The Concept Catamaran Project

Cat Project

I am more curious what your relative short floats are going to do when you pick up speed. If you combine that with a choppy sea with waves of 5 - 6 ft you might sail them under from time to time. Your cat becomes a wavepiercer by then. Have you taken in consideration that shallow seas like the Carib, can be pretty choppy from time to time? If your floats are strong enough, ok, but your pilothouse, is that one sufficiently reinforced to take braking waves? I had a look at the design and the height of your deckhouse is considerable and relatively close to the bows, where you have very little lift. Your bows therefore, might go quickly under in shallow water.
A couple of years ago I raced an ex AC from one of the northern Islands to IJmuiden seaport. The boat went with 9 knots on a windward course head on in a number of fallovers caused by current-against-wind conditions. I knew that something was coming, that part of the Northsea is infamous for those seas, and I had everything closed and locked. The bow went under, I went under (Loa boat 45ft) and after what looked liked eternity, the bow rose slowly, although I thought it was not going to happen.
Just an example....... :?:

 

Hi D'Artois,

When I update the boat this week, I will slide the bridge-deck cabin back a little -- that may help ease off on the forward weight some. I believe there is sufficient buoyancy in the high freeboard hulls forward of center. It would be important not to load the forward hulls with weight for the reason you mentioned. I'm aware of the need for forward buoyancy -- I've only crashed a cat twice in over 30 years of sailing them. Once when a 14' Hobie Wave pich-poled in heavy seas while sailing very fast -- and while flying a hull on an old classic Hobie 14', I "fell backwards" after I ran into soft mud. But I have never capsized a catamaran. I have come very close and have rescued many who have capsized, but so far, I've been careful and/or lucky.

The bridge-deck cabin is not attached yet to the hulls pending the bracket design that would marry the three parts together. I'm still working on the bracket design -- it should allow for a strong flexible link between hulls and the bridge-deck that could be taken apart during overland transit or storage of the C5.

Like my brother's 27' Stiletto catamaran, there are two large telescoping cross beams located aft and center beam that the bridge-deck will enclose. A forward support beam should link the bows together. Working on it...

 

Asymmmetrical Hull Shapes

I would encourage anyone interested in asymmetrical hulls to go find a Prindle catamaran (P-16, or preferably the P-18 asymmetrical model), turn it upside down and do an inspection. You will find a VERY interesting hull shape, and particularly the exaggerated toed-in keel line. The P-18 had even better load carrying capabilities at her stern, and better anti-pitch characteristics.

Then keep in mind that these asymmetrical hull designs were really intended to operate in a one-hull-up attitude to gain their best performance.....not exactly a cruising vessel attitude. Aside, there was also a tunning method that permited the rudder blades themselves come into play as leeway reducers.

It's the really fat load carrying hulls that 'pile' up this peaky wave under the bridgedeck. Either stretch things out a bit to give a better slenderness ratio, and/or create a wave-splitter foil down the center. Wave splitter; First, imagine a flat plate, on edge, mounted down the centerline on the underside of the bridge deck. This flat plate will act as a rib to strengthen the fore-to-aft rigidity of the vessel, a somewhat weaker characteristic in a catamaran structure vs. a keeled monohull. If a tow bundle (rope, etc) of carbon fiber (kevlar, PBO, etc) was laid along the bottom edge of this flat plate, the rigidity could be even greater (sort of akin to a bottom truss structure, or a flange of an 'I' beam). The front of this nacelle/plate could be configured to act as a wave splitter to actually attack, up front, the formation of those peaky waves under the tramp areas that eventually slap at our bridge deck underside. We kind of slice those waves down a bit. A lightweight fairing might also be added to this 'flat plate nacelle' so it appears outwardly much more esthetically pleasing, as well as more curvature to shed those peaky waves."

