Catamaran Evolution

Richard,

I'm not sure I agree. Once in the tunnel, the waves will dissipate with distance if caught at any angle other than from dead ahead. Following seas is a different story and there I would agree. The height of the bridgedeck anywhere on the design is relevant for many different reasons. Slamming, being the most obvious, but I'm sure that someone can make a good argument for longitudinal stability such as may be needed if she is found with both hulls unstuck while riding the crest of steep wave on her centerline. I would consider those moments appropriate for soiling oneself or a classical "pucker" opportunity since there is no rudder control and one good puff means she will be on her ears.

Unless the design is $#^&^%^& or the weather is &%$$#^&, I don't think that the bridgedeck is given significant structural concern for slamming. I could be wrong.

J

 

Hi J. I didn't word it very well. What I meant was this: if the aft beam is clipping the tops off waves, it can be bad enough to bring the boat to a grinding halt, in which case the shaping and height of the rest of the bridgedeck will be irrelevant.
I know that Seawind designs cats which have bridgedecks which are actually higher at the back than they are at the front, to avoid the worst effects of slamming.
With ny design I have just played it safe and kept my bridgedeck fairly high. Feel free to look at the pics I have posted in my thread. "trying to design my own cat". I am not as advanced as you yet. I havent learnt how to use Freeship yet.

- Richard

 

Hello Richard,

Advanced as me? ROFLMFAO!
This is something I like to do and try to learn it so I can do it well, but advanced? Nah...the crew in here is a different story...they are advanced!

I will look at the design you're trying to put together. As far as aft beams getting whacked by waves...those have got to be seriously tsunami types. You have me getting concerned at this point and I will need to look at it further. Maybe give the beam a radius?

J

 

J, my sincere apologies. When you gave the measurements for your bridgedeck clearance....I was subtracting the draft measurement you gave me, from the clearance measurement. I thought your clearance measurement was taken from the very bottom of your boat....hence I thought that was why you were giving me the draft.
After looking at your fbm files, it appears that you have a huge clearance....yes indeed it would take a tidal wave to slap your bridgdeck. Sorry for making you concerned.

 

Your hulls look quite flat on the bottom. I personally don't believe that cruisers should be designed for lots of lift because sea conditions are rarely ideal and in most places, the wind is never strong enough for a cruiser to be flying (dangerously) like a bat out of hell.
I raced for years in a small Phase 2 (I was crew, my uncle was skipper) which is a mono hull designed for planing. We hardly ever planed cos there just wasn't enough wind....but it was huge fun when we did. I think a displacement cat can still go plenty quick enough for safe cruising. (obviously that's why I have chosen canoe hulls for my cat....which is a plain old raft compaired to yours! lol.)
I think your design looks great though, and I like the huge flared cabins. They would have a nice spacious feeling inside.

 

Hello Richard,

No need to apologize. It's good to make observations that open up possibilities not otherwise thought. I did look at the aft beam and the possibility that the waves in the tunnel may strike it since there will be netting there instead of a hard sole, but I ruled it out.

The first thought is that the clearance is pretty damn high at it's lowest point. If a wave were to enter the tunnel as high as that clearance, it would clear the beam by the time it gets to that point.

The second thought is that if a wave greater than that clearance were to enter the tunnel and maintain height until the end of the sole, then the sole would either force the top of the wave down, or it would rise with the wave, causing the aft beam to rise and clear the wave.

The final thought was that even if all of the above failed to happen and the wave somehow oscillated weird frequencies right there and then, then the netting would break it up or chop off the crests and allow it to spill back off on itself before reaching the beam, or at worst, reduce the loads the beam will experience from the bang.

At this point in time, I believe that the risks associated are acceptable. But raising the beam a bit effects the rest of the vessel very little if any, except for the CG, so I am definitely going to look at it further before declaring the design done.

J

 

Hello Richard,

Okay. I understand what you're saying.
Here are my thoughts. I don't intend to have a hull unstuck, but do believe that the design, with a shallow draft, is such that a young, wild whippersnapper, looking for a shot of adrenaline in the veins might be able to do it with little concern for the possible consequences. That is the reason that I designed the beams based on cantilever beam loads...so at least she wont snap in half.

There are many proven reasons to design for a flat run aft. Bouyancy, less hobbyhorsing, easier driven, easier planing, less drag, more lift, less wetted area, better motoring, reduced weight for lack of sole, etc..etc... Could there be a bit more pounding? Probably, but not enough to cause so much concern that it should negate all the other positives to having it. While maintaining way, Idon't think there will be any pounding at all...pounding may be experienced when the hull flies and slams back down...but I believe there is enough forward V to dampen the impact. If seas and wind are such that pounding is persistent, then chances are you should have powered down and maintain way in a manner that keeps all but 4 degrees or less of traverse hull waterline below the waterline.

