The Concept Catamaran Project
Hello fellow boat designers -- the following web link reveals an article I wrote entitled: The Concept Catamaran Project.
Basically, I am seeking feedback on views presented in the WIP article. All constructive views are welcomed.
Comments or questions about the article should follow this post so everbody can read about any changes to the design. The attached image file is what the project looks like at this time -- but could change over time due to new concepts posted here at the forum.
Cat 5 update
Version 2 of the Concept Catamaran Project is ready for viewing. Using the Cat 5 design -- I have changed certain concepts from Version 1. The following points are the changes:
1. Better scaling. Version 1 sported a 36' design -- but after making proper headroom in the cabin, the bridgedeck cabin looked a little stubby -- so I stretched the whole catamaran to 48'. This design action not only allowed for more room for "visiting guest" on our liveaboard home, but the first 10' of the bows are designed to give better longitude stability and are basically empty of weight. The downside of a longer boat will cost more at dockside -- but true liveaboard sailors live "on the hook" where the mooring cost can be next to nothing.
2. Better bow freeboard to handle those big waves at high speed.
3. Material keel framework that attaches to the stern & stem -- and "deck keel". If the catamaran is made from wood or metal and not fiberglass, such a rigid frame would be necessary to give rigidity to the hulls. The widest distance between hull chine lines is no greater than 4' -- making the design composed from 4' by 8' sheets of marine plywood.
4. More detail to the kick-up rudder design. A steering shift cable can be used to move the tiller bar under a rear deck where a small tender craft (yet to be designed) could be stationed. An elevated steering station should be able to see a clear view of the desired heading -- and while standing, should be able to see the bow during docking.
5. A novel outboard electric motor design that could be raised when not in use. There is room for two of these motors that also could be used as water-generators to charge batteries.
6. Some forward support crossbeams that could hold a set of anchor stations and netting for what catamarans are known for -- lots of fun for laying or romping.
Not shown in the latest image is the bracket frame that binds the bridgedeck to the hulls. Interior layout is not fully designed at this time -- but should have a nice galley & at least two bath sites. A roomy center lounge and a computer/navigation station would be nice.
Feedback is welcomed.
Is this a sailing cat or a power cat??? hard to tell, but it seems under-powered either way. Also, have a look at some of the authoritative texts on Aerodynamics, they may clarify a few points in you're article.
Open Source Marine Charting - openpilot.sourceforge.net
Open Source Vessel Dynamics opendynamics.engineering.selfip.org
Thanks Tim for the feedback. The following response is almost the same I gave over at the SimFlight forum regarding reaction to my last post of this catamaran project.
The small sail is better for hard sea condition handling and stability. Perhaps the most common response I received from friends (and family) is that "the sail is too small" -- but there is a reason why it is "small" and I say so within the article.
If sail power were only measured by the square foot size -- yes, the Cat 5 Lateen sail plan is small when compared to conventional sloop or cutter rigs. However, because I believe the Lateen sail rig shapes the wind into a better torque driving device than a comparable conventional sail rig of the same size, the overall size can be made smaller than what may be assumed as the standard sail rig for a 48' sailboat.
I'm sure one could place a very large Lateen sail rig on the catamaran for racing purposes -- but long booms that measure over 24' would be hard to keep in shape in strong winds and over time they would probably also loose their integrity -- unless they are made from exotic material that could handle the changes.
A large sail rig is not fun to handle when it is very stormy. Many large rigs have sunk sailboats when they were not managed properly during "whitewater events".
I remember one day I took off on a tack in my 17' sailing canoe by myself with a Sunfish lateen rig and it was blowing over 20knts -- wow, I had to ride the entire tack to the other side of the sound because I could not come about without capsizing. The forces were just too strong -- so I built a smaller lateen rig with a "anti-roach" design in the sail and, over time, I notice that I could not only handle lots of wind, but never needed to reduce sail because the sail could not luff -- due to the shape of the sail. There is no sail area to luff in the arrow shape lateen rig like the one I designed.
So my point is that a sail that can't luff is a sail that doesn't need reefing -- as long as the sail plan is not too large for the boat in the first place.
I'm sure there would be light wind days when the skipper of a Cat 5 design wished he had the capability of flying more sail -- and I thought about adding a small liftable extension to the mast that could handle a jib or a small genoa sail, but the design started to get complicated and I decided not to go there.
Besides, on very light wind days the electric motor would help. And if the crew is on a time schedule and need to get somewhere fast on a low battery situation -- just run the onboard generator to power the electric motor.
