Simple sail question

[charlief1]

Just for everyone's amusement, I'm a auto tech that dropped out of MTSU just before graduation with a mechanical engineering/education degree. Just didn't enjoy it as much as what I've been doing.

Its not a solution I'd adopt, but I can see that a daggerboard case each side of the hull, built into/flush with the sidetanks, would make for an awful lot more room in the cockpit than a conventional design. It would be an interesting thing to try. I'd probably only make one board initially and see how swapping it from side to side worked. Get a better result with one board with a nice foil shape than two boards that were more plank like. Short tacking you could probably get away with leaving it on one side.

The thing is the purpose of the boat. If its primarily a sailing canoe this isn't the way to go, but the OP makes me think this is planned more as a sail assisted paddling boat. Plenty of motor sailor boats round the world have a rudimentary upwind sailing capability but satisfy the owner's needs, doesn't seem impossible same could be true of a paddling boat.

It's primary use is for fishing, not sailing. As I stated, the sail is just so I don't have to paddle across the large lakes I live around. I like fishing in rivers, creeks, and inlets rather than in the deep sections so this is for use in those areas. The sails main function is to get me from point A to point B (in some cases the distance is several miles) so I can fish and not have jelly for arm muscles when I get there. I fly fish so the width is for standing when needed, and the angles of the sides are because I wanted the extra room for rods and equipment. The full sized version will have a hatch front and rear in case I want to spend several days out and do a little camping.

Conventionally with leeboards, BTW, one is lifted up. I personally think they are a ghastly solution, poor hydrodynamically, structurally and aesthetically, and this idea does seem interesting. Hard to be worse!

I would very seriously consider the traditional two mast setup. Another option that might be worth looking at is that a number of turn of the century canoe rigs had full length battens in the sail something like a chinese junk rig. That would be nice and easy to reef down. It could be that with some careful planning you could end up with a pair of free standing sail mast combinations with which the rigs could be removed, sails rolled round the spars, and the whole lot stowed on the foredeck. Err on the large side with the aft sail and you can just tune balance by making it smaller. Even just roll a bit up at the bottom.

You've got to allow for the possibility that something this radical could be a complete and utter flop of course, but if the materials aren't too expensive and you enjoy the construction for its own sake, well...

I've always though leeboards were a solution for coastal craft (something that has to be beached) and temporary use in a small boat. The bracing involved to make one work would also reduce the area inside the boat, so not just no, but hell no.

2 masts will move it faster, but this isn't about speed, it's about not having to paddle to go long distances. If it only goes a couple of MPH that's more than enough. Once I get to my destination the sail comes down and the mast gets pulled out so I can fish. Both get stored on the top sides so they are out of the way. When it's time to go back to the launch spot, the mast and sail get put back together and off I go. I know this isn't a conventional design and doesn't fit into what is considered normal. but it's purpose built for a use.

When I had a machine shop (part time work) I built several unconventional rifles that everyone looked at and told me they wouldn't work. One I built as a showpeice to show off my skills so others might want me to build one. It's a 6.5 MM Swedish Mauser that came in under 6 lbs with the scope, and will shoot .5 MOA at 300 yards. The tip of the barrel is smaller than my middle finger, but tapers to larger as it goes to the receiver. Sometimes when you think of something that others don't understand, it works better than you believed it would.

 

[gggGuest]

2 masts will move it faster, but this isn't about speed,

No, you misunderstand me. Two small rigs instead of one larger one and about the same area. Much the same speed (except against the wind when definitely slower), but the small rigs will roll up smaller and stow more easily, (one on each side of the foredeck?) there will be much more headroom so its easy to paddle and sail if you want to, and because they are so much smaller will be easier to lift in and out and store while you go fishing.

 

[charlief1]

It's something to think about but what I was thinking with the 1 mast is that I don't plan on a mast over 10' total height. 1 foot is inside the hull to secure it, and at least 1 foot above the deck before you have the sail. Possibly 2 feet above the deck, so the sail in a lanteen rig should be easiest to take down and store on the deck. With 2 it would take up more space on the deck and I'm trying to make it as minimalist as possible.

 

[gggGuest]

It's something to think about but what I was thinking with the 1 mast is that I don't plan on a mast over 10' total height.

I was thinking something like a Lugsail rig with all 3 spars pretty much the same length. Only you can answer what's good for you, but might a rig of say 3 6 foot spars bundled together on the port side of the foredeck, and 3 5' spars bundled together on the starboard side of the foredeck give you more practical working space than 10ft spars which would neccessarily intrude further on the cockpit?

Here's that Sunfish sketch posted earlier with a pair of lugsails superimposed. The total area is much the same, and as you can see the longest spar is under 60% of the length of the lateen rig spars.

