Headsail vs no headsail, efficiency

[dustman]

Originally Posted by Don C L

I am guessing you have looked at the Wharram Tikis? Those are relatively easy to build. If you are going to design trusses and a torsion box, could it on be made to be disconnected easily so that the hulls could be stowed together on a trailer?

Yes, some of the Wharram design concepts are my underlying inspiration.



I have consider making the hulls removable so that I can have more beam while still being trailerable, but am wary of the potential failure points that introduces as well as the increased complexity and weight.

[Mr B]

Trusses and a Torsion box, Make it easy for the centre section to bolted in and removable,
Four thick plates and dozen bolts wont add much weight and the beam, (width) can be what ever you want it to be,
The mast will be in the centre of the removable section,

Food for thought,

[Training Wheels]

Cat2fold!

[Luckyknot]

Sounds like a cool design project. I've been fascinated and obsessed with yacht/ship design for almost 25 years (I'm only 36). I went so far as to minor in it in college. As long as you do the reading and research as you've stated, then you understand that safety is paramount.

I personally think you are putting to much emphasis on which sail arrangement is most efficient. Style, safety, and purpose should be the main factors (not in that order of course). If your main goal is to maximize sail efficiency then you have to look at the system as a whole, in which case you need to change your entire design to suit that singular aspect. It sounds like you've already considered and decided what it is you want and what the pros and cons are. Sketch it out and see if it looks good to your eye. If it does then punch some numbers and see if it will do what you want. That's the beauty of all the sceience and math being added to the art of boat design. IMO it allows a designer to attack a concept where years of experience in building and/or sailing would otherwise be required. That being said, experience is still necessary to understand what it is YOU want personally in a boat.

I guess I don't really have any more technical advice to offer on this but figured I could add some thoughts and encouragement. Those that have responded directly to your question have done a good job. If you haven't, I would recommend reading The Sailmaker's Apprentice and Sail Performance. The former is easier to understand but with more of a focus on making the sails whereas the latter is more technical and would do a great job (probably) of answering your question if you understand it. Full disclosure, I'm still reading the second book but it comes highly recommended and has been very informative so far, though a little dated.

P.S. Remember that this is a cruising forum and not a boat building forum. You may find that you get a lot less support for these sorts of things here. Don't let it discourage you. If you don't get the answers to your questions here then consider joining and posting on more dedicated forums that tend to support and encourage these efforts. One can only take "just buy an old boat" or "what's the point" so many times. I look forward to seeing your concept!

[TrentePieds]

Hello gain Dustman :-)

You are a brave man – you've come back for more discussion ;-)!

So since I've seen no calculations in your posts so far, let me suggest some. Then we can come back to other things after that:

Assume LOA 30 feet and DOH (Depth of Hold – in your case, Depth of Hull) 3 feet. Coefficient of Profile Area: .8

Then each “wall” will have an area of (30 x 3 x.8) = 72 SqFt. There are 4 walls (given that there are 2 hulls). Therefore total area of walls: 4 x 72 = 288SqFt.

Add thereto the area of two decks: 2 (30 x 3 x .8) 144SqFt. Therefore total surface area of both hulls 288 + 144 = 432 Sq Ft.

Assume thickness of walls is 5/8”. Then there is (432/12) x 5/8 = 22.5 cu feet of material in the bare hulls. Red Cedar (the lightest viable construction material) weighs 23lbs/CuFt. Thus weight of wood in the two hulls = 23 x 22.5 = 517lbs (appr). Add thereto weight of cloth and resin for composite construction, say, 520 lbs for a total weight of the two bare hulls of 1,050lbs (appr.)

Do you still think that a displacement estimate of 1,200lbs is within reach? Remember that you still have to allow for the “girder” structure you plan to use. What are the specs of the tubing you propose to use? You also still have to add the weight of the rigging, whatever your choice may be in that regard, as well as any other thing that still has to be added, including yourself and your clobber!

Your assumed input parameters may be different from mine. No doubt they will be. My procedure, however, is correct, and you are welcome to use it and plug in different assumed input parameters since the procedure is one that, in my day, all boys had under their belt by the end of grade X :-)

MySaintedMother used to admonish me: “If it ain't quantified, it don't count!” I have no idea where she picked up such aphorisms since she was a lass from Darkest Denmark where no English was spoken in those days. But be that as it may, I gladly pass on to you her advice to me :-)!

Sømandshilsen :-)!

TrentePieds

[Don C L]

Seems like you could work it out with a Wharram Tiki 26. And I think the Marconi rig it is designed with pretty much will get the max in terms of performance. But I started wondering if anyone has tried rigging one like a proa instead? Kind of an interesting thought... and not too hard or expensive to experiment with?
On second thought... well it would be interesting to see it tested on some models first.

[thomm225]

Originally Posted by tomfl

A-Class cats. I rest my case.