 

C5 update

Hi Brian,

Interesting that you suggested a Wave Splitter stringer device under the bridgedeck cabin -- I put one as a cabin-floor stringer that meets the mast base yesterday. It could also have a small forward "shoe plate" shaped like an arrow "I-beam" to divide any oncoming wave or bow wake reaching the bridgedeck. Like most all catamaran designs, some kind of exterior cable support will be needed to strengthen the middle and forward crossbeams.

Regarding the asymmetrical hulls of the Prindle catamaran -- you are right, they can provide better load capabilities in their stern while flying a hull. Trying to achieve the same foil control while sailing flat is still a challenge in cruising catamarans. The C5 does have a nearly flat bottom at the stern that may help it to plane somewhat.

Anyway -- attached is the latest version of the C5. I do not show the bulkheads and there is much design work to do on the brackets that unite the hulls with the bridgedeck. Designing a small sizable waterproof entryway from the bridgedeck to the hulls is proving quite the challenge. If the C5 was the typical large fixed catamaran design, it would be easier to construct the crossbeam supports -- but I believe it would be better if the design accommodated the concept of overland transportability -- which needs to be modular and yet strong.

 

Hi Duane, have you considered employing chamfer panels between the bridge deck and inboard hull sides? They offer some nice benefits including strength. An interesting article on them can be found at http://www.graingerdesigns.com.au/considerations.php
They may help soften the inner hull to bridgedeck aesthetics. The ones in the sample pic attached only took a day to cut and fit to our 40ft cat.

 

Hi Craig,

The Australian Grainger catamarans look very nice -- years of building experience shows in their designs.

If I understand the chamfer panel concept right, it seems as if it represents a bevel bracket that mounts to both the bridgedeck and the hulls -- which is exactly what the C5 needs at this stage in development.

The article you posted suggested that two types where used in the Alfresco 1060's -- the straight bevel version and a curved version, with better performance from the straight version. If so, then a straight bevel bracket could be created and used that may have a forward angled extension to add angle strength to the concept and help carry the shape of the bridgedeck bottom to the hulls. The bridgedeck cabin topsides should link the top of the hull "keel frames" to the cabin frames as shown in the latest C5 image.

If each bracket were shaped like an "U" while looking forward, they could bolt to both the bridgedeck and the hulls with the nuts protected inside the cabin. The sides of the hulls facing each other would need to be flat to accept the strait longitudinal bracket -- perhaps special faring panels placed between the curvature of each hull and the bracket could make the concept fit snug enough to work properly. The fairing panels would look something like the chamfer panels you posted in your sample pic -- but would be slightly smaller and act more like a "washer" between the hull and the stronger bracket that bolts to the cabin frame.

Back in '81, as part of a crew while sailing a 62' Peter Spronk catamaran (http://ourworld.cs.com/duanekmccullough/sstory3.htm) from St. Maarten to the Bahamas, I noticed the boat overtook some big seas and the foam filler used to fare the link between the bridgedeck and hulls began to break out -- which suggested that the area does take serious stress and should be reinforced.

The C5 design could be made from several types of materials -- including lumber and plywood. I know fiberglass and other composite materials are preferred for large production boats because of the durability of the materials -- but it would be neat to see a large modern cruising catamaran design have the option of using wood or similar fiber material as a primary building material. Moreover, to have this design marketed as plans so that backyard boat builders around the world could afford to safely enter the fast growing cruising catamaran market would also be neat.

The aforementioned 62' Peter Spronk catamaran was "woven together" using African mahogany plywood and the W.E.S.T. system. I remember the veneers were crossed in a hex-system and were very strong. I wish I knew the whereabouts of Spronk's boat and could see how it has faired over time.

Anyway, thanks Craig for your input -- a modification of your chamfer panel concept in linking the bridgedeck with the hulls should help the C5 design.

 

Proportions of hulls?

Hi Duane

Me again. Just stopped by to ask you what the proportions of your hulls are.

1.) How wide are they? At the chine? At the shear?

2.) How high are they? From the keelson to the chine? From the chine to the shear?

The reason I ask is that I am intrigued enough with this design concept to want to run it though PLYBOATS c to see what kind of numbers I get displacement, wetted surface, hull surface, and bouancy wise.

