Catamaran Evolution

I looked at the CR33 and checked it with Michlet. It has a fraction more drag than the SR34. Nothing more than expected for the added displacement.

I am not sure if you realise the capability of some of the layer properties in Freeship. You have all your layers nominated as "Use for Hydrostics". If you limit the layers having this property to just the hull parts then you can get hydrostatic information from Freeship.

I have also attached the Freeship model (only one hull) for the Opt34 so you can load it and move it around. The optimum hull separation was 5.13m between centrelines.

Rick W.

 

Hello Rick,

I changed the layer properties...never gave it too much mind.

I got the file and looked at it. Daaammmmm... you got a lwl/bm ratio of 16+. That is not optimized...that is super optimized for serious racing. Nice draft too. If I assume correctly and your optimized separation is from centerline to centerline then it calculates to 5.13/10.4 = 49% of LWL. That figure should produce good maneuvearbility and handling. I'm going to keep looking at it and make some comparisons with my own.

By the way...I was looking at the stern rocker and I think I can get another 2 feet of waterline if I straighten it out as you suggested. I'll let you know as I progress.

Well...it looks like the poll is over. I guess it is time for me to calculate and hopefully decide which design to "Optimize".

I may start a new thread so that all the steps and changes for the "optimized evolution" are in one thread.

Thanks to all for the suggestions. it is time for the next step.

Thanks
J

 

The Opt34 hull will have little or no potential to plane. It provides a hull that enables good speed with minimum sail. So I would class it as an optimised cruiser rather than racer.

Most of the big, fast cats keep flat aft sections with just enough rocker for the stern to be at surface level for clean exit. They certainly plane. So reducing the rocker in your designs should give a better result.

It is worthwhile noting that Michlet does not allow for hull sinkage and I am sure this would happen with your hulls. This would improve waterline length and may reduce estimated wave drag a little.

That said I have looked at the side view of a few of the modern cats and all found have less severe rocker aft than you have drawn.

Rick W.

 

Hello Rick...

Okay, I got it. It will be the first thing I look at and change. You'll get the hull to look at and test as soon as I have made the first streamline for a list of items I wrote down to address.

J

 

Happy Holidays to all...

I was going to start a new thread but I figured I would just stay here and continue.

Well…the poll is closed. Final findings are.

CR33 = 1 + 1 (All) = 2
RC34 = 0 + 1 (All) = 1
SR34 = 1 + 1 (All) = 2
All = 2
None, I like a specific design as is = 2.

“All” is out because it is already incorporated into the other designs. The “RC34” is out by vote. “None” is a wash for all three. That leaves the “CR33” as a cruiser and the “SR34” as a racer.

Soooo…because I have most everything in parts for the rough designs and I don’t have to start all over with everything…

I will further develop the "SR34" with some incorporations of the “CR33”.

In the end and after all is said and done...the final drawings will be in CAD. The two designs to be combined are the following.

The CR33 is designed for 4 owners or less with the occasional 2 guests in the pilot berths. Make the pilot berths interchangeable for deck hands and you now have a possible 2 more that can be on shift while 2 are at rest for a total of 8 which may translate into 2 owners, 1 paying couple, and 4 paying working hands or any combination thereof. Ideally, the design is best with 1 owner couples and 1 paying/working couple for purposes of privacy and space. The design is round chine vertical foam and the payload is @ a SDR of 18 or 2000#’s. Designed for offshore.

The SR34 is designed for 4 owners or less. They can be single or couples and berths can be interchangeable translating into 2 on shift while 2 are at rest if singles or, 2 on shift while 4 at rest if couples for a maximum of 6. Ideally, the design is best with 1 owner couples and 1 paying/working couple for purposes of privacy and space. The design is hard chine horizontal foam or plywood and the payload is @ a SDR of 20 or 1071#’s. Greater payload to maintain SDR of 20 while cruising would require reducing fluid capacity. Designed for offshore.

