modifying a staysail schooner

[drewcathell26]

Is is possible to modify a staysail schooner to a gaff schooner? If it is possible does it make sense in terms of performance? I am not trying to push the schooner beyond what is reasonable for a limted rig. I have an opportunity to purchase a staysail schooner but have always loved a gaff. If it is reasonable and worthwhile who would I speak with to design the changes?

thanks

drew

[Tcubed]

Staysail schooners can have a number of different arrangements.

Depending on the exact arrangement , geometry , mast placement etc changing to gaff can result in substantial improvement in performance. But it all depends...

Basically your question is too vague to be able to answer with any kind of precision as is. You need to post some pictures or post a sail plan, so i could determine what your options are. Also you need to specify what your specific objectives would be.

I have many years of experience as a rigger on both traditionally rigged and modern boats. I have also aerodynamic training, so i believe i might be the relevant person for you.

[robherc]

I have many years of experience as a rigger on both traditionally rigged and modern boats. I have also aerodynamic training, so i believe i might be the relevant person for you.
OK, I know this is completely-off-topic here, but (in light of your experience) what are the main advantage(s)/disadvantage(s) to adding reverse-marconi sails to a multi-masted marconi/bermuda rig (filling in the gaps between the lower/upright marconi sails & the following mast)?

[Tcubed]

A 'reverse marconi' foresail to fill the gap between main staysail and foremast on a staysail schooner without a boom is extremely inefficient as the sheet has nowhere to go but to the mainmast, ie on the centreline of the boat. This creates a very 'cupped' airfoil section to the upper part of that sail. This in turn creates a very large heeling moment , especially as it is so high up, and a weak forward force component. Furthermore, it will have reverse twist and/or inboard pointing leech . Additionally this shape will backwind the main staysail and mainsail.

This problem is inherent due to the sheeting angle.

These sails therefore require a boom or wishbone boom in order to be somewhat acceptable.

Even with the boom though it is not so optimum as all these sails have a triangular planform which is a drastic departure from the optimum eliptical planform. Also , whenever a sailplan is so heavily subdivided there is loss of efficiency at high angles. Many slots will delay the point of stalling, but i tend to think that upwind is always the point of sail which should take optimization priority.

This is a very deep and fascinating subject, but let me stop there for now.

[robherc]

OK, thanks...your opinion seems to be pretty much agreeing with my calculations that they'd be farily inefficient, and disastrous in the way of heeling moment. I just wanted to get an "expert opinion" as I'm seeing them used on several "modern" rigs...so I wasnted to know if there were benefits that I wasn't seeing, or if they were just that poorly thought out ;)

[PAR]

Simply put, a staysail schooner will perform better up wind then a gaffer, but down wind the gaffer has an advantage given both fly working sails. This is especially true if the gaffer has an overlapping foresail.

Generally the staysail schooner is a handier rig to operate, particularly if short crewed, then a gaffer. Many successful ketches and schooners have utilized a wishbone mule. Sheeting angles can be difficult, but carefully thought out rigs can work exceptional well.

It's unlikely you'll find a reasonably modern design, staysail schooner that wouldn't require considerable effort and expense to convert to a gaffer. The mainmast will probably have to move, possibly the fore as well. This means major surgery to the yacht's hard points (steps, chain plates, torsion rods, plus deck and interior modifications, etc.) to suit the new rig.

[alberto88]

just can use a full batten big roach main to increase sail area up high, and acheive the look of gaff, with better performance?

[drewcathell26]

Thanks for the quick responses. I'll try to be clearer. The attached photo is of a Cheoy Lee staysail schooner which has the very reversed marconi ric that Tcubed mentioned. I am not a designer but it seemed to lack the abilty to form an effective shape to me as well.

My goal is to leave the masts where they are, change the main and fore to gaff rigs and add topsail above each.

I haven't tried to attach a photo before so I am not sure how this will work.

Let me know if you need further information.

[PAR]

Nope, it can't be balanced well with the masts in those locations and gaffheaded sails installed. The CE would move considerable aft of it's current location and the yacht would go "lee" on you.

