Simple Info!

[trackerscout1]

Hi everyone. I am new to this forum and to boat building. I am designing my first build right now, a small catamaran, of either 8 or 12 feet in length. I anticipate having many questions throughout this build, and would very much appreciate any and all help.

For the moment, I have a very pressing question, although many of you may think that the answer is obvious. If I design this boat to be 8 feet in length, how wide should I make both the individual beams of the hulls, and the overall beam with of the completed vessel? My original design of a 12 foot length, had the individual beam width of 1 1/2 feet. The sketch looked good, having graceful lines, but I wasn't sure if the hulls would be sufficient to support the weight of two large adults. Also, I had no idea of what the proper overall width of the vessel should have been, but I figured that about 8 feet would be the best balance between stability and speed. I have researched the subject, but I am no mathematician, and the information I found was indecipherable. So what do you folks think, am I crazy and way off in my thinking? Am I relatively on the mark?

I am building this boat to be mainly a fishing boat for my father and myself, but also to eventually rig with sails and get some experience with that as well. As such, I need it to be a fine and dependable vessel, for at least a few years to come. Thank you all for you help.

~CJ~

 

[redreuben]

I think your crazy to design your first boat.
Buy a set of plans, build it, sail it and then do your own if you feel you need to.

http://www.duckworksmagazine.com/09/designs/slider/index.htm

http://www.teamscarab.com.au/scarab350/design.html

 

[Richard Woods]

Have you looked at the Livingston dinghies?

http://www.livingstonboats.com/lv9-livingston-powercatamaran/

is that the sort of thing you are after?

A general rule "use your eyes and plagiarize"

A cubic foot of water weighs 62lbs approx. So you will need at least 6 cuft to carry your load.

Richard Woods of Woods Designs

www.sailingcatamarans.com

 

[jamez]

Or maybe http://www.duckworksbbs.com/plans/jg/hotchili/index.htm
For anything other than a kids boat build a bit longer than 12' if you can.

 

[PAR]

Welcome to the forum CJ.

If you have to ask as basic of questions as you have, you're nowhere near the understanding necessary to design a boat successfully.

This isn't a personal dig at you, just an observation based on you post. If you want to design a boat, there's several texts that will help and you'd be best advised to absorb the information within. Try the book store on this site, with boat and/or yacht design as the topic.

The math isn't hard (high school level), but you will need to at the very least understand the physics, dynamics and fundamentals of the various issues involved. Of course this assumes you'd like it to float with the decks facing up on launch day, preferably at the waterline you've paint on her too.

I'd strongly recommend you look at the L Gato over at Glen-L.com

It's 12' (8' is just ridiculous for a cat) and a relatively simple build. Of course a mono hull would be a simpler build (only one hull to make), but you mentioned a cat.

 

[hoytedow]

Welcome to the forum.

Welcome to the forum CJ.

......

This isn't a personal dig at you, just an observation based on you post. If you want to design a boat, there's several texts that will help and you'd be best advised to absorb the information within. Try the book store on this site, with boat and/or yacht design as the topic.

............
......
I'd strongly recommend you look at the L Gato over at Glen-L.com

It's 12' (8' is just ridiculous for a cat) and a relatively simple build. Of course a mono hull would be a simpler build (only one hull to make), but you mentioned a cat.

I agree. Very nice looking sailer.

 

[trackerscout1]

For those of you who suggest that I do not have the proper understanding to build a boat, I would suggest that assuming things about people you don't know is a very foolish mistake to make. I have been in boats, and around boats for most of my life, I am an accomplished wood worker, and I have a keen mind. Do not tell me I cannot design my own boat! Their are no prerequisites for passion. Thank you Mr. Woods for your more positive reply. The boat you linked me to is not something I would be interested in owning or using unless I had no alternative. I want to build a catamaran, because I love them. I love their look, their support characteristics, their steadiness, and everything else about them. I like trimarans as well, but for my first build I want to keep it as simple as I can, without building a monohull.

