Little flattieboat with twin skin sprit sail

[messabout]

The last picture shows the flotation bags lashed to the floor. They are also located far aft. The bags will no doubt displace enough water to float the entire boat. When placed aft as in the picture, the back of the boat will remain afloat but water will run toward the bow of the boat, potentially sinking the bow. The flotation bags need to be centrally located, but in a boat of that size the bags will not allow the skipper to move from side to side enough to counteract heel. The skipper might possibly be able to sit atop the bags as needed.

My flattie/skiff/ sharpie is 4.8 meters x 1.3 meters, it's flat bottom is one meter wide. It has a 5.5 square meter sprit boomed sail and an alternative 7.5 meter square lateen rig. The boat goes like a bandit with either sail. The sprit boom is my usual go to rig for its simplicity and ease of storing. Wind the sail around the free standing mast and the job is done. I have some lines wrapped around the base of the mast and the ends led aft to cleats. By pulling the correct line the mast will rotate and douse the sail entirely. Pull the other string and the sail unwinds from the mast.

I have never capsized the boat in all these 15 years. I am a light weight guy of about 72 kg and the boat has been sailed in some vicious weather with out dumping it. I do have some flotation foam blocks that are sufficient to keep the boat afloat if capsized. The foam is placed at the approximate center of gravity of the boat.

I am being a hard head and continue to insist that a simple sail with light spars are the best option for old guys like me (and you). The sprit boom keeps that weight down low where it makes the aloft weight modest. Every centigram aloft matters because of leverage which magnifies inertial forces.

My book; The Encyclopedia of Wood, does not list Paulownia or KiriKiri. The closest one I could find was Obeche, which is light, fairly strong, and has color similar to that of your boat. Perhaps Paulownia has a different name when translated.

Best wishes to you from another old sailor in Florida, Dieter51

 

[Dieter51]

Thanks for this answer, there is also a flotation bag in the front. I will send a photo. It is rough calculated, that if I stand behind the thwart, it should float horizontally- swamped. But I'm late this year, and still have to test it.

 

[Dieter51]

Opps, Id did nor want to end. Anyway, Paulownia is also called Kiri Kiri, maybe you know it under that name? Everything is fine with that wood, you can work with it, as if it would be hard foam. And once oiled with a special oil, which gives a rough instead a slippery grip, you are ready with such a boat within a week, if yo want to. We glued with epoxy, a good D4 adhesive will do the same job - in Germany Bindulin D4. But we had to cover it with glass and epoxy, because the sheets were only glued together with an D3 adhesive. I would never build a boat like this in ply, epoxy and stich and glue. My body does not like it.

The boat I had from 2000 till 2017 was light and about 4,1 m x 1,3 m with 9 sqm sailarea. I never capsized. It was the flattie which made me swim - or the years and its special behaviour.

The sprits of the sail are now very light, but the weight for the doubled size to hide the spare is still increased. I have no shop where I could shape a free standing mast, I had a guy to build that boat with me in a rural building. And I wanted to know, if the spar (mast) can be made out of Paulownia - without problems. The aim was, to be able to build a boat in a short time from one type of wood, 1,8 cm sheets. That is possible and it is much more easy than with other materials. I have built some boats from ply and polyester, 50 to 45 years ago.

Next week I'm done with other duties and have time to sail this little boat and test it.

I read about you and your boat years ago and you mentioned, that those boats are nearly all the same after the long time in service. I think that is true. I guess it was your writing, which convinced me years ago, to build such a boat, but only the Paulownia-wood made it become a reality.

Best wishes and good health

Dieter

 

[Dieter51]

Are there photos from your boat, messabout?

 

[messabout]

I will try to find some photos and post them.

Goldilocks is a boat that I designed and built a few years ago. The lines were drawn such that it is better as a one person boat, or lightly loaded. That implies that I have limited the rocker, particularly aft. The whole idea was to have a near straight run and sufficient rocker to clear the transom when at low speed, as in light airs. I tried to keep the angle of the run at a minimum that would allow the transom some clearance when at low speed. The notion was to let the boat plane readily, which it does when the breeze is above 10 or 12 knots.

I called the boat Goldilocks because it is too wide for rowing and too narrow for carrying a lot of sail or carrying a crew. It does row nicely but is certainly not the best for that kind of propulsion. Rowing, I can maintain about 3.3 knots, and for short bursts about 4.1 knots. I have an oarlock at the transom to use when sculling. I mess around with a sculling oar just for fun. I have experimented with a yulow without much success. The boat planes happily, with my little 2.3 HP Mercury outboard. I do not use the outboard often because I dislike the noise.....and stink.

Flat bottomed boats have the most wetted surface of any bottom configuration. That is not ideal but the wet surface can be reduced significantly when the boat is heeled. It can be argued that the flat bottom in heeled attitude has less wet surface than a similar size, vee bottomed boat would have when heeled. That suggestion could make for some interesting arguments. The flattie will pound when upright but will become quiet and reasonably smooth when heeled ten degrees more or less. Encountering a big wake, from powerboats, makes deliberate heeling a standard practice.