Speed is overstated more often than not. Even if the design could fly along at large V/L speeds, it would be a lot of work and stress to maintain it and the body would be wracked after a couple of hours from herculean efforts to maintain those speeds. It's nice to know the potential is there in case you have to get to port quickly or need to outrun a gale, but it just wouldn't be cruising if it had to be that way all the time. I suspect that (1.5-1.8)(lwl^.5) is borderline for cruising comfortably or requiring chiropractic care after every cruise. At least at my age. Besides, the benefits of sailing flat at monohull speeds far outweighs the same speeds at 30 degrees from vertical, so even a little bit above that V/L is gravy. Why is everyone so concerned with getting nowhere so fast anyway? The destination is always nice...enjoying the journey is better. Anything faster than that...build a damn plane.

Outside of maniacal racers whom we need to thank for developing the sailing industry and teaching us to know better, whom do you know would enjoy a wild eyed, white knuckled trip from clinging to the rails? My friends would have me commited to save me from myself.

I don't think your design is a raft and neither should you. It is coming along very nicely.

I will have something to share in the very near future in this thread...I have been inputing offsets and my eyes are crossed. Maybe tomorrow.

J

 

I don't think my design is a raft I just mean it is very simple compared to yours....or most other larger cats for that matter.

You say that speed is over-rated, but you want to give the boat the ability to go fast if a wild helmsman wants to push it. Fair enough. I can understand that. In fact it would probably make the boat sell more easily....you know...people saying "how fast can she go?" For that reason alone, your hull shape might be the wisest choice, from a commercial point of view.

From a scientific point of view, your hulls should have MORE drag MOST of the time. So that's why I chose the optimised hull for the most usual weather conditions. Do you disagree with this?

- Richard

 

Hello Richard,

No sir. I don't disagree. You can't beat science. In fact, I have been giving significant thought to asking Rick if there may be any objection to using his optimized design below the waterline since pride and ego are expensive emotions to absorb. If I do this, I will once again have to go back to learning about the canoe hull and then have to consult with the NA that called out my scantlings for the design if I decide to use it.

I do have to justify my insistence so that you may understand that I admit my design is inferior to the optimized hull, but not to me. My whole idea 3 years ago was to design a boat that I would like to build for retirement and things started simple enough. Then I liked it and decided to get deeply involved. Right from the beginning...my intention was to design it from what I learned in order to see the best I can produce. I never really gave a lot of thought to "computer enhanced, engineered or optimized hulls." I wanted it to come from my mind and hand and not artificial intelligence. I guess I'm still a firm believer in propagating the species the old fashion way by coitus instead of optimizing the species by way of a laboratory tube.

What does that mean? Well, it could mean a lot, it may mean nothing. That depends on individual points of view. Take no offense as it is not meant to offend, but you may have an optimized hull that will out perform mine any day in this century, but what hull would you have if you designed it yourself based on what you have learned and understand about the art and science associated with designing? Conversely, I may never be able to produce a hull that could ever be as optimized as a hull generated from the table of an experienced and knowlegable NA/NE and I accept that with humility, but, I believe my hull is optimized for my knowledge and experience.

More drag, most of the time is relative. An optimized hull that gets used twice a year may have less drag during those times of use, but all other times my hull will have less drag and logging miles under her keel. Hour for hour and mile for mile, maybe. Based on numerical data, absolutely.

The simpler the design, the better. I try to follow this thinking and you should continue to do so also. Mine only seems more complex because there are other elements given to the design.

I said speed is over "stated", but I guess for the true cruiser, it could be as you've said over rated. As far as people asking how fast it will go...well, I know that a question should not be answered with a question, but I would ask at what speed do you want to die? If they respond with any number, they need to be committed, if they say they don't want to die at any speed, I would tell them the design is perfect for them.

Thanks
J

 

JCD
One of the advantages of the stern rocker is that you can mount a rudder under the hull and not increase draft as dramatically as required with a stern mounted ventilating rudder.

With a powerful rudder section like a NACA0020 you do not need a lot of area if the rudder does not ventilate. The area would be around 1/3 - 1/2 of a surface piercing rudder to achieve the same steering force.

I know you are considering a 16% section but you should compare it with a smaller 20%. A rudder about 8" long and 2ft deep should be sufficient. This rudder will have peak force of 1350N at 10kts and in line drag of 16.5N.

If you go to a 16% foil that is 1ft long by 2ft deep then you get maximum force of 1237N and in line drag of 22.5N. So less steering force but more in-line drag. I have attached the JavaFoil screen dumps of the two cases.



Rick W.

 

Hi J
Going by your response, I get the feeling you may have interpreted me as being a bit cheeky....like....showing off my new cat and rubbing your face in my 'superior' design.
That's not what I meant at all.....but I can see how you could interpret it that way.

I was debating your choice of hull because I wanted to see if I had overlooked some of the advantages of your design (of which there are many ofcourse). Basically, I want to confirm that the canoe hulls are a good choice for ME, not necessarily for YOU.

