Desperate to sail 2015

Hi Laukejas.

As promised, here is my Lee Board rack design (see first attachment).

The Lee Boards (5) are attached to two cross beams (2 and 3) with two fore and aft blocks ( 1 and 4). The blocks are through bolted to the ends of the cross beams and the Lee Boards are bolted to the blocks.

This structure sits on the deck behind the mast with one or two lines (6) tied to the mast step structure to keep it from sliding aft. There are no other attachment points to the hull.

The weight of this structure will hold the Lee Boards down, but bottoms of the Lee Boards will be able to pivot aft, as there is nothing holding the aft cross beam down, other than its weight. A second line could be rigged, with a hook, to hold the aft cross beam up, if desired. For rowing, the structure could be flipped upside down, with the Lee Board bottoms facing up, and moved to the back of the boat.

Due to the shape of the hull, with its deeply immersed transom, The Lee Boards are probably going to have to go much further forward than usual. This is because the drag of the immersed transom is certain to cause a down wind turning moment. Moving the Lee Board area further forward is a way to compensate for this. It is much better to have them too far forward than too far aft.

This is also a big reason I recommend a Standing Lug over a Dipping Lug (see second attachment). The idea is to create a rig that is:

a.) still relatively simple,
b.) has a low Center of Area, and
c.) has its Center of Area as far aft as possible.

You are probably going to need a powerful rudder for maneuvering and for making up for any lack of balance.

Best of luck. Please send us pictures.

 

I'd leave it crooked. Much better it be strong enough than be straight.

 

Sharpii2, thank you for the effort you give to help me out. Sketches are clear and understood, except for this: are these cross-beams attached to leeboards permanently? Because if so, this structure will be very awkward to handle and will take a lot of space when removed from the boat. Maybe you had in mind that it could be un-screwed after sailing season so it could fold, but still, that is quite messy... And in your sketch, it appears that leeboards have only one connection to handle the loads - the one with the cross beams. Are you sure this part won't break?

I have dropped the dipping lug idea, but I still can't decide between standing and balanced lug. Balanced is self vanging, which means one less line to fiddle with. Can you or someone else list differences in handling and performance of these two rigs? As I said, my goal is maximum reaching ability, decent performance in near-calm winds and adaptability to unpredictable wind shifts and gusts.

As for rudder, I think I can shift leeboard position until I find the sweet spot for minimum helm...

 

No, I'm not entirely certain the connections can take the loads. I haven't done the math.

But the Center of Area of the Lee Board is about 63 cm from the lowest attachment point, at the cross beam. Since the Lee Boards are bolted to both the upper and lower block, there is about a 10 cm spread between the center of a bolt, in tension, and the edge of a block, that is under compression. So the leverage the Lee Board has against the attachment point is 63:10, or 6.3:1.

Since there will be at least two through bolts, holding the upper and lower block to the end of the cross beam, and at least two bolts, holding the Lee Board to the blocks, this system is at least 10 times stronger than the one you originally proposed.

I agree that my rack design is awkward, bulky, and probably a bit heavy. But it is both simple and strong.

Actually, we aren't really talking about Lee Boards here, as real Lee Boards only have one board down at a time. The windward board is retracted, pivoted aft, allowed to pivot outward, or a combination of the three. What we have here are duel dagger boards, or duel clamp keels.

If you are willing to give up having both boards down at the same time, you can really simplify the engineering.

Otherwise, I stand by my rack, as being the simplest system that is likely to work.

The twin case idea, you have drawn, will probably work too, as long as the boards don't hit an underwater obstacle, and a line under the hull connects the bottoms of the two cases. The rack I designed can take hitting an underwater obstacle, as the boards are able to pivot aft, raising the rear cross beam.

As for sails, a balanced lug can work just as well, but the pivot point to the Yard might have to be a bit further forward and there is no way to let the Boom cock up. If you set it high enough, that should not be a problem.