BTW -- the concept of an electric outboard motor is somewhat experimental for a 48' catamaran. I'm not aware of one that large even exist -- but because I've used one on my 20' sailboat for over a decade with excellent results, perhaps the idea of creating a larger version for a larger boat is not too unrealistic.
Regarding your statement about the aerodynamics of my catamaran sailboat article, could you be more specific? Am I misunderstanding some aspect of wind-flow around a foil -- or something else?
Sail design of the Lateen sail
Over at the SimFlight forum a question came up regarding the sail design of the C5 catamaran. The following attachment is an explanation of the "anti-roach" concept and how it can improve the standard Lateen sail rig design.
keep going Duane i think thats looking sharp. your asking feedback so is that standing headroom in the deckhouse? perhaps rounding the edges a bit for streamline? having the house even bigger? like to see that bracket frame, what materials and more. anyway i like it, looks big enough, simple and quite atractive to my eye, ok, i first better read http://ourworld.cs.com/duanekmccullough/newcat.htm
headroom and more...
Thanks Yipster for the feedback -- the headroom in the deckhouse/bridgedeck is perhaps 6.5 feet according to the model. By creating several simple standing and sitting human models in the CAD program, I can adjust the interior to just the right height.
After all the main parameters are met, I will "smooth" the model with extra polygons and bevel some edges to make it less "edgy". That should streamline it some like you suggested.
The free Anim8or CAD program is a great tool for creating models and the Virtual Sailor watercraft simulator program is a wonderful program environment to water test the design -- check them out when you can.
Well, here's another update on my Cat 5 concept catamaran project I started a few months ago. Changes are found in the following statements.
1. I raised the decks to give standing headroom in most of the hulls and to better allow for a greater clearance from wave action under the deckcabin that has a passageway to the hulls. This change added more freeboard/windage to the boat -- but I believe the benefits of a high dry deck in rough seas outweigh the cost of windage problems at anchor during a strong wind.
2. The deckcabin was modified by making it longer and now has two "keel frames" instead of one as before. "Keel frames" are support frames that help give longitude support -- both the deckcabin and the hulls have them and the design lends itself to the idea that the Cat 5 could be built out of marine plywood & boards.
3. The addition of a high steering station atop a rear deck bar frame that could use a modified tiller rod extension from the tiller bar to steer. A teleflex steering cable could also be attached in such a way as to allow steering from the high steering station.
4. Although not a change -- but just to note that the large adjustable electric outboard "trolling motor" could be doubled if needed -- and also could be used as a water-generator underway.
At work just now - will blush when I get paid...
Very interesting 'stuff'...
For those interested see http://hangsim.com/vs/ ...
Reminds me of 'the good old days' of Interstate 76 and 82 by Activision - open code and lots of great idea developments...
What I would like to see is some monster deep vees in Virtual Sailor with rocket launchers and a couple of 20 mm cannons on them - that would be some fun...
i think your design could be improved if you would consider a center cokpit rather than the raised area at the rear. the only reason sailboats have a rear cockpit is the tiller... if you change to wheel steering the placement can be anywhere... a center or front cockpit puts the helmsman up front where he can see better, keeps the center of gravity lower, keeps the person near the rigging, and drier? maybe/ inside 2nd sreering station out of weather...
a rear area can be used for deck lounge and toys...
alos i recommend you widen the boat a bit... 48 ft long x 24 wide...
also the most recent issue of multhull has a article on electric generation using a sterling engine... have you read it?
Hi Jim -- and thanks for your feedback.
Your suggestion about a center cockpit on a sailboat does have certain advantages. Dividing a catamaran bridge-deck into efficient working parts has many options -- however, not including the forward lightweight deck area, there seems to be three aspects found on modern catamaran designs.
First, the forward enclosed cabin area is followed by the second aspect of a main cockpit and steering station out of the wind & wave action with perhaps some stern space to keep a tender on davits. And third, a growing design aspect on some new catamarans is the secondary steering station atop of the main cockpit with better visibility.
A problem can arise in the third aspect if the space of the secondary steering station interferes with either the rigging movement or the easy access space into the forward cabin from the main cockpit. That's why I relocated the secondary steering station of the Cat 5 design atop the stern bar support, which has a good steering view in fair weather and does not consume access space from the main cockpit into the cabin -- or interfere with the rigging movement.
If the steering station was just a place to steer a boat, placing remote controlled steering wheels or even joysticks anywhere onboard that has a good view of the course would work -- but the steering station aboard a boat is also place to gather with friends around an area in fair or bad weather while controlling the boat.
Because of this concept -- and your suggestion, I will review the existing Cat 5 design and see if the upper rear steering station could be consolidated with the main steering station near the main cabin entrance with some possibility of enclosing the area in bad weather. The stern bar support could be left for electrical generation space like solar panels or wind generators.
