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Old 20-01-2020, 15:22   #16
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Re: Headsail vs no headsail, efficiency

The foresail feeds “wind”. To the back side of the mainsail. Ventilates it and prevents the mainsail from stalling

This increases the efficiency of the mainsail
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Old 20-01-2020, 15:33   #17
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Re: Headsail vs no headsail, efficiency

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What I am gathering so far is that there is not enough difference in efficiency to make it a deciding design factor.


Not sure exactly what additional info you need, but I will give a brief description of the boat I plan to build.


My first boat will be for cruising the Bahamas and perhaps more of the Caribbean, I'll likely be dropping it in the water at Corpus Christi and working my way over. Later, after having gained experience, I will be building a much larger version for ocean crossings.



It will certainly be a catamaran, approx 30' waterline, 12' beam, either a schooner or ketch, leaning towards a gaff rigged ketch with freestanding masts. Since I am limiting the beam so much I want to split the sail plan up to keep the center of effort low. A ketch, in my limited experience but abundant research, seems like it gives you a lot of options and control. The hulls will have no storage or accommodations, being something like scaled up versions of hobie 16 hulls but not quite as skinny, there will only be a very small, highly aerodynamic cabin on deck, everything mounted on an aluminum frame. The whole idea is simple, cheap, light, minimal windage, minimal draft, and easily handled by myself alone and an eye to reducing/eliminating potential maintenance and failure points. The loaded displacement for myself alone should wind up being about 1200 lbs, with a sail area of 120-150ft2, divided between fore and aft masts, thinking about a 60-40 sail area distribution, with sails of 3 to 1 aspect ratio.


I hope you guys can make sense of all that, writing is not my strong suit.
Good luck with your pipe dream.
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Old 20-01-2020, 16:32   #18
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Good luck with your pipe dream.
Thanks for the thoughtful, informative and helpful reply
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Old 20-01-2020, 16:37   #19
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Re: Headsail vs no headsail, efficiency

Dustman:

You say: “What I am gathering so far is that there is not enough difference in efficiency to make it a deciding design factor.”

No! That is a misinterpretation of all that has been said. It is far from as simple as that! I feel that in conscience I must warn you against spending substantial money on the construction of ANY boat, mono- or multihull, before you have spend AT LEAST an amount of money equal to the construction cost of a 30 foot mono on the formal study of yacht design! Yacht design is a CLASSIC case of “knowing just enough to be dangerous”!

Catamarans are not my area of interest particularly, but the length, beam and displacement you give strike me as being WILDLY out of sympathy with each other. Perhaps I'm wrong. For your own good, DO prove me wrong!

Start with letting us see the calculations for your proposed boat's displacement. When you have that number, you need to proceed to calculating your proposed boats Length to Beam ratio. Again, do let us see your calculations! If I recall correctly, that ratio should fall between 2.2 and 3.2. Again IIRC, at a ratio of 2.2 Transversal Stability and Longitudinal Stability (which is not something we bother much about in monos, but is EVERYTHING in regard to seaworthiness of cats), If the transversal stability is too low you cannot carry “enough” sail, and it it is too high the boat will be slow. Only after you have these things under control can you begin to consider the amount of sail.

It is possible to rig a catamaran as a ketch – but why would you? Do you understand why the ketch rig exists at all? And what it's drawbacks in terms of “efficiency” are?

You cannot circumvent the need for learning and understanding by using a “design program” or by asking us in this forum about this and that minuscule element of design. As that doyen of Capitalism, Malcolm Forbes emblazoned on the cover of his Forbes' Magazine: “With all thy getting, get understanding”!

May the wind be ever at your back :-)!

TrentePieds
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Old 20-01-2020, 17:15   #20
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Re: Headsail vs no headsail, efficiency

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It will certainly be a catamaran, approx 30' waterline, 12' beam,


With that size a sloop or uni rig would make sense. The sails would be easy to handle, it would be less weight and less complication than a schooner or ketch.


I am limiting the beam so much I want to split the sail plan up to keep the center of effort low.

Put a bow sprint (many cats have them) on it for light air area if you want to stretch it out and keep the effort low.
.........
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Old 20-01-2020, 19:06   #21
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Re: Headsail vs no headsail, efficiency

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Dustman:

You say: “What I am gathering so far is that there is not enough difference in efficiency to make it a deciding design factor.”

