How Do I Design a 3' Draft Boat to Be Seaworthy ?

[aquarian]

Shallow draft fan here. I have a swing keel a little like your illustration. My keel (500lb) rides inside a balast filled shoal keel about 1 foot (30cm) deep. It does swing from a pivot near the front, and I raise and lower it from the cockpit with no trouble (my boat is not a bluewater baby). Yes definitely raise and lower it to suit your point of sail. Into the wind and reaching = keel down. Running = up, definitely - you'll make much better time. Up is also great when under motor.

[ozskipper]

Originally Posted by Thames

Hello everyone and thank you for such a rich and informative forum! I'm Richard, I'm 28, and my dream is to build a sailing boat that I can live on and explore the whole world.


My home port will be the upper river Thames which is navigable through Oxford where my parents live. This requires a draft of less than 3' and a mast that can be lowered to clear 70 bridges. I also want the boat to be sea-worthy enough to cross the North Sea. Ideas:

• smallest possible live-aboard, perhaps 20' LOA?

• cold-molded

• flat-bottomed for beaching

• leeboards

• mast in tabernacle

• well secured internal ballast

Obviously this would be great for creek-hopping, rivers and canals but could I still sail out into the Atlantic and visit my granny in Argentina? How would you design it to make it more sea-worthy? Your first thoughts are much appreciated.

20 foot is extremely small as a weekender let alone a liveaboard. You may want to upscale the size somewhat.

Bilge keels will be better than flat bottom. More stability but you can still beach the boat. These aslo hold the ballast.

Why cold moulded and not glass?

I really think you are after two boats. One to sail the world and one to cruise the rivers. Have a look at a moody 33 bilge keeler to sail the world and live on. Use the tender to go upstream and see your folks

[Thames]

I think wood would be nicer to work with, I'm used to veneers (pianos) I don't fancy casting a fibreglass mould and I'd rather live in a wooden boat than a plastic one. I read cold-molded is just as strong and low maintenance. I agree 20' is uncomfortably small but if I'm going to build it I think I'll start small build bigger later.

Originally Posted by boatman61

The average/majority small boat is the former... as I said... ballast in the hull... not the keel.. these keels are winched up by hand in the cabin...

Hmm I thought the whole point was to get the ballast as low as possible i.e. right on the end of the swing keel - having it up in the hull defeats the object, I might as well use leeboards.

How much ballast can you safely put in a swing keel? I suppose it's all down to the strength of the keel bolt and it's support.

[rtbates]

Originally Posted by Thames

A Cape Dory 25D appears to be fin-keeled and would fall over when beached as the tide goes out.

Bilge keelers are of interest. I've seen some secondhand that look ok for less than £3000 (although GRP ). I've inquired about the Eventide plans, although one sentence in the description worries me: "well able to face conditions offshore, to the extent of being able to right if ever knocked down." I always thought any boat going offshore must not only right itself when knocked down, but right itself even when upside-down! Although it's encouraging to hear that they've cruised the Med and Caribbean. An Eventide:

What is the average draft for a sea-going bilge keeler? And has anyone crossed an ocean in one?

No NO NO...The Cape Dory is a full keel with a cutaway forefoot and a keel hung rudder..

Designed by Carl Alberg...No FIN KEEL EVER, bite your tongue,sir!!!
http://www.capedory.org/specs/cd25d.htm

[boatman61]

Originally Posted by Thames

Hmm I thought the whole point was to get the ballast as low as possible i.e. right on the end of the swing keel - having it up in the hull defeats the object, I might as well use leeboards.

How much ballast can you safely put in a swing keel? I suppose it's all down to the strength of the keel bolt and it's support.

Now your going beyond the realms of my knowledge... my statements to date have been based on what I've seen and/or owned...
Maybe its time for the more knowledgable to step in... my gut instinct is all the weight needed to counter the weight above the waterline (Cabin/fittings/gear/mast etc) would place a hell of a strain on the pin and housing under sail making housing failure more likely...
With the stub keel you'll still have a topple effect unless your sitting on/in a soft mud bottom... unless you put bilge plates on and the more clutter below the more effect on performance.. or set up for legs when drying out..
I reckon the Bilge keelers your best bet for a more stable life..

[Thames]

Yes I agree, although the ballast might not be the killer - even with no ballast when you're close hauling with a tall rig there must be an incredible amount of force on a deep swing keel. Are there many ballasted swing keelers available cheaply secondhand?

