Will RSS Stock Lug Sails Work on my Boat, check boat balance, spar lengths, sizes.

Our stock sails are used on different boats and are available off the shelf at reasonable prices In North America, otherwise we make and ship any sail/s worldwide. This page gives a guide to suitability of the stock sails for your boat, the spar lengths, spar cross sections that can be used on your boat and goes through some of the choices for aluminium spars, timber spars and cost effective carbon spars to match our stock sails.

First .. where to get the sails, then after that all information to assess suitability and then set up your rig with our sails.

Really Simple Sails Suppliers and Availability

Order from Us – Online Enquiry Form for Stock or Custom Sails of any specification.

Stocked by Duckworks USA – Click for list – Full Range – Five lugsails

Arwen Marine France – Arwen are a new stockist and still building their stock.

Guidelines for Sail Area and Balance to assess sail suitability for your boat.

The most critical component of setup is to get the balance of the boat correct – drawing right is an example of how different foil configurations can have the same centre.

The best way is to scale it from the designer’s drawing. But I will provide some guidelines below.

If the centre of the sail area is in the right positions relative to the position of the centreboard, leeboard or keel then the boat will be a pleasure to sail.

Get it wrong and the boat will be a cranky pig.

To test the balance of an existing boat sail it flat with no heel in flat water and steady breeze and see if you have to do much pulling or pushing on the tiller to keep it in line.

The table below has the distances between the mast partner and the sail centre for each sail in the design position.

The second table shows typical distances between the centreboard or leeboard and the mast. Note that the centreboard/leeboard leading edge is measured in the elevation view and to halfway down the underwater part of the foil.

NOTES
There is no substitute for working from a scaled drawing from the designer where the centre of the sail is marked. Or seeking their OK.
THIS ASSUMES A SINGLE SAIL AND MAST IS NOT HEAVILY RAKED
To Convert mm to inches divide by 25.4

If using two sails then it will have to be worked out on paper. If there is a mizzen it is normal to only consider 50 to 60 percent of its actual area. By underestimating the assumption is the mizzen will be slightly luffing. This allows the mizzen to be trimmed in to tune in the amount of weather helm you want to sail with.

Range of Centreboard or leeboard position relative to mast relative to sail.

The maximum position here is about as far back as you can push a single sail.

If under the existing rig on the boat it has weather helm in 10kn of wind, smooth water and being sailed without heel, then it is practical.

Second figure is for more practical “average” position for a single sail setup.

Third figure is for a leeboard on a dinghy. Leeboards need to be a bit further ahead of a centreboard. The table below gives an approximate guideline. Not so critical if the leeboard pivots as the approx distance can be corrected by adjusting the leeboard rake.

They will have a little bit more weather helm on one tack and a little bit of lee helm on the other.

So this position sets them up with a little extra weather helm. Convert to Inches by dividing by 25.4 (Don’t convert boat plans this way – but ok for a single linear measurement).

Mast Lengths above deck to go with Really Simple Sails Stock Sails

There is usually a need to change the length of the mast ABOVE THE MAST PARTNER to match the new sail. Table below. See notes at the end about Carbon options.

There is usually no need to change the diameter of the mast, even if the sail is larger than the original sail.

The reason for this is that the responsibility of the mast is to be strong enough to capsize the boat without breaking. The cross section of the original mast should have been designed to do this.

When the boat is lying down the mast is unstressed.

A larger sail means that the boat will lay down (be overpowered and capsize) at lower windspeeds. The mast only needs to be strong enough to make the boat lie down and stiff enough to give the boat good performance.

If the stability of the boat is changed – ballast keel changes, bigger crew hiking out hard, then the mast might need to be enlarged. Very small amounts of diameter increase are needed to strengthen and stiffen a mast substantially. Sometimes as little as 3 to 5mm extra cross section.

IMPORTANT NOTES
LENGTH SHOWN IS NOT TOTAL MAST LENGTH – ADD THE ABOVE PARTNER/DECK MEASUREMENT TO THE BELOW PARTNER/DECK MEASUREMENT FOR TOTAL MAST LENGTH
To convert mm length to feet divide by 305.

If you wish to build a lighter hollow mast a cheap way of getting drawings to work from and a full method explained is to use the Oz Goose Plans. There is a simple to build hollow square mast that is well proven, also details. It can be scaled up to suit other boats using their existing mast diameter as a guideline.

https://www.duckworks.com/product-p/oz-goose-id.htm

Yard Cross Section and Length

LINK – Here is one of the few sources of actual measured information on actual spar bends across a range of boats of the same type.

The Yard stiffness is critical to boat performance.

These are the sizes from our boat designs.

If the boat is heavier, significantly wider (eg a dinghy rather than a canoe), heavier or has more crew or a more active crew than the boat it is designed for a slight increase in the diameters recommended is acceptable.

IMPORTANT NOTES
For a more stable or heavier (over 300lb hull) monohull, add 2mm to the yard diameter.
Taper Option – follow taper schedule of the hull plan
For a multihull add 5mm to the yard diameter
To convert from mm to inches divide by 25.4

These sizes are for Spruce, Fir and Pines of similar density to Fir.
Aluminium tube of a similar diameter can be used. Recommend wall thickness of 1.5mm (0.06”).

