My first boat

I've been doing a lot of planning lately and I've decided to build my first boat. I'm and experienced wood worker but I've never designed a boat before so I would love some feed back on my initial design. I've included and image and a zip of the google sketch up 3d modle I built this weekend.

I settled on a flat bottom design for my first boat because I thought it would be the easiest. I was thinking of using 1/2" marine plywood for the hull and frame with a 1" x 4" gunwale.

Couple of questions.

1. If I fiberglass the bottom will 1/2" sufficient to handle a small 2.5hp Honda outboard.

2. My design is pretty tiny and I'm about 250lbs, I think it should hold me but I don't know much about displacement and hull depth or angles that should be used. Has any one build a 10' dingy with similar proportions?

3. will 1/4" marine ply be sufficient for the sides if I intend to fiber glass the entire hull?

Most of my dimensions are in the attached images but basically the the boat will be 10' from bow to stern with an 8' flat bottom 4' at the bottom and 5' across at the gunwale's widest. 24" stern and 28" bow. Any suggestions on the design would be extremely appreciated since I have 0 experience at this.



Best Regards,
Mario

 

You would do better to purchase plan and build your first dinghy off that. Then you will gain a practical understanding of boat design. There lots of god plans available.

 

I appreciate the advice, but it's not really my style. How hard could it really be to design such a small boat? I'm willing to make some scale model tests if you all think I should before investing the time in the full build, but I really have my heart set doing everything from scratch. hoping someone out there has built something of similar length and width that could relate and share some advice.

Mario

 

How hard it could be to design such a small boat depends on you. You ask if 1/2" fiberglass is sufficient for the bottom. That shows a basic misunderstanding of the materials you want to use. If that is typical, it might be very hard indeed.

If you are serious of about starting for scratch, I suggest that you actually start from scratch and learn a bit about the subject. This forum repeatedly hands out this small piece of advice to an uncounted number of people just like yourself.

The simple answer to you question about the boat bottom is that 1/2" is an adequate thickness of fiberglass. Of course that answer is about as useful as the question which is, not much.

If this reply appears disrespectful, please consider that your request may be disrespectful of all the time and effort that knowledgeable people here have invested to be able to do what you think of as trivial.

 

You can build the whole boat with 1/4" plywood in that size with only 2.5HP. If you are fiberglassing it, 5mm would be plenty. Frames spaced about 2 feet or so and maybe a couple of bottom battens.

 

Cool,

Thanks Gonzo. I really appreciate the quick insight.

No-disrespect tom28571. I most likely should have searched the forum a little more before making my first post. I've been building traditional bows for ten years and could write a 500 page book about all of their intricacies. But the truth is it's just a bent stick and every time someone asks what type of wood is the best or which tiller is superior I'm as helpful as I can be, but to each their own.

I'm not expecting to max out the full potential of my materials on a 10 ft row boat on my first shot I just wanted to know if I was way off base or on the right track. And no I will not be buying plans. If it floats great if not then I'll have a nice little tutorial on what not to do for your forum. Also I am still in the information gathering stage and this is by far not my last design before I build what I want.

Mario

 

Myself. I wouldnt kep thd flat part of the bottom that length.. i would suggest something more like 6 1/2ft. . It wont mater much with only 2.5 hp. Carolina Skiffs Had That Problem In The Beginning. Very Wet Ride. AND DONT USE STAINLESS SCREWS. I prefer Stainless Ring Shank For Plywood If Your Not Gonna Glass . When Stainless Screws Tighten Up It twist The Screws head from the screw shank. it changes the temper of the screw and under pounding conditions it pops the head off of the screw. and if this is your first boat..... dont glass it. dont waste the money. if your carpentry skills isnt good enough for it to float without glassin it. then you need to back up and regroup. im not doubting anyones ability. just tryin to save you some time and money. another major factor is gonna be your choice of materials. you are doin the right thing by starting small... . just remember that lifes most valuable lessons learned are learned from failure.. not success. but its a lot cheaper to ask somebody

 

Your design is much deeper than most dinghies of similar size. It will be very difficult to row unless you put the seat very high which will adversely affect stability.

Spend some time looking at similar boats, either in person or online.

 

Suppose I asked a similar question on a bow making site. I mean how hard can it be to make a bow. As you say, surely it's only a stick and a piece of string?

It doesn't have to keep you alive when on the water nor allow you to move efficiently. I could write a 500 page book on the intricacies of designing a 10ft dinghy

Or you could look at my 10ft Duo dinghy design, built with two sheets of 4mm ply. Yet it can be sailed and will take a 2.5hp outboard

Richard Woods of Woods Designs

www.sailingcatamarans.com

 

welcome to the forum.

Everyone here is trying to be helpful. There are reasons most dingys are not designed that way. you will not be very happy with its behavior on the water. It is fun to design your own boat, but some designs would be a waste of time and money because they would be unusable. I was on a walk on the Puget sound yesterday near Seattle, there was actually very similar designed dingy that someone spent a lot of money in materials (all way too heavy), and after lots of abuse had abandon it on a public beach. No no one wanted it, there it sat on the sand, more like a child's ply box than a boat.

those high sides will make it difficult to get in and out of, and see over. If you sit up high as suggested above, it will be tippy and uncomfortable. the flat bottom will be difficult to control in uneven seas, it will be very draggy (take more effort to go the same speed), and not particularly attrative or graceful looking.

there are lots of free plans for good popular dingys on the internet, study them. also, see if you can go out and try a few different designs out on the water, it will help you understand better why they are designed that way.