[drewcathell26]

I was hoping to not only keep the masts in place but keep the center of efforts close to the same as well. The following is a poor quality photo shopped version of what I had in mind. In the photo the center of effort seems to remain the same. I have no idea if the sail shapes are appropriate or not.

[Tcubed]

I think you ' re thinking pretty logically but you still haven't stated what your precise objectives are in doing rig changes.

Seeing the first picture , it is in fact possibly one of the worst examples of a mule i have yet seen.

That boat is quite small and does not need the sailplan so divided.

I agree that moving mast positions is suddenly a lot more work, so would avoid such drastic changes.

It is important to realize that if the center of effort is lowered it must also shift aft to achieve the same balance, but will be less affected by heel.

You seem to anticipate shortening and/or lengthening spars.

I would recommend; leave the foremast same length. Lengthen bowsprit and cut down mainmast. Have only a main tops'l , set on its own spar and made quite generous. I would also make the foresail overlapping, since the masts are quite close together. You probably don't want to mess with the jibs but if you had one self tacking jib instead it would be more efficient and you would end up with only the foresail to deal with when tacking.

I disagree with PAR's last post.

I also, PAR, do not understand how someone of your authority can come up with such a generalization as <<<Simply put, a staysail schooner will perform better up wind then a gaffer, but down wind the gaffer has an advantage given both fly working sails.>>>. What aerodynamic reasoning did you use to make that claim?

[Tcubed]

Here is a very quick and crude picture of what i'm imagining spur of the moment. Needs refining obviously. The foretriangle could just as easily be jib and stays'l instead. the boom could be a foot or two longer two to get some more area low down. Cutting the masts removes weight high up which does wonders to righting moment , not to mention windage.

[timothy22]

You can spread out the expense a little by just going to the gaff foresail, leaving the main as is except for removing its forestay and adding a spring stay. Several great old schooners were designed this way by John Alden and others. This will give you half the look you are going for, at considerably less than half the expense. Then you can be sailing whilst saving up to rerig the main and fore triangle.

[Tcubed]

That is a very good alternative also.

[drewcathell26]

Thanks again for all the good ideas. Doing the changes in stages would be a real help.

As to my real objective... I love the look of a gaff rigged schooner. I have seen staysail schooners, Cherubini come to mind, that seem to have a real grace under sail. The schooner I am looking at does not seem to fit in that category. That may be a result of what you describe as "the bad mule plan". I am aware of the old saying that it is nicer to sail near a schooner than on one. I know they typically don't perform as well as other rigs. That being said I am willing to tolerate that loss of speed. I have sailed for years on boats that were not racing boats and have enjoyed the speed at which I sailed. At times right past larger, faster boats. There is nothing about the staysail rig as currently photographed that appeals to me in appearance or function.

I realize the boat is small for a schooner rig but I am trying to keep the size manageable (even if I am not keeping the rig manageable). These questions are simply a last ditch effort at creating my dream boat before I give up and buy a great 37' cutter.

Adjusting the spars, sail and rigging is a completly acceptable list of tasks. Particularly if they can be done in stages as timothy22 suggested.

Regarding the comment suggesting increasing the roach I am not a fan of roach or battens at all and would rather have a leech line if the sails are to be new or cut.

[PAR]

Maybe it's just me, but am I the only one on this thread that recognizes that schooner pictured above? Possibly I'm the only one with the spec's and sail plan in my data base. Could it be, I'm the only one that knows where the CE is on that particular design or how much lead, Bill Luders incorporated into it's sail plan.

Then again maybe I'm just talking out my ass and haven't a clue.

Look anyone with even reasonable design experience understands that a sailsail schooner will crush a gaff schooner close hauled and that as the sheets are eased the roles will reverse. This of course assumes the hulls are the same, the boats sailed equally, neither hoists additional sails and they're not fouling each other. It's the very reason the rig was invented.

It's also the rig that continues to this day, to win races and by no means requires you to take a speed or performance penalty in any fashion. Hell, a well designed schooner will usually show it's transom to any boat of similar hull and appendage configuration on a reach.

