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short gaff rig


pointeroche

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Greetings, fellow enthusiasts,

I am converting an Alberg 22/CapeDory22/Pearson Ensign to a short gaff rig, am open to suggestions, particularly on standing rigging and staying. Inspiration came from Michael Kasten's designs: high aspect ratio like a Baltimore pilot, short gaff like the Dutch.

Plan is to use the stock mast (25 or 26 feet long), in case any future owner regards my work as heresy. Gaff will only be about 3.5 feet long (carbon fiber tubing purchased already) with a single halyard on bridle. Throat of gaff would be maybe 2.5 feet down the mast to keep mainsail luff long.

I will stick to the working jib and forgo a genoa, in favour of greater area in the mainsail. Stock masthead main is only about 118 sq ft, mine would bump that up to 150 or 160. Obviously, the mast will have to move forward a bunch in order to maintain balance.

If I move the mast forward a foot, it will be in line with the chainplate that was used for the forward lowers. I will use this front chainplate for the uppers and do away with forward shrouds. Is this scary?

The middle chainplates would now be used for the aft lowers, at about the same angle as always.

This leaves the aft chainplates. I could run intermediate shrouds from them to a point between the spreaders and the masthead, seems prudent. Maybe someday (in phase 2), I will bring the jibstay about 3 feet down from the masthead, and have it meet the mast at these intermediates so they can help tension it. But I would still need running backstays (at least in anything but light air).

Since I am going to need running backstays anyway, I wish to launch (phase 1) with the jibstay remaining at the masthead. I realize this means I will need to make greater use of masthead running backstays to tension the forestay. But I have freed up my winches (no genoa sheets) so I may be OK on that front.

So my first question is this: If I have to use masthead running backstays all the time anyway, do I need to install the intermediate shrouds going to the aft chainplates? My initial reaction is yes, it would help prevent losing the stick in case I blow a tack and don't get my runners sorted out in time. I just wonder, though, if they are worth the extra weight and windage aloft. If these intermediate shrouds only have 2 feet of sweep aft the mast, would I be better off with highfield levers that anchored farther back, and would allow me to get rid of the running backstays?

I look forward to drawing on your impressive pool of expertise,

Vincent

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I have a good bit of experience with high aspect gaff rigs (short gaff) and I think the first thing you should do is nail down where you expect the CE needs to be on this revised sail plan. Since moving the CLR around will be much more involved. This will be the only way to dial in you rig, without resorting to adding or subtracting length from your sprit and/or boom(s), recutting sails and raking the stick. This kind of guess work can drive a person nuts, so work up some drawings of the sail plan and balance them over the CLR with the lead you'd like with this rig (if I had to guess, try 7% as a starting point)

It would be nice if the chain plates fell where you need them. This may not be the case, but you may get lucky. Don't discount the jib. It's a real work horse in a high aspect rig especially with some overlap, which will be able to sheet in tighter, because the mast is closer to the eyes of the boat. Which brings up another issue, staying base spread. With the pole much farther forward, because of the bigger main to jib relationship, the stay spread on deck isn't going to be as wide as farther aft. Typically this can be handled by using a stiffer sectioned mast and double lowers, which means some (if not all) of your current chain plates will need relocation.

You should also do a series of loading calculations for the new standing rig plan, to insure you have sized everything to tolerate the changes. Lets look at some of them quickly; increased the main by 50+% (I'm assuming you have around 185 to 200 total sq. ft. in the stock configuration, which would be typical for a boat this length), intending on moving the stick forward a "bunch", but would like it to be a foot so the forward lower chain plate can be used, adding a sprit (my assumption, because of the hanky sized jib that's left after you subtract the main from 200 sq. ft.) to increase the fore triangle and some rigging questions that need not be addressed until you sort out the rig placement. Can you provide a drawing with the CE and CLR marked?

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Good points, thank you for the input. Indeed, I did a bunch of sketching and number crunching to plot the CE and its relationship to the CLR at various stages of reefing. At that time, I was plotting with the mast 15 inches forward of its existing position. If the chainplates are only 12 inches forward, is the 3 inches of difference a big problem? Could this problem be mitigated by the use of swept spreaders? Could it be more easily mitigated through the installation of intermediate shrouds to the aftmost chainplates?

