Design thoughts on a 9" wooden Sailboat

Hello... I am trying to Design and build a 9" Sailboat...

I know some of the basics of sailing, and basics of boat parts.... but... Im not quite sure how this is all going to work out...

First, My Sketches....



one square= half foot

I have NO CLUE wether or not these are on par with anything at all... I just threw something out there...

You think I should Have 3 chines like that? or 2? and make it a flat bottom for an easyer build?

I wanted the Transom to have a spot for a rudder and a 2 horse outboard (and no, its not that big... and Im not ashamed of having one on their either... like some sailors i know...)


and an explination for wideness...

well... not really any... but it would be nice to be able to fit two people in it... comforatbly...

How do you think the wide design will effect speed/stability?

Should I have the Centerboard somewhere else? or is it in a good spot?

also, I have the mast in 2 different spots on the profile drawing... which do you think is better? farther up in the bow? or farther back?

Im basically looking for a quick and stable little boat for two....

also... Im going to need A LOT of help learning to build it... I know i need marine grade plywood (or at least, thats what Im going to use) and the hard part is making the spine, or ribs...

but other than that... I know nothing...

thanks for all your help...

PS... If this thread needs to be moved, please inform me...

Thanks!!!

 

My advice is to put your design on hold and get a book or two on designing principals.

My recommendations are:
Understanding Boat Design by Ted Brewer
Preliminary Design of Boats and Ships by Cyrus Hamlin
Skene's Elements of Yacht Design (the one by Francis S. Kinney)

I know you aren't interested in building a yacht but the same principals apply.

you will also need to learn about building with plywood or whichever method you choose to build it.

Asking a forum to teach you enough to design and build a safe and seaworthy boat is stretching it a bit.

models are a good way to test principals and a whole lot cheaper than building even one full sized boat. Try using a free design software like Hulls or Carene or even FreeShip (a bit complicated but more complete than the others). These limit you to hulls that are developable and give feedback on your design in terms of #s (go back to the books to interpret these #s).

Finally...Look at all the designs that would be similar to your design as far as length and overall use and compare them to your design. I think you will find that yours needs a bit of massaging and fine tuning (a slight understatement).

Steve

 

You are in luck! My boat in progress is only 2.5 hours from your house. Just think of all the good experience you could get helping me to bond strips, lay glass, and other fun boat building stuff.

... I suppose you already read Tom Sawyer?

 

um... yeah... but seriously, I forgot it allready....

I didnt much enjoy it... All i remember is boys on an Island, then in some boats, and then they got lost...

thats it...

but no comments on my design?

what does everyone think?

ps. Im planning on getting a book or maybe even buy some plans... because I have no clue how i would get this design off paper... and plans are full size right? or no? oh who cares...

well anyway.... thanks for what you gave me... but what do you actually think?

 

First of all, you better be talking about mighty small people if you want to fit two of them in an 9" (nine inch ) dinghy

I'm no expert on hull design, so I will not comment on your hull. I will suggest that you look at other existing designs in the same size to get some idea about hull shape, layout, etc. Who knows - you may find a design that you like and you'll save yourself a lot of headaches by buying the plans.

One thing you will see is that most boats in this size range are prams - they do not have a pointy bow. This maximizes the capacity of the boat for the given length, so you can carry a reasonable load (i.e. two adults) in a very small craft.

Anyway, here are a few links to check out:

http://www.selway-fisher.com/Highup13.htm (see the Highlander 9)

http://boatdesigns.com/products.asp?dept=507

http://www.woodenboatstore.com/prodinfo.asp?number=400-057 (9' 6" Nutshell pram) this is a highly regarded boat that has been built by many beginners. Note that there is also of "how to" information available to guide you through the building process- definitly worth careful consideration

http://www.boatplans-online.com/proddetail.php?prod=V10

http://www.boat-links.com/Atkinco/Dinks/FinkelDink.html

http://www.clcboats.com/boats/passagemakerdinghy.php This one's 11 feet long, but comes apart and "nests" to take up much less space for storage or transport.

 

Plans aren't necessarily "full size" Heck - when I began builidng my small bagger, all I had was some numbers, taken from the center line and the base line. So, no, "plans" aren't necessarily "full size".

Gees, I feel like a party pooper today. feel free to give me a bad rep, I think I have it coming, lol.

 

OK, to put it bluntly...I think it is WAY too short for the width, you don't know the displacement, you need to figure out the CLR, CE, D/L ratio, L/B ratio... When you have these worked out, you will know if the design is viable. Right now the length beam/ratio (L/B) is 1.5:1. I have yet to see a design that is less than about 2:1. Your design water line shows a very heavy displacement in relation to the length (D/L) so it would take a lot of sail to move it in light winds. The deep Vee bottom won't give much stability for such a small hull so it will be tender despite the huge beam. With a 6' beam it will even be a bit difficult to row. The daggerboard appears to be too large and you can't determine size and location until you determine what kind and size of rig the boat will use. You will need to determine the Center of Effort (CE) of the sail in order to place the Center of Lateral Resistance (CLR) and determine it's size. Your Maximum Beam is forward of the DWL mid point and this will be detrimental to any kind of speed, and could possibly be detrimental to helm balance too.


