Thread: Sail design

If you want a rig which is a bit more efficient than a spritsail, but don't want to make a new mast, a gunter rig, similar to a Heron, with a small jib will do wonders for your windward ability. The text which had the lowdown years ago was "Build Your Own Sails" (or something like that) by Bowker and Budd, if you can find one in your council library or second hand bookshop.

I am wondering about sticking with a spritsail and adding a jib.

Thanks guys.

I'm thinking that the first step would be to put a boom on the spritsail and see if that helps.
I'll see if I can get the bowsprit worked out this weekend.

Howdy Clinton,

The Catspaw is a real classic, designed originally by Nat Herreshoff and redrawn by Joel White. It was originally a lifeboat for a very large yacht, but was rigged with a small sail for basic sailing ability.

Having the sail in the right place relative to the centreboard position is probably the most important determinant of windward performance. Putting a jib on it would require adding a similar area to the back of the mainsail to retain balance as the boat is well designed in the first place and the sail is currently in the right position.

In general a single sail is almost always more efficient than two sails except for reaching, but much more important than the choice of sailplan is setting it up properly. Many of the traditional sailplans are very close to the efficiency of the modern stayed two sail rig if set up properly.

Adding a jib always requires the adding of sidestays if you want to keep the jib luff straight and also the bits and pieces to control and attach the jib. Additionally two sails are usually 50% more expensive than a single sail of the same area. So there is a surprising amount of cash consumption for a performance improvement that can be almost free in comparison.

Traditional vs Modern ... there is very little fundamental difference in performance if both are set up properly according to modern thinking. The only place a modern rig gets additional performance is through expenditure on bigger sails and elaborate control systems. However you can get the benefits of the elaborate control systems very easily and simply if you know what you are aiming for.

So the rig itself is not a problem .. so lets look at the fundamental limitations of the boat and work out the best way to deal with them.

The Catspaw has poor upwind performance for three reasons, plus maybe some others based on how you are setting up the rig to go sailing. Don't despair with the first point .. there is still a lot you can do.

1/ The centreboard is VERY small. This is the single most important basic reason for poor upwind performance in "traditional" designs. The chap who redesigned the catspaw put a very small centreboard in it. It has almost half the area needed for good upwind performance.

http://www.woodenboatstore.com/images/400012.jpg

There are two options

The first is a sailing style one ... don't try to point super high ... always feel the speed of the boat ... if it starts to feel slow going upwind when there is wind about it is usually because it is going too slow. Ease the sails a little, get the boat moving and then try to point up again.

The second is to optimise the little centreboard that you have now. on shore lay the boat on its side and see if there is any limitation to prevent the centreboard going down as far as it possibly can.

I am really bad at counting so ..

Final is to check the shape of the centreboard. The difference between a mirror polished foil shaped by eye according to theory compared to one made with a template and brought to the same finish is that the one made with a template is about 10% faster. So if it is poorly shaped or poorly finished it is going to make it very difficult to get going well upwind.

2/ The original rig is boomless - no boom on the sail. This is the single biggest area for improvement. Put a boom on it.

Having no boom means no accuracy for the sheeting angle and no control over the depth of the sail and most critically, very poor control over the TWIST of the sail. Twist is the single most important performance factor and is responsible for almost all the performance increase of modern rigs compared to traditional ones. You get the twist of a traditional rig to be similar to a modern rig and the performance is very close to identical. And for a particular boat the traditional rig might have considerable performance advantage in some areas. For example, whatever you do a jib will not work efficiently downwind compared to putting the area in the mainsail.

The only reason to have a boomless rig is for a boat that is really quick and easy to set up where you don't care much about sailing performance. The sail bags when you ease it in a gust, it bags on a reach and you get only about half the projected area when you head deep downwind. The only exception is some high performance multihulls that have special tracks that circle the mast and allow accurate control of twist.

This is the single most important improvement you can make.

More here Tuning and setting up lug and sprit sails and rigs for performance - Michael Storer Wooden Boat Plans

3/ The sail area is quite small. This is not necessarily a huge problem ... after all the boat will start going better in stronger winds ... but currently it won't because that is exactly where the boomless rig lets it down.



