"A Class" Sail Dimensions - please help!!

Hi there,

I have come into possesion of a ‘classic’ style A class rc yacht. It has the long leel integral to the hull rather than the detatchable fin keel in use today. I have no sails however am fortunate enough it did come with a mast. I have sailmaking skills.

I would like to know what some other A class owners sail dimensions are. I know some are ‘secret’ - but I am just after ball park figures at this time.

If you can help me out - I am ideally after Luff, Foot, 1/4, 1/2, 3/4 widths of the A rig main and jib.

Please help me - I am desperate to get this ‘lady’ on the water and see how she goes!!


From my limited knowledge of the A class, the sail area for each boat is different based on the measurement of the hull. So you will need to know what your max allowed measured sail area is, based on your hull.

There is an active A class fleet in Australia. You may get a better response if you post this question on the Aus forum.


There is an active fleet in the UK. They have a web site.




The A Class uses a meter rule based measurement system. This kind of rule is quite involved. The allowable sail area is a result of the hull dimensions. A formula takes into account the various measurements of the hull and sail area to achieve a rating. The hull measurements include LWL (floating load waterline length), QBL (quarter beam length, a measurement that approximates the heeled waterline length), displacement (weight), LWL beam, total draft, and freeboard (height of sheerline above the water at three points), to determine sail area. Sounds complicated doesn’t it?

Doing a proper job of determining the sail area would require a float tank or other still body of water to do the hull measurements in. It would be a whole lot easier if the original source for the A you have still had the rating certificate which would have all the information noted down. I would try to track that down. If there is a number inside the hull somewhere then she was rated at some point in her history. If you know the design name of the hull then you might be able to track down someone in the UK that has a sister and her info.

Well, if you are just looking to get her on the water and you are not interested in having her rated for competition then some ball park numbers for sail area depend on how much she weighs. Heavy boats in the 50 pound range with a waterline length over 50 inches, about 1620 to 1700 sq. inches (the units that were in use before the rule change in 1996). Current light weight boats in the 30 +/- usually 1450 to 1550 square inches. These are just rough figures based on some of the different plans sets that I have. You may want to start a bit on the large end of the spectrum because you can’t make small sails larger but if the boat is overpowered you can always cut the sails down a bit.

I hope that this helps some.

Brad, I have several old plans and a copy of the Priest and Lewis book with several “A” boats described . If you can supply the overall length and approximate weight of your hull, I could give some ballpark dimensions for a sail plan. It wouldn’t be a legal “A” boat , but would get you sailing.

Hi guys,

Thanks for the replies. I do have a copy of the class rules and have put together a neat excel program together to decipher it all. What I am really after is some idea of what other people are using in the way of boom lengths and mast heights. I have no A class boats in my area at all so I have to ask for help on here.

Sadly the boat does not have any documentation or sail/hull number. No plans. When I get a chance I will draft some up on the computer. The boat is 23kg and 2050mm overall. I think the WL is 1650 but I havent had it fully loaded and floating yet.

Surely these measurements are not that ‘secret’!! Please help!!

Brad, its not that spar lengths are “secret” or that all sailors are selfish sons-of- b-----s. Its because in the A Class everything is relative. That is what we’ve been trying to tell you. If you got spar dimensions from one of us they could be either too long or too short for any guessed at sail area plan. If you have an idea of the LWL and weight take up cbinfl’s offer and once you have a rough sail area divide it so about 35% or less is in the jib.

On older boats, that is pre-rule change, the rigs are usually fairly far forward because the bulb counterweight was not allowed to extend in front of the leading edge of the keel back then. This means that most of these older boats teetered on the edge of being unbalanced. If you have the original deck on her or have her opened up so you can see her beam structure then you can glean the original position of the mast. If you can float her with her overall weight (that includes everything that will comprise the completed boat) on an approximately accurate waterline (what looks best (remember that in original trim she had a vane gear aft)), then you can get an approximate balance point of the hull by carefully shifting the weight to the side to heel her (try not to shift the weight fore or aft) and pushing the hull sideways through the water will give you an approximate balance location for the hull. The center of the area of the sails should be just forward of this spot and vertically above it.

The center of area of the sails is derived by drawing a few lines on a scaled down plan of your sails. Draw lines from each corner of each sail to the midpoint of the opposite side. Where the lines intersect is the center of area of the sail. Then draw a line connecting the the centers of the jib and the main. Divide this line’s length in correlation with the area percentage of the jib and take that measure and find the center of area for the sail plan at a point on the line measured from the mainsail intersection point. Sounds complicated, more so than taking the actual measurements.

If you know the approximate heeled center of balance and the original mast position then you can play around with different arrangements of the sail plan until you get one that works for the boat.

This is naval architecture in a nutshell and I’ve changed some of the terms to make a difficult subject more approachable. There is certainly more to all this but since you have virtually no information about this boat there isn’t much specific information that anyone can reliably give you. I suggest you get in contact with the “Vintage Model Yacht Group” here in the US. They might be able to supply you with more info and if you send them a photo of your hull they might be able to identify her. At the very least they should be able to supply you with a copy of the pre-1996 A Class rules.

Best of luck.

Brad, Attached is a sail plan for an “A” boat. This boat was 82" OA with a 54" LWL and weighed 54 lbs. ( 24.5 kg, 2082 mm LOA and 1371.1 mm LWL }. Your estimate of 1650 for LWL might be off ?? LWL will also depend on the displacement, lighter boat will float higher. Mast height is limited to 84" so that’s what all first suits had. Since you do’t seem to have any boats to compare with, this sketch should get you around the pond ?

Good luck, Charlie