You no doubt have excellent wood working skills, it would be a real shame to waste that talent on a design that performs very poorly on the water. You would end up with a very nice looking (and expensive) planter for your yard.

You might study some designs of similar sized boats, and than from those develop your own design to build. That way your starting point is at least a well behaved boat.

here are some sites with free plans to study:

http://svensons.com/boat/

http://koti.kapsi.fi/hvartial/skiff12p/skif12p.htm

http://boatplans-online.com/catalog.php?category=smallsail

http://www.polysail.com/oldboats.htm

 

Welcome to the Forum

I can only echo a lot of previous comments. Mainly have a good look at existing (and older) designs. There are lots of reasons why different shapes have evolved and an understanding of that is useful.

6mm 5 core marine ply is fine on the bottom with battens at least 15+mm (5/8") thick and say 45-50mm (1 3/4 - 2") wide. 5mm is fine on the sides, but make sure the transom is at least 25mm (1") at least for the top 150-200mm (6-8") to spread the load of the motor. Add packers too locally but they don't need to be permanent to the boat. You don't need to glass at all, but an external epoxy coat would help long term durability.

Interesting small tender type boats might include those linked to in Richards Woods' website on the Duo page, as well as his nice Duo. Also the older Fairey Duckling (for Uffa's take on it!), Mirror dinghy, Nestaway boats, maybe the Fyne boats prams etc etc.

All these will easily handle a 2.5Hp but maybe give other options. As you are already a woodworker you should not have any problems with construction. The key thing is setting up reliable Datums and ensuring any frames are true.
Personally I am quite happy to use stainless screws in a timber build (A4 or A2) and have had no real problems. However with respect to boatbuilder41, there are issues with quality control and manufacture of some stainless fasteners, involving poor rolling etc. A colleague and myself have run into this and now test or get certification or known manufacturer status, prior to selecting them.

Good luck. Building with curves isn't so hard.

 

The problem you're finding here is most of us can see many things that will cause you issues, down the road, during the build and underway. Things not easily seen by a budding or novice designer.

Simply put, your shape isn't going to be good for much. It'll turn poorly, row like crap and create drag. You have frames on what appears to be 16" centers in a boat that doesn't need a single one, or if you insist only needs one or two. This is just excess weight, which costs money to purchase, you have to cut it out, install it, then burden the engine with it's mass underway. The topsides seem to have a awful lot of freeboard, which is more weight and windage. You look to be employing a 2x4 keel, which is wholly unnecessary and there are countless other "items' we could nit pick you about, which really doesn't serve much.

Properly designed, a boat this size needs only a couple of sheets of plywood, no frames, no keel and will be light enough, that it might plane off, if it was shaped properly and lightly loaded. These considerations are more then you apparently are aware of (yet), but consider this. The hull speed on a boat like that would be in the 4 MPH range. Burdened down as you've envisioned her, you might manage 3 MPH if the wind was at your back. On the other hand, how's 8 to 10 MPH sound (same engine), with far fewer parts to purchase, cut and install? This is the difference between "how hard could it be" and buying a set of plans where the real work is performed and you can get it to do much more, with less materials. Simply put you can build this with 2 - 3 sheets of plywood, 50' - 60' of 1x2's (ripped from a single 2x12), a single roll of 6 ounce 'glass tape and a couple of gallons of epoxy. It would have a couple of seat boxes (storage under), rub rail, chine logs and it would weigh in the neighborhood of 60 to 80 pounds, so the small outboard would have a chance of pushing you along faster, then you can walk down a street. It's your call . . .

 

Go to library and borrow "Nature of Boats". Its written in an easy to read format and does a great job at explaining the fundamentals.

 

Mario; You are being politely hammered here. Please do not take offense. The knowledgeable people here want to help you avoid mistakes and/or disappointment. Designing a boat even a little one, like your drawing, is not as elementary as designing a box. Boats appear deceivingly simple, they appear to be as simple as a box with a point on one or both ends. Actually some very serviceable boats do not even have pointy ends.

Boat design is not some secretive art that advertisers pretend it to be. It is an art and a science too. There is nothing secretive about it and there are many easily available books that can guide you on the way to proven design principles.

Almost all of us will encourage you to build a boat. We admire and respect craftsmen who build nice things, including bows. We are not likely to encourage you to build an ill conceived waterborne piglet.

Several of the people who have posted comments above are some smart and generous individuals who know their stuff. This forum is loaded with very knowledgeable people from all over the world. Accept their critiques.

 

Just to add to the verbal onslaught, I have been around boats all my life, have designed a few and built some. I worked as an engineer with the Coast Guard working with boat builders to meet Federal safety regulations for boats (Yes, there are laws you have to follow!) But when I retired and wanted t build myself a rowboat to go fishing I simply bought a design. Why do all that work when there are hundreds out there where all the work is already done and it is a tried and tested design? I would not try to design a bow (I used to do archery in my younger days) without a lot of study about design and various woods and glues and so on (and I am probably showing my ignorance). You can still design your own, but one of the best ways to learn about boat design is studying existing designs, and asking why did they design i that way?

Everything in a boat, even a 10 foot boat) is a trade off. How much load or people do you want to carry? How much do you want it to weigh? How fast do you want to go. How stable should it be. How much power should it have or should it be manually propelled? My 12 foot rowboat goes almost as fast under oars as it does with a 2 hp engine, which happens to be it's maximum horsepower rating. Yes there are formulas (it's the law) for determining max hp for a boat under 20 feet in length. What do you want to build it out of. This alone will determine many things like load carrying, strength, hp, and the list goes on.

So take the criticisms to heart and do a little studying of designs. There are lots of books available on building little boats and web sites too.