Reading, videos etc on displacement hull design theory

Hello, I am new here, and have no background in boat design or building. After following some boat building communities on Facebook for some years, I’ve become determined that I want to give boat building a try. Id like to build an outboard powered flat bottom 17-19 ft small displacement cruiser, with a cuddy cabin and an open cockpit, using sheets of plywood bent around wooden frames. Before building this one, I’d practice the methods by building a small 10-12 ft rowing skiff, that could also be powered with a 2-4 hp (or electric) outboard.

I know most would recommend buying a set of plans, but I would also be interested in creating my own designs. I’ve been doing some sketches with a 2d cad program, but of course I don’t have all the theoretical knowledge about what makes a good displacement hull. I kind of know how they usually are shaped, and I know what pleases me aesthetically, but, again, no real theoretical knowledge.

Could anyone suggest some good reading, or YouTube videos etc, that would help me understand what I’m doing? I do understand the difference between a displacement and a planing hull, but only scratching the surface.

Also, if somebody would like to comment on my sketches, I’d be more than thankful!

 

Welcome to the forums.
Don't worry, I'd say a reasonable guess is ~60-70% of all the boats built in the world were/are not built to a set of plans. What they are built to is copies and slight variations for older boats in the area that are successful. So while a flattie skiff is fine for the very shallow inland sounds of North America, they may not be good for working around exposed rocky islets in the Gulfs of Finland or Bothnia; you may need some V in the bottom. So walk the docks, see what the watermen are using where you think you want to operate. Most experienced people will share their opinions...perhaps too much.

As far as ply over frame construction is concerned, go over to the Wooden Boat forum and ask around. There are several entry level books by Harold "Dynamite" Payson on how modern stitch and glue construction goes together quickly, or Boat Building with Plywood by Glen L Witt for a more traditional method of frame first construction. As far as videos, go to YouTube and enter "instant boat building videos" and you will get a large choice, mostly stitch and glue or ply over frame.

Edit
Re-reading this, perhaps I did not fully answer your question. Are you looking for a book that tells you how to design a small boat...i.e. make it go a certain speed and have good stability characteristics? That is a whole other discussion. I'd start with 'Skene's Elements of Yacht Design' by Kinney and Dave Gerr's 'The Nature of Boats' to ease you into the basic concepts of the how and ways of design vice building.

 

Thank you so much for your reply! You’re right that flat bottom skiffs are quite rarely seen in my country, although I’m not quite sure why this is so. Sure, the archipelago can be really rocky, especially in the Gulf of Bothnia, because of what the last ice age did I know, because that’s where I spent my childhood… But why is a flat bottom boat not good in rocky waters? Is it because running on an under water rock might leave you stuck right upon the rock or rip up the whole bottom, while a v-entry will push the bow away from the rock? Still, my fellow countryman Hannu, at the Hannus Boatyard site, is speaking warmly about flat bottom boats. Regarding my question, he actually also has some displacement hull design theory embedded in some of his building instructions.

I could actually also join a Finnish wooden boat forum, and ask around. Tbh, I’m not sure the average boat owner at the dock has that much knowledge about hull design. Back in the days it might have been different…

Thank you also for the suggested reading, I will look into that! To clarify what kind of information I’m looking for: how do I design the shape of the hull, so that the boat will float the way I want it to, without the fore or aft sinking too deep, for example? And what makes a hull shape economical and/or stable, for certain speeds?

 

Calculation, trial and error, or by following a proven design. Sometimes a combination of all three.

It depends, usually design but sometimes chance, but don't count on it.

I realize these answers are odd but so are the questions you ask.
"How long is a piece of string?" -PAR
It depends so much on what you want the design to do.
The Statement of Requirements ( SoR ).

 

Thank you for your reply! These were just examples of things I’m interested in learning about. I understand that the answer to most questions will start with ”it depends”, so I’m maybe not so much looking for direct answers, but rather directions to where I can find material to study, to learn and understand better.

“Following a proven design” is very good advice, and for any boat I decide to build, I will probably use that. But for making slight modifications to an existing design, some theoretical knowledge would probably be a good thing

 

It's not so much the rocks, but what a rocky coast means. Flat bottomed boats work well in sheltered waters with little energy in the seaway. In more energetic seaways they tend to pound while running and have jerky motions while stopped. In this case, the sandy, marshy islets and bays of the North American east coast are thin water, low energy environments where flaties work well. However, a rocky coast with few sand beaches (the the NA west coast or the Gulf of Bothnia) are that way because they have high energy seaways that do not allow sand islets or marshes to form. Here a different style of hull is needed, much like the traditional nordic lapstrake boats with pronounced deadrise. The only real exception to this is the dory style hull, that has a flat bottom, but with pronounced rocker and flare.

 

Thank you for clarifying, that all makes sense. Still I think the smaller one could be a flat bottom, since a 10-12 ft skiff isn’t anything you’d take out in bad weather in the first place. Since I’m more into displacement boats, any boat I’d build will have some rocker in the bottom.

But I think the eventual bigger build should be able to handle some slightly rougher waters, although most of the archipelago where I’d use the boat is protected waters, and most often there is an ”inner” route one could choose, if the weather gets bad. So maybe I’ll take your advice.

Actually, what got me interested in boat building in the first place, was when I for some reason stumbled into an article with the plans for a small displacement power boat called The Dolphin, designed by naval architect William D. Jackson in 1946. This is a hard chined boat with a v-bottom. So maybe I could return to where it all started, although maybe with a slightly extended version. It’s not designed for rough waters, but I don’t think it’ll have any problems handling what I’d use the boat for.