Jib question

[upchurchmr]

Eric,

Would you have any more illustration of your test?
This seems similar to what is done on "Maddness" and other proas where the mast is displaced to weather and the jib tack is on the centerline, giving the increased separation you are discussing (assuming I understand). I asked the same question (different thread) but got no responses previously. Do you think the jib should then be cut differently since the interaction with the main would be somewhat different?

On biplane aircraft the conventional separation for best lift is to make the separation = the chord width. Do you think there is enough analogy to make this a goal?

I have in the past thought about using a bow pole similar to modern day sailing catamarans to place the tack much farther out than just the width of the bow. Too much? It would be lots of complication to go that far.

Marc

Originally Posted by Eric Sponberg

Good luck. This is a good example of "thinking outside the box." You may have seen on another active thread here with a wonderful quote by Richard Woods who said, "You need lots of experience, because you need to know what the current box size is before you can get outside it." (Link: cheap and simple rig).

Good luck, and I look forward to the results of your efforts.

Eric

[Eric Sponberg]

Originally Posted by upchurchmr

Eric,

Would you have any more illustration of your test?
This seems similar to what is done on "Maddness" and other proas where the mast is displaced to weather and the jib tack is on the centerline, giving the increased separation you are discussing (assuming I understand). I asked the same question (different thread) but got no responses previously. Do you think the jib should then be cut differently since the interaction with the main would be somewhat different?

On biplane aircraft the conventional separation for best lift is to make the separation = the chord width. Do you think there is enough analogy to make this a goal?

I have in the past thought about using a bow pole similar to modern day sailing catamarans to place the tack much farther out than just the width of the bow. Too much? It would be lots of complication to go that far.

Marc

Upchurch--we think along the same lines, I guess. I remembered that I published something in my newsletter, The Design Waterline, (before the age of websites) on my open class 60 design of the time and some mast projects. Issue #11 from the Spring 1994, featured, on the cover, a design study I did for my client Sebastian Reidl, for a boat which eventually became Project Amazon. I attach a pdf copy of this issue below. The sailplan shows an articulating headsail pole, and a very brief description of it is on the next page, right-hand column, about a third down from the top. This is all I have that I have documented.

In the end, we did not include this option in the final design for Project Amazon, the client's budget was only so big. But the sailplan and the sketch of the deck plan on the cover indicate what I was thinking at the time. This is 18 years ago, now, wow!

As for how far to separate the sails and how the jib shouild be cut--all those details are up for grabs and require research and testing. I could not say where the best position is to place the jib tack, and I would welcome the input of sailmakers who know better than I how to build sails.

Building and testing ideas like these require interested clients with large checkbooks to pay for the development. It is very difficult to do the work on one's own checkbook unless you have your own large discretionary funds available to do so.

Eric

[upchurchmr]

Eric,

Thanks very much.
The other way to test such an idea is on a small boat.
Since that is all I will be playing with it might be a possibility.

I have an old Tornado catamaran. Do you have a freestanding carbon mast design that would be adaptable? 30' plus or minus. I actually am thinking about making a tri from the boat. The current 32' aluminum mast is ~60# and bent. The 17' boat in the pdf you sent sparked the question. Actually I was thinking about a rotating mast braced at the heel/keel and at boom level.

I don't really have enough information to give you to specify real design loads but most of your discussion is based on bigger yachts, so I thought I would ask.

Marc

[Eric Sponberg]

Originally Posted by upchurchmr

Eric,

Thanks very much.
The other way to test such an idea is on a small boat.
Since that is all I will be playing with it might be a possibility.

I have an old Tornado catamaran. Do you have a freestanding carbon mast design that would be adaptable? 30' plus or minus. I actually am thinking about making a tri from the boat. The current 32' aluminum mast is ~60# and bent. The 17' boat in the pdf you sent sparked the question. Actually I was thinking about a rotating mast braced at the heel/keel and at boom level.

I don't really have enough information to give you to specify real design loads but most of your discussion is based on bigger yachts, so I thought I would ask.

Marc

Marc, unfortunately, no, I don't have any mast designs for a boat that small.

Eric

[upchurchmr]

Thanks anyway.