That's nice, but you really can't compare a 165 lb 18' A Class Cat with it's high tech, square top, high aspect ratio main sail plus rotating carbon fiber mast and controls to say an old cruising boat sailing with an old low aspect main only

If I tried to sail my boat (a Bristol 27) in light winds with waves main only it woud barely move.

Whereas with a jib of maybe 120 % or so added it would do much better.

My last racing Beach Cat was a Nacra Inter 17 (later a become the Nacra F-17 used in the Olympics).

It was built for single handed racers and had a main and spinnaker only. I bought the option jib for mine it for distance racing. It would then perform much better on the upwind in wind say 12 and under. Much more than that and it was over powered and easily pitchpoled.

Downwind it also had the spinnaker. All together about 333 sq ft of sail on a 300 lb boat. Same sail area as my 6600 lb Bristol 27

It was faster than an A Class cat with that setup

Picture is of the early Nacra Inter I17R which came out around 2001......

Latest rev of the Nacra 17. See link. They made the jib standard for more power and changed the boat to 2 up. A 2 man boat and improved the hulls with wave piercing bows. The spinnaker retreival system was improved also. And now has foiling boards

We could hit low to mid 20 knot range back in the day one up but these are faster

https://sailboatdata.com/sailboat/nacra-17

https://www.youtube.com/watch?v=M1rZUMkisjA

[Don C L]

I can’t link it now but if you google “36 foot bluewater cruising pacific proa conceptual design” I’m curious what you think of that? I bet it would be fast, relatively easy to make detachable but it is pretty long! Still, other than the odd way of tacking and need to rig the steering boards and steering oars, I think the design is really intriguing.

[Don C L]

Check also: “tacking outrigger.com/25_proa_design.html”

He has a schooner rig for it to. I bet it’s fast! Looks like the ama can be folded up or removed easily too. I’d sure love to try one!

[Cheechako]

Depends a lot on the boat, but mainsail only can limit your ability to steer/control the boats sometimes. As can headsail only.

[sandy stone]

Originally Posted by dustman

Sandy Stone, the boat I intend to build would cost less than a used stiletto, minus the potential problems with a used boat. I have seen one too many horror stories about dumping money into used boats. Also, part of my whole reason for building my own is the experience of doing it, and all that I will learn, and the feeling of accomplishment. It would also be more practical for the type of cruising i intend to do.

OK, I get that, even if it's not something I personally would want to do. I wish you all the best.

[dustman]

Originally Posted by TrentePieds

Hello gain Dustman :-)

You are a brave man – you've come back for more discussion ;-)!

So since I've seen no calculations in your posts so far, let me suggest some. Then we can come back to other things after that:

Assume LOA 30 feet and DOH (Depth of Hold – in your case, Depth of Hull) 3 feet. Coefficient of Profile Area: .8

Then each “wall” will have an area of (30 x 3 x.8) = 72 SqFt. There are 4 walls (given that there are 2 hulls). Therefore total area of walls: 4 x 72 = 288SqFt.

Add thereto the area of two decks: 2 (30 x 3 x .8) 144SqFt. Therefore total surface area of both hulls 288 + 144 = 432 Sq Ft.

Assume thickness of walls is 5/8”. Then there is (432/12) x 5/8 = 22.5 cu feet of material in the bare hulls. Red Cedar (the lightest viable construction material) weighs 23lbs/CuFt. Thus weight of wood in the two hulls = 23 x 22.5 = 517lbs (appr). Add thereto weight of cloth and resin for composite construction, say, 520 lbs for a total weight of the two bare hulls of 1,050lbs (appr.)

Do you still think that a displacement estimate of 1,200lbs is within reach? Remember that you still have to allow for the “girder” structure you plan to use. What are the specs of the tubing you propose to use? You also still have to add the weight of the rigging, whatever your choice may be in that regard, as well as any other thing that still has to be added, including yourself and your clobber!

Your assumed input parameters may be different from mine. No doubt they will be. My procedure, however, is correct, and you are welcome to use it and plug in different assumed input parameters since the procedure is one that, in my day, all boys had under their belt by the end of grade X :-)

MySaintedMother used to admonish me: “If it ain't quantified, it don't count!” I have no idea where she picked up such aphorisms since she was a lass from Darkest Denmark where no English was spoken in those days. But be that as it may, I gladly pass on to you her advice to me :-)!

Sømandshilsen :-)!

TrentePieds

You are correct, my input parameters are much different.