Boom Length and Stiffness for standard RSS sails

Main consideration is that some booms are laced and some are loose foot

The Oz Goose and Goat Island Skiff can be set up either way

The other sails are loose foot with no lacing possible.

Loose footed is best for performance but need a stiffer boom. If your boat has a laced boom can convert to Loose foot by adding 9mm depth to the boom design that came with the hull as long as most of the blocks on the mainsheet are attached to the back end of the boom

There are examples of lightweight wooden boom construction for loose foot booms in the GIS group on Facebook – Good for the Oz Goose and Goat sails. Ply sided hollow boom and Ladder Frame Boom. Important with the ladder frame boom to put any loops for downhaul or other attachments around the whole boom and not just the bottom rail
https://www.facebook.com/groups/GoatIslandSkiff/files/

NOTES
Convert length to feet by dividing by 305
Convert cross section to inches by dividing by 25.4
For existing boats can just change the length of the boom using the rig design that came with the hull keeping the cross section
All Booms can be tapered 350mm/14” can be tapered Rear 1000mm/40” can be tapered

Suggested Aluminium Boom Dimensions for Lug Rigs

Ideal wall thickness 2mm/0.08” or slightly larger. 1.5mm would need an internal sleeve in areas of maximum load

Lightness of Aluminium tubes makes booms suitable for laced and loose foot.

Carbon Masts for Sail Boats are Becoming Affordable in some Regions

Carbon Masts are still pricey. Recommend a minimum of 3mm wall thickness and will need some extra glass around the partner area. 2.5 can be OK. 2mm with care and reinforcement of load points by wrapping glass cloth in those areas (step, top and around the partner area).

Why Windsurf masts are not suitable for most boats.

This is a very big mistake for unstayed masts on boats much bigger than a canoe. Diameter is king in determining stiffness and small reductions in diameter reduce the stiffness considerable. For an oz Goose sized boat (12ft) a windsurf mast will be too flexible by a factor of 3 to 4 because a windsurf mast is a reduction of stiffness by a factor of 3!

Some say just add more carbon as a sleeve. This is also a mistake as to increase wall thickness to make a mast three times stiffer means making the wall three times thicker than now.

Result – a carbon mast that weighs more than a correctly designed wooden mast, costs more in carbon and resin and is a lot of messy labour. A comparison of mast diameter for wood and carbon is below.

If wanting to make a carbon mast yourself – start with the correct diameter and follow sophisticated carbon mast home building techniques as used by the UK Cherub Boat Class. Choose the correct starting diameter is essential if you want a light mast and optimise the amount of carbon. Excess weight is expense and labour and makes a timber mast much more competitive in those areas.

Link – Windsurf masts do make quite decent Yards and booms for boats with sails from around 50sf and up.

Important that manufactured carbon tubes have some woven or braided component. Some are pultruded which will split. The addition of cloth (braided or plain weave) in the manufacture will prevent pultruded tubes from splitting.

To give a ball park figure, the hollow square timber mast of the Goat island skiff compared with a carbon mast of the same stiffness. This is for a freestanding mast. If you have an existing timber mast you can scale directly. But follow the note about the wall thickness above. Too thin and the spar becomes fragile.

* We are still experimenting with carbon mast alternatives. Some carbon mast have been down to 2mm wall which seems satisfactory but some say they are a bit bendy. We probably recommend 2.5 to 3mm for masts and yards and booms can be 2 to 2.5mm wall.

Given a Wooden mast diameters or cross section, a carbon mast can be smaller in diameter by the same proportion as the example above. We have directly compared the stiffness with wooden masts for the same boat. But be aware that the wall thickness cannot be reduced much. The Viola, Oz Goose and Goat Island Skiff will require a wall thickness of 2 to 3mm or in many cases use recycled carbon windsurf masts for yard and booms. The smaller sails can go down to 2 minimum

Cheaper Sources for Carbon Yards and Booms for Sailing Dinghies

A cheap solution is to use a carbon windsurfer mast. This has been done satisfactorily with the Goat Island Skiff and is recommended for the Viola 14 Sailing Canoe.

The cheapest option is a 50% carbon windsurfer mast of sufficient length to get the yard and the boom from it for up to Viola size sails. Goose and Goat sails will probably require one windsurf spar for the mast.

Here is an online article about getting a yard that matches the properties of the designed wooden spar.

Rigging Details for Lug Rig

We have worked out some great methods of doing economical and effective rigs with a minimum of fittings. There is little performance sacrifice as this setup is used for racing our fleet of 74 Oz Geese in the Philippines.

Two most critical setup requirements

Low stretch halyard and downhaul. 4mm Spectra or Dyneema with polyester outer for both for all sails but GIS.

5mm halyard for the GIS sail but all other lines can be 4mm.

Some Plans From storerboatplans

These are the boats the sails are designed for originally if looking for images of how they look when set up correctly

See our list of boat plans.