Low-speed sailboat hull

Thank you for your advice, sharpii2. I'll think of some way to strengthen mast partner joint.

As for the belaying pins - but what about downhaul? Shouldn't it be on a centerline too? Because I can't fit 2 pins on the centerline, this is why I placed both downhaul and boom vang pins a little off the centerline.

If both have to be on the centerline, where can I fit them?

 

I wouldn't use a belaying pin for a Boom Vang attachment, or a down haul.

This is because I'd have to lead the lines in question through the mast partner assembly, so the ends end up under it. There, they wrap around the bottom of the belaying pin and are tied off there.

The purpose of the belaying pin is to allow sudden release of a sheet line. Once the pin is pulled out of its hole, the sheet line is stripped off its bottom. Neither the down haul nor the Boom Vang seem to need such treatment. And sheet lines do not need the very precise tension that Boom Vangs do. I think you would find it quite frustrating getting the Boom Vang tension you want with such a system.

What I'd do instead is make my Boom Vang out of wire rope with snap hooks on either end. One snap hook would attach to a strap eye on the mast and the other would attach to another strap eye on the bottom of the mast or on top of the mast partner assembly.

To get this Boom Vang line the precise length needed, I'd seize only one end. For the other end, I'd use cable clamps, until I got it just the right length. Then I'd remove the cable clamps and seize that end too.
Then I'd have a Boom Vang that is very quick to set up or put away, that is always the right length.

The Boom Vang serves the function of the Down Haul, because the Boom ends at the mast. In other words, a Down Haul serves exactly the same function as a Boom Vang, but for a Boom which extends past the mast.

If you want to have a block and tackle on your Boom Vang, to deliberately bend the boom to flatten the sail, a belaying pin could then be used. If using just one pulley, the pulley would attach to the Boom, or to a pendant attached to the Boom. One end of the line would attach to a strap eye on the mast, underneath the Mast Partner assembly. The other end would be belayed on the belaying pin.

 

If you mean that the lines are fed through the same hole in partner as the mast, then no, that's not what I had in mind. I though these lines would run directly to each pin.

The reason I chose pins here is because these lines arrive with a significant angle to the partner plate. If I were to use clamps, there would be a lot of force trying to tear those clamps off the partner. I could drill several holes in the partner and lead those lines through before clamping, but I'm not sure if this is a good idea.

That's an interesting idea. I kind of like it, but I'm a bit scared about boom vang being non-adjustable. After all, the downhaul is often described as the main line in the lug rig. It might need to be adjusted for different wind conditions. Those adjustments will change boom height above partner. If this height changes (for example, when I tension downhaul a lot in high winds), the boom vang wire may become slack, which is opposite of what's needed in high winds.
Also, having sail reefed also changes the boom angle. I can modify reefs so that it doesn't, but it's some precision work.

Please tell me if my fears are ill-founded. I like your idea a lot, I'm just not sure if it will work with different downhaul tensions.

I'd really want to have boom vang attached no lower than the mast partner, because it will get in the way of bow crewman. I'm sure it would be more effective to have it lower, but the price is too high.


I've been thinking. Boom vang will probably be needed in high winds mostly. The higher the wind, the higher the speed. Thus, the apparent wind should blow more from the side than back. Which means that the sail will have to be sheeted in quite a lot.
My mainsheet traveler will be located at the transom, and the sheet attaches to the end of the boom. When the sail is sheeted in, this traveler also brings boom down as I tension the maisnheet. Since transom is considerably wide, it may be possible that in downwind sailing, the boom won't be that far from the traveler; thus, it may still be effective somewhat.

If it's not, I could add another traveler at the thwart (simple rope running along the thwart) , like you suggested earlier, and have the boom vang wire run from this traveler to the middle of the boom. It would slide along the traveler freely. This arrangement would limit how much can I sheet out the sail, though. That might be dangerous.


You're being very helpful, sharpii2. Thank you. I hope this isn't becoming boring for you. This is one of the last issues with this boat before I can start producing plans for it. The end is near, please bear with me!

 

Many boats use a fairlead at the mast base which the vang and downhaul tails go through, you can easily lead two or three ropes through the same fairlead. A simple U bolt is all you need. I've never used belaying pins, they don't look very handy for ropes that need to be adjusted. I would use butler cleats for the vang and outhaul, if I was to make cleats.
http://www.unlikelyboatbuilder.com/2012/06/cleat-for-every-line.html

You may not need a vang on the lug sail, especially if the wind is light, as intended. For strong gusts, not having a vang would allow more wind to spill, which might be a good thing.

 

Great idea. I could use u-bolts on mast partner. I'll look at those cleats too.

Well, I've been advised on this very thread that having no boom vang will spell disaster on a standing lug in high winds when going windwind. What's your opinion on this?

 

Boom Vangs and Reef Points

Hi Laukegas.

I've reviewed your reef point drawings and noticed that the boom stays pretty much in the same orientation. It's the Yard that changes.

This being so, a single cable with two snap hooks will work. The tension is created by the halyard, which has to bear anyway.

The Boom Vang is not needed so much when sailing upwind. This is because the sail is then brought pretty close to over the center line of the boat. The Sheet Lines are then pulling the Boom more down than toward the center line of the boat.

A Boom Vang is most needed when the sail is sheeted out, on a reach, broad reach, or a run, and the Boom is way over the side of the boat. Then the Sheet Lines are pulling the sail more to the center line of the boat than down. It is in this condition that the aft end of the Boom starts to rise.

When this happens, the top of the sail sags off downwind and it's drive is reduced. When that happens, there is less upward tension on the Boom. The Boom comes down and the upward portion of the sail regains its drive.

This can happen in a repeating sequence, causing the boat to roll. If the rolling gets too harmonic, it increases until the boat capsizes.