No! That is a misinterpretation of all that has been said. It is far from as simple as that! I feel that in conscience I must warn you against spending substantial money on the construction of ANY boat, mono- or multihull, before you have spend AT LEAST an amount of money equal to the construction cost of a 30 foot mono on the formal study of yacht design! Yacht design is a CLASSIC case of “knowing just enough to be dangerous”!

Catamarans are not my area of interest particularly, but the length, beam and displacement you give strike me as being WILDLY out of sympathy with each other. Perhaps I'm wrong. For your own good, DO prove me wrong!

Start with letting us see the calculations for your proposed boat's displacement. When you have that number, you need to proceed to calculating your proposed boats Length to Beam ratio. Again, do let us see your calculations! If I recall correctly, that ratio should fall between 2.2 and 3.2. Again IIRC, at a ratio of 2.2 Transversal Stability and Longitudinal Stability (which is not something we bother much about in monos, but is EVERYTHING in regard to seaworthiness of cats), If the transversal stability is too low you cannot carry “enough” sail, and it it is too high the boat will be slow. Only after you have these things under control can you begin to consider the amount of sail.

It is possible to rig a catamaran as a ketch – but why would you? Do you understand why the ketch rig exists at all? And what it's drawbacks in terms of “efficiency” are?

You cannot circumvent the need for learning and understanding by using a “design program” or by asking us in this forum about this and that minuscule element of design. As that doyen of Capitalism, Malcolm Forbes emblazoned on the cover of his Forbes' Magazine: “With all thy getting, get understanding”!

May the wind be ever at your back :-)!

TrentePieds

From my understanding ketch/fractional rigs have several advantages:



-the ability to balance the helm by adjusting sail balance
-lowering the center of effort by splitting one large rig into smaller ones
-easier sail handling by reducing the size/weight of each individual sail
-less weight up high


Also,
-i won't have to climb up a high mast for any reason, won't need a harness, hoist and all that
-in my situation it will be cheaper than a larger single mast
-the two masts will align with my existing planned framing system and not require additional structures and reinforcement


The only real drawback i can see in my situation is that ketch rigs supposedly don't point as high into the wind, but i feel this will be made up for with the extremely low windage overall of my design.


When I said this: What I am gathering so far is that there is not enough difference in efficiency to make it a deciding design factor. I meant simply that the difference in the power per sail area doesn't seem significant enough for it play a big role in the design decision.



The design I'm considering is almost twice as long as the hobie 16 and 50% wider equating to well over 4 times the initial stability while carrying around 2/3 the sail area with a relatively lower CE. That said, you can rest assured that I will carefully calculate the righting moment, etc before finalizing my design. I am terrified of dying, believe me when I say I will do everything in power to keep that from happening. When I have a final design I will post it here as well as have a structural engineer and catamaran designer analyze it.



As far as the dimensions and displacement... Aside from stability, the length to beam ratio of a cat seems of concern because of wave interactions between the hulls. With such long skinny hulls the wavemaking of this design will be practically nothing, especially at the lower speeds I will be going. The real reason I am limiting the beam is so I can trailer it to where I intend to launch it. If I can't do that the overall cost of the project would likely be nearly double. I had already done some rough calculations on what the frame, hulls, rigging, cabin, person, propulsion, supplies, etc would weigh, and that's how I came to the 1200lb displacement. I feel like people's imaginations aren't grasping the design. It will be extremely basic with few amenities. I already live very simply in a very small space. I will have nothing more than what I actually need. Think tent camping on an oversized hobie 16.



I have read hundreds if not thousands of articles, studies, forum posts, etc about hull/yacht design along with several of the most highly regarded books on yacht design. That said, I am here to learn more and hope that some of you will help me hone my knowledge and realize my dream.


So back to the sails...... Is there any really good reason not to eliminate the headsail? Any good reason not to go with a ketch?
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Old 20-01-2020, 20:02   #22
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Re: Headsail vs no headsail, efficiency

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So back to the sails...... Is there any really good reason not to eliminate the headsail? Any good reason not to go with a ketch?
Well, I have seen a Freedom 28 cat-ketch under sail, and it looked like about the most miserable rig ever for even attempting to go upwind.

What you're proposing reminds me of a Stiletto 30, with some important differences. The Stiletto has some accommodations in the hulls, leading to (I think) a 2000 lb displacement, plus it has a fractional sloop rig and an 18 foot beam. Are you sure it wouldn't be easier to just buy one used rather than design and build your own boat?
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Old 20-01-2020, 20:40   #23
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Re: Headsail vs no headsail, efficiency

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Well, I have seen a Freedom 28 cat-ketch under sail, and it looked like about the most miserable rig ever for even attempting to go upwind.