Marc

[powerabout]

Eric

In my previous post I was wondering what happens to the sheeting angle when you drop the tack to leward?
Was there much experimenting with that?
Cheers

[Eric Sponberg]

Originally Posted by powerabout

Eric

In my previous post I was wondering what happens to the sheeting angle when you drop the tack to leward?
Was there much experimenting with that?
Cheers

Powerabout, Most tracks or jib sheet fairlead attachments have some fore-aft positioning, but not athwartship positioning, so that limits you right there. As the jib tack falls off, the jib itself will tend to go fuller, so you'll likely want to pull the fairlead back to pull the extra camber out of the jib. Likewise, when sailing off the wind, as the tack goes to windward, the fairlead will likely go forward. You can experiment with your own boat to see which settings are best.

Eric

[upchurchmr]

My assumption would be that the angles would want to be the same, that should cause you to move the sheet position outboard on a tack. If you actually set this up for swinging the jib each tack the jib tracks would be permanately moved outboard as much as the tack, for a starting point. Probably lots of experimenting after that.

[Eric Sponberg]

A lot of boats have the jib sheet turning block on the rail already, so you can't move it outboard, and that is why I suggested that your only course of trimming would be to move the turning block forward or aft. Yes, lots of experimenting after that.

Eric

[powerabout]

Originally Posted by Eric Sponberg

Powerabout, Most tracks or jib sheet fairlead attachments have some fore-aft positioning, but not athwartship positioning, so that limits you right there. As the jib tack falls off, the jib itself will tend to go fuller, so you'll likely want to pull the fairlead back to pull the extra camber out of the jib. Likewise, when sailing off the wind, as the tack goes to windward, the fairlead will likely go forward. You can experiment with your own boat to see which settings are best.

Eric

cruising yes but just even every modern cruise / race boat has in haulers

[BobBill]

First, you guys are educating me and I appreciate it...I actually think I have an idea what you are driving at.

Does this sound about right?

Standard sloop, with jib/forestay...but stay (tack) can be moved port/starboard.

I know it seems too simple, but that about right, essentially. I just want to be sure I caught the drift here.

[daiquiri]

Originally Posted by BobBill

Does this sound about right?
Standard sloop, with jib/forestay...but stay (tack) can be moved port/starboard.
I know it seems too simple, but that about right, essentially. I just want to be sure I caught the drift here.

Yep...

[BobBill]

Daiq etal, made my gray day here shine...

I have a plan in the oven for a device to use on my new little bateau, to a point. Question would be would the output equal or exceed the input. (I like many sailors, do lots o input, and reap moderate output for the labors. Love it.

[Paul B]

Originally Posted by upchurchmr

My assumption would be that the angles would want to be the same, that should cause you to move the sheet position outboard on a tack.

Your assumption is pretty good.

If you don't move the lead outboard the same amount as the tack your drive vector from the sail will move to leeward at the same angle as the tack change. That will increase your leeway angle, and the drag of the hull and appendages.

Of course this is assuming you do not want to rotate the hull to windward as Eric seems to think is a viable option.

Either way you are going to increase the hydro drag and you don't want to do that.


To give you an example, my own boat originally had a sliding tack. This was used because the mast was set up for non-overlapping headsails and the idea was to use genoas.

Since the spreaders were too long to sheet around at the required 8 degrees or so, the tack was allowed to slide to leeward (on a T-track) and the genoa track was set up at the same 8 degrees or so from the new tack position.

This generated a similar force vector and a slightly more open slot. The hull and keel and sailplan were still "parallel" to one another, so we were not adding additional hydro drag.

The tack was centered when the sailplan was changed to eliminate the overlapping sails.



Then you have the I14s with their gybing boards.

These boats are set up to basically sail with the board lined up with the direction of travel of the board of a "normal" boat. The hull is then rotated TO LEEWARD to be lined up with the direction of travel (including leeway). This, in theory, reduces the hydro drag and makes the boat faster.

However, this has an effect on the sailplan. The drive vector from the sailplan is now pointed more to leeward than a normal I14. So you need to normalize the sailplan to the board, not the hull. So the sails are sheeted wider.

If you draw this up you will note that you have essentially dropped the tack to leeward when you rotated the hull to leeward. So by sheeting the sails wider you end up with a sailplan similar to the way my boat was originally set up. This is also similar to your assumption.

Some people think the wider sheeting/open slot provides a more powerful sailplan. Others disagree and think it may hurt performance.

[powerabout]

there's power and there's fast
Sheeting angles are getting smaller and smaller on Grand Prix boats that point higher and faster than the old days