My guess bestimates are that the displcement will be around six metric (or long) tons. I would really like to see how close to the mark they are.

Thanks

Bob

 

Hull data

Hi Bob,

Attached to this reply is the hull layout graphic data of the current C5. The free Anim8or CAD program is great -- but it doesn't have measurement data tools. No problem though -- I just created a reference grid to measure objects, making sure I kept the scale between the objects equal during the copy process.

I hope this data can help your PLYBOATS test -- I'm also curious as to the data. Thank you for helping out on this project.

The exact total width/beam measurement of the C5 may still fluctuate depending on what numerical data seems best. A wider beam value will help in banking stability -- but at a performance cost to pitching stability I believe.

Again -- thanks!

 

PLYBOATS c Cat 5

Hi Duane

Me again. I drew as best I could your Cat 5 hull design using Plyboats. Here's what I came up with:

Length 47ft
Beam 5ft 1in
draft 1ft 8in
Freeboard M 5ft 10in
Freeboard B 5ft 4in
Displ. 7,000lbs
PPI 793lbs
CP 0.56

My guess is that with proper scantlings each hull sould wiegh around 3,000lbs.
Your cross beams, wing deck, and cabin will probably come in at another 2,000 lbs, leaving you around 6,000lbs to play with for your engine(s), rig, fuel, water, and stores which is probably not a lot for a 47 footer.

I thought a little about your latteral area. Since the 'V's of your hulls are so shallow (1 to 4) they shouldn't be counted. I have written a spread sheet for this purpose. It takes into account that long shallow keels are not as efficient as short deep ones. It also takes into account profile area. According to my spread sheet, a 30ft long keel would have to project 11 inches below each hull. This, I hope will give you the abillity to sail 100 degree tacks (50 degrees off the wind). I would start this keel about 2.5ft forward of your transom.
It can be pointed out that such keels will add considerable wetted area to your boat. This is true. But it is also true that such keels will bring your draft to a little (1.5in) deeper than originally specified. And it would have no moving parts. And no cases to project into the hulls or wing cabin. I would further like to point out that such keels could be copper clad and not need bottom paint that can be scraped off during groundings. The rest of your bottom could then have bottom paint which would be easy to apply when the tide ran out because the entire bottom would be exposed and easy to get to.
Such keels could also protect your rudders and propellers from floatsom and groundings.
A center board case could be placed underneath your wing cabin to do the same job. And it wouldn't have to be above the water. But it would have to be long and well braced. It could easily add several hundred pounds to your weight and increase your sailing draft. And much of the wieght will be above the waterline (the case, the bracing, and at least 1/3rd of the board itself). And it would not protect your rudders or propellers. Even so, It may allow you to sail closer to the wind (45 dgrees rather than 50) and the wetted area would be gone once it was cranked up.

Such are the compromises of boat design .

I also thought about your mechanical propulsion. I thought of the idea of puting a single diesel in just one hull. It could turn a feathering propeller through use of a sail drive unit. That way the engine could be tucked away in the stern of a hull (the choice of which would be based on propeller rotation), close enough to get to, but far enough to be out of the way. It would be about 12hp and would usually run at 1/3rd to 1/2 throttle. It would be belted to a 90 to 150 amp alternator to provide most of your ship board electrical needs. Because of your small sail area, it would usually be running.

You originally showed 'electrical outboards' that resembled large trolling motors. I liked the idea but thought they looked vulnerable to wave damage and looked heavy as well. Also, in order to transmit electrical power over any distance, higher voltage is needed. Otherwise, the power losses due to impedance can be substntial.
With some ingenuity, I am sure the problems can be overcome. It might be an interesting idea to put an electric motor in the other hull. This way, short movements about the harbor (as well as changing tacks) could be done without starting the diesel.

Bob

 

Hi Bob,

First, thank you for your work in translating the graphical data into numerical data. I appreciate your participation in this Concept Catamaran Project.