What you're proposing reminds me of a Stiletto 30, with some important differences. The Stiletto has some accommodations in the hulls, leading to (I think) a 2000 lb displacement, plus it has a fractional sloop rig and an 18 foot beam. Are you sure it wouldn't be easier to just buy one used rather than design and build your own boat?

I just looked up the Freedom 28 cat-ketch. It gave me a good chuckle, it looks like a floating turd with sails. I would not expect it to go well into the wind just by looking at it. That has little to no relation to my design. It weighs 7000lbs, has length to beam ratio of around 2.6 to 1, I'd be surprised to get 6.5 knots out of that thing at the best angle in the best possible conditions. The sails look like they would not get along well.



The Stiletto is more the idea, but more streamlined hulls and structure, less windage and much less weight. The stiletto displaces 2100lbs, I imagine that is before crew and supplies.
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Old 20-01-2020, 20:45   #24
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Re: Headsail vs no headsail, efficiency

I have misused the term "fractional rig" in my post, forgive me.
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Old 20-01-2020, 21:19   #25
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Re: Headsail vs no headsail, efficiency

I dont sail upwind, Too much effort required, Im a cruiser and will wait for the right winds going my way,

Im 34 foot long Cat, and 14 feet wide, With a fractional mast,

After a lot of Nmiles at sea, I found my 150 Genoa was all I needed, For the extra knot on the GPS, I packed the main away and never used it again,
I weigh 4.5 tons, Pulls 18 inches of draught with the boards up, 5 feet with them down,
My Gemini 105MC sits on top of the water, Not in it,
7 knots on the diesel, I had 14 knots with a sail chute up,
But 12 knots on the genoa is easy,

Hope this helps,

Cheers Brian,
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Old 20-01-2020, 21:28   #26
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Re: Headsail vs no headsail, efficiency

There are quite a few cat ketch rigs on monohulls out there. I haven't sailed one but I bet they do well to windward. I just can't imagine right now how you rig that on a catamaran if masts are to be free standing. In fact I can't say I have ever seen ketch rig on a catamaran. Is a trimaran ruled out for you? There are some nice trailerable ones out there, and they will be considerably more stable than a narrow cat.
There is also one called a Sea Pearl, but I am not sure if that design would interest you:
The Versatile Sea Pearl Trimaran | Small Trimarans

edit:
ok, I forgot about proas, have you looked into those? here are just a couple,
http://wikiproa.pbworks.com/w/page/1...22Ping-Pong%22
https://www.clcboats.com/modules/cat...t-pacific-proa

probably too beamy for you though.
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Old 20-01-2020, 21:31   #27
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Re: Headsail vs no headsail, efficiency

Mr B, thanks for the info.


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.
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Old 20-01-2020, 21:47   #28
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Re: Headsail vs no headsail, efficiency

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There are quite a few cat ketch rigs on monohulls out there. I haven't sailed one but I bet they do well to windward. I just can't imagine right now how you rig that on a catamaran if masts are to be free standing. In fact I can't say I have ever seen ketch rig on a catamaran. Is a trimaran ruled out for you? There are some nice trailerable ones out there, and they will be considerably more stable than a narrow cat.
There is also one called a Sea Pearl, but I am not sure if that design would interest you:
The Versatile Sea Pearl Trimaran | Small Trimarans

Hard to explain without illustration, but the crossmembers would be like a truss made of rectangular aluminum. The round aluminum masts would be inserted through the bottom and top chord of the trusses so would be supported at two points. The hulls and crossmembers would be further braced at various angles, basically creating a torsion box.
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Old 20-01-2020, 21:55   #29
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Re: Headsail vs no headsail, efficiency

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There are quite a few cat ketch rigs on monohulls out there. I haven't sailed one but I bet they do well to windward. I just can't imagine right now how you rig that on a catamaran if masts are to be free standing. In fact I can't say I have ever seen ketch rig on a catamaran. Is a trimaran ruled out for you? There are some nice trailerable ones out there, and they will be considerably more stable than a narrow cat.
There is also one called a Sea Pearl, but I am not sure if that design would interest you:
The Versatile Sea Pearl Trimaran | Small Trimarans

I have considered a Trimaran, but would be more complex to build and not really be practical for my intentions unless significantly larger. The imposed layout on the trimaran would also not be what I'm looking for. I really want to build my own boat, and create something special, rather than just buying something. The whole process fascinates me.
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Old 20-01-2020, 22:10   #30
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Re: Headsail vs no headsail, efficiency

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?
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