Catamaran Evolution

Hello Richard...

Been busy? I agree with all of the above and thanks.
I duess the study plan is a little lengthy because it has a lot of spaces? HAHAHAH. No really, I guess I was trying to "define" the design and what everything means. I also got a little crazy with pointing out the different sailing characteristics for inshore and offshore. Sorta proudly.

Little persons have been posted and it made a hell of a difference. Yipster gave them to me. Made a huge difference and it made me realize that the design is a hell of a lot of boat for the size. Huge open space outside and inside because of accommodations for a smaller vessel. Definitely worth the cost.

I never really liked racy or sporty names either. I like the name as when built and raced, it be be liked for performance and name.

Oh damnnn for got to post the fbm for viewing. Here it is. Sorry.

Thanks
J

 

only saw jules verns 20.000 miles on tv, so your fast and in 200% view that looks better
although i do draw occasionally i must say that the figers are freeware and the sail was placed
on my first freeship tryouts in the software forum by a member here

 

Yipster...

Then in that case, kudos for them and thanks to you again.

J

 

Okay...

By popular demand...here is the condensed study plan with the Green Lantern in her color scheme.

Also...I corrected an error. The draft with the boards doem has been changed because I failed to add the hull draft in the last study plan, so now it is correct.

Any other comments?

J

 

This doesn't look at all workable. You're cutting the main structural member of the rudder and there's no material at the trailing edge to support the hinge. The deflected tip will immediately twist off once it's freed.

Take a look at Chris White's book, "The Cruising Multihull". He shows a number of different kickup rudder schemes.

 

Hello Tom...

Thanks for the response. Been following your work for some time with substantial pain to the noggin from complex solutions.

The above quoted is correct and has already been ruled out. Now it will be more along the lines as described in post #107. I am enclosing a rough picture of the idea.

If you would care to share your opinion on any part of my work it would be greatly appreciated.

Thanks
J

 

Hi J
What about designing the rudder to take a big whack, like Rick suggests, but make it slide up like a dagger board for beaching. I imagine this would be a good compromise (I am thinking of doing this for my boat). The well that the rudder slides in would need to be precise and well integrated with the hull.

I was just looking at the condensed study plan. I think it's good. I particularly like the detail you provide about costing techniques and what to look out for.

 

On second thought, I don't think the sliding rudder is going to work with the angle of your hull....so forget that idea! I don't think I will bother with it on my boat either

 

J, the more I think about it, the more I think that Rick is right about the rudders. I didn't like the idea of letting the rudders take a big impact....but then I started to visualise the loads and strength requirements of the hulls and rudders, and I realise that they are going to need to be very strong anyway.
I will probably just go with 'permanent' rudders.
When beaching, I will attach a couple of wide skis onto the rudders (using a sleeve system) and winch the boat up onto the sand.

 

Hello Richard,

A little undecided about rudders are we?

I am definitely going to design the rudders to take a good whack as suggested by Rick...but mine will kick back into a well that will have a skin of glass enclosing it for better flow. The skin will just crush or shatter or explode or something when the rudders kick back. Hopefully, it will never come to that.

The rudder would have to be enclosed in a box off the transom if it is going to slide up and down...a lot like a daggerboard case. I don't want that because it takes away from the streamlined look of the hull.

I'm having a hard time moving the file over to AutoCad so I'm back to reading. I did start to print the stations so that I can start working on the model. I'm undecided about what material to use, but i want to keep it all as close to scale as possible. I'm going to try and simulate the build from start to finish as closely as possible so that I can take notes and pictures and maybe put together a construction manual for the design. This should help me find errors during the construction of the model and provide a nica manual for anyone that might want to consider building the design.

My wife freaked me out the other day. She looked at everything...was sincerely impressed, pointed out some things and, then she said that maybe I should build a 12 footer after the model to see if I am really up to it. If I go ahead with the build, she said, I can have a "mini me" Green Lantern as a tender and if I don't, then I can just have a "baby" Green Lantern for camping.

The condensed plan is still in the rough because the true material list will manifest itself when the model is complete...or almost complete anyway. Then I'll go back and rework the whole thing.

Have you had a chance to use any part of the spreads that I created for the GL? I got a hold of some published data for other "reputable" designs and ran them through the sheet and found that the Green Lantern smoked them! Here is one of the estimated results against the Green Lantern.