I don't even consider my boat to be my design. It is my 'collection' of information gifted by others. I am quite happy to shamelessly accept the opt hulls from Rick. If he wasn't so generous, I would have eventually found my way to Godzilla and grabbed the opt hull shape after playing around with the software. The thing is...it might have taken me another year to find that out. But even then I doubt I would have wasted my time cos I would have learned a lot while I was 'wasting my time'.

What I am saying is.....I don't think for a second that you have wasted time....and learning about planing/lifting hulls etc. is obviously a crucial part of being a competent boat designer. I'm not interested in being a boat designer....so I will never develop the detailed knowledge that you are aquiring.

I am just glad there are people like you and Rick who are so willing to share your knowledge on the internet.

By the way....if you do decide to go with canoe hulls, you shouldn't think of it as a 'defeat' over your 'human' accomplishments.

I think you're just putting too much pressure on yourself. I do that all the time....but not with boat design lol.

- Richard

 

Hello Richard,

Offense never crossed my mind, neither did "cheeky". No rubbing faces in anything either. I just wanted to make the point that science can't be beat and it would be most difficult for anyone to draft out a hull that will match or excell the computer optimized hull...not impossible, just highly improbable.

I guess that my design is the sum of many concepts and not just my own as you have pointed out about yours too. I didn't wake up one day with all of these concepts and had to learn them somewhere.

There is no way that I can honestly tell you that the canoe hulls are not a good choice for you let alone tell you that it is not a good choice for me. The numbers speak for themselves and the optimized hull is superior. Period. I think it is an excellent choice for you, and it would be for me. Accept the design proudly and not shamelessly, it is an excellent hull...irrefutably. But again, I wanted to test myself to find out what would be the best I could produce...I'm old school...what can I say? In the end, I might say, I did the best I could, but the optimized is better, so why settle for less? That would be logical.

LOL...competent boat designer. Geez...you are good for my ego. I acquire this knowlege because it's something I like doing, and because I really want to design something that I can build or have built and live with in the end. Don't worry, you will acquire plenty of detailed information before it's all over, trust me on this one.

I do push myself...not pressure, just push. And yes, I look at designs and try to better them in my own. What can I say, I'm competitive and racing myself all the time. A race I can never win or lose.

I did some heavy duty work over this week and believe I have taken the design to the next level before I begin to streamline again. Will have something in here today:!:

Thank's
J

 

Green Lantern

Hello all...

Okay here is the latest. The time is here to reveal secret design weapon number 1. Not sure if anyone else has done it...I'm sure someone has...but if not...here it is. Pro's or cons are appreciated. I would like to call your attention to (drum roll maestro)...the Green Lantern's Fighter Stick Steering!

Yeah, yeah...I know. Well, it was kind of tight to place 2 pedestals and wheels up in there and I just figured keep it simple with forward/aft action for starboard/port steering on cables. The mechanism would be light, strong and take up little space. Gotta design it but it is pretty close where it should be.

I reworked most of the rest of the hull and I am attaching the spreadsheet for comparison. I failed to keep the weight where I wanted, but in my defense a square foot of callout is supposed to weigh 1.01#'s and I added .09#'s per square foot bringing it to 1.1#'s for associated reinforcement and oversight. Also, the design is built with all fluids at maximum. Nonetheless, I will be going back to see what else I can do.

The next step after comments, questions and suggestions is to:

1. Reduce final weights.
2. Establish Racing Trim Weights and CG.
3. Optimize Lead for Boards.
4. Finalize Board design.
5. Optimize Waterline Length.
6. Finalize and Optimize Sail Area.
7. Design Rudders...(looks like I'll be looking at Rick's suggestion closely).

I was giving some thought to considering different rig configurations in line with my thinking of keeping the design unique and the way "I" would like it. I know that it will mean more studying and looking for others to comment, but if anyone can just either support or reject the following ideas and why, that would be great.

My first thought was "redundancy"...therefore, lateral twin rigs, in case if one is lost, but that automatically said double everything, including the biggest no-no's, weight and drag.

My second thought was "simplicity"...therefore, freestanding mast, but that automatically said where the hell would I put it and how much added weight can I expect from the extra beef needed, but I would imagine drag is reduced.

My final thought was "cool looking"...therefore, mast aft, but that automatically said I don't know a damn thing about them nor is much documented about them, good or bad, other than they look cool.

This is just forward thinking and might not be anytime in the near future, but I wanted to throw it out there to see what comes back. I'm placing a couple of pics for those that can't pull the drawings.

Thanks
J

 

cool (in response to your previous post) you just snuck in before me.....I'll check out your boat now

- Richard

what the......the timing is all screwed up on my computer.....I'm not getting posts at the right time.....oh well

 

One fine boat! If mine could be half as good? All praises.