One reason why I have slowed down on the number crunching on the CE location is that I have learned of an adjustable mast step. This is made by Ensign Spars in Florida for the (nearly identical) New Ensign, and I believe it could avoid resorting to the adding/subtracting from 'sprit and boom, recutting sails and raking the stick that you mention. Yes, this approach may require altering the length of stays - certainly no picnic but still.

I promise I won't discount the jib. I'm counting on it being similar to the stock working jib: around 85 sq ft. Probably only overlap the mast by about 6 or 8 inches, but I agree that even that should help smooth out airflow on the main.

As for total sail area, the rated sail area for the Alberg22 with 100% foretriangle is 236 square feet. I gather people go a bit beyond that with 130% and 150% genoas. I do not plan to use a spinnaker, and I do not mind reefing early. So I have been looking at 160 in the main (up from 118 in the stock masthead sloop rig) plus 85 in the jib for a total of maybe 245 sq ft. If you feel this is too greedy for a boat with 7' beam and 3' draft of 3200lbs displ and 1540lbs external ballast, by all means let me know.

I had originally been thinking of a short (18 inch) plank bowsprit, but now think I should be able to keep the rig all inboard. Since the short gaff rig I envisage will be rather like a bermudan rig with the head (and foot) lopped off, its center of effort will move forward as it is reefed, to a greater extent than more traditional gaffs. So my hope is that this move of the CE forward will maintain or re-establish helm balance as the wind increases, without the 'sprit.

Promise, I'll get a sketch out before too long, but it is very helpful to me to get some of these issues sorted out first, so I don't embarrass myself or anything. Thank you again for your input.

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I know the boat, which you are making these changes, but am not intimate with the rig dimensions, so I hesitate to offer much without looking at the original and revised sail plans. It sounds like you are working through it, though the panel loading calculations will determine if you can get away with using the old chain plate locations. On that topic, if the leads to these plates differ much from the original rig, then you'll have them out of column or alignment, which can strain them past working limits. It may be possible to reorient them to the new lead, but you may as well move them if you need to do much bending, drilling and reinforcing.

Personally, I like pretty conventional staying arrangements on gaff rigs, though you surly could use swept spreaders and a few other cute devices to help share the loading. I like to see double lowers, an upper and running backs on cruising craft. Racers may want to keep things light, adjustable and higher tech, but cruisers have different needs and the rigs tend to be stiffer and more redundant. By all means, take the jib to the masthead, get as much headsail luff as you can.

I look forward to seeing your drawings.

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  • 6 years later...

Hi,

I am wanting to convert an O'Day 23 (1973) to a gaff rig. I dont mind adding a bow sprit or moving the mast as I have the poptop model so the mast is to the cabin sole anyway. Could you tell me where to place the mast and how long it and the boom should be? Will I need a bow sprit? Thank you.

Drmyy

I have a good bit of experience with high aspect gaff rigs (short gaff) and I think the first thing you should do is nail down where you expect the CE needs to be on this revised sail plan. Since moving the CLR around will be much more involved. This will be the only way to dial in you rig, without resorting to adding or subtracting length from your sprit and/or boom(s), recutting sails and raking the stick. This kind of guess work can drive a person nuts, so work up some drawings of the sail plan and balance them over the CLR with the lead you'd like with this rig (if I had to guess, try 7% as a starting point)

It would be nice if the chain plates fell where you need them. This may not be the case, but you may get lucky. Don't discount the jib. It's a real work horse in a high aspect rig especially with some overlap, which will be able to sheet in tighter, because the mast is closer to the eyes of the boat. Which brings up another issue, staying base spread. With the pole much farther forward, because of the bigger main to jib relationship, the stay spread on deck isn't going to be as wide as farther aft. Typically this can be handled by using a stiffer sectioned mast and double lowers, which means some (if not all) of your current chain plates will need relocation.

You should also do a series of loading calculations for the new standing rig plan, to insure you have sized everything to tolerate the changes. Lets look at some of them quickly; increased the main by 50+% (I'm assuming you have around 185 to 200 total sq. ft. in the stock configuration, which would be typical for a boat this length), intending on moving the stick forward a "bunch", but would like it to be a foot so the forward lower chain plate can be used, adding a sprit (my assumption, because of the hanky sized jib that's left after you subtract the main from 200 sq. ft.) to increase the fore triangle and some rigging questions that need not be addressed until you sort out the rig placement. Can you provide a drawing with the CE and CLR marked?

