Low-speed sailboat hull

Hi everybody, I hope you had a great holiday! I was away to London, so my little project was left in dust for several weeks. But I saw the speedy Cutty Sark, which left me in awe.

I came back with several ideas. While traveling, I saw a picture of traditional Nile sailboat Felucca, lateen-rigged, although it has similarities to lug rig. It's yard is raised all the way to the mast top, and never lowered (I think so). I thought that if I forgo the GIS-like halyard attachment, then I can do pretty much the same - raise the yard almost to the mast top, only leaving enough space for halyard block and knot. This would eliminate guesswork about yard swinging, and would require no parrel beads (although they would still be needed when sail is reefed). Sail area is now 7.34m^2.

I also modified the rudder box, so it looks nicer while probably losing no strength.

Here's how it looks.

You're right. I think current compromise is a good one.

I see. But is this really so hard to calculate? It seems like a lever exercise to me. Considering that halyard attachment point is the pivot of the yard and that the yard is of uniform weight distribution, it should be balanced at 50% of it's length, no matter it's angle to the mast. If halyard is attached, let's say, at 40% point, then the back of the yard will swing down, unless the front of it is held by a force (luff tension). The more we move halyard attachment point towards the front end of the yard, the more force will be required to hold the yard in place.

Am I right, or is this far more difficult to calculate? At some point, I'll be making a 1:4 model of my boat, and test where to attach halyard, but it seems to me that it should be possible to estimate accurately with some basic physics calculations. Can it be done?



Petros, if you're reading this, I've considered your advice about boomless sail, and researched it, but came across a problem. It is generally advised that with a boomless sail, mainsheet should be at an half angle between foot and leech, which makes lots of sense. So, in my boat, the sheet should be attached on a point which is about 90cm aft of transom. See this:



To compensate for this, I'd have to move the sail forward, or make the foot shorter. I tried designing this, and it results in a very small sail. The other option would be to make an wooden frame which extends past the transom, and holds the mainsheet block. But it would be very bulky and weird.

Do you, or anybody else, know how can I solve this problem?



There's some more questions I've been meaning to ask. One is the tiller extension. What can be used for tiller joint except for rope (rope can make a joint too lose, with considerable "dead zone")? Using a bolt will provide rotation on only one axis, and can easily break the timber if I'm not careful. Marine tiller extension joints are hard to come by, as well as expensive. What would you suggest?

Another thing is tiller "autopilot". That is, a quick way to lock the tiller in any rudder position so it stays there. You might say that this is unneeded and even dangerous on a small boat, but there have been a number of occasions when I needed the rudder to stay in place while I do something, like adjust sail, eat, or just mess around. It would be very handy in low, steady winds. Of course, I can always lash the tiller with rope, but that is time consuming and hard to adjust once lashed. Any suggestions there?

Looking forward to your replies!

 

Consider a wishbone boom

Google "tiller tamer"

Use a rope threaded through a plastic waterpipe for a tiller extension/joint

Read this book

http://www.timseverin.net/books_sindbad_voyage.html

RW

 

Thank you, but how would I use wishbone boom on lug? I have never seen such an arrangement. Or are you suggesting for me to go with triangular sail?

On tiller tamer, I mostly found this:



Seems too difficult to make myself. This looks simpler, yet I don't know if it's reliable enough:



Or, I could try to go with this idea:



For example, I could lead the tiller extension to the gunwale, and somehow attach it there:



Only that I'd need to make it attachable there at any rudder angle, and as of now, I can't visualize any solution.

 

I was thinking of a one sided "wishbone" no idea if it would work on your rig. A bit of a mess when lowered and rowing I would think

shockcords work to hold the tiller

RW

 

See comments in text.

 

since you will have a boomless rig, you can lower the leech all the way to the gunwales, and move the sail forward a bit (along with moving the dagger board forward with it), to get the main sheet to land near the transom. it means you would have to duck when you tack, but there is no boom, the first full length batten can be higher up, and it will just swipe over your head and back. visibility will require a window in the lower edge of the sail. this is easy to add with duct tape and clear plastic sheet. This will also lower the center of effort on the sail.

I have made very simple tiller extension by putting a loop of bungee cord in the end of a stick. the loop is small enough so it fits tight over the tiller. this allows you to slide it forward or back, or yank it off in a hurry if necessary. It helps to make the tiller deeper near the end (like rounded knob at the end) so it does not slip off unintended. you just cross drill a hole in the end of the extension stick, and put a loop of bungee cord through it, knot on one side and the loop on the other, makes a nice tight universal joint for a small sailboat tiller extension. you can also use a strip of inner tube if you can not find bungee cord, or perhaps a strip of leather.

looks like a good design your are developing there.

 

I decided that since lug sail has it's luff tensioned by downhaul after the sail is raised with halyard, the friction in the mast-top halyard block isn't very important as long as the sail can be dropped without getting stuck.
So, why do I need a block, anyway? It is expensive, takes some space, adds weight, can be tricky to mount on the mast top without damaging wood.
Maybe I can just drill a hole a centimeter below mast top, and run halyard through. This hole would need to be led down a bit so that halyard would run up and down smoother.