Now, someone suggested that an 8 foot cat was ridiculous, or something to that effect. My response to that is, why? Can one not build the hulls properly to support it? Is their some unwritten law of physics somewhere that says catamarans have to be a specific length minimum in order to float or move on the water? Lets not forget, that when Multihulls were first being built and sailed in Europe and the States, people referred to them as freaks. Lets not hastily jump to conclusions about anything.

That being said, I would prefer to build to a 12 foot length. the issue with that is cost of materials, as in I don't have the money to buy a ton of lumber. Who knows, maybe with some fancy saw work, I can make the ply stretch. Interestingly enough however, no one actually answered my questions, except Mr. Woods, and that was in a very non simple way. So instead of actually asking the question again, I will just say what I am thinking. As far as the width at the beam of the individual hulls, the general rule that I have come across is 11:1 ratio, length to width. Assuming that is mostly correct, that would put a 12 foot hull length, at just over one foot in the beam, and I figure, allow a few extra inches for stability. I was asking about the eight foot length, simply because I want to conserve materials as much as possible, but don't want to have a hull beam of less than a foot, as that seams very small to me.

I will use the info Mr. Woods provided and the others who provided positive information to the best of my ability. I love that line, about plagiarizing hull shapes, it is great, and in essence, what I do when attempting a first build at anything. That is how I learned to build guitars after all, and it worked quite well. So thank you for that.

One final comment, I have read many posts on this forum and others, and must admit to being disappointing with many of the posters. Not in any way because of the information provided, but because of the apparent disdain that some of you have for the home builder without a lot of knowledge. The point to forums like this is to discuss boat design, and to help others as they attempt to learn the craft. Comments telling people to buy plans, are not helpful to those who are interested in designing their own boat. Comments suggesting that someone dose not have the necessary skill level or intelligence, are reprehensible in my opinion, especially when that comment contains no useful information to help bring that person's skill level up to the adequate level. It almost seams like some of the people on this forum and others think about boat design and building like their own little country club or other elitist group. If you do feel that way, then why are you a part of the forum at all, just to share pictures and stories of your success with other successful boat builders? That seams like a waist of time to me.

So again, to those of you who actually posted some positive feedback and provided useful information, I thank you from the bottom of my heart, and look forward to further communication. To those of you who took my question as an invitation to ridicule an amateur, to blast me and insult my level of skill and intelligence, I can not wait to prove you wrong! Any continued positive feedback and useful information is greatly valued and appreciated. Negative remarks will be ignored.

Thank you all.
~CJ~

 

[hoytedow]

Everyone should build a first boat.

My first build was an 8' cat, powered by a 5 horse outboard. It worked well for its purpose, which was on very protected waters. It would not have passed a marine safety inspection as it was very basic, lacking even the most basic flotation. It was fine on protected water where no idiots were running their own boats. When one did show up, it was lucky I was young and a good swimmer, if you get my drift.

 

[DGreenwood]

First off hotshot, the guy that you are blasting as unhelpful in your quest to be a designer/builder, puts enormous effort on a daily basis in helping people to actually achieve their boatbuilding dreams. He has spent in recent years what must have added up to hundreds of hours of his time typing complex explanations for beginners and pros alike. Way more patience than me. IF you had actually read as much as you claim of the info on this forum you would already know this about PAR.
As to your ability to actually succeed at building a useful boat I would say you are off to a very bad start. Ego damaged, not listening and mouthy all are signature traits of a character that has come and gone here many times. You want to build a boat. Great! There are many here including PAR that can offer you good advice to get you there.
As to positive feedback...your attitude will get you none.

 

[lewisboats]

You need to get off your high horse a bit. Many people build boats and guess what... not one person here said you couldn't. Designing a boat is a whole different kettle of fish. I am an amateur designer/builder and I have been doing it for about 15 years now... and only in the last 10 yrs have I learned enough to consider my designs to be decent. I have also spent close on $2000 on books and a few hundred hours studying and applying the design principals that go into a workable design.

No one has said one damn word about your Intelligence... however... you show a distinct lack of Knowledge about boat design which is what PAR is referring to. Being able to use a boat safely is a far different from being able to design a boat that is safe to use and actually usable. You are taking potshot guesses at things which should be calculated to ensure the boat will perform like a boat. PAR is a knowledgeable designer who makes a living at it... he knows what he is talking about. I suggest you take your ego and shove it in your back pocket, pull your pants up and start learning what you need to if you want to design a boat that will not try to kill you.

