Sweet Rhode Island Red
The edges would be hard wood—not foam, in case that wasn’t clear.
I think it would work fine, but we’ll have to find out. The nice part about putting the light part on the inside is that you can always throw some glass on the outside.
The alas are only 6’ apart.
Mike Leneman has made some pretty awesome structures with blue foam and plywood—you’d be amazed how strong they are!
I’m a real fan of foam core construction but would recommend a trial piece first, blue foam is pretty weak in shear. Rather than hardwood edges consider cedar or paulowonia, only thing hardwood adds in this case is weight. P52’s slats were 1x6 cedar with a 2x2 piece glued on bottom for a Tee section, leg reinf with some unidirectional glass on the bottom of the Tee 6oz biaxial shear webs up the 2x2, Spanned about 5’-8” , wouldn’t want to jump up and down but fine to stand on.
cheers,
Skip
The safety ama shape is my idea, but its placed based on Sven’s description of Pacific Bee’s stability curve. The pod touches when it heels 15 degrees. At that point the ama is about 28” off the water. Time to come down! The Concave shape is hopefully to trap some air and make it bounce with ground effect. Also, I don’t have any restriction on shape because its machined, so I went nuts.
I want a proa that puts itself back on its feet when the ama gets too high!
I think that this is a very important invention. Perhaps it still needs experimentation to prove it, but the idea behind it is very good.
Have you figured out how high Proud Mary is pointing? Maybe a GPS is the best way since it takes out the error of leeway you might encounter with a compass.
Funny you ask… I’m in NYC at the moment, and one mission of mine for the next 2 days is to try to get a GPS to play with. I’m quite lost on what to get, looking for something cheap that does that job, as I don’t really need a GPS for anything else…
Any suggestions?
It you have a smart phone use that, I have an iPhone and cycle tracker app
Tink
Let’s hope Tina approves. I think naming a line of proas after Tina Turner hits makes a hell of a lot more sense than most (thinking Mac OS naming conventions here).
I am totally with ya on the foils issue. They take as much time and effort and skill as an entire hull, and well…. wouldn’t it be cool to do without carefully machined foils and their cases, especially since with proas the whole rudder/daggerboard issue is fraught with negative trade-offs that cause us nightmares and really don’t contribute to the zen simplicity we are seeking with the type anyway?
As per, the presentation is flawless - I’ve tried a bit with Solid Works but honestly, I thought that doing carefully placed machine screws in an electronics panel is what it’s good for. Hat’s off for what is obviously maestro work here.
I must have missed it, but how long is SRIR?
Here’s one showing the bulkheads. There’ll be a stringer at the cockpit floor level on both sides, running the length of the boat.
At 16” immersion, Red is displacing almost 1400lb. The cockpit floor is 22” above the keel and the cockpit is 14” deep.
The water is a lot colder here—I need some freeboard! I wonder how that increased windage will effect the handling.
How do you decide what is a good displacement and depth to measure displacement?
Michael; SRIR is 24’ long over all. She’s 18” on the waterline. The ama is 16’ long and the safety ama is 10’.
skyl4rk: I have no idea what I am doing. I take the shape of the hull, guess about how deep it would immerse, create a solid that’s the same shape and size of the immersion. Then I assign that solid the density of water, and that’s the size of your hole in the water. I would like SRIR to be a bare bones backpack camper, so for two people that’s 700lb. plus a boat weight of say 500lb. so a lightship displacement NEEDS to be about 1200lb. does that include an anchor? 2.5 hp outboard? Can we still steer with weight when our weight becomes a smaller proportion of displacement?
That’s what I’m struggling with now. I could copy Proud Mary’s simple 3 stays and a slot rig.
Or I could build a rig on a central aka that pivots back and forth and is also adjutsable windward and leeward like Equilibre’s. I think the magic compromise there is that the yard travels up and down the leeward stay, not the mast. Its essentially “hanked on” to the leeward stay, keeping all that stuff to leward when it comes down.
Then there’s the question of rocker. Hugo thinks the squareness of Proud Mary makes her a good butt steerer. But micronesian canoes have lots of rocker. Gary Dierking makes the point that maybe that’s just to get more boat in the water—create lateral water plane.
How much waterplane do you NEED to go to windward like a champ—if a foil-less boat is capaple of that? How much does rocker effect butt steering? How necessary is it to move the rig to windward to go down wind?
And while we’re at it, why not design the waterplane of the boat to Tom Speer’s magic proa foil shape?
Here are some new renderings with more rocker, more spring in the sheer, and a different ama.
But they are already obsolete ideas as I am thinking about doing a more Brown-ish pod now that is one piece with the vaka. It will have a self draining well in it for fenders, dry bags and other light stuff.
Anyway, here’s a refinement of the hull shape.
chris
Michael; SRIR is 24’ long over all. She’s 18” on the waterline. The ama is 16’ long and the safety ama is 10’. She’s sporting 120 sq ft of sail—the same as a core sound 17 which feels like a fitting comparison.
skyl4rk: I have no idea what I am doing. I take the shape of the hull, guess about how deep it would immerse, create a solid that’s the same shape and size of the immersion. Then I assign that solid the density of water, and that’s the size of your hole in the water. I would like SRIR to be a bare bones backpack camper, so for two people that’s 700lb. plus a boat weight of say 500lb. so a lightship displacement NEEDS to be about 1200lb. does that include an anchor? 2.5 hp outboard? Can we still steer with weight when our weight becomes a smaller proportion of displacement?
That’s what I’m struggling with now. I could copy Proud Mary’s simple 3 stays and a slot rig.
