Using Really Simple Sails on other boats. Advice and dimensions

The Really Simple Sails are so cost effective that many have asked about fitting them to other boats.

One example is the article on Oz 89sq ft sail on John Lizardi’s North Easter sailing dory.

There are a number of risk, but with some careful homework on the buyers part it is usually OK.

It is all at your own risk, but info below will help avoid troubles.

Cheap but good sails for the Goat island Skiff, OzRacer, Oz PDRacer and Ocean explorer

So from Michael Storer …

Weight and type of boat.

These sails are the correct weight cloth for trailer boats held up by the weight of their crew.

They are not suitable for keelboats and water ballasted boats, unless they are small and light – smaller than 14ft and not too heavy.  The SCAMP comes to mind as being OK.

Also use on heavy trailerboats (say hullweights over 300lbs) or multihulls constitute a larger risk.  The 4.1 oz cloth will be overloaded outside that envelope because of excessive hull stablity.

If in doubt, check with the designer of your boat.

Experienced hands who know a lot about balance and weather and lee helm can skip the next bit and go straight to the “Special note about leeboards and helm balance”

Very experienced users can skip to the bottom and download the PDF to enable them to work out if the sail will fit quite different hullshapes using standard methods or their own recipes.

Helm Balance

Balance is about the relationship of the centre of the sail with the centre of lateral resistance (CLR) of the hull.  Usually CLR is centred on a keel, leeboard or centreboard, though it can get cloudy with long keels or where the boat is fitted with a rudder skeg or deadwood.

Note that a centreboard and leeboard (or bilgeboard or offcentreboard) are in relationship to where the board is laterally in the boat. Many consider that a centreboard is a swinging board. This is not quite logical. For the mechanism or the way the board works there is a swinging board or a dagger board. So thus there is a swinging centreboard, a dagger centreboard, a swinging leeboard or a dagger leeboard. One term is the mechanism, the other is the location Centre=Center 🙂

I’m niggling on this because some will be confused if I don’t spell out what I mean in a precise way.

If the relative positions of the CLR and the Centre of the Sail is too wrong the boat will be a cow to handle.

It is easy to see if this is wrong as the tiller will have to be pulled or pushed dramatically away from the standard centreline position.

Sail Centre too far back relative to CLR – Weather helm

If the Sail Centre is too far back the boat will want to point up towards the wind in gusts and the tiller will have to be pulled hard to windward, particularly in gusts.  This is called weather helm.

A small amount of weather helm is OK or even good.

For light boats with pointed bows and transom sterns which depend on the weight of the crew to hold them upright, weather helm can also be caused by heeling too much.  So if you have weather helm problems a combination of leaning out harder, sailing closer to the wind so the sails partially luff and easing the mainsail can help sail the boat level.  Some always say that they are not heavy enough to hold the boat upright, but such people are often passed by lightweight crews that keep their boat level through practiced handling.

In strong winds weather helm can be reduced in a daggerboard boat by pulling 6 or 8 inches of centreboard up when going to windward.

With a swinging board you can swing the board a little further back or ease the mainsail to get the correct balance.

Apart from stretching your arm if the centre of the sail is too far back the boat will not like to tack easily and sometimes get stuck halfway through head to wind.

Sail Area too far forward relative to CLR

This is generally quite bad for sailing performance.  It feels like you have to push the tiller away continually to keep the boat going to windward.  It will often stall when tacking, not quite getting head to wind before it stops and then fall back quickly onto the original tack when you try.

If the boat has a swinging leeboard or centreboard you can swing the board more forward to help balance the sail.

In most other cases you have to bring the mast further back or move the centreboard or leeboard further forward.

Special note about leeboards and helm balance

A single Leeboard boat is an interesting exception to the normal way we calculate the relationship of the CLR and Sail Centre.

The drafting or calculation method is a pure 2D method, which is why it always has a fudge factor that is a bit different for every designer.  It is an OK method when boats are symmetrical.  But when a boat has a single leeboard the 3D situation needs to be addressed.

The 2D method assumes that the force from the sail when the boat is going upwind is purely lateral.  But in reality it is lateral but also somewhat forward.

Think of the case where we position a leeboard on the leeward side of the boat using the 2d method.  Because the sail is directing power forward as well as sideways the power arrow would go in front of the leeboard.  Lee helm!

Now put the single leeboard on the windward side.  The same arrow has its nose pointing forward slightly, so its tail end would be already pointing behind the leeboard.  Weather helm.

So a boat with a single leeboard will change from having weather helm on one tack to lee helm on the other.

We know in general that lee helm where the sail is too far forward is bad for performance and some weather helm is OK.  So I work out the relatioship of the sail centre and CLR as per normal but then either move the sail back slightly or the leeboard forward to compensate.  With a swining leeboard you can often compensate for both with different angles of the board.

The wider the leeboard is set from the centreline, the more this adjustment will have to be.

