Aftmast rigs???

Main Sail Less

....interesting letter I received last summer, '07


Hi Brian, my name is alan smith...I am looking at an Ian Farrier Design 39 foot trimaran....I have enough sailing experience both in chartering and racing to know that what you have postulated in your article on aftmast propulsion to be exactly what I have been looking for....I am 56 years old and with that comes loss of muscle mass and flexability.

I want to world cruise and my biggest seagoing dilema is the mainsail. As you mentioned the full batten mainsail is a beast. i had considered putting a power wench near the mainsail for aid in lifting it....but when you are at sea and singlehanding...it can be so frightening ...when in the middle of the night
some weather blows up quickly...your thoughts are muddled and you are trying to figure out your best course of survival...ha ha ...even on a rotating mast getting the slides to cooperate, the battens not to get hung up on the jiffy sail lines is no laughing matter.

Recently while on a 41 foot Lagoon cat in Greece we went from 15 knot breeze to over 40 knots in a channel between islands. Now mind you, there were 8 of us board this monster of a boat. It took one steering into the wind, one on the mainsheet traveller, one on the mainsheet rope clutch and wench, two handling the mainsail...clawing like hell to pull the slides down, and one lookout watching the battens didn't get hung up in the jiffy lines...which happened several times...up a little...no, down a little,,,,no damnit...up a little you idiots...and so it went.

With your idea we would have just furled the jenny half way and struck the mizzen and we would have been fine...It is a brilliant idea. Just fricking marvelous brilliant....

Now I have a few questions for you....Sailing downwind....dead downwind....of course a spinnaker is completely out of the question for a singlhander...too bloody much work and nervous work at that..Ian Farrier has a good set up with the screecher on a bow pole...you can wing and wing the main and screecher if you get lucky with course desired and wind direction...but I am interested in what you would recommend for a 3/4 wind or full aft wind?

Is the narrow hull of a trimaran going to present in back stay problems for the forward leaning mast? Does the mizzen need some sort of boom? What percentage decrease in mast height will effect the same capacity of sail area with the 3 sails versus two sails of a bermuda rig....

Thank you Brian....I am hoping that you will take a few minutes to answer my questions...it is so refreshing for me to have found this article....your idea hit home like the truth of god...ha ha ...well, fair winds to you...alan smith

 

Main-less Rig

I post this as a cross reference of discussions for some future time.

Here is another forum discussion initiated by a gentleman interested in a Main-Less Rig combined with a bi-pod mast for easy lowering:
http://www.boatdesign.net/forums/showthread.php?t=21274

 

Well Brian, it seems your aft mast setup is finally beginning to enjoy some more attention. And rightly so. There are numerous advantages compared to the conventional bermudan boomed sail setup.

I have a few experiments to do on the little trimaran I've built for testing and gaining a little experience using it before I am going to apply it to my boxy fisher cat currently under design.

I have a friend who also has a small trimaran but with a bermudan sail setup. I must admit that it's much easier and quicker to furl my main sail than it is for him to rotate his mast to control the sailing area.

Also the down force of the bermuda sail rig pushes his leeward hull under the water while the aft mast sail provides so much lift I hardly notice it. Maybe I've got too much boyancy but I get the feeling if the windspeed picks up enough one could well see a planing displacement hull (or three).

Currently the sails are in for modification - I'm adding another 30% sailing area combined to the leech and the foot of the sail. Could make for a slight increase in performance and better control since the centre of sail force is moved more amidship.

Anyway, so far I'm glad or rather relieved that I did came across your article on this sailing setup. Liked it right away and it makes more sense. I'm sure once the nitty gritty is sorted out it's going to be a winner.

 

Brian,

With reference to the letter you received last summer from Alan Smith, did you suggest a traction kite as part of your reply? Hope you don't mind me asking.

Regards,

Perry

 

Actually Perry, I did not. I was not so convinced of their viability at the time.

 

Tom Speer,

I admire you greatly for your "show me the numbers" approach.

But you torpedo that approach when you say, "The drag of a circular cylinder can be the same as an airfoil ten times its thickness and a hundred times longer."

Yes, there are NACA airfoil tests in a wind tunnel that numerically support that statement. But you discourage new rigging designers with it.

Do you really believe that in the sailing environment a 50-ft x 1-ft diameter mast has the same drag as a 10-ft wide x 100-ft long x 50-ft high NACA shape on the same hull? If you do, even within the "20-30 degrees either way", then "show us the numbers" or please withdral from this forum. If not, please retract the statement and never use it again to criticise another design.

Larry Modes

 

Larry
I think the message is that with the wind off the foil axis the drag can be considerable, for example consider a cylinder........... (at least that is how I read it).

Tom has been very forthcoming and helpful in this forum, occasionally all of us manage to misrepresent what we are trying to say particularly when trying to popularize a subject for a layman.

I don’t think there are any grounds for your rather brusque demand of a retraction and I very much hope that Tom does not withdraw from our forum since he is a knowledgeable, educated and willing contributor.

A more genial approach would be better in the future even if you are (?) an expert in this field.