 

Okay, I see. I need to think about it, if having such bulky item worth it. For now, I'll just continue working on the mast and the sail. I guess that will take around 2 days. Then I plan to make a test run with a single leeboard attached with no box or anything - just two lines at the handle and below, running around the boat. If that won't work, then I'll make another leeboard and decide on which attachment system to use.

Bad thing is that I'm running out of wood. I'm not even sure I could make one leeboard box.

Sharpii2, what's your opinion on using just one leeboard? Would it be enough? I wrote the math several posts back. If so, then I would still have 3 100x9.5x1.8cm boards for whatever use.

Also, if you have an idea for a single leeboard attachment that is less bulky, but still has all needed qualities (working on both tacks, retractable quickly), it'd be great.


About boom cocking up in balanced lug - what if I use this kind of lashing? It should allow cocking up.

P.S. Maybe you could show your one-leeboard-at-the-time design after all? Maybe it's not that difficult to handle... I'm just afraid that if boat tacks on it's own, I won' have enough time to react before leeboard breaks off.

 

It is most likely uneven moisture levels. Wet wood is larger than dry wood. More so against the grain than with it. For example a piece of wood laying on moist ground in the sun will warp up at the ends by dusk. If it was straight as a tree trunk it will most likely be straight again when it is evenly dry. So to answer your question, yes you will want finish on you mast to stop moisture changes.

The only way to bend (straighten) wood from it's natural shape is to steam it. Cellulose gets pliable when hot and wet. Steam bending can reduce strength. Wood strength is mostly in the rings.

All this adds up to the rule DON'T CUT WOOD TO FINAL SHAPE UNTIL IT IS EVENLY DRY.

Straightness is more important for column comprehensive strength than for bending so an unstayed mast doesn't need to be straight. The other point is that lug masts are asymmetrically loaded anyway unless the halyard shiv turned with the boom.

So, are you sick of hearing about all the imperfections? Then don't worry, don't waste time thinning, put the bend in a good direction and go.

About flotation, I think the seat pedestal is the flotation on that hull so check there are no holes in it. Cotton has odd properties in water. A high thread count pilllow case is air tight when wet. Try it. You can put one in the bow for extra flotation on rough days. Yeah Leonardo did not have to die in the movie titanic -he could have made his own inflatable boat out of bed sheets and floated away with the girl and the big diamond.

 

You can tie in air mattresses or inner tubes or if nothing else tie some plastic bottles to a rope, so if it does sink, the bottles will float and then you can pull it up with the rope.

 

I understand... Well, the mast was made from the tree that I fell last summer. It had a diameter of 8cm at the base. It would probably take years to dry completely, so I used what I had... And then it stayed under a wooden house for a year. I expected that place to be dry, but the grayness on the mast shows that it wasn't. I removed all the gray wood from the mast, and ended up with 4.75cm diameter at the the base. I'm a bit afraid this is a bit on the low side... But there ain't nothing I can do, right? Varnishing probably won't add any strength, but I'll do it anyway.

About straightness - well, this tree wasn't straight to begin with, but it was the best I could find in the area. So I guess I'll just go with curved.

There aren't any tricks to make mast stronger, are there?

 

Add stays.

 

Yeah, but you said that curved mast and stays don't work well together...

 

The work is going well. I almost finished the mast attachment system. As promised, here are some photos

http://www.boatdesign.net/forums/attachment.php?attachmentid=93329&stc=1&d=1407073200
http://www.boatdesign.net/forums/attachment.php?attachmentid=93330&stc=1&d=1407073110
http://www.boatdesign.net/forums/attachment.php?attachmentid=93331&stc=1&d=1407073202
http://www.boatdesign.net/forums/attachment.php?attachmentid=93332&stc=1&d=1407073293
http://www.boatdesign.net/forums/attachment.php?attachmentid=93333&stc=1&d=1407073379

The whole thing looks like it holds together strong enough. It's just the mast that gives me creeps. It looks too thin to me. But then again, looking at other boats, I've often seen thinner...

I now realize that the screw with loop wasn't such a good idea. My initial thought was that I would place the cross beams on top of the holes, thread the screw in and screw by hand. Now for some odd reason, these screws don't really want to go in. There just ain't enough strength in my fingers to screw them in. So I have to do it with pliers or some stick put in inside the screw loop to act as a lever.