Reefing and Helm Balance

These two sails are designed so the Sail Centre will not move much forward or aft if the sail is reefed.

Boat Setup – rope types, tensions, how to rig.

Even with boats following my plans carefully there are sometimes problems in the way the boat handles.  In every case this has been solved with a bit of tuning up.

First the sail must look in about the same position relative to the mast and for the angle of the sail’s front edge with the mast should match that of the drawings below.  You can move the sails a little forward and back to get better balance, but it is no more than a couple of inches (50mm) either way before you start having problems.

Also recommend following the general lug rig rigging guide here – bookmark it as you WILL need it later.  The only area that might not be relevant on those pages is the mainsheet which should follow what your designer recommends, but with a sliding traveller as in the link.

It is worth mentioning and repeating the importance of setting up the downhaul with light tension when the boat can barely move.  A lot of tension once the boat had reliable speed and enormous/bizarrely high tension when the wind is strong.

There is an extremely helpful pictorial on the rigging steps and setups for a lug sail on the OpenGoose group

It is worth mentioning and repeating the importance of setting up the downhaul with light tension when the boat can barely move.  A lot of tension once the boat had reliable speed and enormous/bizarrely high tension when the wind is strong.

Adequate Centreboard or leeboard area

Several people have asked if a sail from ReallySimpleSails will make their boat go better.   But it won’t work if other things are wrong.

You can use the information in the Boat setup to improve your current sail setup.  If you need a bigger sail or your existing sail just looks bad even following our setup instructions, then an RSS made sail might well help.

However, one area where a little bit of work makes a huge difference.  For boats that suit these sails, I would consider any of them to have inadequate centreboard or leeboard area if its dimensions below the bottom of the boat were much less than 2.5 ft deep (750mm) and having less width than 10 inches (250mm).  In that case a bit extra on the bottom of the leeboard or centreboard might make a lot of difference too.

Hull Shape Considerations

I have two drawings below, one for each sail.  If you boat is shallow bodied with the transom and the bow not deeply immersed with only a centreboard or a narrow fin keel and rudder (no skegs, keelsonsyou can use these directly.  I have marked a probable range which is likely to be OK for this scenario.

It is based on the assumption that the hull will end up being close to symmetrical in profile

So if your boat fits the type of boat criteria and the hull shape considerations then these drawings provide a ready reckoning possible.

At your own risk of course.

Balance measurements for the GIS 105sq ft sail – for use on other boats

GIS Sail, Goat Island Skiff.  (This drawing and a version in inches are in the PDF file at the end of this article)

Note how the three versions of the centreboard all have the centre of the underwater part of the leading edge through the same point.

Low cost stock sail - balance lug

Balance measurements for the OZ 89 sq ft sail – for use on other boats

OZ Sail – OzRacer Mk2, OzRacer RV, Some PDRacers, OzGoose, Perttu Korhonen’s Ocean Explorer.   (This drawing and a version in inches are in the PDF file at the end of this article)

OZ sail centres

If in doubt the centre of the sail being a little bit further back relative to the centreboard or leeboard is the best choice.  If your boat is longer than these two then the sail centre could be even further back relative to the centreboard or leeboard.  Particularly with the OzRacer where almost any boat will be longer than that 8ft boat.  Putting the Oz sail on a 14 or 16ft boat would allow the sail to be a further 200mm back from the rear position shown.

You can see how the Goat Island Skiff is set up with the centreboard at the back of the range, while the OzRacer Mk2 has the centreboard at the forward end of the range.

The reason for this is that the Goat is easily driven and will travel fast, responding well to the helm.  It is also a shape that will develop a little weather helm when heeled (pointy bow and transom stern).

The OzRacer is a slower boat which will be knocked around more by waves so needs a bit of extra weather helm to stop the nose from being knocked away from the wind.  It is also a trainer style boat so a bit more weather helm makes it more forgiving than the more agile Goat.  The boxy OzRacer shape also means the boat doesn’t generate much weather helm when it heels (not a pointed bow, transom sterned boat) so some extra needs to be dialled in from the start.

Spar dimensions and sizes for the OzRacer sail – one or two person boat with width less than 4’6″

As far as spars for the Oz Sail by really simple sails. If you want to use untapered aluminium tubes – preferably one of the 6000 series alloys (eg 6061) but others might be OK

Mast 60 to 65mm diameter or larger if your boat plan specifies. You need the halyard point to be 3530mm above the deck or gunwale, so you need to add the distance from deck to the bottom of the mast to get the full mast length

Yard and boom – swapping units unfortunately – this is the information on the spars that Brad Hickman used to win the PDRacer worlds a couple of years back

For my balance lug rig I used 6061 T6 tube with 0.065″ wall (approx 1.5mm). The longest length available here in that alloy is 12′ so for the mast I used 12′ of 2.5″ OD with a 2.5 (62mm) foot length of 2.25″ OD (55mm) overlapped 1 foot at the splice to get 13.5 feet total length, 2″ OD (50mm) for the boom, and 1.5″ OD (38mm)  for the yard.