This is why I think a Boom Vang is actually a safety feature on a boat.

On a small boat, such as yours, to be sailed in summer weather, not far from shore, this is not such a big deal. And even with out a Boom Vang, you probably won't get into too much trouble. But a Boom Vang, even a crude one, like the two I have suggested, will certainly improve your boat's performance.

 

All right, you've convinced me. I'll design this in the way you described

I have no more questions as of now. I'm finalizing the design and producing building plans. That will take a while, but I'll report back when it's done. Still 4 months left until I start building, plenty of time.

 

Hey guys, I'm going well with this project. I have produced around 50% of the plans.

Now in my list is the rudder. As I've started to think how am I going to build it, I realized there is a problem.

You see, I plan to make my rudder NACA shaped, just like daggerboard. I'll epoxy together some timber beams with pre-calculated widths, and then, using hand plane and sandpaper, smooth it to final shape.



I think you got my idea. Now, this would work perfectly for centerboard, but for rudder - well, I need to have a bit different shape, which is like this:



The upper part must be flat, because it will be housed inside rudder box, and will pivot on a bolt (hence the hole there).


The problem is that if I go with timber beams method, the upper part won't be flat and of exact thickness, which means it won't sit properly in the rudder box, and all the forces will be exerted on the bolt.

I simply can't wrap my mind around how can I make this rudder blade. I could, of course, just take those timber beams and epoxy together without milling to individual widths. Then I could NACA-shape only the lower part, and cut the shape of the upper part with jigsaw. But that would mean a lot of precision work making that NACA shape with no aids. Much more difficult.

Another option I thought of is to make both parts separately (blade with pre-milled timbers, and upper part with uniform width timbers), and then butt-join together with epoxy and fiberglass tape (I don't have access to cloth). I could also drill several holes in both parts and insert steel rods to make the joint stronger. But I'm still afraid blade might break off when sailing.

Can anybody please advice how can I solve this problem? If what I wrote is in any way unclear, please let me know and I'll explain in a better detail.

 

The brute force solution is to lay up a rectangular blank and carve away all of the rudder blade.

 

Well, that's one of the options I mentioned. It would be very time consuming and hard to make accurately. I could make a a plywood template of desired NACA shape and check with it as I go, but it is still very difficult.

I need to find some more intelligent solution. I don't have a router, you see, so that kind of limits my options. I only have hand tools and orbital sander.

 

What you are trying to do is cussedly difficult, because you are trying to make a symmetrical foil with no flat surface to work from. Instead, all you have is an imaginary center line, which runs through the foil.

If it were my boat, I would abandon the foil shaped rudder blade and go with a rounded leading edge and a tapered trailing edge, and end up with a stronger rudder. It may lose a few percent less efficient, but I'd get it built in a reasonable amount of time.

It may even work better than a poorly executed foil.

If I were to attempt the foil shape, I'd approach the problem this way:

1.) cut the entire rudder blank at maximum thickness,

2.) make "body" templates for the middle 1/2 of the rudder length (you will be making two. One each for the port and starboard sides),

3.) Mount these on two straight edges, which are joined at the ends, creating an open frame, which has an inside length equal to that of the rudder length. The ends of this frame should have marked center lines.

4.) Use this to guide carving the body portion of the foil,

5.) make a "nose" and "tail" template, with each being equal in length to about 1/4 the fore and aft length of the rudder blade,

6.) design these to be mounted on a straight edge that is equal in length to the rudder blade,

7.) use these to guide the carving of the nose and tail shapes of the foil,

As you can probably guess, a lot can go wrong with this system. Getting either frame cocked at any angle, other than parallel to the imaginary center line, will totally botch this attempt.

 

Another approach that might work better would be to make a cardboard pattern of the foil shape and glue it to the bottom of the rudder blank.

Then just carve the blank to that sectional shape, just a few centimeters up.

This will give you a definite reference point to set later templates to.

Doing it this way, you may need to make only one full length (fore and aft) fairness checking template. This would be used on both sides of the rudder.

Use it to work up the height of the rudder, one side at a time.

Still, the chances of this going awry are quite great.

 

Thank you once again for these numerous methods you provided, sharpii2. But maybe you're right about this. Complexity and potential risks doesn't justify that marginal improvement in performance. I already have enough work on my hands. I really want to make this boat in 1 month, working all day, every day. So I'll ditch NACA-foiled rudder idea. I hope that NACA-foiled daggerboard will be enough on it's own.

So I'll round leading edge and tapper trailing one, like you suggested. Just a question, then - how much do I tapper to, and at what length? Any guidelines there? Right now, my rudder blade is 1.95cm wide (because it needs to fit in rudder box slot of this width), and 23cm long (chord length). I can make it longer if needed, but it is big enough already (50% of daggerboard area).
So, to what thickness do I tapper to? I know that the sharper the trailing edge, the smoother the waterflow, but I don't want that edge to be too thin and break off. What's a good compromise? Please remember that I won't fiberglass this part. And where does the taper start at? 1/3 of chord length, maybe?

 

It's much easier than you think -- see attached PDF. This technique is mostly methodical rather than cut-and-try, and doesn't require templates.

For a hardwood rudder I think you will need a power sander of some sort rather than the sanding block to remove most of the wood, and then switch to a big very coarse sanding block only at the end. So the basic approach should still work. For a constant-chord rudder you can skip the initial tapering steps.

Note also that a boat rudder will be almost fully turbulent, so the precise airfoil shape won't be too critical. And something like a NACA 0010 or 0012 is already very insensitive to waviness anyway.

 

I'd taper the trailing edge to about 0.5-0.3 cm.

I'd start the taper at about 6.0 cm from the trailing edge.