That 8 ft cat you were talking about...? Have you ever heard of the term "Pitchpole"? How about initial and ultimate stability... or lever arm and how to calculate it? What about Center of Flotation and Center of Buoyancy (and the difference), Center of Gravity (vertical, longitudinal, transverse)? How about Metacentric height and heeling moment? Modulus of elasticity and torsional rigidity? Center of effort and Center of lateral resistance? I could go on and on. Can you calculate these things? Do you know how to apply these things and how to correct them when the application gives an undesired result?

I was just as green as you are but I didn't come in with quite as big of an ego riding my shoulders so I shut up and listened to what the experience said and did a lot of studying on my own. Now I feel pretty confident designing something that won't kill myself or my family when the squall comes up in 3 minutes and the waves go from ripples to 3 or 4 times the depth of my freeboard faster than I can **** my drawers.

 

[trackerscout1]

DGreenwood, I was not blasting Par. And yes, I have seen several of his other posts on this site, and yes he has done a great deal to help folks answer their questions. However my comments still stand. I was not actually speaking about Par when I made that comment, but several other posters who I have come across who seam to get very upset when someone new to boat building suggests that they will build a boat without a lot of knowledge. In fact one poster went so far as to suggest that a novice builder take their boat out on the sea, with no flotation or life jackets, and pray they didn't sink. That is arrogance, that is unhelpful, and yes, reprehensible. And I have seen posts like that on many occasions, usually from established boat builders, and usually directed at the novice. Yes, when par said that I was nowhere near the level I needed to be, I became upset. As I said in my last post, he doesn't know me, he doesn't know what level my understanding is at. However, my ire was short lived as in the next line, he said, "This isn't a personal dig at you, just an observation based on you post." He then proceeded to post a picture of a nice little cat, that I would be very happy to have built myself. But on the other hand, their was no information shared. So my comment, was not directed at Par, I am in no way upset with Par, he offered his opinion and I offered mine. You, I am upset with. You call me hotshot, claim I am ego damaged, I don't listen, and I am mouthy. I am no hotshot, and if you knew me, you would understand why I say this. As far as the Ego thing is concerned, I find that it is usually the person telling everyone else that they have ego problems, who has the biggest ego in the room. I listen very well, and have spent the last bit of time this morning, attempting to put the useful information that was offered, to good use. As far as mouthy is concerned, you bet your *** I am! You want to blast me for my comments when they were accurate and presented in a tactful way, expect to get blasted back! I was addressing a problem that exists on this forum and many others, a problem related to arrogance, and self centered thinking. I was not blasting anyone in particular, nor was I attempting innuendo or insinuation. And yet your response was targeted, directly at me, and my character, and you in essence called me a lire! So who needs to adjust their attitude here? The guy who is asking for helpful information, and saying that telling someone they don't know enough, is not in and of itself helpful, or the guy blasting the first guy, for a perceived slight against someone else entirely, that never actually happened. In my opinion, I think you were offended by my country club, elitist comment. I think that you took it personally for some reason, even though you had not posted a single thing on this thread up until that point, and as such were in no way included in my mouthiness. So I will say it again, who is mouthy, the guy asking for help, not critical comment about his abilities, or the guy jumping in and calling people names? Check yourself, Mr. senior member, before you wreck yourself.

PAR, if I offended you, I do apologize. Perhaps I should have outright said earlier that I was not blasting you personally, that my comment was also not a personal dig, just an observation. Anyone else who became offended at my comments, especially if they were not a part of the thread before that point, should reflect on why those comments offended them. Do not jump down my throat for pointing out that something is not helpful! Do not begin making personal attacks against me, someone you do not know in any way shape or form, for stating my opinions in a non confrontational way! If I get banned from this forum for my comments, then so be it. If calling out elitist pieces of crap who are not interested in helping others out gets me banned, then I don't want to be a part of this forum anyway. As far as Mr. senior member is concerned, If you don't like the truth, don't read my posts!
~CJ~

 

[DGreenwood]