I don’t think tapering the Aluminium mast is at all important – it was an expedience because Brad couldn’t get the length.  Timber spars will have similar diameters to the Aluminium spars, but masts need to have a minimum 12mm wall and most yards and booms will be solid in this size of boat.  Mainmast tapering is highly recommended to save weight and it is easy to achieve with wood.

On bigger, wider and heavier boats the mast will have to follow the specification in the plan.  And the yard and boom diameters increased by 3mm or 1/8″.

PDF file with all information on sail dimensions and centres in metric and imperial



16 thoughts on “Using Really Simple Sails on other boats. Advice and dimensions

  1. […] Our sails on other boats […]

  2. […] Our sails on other boats […]

  3. I have a question: For the Oz sail the halyard point needs to be 3530 mm above the deck/gunwale from what I can see, but what distance does it need to be for the GIS sail?

    • Hi Alex,

      The GIS halyard point is 4380mm above deck. The sides of the boat come up 200mm higher than the deck, but are low enough to not interfere with the boom’s range of movement.


  4. I have a question: I am looking at putting a lug sail on my El Toro if it is possible. The boat length is 8ft. The center board is 780mm behind the mast. Based on my reading, the canoe/dinghy sail will not work, however the Oz sail might. Any advice?


    • Hi John,

      I think that none of our sails really suit the El Toro at this stage. The normal sail area of the boat is 50 square feet. A lug rig often means you can carry a bit more sail as the sail is quite simple to reef.

      However with the normal El Toro sail at 50 square feet our canoe sail at 36 or the oz sail at 89 are just too far away from the normal range.


  5. James Buttrey says:

    Hi John
    I am currently building a 16′ Grand Banks Dory from (it’s the Nova Scotian). The plans call for a Sprit and jib but I would like to install a lug. Any help in this area would be appreciated. Length is 16′ 2″, beam is 4′ 10″, and it weights about 190 lbs.


    • Hi Jimmy,

      Edna asked me to look at your info.

      I looked at the online page for the Nova Scotian. I don’t think any of our sails will be suitable.

      The two big sails are too large and the canoe sail is too small to move the Dory along well.

      Sorry about that. But thanks for checking with us!

      Best wishes
      Michael Storer

  6. Hello, I am currently building a 16 ft lapstrake Whitehall with a centerboard based on a Chapelle design. I have seen several of these rigged with a balanced lug and was curious if you thought the GIS sail might be appropriate. Length is 16 ft, beam 4’10”, weight 350ish?

    • I think the GIS and Oz sails will be too big for the Whitehall. The normal whitehall hullshape doesn’t have a lot of stability. I think if you chose an Oz sail, the sail would have to have one or two reefs in most of the time.

      This is also a characteristic of most good rowing boats and canoes. They give up stability to reduce drag so they can achieve good speeds rowing.


      • Thanks Michael,

        After some wishywashying, I have decided to just use a spritsail of small dimension as Chapelle shows on his chandlery Whitehall of that size. I wanted to run more sail, but as you said the Whitehall is tender. That’s okay, she’s a beautiful rower with an auxiliary sail.
        Thanks again,

  7. Donna Saperstone says:

    Hi! I am interested in putting a lug sail on my 12 foot Snark Sunchaser II. I like the lug sail because the yard and boom will be easier to stow than the lateen spars that I now have. I like the Oz sail, but I am concerned that I may have too much weather helm with it. The mast is only approx. 30 inches in front of the daggerboard. Also, the mast is 9 feet 9 inches above the deck. Will the Oz sail be a good choice for my boat? Thanks for your help!

    • Hi Donna,

      The centreboard of the Snark Sunchaser is around 200mm further forward than the one on the OzGoose and OzRacer RV. However both of these boats have a second mast position 186mm closer to the centreboard and they work OK in that position.

      By working OK I mean that with the flat bow of the Goose and OzRacer you need a very neutral helm to enable steering around the biggest wave crests when racing. But with the mast in the aft position there is a little weather helm making it a little harder to steer a few degrees downwind to avoid wave crests.

      The pointy bow of the Snark would mean that you are unlikely to need to steer down and the weather helm would work OK.

      The other thing is that the mast height above the deck for the Oz sail is 3700mm.

      The halyard block or eye position on the mast would be about 50mm below that. There would be no need to trim the mast above that … so if the Snark mast is longer above deck (I think it is) it won’t need to be trimmed … just a small fitting on the back of the mast at that point.

      Hope that helps


      • Donna Saperstone says:

        Thank you for your reply. I can see that my mast (9 feet 9 inches) will be too short for the Oz sail. Too bad, I would like to have tried it. Thanks again!

  8. […] Affordably Priced Sails for Storer Boats and other boats too – see this article to see if the stock Really Simple Sails might be suitable for your boat. […]

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