 

[messabout]

Sawmaster; The main reason for lead is that the sail is never at the midship location. The farther out the sail goes the farther forward the center of sail effort is positioned with respect to the CLR of the hull and board combination. You can verify this with a little bit of trig or alternatively with a simple drawing where the sail is eased to different angles from the centerline. When the sail is way out, as in a broad reach or run, the CE of the sail is well forward of its midship position.

Let it be said that the lead percentage is a function of the configuration of the underwater parts of the hull and its appendages. Guessing at the most efficient lead percentage is a work in progress. Butt trim is a real factor in small boats but maximum hull efficiency is affected by fore and aft trim angle.

 

[charlief1]

I've been looking at different sail rigs and I think I've found one that will be much simpler to use as well as more compact for what I want. The Una design looks like the simplest one I could use but there's also the sprit and leg o mutton design that look simple enough to rig and take down. Leg o mutton will give me more than enough room and the least amount of space it seems and I'm leaning towards it because it would be really easy to set up and take down.

http://www.pdracer.com/sail/mutton/

 

[PAR]

I suggested the lead based on a typical lanteen, which would be the same recommendation if a fairly low aspect leg 'o mutton. If it's more Bermudian cat proportions, you'll likely need more lead. If it's a lug, probably a bit less. An adjustable mast step would be a good idea, so you can "tune" and find the best location, at which point you make something more permanent. The same would be true of a dagger or leeboard. Maybe something take simply clamps or wedges over the rail, so you can move it around until you find the spot, then mark the rail, for future sails. This arrangement can be stowed, you don't have a case screwing up the internal spaces, it can be left ashore if your not needing it and it's a lot lighter too.

Lead decisions are one of the black magic things about yacht design and can be affected by several things, including hull shape, entry type and angles, bearing are, Cp, speed potential, appendage location and type, etc. With boats of this size, you have a good bit of latitude, as you can butt adjust, to get reasonable trim and helm pressure.

The reason canoes and kayaks have quite a few divided rig options, is to lower the CE, provide small in boat stowable spars and offer less head bonking with the widely separated sticks, on a usually pretty tender hull form. A PDR rig on a canoe might place the RM too high to make it impractical.

 

[SukiSolo]

Lead decisions are one of the black magic things about yacht design and can be affected by several things, including hull shape, entry type and angles, bearing are, Cp, speed potential, appendage location and type, etc. With boats of this size, you have a good bit of latitude, as you can butt adjust, to get reasonable trim and helm pressure.

Agreed, I doubt anyone has had the good fortune to put the mast in and go with perfect balance on initial sail!. I've had to move a few masts around to get the balance right up to 75mm+ at the heel. Well, easier than moving a centreboard case or keel.... though even those need changing sometimes...

Give yourself a reasonable amount of adjustment to find a good balance point. Even better if you can clamp a temporary fixture in different places, whether for mast or whatever you plan to use to resist leeway. Then you can eliminate any error before fixing.

 

[charlief1]

I may end up going with a 12' mast which would give me a sail that's 10' tall and 8 feet long so the total area would roughly be 40 sqft, which should be big enough to get me going much faster than a paddle. Even if I cut it down to a 10' mast which should be around 32 sqft. Remember that this isn't the primary propulsion but a secondary design so I can make it across water to get to a different fishing location. The mast looks to be about 3' off the nose with a total length of 13.4' so this will place the daggerboards about mid sail if I don't go over 8-9' back from the mast.

 

[ImaginaryNumber]

A good general guide will be to place the leading edge of the daggers just a hair forward (a few inches) of the sail's CE, regardless of its position in the boat (mast location)...

... Place the leading edge of the dagger, a few inches aft of the CE and for this boat, you'll want a fairly modest lead, say in the 14 - 15% range for good balance...

So which is it -- forward or aft?

 

[PAR]

Good catch. I've corrected the errored post, which should read "a few inches forward".

 

[charlief1]

So which is it -- forward or aft?

One of the interesting things I've found out is that Chinese junks had the daggerboard in the front, and the rudder was under the stern to some degree. A bit different but it is an interesting design.

 

[Petros]

Welcome to the forum,

a simple modified junk rig is perfect for this application. it performs well and is easy to handle and rig, it will not flog and can be made out of a flat piece of poly tarp or tyvek (house wrap), and does not require a boom, just full length battens every few feet. You can use a cantilevered 12 ft mast, and other than a halyard, and a single sheet, has no other rigging. It goes up quick and easy and not pron to fouling.

the one pictured below won a race in a contest where we had less than 24 hours to build the boat (from raw materials, no prefabricated parts) and than race a triangular course. there were many boats with much lighter crews and much larger sails, this sail out performed them all. The sail is made from a poly tarp, three battens, and colored duct tape took less than an hour to make. The mast is a single 2x4 cut tapered, no stays. That tri took about 9 hours total time to built with a two man building crew. A more carefully built one could perform even better.