So, the hulls are going to be made of rigid foam formed around rectangular aluminum tubing and finished with minimal fiberglass, reinforced in key areas, such as where it will be beached. There will be aluminum mesh welded to the tubing so that the foam can become one with it. The hulls will be approx 60 degree vees, approx 18" top to bottom, approx 16" wide at the top, slightly rounded over to shed water faster. The front will expand upward gradually to 24" above waterline for reserve buoyancy, to prevent bow burying, and maybe 18" at the back. Minimal rocker towards the ends. The draft will be about 9" at 1200lbs(30' LWL). About 100ft2 of wetted surface area. I figured out in the past how much fiberglass, but all I remember is that it will be less than 100lbs. The foam should come to about 150lbs. The aluminum frame for the whole boat, including the aluminum masts and the parts embedded in the hulls should come in at around 400 lbs, maybe less if I do some fancy engineering and welding. The upper crossmembers and "posts" leading into the hulls will be 4"x6" with 1/8" walls, bottom chord and various bracing will be lighter duty. Using 1/4" plate aluminum to reinforce all joints, so I can have more weld contact if that makes sense. The welds are what I'm worried about more than anything else.



I'm going to use rain catchment and a solar still for fresh water so I won't have to store much. Lightweight flexible solar panels, lithium batteries, light electric propulsion system. Light everything, including myself at 155lbs. Keep in mind I'll never be more than 50 miles from land on this thing.



Sorry I'm not going to write out all the calculations or address every other point you made as I don't feel it's terribly relevant at this point. But please do feel free to critique(critique, not criticize) what I have offered thus far. At some point I will create some reasonably detailed drawings and post them. I still have a long way to go and a lot of details to work out before I consider starting to build.



Thanks for taking the time to give your input.

[dustman]

Originally Posted by Don C L

I can’t link it now but if you google “36 foot bluewater cruising pacific proa conceptual design” I’m curious what you think of that? I bet it would be fast, relatively easy to make detachable but it is pretty long! Still, other than the odd way of tacking and need to rig the steering boards and steering oars, I think the design is really intriguing.

That is a quite interesting concept.


I like the idea of using a symmetrical schooner rig with rotating masts and roller furling headsails on either end with this design. Seems like it would be a much more difficult engineering challenge to make safe than a simple catamaran. One of the coolest proa designs I've looked at though.

[dustman]

Originally Posted by Luckyknot

Sounds like a cool design project. I've been fascinated and obsessed with yacht/ship design for almost 25 years (I'm only 36). I went so far as to minor in it in college. As long as you do the reading and research as you've stated, then you understand that safety is paramount.

I personally think you are putting to much emphasis on which sail arrangement is most efficient. Style, safety, and purpose should be the main factors (not in that order of course). If your main goal is to maximize sail efficiency then you have to look at the system as a whole, in which case you need to change your entire design to suit that singular aspect. It sounds like you've already considered and decided what it is you want and what the pros and cons are. Sketch it out and see if it looks good to your eye. If it does then punch some numbers and see if it will do what you want. That's the beauty of all the sceience and math being added to the art of boat design. IMO it allows a designer to attack a concept where years of experience in building and/or sailing would otherwise be required. That being said, experience is still necessary to understand what it is YOU want personally in a boat.

I guess I don't really have any more technical advice to offer on this but figured I could add some thoughts and encouragement. Those that have responded directly to your question have done a good job. If you haven't, I would recommend reading The Sailmaker's Apprentice and Sail Performance. The former is easier to understand but with more of a focus on making the sails whereas the latter is more technical and would do a great job (probably) of answering your question if you understand it. Full disclosure, I'm still reading the second book but it comes highly recommended and has been very informative so far, though a little dated.

P.S. Remember that this is a cruising forum and not a boat building forum. You may find that you get a lot less support for these sorts of things here. Don't let it discourage you. If you don't get the answers to your questions here then consider joining and posting on more dedicated forums that tend to support and encourage these efforts. One can only take "just buy an old boat" or "what's the point" so many times. I look forward to seeing your concept!

The sail efficiency thing is a side note to the rest of the project, just wanted to get a feel for what everyone thinks. These posts always get off track and sometimes misconstrued. This is one question of many I have. Most have been answered decidedly through my reading of studies and books, the rest I bring here. What I've realized is that there are many different opinions on some fundamental principles, so I'm trying to iron these things out in my mind.



I do understand that safety is paramount, that is my primary design goal within the limitations I am given.



This boat is going to be somewhat ugly, and minimalist, but honestly I don't care. As long as it gets me where I want to go safely and at a reasonable speed I will be happy.



Thank you for your input, concern, recommendations and encouragement. It is much appreciated!

[Don C L]

Originally Posted by dustman

That is a quite interesting concept.


I like the idea of using a symmetrical schooner rig with rotating masts and roller furling headsails on either end with this design. Seems like it would be a much more difficult engineering challenge to make safe than a simple catamaran. One of the coolest proa designs I've looked at though.

Huh, I kinda think it would be just as safe as a cat, with the advantage of rigging a possible way to detach the ama and right the main hull in the event of a capsize. I'd love to hear from some proa sailors, but that design really has me thinking now that a cruising proa like that has real potential, for those who want to trailer, go fast, and don't mind the spartan accommodations.

Anyway, looking forward to see what else you can find.