Cheers

 

Mike,
I appologize for the brusque tone of my post. I don't want Tom Speer to withdraw. That would be a targic loss. There should always be someone in this forum who demands to see the numbers. It spurs us to go beyond the qualitative hopes, to the quantative modeling of our claims. And Tom is that person for us.

I'm asking of Tom no more than he has asked of others, to "show me the numbers" for his claim of the 10x100x example, or stop using it.

I fear that he believes the 10x100x numbers are applicable in the world of sailing and because he believes the 10x100x example somehow helps new designers in mathematically modeling their inventions.

I dread the possibility that he is knowingly or inadvertantly discouraging amateur designers by using wind tunnel numbers that are irrelevant and counterintuitive in the real world.

None of the newbies are going to challenge his example. Tom is a giant in our field, and they are not Davids.

However, "show me the numbers" is a valid request, perhaps THE valid request, from any member or guest of this forum. I am requesting it.

Larry Modes

 

Fanie, I like the way you take a big bite into a new project, and work with enthusiasm, and 'gut instinct'. But man...don't work with too much gut instinct!! You should do some maths or listen to those who have already done it.
Tom Speer raises some important issues regarding the aft mast setup....and your boat is going to be dealing with very large forces. Also, with all the windage from your huge cabin, you will need all the aerodynamic efficiency you can get.
I would hate to see you jump in with all that passion, and work all those hours, and then end up with disappointment.
I know you have the boatbuilding skills and you can't wait to see the thing growing in front of you....but geeez....slow down dude!!
The aft mast might be a good idea for your project, but you don't know that yet.

 

Hi Richard,

He-he-he... Yeah !! By the time you guys are done talking I'm fishing from it already !!

I feel flattered that you can see the enthusiasm I'd hate to do this size a project without it

I haven't done anything wrt the cat, all I have is the little tri and I'm doing some experiments with it to try and figure out how and if what will do when and where. If it doesn't work well on the tri it won't work on the cat either.
If it works well on the tri, there could be a very good above avarage chance it's going to work on the cat as well. As a comparason I sail the bermuda and compare that with my aft mast.

I'm not going to run blind into this project. (The cabin is not really the windy problem - the hull's are ! but does contribute.)

Nothing is carved in stone as yet - remember I was looking for an excuse to go 12m instead of 10m and couldn't rely on you guys for the motivation ? Well. it's still haunting me.

The following has to be set up here before I can commence -

Another looong (for10m) or loooooooong(for12m) double garage (plans already approved)
I have to finish my laser cutter - measuring and working by hand... Yuk, no way hosay !!
Accessories - the list seems endless I guess this would be where the most work would be in, not the hulls or the cabin...


So, relax, take a load off. I'm reading all I get on the subject, and I'm watching Brian Eiland's every move ( just pretend so it's not that obvious). I'm sure he's hiding some secretive tricks on the matter, but sooner or later he's going to slip up and I'll get something from it.

 

Okay Fanie. I feel better now During your experiments, see if you can compare your aft mast rig results with a bermudian WING mast rig. That would be very interesting.

 

As I've said in my 'sailing experience' thread, the downward force of the bermuda defenately pushes down quite a bit (my friend's tri). Then with a jib fitted as well there is an improvement due to some lifting force from the jib. Makes almost say 10km/hr difference before the hulls goes under water again and drag limits speed.

My little tri has only the mainsail that is a jib on streroids , there is no sign of the downward pushing into the water, so with the angle my forestay sits I can almost assume the foreward thrust and the upward lift is close to one another. If it could happen the wind would lift the little tri up ( like in planing) it can easily be adjusted by making water or simply by letting the sail out

I cannot compare sailing to windward yet as my forestay is too limp due to mast bending and no keel or daggerboard so I have a lot of side drift.

 

Here I go again... Me pontificating, I mean... I like part aft mast idea well just stepped back a bit so NO MAIN and 2 roll-up genoas on each side and a blade-jib/storm sail between the hulls a-la hitch-hiker - look up "X-it" on this forum...

I reckon the genoas could be positioned so that all 4 sails are the same size... the foot being around the distance between the fore-stays to the respective hull bows... Use the leeward sails... Lazy sailing and comfortable setup... Not so much "downward force" as position of sails will apply lift - as in less heeling moment...

 

Having lots of smaller sails with sharp leading edges is good for versatility, and each sail should perform well in it's own right....but when reaching or running, small sails lose more wind around the edges than a big sail. Also, the best foil shape is achieved when the rig consists of only one sail (no gaps between sails).

So...in theory, the most ideal rig would be just one big self-supporting sail with no mast or stays. The sail would magically stretch to become tall and narrow when beating to windward, and round when sailing downwind.

I try to keep this image in mind when I am looking at various rig possibilities.

 

Richard, in my case I am talking of a 12m LWL cat with 6m separation on the centreline of the hulls, so I figure on a foot of around 6m on all 4 sails plus the blade jib/storm set mid beam forad of the mast. No main as it is next to useless... Search for "John Hitch" & "X-IT" on this forum to see one version...

For your purposes look at a foil-kite sail as used by performance "hang gliders"