The rig can be changed, but it's not a very practical thing to do. The boat has a primitive liner and grid, making moving masts quite troublesome and costly. You can hang half the main off the stern and double (+) the length of the bow sprit, to gain back the area you remove from the top of the rig, but it will not be especially pretty in terms of traditional schooner proportions. The foremast is just to far aft for that at the very least. This change, when all said and done, will rival the full value of the boat, which has been around 30 to 40K for brokerage average examples.

If you intend to do this and can't be convinced other wise, might I suggest you start with one of the ketch versions of this particularly heavy vessel (D/L 465, 8 tons on a 25' LWL). These can be had at a much less expense, then the one you're currently looking at, with the savings placed toward the revamped rig. It goes without saying (I hope) that you'll need a designer to arrange a new sail plan and structural accommodation to the grid, liner and possibly interior.

[Tcubed]

<<<<Look anyone with even reasonable design experience understands that a sailsail schooner will crush a gaff schooner close hauled and that as the sheets are eased the roles will reverse.>>>> Par

Sounds a little bit like one of those self evident truths that when actually scrutinized a little more critically turn out to be not so true.

I thought there was an actual aerodynamic reasoning behind it rather than just a 'everybody knows that' justification.

I don't mean to be irritating just like to see real reasons.

[PAR]

You're the boat designer, at least the line below your handle suggests such.

Gaff schooners have huge windage issues, short luffs, heavy spars and gear making for a fair amount of weight well aloft. Staysail schooners have longer luffs, cleaner rigs, much less weight aloft, etc. This coupled with typical gaff schooners having considerable appendage drag and wholesome hull forms, it's would seem reasonably obvious.

On the other hand a particularly well designed staysail schooner I'm familiar with, has the obnoxious habit of repeatedly winning the Regatta Del Sol Al Sol, the race from St. Pete, Florida to Mexico as well as other events.

I've sailed on the Cherubini 48' staysail schooner (the 44' ketch as well) and it's not slow by any means and can hold it's own with the best in style and comfort too.

Most have many misconceptions about schooners, much of which is unfounded wives tails and handed down rumor or speculation. Both the traditional and staysail versions, like all rigs have advantages and disadvantages. I too love the look of a traditional gaffer, but would rather the performance of the Cherubini.

[drewcathell26]

I don't have the background of either of you but would appreciate help clarifying a few simple questions. It would help me for a minute if we could set aside the question of staysail and gaff efficiency and focus on center of effort.

If you replace the marconi mainsail on the cheoy lee with a gaff and a topsail of the same relative size and combined shape won't the center of effort when both are flying be the same as the single marconi?

If you drop the topsail don't you end up with a size and shape similar to a reefed main?

I am bringing little more than a basic undersatnding of geometry so I may be missing something critical.

I do agree with PAR that the Cherubini is sweet. If I had an extra million I might even buy one. In fact it was the reason that the Cheoy lee caught my attention. It certainly speaks to the combined value of subtle differances.

drew

[drewcathell26]

I don't have the background of either of you but would appreciate help clarifying a few simple questions. It would help me for a minute if we could set aside the question of staysail and gaff efficiency and focus on center of effort.

If you replace the marconi mainsail on the cheoy lee with a gaff and a topsail of the same relative size and combined shape won't the center of effort when both are flying be the same as the single marconi?

If you drop the topsail don't you end up with a size and shape similar to a reefed main?

I am bringing little more than a basic undersatnding of geometry so I may be missing something critical.

I do agree with PAR that the Cherubini is sweet. If I had an extra million I might even buy one. In fact it was the reason that the Cheoy lee caught my attention. It certainly speaks to the combined value of subtle differances.

drew

[drewcathell26]

Opps. I just sketched out the marconi I just wrote about and realized that when you reef the marconi the center styas forward and when you drop the topsail over the gaff main the center moves back. So clearly the center of effort move once the sails are reduced.

Are sail plans typically draw so that the rig can stay balanced throughout reefing?