I suspect you're not as gutsy a guy as you like to play on the other side of that screen, Mr. Brand New Member.
People try to welcome you, to put you on track to success, reign in your ego, set you on a coarse to building your own boat. Still you blow up like a toad.
I don't need to check myself and have no fear of wrecking 30 years of boat building skills. And as a long time member and a contributor to the skills of many new builders I suggest you listen for a minute.
No one here is trying to be elitist or stop you from building a boat. It is just that, to a skilled builder, it is obvious you are headed in the wrong direction and are getting all hurt about being told so.
So I'll repeat what has been said to you already. You are not going to build any kind of useful 8 foot multihull that you and your dad can sit on and fish, unless you both weigh less than 25 lbs each. Consider starting with an existing design and work your way through building techniques first, then move into design. There is some useful advice coming from a very experienced builder. Do as you wish with it.

 

[Richard Woods]

I based my Livingston suggestion on this

I am building this boat to be mainly a fishing boat for my father and myself, ~CJ~

In any event, it gives you an idea of the hull form necessary to carry the load you want. One reason why there are no 8ft sailing catamarans suitable for adults. In fact even 12ft is really too small

The hull cost is minimal relative to the rig. Even a 16ft catamaran will only use 6 sheets of 4mm (3/16) ply and a gallon of epoxy. Certainly the engine (if a powerboat) or rig (sailing) will cost much more.

I can understand your irritation, you ask about a catamaran and people reply with links to trimarans. They might as well have linked to boats with one hull less, not one more

Having said that, as you know from viewing other similar threads, the usual problem is the OP doesn't give enough information first time round. So people jump on the few words written (like "new to boatbuilding" in your case)

re the El Gato, I wounder how it behaves in waves and how well it tacks in strong wind with a rig positioned so far forward

Richard Woods of Woods Designs

www.sailingcatamarans.com

 

[trackerscout1]

Thank you again Mr. woods! This first boat will not be out on any very big water, just lakes and small rivers, with the St. Lawrence river as the biggest source of waives. To begin with we will be powering it with just a little trolling motor, and depending on how it behaves, I may decide to put a small sail on it, nothing very fancy.

Now, when you say that 12 feet is too small, you do mean for rigging with sails correct? Or is it too small because the hulls are insufficient? I would imagine that under sail in strong winds it would be pretty easy to pitch pole an eight or twelve foot cat. I just did the calculations on the Hulls I wish to build, and unless the formula I found is wrong, each hull should support well over a thousand pounds. My dimensions are basically 12' x 2' x 1', length, height, and then width, and that one foot width is only at the bottom, the entire hull widens to two feet at the beam on the top.

I see your point about L Gato, it seams as if a strong enough wind would punch the bow down rather quickly. Interesting observation.

My irritation, is not really about people posting links to mono hulls or trimarans, I like looking at boats. it is about those who somehow thing that telling you you need to spend another thousand dollars on book, and several more years reading them before you can build a boat. I am a country boy and have always learned much better by doing, than by reading. I am not looking to create the perfect boat on my first try, just a nice one. So, comments that are like the ones I mentioned get my motor running so to speak. After all, did the Polynesian and Indonesian boat builders of several thousand years ago sit down and scratch out complicated mathematical equations in sand before going to work? I doubt it. That is why it is called a first try. Anyway, thank you for your advice and input, and I look forward to hearing from you again soon.
~CJ~

 

[Corley]

I agree with the others that 8' - 12' is too short you want to keep a reasonable fineness ratio for good performance 16' to 20' is probably a better target multihulls thrive on length. You might like to have a look at the thread I put up on tortured ply construction. It has some plans attached for tortured ply type hulls which is still a cheap way of achieving a round bilge (well more parabolic or V) but roundish hull. I've seen some interesting outboard conversions on the Tornado catamaran and they have the runs on the board as a sailing catamaran.

http://www.boatdesign.net/forums/mu...ld-mosquito-catamaran-tortured-ply-43934.html

also worth looking at the Gougeon Brothers on Boat construction which is available for free download as a .pdf

http://www.westsystem.com/ss/assets/HowTo-Publications/GougeonBook 061205.pdf