 

[Dieter51]

I tried to stay at 3 square meter max wetted area due to the very low winds here in southern germany. I concentrated the volume in a way, that sitting forward gives a transom well over the waterline, also when heeled, and it should give a rather flat bottom, if the boat rises the bow to glide. Perhaps not the best decision. With 12 knots it will glide with 2 people, but it is another feeling than in other boats. Usually I look behind, to see if the boat fells well. Quiet and flat water with a rising middle line. With my flattie you get the same look everytime, the difference between gliding or not is just the speed, not the look of the water behind the transom. What I really dislike is the feeling of the sail, you get no response from it. It is, as if you would hold a plank in the wind. You feel a force, that's all. The difference between this boat and all I have sailed in my life is astonishing. And if you sit on the wrong side for a second or shorter, when the wind alters sharp the direction, will make you swim beside a swamped hull. The good is, you can enter the swamped hull without any effort swimming on the daggerboard and rising the hull. Then the pump will do her work.

 

[messabout]

Dieter51, when you use the word glide, are you using that word in the same way that I might use the word plane? Translation may be responsible for the difference, or sameness, of the word.

In the general use of the English word glide, it means to sail, slide, coast, or fly along smoothly, hopefully under control. This is not to question your selection of words. Only to know whether we are talking about the same thing or something different. As a matter of fact I think that to glide is pretty much the same as to plane, except for the control part.

With a conventional sail, careful management of the mainsheet can avoid capsizes when exposed to sudden a gusts. Cleating the main when planing/gliding is not advisable as I am confident that you know. When a gust hits a conventional sail, the sail will usually respond by softening the leech a bit, so to spill some of the sudden force. That is why it is sometimes wise to ease the boom vang a little bit. I doubt that your two ply sail is capable of responding in that way. I accuse your double sail rig of causing some of those unwanted swimming exercises.

I love your pretty little boat, but not the rig.

 

[Dieter51]

Yes you are right, my English is terrible when I don't use an automatic translator. I mean to plane, the hull then provides less static and more dynamic lift.

Yes, the sail worries me because it doesn't feel like a normal sail. It gives way in gusts with the top, but not like you see in modern sails which spill out much more than my sprit.

I think I'll look around for a usual sprit sail because I don't want a classic Marconi (triangular) sail. I had that 20 years - photo.

I have read that if you would rather not buy or sew a new sail, it could be a good idea to cut the sprit sail from a larger old jib because you will get a useful shape in the sail.

What do you think of this?

Best - Dieter

 

[messabout]

I think that cutting a jib sail down to make a sprit sail is possible. But only if you manage to find a jib that has appropriate dimensions. Forgive me while I think in terms of antiquated Imperial measure that American so doggedly cling to. Lets imagine that you find a jib with a 15 unit luff and a 5.4 unit foot. the peak angle is 5.4/15 = 0.36 which 19.79 degrees, ignoring the roach.
You could cut off the top so that the luff is 12 units high. That means that the top of the sprit sail would be approximately 4.3 units wide. The area would be about (4.3 + 5.4 )/2 x 12 = 58.2 which is not much sail............lets let the luff be 13 units tall......top shelf will be 4.7 and the arithmetic will give us 65.5 square units..translating that into metric measure it becomes just about 6 square meters. A modest sail but enough to make the boat go pretty well.

If you choose to remodel a jib then you will need to find a jib whose dimensions are appropriate for the dimensions that you want your sail to have. I would not want the peak dimension, the aloft sideways or almost horizontal dimension, to be too large. Keeping the geometric force center of the sail low, will surely be a prudent aim. Here, I am thinking like an old guy who is no longer the nimble, acrobatic, sailor that he might have been many years ago.

In the final analysis, I believe that it will be in your best interest to buy a new, custom made sail, from a reputable sail maker . You would need to search to find a used jib that suits your needs. You will have to pay some amount for that used jib. Then you will have to spend some more money for the modifications, even if you do it yourself. In the end, you cannot be confident that the clever modification will be as good as you had hoped.

I suggest that you shop around for a suitable new sail that will serve your purpose better than some sort of compromised old sail. I am fully aware that the going price for a good new sail is a bit much if your budget is limited. I suspect that 300 Euros will buy a good new professionally built sail of about six M^2. I do know that, for many of us, 300 euros does not grow on trees.

 

[Dieter51]

Hello, I have followed your calculation and you are right. It is not so easy to find a suitable foresail or even a mainsail, because in order for the sprit sail to fit in there without becoming too narrow at the top, the sail must become large. But then it also becomes quite heavy for a 6 square meter sail.

I estimate after first research that a 6 sqm sail will cost me around 500 euros, because 80 euros per m^2 for a sail whose dimensions you don't have in stock is probably the usual price today even for a light sail.

I will have one made over the winter, but must decide beforehand whether the mast will then remain stayed with wires. If not, so if the mast is to stand in a mast partner, then I must take a completely different mast, or sheathe the current Paulownia with fiberglass and strengthen where it stands in the partner.

This season I will probably cut the double sail in half and make a single sail out of it with spars on the outside. I can do that here on the deck of our little house. I don't have a store, that would be much too expensive in Munich, because here in every shed there is an expensive oldtimer and for the price that goes with it, every wooden shed is also rented out.