BTW -- wind generators can be annoying and dangerous, but at anchor on a cloudy windy day, do perform necessary power generation needs on an electric liveaboard.
Regarding the sterling engine and its electric generation capabilities -- I'll have to read the article in Multihull Magazine you suggested. It's sounds interesting.
And regarding the width or beam of the Cat 5, like I've suggested in the article, the proportion formula of 5/8 is being followed. If this formula is not followed, perhaps the strength of the design may be compromised. For every foot gained in width, more cost and stress is added to the project.
Again, thanks for your input on this project.
I helped assembled my brothers 27' Stiletto catamaran last week and learned a few interesting aspects that may help in the design of my Cat-5 concept catamaran project. The latest update includes the following:
1* Simplified bridge-deck cabin design that fits better to the hulls and allows for a forward trampoline area.
2* Steering station placed inside cabin near main hatch/door with rear deck cover.
3* Slightly larger sail rig should help on light wind days.
The boat is looking more like a motor-sailor with a pair of electric outboards. STI (Solomon Technologies Inc.) is working on a new 20hp electric motor design that may someday be placed within an outboard/shaft casing. If doubled, such a concept could give a serious 40hp push to a 48' catamaran.
I was hoping to have the Cat-Five design finished before Christmas -- but while trying to add and polish some details, the modeling has taken longer than I expected. Trying to design a 48' catamaran that could be made from a wide range of composite flat surface making materials is not as easy as I thought.
In fitting the major parts together, I feel like a CAD carpenter wherein the parts need to be interlaced in a way that needs to be simple and realistically cost effective during fabrication and assembly.
The following design changes and additions are the latest improvements.
1* The hulls have been rebuilt again and each half side is now symmetrical.
2* The Cabin-deck has been reconfigured again with more space and better support to the mast. Further work is needed to mount it to a bracket that links it to the hulls.
3* The addition of two bulkheads per hull now divide the hulls into three compartments.
4* Support for a dingy lifting station near the transom links to the rear bar and deck roof.
Perhaps next month the Cat-Five may be ready for some virtual sea trials in the Virtual Sailor program. Stay tuned...
With my best guestimates, your proposed catamaran would displace at least 10,000 lbs or roughly 150 cubic feet. And my best guestimates on your rig indicate less than 140 square feet. This with your high house and hull windage may not be enough to make windward progress even in a strong wind. I would suggest increasing your spar lengths by about 30%. That would nean adding about six feet to both the boom and the yard. This would give you about 210 sft of sail. Still a modest amount of sail but, hopefully, enough to do the trick.
By doing this, you could also cut down on your engine power. Maybe you could get away with as little as 1 hp per ton. That would move you along at at least six knots in a dead calm. As it breased up, you would need the help of the sail. But, with a sail as modest and easy to deploy as this one, I think that would be little trouble except in a high wind dockin situation. How much fuel do you plan to carry?
Other than that, I think its a really neat design. What I like most about it is that it defies the trend of multihulls being designed primarily for speed. The rig has a classical look that would give a polynesian joy.
Thanks Bob -- it's feedback like yours that the Cat-Five project needs.
Regarding the sail size -- you are probably right about how hard it may be able to sail to windward with such a small rig and all that freeboard. I was hoping that a full keel with a little stern fin would help on a windward tack based on the experience of my old 37' Skipjack design wherein it drew only 18" -- but had a similar keel and could sail to windward pretty good. I will increase it to your specs asap and see how that looks.
I've avoided making the Lateen rig larger because a very large rig could be hard to handle in strong winds, but based on the unique "anti-roach" layout of the sail, the sail may be "self-reefing" -- which suggest even in a high wind docking situation, the sail should not luff significantly because there is no extra sail along the leech line to flap as the sail is aimed into the wind.
I'm sure the rig design would catch the eye of any sailor -- Polynesian sailor included. The Lateen rig is the very rig design that started windward sailing -- it has a lot of history in the concept. I could talk for sometime regarding why I chose it for the rig of the Cat-Five.
Regarding the motor needs of the Cat-Five, in choosing two electric outboard motors as propulsion and charging units (that haven't even been built yet) is a radical concept indeed. Any fuel onboard would be needed to run the generator system that would charge the battery bank during motoring on no wind days. The exact science in making this concept work efficiently is still in a state of flux -- but the trend is to go electric propulsion these days. In the meantime, a drop down fossil fuel outboard may have to do.
Anyway, thanks again Bob for your help. I will try to accommodate your suggestions.
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