You could get a bigger sail made, but I would really recommend you sort out as much as you can with the existing sail. I've run into similar problems with other boats before and there has almost always been a lot of performance to be gained by making little changes as I am suggesting.

MORE.
Once you have a boom you need a light traveller going across the boat (4mm synthetic rope) this allows a block to slide across. It is important for upwind performance that the angle of the boom ends up at about 10 degrees from the centreline. Well worth measuring. This won't give much performance by itself, so it not worth doing without adding a boom. So with the traveller you just tie a knot in each side to make sure the block sliding on it will stop when it hits the knot at 10 degrees from the centreline.

Another later thing that could be considered is adding a boom vang ... but I would like to see how you can get the boat going without it. The knots on the traveller are having the same effect at this point.

Mainsheet should not be too thick. With a little sail like this 6mm is probably enough, but if really concerned then 8mm is heaps. Make sure the blocks are a little oversize so the rope goes through them very easily. This slight oversize is much more important than having ball bearing blocks - it reduces basic friction in the system.

Steering - fit a tiller extension to the tiller so you can put your weight on the gunwale when the wind gets up a little. This will give you much more power. Get used to steering solely with the extension and your sailing and boatspeed will improve. It often feels strange at the beginning, but one thing humans are good at is to keep going until they get used to the new method .... then they are very reluctant to change back to the old one.

This is perhaps more powerful than the combined needs for food, shelter and procreation!?

Give these things a go .. it will make a huge difference and almost all of them will make a very significant difference, particularly adding the boom, both for its own sake and also for the other tweaks it makes possible.

The improvements will also apply to any new sail. The only thing I would suggest is to make the boom a bit longer than you really need as it may be useful for the next development if you choose to change the sail. In any case ... it is just a piece of wood.

Best wishes

Michael Storer

Howdy Clinton,

The Catspaw is a real classic, designed originally by Nat Herreshoff and redrawn by Joel White. It was originally a lifeboat for a very large yacht, but was rigged with a small sail for basic sailing ability.

Having the sail in the right place relative to the centreboard position is probably the most important determinant of windward performance. Putting a jib on it would require adding a similar area to the back of the mainsail to retain balance as the boat is well designed in the first place and the sail is currently in the right position.

In general a single sail is almost always more efficient than two sails except for reaching, but much more important than the choice of sailplan is setting it up properly. Many of the traditional sailplans are very close to the efficiency of the modern stayed two sail rig if set up properly.

Adding a jib always requires the adding of sidestays if you want to keep the jib luff straight and also the bits and pieces to control and attach the jib. Additionally two sails are usually 50% more expensive than a single sail of the same area. So there is a surprising amount of cash consumption for a performance improvement that can be almost free in comparison.

Traditional vs Modern ... there is very little fundamental difference in performance if both are set up properly according to modern thinking. The only place a modern rig gets additional performance is through expenditure on bigger sails and elaborate control systems. However you can get the benefits of the elaborate control systems very easily and simply if you know what you are aiming for.

So the rig itself is not a problem .. so lets look at the fundamental limitations of the boat and work out the best way to deal with them.

The Catspaw has poor upwind performance for three reasons, plus maybe some others based on how you are setting up the rig to go sailing. Don't despair with the first point .. there is still a lot you can do.

1/ The centreboard is VERY small. This is the single most important basic reason for poor upwind performance in "traditional" designs. The chap who redesigned the catspaw put a very small centreboard in it. It has almost half the area needed for good upwind performance.


I just observed the chap in the pic is putting some downward pressure on the mainsheet with his hand directly to overcome some of the sail twist control problems. mentioned below

There are two options

The first is a sailing style one ... don't try to point super high ... always feel the speed of the boat ... if it starts to feel slow going upwind when there is wind about it is usually because it is going too slow. Ease the sails a little, get the boat moving and then try to point up again.

The second is to optimise the little centreboard that you have now. on shore lay the boat on its side and see if there is any limitation to prevent the centreboard going down as far as it possibly can.

I am really bad at counting so ..

Final is to check the shape of the centreboard. The difference between a mirror polished foil shaped by eye according to theory compared to one made with a template and brought to the same finish is that the one made with a template is about 10% faster. So if it is poorly shaped or poorly finished it is going to make it very difficult to get going well upwind.

