Low-speed sailboat hull

two really light folding canoe hulls to form a catamaran, trampoline deck. You can carry a lot of sail, or fully reefed, canoe stern would be very low drag at both low and high speeds.

stow gear inside the hulls and plenty of room on the deck for passangers or additional gear, very stable and easy to manage.

design the two hulls as folding kayaks than when you get to camp you can disassemble the deck and use the hulls as a one person kayak to explore local shallows. the whole thing should not weight more than about 60kg including rig and deck.

 

Thank you, rwatson. Do you have any eyeball estimate on CP of Annabelles hull? I find little information on hydrostatics and hydrodynamics of this little boat.

Also, do you think it's 29kg for hull only, or if that's including spars, rigging, daggerboard and rudder?



Ah, yes, Blivit13. I was more or less basing my design on it. I thought I could substitute Dacron with nylon or polyester fabric coated with polyurethane, forgo the kevlar at all, and as for the rigging, go with birdsmouth mast and Tyvek sails. Maybe it would end up a little heavier, but I can't see why it shouldn't fit my budget...



Ben G, thank you for your advice. It's just that last time I sailed, I had a horrible make-do boat with zero rocker, which was way too heavy, had immersed transom, and no arrangements for sailing rig (things I had to improvise). And I sat at the same spot in the lake for hours. So, knowing these conditions, I want to find or design a boat that would spare me the torment.


Thank you, Petros, but as I said, I have to make this car-toppable. My car has roof rack limit of 35kg, and there ain't a lot of space in the trunk. I'm not rejecting multihull idea as of now, and folding design (either multi or mono hull) is also an option I'm considering, but right now, I just wanted to ask about non-folding ultra-light car-toppable monohull.

 

I went ahead and tried to replicate Annabelle's hull in Delftship.

Attaching file in 4.03.68 version. If someone could open it, please take a look.

Of course, this is rough eye-ball estimate, but it seems about right. At 210kg displacement (29kg boat + 182kg of maximum load stated in website) it doesn't look too overloaded.

 

Why ?

Once again, don't make it a 'mind trip'. You either want to sail, or you want to chat

You are going to take several years to learn to sail a small dinghy efficiently, and the CP and any other characteristics will fade into total insignificance against the realities of wind, water and waves.

Besides, the underwater hull form on dinghies changes dramatically with operator controlled trim, weight of gear etc.

Just do it !

 

I've read this entire thread.

I'll give you my thoughts on the matter. They are based on theory as well as a lot of experience sailing on small lakes.

What I think you need is a very short boat.

The reason for this is a short boat will have a much higher Displacement/Length ratio (D/L) for its weight than a longer boat will. The hull is also likely to be lighter.

A mono hull with a high D/L is more likely to coast between zephyrs than a low D/L one

I think a pram dinghy in the 2.5 m range could work quite well.

Next you need a fairly generous Sail Area (SA). It is probably best that this SA is is tall, as well as large, so it can use the slightly faster winds that are higher off the water. It may even be argued that a taller rig may be more effective than a shorter one, even with more SA, in these conditions.

I'd go with a triangular rig, a Lateen, Bermudan, or a Leg-o-Mutten, as these are usually tall, to get sufficient SA, anyway.

Just look forward to having either a very long yard, or a very tall mast.

It is possible to make either so it can break down into smaller pieces.

I'd be tempted to go with a Leg-o-Mutton, as its boom is really a sprit, and it is usually quite high above the cockpit.

You said that you expect this boat to displace between 120 to 200 kg.

To pick a good SA target, I averaged these two to come up with a displacement of 160 kg for my target SA.

Aiming for a Sail/Displacement (S/D) of at least 20, I came up with a target SA of about 6.0 sm.

With a 5.0 m mast, assuming a 0.5 m bury, I end up with a 2.67 m long 'Boom'. Since this 'Boom' is really a sprit, it must extend past the mast some. More likely it will be 3.0 m long, or longer.