Sorry rtbates a full length keel looks much stronger but still wouldn't dry out flat. Cape Dory does look lovely though.

[sandy daugherty]

Swing keels were a common solution for seventies-era small trailerable sailboats in the US. I would guess more than ten thousand were built and sold in their haydays. They were also the most common failure point, since the axle or pivot bolt were below the waterline and bore incredible cyclic loads.
the cheaper boats used cast iron centerboards which served fairly well, but if they were not properly secured in the down position, they could swing back up into the stored position in a knockdown and cause no end of anguish. Add the complication of a winch or windlass, steel cables to hoist the heavy board, and the obstruction of valuable interior space, they are the achiles heel of this design. Several amunfacturers now build dagger style boards. With a very strong case, the boat just stops when it runs aground, or in the worst case the board is designed to break before the case does. Winch it up a couple of inches, and resume your journey. The advantages are numerous: the board can be built with an optimal foil section, a bulb on the end can contain ballast and extend it deep enough to provide great lateral and pitch stability, it can be designed to use a sheet or halyard winch, or even have positive bouyancy if the boat is ballasted some other way. It can be located in the hull where the water will flow smoothly around it. Bilge boards are inefficient in this respect; they penetrate the water surface and a large portion of their foil area is spoiled by aeration when air is sucked down the low pressure side.

All boats are a compromise, from the perfect sphere mentioned above to an all out racing multihull with huge sails and coffin-like interiors. It takes a half a lifetime to learn all the ends and outs of delicately ballancing the myriad factors that come together to make a good vessel. It takes nothing more than an axe and a box or matches to hollow out a log. That's why we pay Naval Architects for their designs.

That has not kept enthusiastic novices from pouring their lives into ill-fated efforts. Boaty places all over the world are littered with the dead dreams of every one of them. No such dreamer has yet come up with a new design that works the first (or fifth) time without borrowing from older designs.

Should you give up this common dream? No. Just don't take anyone with you, and realize from the outset that unless you are a demonstrated creative genius, a master craftsman with unlimited tools and work site and independently wealthy, with ready sources of quality materials and precious unobtainium (a rare, coveted, rust-proof and easily workable metal of ultimate strength and minimum weight) you are just dreaming your youth away.

My advice (fully worth the price) is: Sail everything you can get on. Sign on as a crewman on a smallish vessel in challenging locations. Get a job in a boatyard. Try working with every material and process used in boat building. Stop thinking of GRP as "plastic" and come to understand all the reasons why it is the universal first choice for boat building. Make something with it.

Look at a lot of boats; get on them, crawl thru them, imagine yourself fixing them, imagine yourself keeping them afloat in a cold gale at night off a hostile lee shore. Look up all those salty phrases, and learn to sift first hand reports from tenth-hand rumors and cherished mis-information. and start NOW!

[Thames]

This has been an amazing discussion and I thank you all for enlightening me on so many aspects of sail boat design. Unfortunately I've spent a lot of time doing research on the internet and I need to get back to work, otherwise I won't be able to buy or build! I'm still paying rent to the rich like a true landlubber...


Thinking of building cold-molded, I had a similar discussion on the Wooden Boat Forum, link here Shallow draft but sea-worthy live-aboard of simple construction - your design ideas?


Based on people's recommendations I've purchased the following books:

-Boats with an Open Mind by Philip C. Bolger
-Voyaging on a Small Income by Annie Hill
-Living Afloat by the RBOA
-Two Girls, Two Catamarans by James Wharram
-Shrimpy: A Record Round-the-world Voyage in an 18 Foot Yacht by Shane Acton


Conclusions...

• If I need a quick fix I'll get a secondhand GRP bilge-keeler as they're readily available secondhand here in the UK. Even if that's not my dream boat at least I'll learn a lot. I could always try building one later.
• But if land life suits me for a while longer I may spend a lot of time viewing/sailing other boats, indulge in a few boat building courses and see where I get to. Build a dinghy first and have some fun with it.
• I've been very encouraged by suggestions that one man alone can quite easily build a 20' boat cold-molded with enough patience.
• I've come to appreciate that building someone else's design and designing your own are not necessarily two different things. On the contrary, most new designs are just old designs incorporating a couple of new ideas. And in 2010, there's not much that hasn't already been done before.
• The ultimate go-anywhere boat will have a lifting or swinging keel with the ballast on the end, but there are more moving parts that can go wrong and loosing the keel in the open sea could be disastrous.
• The most simple build might have internal ballast and leeboards, but won't have anything like the righting moment of a long, ballasted lifting keel.