Everything you suggested to improve the C5 makes sense -- particularly the idea of compromising the mechanical propulsion system from a total electrical outboard system to a split inboard diesel and electrical system. The inboard electrical motor could also have the option of being a generator under off wind sailing situations using the Electricwheel motor system from Solomon Technologies.

Some may say that the technology of going full electric propulsion is possible -- but since I have no real experience in working with large conceptual electric outboard motor generator and propulsion units as imaged in the current C5 project, I am open to your idea of changing the design. Perhaps on a smaller catamaran design, the idea of twin electric outboard motors with proper flexible shafts would be better. The C5 started out as a 36' catamaran, but grew another eleven feet to add offshore stability and headroom in each hull.

Regarding the modification to the keel -- I see no problem with making the changes you suggested. The original keel shoe is designed to add strips of 2" by 4" material like wood or other more durable material onto the keel frame. Coating these strips with copper should be easy enough. The only problem with full strait keels would be the lack of a pivot point from which to rotate while tacking to windward. Also -- without the ability to backwind a jibsail, coming about could be problematic on a large catamaran.

Speaking of pivot points from which to rotate while tacking to windward, perhaps a "wave splitter" centerboard design like in Brian's catamaran project could be created that would help the C5's ability to come about -- and help it point to windward better.
Brian has some great concepts in his designs -- the challenge is to project strength to the centerboard system without obtrusive spars or cables that could add drag in high wave action.

My brother's Stiletto uses stainless steel support spars that project to a support beam from which the daggerboard rest on. These support spars are apparently designed to collapse if the catamaran runs hard aground -- he just had them fixed during a recent refit. These support spars do cause drag in heavy seas, but also provide adequate support to the daggerboard under the bridgedeck. In the C5 case, if there was centerboard instead of a daggerboard, then perhaps the design could be better supported with angled supports to the pivot point of the board. Finding the proper size and placement of the centerboard underneath the bridgedeck on the C5 may need some aeronautical math -- or I could try some guesswork for now.

My 20' Mirage sloop uses a "swing keel" that when the board is down a small area of the board rises up into a small trunk -- perhaps a similar design can be used under the bridgedeck of the C5 project. I will play the concept this week and see what may look feasible.

I had to slightly flatten the sides of the basic symmetrical hull form of the C5 last week to accommodate a flat surface so a mounting bracket between the bridgedeck and hulls would fit better. If the bridgedeck were permanently mounted to the hulls, then gluing a simple triangular bracket would work -- but because the C5 is designed for transportability in mind, a removable bracket is needed instead. I will show the design change soon.

In fact, I will show all the above changes in the next update soon. Again -- thanks a lot Bob for your help.

 

My previous company, the original Chespeake Catamarans, sold over half of Stiletto's production, so I am well aware of their CB design. I would NOT advocate a design such as their's.

I am 'pressing' the CB loads onto the 'flat-plate nacelle board', that in turn can be stabilized athwartships via two diagonal support 'wires' (maybe spectra or PBO) that carry the bending load imparted to the flat plate to an athwartship frame member (sub-bulkhead). Thus, very little exposed structure to create drag (flat plate aligned with water flow and two wires attached to bottom edge). Further I would recommend VERY large diameter CB bearing(s) to spread the CB bending loads to the flat-plate nacelle.

 

Hi Brian,

I agree with you Brian -- the CB design of the Stiletto is not a good example to follow because I have seen what can happen to the stainless steel bracket frame when the craft runs hard aground. It can be expensive to replace or repair the SS brackets.

Your large "flat-plate nacelle board" design of your latest catamaran looks interesting -- instead of wire/cable support lines to support the CB area, do you think it would be possible to laminate several progressive in size "L" shaped aluminum support beams lengthwise underneath the bridgedeck that could support the CB area to the nacelle board?