2/ The original rig is boomless - no boom on the sail. This is the single biggest area for improvement. Put a boom on it.

Having no boom means no accuracy for the sheeting angle and no control over the depth of the sail and most critically, very poor control over the TWIST of the sail. Twist is the single most important performance factor and is responsible for almost all the performance increase of modern rigs compared to traditional ones. You get the twist of a traditional rig to be similar to a modern rig and the performance is very close to identical. And for a particular boat the traditional rig might have considerable performance advantage in some areas. For example, whatever you do a jib will not work efficiently downwind compared to putting the area in the mainsail.

The only reason to have a boomless rig is for a boat that is really quick and easy to set up where you don't care much about sailing performance. The sail bags when you ease it in a gust, it bags on a reach and you get only about half the projected area when you head deep downwind. The only exception is some high performance multihulls that have special tracks that circle the mast and allow accurate control of twist.

This is the single most important improvement you can make.

More here Tuning and setting up lug and sprit sails and rigs for performance - Michael Storer Wooden Boat Plans

3/ The sail area is quite small. This is not necessarily a huge problem ... after all the boat will start going better in stronger winds ... but currently it won't because that is exactly where the boomless rig lets it down.



You could get a bigger sail made, but I would really recommend you sort out as much as you can with the existing sail. I've run into similar problems with other boats before and there has almost always been a lot of performance to be gained by making little changes as I am suggesting.

MORE.
Once you have a boom you need a light traveller going across the boat (4mm synthetic rope) this allows a block to slide across. It is important for upwind performance that the angle of the boom ends up at about 10 degrees from the centreline. Well worth measuring. This won't give much performance by itself, so it not worth doing without adding a boom. So with the traveller you just tie a knot in each side to make sure the block sliding on it will stop when it hits the knot at 10 degrees from the centreline.

Another later thing that could be considered is adding a boom vang ... but I would like to see how you can get the boat going without it. The knots on the traveller are having the same effect at this point.

Mainsheet should not be too thick. With a little sail like this 6mm is probably enough, but if really concerned then 8mm is heaps. Make sure the blocks are a little oversize so the rope goes through them very easily. This slight oversize is much more important than having ball bearing blocks - it reduces basic friction in the system.

Steering - fit a tiller extension to the tiller so you can put your weight on the gunwale when the wind gets up a little. This will give you much more power. Get used to steering solely with the extension and your sailing and boatspeed will improve. It often feels strange at the beginning, but one thing humans are good at is to keep going until they get used to the new method .... then they are very reluctant to change back to the old one.

This is perhaps more powerful than the combined needs for food, shelter and procreation!?

Give these things a go .. it will make a huge difference and almost all of them will make a very significant difference, particularly adding the boom, both for its own sake and also for the other tweaks it makes possible.

The improvements will also apply to any new sail. The only thing I would suggest is to make the boom a bit longer than you really need as it may be useful for the next development if you choose to change the sail. In any case ... it is just a piece of wood.

Best wishes

Michael Storer

Thanks Michael.
Apologies for the long time between your post and my response... I had to cut some activities out due to other committments.

I readily understand your comment about the sail 'bagging', and adding a boom (and changing the sheeting) and tiller extension are probably the easiest changes for me to make. (once work slows down)

The centreboard was sticking up in its case a few months ago, and I sorted that out... and it does go all the way down.
I'll leave the centreboard 'issue' until last and see how I go with the boom first.

Again, thanks for the detailed reply, very much appreciated.

No wuz!
Mik

Originally Posted by Clinton1

I'll leave the centreboard 'issue' until last and see how I go with the boom first.

Clinton, I don't know how long the foot of your sail is, but I have a 2 metre length of oregon with a boltrope groove in it that you can have for free, which might help.

Originally Posted by Clinton1

Thanks Michael.

I'll leave the centreboard 'issue' until last and see how I go with the boom first.

.

Clinton,
I also have an old, but good, centreboard from an NS14 which you are welcome to have to play with. From the look of the pictures, you would have to open the top of the centrecase and convert the board to a dagger type to get the extra length needed and you could probably cut the board down a bit if it was too long, but that would give you the extra area without having to make a longer case.

could you pm me with a phone number please Graemet?