Low-speed sailboat hull

The rudder down/up haul you show is pretty much universal in dinghies for at least 50 years (as long as I have been sailing them at any rate). But I suggest putting the cleat on the tiller. Two reasons, you can tension the line better. Second if the cleat is on the rudder head you have to lean back to release it, which sinks the stern at just the wrong time

Richard Woods

 

That picture you found is by Todd Bradshaw who knows his stuff. Seems like you're on the money!

I think you are overcomplicating some things, for example, I've never sailed a dinghy with a rudder uphaul. Also, chafe; how often are you planning to sail? It probably won't be much of an issue.

The most clever system for rudder up/down I've seen is an elastic loop which goes from the rudder stock, to the blade. The placement should be such that with the rudder halfway up the elastic goes across the pivot point. This way, when the rudder is down the elastic holds it down, and when the rudder is up the elastic holds it up. No adjustment needed.

 

I believe you, but I actually haven't seen this kind of system with a single line. Anyway, it's good to know I'm not off-track.

I considered putting cleat on tiller, but as you can see, my tiller can be raised if it gets in the way or when rowing. I'm worried that if the cleat will be on the tiller, these two systems might prevent each other from working correctly (like being unable to raise tiller, or a line jamming). If you know any simple system similar to mine, could you please share it? I could improve current design.

Yeah, I gather that Todd is very highly respected builder in that forum. He really kind of strikes me as a guy who knows pretty much everything there is to know about boats. And he loves standing lugs, which is reassuring.

Hey, I actually wanted to make this kind of system like you described, just a week ago! I actually even drew and tried it. But then I figured that every time I'd need to lower or raise the blade, I'll have to go all the way to the transom, lean over, and reach my hand into the water to push the blade down or up. Of course, I can run several lines into the cockpit, since they don't need to be cleated, but it would complicate things again. This is why I have dismissed this idea.

But maybe this isn't an issue? What would you say?

 

How often are you expecting this to happen? I typically push the rudder down once, and pull it up once for every sailing trip. Unless you have a lot of weeds or something that require lifting the rudder all the time, why would you be adjusting it while sailing?

 

Yeah, I'd typically also do this only twice per trip, but who knows. Maybe you're right. Richard scared me by saying that going to transom to lift the rudder might sink the aft section at the worst possible time. I'll run simulation on Solidworks and Delftship to see if the transom can stay above waterline with center of weight all the way aft.

 

Boom hold down, rudder raising and lowering system

Hi Laukegas.

There are no examples of my suggested boom hold down system that I can think of. I suggested it mainly due to the design choices you have already made, such as seating a crew in front of the dagger board case.

My suggestion will probably work to some extent and would certainly be better than nothing at all, or even the very short vang you suggested. Most small boat designers try to keep all the crew behind the dagger board case, even at the expense of weather helm. This way there is room for a decent vang

You chose to do it differently and I made my suggestion based on your choice.

The rudder raising an lowering system you drew is almost exactly like the one I had on a boat I used to own. I found it somewhat inconvenient to use, but workable. But the boat I had weighed over 600 lbs.

Attached is a drawing of a rudder I designed for a pdracer. There is only a lifting line. An elastic cord attaches to the leading edge of the rudder and to the stern of the boat, to pull the rudder back down, once the lifting line is relieved.

The lifting line can cleat off at the end of the tiller, even if the tiller can pivot upward. Yes. the blade will come down a little, when you raise the end of the tiller, but not that much. The key factor is how low on the trailing edge of the rudder yo attach the lifting line. The lower it is attached to the trailing edge, the less the rudder blade is going to sag down when you raise the tiller end.

 

Thank you very much, sharpii2. This is by far the best idea I've seen for rudder control. Only one line, can be controlled from end of the tiller, while retaining shock-absorbing capability. Perfect.
Only that I think it might be better to attach this cord to the rudder box instead of hull. I just need to figure out a way to have enough length of that cord so I won't have to fight it with lifting line.

I'm kind of surprised to see so many parts underwater on a racer. Elastic cord is underwater, the blade pivot screw is too, it seems that even the rudder box coincident with waterline at least. Doesn't these things slow down the boat? Not to mention that this elastic cord can catch weed pretty quickly. In my design, I'm trying to keep underwater parts to a minimum, so that nothing would add unnecessary friction. And it's not even a racer.



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I'd like to ask again several questions that got lost back in this thread. These are issues that I haven't yet figured out, and are very important before I can move on with my project.

1. Yard bend. When making sail, I know I must anticipate yard bend, and create an appropriate hump in the head of the sail 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 how much of that yard bend should be expected? 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?

2. Mast taper. 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?

3. Buoyancy tank hatches. Bow and stern tanks will need ventilation, but they could serve as a useful dry storage space too. I could buy several plastic hatches like these:



They come 6.3$ each, and have 15.2cm inner diameter - just enough for a hand. Am I better off by buying these, or should I try building plywood watertight hatches? I tried researching it, and it seems like a lot of subtle work. I'm not sure if I should chose time over money here. Any comments?