I should have made a simple screw with screw-nut which features handles. But since there are these bronze plugs inside those holes, and they are glued in damn tight, I don't know how I can get them out. I could just take a metal-graded drill, and drill through everything, destroying the plug, and then inserting a simple screw (and gluing it in). But I'm afraid if that's gonna ruin the hole or the drill.
Can anyone advice me here, and soon, if possible? It's a very huge problem now, adding about 10min every time I'll have to assemble and disassemble the whole thing. Is my idea to drill through everything reasonable?

P.S. Never mind the last question. I managed to remove these miserable plugs with a heavy hammer.

 

It looks like you made progress. The question of strength now depends upon performance. How much sail and displacement in how much wind. You can stand in the boat and push on the mast at a known height and compare to the weight you intend to carry and it's distance from the center of buoyancy.

It looks to me like you could cut top of the mast off and get a nice long yard for a lanteen sail. I think Petro's advice was good that it is easier to make a good controllable lanteen than a lug. A lug sail is easier to hang more area but your mast size might be too limited in strength to benefit.

If it was me I would make the sail, strap on your nice leeboard as a rudder and take it out for a sail to see what your speed and pointing angle is. The benefit of a leeboard can be calculated. If you are running out of wood and will only use one board you might consider a small board at the bow as a canard arrangement.

 

I'd really like to try out the lug... But... What goes better to windward, lug or lateen? This is biggest worry for me. I'm very afraid to make something that takes hours to gain any reasonable windward distance.

I will shorten the mast, that's for sure. But I'm delaying it because if something changes, I can't put it back together...

Skyak, if I were to go either with lateen or lug, what sail area do you suggest? My current lug design aims at 5.5m^2.

 

I don't know how much displacement you will carry or how much wind. Remember the ballpark figure of one pound per square foot at 15 knots of wind. I think that's 4.6 kg/M^2.

The lanteen gives better control of twist and can keep a sail tight and flat. In good wind it will do well upwind. With a lanteen I suggest you draw it to see how much big you can make it. The answer will be in how much sail you can put up.

The lug is easier to put more area up higher but it is harder to control twist and puts more stress on the mast. It's a bigger but likely higher drag sail. If you don't have enough wind it could be better but gusts will send you for a swim or break your rig. When a big gust hits and you let the sheet go the sail will flog and still take you over. The lanteen easily pivots into the wind and can go to very low force in high wind, the lug will not.

 

It's hard to estimate displacement in this case... I don't know how much the boat weights. Maybe 60, maybe 100 kilos. When it's so big, I can't just lift it and compare to what I know. And I certainly don't have scale that big!
With that in mind, is there some method to weight very heavy objects, with no machinery included?

What else adds to displacement is the whole rig, maybe 15-20kg, and currently, me (76kg). Later on, I'll take another person on board. So for now, my estimate is about 175kg displacement. If I knew how to weight the boat, I could tell more accurately.

Well, I certainly have "good winds" about 10 minutes per day, total. Other than that, conditions are completely unpredictable, from dead calm to gusts up to 30 knots. I know it sounds rather ridiculous, but something here in the lake (trees, hills, narrow branches of the lake) combine together to create very rapidly changing conditions. However, most of the time it is 1-5 knot wind (with fore-mentioned 30kt gusts) from changing directions.
I know what the usual "sailing wind" looks like. I've been at large lakes, or by the sea or lagoon. Constant direction, constant speed, gusts never exceeding 50% of the original windspeed, non-turbulent. If only I had this here...

So the thing is that I need a sail that would work well upwind in these very light and unstable winds, while strong enough to survive these gusts.

Is it lateen or lug for me then? I know nothing about lateen, I'm researching it now and will try to draw what can I make from what I have, but I need to know for sure if it will work.

Will post sketch in the meantime, but if you could provide any more information, I'd be grateful

P.S. The mast is currently 480cm long. So if I have to cut it, that's the length I have to work with. Just sayin'.