The rudder and the 'board need to be efficient as possible. They both need to be at least 2:1 Aspect Ratio (AR), meaning, measured from the Water Line (WL), they are each twice as deep as they are long. They should have at least a rounded leading edge and a tapered trailing edge. Having an actual airfoil section would be even better.

So that's about it.

There are many pram dinghy hull designs on the market that will probably suit your needs, or come close. Phil Bolger's "Elegant Pram" is what first comes to mind. It is just two side pieces bent around just one mold, and attached to bow and stern transoms. The single bottom piece is then screwed on. He designed it with a 5.5 sm Leg-O-Mutton rig. He once complained that it "embarrassed" some of his more expensive designs, by sailing so well.

Some pdracers (see www.pdracer.com) have been built at around your target weight, though most are much heavier. One had a hull weight of just 25 kg. It is about the crudest pram dinghy there is. Just a rectangular box with a curved bottom.

If you want to design your own pram dinghy, just make sure both bow and stern transoms are out the water, at the 200 kg maximum displacement. From there, just imagine the water going around the hull. Try to make its path as easy as possible.

 

You're right. It's just that I know nothing about this boat except what is on that webpage. No information on materials, required tools, and so on. For example, I don't have table saw, nor buzz-saw, only jigsaw. Marine plywood is unavailable in our country, only exterior grade. It is impossible to locate mahogany. Dacron can be only obtained if ordering from USA, as there are no manufacturers in our continent that I know of. I have never seen nylon/polyester above 2oz in my country. Fiberglass cloth? I looked for it extensively few years back, and the there was only one source - and it was light stuff used for model planes. Anything unobtainable could double my budget quickly if I had to order from abroad.

I'd really love to build this Annabelle boat, but I hope to gather more info before I order up the plans...

Skyak, thank you for joining. As I mentioned, I'll often sail with a passenger on whole-day trips. It might get cramped in 2.5 boat... I started my considerations with 3.5-4m hull, MAYBE 3m, but lower than that... It would have to be very beamy to support weight of 2 sailors, and that could mean poor hydrodynamics... Am I not right?
As for the pram itself, some time ago, I considered Nutshell Pram (simplified to cut down costs), but dismissed it in the end because I saw that prams tend to slam into the waves with the bow plate, slowing them down a lot, and they tend to make huge wave of their own at the bow in higher speeds, creating lots of drag.

Why would bow plate be preferable to wave-piercing, narrow bow?

I know you're right about this. Taller rigs have better aspect ratio, and they perform better in any conditions. But they add lots of complications. Long mast, stays (I haven't yet seen unstayed Bermudian sail that keeps proper shape), lots of weight aloft, expensive materials for sails and rig for them to hold together, high CoE, more prone to capsize, and so on...

So in spite of better performance, I would prefer to have more practical, simpler rig... I mean, if what I said isn't true, why are traditional rigs still in use on small boats?

Agreed. Actually, since I'll be doing sails myself from Tyvek or tarpaulin, I can make several sails for different conditions (apart from reefing). But for really light winds, yes, 6 sm is the minimum, I believe.

As for rudder and daggerboard, I completely agree. Waters aren't shallow where I'll sail, so no limitation there on their aspect ratio. I guess I'll need them big anyway, for most of the time, I'll be reaching in 0-2 knot winds, and with little speed to create lift from airfoil shape, I need something extra to negate the drift.

But I'll go with NACA profiles, that's for sure.

 

Because you can get a ton of reserve buoyancy with a spoon shaped bow without a long overhang. Boats that are short compared to their beam and sail area (most small boats) will pitch down too much on a broad reach. Either you need to be able to shift your weight far enough back to compensate, or you need lots of volume forward. You gain a lot more than you loose on a small boat. See the Mirror Dinks, Y-flyers, Pelicans, etc. My pram bowed 16' pocket cruiser would hit 15 knots with a modified Hobie 16 rig. No trapeze, just kicking straps, and really terrible foils as well. It would also carry five adults in comfort daytripping around the Keys. The bow plate doesn't slow it down because the shape of the bow generates lift and helps maintain the correct trim. And you can actually stand right on the bow with both feet, very handy when beaching ,etc.