[Tcubed]

Yes you are right , if the new gaff main + topsail has the same total planform as the sail it is replacing the center of effort will indeed be unchanged. However, drop the topsail and it does not have the same planform as the original sail when reefed. Rather its center of effort will be further aft and this must be taken into consideration, when rebalancing the entire sail plan, naturally.

However i think that if you merely do that you would not be gaining any kind of advantage over what is already there.

I would say replacing the mule and staysail with a gaff foresail (not nescessarily with tosail) would be an improvement for not much more cost than a new sail and spar, especially if it is loose footed. This is because you would get more area, lower down , less divided , with a better shape and a better planform.
Changing the mainsail is a lot more complex as its cenetr of effort would move aft and would thus require changes to the foretriangle in order to balance, or you're stuck with no significant change or advantage to what you already have with the mainsail. In fact it would be a disadvantage.
To make the mainsail change into gaff be a improvement requires taking advantage of the the gaff's qualities, thus changing more than just replacing the same shape and area into two sails.

I get where you're coming from Par, and i am not saying staysail schooners are slow as your examples and many others have demonstrated. My point on the efficiency of a gaff rigged planform must be compared with other things equal or it is not really a meaningfull comparison. So just because it is gaff rigged does not imply solid spars etc... And when you compare the gaff rig made with the same level of technology , weight, aspect ratio , to a marconi sail it turns out the gaff planform is considerably superior simply due to its closer aproximation to the elliptical planform at all angles. Of course if you give the marconi sail some generous roach this difference disapears . Bottom line, triangular sails due to their area distribution suffer from much greater induced drag than their aspect ratio alone would suggest. This is known as the k factor in Prandtl's induced drag equation.

[Tcubed]

Crossed posts there.

Yes reefing is taken into consideration. The boat must always be balanced. However it is important to realize the center of effort is not set in stone, can and does move around slightly in any rig as it goes through the various sail reductions and combinations. Also as i already said lowering it means it needs to move aft slightly.

[drewcathell26]

It sound like changing the foresail into a gaff would be the simplest of the desired changes and improve the look of the rig as well. Thanks to all who responded.

drew

[timothy22]

On the off chance you would like to have some fun with scale drawings, I attach one longhand way of finding the centers of areas of sails and groups of sails. If you do the current rig first, you just need to make sure your changes keep the center of areas the same or perhaps a few inches further forward to account for the gaff sails and the schooner rig. As far as efficiency goes, in a small schooner it is hard to beat the drive of an overlapping foresail. With the staysail rig, the gollywobbler, or foursided fisherman's staysail sheeted to the main boom end is a wonder reaching in light air, almost like an asymmetrical spinnaker in its effect. A smaller foursided fisherman is good if it is cut flat for windward work. Both of them can be the devil's own job to set, tack and strike shorthanded or in a strong breeze without a lot of experience. A threesided mule might be better sold to someone else. Few staysail schooners bother with them.

[drewcathell26]

Thanks for the diagrams. Anyone want to answer the more complicated question of how to calculate the center of effort of the jib and staysail on cutter.

[robherc]

Find the center of area (viewed from directly abeam the ship) of each sail, and calculate the total area of each sail. Draw a line between the two Centers of Area. Now, find the ratio of the two areas, and place a point at the same ratio along the line. There is your CE between the two sails.
You can actually find the CE of an unlimited # of sails in that way, by simply pairing them up, finding the CE of each pair, then pairing up the pairs in the same manner as you did the single sails.

[Tad]

Oh lets have a good argument.....

Talking about center of effort in a schooner is (almost) a total waste of time. The reason for having a schooner is that the boat can easily be balanced on all points of sail in any amount or angle of wind. You can do this because you have (literally) dozens of controls instead of the sloop's handful.

Who here can point out an normally proportioned schooner that had balance problems? Balance.....let (one of 4-6) the sheet out a bit, or pull it in a bit.

Catboats and sloops have one or 2 sails that we can find a theoretical center for and pretend that we know whats happening. Far less margin for error, fewer options. With a schooner you have four or five sails to adjust on the wind, the chance that one will overpower the others is almost nil.