Yesterday we had 10 kn gusty wind, the hull behaves quite well, but the sail does not feel like a normal sail. You can't use it without looking closely at how it is in the wind, because you never see a difference. This is a bit strange and quite against my previous experience with sails.

On another subject: I haven't rowed the boat yet, the mounts for the oars that came with it are not good. But your speeds are amazing, how long are your oars?

 

[clmanges]

Hello, I have followed your calculation and you are right. It is not so easy to find a suitable foresail or even a mainsail, because in order for the sprit sail to fit in there without becoming too narrow at the top, the sail must become large. But then it also becomes quite heavy for a 6 square meter sail.

I estimate after first research that a 6 sqm sail will cost me around 500 euros, because 80 euros per m^2 for a sail whose dimensions you don't have in stock is probably the usual price today even for a light sail.

I will have one made over the winter, but must decide beforehand whether the mast will then remain stayed with wires.

Off-the-shelf premade sails are a reality; sailrite.com has a great many. Perhaps you could tell them what you want and they might find something close enough to adapt without much trouble. There may be other companies doing this, as well.

 

[Dieter51]

To decide whether to buy a classic square sail from the sailmaker, I will now first make a polytarp sail of the intended size to see if it runs better than with my "identical", but doubled sail.
This is, I think, the most sensible step for me to make at the moment and possible in a short time for no money and there is no need to destroy the double sided sail and other things.

 

[messabout]

On another subject: I haven't rowed the boat yet, the mounts for the oars that came with it are not good. But your speeds are amazing, how long are your oars?

The oars are 7 feet long. 2.13 meters. I made these many years ago of ash wood. They are too heavy. I also made the oarlocks from some stainless steel material that I had on hand. The design of the oarlocks is from a Phil Bolger article from long ago. The string is merely a 3mm cord. one end of the string attaches to the oar shaft, somewhere outboard of the oarlock position. By adjusting the length of the string you can vary the leverage ratio. Also the oarsman can let go of the oars while in rowing position, the oars will then trail alongside the boat. The string keeps them from escaping. If I leave the oarlocks tied to the oar, then I will be able to find them when I want to row the boat. The artwork on the blades is merely a bit of foolishness that does not make rowing any easier.

 

[Dieter51]

The design is pretty, maybe you can't measure the support, but it's there anyway ;-) The Oarlocks are interesting and cleverly thought. When I think of the things that came with the paddles (see picture), you do not like to row with. The screw is not quite tight, so there is play in this "joint" and with each pull it cracks loudly when the oar finds the right angle.... This can be done better.

Yesterday 4-5 Bf from the west, which means some wave for us then. My poor little wife, 48 kg, got a lot of water and had to scoop a lot. We were therefore not out for long. The current sail with open mouth is definitely much worse than the previous one where the sail ran around the mast.

I am curious if the single ply sail (I'm making it out of the existing double sided sail after all because the polytarp stuff seems way too soft to me) is better and if so, how much?

Greetings - Dieter

 

[Dieter51]

It goes on ...

After the sail with an open leading edge was just as unsatisfactory as the previous twin-skin-sprit-sail, I converted one side to a one-skin-sprit-sail. With a mast pocket all around.

The sprits now sit on the outside, fixed at the front in a ball-and-socket joint each adjustable for a variable length at the side of the mast, and at the back the spriets are in a pocket with webbing. The upper sprit is fixed in this sail-pocket and is rolled up with the sail. The mast and sail fit then into the boat and can be easily laid or positioned by one person. Only the forestay is detached.

With the current construction ist would be easy, to attack the sprits with 10 cm distance to the mast.

The sail now works like a normal sail and the surprises of the twin-skin sail (sudden jump in performance) are absent. You can sail well from Bf 2 to Bf 4, at Bf 5 the boat runs better with a crew of 2. The second man should then sit (high on the wind) to leeward - we had 2 x 90 kg.

Sailing is then sometimes a wet affair and once we had taken on so much water that the pump got work. In 1 minute 10 cm of water had been drained - the pump manages about 10 m^3/h on the small motorbike battery.

Actually, I am satisfied with the boat, with the construction in Paulownia anyway. I have built several boats in my student days and I know that after the building comes the painting and that it takes the same amount of time to fill a stitch-and-glue boat. With paulownia you glue the components together, sand over them, impregnating oil, special oil, done. It doesn't take very long, maybe 7 hours to oil the complete boat. So three short afternoons every year, because the oil also has to soak in and dry. Outside in the sun, the surface becomes then even harder and less sensitive.

Next winter- action: The tubes are removed and replaced by short half decks that enclose the same volume without looking as if you had rammed an inflatable boat from behind. Maybe a small self-tacking jib to make the boat faster. Sail area now ist just 6 sqm für a boat 4,5 m long with 55 kg now full equipped. But for its sailarea she is fast.

If I were to plan the boat again, it would be with vertical sidewalls, which is not slower, but the construction is certainly simplified by 1/3 with the 1.8 cm thick paulownia panels. If you paint the sidewalls cleverly, it is not noticeable either.