It probably depends on my personal life in the next few months - if my girlfriend doesn't move in (and share the rent) I won't renew the contract - I'll just jettison everything and buy a boat

The Thames near Goring:


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[Cormorant]

Good luck with your project.

Another good book is David Gerr's "The Nature of Boats," which outlines many basics of the design process.

He also has a book called "Elements of Boat Strength," which I haven't read but sounds like it would be helpful.

[Fred Amor]

At the moment there are vast numbers of very inexpensive boats for sale in Canada and other parts of the world I am sure - and while it is true that you will be hard pressed to build a boat as cheaply as you can buy one I know from personal experience that there is nothing quite like learning how to design a boat, designing your own boat and then building your own boat and sailing off to distant shores in said boat.
If you are willing to apply yourself seriously, you can learn enough theory and design your boat in less than a year. Start with Chappel's yacht designing text, study Uffa Fox and Phil Boldger's designs.
Keep the displacement similar fore and aft, make cockpit self bailing, imagine what the boat will do when it is upside down and design your sleeping and cooking spaces to be in the area of least motion. Leave the bow for storage!
Use a door - not drop boards on your companionway you can't loose them when you are upside down! Make the forefoot sharp and vee shaped not flat or it will slam. Make the bow vertical to improve your speed and comfort as well as get more space inside. Consider bilge keels - look at the Bluebird of Thorne design. If you are indeed heading for Argentina, learn to use a sextant, catch water, fish and pray! Have fun - life is much to short for anything less!

[bljones]

Building a boat big enough to live aboard, even a relatively small and simple boat like an Eventide, is a 2000-5000 hour project. At 40 hours/week that is one to three YEARS, as a full time job. As a hobby after school/work, figure 3-10 years. Figure #5-50 000 in after-tax money invested as well (sorry about using the pound sign- my yankee keeyboard doesn't have one of them fancy looking "L" thingies). THAT is if you are working from plans. if you are designing from scratch, double both the time and money estimate.
I am NOT trying to discourage you, I want you to know what reality looks like.

Here's an idea, and it is something i have done on every major boat build I have done-
build a 1" = 1' scale model. not a half hull, not a waterline model, but a miniature version of your dream. Every detail right down to the heads and galley stove.
Start tonight. Even if you only sit down and rough out a list of features you want to incorporate, start tonight. and then keep going. One little, or big, task, every day. At least an hour. Every. Damn. Day.
Christmas Day? Do something.
New Years Eve? Do something.


If you find yourself skipping more than three days in the first month, go buy a boat, because building is not for you.

[Mark Johnson]

bljones speaks the truth! My projects were 3 years, 8 years, and the last one 10 years. The last one I had just gotten married, so had the help of my long suffering wife for part of the day. The rest of the day she worked as a lab tech part time to bring in the $. I put in 70 hours / week on the boat, and she worked 30 / week on it.

We kept up this 100 hrs / week for the first 3 years without a SINGLE day off! Then, still @ 100 man/woman hours a week, we relaxed a bit and took 2 or 3 days off ... A YEAR. The last few years being outfitting while living on the boat, we finally started working at just a standard work week of 40 hours each.

Building a boat is not for the timid, It takes a level of single minded determination that is hard to believe. BTW... before building the boat, we had just built a very nice house and workshop. NOT hired it built. This only took a year! This is how much more work a boat is.

I don't mean to discourage you... It is a great endeavor for the right person. I don't have regrets. Just think about if you really want to go this route.

All the best, Mark

[Cormorant]

And if you count the hours thinking, obsessing, building the boat in your head over and over before you set saw to wood . . . it's nearly every waking hour of your life. And I mean that in a good way. . . .

It is surprising how, when you're obsessed, you can find time to do anything.

Our boat is a very simple modified sharpie, probably 800-1000 hours building time over two years. It completely overwhelmed my "normal" life, and left me exhausted (but very happy).

Sure beats sitting around watching TV!

[jck339]

Look also at Shannon's shoal sailer boats. Pretty cool.

[pressuredrop]

id look for one of these built by Royal System Yacht Yard of Denmark i believe
SAGITTA 20 Sailboat details on sailboatdata.com

< 3' draft (2.84' to be exact), HUGE interior for a 20 footer, and very very very very well built.

there is a freebie one (that obviously needs work) over here in south florida that i am having a hard time passing up because it is built so well