Or I could build a rig on a central aka with a mast, set to windward of the vaka, that pivots back and forth between a windward and leeward shoroud, and is also adjutsable windward and leeward like Equilibre’s. I think the magic compromise there is that the yard travels up and down the leeward stay, not the mast. Its essentially “hanked on” to the leeward stay, keeping all that stuff to leward when it comes down—a little bit of Mary’s simplicity.
Then there’s the question of rocker. Hugo thinks the squareness of Proud Mary makes her a good butt steerer. But micronesian canoes have lots of rocker. Gary Dierking makes the point that maybe that’s just to get more boat in the water—create lateral water plane.
How much lateral waterplane do you NEED to go to windward like a champ—if a foil-less boat is capaple of that? How much does rocker effect butt steering? How necessary is it to move the rig to windward to go down wind?
And while we’re at it, why not design the horizontal waterplane of the boat to Tom Speer’s magic proa foil shape?
Here are some new renderings with more rocker, more spring in the sheer, and a different ama.
But they are already obsolete ideas as I am thinking about doing a more Brown-ish pod now that is one piece with the vaka. It will have a self draining well in it for fenders, dry bags and other light stuff.
Anyway, here’s a refinement of the hull shape.
chris
Here’s one showing the bulkheads. There’ll be a stringer at the cockpit floor level on both sides, running the length of the boat.
At 16” immersion, Red is displacing almost 1400lb. The cockpit floor is 22” above the keel and the cockpit is 14” deep.
The water is a lot colder here—I need some freeboard! I wonder how that increased windage will effect the handling.
How do you decide what is a good displacement and depth to measure displacement?
Skyl4rk,
It’s an iterative process, and you should KNOW what displacememt you need before you calculate it from the shape of the boat you design.
Or more exactly, you should know how much PAYLOAD you are going to put in that boat.
Is it a beach multihull, where you want to sail alone, with a knife and a bottle of water?
Or is it a weekender, with cooler, camping gear, food for 4 days, safety gear?
Or is it an offshore cruiser with all amenities, diving gear, a windsurfer, enough fuel for 400 miles without sails, etc?... And oh yes, that piano your wife want to play in the middle of the ocean…. (you get the picture…)
Some books provide standard lists to go through to make sure that you do not forget any heavy component. I believe the Gougeon brothers book on boatbuidling with epoxy has one.
Once you know the payload (and volume of accomodations) that you want, then you design the boat around it. You start with estimates on weight of the boat itself (hull, rig, sails, etc…) and come up with a design. From that design, now you can have a much more accurate boat weight. Adding the boat weight, and the payload (the crew should be part of the payload, by the way), that gives you a total weight.
Then add some safety factor… Depending how accurate you are, you can reduce it…
That will give you the displacement of the vessel. With your nifty software, “sink the boat” until you get that displacement.
Is it on your planned water line? If not something has to give; you have to build lighter, you have to reduce payload, or you have to reshape the boat to give it more buoyancy for no (or limited) added material. Or you accept that you will sail a dog…
Obviously, I oversimplified above; but the point is that it should be an iterative process. You start with wide brush strokes of general specifications, and at each iteration, you come to a more detailed and precise design and verify that you are still in the ball park for the way the boat is going to float once with everything on board.
For general specifications, it is good also to look at other similar boats; what Displacement to Length ratio do they have? What sail area to displacement do they have? etc…
My personal experience is that you usually tend to be over optimistic. My boat floats deeper than I originally wanted…
Regards,
Laurent
skyl4rk: I have no idea what I am doing.
😊
thats pretty much how i did my boat design. I was hoping somebody knew more than me.
So if we want to have a slot for the mast, to support it aback, why not put the mast to leeward of the gunlwale—the strongest thing around there.
The more I play with goofy ideas for safety amas, the more I want to build a simple, stitched on pod.
Now, with the pod, and the mast in a self draining locker 12 inches wide, the mast step can slide to leeward, while the mast still rubs the gunwale, and move the tip of the mast 32” to windward—the pip of the yard a lot more. That might be an interesting thing to try.
I don’t imagine any fancy track—more like you take the yard down, move the mast step, adjust the shrouds, and go. Maybe the trick is to move it as leeward as you dare and just adjust the shrouds to move the rig windward and leeward—like equilibre.
The bottom of the pod is 8” above the 1600lb waterline. It is immersed a couple of inches at 15 degrees. The total floatation is about 1200lb—if the pod is sealed. But with a 12” wide self draining locker in it, for dry bags etc. the displacement is more like 700lb—the same as my big concave board-ama. That space will come in handy.
But even better there is now NOTHING in the cockpit.
I like that.
here’s one more…
Looking good Chris, the pod does seem a little simpler/elegant. It’s hard to simplify simple designs but so very worthwhile. The “double tee” legs on the slats are probably deviating from that simplicity. P52’s slats were simple spans rather than cantilevered in SWIR plus there was some expediency involved. Not sure which way Nomad will go when the time comes. Still if the double tees were a result of my previous post, I’m honored.
Regarding displacement - 24 feet long foot and a half wide at the waterline is pretty much 24 square feet of water plane area which translates into two cubic feet (128# +/-) for an extra inch of immersion.
off to take another nap
Skip
Be sure to put a strip of something connecting the ends of those hiking slats, or every line on board will get caught in the slots. Don’t ask how I know.
I would want as much bury on the mast as possible, so I would put it on the inside of the hull, above the self bailing floor.
the difference is 2”, and you save yourself the trouble of making the slot piece—you get it for free from the pod, and its leaning along an already strong thing the raised gunwale, instead of adding a heavy, strong thing for the mast to lean on.
And you get an empty cockpit. And you get the option of moving the mast step to leeward to move the rig to windward.
I prefer the pod.