 

If you want to fit hatches, the Allen or formerly Holt/Holt Allen ones are some of the best. Better screw pitch, O ring outside of screws etc, but put a doubler on the inside for 6mm long CSK screws so they don't pierce the tank... btw the grip on the Allen ones is also better than some of the competitor brands. I have no connection with them other than as a happy user. Actually the 100mm (4") ones are enough for a hand unless you have very large hands....

If you choose to make your own hatches, you can do round and/or oval in ply. You will need to create a step and use a squashable rubber seal such as an aerated EPDM or similar super glued at the ends. These were used in the late 50s' early 60s' and work ok, the method of attachment is a strong elastic (inside tank) to 'pull' the hatch shut. I have known these to be air tight. One other thing is the hatch should be placed above the level you expect water to be when righted and full of water and people, yet at a level where you can put your hand to the bottom of the tank to ensure sponging out and feeling for any water.

One more point, when not in use the hatches need to be slackened to allow air movement or the tank(s) will pant, ie expand in the sun, and shrink in the cold.

 

I'd go with making my own, if I wanted them on top of the compartments, even if they weren't entirely water tight. Even not so water tight hatches can keep the compartments from quickly filling, if the boat capsizes. I'd be more interested in being able to get the water out quickly, than keeping it out. If the hatches are on the center-line, they won't even take on water unless the boat flips over. Having box like hatches, which fit over a raised coming, will keep the vast majority of the rainwater out, and if held on with lashings or elastic cord, will keep almost all of the flooding water out, in the event of the boat flipping. The home made hatches will also make these compartments much more useful for stowage.

 

I'm okay with having no fullness added by head's rounding, but I definitely want to be sure that the rounding will compensate for the yard bend. What I'm afraid of is that the yard will bend more than the rounding allows, and the sail will wrinkle, like it happened this summer when I made the head of sail completely straight.
I'll be using Tyvek for sail this time - it's less stretchy than polytarp, yet not even close to Dacron.
So are you sure 1/100 is enough to compensate for yard bend? Maybe I should go with 2/100, just to be safe?

Hehe, that adds to the confusion! Actually, I know these factors you mentioned, but with little experience, they don't tell me what mast thickness should I choose in this particular case.
In one page, Skene gives a formula for unsupported spruce masts:



I chose a safety factor of 2, and arrived at 7.8cm mast diameter. I downsized it a bit to 7.5.

However, in the following page (the one I posted in my previous post), Skene expresses mast diameter in a different way: Length x .0165 (.0155 for unballasted boats). Since mine is definitely unballasted, the resulting diameter would be 6.2cm. That's a lot less. Maybe I should strike the middle ground with 7cm at partner, wouldn't you say?

Good advice! So, I take that my mast tapering proportions are okay?

Hm, would you be so kind to share how would you do it? I searched several tutorials on google, but these methods are very complex. And for hatches, I'd like to re-use the same cut-out plywood, since I don't have any to spare, unless I plan for whole new sheet.




Update.

There was a major sale in our local department store (30% of for everything), and since I already had my list of tools, I went ahead and bought 230$ worth of of them, including drill, orbital sander, table for jigsaw which turns both into a tablesaw, Japanese pull saw, and lots of random things (files, pincers, hammers, chisels, rulers, straightedges, battens, T-squares, etc, etc, etc). Quite an investment, but consider that I had absolutely nothing except a jigsaw (all tools in my previous projects were borrowed).

So, there is no turning back now. The game is on.

Oh, and by the way, C clamps. You guys say there are never enough of them. No matter how many you buy, there will be always one more lacking. So I bought 10. I guess that's not even close to enough, right?

 

Hi Laukegas.

For the sails I'd now go with the traditional 3/100ths rounding and round both for the Boom and the Yard.

As for the hatches. They must be bigger than the openings, but do not have to be made out of single pieces.

The first thing that you do is build a frame around the hole, which projects upward and has no gaps.

Next, you make your hatch cover. It is a simple box with low sides, which fit over this frame. Allow a few mm on each side, so the wood has some room to swell when it gets wet, so the hatch won't get stuck.

These sides can be made of timber, if you want, and can have some other material than plywood for their tops.

Now you need a way to hold it down. An eye bolt on either side and an elastic cord or even a shoe lace will do the trick.

It won't be water tight but it will be close enough. It will keep rainwater and spray out. These are lift off hatches, with no hinges or any other permanent attachment to the boat, so when you take them off, be sure to put them in the cockpit so they don't go overboard.

As for your mast diameter. 7.0 cm seems generous enough, or already over doing it. I'd definitely stop there, as I wouldn't want the mast to be too heavy.

 

One thing to keep in mind is that it's easy to remove material, but hard to put it back. If you cut a sail with too much round, you can always reduce it. Same with mast taper.

The laser sailing dinghy has a mast with an outer diameter of 63 mm and an inner diameter of 57 mm. You could calculate the section properties and convert to wood. I think solidworks can do the calculations as well.