This is a cross-cut section view of what I'm implying:



The hole itself could be drilled through easily, but the curve down is something I can't figure out. How can it be done? Maybe it's possible to work with rasp and rough sand paper, but it might be very time consuming. Any ideas how to cut such profile in my mast? I can't be the first to think of this.

I see. This raises another question. When making sail, I know I must anticipate yard bend, and create an appropriate camber in the head to compensate for it, for if I won't, the sail will wrinkle (exactly what happed last summer with my polytarp sail which had it's head straight).

But what is an appropriate camber? My yard will be 4cm diameter, 300cm long, made from single piece of knot-free pine or spruce. No taper. Since the head of the sail is 290cm (leaving 5cm on each end to allow for knots and stretch when bending sail), I planned a camber of 2.9cm, 1/100th of head length. Is that enough, or should I go for more?

That depends on where I'll put the boom vang. I guess the perfect angle for vang is 45°, and if vang attaches on boom 20-25cm away from boom jaws and same distance down on themast (so the vang itself is 35cm long) is enough to give needed leverage, then front crew member can still avoid being hit. 30cm may be too much.

Is 25x25x35cm vang "triangle" enough to give proper leverage?

Sounds a bit lengthy to rig, but I'll keep this in mind if boom vang turns out to be impossible.

I tried designing what you described. The sail results in a massive 8.15m^2. Of course, I can always make mast shorter, and thus reduce sail area to something more manageable.
This boomless arrangement looks like this now:



(Comparison to previous one with boom, where sail area was 7.45m^2):



My concern is that even without the boom, it may be difficult to duck under this sail when tacking, as sheet tension will translate into sail foot tension, making it hard to "carry" over head.

I am also not entirely sure what points can be sailed without the boom. I red that while beating there are no problems, but when running, boom or some substitute is needed. But what about close, beam and broad reaching? Can boomless be effective on these points?

This is a great idea. Thank you very much. I'm definitely choosing this.

Thank you for your compliment! I still have some time until this summer, when I have to start building. There are 20 (or so) problems to solve in my to-do list before I can commit to buying tools and materials to start building. I'll try to solve as much as I can and ask only about the most puzzling issues

 

Dumb sheeve, halyard lead, + hold down horse.

Hi Laukegas.

To make a dumb sheave, you first drill the hole through the mast, then, at each end, you hog the drill downward. Remember. It's only the shape of the bottom of the hole that counts. That is the part the halyard line bears against. Once this hole has been drilled, it should be epoxy coated, with graphite powder added, if possible, so the line will slide through it with less friction.

Unless you plan on having the mast rotate with the yard, you need much more halyard lead (the distance between the hole, where it leaves the mast, and its attachment point to the yard, fully hoisted). You might need 30 cm or more. Otherwise, you may get a lot of chafe, and wear out the halyard in a short time.

The problem with your 45 deg. vang idea is that it attaches too close to the front of the boom. As a result, the boom may bend significantly aft its attachment point. You can, of course, engineer the boom to take this load, but this will call for a much heavier design.

The horse idea I proposed in my last post is really quite simple. It calls for four things:

1.) a line or cable that attaches to two pad eyes on the front of the bench.
2.) a pulley that stays on this line, which has the hold down line attached to it.

(these first two items stay on the boat)

3.) a second pulley, attached to the boom, which the hold down line goes through.
4.) a pair of jam cleats, one on each side of the boat, for the end of the hold down line.

This set up would be used only when the end of the boom rising becomes a problem.

On light wind days, the weight of the boom will probably be sufficient to hold it down.

 

Okay, I'll re-do it into a half-circle profile, like here:



Also thanks for naming this thing. Much more easier to google now!

Well, as of now, there is nothing that would prevent mast rotation. Mast is free standing, and I don't plan on adding anything that would jam it in place.

Why would exactly this halyard wear occur? I am not sure which part would create that much friction...

You see, I want to minimize the halyard lead, because it allows more sail area on shorter mast. Lead is now 5cm now, just enough to allow for a knot. 30cm is quite a lot... Would having mast rotating with the yard prevent chafe? If that's not enough, are there any other solutions apart from having long halyard lead?

P.S. Just found this:



I want pretty much similar thing, except that the halyard attaches directly to the yard. Would you say that this system in this photo is prone to chafe?

So, as I understand, I'd need to uncleat the hold down line and cleat on another side each time I gybe, right?

Also, wouldn't this system also hold boom quite close to the centerline of the boat? (The job for mainsheet). If so, what if I want to let the sail out all the way, like 90°? Will this system allow that?

 

Yes, if the hold down line is long enough. This also depends on how far forward you put the cleats. The down side is that the further forward you put the cleats, the harder it is to reach them, while sailing alone. To have this system while double handed, and to have a vang, while single handed, will give you the best of each.