Layouts for both designs are linear and provide ample openness for the more claustrophobic outdoor type that experience cabin fever during inclement weather. The CR33 has conventional outfitting for interior accommodations and the SR34 has a minimalist approach with cabinetry, settees, berths and all weight bearing horizontal surfaces designed to be tube frames with canvas panels. Both designs have maximum cruising resources such as adequate water, fuel, cooking, power, fuel and, restroom facilities at their disposal with the SR34 capacities nominally smaller.

Deck layout has all lines set up for single handed action leading to the helmsman cockpit for both designs. The helmsman cockpit on both designs has fully enclosed dodgers available for use during inclement weather. The SR34 is designed with structural netting in the rear cockpit opposed to the solid sole for the CR33. The CR33 has a longitudinal open salon aft of the helmsman cockpit and the SR34 has the same in the helmsman cockpit.

Powering for both designs is with approximately 500 square feet of sail and dual 9.9hp inboards that raise and lower into self closing stern wells. Dagger boards are NACA 0012 with the leading edge 2 degrees inboard and the rudders are NACA 0015.

That is pretty much the meat and potatoes of both designs. The new design evolving from these will have a little of both as long as it serves the intended purpose and it will be streamlined above and below the waterline. Those weren’t exactly mission statements but at least I kept to a plan.

J

 

Rick, thanks for the opt.34 file. i'm having Leo's shortcut list up but found holes in my own drawing, tomorrow
JCD, i would just draw what you got in mind and not take this pole results to serious
looking forward to your choices in boards rudders rigs accomodations

 

Okay Yipster...I was going to design it anyway. I figured several heads are better than one so I asked.

I started working on it already and have done quite a bit since I took a couple of days off.

J

 

The GREEN LANTERN

Hello...

Found a name for the design. The GREEN LANTERN.. Why? Well according to Wiki...

"Each Green Lantern possesses a power ring that gives the user great control over the physical world as long as the wielder has sufficient willpower and strength to wield it..." and since the design has "ring" frames...there it is. Not exactly. I like the superhero too...and I, the user, have sufficent willpower and strength to wield it...well, perhaps design it and hopefully build it and then wield it with great control over the physical world.

Okay...enough of the storytelling.

Well, here are the significant hull improvements thus far. The current and the old hull hydrostatics are attached for comparison. The draft has been maintained as the base measurement for all the modifications denoted below. Anything in red means a worse design result.

1. The design has been modified for round chine and vertical foam with glass skin construction.
2. Reserve buoyancy has been increased in the bows in case of burying into a wave.
3. The forward waterline sections have been made into wider vee’s and the aft waterline sections have been made almost vertical so that the CB moves forward when the hull is pressed.
4. The entrance angle has been increased to provide a drier ride.
5. The forefoot radius has been increased to provide more resistance when tripping.
6. The LOA has been increased to 34.25 feet.
7. The LWL has been increased 8.3% to 33.09 feet.
8. The LWL/BM ratio has been increased to 13.18.
9. The LWL BM has been decreased to 2.574 feet.
10. The hull beam has been reduced to 6 feet or 17.7% of loa.
11. The hull height has been reduced to 7 feet.
12. The vertical CG has been reduced 20.2% to 3.715 feet.
13. Windage has been decreased to 16.38% of LOA.
14. All corners have generous radiuses to promote flow and reduce drag.
15. The sides of the hull have been streamlined to promote flow and reduce drag.
16. The transom has been given curvature to increase strength and reduce possible wave impact. (Considering steps)
17. The lowest bridge deck clearance has been raised to 2.4841 feet or 7.5% of LWL.
18. The total area of each hull has been reduced by 102 sq. ft.
19. The total weight of each hull has been reduced by 112 pounds.
20. The rocker has been lreduced in rise.

A hard chine hull has been produced at this point and saved but will not be developed any further. If anyone would like to have it to work on it just ask and I'll send it.

The next step is to streamline the above and fine tune it if possible. Any questions or comments would be appreciated. If you notice anything I should consider addressing of the hydrostatic results, please advise. If I don't respond right away...be patient as I am working.

J

 

Here we go.