Early aircraft once used cables in their wings to "support the load" -- then the idea of beefing up or laminating material strength where the wing meets the fuselage eliminated parasitic drag and simplified the design. If the CB represents an adjustable "underwater wing" to a sailboat, then perhaps by designing a laminated beam lengthwise that bolts to the crossbeams of the bridgedeck could eliminate the need for exterior cable wire support.

I will try to illustrate this CB design without cables theory for the C5 later this week.

 

C 5 tacking

Hi everybody

I can see that you have rejected the long keel idea. And probably for good reason. It never accured to me that a boat as light as this and with this much profile would be difficult to bring about. My solution would be to do the manuever with one or both engines running (whatever the case may be with the final design decisions), or to simply wear ship. Wearing about (or jibing) usually makes for and aft sailors cringe. And for good reason. On most for and aft rigs, all the sail is behind the pivot point (be it mast or stay), so when the leach puckers on the other side of the wind, the sail swings over with nothing to slow it down or stop it untill it reaches the end of the sheat line. Then it stops with a mighty slam. The slam can be so mighty that it throws the boat over on its beam ends. I once capsized a super snark that way. I was looking at the bottom of the lake before I knew what hit me.
With the 'Cat 5' rig, things may be very different. There is considerable sail area ahead of the pivot point (mast) with this rig. This sail area could act as an air brake to slow the sail's swing and that way make the manuever that much less dangerous. On my light beamy centerboarder I often had to jibe in order to get out of trouble. By adroit sheet handling, I was able to vastly lessen the jarring slam.
I think that with this design, such a manuever must certainly be anticipated. Even with a single, deep, centered, centerboard, there is a lot of windage up there. High hulls and a substancial wing cabin to boot. Without at least one engine to help out (and indeed even with one in scary conditions), you may still have to do it.
Even so, I have put my mind to how to take the side loads of such a board. I have come up with the idea of a 'V' sectioned fairing. It woould almost be like a third hull except that it would never touch the water. It would be cylindrically developed, so it would be simple to make. Its deepest and widest point would be in front of where the pivot axle goes. The axle, by the way, would be toward the trailing edge of the board rather than the leading edge which is the usual practice. that way a portion of the board would reach all the way to the top of the case when the board is all the way down. This would give the maximum support.
There is both a 'down' side and an 'up' side to this scheme.
The 'down' side is that this fairing will, in all likely hood, project beyond the front of the wing cabin forming (from the top and side view) a sort of beak or ram.
The 'up' side would be that even if this fairing were not entirely water tight, it would put a substancial amount of bouyancey below the wing deck in a way that would build up exponentially as it is immersed into an on comming wave. It would have the same effect as a wing to hull fairing (mentioned in earlier posts) in limititing or eliminating wing deck slams in rough seas.
As for the board itself, I estimate that ith a 2ft chord (width) and a 2in thickness it would have to be at least 9ft long and wiegh between 100 to 200 pounds (weight needed to keep it emersed) just for the board.
And thats my two cents worth for today.

Bob

 

Hi Bob,

The long keel idea still has merit -- if a pivot point from a CB unit could be established properly on the C5, then it may help it come about better. I will try to create a CB unit -- and add another layer to the keel shoe and see if that helps with your earlier math results.

As long as there is enough momentum during the tack and the turn is not too sharp to cause unnecessary water drag, the C5 with the Lateen Rig should come about well enough. I was tempted to reduce forward hull windage problems of the C5 by lowering the freeboard near the bow, but I believe the bow needs all the buoyancy it can get while operating in heavy seas -- so I will leave it as is.

Regarding your jibing story, during sailing lessons at a nearby resort, I demonstrate the "control jibe" to students by taking in most all of the mainsheet at the moment nearing the jibe so that all play in the line is reduced and the chances of somebody or something getting hurt is reduced. After the jibe, the mainsheet is then let out and the boat continues on a new tack. Without this technique in heavy wind and seas, chaos can happen aboard that can be dangerous.