 

That makes a lot of sense. Thank you. Also, come to think of it, prams are often described as boats which are built when you don't have specific displacement in mind. But what about that bow wave I mentioned? Here, take a look at this video. It seems to me that this pram slams and sprays much more than it should.

Do you know any pram designs that would fit my criteria? 800-1000$ budget all included, 3-3.5m LOA, under 25kg, spacy enough for whole day cruise, designed for extremely low winds? It'd also be great if none of spars were longer than the hull itself (or would fit onside).

P.S. By the way, what are the advantages of Annabelle bow compared to pram bow, then?

 

You could use a fully battened rig, it does not need any significant shroud tension. For simplicity, perhaps not even square headed. The old inland central European lake boats used these probably a century ago and they still work OK. Gives a better aspect ratio to the main AND holds a good shape in light airs. Check the Thames A Rater and Solo boats for examples, the former has a jib of course, however both are well known for ghosting in light air very well for their length and size over wetted area etc etc.

They are actually very simple, and roll up perfectly. You don't need much broadseam and the key is the luff curve when designing the sail.

 

lakejas, how much sailing experience to you have? What size boats?

 

Well... That's the thing. I never had a proper boat. My whole experience was trying to make some kind of junk rig or adapt some poor fishing boat to become a sailboat. I have built bottle raft, 3m catamaran, and rigged 2 fishing boats. All of these projects were not very successful, although one of these fishing boats was barely acceptable as a sailboat. Conditions in which I sailed were usually horrible (dead calm with gusts up to 25 knots from any direction). So I've got some experience, but I don't know if it counts.

I never had a chance to learn with proper sailboat. Mainly because of lack of finances. Now that I, besides studies, have a job, can finally save up and build a proper boat to properly learn with.

Take a look at my previous posts about my projects. You will finds photos and descriptions of my adventures.

 

A lot has happened while I went to go scan a picture. My dad died a couple weeks ago and I've been going through his old photos. Found this one of a Mac 14 that he bought. The photo must have come with the boat. I have no idea who the people are.

Yes, versatility is under rated. You can't get more versatility than with a pram.

 

pram type dinghys are compact and versatile true, and they can carry a lot for their size too. but their performance really sucks, that flat front plows through the water like shoe box, the short length means it will feel like you are dragging a rope through the water unless you can get them up on plane.

When I was in elementary school we had a great wood shop class, and the "rich" kids would build the El Toro prams from kits (which were too pricy for the rest of us normal families). I wanted one so bad, I had always longed to have one and they still get my attenion when I see a nicely made one. Now some 25 or so small boats later, I had finally built one from salvaged wood for a $50 sailboat race (from published plans, which I rarely do). I wanted to finally see what they were like and why they are so popular. it was roomy and stable for such a small boat (8 ft long), but I just could not get it go very fast. It was a total pig in the water and I was really disappointed.

For a kid's boat, or perhaps a compact tender for a yacht, fine, but if you want something that performs, build a bigger better boat.

 

Phil, my condolences about your father, I'm sorry to hear that.

Thank you for the photo you provided. Still, do you agree to the concerns about performance of pram I mentioned?

Well, that's what I'm afraid of. Out of existing designs, Petros, what would you recommend to fit the criteria I described? What do you think about Annabelle?

 

It looked fine to me (in the video). It was a really small boat. Prams may be the plowhorse of small craft, but they are good-natured and reliable. I ended up converting my 16'er to a trap tender and fishing skiff. I'd be the smallest boat out ocean-side pulling traps during the Christmas trades by about 10 feet. My neighbors would go out with me when it was too rough for their 21 footer. And they needn't be slow. They are able to carry more sail and generate more righting moment and not stuff the bows compare to other small boats. I kept mine for 25 years. Having said all that, I think there is a fairly small size niche where they really excel, but there are an awful lot of boats about that size.