SA/D
34.75309978 GL- 24.06071399
LWL/BWL
9.731543624 GL- 13.14948454
Windage % of LOA
12.58% GL- 16.33%
Bruce #
1.475071424 GL- 1.227355948
RPI
1.283604949 GL- 1.305090682
Stability #
0.870198505 GL- 1.063335119
Stability Speed To Lift Hull
16.05562328 GL- 19.63602525
Reef (Knots)
12.04171746 GL- 14.72701893
Clearance
84 GL- 45.915
Lowest Bridgedeck Clearance
3.5 GL- 2.5679
D/LWL Ratio
61.8742319 GL- 87.80464153
Speed Knots
15.13041123 GL- 10.54833259
Velocity Ratio
1.71626496 GL- 1.582357136
PIC
1.022702798 GL- 0.802397994
Base Speed
14.09020337 GL- 9.590307027
Texel
77.52027912 GL- 100.1153904
Texel K =
0.397690502 GL- 0.403670063
Stability Capsize
2.133992583 GL- 2.942242029
B/T Ratio
2.709090909 GL- 1.79246624
BCL/LWL
0.374137931 GL- 0.482465398

It has me beat in some instances but definitely not in stability. If I were to compare these figures to scale per waterline length, the Green Lantern would be superior in many respects. I won't pull out any names in here because I don't want to hurt any feelings but if there was any boat that needed a gun to beat the Green Lantern, it would be this one. Take a look at the stability and Bruce calculations. Her bridgedeck clearance which is only 6% of the LWL. Look at how close our Texel K is...which is used for handicap purposes.

Of course the offended will say... "hey, The Green Lantern is only a concept on paper."

Thanks
J

 

Well, I cant make sense of all those numbers....I do understand some of them. I've been too busy with my jobs to knuckle down into a good yacht design book. (too tired at the end of the day). i like to come onto this forum at various times throughout the day, when I'm having a coffee or something (I work from home). So forgive me if my contributions are not so scientific!

From what I can see though, your boat definitely looks competitve in the commercial and racing arena.
I wouldn't underestimate the knock-on effects that show themselves in a real-world test run. A number that looks good on paper might prove to have an unforseen negative effect, when this factor mixes with all the other complex dynamics.

I'm just wondering if those other designs APPEAR to be inferior, when in fact, they have been altered after some real life test runs.

I honestly believe that boat design is probably more complex than rocket science. Rocket science is all about dealing with many sequential details....so it is time consuming and requires a great deal of accuracy and diligence. But rockets are dealing with very constant and predictable forces. Yachting, on the other hand, is dealing with way more dynamics.

I sound like I am lecturing don't I. I'm just giving you my thoughts.....cos I have witnessed so many differing opinions by experienced yacht designers in this forum. Probably cos boat design is just so complex.

I like Rick because he is so unbiased in his opinion. He thinks like a scientist and doesn't have an ego getting in the way. That's why I am always asking him questions. And J, I think your lack of experience is a good thing too. It is impossible for you to be lured into the safe 'old school' ways of boat design.

I am learning that 'old school' can be good....but not always.
So who knows....maybe your test model will sail as predicted and the final boat will blow the pants off all the expert designs. Then the experts can learn a few things from your design

Man......look at all this drivel. I should be embarrassed.

- Richard

 

LOL...

You are sooooo funny.

The design will sail as predicted but forget about blowing off the pants off of anything. Those are just numbers to play with and yeah, the experts are going to learn a lot from my design. A lot of do not's.

I do however believe that the fighter stick concept is a good one for conserving space or for purpose of leverage and it may catch on.

J

 

I am stealing your fighter stick idea. But my tiller is more like the arm of an office chair. My arm will rest on it from elbow to hand. I will have an impressive array of buttons and toggles at my fingertips, to control electric winches etc. I like the idea of controlling everything without having to bend and stretch my body. That sort of comfort would probably make me sail the boat better....and let's face it, it's very cool.

 

Saw a 125 Dinghy (I think --- memory) had a dagger blade rudder with an open ended box. The rudder was held in place with a rubber band (plumbing ring) and tethered to the boat. Gave the advantages of a dagger rudder but with a fail safe if you hit the bottom/object. I have wondered if this concept could be scaled up.

 

My Chris White designed Hammerhead 34 has a kick-up rudder similar to the sketch in your Excel file. It pivots back in a slot in the stern. However the cable arrangement is different.

The cables come through the transom to turning blocks that are in line with the kick-up axis. Then they go around a conventional quadrant on the rudder shaft. Since the turning blocks are on the axis, as the rudder kicks up, there's no change to the length of the cables, and steering is still functional.

In order to clear the end of the slot in the sugar scoop, the upper part of the rudder doesn't turn, and only the lower 2/3 pivots on the vertical shaft. The depth of the skeg has to be just greater than the distance from the kick-up axis to the end of the stern. That way, the movable part of the rudder doesn't come into contact with the stern. The boat remains steerable even after the rudder kicks up.