So, you once had a Super Snark? Other than a family 17' sailing canoe, my first sailboat was a Snark made from Styrofoam back in '71. They were great fun -- you could carry the whole boat under your arms to the shore and sail almost anywhere. Before there were windsurfers -- there were Snarks. Their simple Lateen Rigs were as simple as any sailboat could have. There is something very nice about simple designs -- less can be more.

Regarding the CB design you suggested -- again, you have proposed a very interesting concept. Somewhat like Brian's CB design, a CB unit within a fairing torpedo tube like structure under the bridgedeck and just above the water line may work. On one version I played with the idea of a narrow CB unit that would protrude from this fairing tube case and could also be used to steer the sailboat -- something like a forward rudder pod device. But that design may be asking for all kinds of structural problems -- so that concept is on standby for now.

However, the idea a ram-like fairing pod under the bridgedeck that holds a CB unit seems nice to contemplate. I'll see what can be done in that department. If this concepts works, it will be necessary to beef up the bridgedeck to hull brackets to carry the upward push from a high wave going between the hulls.

It all sounds interesting... Thanks guys!

 

Hi Bob -- again,

After reviewing the design options in powering the C5 -- and the CB unit under the bridgedeck concept, I have decided to stay on the simple side of things for now because of the following reasons.

Regarding the idea of changing from the Electric Outboard Motor System option to the conventional inboard motor option -- let's review why I favored the outboard version in the first place.

1: The Electric Outboard Motor System (EOMS) can easily be raised out of the water stream -- thus making less drag than the props of inboard motors.

2: EOMS can be replaced or serviced much easier than inboard motors.

3: EOMS do not need to provide for cooling and exhaust systems as in inboard motors that require holes through the hull that may someday be very problematic. Pound for pound -- EOMS may be as powerful as fossil fuel motor system if the weight and mass of the cooling system is taken into consideration.

4: EOMS are quiet to operate and when powered properly provide instant propulsion needs.

5: EOMS do not need flammable materials as in inboard motors to operate (less the hydrogen gas that may be a byproduct of battery charging) that may someday destroy or harm the boat.

6: EOMS -- if encased properly in new composite materials, are very resistant to marine corrosion and can be designed to help steer the boat. The shaft can be made to flex properly instead of breaking during ground impact or water objects.

7: EOMS can be designed to generate electrical power in offwind sailing or anchoring in tidal current situations.


The bad news are that there are a number of things that I believe are currently negative about the EOMS when compared with inboard fossil fuel burners -- such as:

1: They need a heavy bank of batteries to operate properly that does not get any lighter after use.

2: There exist an impedance problem between the batteries and the motor which cannot only reach very hot dangerous temperatures, but waste power.

3: Electrical power systems and the environment of water have an inherent problem of not working together over time because the metal pathways necessary for electricity are easily affected by water or the decaying process of when water chemically weakens the metal material.

4: The latest EMOS technology has not yet produce a large commercial version needed for the C5 -- so, enduring a testing phase will take time and money.

Unless the EOMS is designed and serviced properly, it will have serious problems -- but considering the known problems associated with fossil fuel inboard motors, the problems are overall less and should be explored as a means of propulsion for any large watercraft.

However, I will include a fossil fuel genset system that should augment the power needs of the C5. Together with the solar and wind-generator systems, perhaps there will be enough electrical power to safely cruise in the tropical latitudes.

Regarding the CB unit under the bridgedeck as recently discussed, I have decided to avoid adding any heavy device that would be more problematic than helpful. The more I added to the design, the more it seemed to be complicating the simple concept of a bridgedeck.

I even tried to see what two smaller Center Boards would look like as inside "leeboards" on each hull because they could snug up to the hulls with large washer bearings -- but even that was getting complicated in the design. The hulls provide better near the water strong points for a CB unit than trying to build and support a CB unit under the bridgedeck it seems.

If the only purpose of a CB unit is to help sail closer to the wind source in deep water -- then I could live without one, but the need to pivot during coming about is also a good reason to have one. However, in both cases, a little motor help should solve those problems.

Anyway, I welcome replies to the aforesaid statements. The Concept Catamaran Project is still open for change...