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Hi,

I am wanting to convert an O'Day 23 (1973) to a gaff rig. I dont mind adding a bow sprit or moving the mast as I have the poptop model so the mast is to the cabin sole anyway. Could you tell me where to place the mast and how long it and the boom should be? Will I need a bow sprit? Thank you.

Drmyy

First you need to decide how large the new sail needs to be. Even if it's the same as the old one, you have a huge number of choices in mast height, aspect ratio, gaff size and boom size. Try to nail a few of these down first then work out the rest. Use a good ruler and graph paper to calulate surface area (since a gaff sail is polygonal, you need to divide it into a trapezoid and a triangle by drawing a line through the throat parallel to the foot).

The mast placement depends on the new Center of Effort (the geometric center of the sail). It needs to be in the same place as the old one vis-a-vis the centerboard or keel to maintain balance (assuming you don't change the foresail(s), which it seems you intend to). The calculations are not too hard but I can't explain them here. Best to look at some other source such as David Nichols' book http://www.duckworksbbs.com/media/books/tradsails/index.htm

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Hi,

I am wanting to convert an O'Day 23 (1973) to a gaff rig. I dont mind adding a bow sprit or moving the mast as I have the poptop model so the mast is to the cabin sole anyway. Could you tell me where to place the mast and how long it and the boom should be? Will I need a bow sprit? Thank you.

Drmyy

As for a bowsprit, again it depends. If your new mast is moved forward, and the mast would be shorter too with a gaff rig, then you do need a bowsprit to support a large enough jib or jibs. But the bowsprit will move the Center of Effort forward and you need to take that into account in your canculations about mast placement.

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Hi,

I am wanting to convert an O'Day 23 (1973) to a gaff rig. I dont mind adding a bow sprit or moving the mast as I have the poptop model so the mast is to the cabin sole anyway. Could you tell me where to place the mast and how long it and the boom should be? Will I need a bow sprit? Thank you.

Drmyy

An example from my own boat which I designed from scratch (see "new design 15' cat ketch" thread). I first decided on a cat ketch rig. The placement of the masts and the centerboard was more-or-less dictated by the placement of the boat's frames and bulkheads. The distance between the main and mizzen masts dicated the size of the mainsail boom, and the distance between the mizzen mast and the transom limited the size of the mizzen boom. Once I set the boom sizes, the height of the masts was influenced by the desired sail area, and the maximum mast height I was willing to live with (I wanted them unstayed, removable and fitting inside the boat). The relative size of the two masts and sails I worked out by trial and error by calculating the combined Center of Effort (CoE) of the two sails (takes a lot of paper and pencil geometry). As long as the CoE is close enough to the center of lateral resistance (CLR-which is given mostrly by the centerboard) then the boat will be balanced. If you have a fixed keel you need to be more careful because of course you can't adjust it, unlike a pivoting centerboard. Generally you want the CoE to be slightly aft of the CLR so you can have a slight weather helm which is much safer than the alternative.

Confused yet? None of this has a simple answer. Good luck!

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Hi,

I am wanting to convert an O'Day 23 (1973) to a gaff rig. I dont mind adding a bow sprit or moving the mast as I have the poptop model so the mast is to the cabin sole anyway. Could you tell me where to place the mast and how long it and the boom should be? Will I need a bow sprit? Thank you.

Drmyy

Having looked up basic info on the O'Day 23, I see that the mast is almost amidships. Also I see that the foresail (as is normal with modern Bermuda-rigged sloops) is larger than the mainsail. With a gaff rig this won't be possible, given the shorter sail and mast, plus I don't think that gaff sloop jibs can reach as far aft as Bermuda sloop foresails. A gaff rig sail is shorter and wider on top so its CoE is farther aft. The smaller jib(s) of the gaff sloop also move(s) the CoE but I'm not sure in what direction. So it may be possible to design a gaff rig that does not require moving the mast forward or adding a bowsprit, but I think it's unlikely. You have to work that out yourself with pencil and paper as I said.

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