

I'm working on a modification of the Solitary Island 12m design for an aft-mast rig. I think its going to work out real nice. I think this vessel design has lots of potential. I'll post some sketches soon.

Solitary Island 12m