So...all in all I think you should go with my original suggestions and bone up a bit on designing and browse the web for designs in the same range as yours and see what others have done and what works

Steve

 

hokay...

Even though my design was just ripped apart, Im quite happy you did it... THAT^ was what I was looking for guys, and thanks...

I understood about the 2:1 thing width...

Ive seen some sunfish that were pretty wide, but now that I recall, It wasnt that bad in relation to length...


Im pretty sure I get what you said about the D/L ratio... you meant mine was too big right? Or if not, what did you mean?

and you meant that my max beam was to far forward for it to be a racing machiene...

thanks for the help!

Ive been messing with it allready, Ill try and get a better design up soon!

 

Sorry to put it quite so harshly, but I think you asked what we thought about 4 times so I had to tell you.
The D/L ratio is calculated by dividing the displacement of the hull (in long tons{2240lbs}) by (.01 x the waterline length) cubed or Dl/(.01xLwL)^3

Your sketch shows a waterline of about 7 ft so (.01 x 7)^3 would be .000343

If your boat displaced .2 tons with 2 people (just under 450 lbs) your D/L ratio would be .2/.000343 or 583.xx. Anything over 350 is considered heavy displacement so yours would be pushing Super heavy. Getting 2 people into a 9 ft sailboat is tricky...It usually isn't done on a boat with a pointy front end. The way around this is to design a longer boat and chop the front off...in other words...A pram style boat. Here you can get near the same performance of the longer boat in a shorter format. With an 8 ft waterline the same displacement gives you a D/L of 390. Not a racer but on the lower end of heavy displacement rather than pushing the ceiling. Most pointed boats don't start looking at 2 people until they grow to about 11-12 ft.

Steve

 

Ok...

hmm...

so your saying my boat didnt cut to deep, It would just be way to heavy with two people in it, and it would sit real low in the water.. therefore being exeptionally good if you dont want to move at all...

Ive been thinking about it... And I decided to screw the whole 2 man Idea... But In doing so I would like to cut the length down a little... Is 7 feet two small for a one manner? Ive got some different figures drawn up in a 7 foot length...



the profile view was drawn in an attempt to copy another design Ive seen..

and Im wondering wether i should go with 2 chines for simplicity or 3 for speed... or wether or not it will make much of a difference...

thanks for telling me whats up... I really appreciate it... and it wasnt harsh... it was informative!!!

 

Hold it there!

Hi John, you have posted on another thread by Daywalker who is trying to do the same as you, but a little larger. Again he has no clue just like you.
Don't take this as an insult, we all have to start somewhere. I strongly advise that you do NOT build your own design but get a kit or at least plans for a very simple pram dinghy, or flat bottom skiff. Also consider going a little bigger than 9 feet if you want to sail with a second person. See my posting in that thread as well and maybe look up CLC boats for excellent simple designs and kits.

 

sketches to 3D

Just to show you what your first sketch looks like in 3D. Probably nothing like you dream about. Certainly not worth trying to build.

Not to be cruel. I used to sketch the views somewhat like yours (of multihulls) 20 years ago. Then I made a model of one and found that the sketches did not look like the resulting model. It is an educational process. Now days, it is a lot faster to quit sketching and learn how to model in 3D.

 

I tried the file and Quicktime didn't understand it, same for RealPlayer. Is it a movie or something else?

Steve

 

I think my point was that unless you go pram-ish, 9 foot would be the SMALLEST I would consider for a SINGLE person if you intend to put a sail on it. Longer is better, not shorter. A 7 ft boat would only have a 6 ft or less waterline (as drawn). This translates to a max speed of 1.2 x 6^.5 or around 3 kts. Careful, knowledgeable and skillful designing and sheer luck MIGHT get you another .5 kt. You would only be able to sail it in close to mill pond conditions, so you could only expect about 60% of that speed before you capsize or otherwise give yourself a bath...so that is about 1.8 kts or about 2 mph. You will have very little stability...even getting in will be tricky. If you give the sides enough freeboard to be somewhat safe it will present quite a broadside to the wind (in relation to the amount of boat in the water) and will be pushed around (windage). Lowering the freeboard to make the boat look decent and reducing the windage will increase the likelyhood of swamping when you sneeze.

Here is my best effort at your 7 ft skiff...displacement is 175 lbs and the hull and rigging would run about 40 lbs. This is a kid's boat or a rowboat, but not an adult's sailboat. I advise 10 ft minimum, beam about 4 ft, single chine, flat bottom...OR a pram of at least 8 ft, designed for sailing. Note that L/B ratio is about 2:1, D/L ratio is 365...quite the pig but within tolerable limits. A curious thing is that the smaller the boat the looser the tolerances on the #s...to a point.

Steve

PS: The design below is a tub... but any narrower and it isn't worth drawing. I would consider building this for an 8 or 9 year old to learn to sail with...on a shallow farm pond. It would go together cheap and burn well when the kid out grew it.

 

It is a quicktime movie showing a 3D model spinning around once. I just downloaded the file, double clicked the .sit and the double clicked the .mov file. It works fine. Maybe a mac only format? I will do some checking into it, since I would like to use this feature of TouchCad for other things.

Steve your design looks like a boat!