A separate sheet line will be able to be attached much closer to the aft end of the boom and provide much greater sheeting leverage.

The hold down line will then be at a much steeper vertical angle, and be much more effective at holding the boom down. By having two separate lines, you can have much greater tension on the hold down one than on the sheet line.

 

Maybe something can be done about it, like wrapping heavy duty duct tape around a portion of halyard where it contacts the mast sheave? When it wears out, it can be replaced. Maybe smoother surface of tape would also erode sheave coating less.

But why would I want a hinge? Since this is a lug rig, I'll need a downhaul to bring the boom down to tension the luff. With hinge, boom would be fixed in place. Did I misunderstand what you meant here?

Do you know any existing design which uses the system you described? I'd search for some photos to better visualize your idea.

P.S. Another question. I've asked a while ago about mast tapering, and I was advised to follow Skene's book. There were some proportions given for several different masts, as seen here:



I chose to go with "jib headed mast with no shrouds", since this is the only unsupported mast given here. Since my mast is 4m, the recommended diameter is between 6.2cm and 6.6cm. But since in previous page there is a formula which relates to sail area, I decided to be on a safe side and designed my mast with 7.5cm diameter. Is that an overkill?

As for taper, the top of the mast results in a 3cm diameter. It looks good, but here's the thing. Since the lug sail's luff isn't attached to the mast, the forces are somewhat different - I believe all the force from the sail is projected on the mast top, where mast meets the yard. I am not sure whenever this means that the mast is more likely to bend, and therefore, is this taper not too much.

Can anybody comment on my speculations and advise if I chosen proper mast diameter and taper?

 

ballshaped rasp?

 

With regards to the dumb sheave, It's a very good and simple solution. I've made one by drilling a hole and then attacking the rest with a sharp chisel and file. It's not very hard, just find a piece of wood and try it!

The alternative is to cut it into the mast at the very top, and then glue on a cap. You can set an actual sheave into the mast in the same way.

 

Thank you both for your suggestions. With these options, I believe I won't have lots of problems making the sheave. Still wondering why it's called dumb, though.


An update. I finally solved my rudder downhaul/uphaul problem. I believe that instead of making two separate lines, there could be only one line which does both jobs. One end of the line attaches to the front of the blade, another - at the rear. Then the line follows a groove on rudder box, forming a semi-circle path. At the top of the rudder box, there would be a cleat, so that this line could be cleated at either blade-up or blade down position.

This might be little difficult to visualize, so here I'll show how it looks.









Now, a section view (with several layers of rudder box removed):



Please notice the groove in the forward portion of the box. The downhaul line woud run from the front of the blade inside this groove to the cleat. From there, it turns to uphaul line, and then runs along the hump of the rudder box to the hardware eyelet. There would be a lot of slack in this line so that it could be easily cleated.

Here I drew how this line would run in downhaul mode...



...and in uphaul mode:



I am not sure if the idea is clear enough. I've been thinking about this for a while, and I can't find any major flaws. Please let me know what do you think of this system. Oh, and I forgot to mention, this line would be a bungee chord, so that it would absorb forces if rudder were to be grounded.

I'll soon post update on reefing.

 

Here goes update on reefing. Since I've decided to go with parrel beads for the yard, it goes without saying that the halyard attachment point will stay very close to the mast, and cannot be moved along the yard in a hurry. Hence, the reefing arrangement is worked around this limitation (it's not so bad, really). Another thing is that I tried to keep the boom at the same angle (nearly horizontal) at any reef, even though the angle of the yard is changing.

So, here it goes. Full sail, a massive 7.3m^2 for very light winds (from 0 knots to 12-16 knots (meaning that anything over 16 knots would capsize the boat)). Notice the grey lines on the sail, they represent reefing points. Yes, I know they look weird, but resulting reefed sail requires this.



Next, first reef, 5.1m^2 (30% reduction), for winds up to 16-22 knots:



And the last reef, bringing area down to 3.6m^2 (another 30% reduction from the first reef), and basically turning lug sail into lateen sail, for winds up to 19-27 knots:



I believe further reduction of sail area would be only possible by swinging the boom up, because the leading end of the yard meets the boom jaws at the second reef, leaving no luff to fold.

Also, I think that having 3.6m^2 for very high winds is as low as can be practical, because if I reduce sail area any more, the hull windage will become too proportionally large to sail efficiently... Anyway, I don't plan to sail in the storms, so I think 27 knots survivable wind speed with second reef should be enough.

Could anybody comment on my work on these reefs? I know it looks kind of unorthodox, but I don't see why it wouldn't work (optimism and inexperience often walk side by side... ). Well, actually, I have doubts if the last reef will work well because the yard is nearly vertical, and the halyard is still attached to the 40% point. This could result in an extensive twist. Maybe I could add another halyard point on yard (near the trailing edge) for this reef. I really don't know.

P.S. I just found this:



Looks very similar to what I drew. So maybe this isn't such a bad idea?