I am attaching the hull for the Green Lantern for perusal and comment.
I am not sure how much more I can do to streamline her further and still be able to produce a design which will be fast and cruisable.

Please take notice that I have made all the changes thus far by maintaining the draft constant. I am hopeful that I will finalize the design at a lighter displacement. If it happens to stay there...then I may call out for a different rig to reduce the CE and increase SA. Lateral rigs sure look nice but it may mean more studying since I know little about them or their efficiency. That will be considered down the line.

My next steps will be the following:

1. The hull will be duplicated to create a catamaran planform. The distance between center lines will be 16 feet and optimum distance will be calculated afterwards.
2. Transom steps will be added to the hulls.
3. Cross beams and the aft beam will be added to the design. The cross beams will be mast sections and the aft beam will be box section. All will be designed to safety factor of 3+.
4. The bridgedeck will be added to the design.
5. A preliminary cockpit layout will be designed to attempt to visualize the most efficient layout.
6. A preliminary dodger will be designed to attempt to visualize best aerodynamic design.
7. The mast and boom will be incorporated into the design. This may be totally re-designed if the cockpit layout is hindered.

An attempt will be made to design the above to have the CG be as consistent with the CB as much as possible without compromising structural strength so that the design can be sailed while fitout takes place if it is built to this stage.

Once again...comments and suggestions are appreciated. Be cruel...my skin is not that thin.

Rick...if you don't mind running the model through the program and possibly PDF'ing the results and pointing out what I may be doing wrong I would appreciate it. I'm now starting to read the material but I'm not sure I'll get it right yet.

Thanks
J

 

I checked GL with Michlet. I now have four hulls for comparison. It is hard to pick the difference between GL, SR and CR.

Some things to note:
Gl is the heaviest displacement. The numbers that Michlet gave for the set drafts on single hulls are - CR33 is 1.519t; Opt34 is 1.481t, GL is 1.543 and SR34 is 1.467t. (These vary a little with you spreadsheet)

The extended waterline has made a very slight increase in speed to where the wave drag kicks in for GL compared with the others.

GL is slightly better than CR33 throughout the range.

SR34 has a very slight advantage above GL above 9kts.

Given that GL has extra displacement it is doing reasonably well. The only way you would do better from performance perspective is move more toward the canoe type hull shown on the Opt34.

Rick W.

 

Okay...

Here is the Green Lantern Catamaran with the transom steps, beams and bridge deck. The rest is being worked.

No comments on the prior stuff?

Wow...this crowd is easy.

J

Whhoooopss...Rick commented. Got in before me.

 

Hello Rick...

Guess what????

I have placed your OPT34 waterline area on my design and it looks pretty damn good. I hope you didn't mind me playing with it as I had to 'visualize it! I did have to modify the hull a bit in order for it to look right...but it looks damn good.!

J

 

I built/purchased 10 boats over 3 years before I found Godzilla. It can do about 1100 iterations a second and I usually let it optimise for 30 seconds. So in terms of building 3.3 boats a year it would take me a 1000 years to do what Godzilla does in 30 seconds.

Opt33 is a product of Godzilla with your hull constraints and an optimised speed of 5m/s (almost 10kts). Anyone with Michlet/Godzilla can poroduce the identical design. Leo Lazauskas is the one to thank. I am hopeful he will one day put his mind to a similar optimiser for propellers. My semi-analytical prop optimiser is OK but it can give inconsistent results if I make a more radical shape.

Inevitably hulls have compromises but Godzilla is a good place to start. I keep checking the modifactions so I know what each change costs in terms of performance.

Rick W.

 

Hi JCD. Would you mind posting a few jpegs of your designs?? I have nothing that will read your attachments.

- Richard

 

Hello Richard...

I would be happy to do it if I can just figure out how. I'm still trying to figure out how to get pictures out of the program. I create what I believe are bitmap images but then when I try to download them it states "invalid file".

Until then...it would be a good idea to get FreeShip into your computer. It will take a little getting used to but once it is done...you can do pretty much anything.


J