You could also try searching the woodenboat.com forum for dimensions, or even start a thread. I guarantee you they will know the answers, they all use a lug sail over there

 

I built a hatch like the one being discussed. Not only water-tight, but air-tight I found.
Left the hatch off until ready to launch. Then sealed it. Either the water cooled the hull or just the afternoon temp dropping slightly was enough to create a slight negative pressure. Very hard to remove the hatch at home.

I used window/door rubber seals both on the top of the hatch frame and around the perimeter of the frame on the deck.

Of course the hatch is so overbuilt to be ridiculous. 1/4" ply with 7 oz. glass on both sides with 1x2s for all framing.

Edit: I think I finally bought around 60 cheap C-clamps from harbor freight as they had $2 a clamp sales.
2nd edit: I too considered a couple of smaller hatches but then decided I REALLY wanted to be able to drop camping gear in without any hassle so just built the one huge hatch. Also why I over-built it. I really don't want that sucker failing at a bad moment.

 

Thank you both, but you know, reading this, I think there might be already enough complications in my project! I think maybe for now I'll just by those hardware hatches, but if they turn out to be bad in any way, I can always make my own. It'll just take some time.

I plan to present my entire project there after I consult with you guys. Maybe they'll also give some insights when they see this project in finished state, not knowing how it all got started



Another update. There wasn't a lot done this time, since my to-do list is getting shorter and shorter. But there are still some several large issues.

I decided that it would be cheaper, easier and faster to use belaying pins instead of cleats wherever possible. I could easily make lots of them following this tutorial (with some to spare if they get lost).

For example, this is how I designed mast partner now:



3 pins in use, one spare for some other line that I can't think of right now. Both downhaul and boom vang pins are a little off-center, but I don't think that will affect performance a lot on different tacks.

The partner itself is 4 layers of 6.5mm birch plywood epoxied together to a total thickness of 26mm. I'll just remind that this partner, together with step, will hold 4m long solid pine mast (diameter at step 6.3cm, at partner 7cm, at top 2.87cm) with a 7.3m^2 lugsail. The partner will be attached to a 6.5mm birch plywood bulkhead (with some timber on the other side) utilizing epoxy and screws. Partner will also hold these belaying pins with tension of halyard, downhaul, and boom vang.

My question - is this partner strong enough to hold all those forces? I am not sure if I'm over-engineering or under-engineering it. This is an important piece, and I'd like to be sure that it's up to the task.



One more question, and a plea, if I may. I am now heavily researching sail broadseaming. I know what shape I want, but I don't know how to translate that shape into broadseams. The only reference most people provide is "Sailmaker's Apprentice". It is a great book. And I have it. But there is a catch.
I got this book from my friend, in a PDF file, once copied from Google Books Preview (not available anymore). Sadly, there are a lot of pages missing, about 1/3 of the book. As fates would have it, the most important pages which deal with formulas of broadseaming are missing.

Being stationed in Europe, I have no chance to buy or find this book in libraries. The only option is to ship from US, which would cost trice as much as the book itself, even if from a second-hand source.

I am wondering if anybody here has this book in electronic format, and would be kind enough to share, or at least those missing pages (there are lots of them, but basically from page 250 to the end of the book). Or maybe a scan, if that wouldn't be too bold to ask..?

I am not entirely sure if what I'm asking is legal, but I can at least assure that my intentions are noble. I only wish to learn. And should my project be successful, I will make no attempts to make money from it. I shall release plans free of charge on the internet as a token of gratitude to people who helped me in the bumpy road of designing this little boat.

I know I'm asking a lot, but it is very, very important. PM me if needed. Thank you in advance

 

Mast Partner

My only concern is about how well this partner structure will attach to the bulkhead.

I appears that you plan on screwing it to the bulkhead, with the screws going into the edge of the plywood. this is not very strong, because the screws will tend to get between the veneer layers and pry them apart.

Bolts with washers on both ends would be much stronger.

Of course you could glue this partner structure to the bulkhead with epoxy, with a generous fillet on both the top and bottom. But then you're relying on the peel strength of the top veneer of the bulkhead. This may or may not be strong enough. The bigger the fillet, the greater the area the stress is distributed across, and the less tension per square cm.

You could bolt two pieces of timber to the bulkhead, one above the partner and one below, then screw or peg the partner in place, with the screws or pegs coming in through the top and penetrating the top timber, the partner and the bottom timber. This would probably strongest arrangement of the three mentioned.

Each timber would be as long as the partner and be about 4.0 cm square in section. At least three bolts would hold each to the bulkhead.
One in the middle and two at about 4.0 cm from each end.

I would also want to have a relatively hefty timber (say 4.0 cm square) joining the bulkhead to the fore deck to bolt the top timber to, and have a similar timber, lower down on the inside of the bulkhead, to bolt the other timber to.

The bolts would go through all three (the timber joining the bulkhead to the fore deck, the bulkhead, and the timber joining the partner to the bulkhead)

This arrangement not only distributes the load over quite a bit of bulkhead, but successfully distributes it to the fore deck as well.

The mast partner and step area needs to be the the strongest part of the boat.

The Boom Vang attachment point needs to be on the center line, otherwise it will too tight on one tack and too loose on the other.