Topsails do not enter into the CE equation. Just like spinnakers, yes you can feel it in the helm if there's a problem, but calculating a geometric center is a waste of time. Hoist them when conditions are right, drop them when they're not.

[robherc]

...Can't argue that Tad, but I'll still answer his question. ;)
...and I'll still try to figure the CE of my schooner-rigged boats & try to put the CE of the keel close to there, so it's EASIER to balance it while underway (or, at least, so I feel better about it :P).

[Tad]

rob...

In a schooner put the foremast about at station 2 and the mainmast at station 6....she'll probably work just fine. A masthead sloop has the mast at station 4, frac sloop station 3, ketch main at station 3 and mizzen at station 8.

Be aware you are calculating geometric centers of what are 3 dimensional foils. All sails aft of the headstay lose effectiveness due to the junk (masts, sails, etc) ahead of them. When calculating CE I use a sail area loading system devised by Davidson Laboratory. Load the fore triangle (clean leading edge, no mast ahead) to 1.7 * SA, set the main (or fore'sl on a schooner) at 1, and the mizzen (schooner main) at .5.

[PAR]

Tad, the original sail plan for the above pictured Choy Lee, shows the main of the ketch and the fore of the schooner in the same location, which to me makes perfect sense from a production point of view. My examples of the construction, deck and accommodations plans don't show a schooner mainmast but the mizzen of the ketch, which divided the cockpit in half (typical). I would have to assume that they offset the companionway and dropped the main down to the sole, where a very heavy athwart bearer took it ("U" shaped?), as the shaft is directly under the main.

[drewcathell26]

No one answered my question about cutters. I am still interested in knowing if there is a value and a way to locate the center of effort when one sail is covering a substantial amount of another sail.

You did however answer a question I hadn't yet asked and that was going to be regarding the difficulty in locating a usable center of effort on a bunch of sails some of which draw poorly. It leaves one question unanswered... does a sail create a rotation based on its size even if it is lousy at providing drive?

One other question. When you are calculating the ratio of sail area to displacement ratio for a cutter how is the foretriangle calculated.

One last thought. I have spent my life working with strucural engineers who all know the answer to practically every question I need to put to them. I was always amazed at what would happen when you broguht more than one to the mix. I am glad to see that boat design\building provides such a wealth of things to disagree about. I would hate to think the rest of the world had been relaxing while we homebuilders were living in the fog.

[drewcathell26]

In regards to PAR's question about the location of the mainmast and the companionway see the attached photo. The main mast lands on top of the frame in the photo. It was one of my concerns about enlarging the mail sail and placing more load on that frame.

[Tcubed]

Despite what has been said and written about centers of effort it is actually a simplifying method for a very much more complex problem.

Each sail will have a pitching moment about its aerodynamic center (0.25 mean chord) dependent on its section.
Furthermore there is the interaction of the sails upon one another (superimposition of up/down wash streamlines) .
So there is for each sail a total force vector acting upon its aerodynamic center (not the center of effort) and there is a moment about its aerodynamic center as well. These can all be summed to produce the total aerodynamic force and moment. This also does not act at the boats centerline due to the general angle of heel.

So you see that how one measures overlapping or not is a matter of convention , one that has been found to be a reasonable general approximation to the full model of the process as outlined above. Yes overlaps and individual sails are used , not foretriangles. But you never know , as each designer tends to develop his own methods over time.

[robherc]

@Drewcathell26

Usually, it's easy enough to ignore the part of the sail that is masked by another, as it isn't directly exposed to oncoming wind. IMO
But, as Tad so well put it, you can easily move your CE to just about wherever you need it by tightening &/or loosening a couple of sheets.

[drewcathell26]

I appreciate each of you taking the time to answer questions that must seem incredibly basic in your world. I started sailing 10 years years ago at age 40 and have been amazed at how wonderfully complex sailing is.

Your comments support the conclusion that two different boats of theoretically identical design elements will still sail differently based on the skill and experience of the person making the decisions. That being said it doesn't reduce the value of great design. Or learning more about it.