New to Design, will this work?

Ok, I am brand new to this (so take it easy). I have spent 3 (sarcasim on) whole days (sarcasim off) reading about boats. I do this partly because I want a boat, and partly because the thought of building my own brings me some level of satisfaction. I plan to research this topic for a while before I acctually do anything.....

I should probably tell you what my prersonal requirements are. That may help you to judge what I 'need'.

I'm no idiot, but I don't have a lot of practical boating expirence. I did manage to sail a 15' (dingy style?) sailboat around a harbor in fairly high winds w/o any instruction or help. It was that day I learnd about letting the ropes get tangled, but other than that incedent, it went well.....

I'm a 1/2 decent with wood and have built my own furniture.

I want a boat mostly for fishing, that will hold 3 adults.

Some of the places I go are electric motor only. If I were to use an outboard I would expect to accomidate no more than 10-15hp.

The places I go can be pretty shallow (1' or less in some places).

I will use standard boat ramps and will have a boat trailer.

Some of the places I go will be slow flowing rivers (Potomac near the dams). I dont expect to see waves except those from other boats.

I expect to pay less than $300 to make the boat (not including motor). Though I hear resin can be pretty expensive (though I realize that $400 is a real possiblity)



Ok now on to my design......

My design is made of entirely straight edges. This is done to keep complexity to an absolute minimum. Is this practical?

The bow on my design is the same hight as the rest of the boat. Most designs I see have the bow higher relitive to the rest of the boat when out of the water.

Eventially a 4-6hp electric motor will be used.

I expect to use 1/2 ply on the bottom, with almost everything else being 1/4"

I was thinking about using a 2-3" high by 10-12' long double keel just inside the chines (though my drawing show a single keel). The thought being that this would help decrese roll in the event somone leaned over the boat.

The Transom will be 1 1/2" though I relize I may have to beef it up if I get an outboard motor.

I went long and thin mostly because its practical and gives me the most boat/ least material.

I'm not sure how much resin/fiber glass I need. From what I have read some people only use it to just above the water line......Thoughts?

Here are links to pics of what I have put together in CAD......

Kinda interested in the replies....

Thanks everyone..

CB

Top front 3/4 view
http://img503.imageshack.us/img503/6714/boat2frontperspectiveow6.jpg

Top rear 3/4 view
http://img208.imageshack.us/img208/7381/boat2rearperspectivegk2.jpg

Bottom front 3/4 view
http://img470.imageshack.us/img470/3632/boat2bottomfrontperspectiveuq0.jpg

Bottom rear 3/4 view
http://img208.imageshack.us/img208/9890/boat2bottomrearperspectivefi3.jpg

Wireframe side view w/ mesurements
http://img503.imageshack.us/img503/468/boat2sidedimentionsdu8.jpg

Top w/ measurements
http://img178.imageshack.us/img178/1874/boat2topdimentionshe4.jpg

 

The numbers look good but you will need a bit of a cut out for the motor, short shafters need a 15 inch transom, with a 13-15 degree rake (measurements are made vertically). Curving the bottom at the bows will smooth the transition from displacement to planning speed and is just as easy or easier to build as you can curve your chine log rather than cutting it and having a joint(weakness) to deal with. For a 15' boat I would go with 3/8 for the sides rather than 1/4 but all the furniture except for the deck could be 1/4. If you are going to run an outboard, you will need to position your rear seat further forward. Your back should be no less than 18" from the top of the transom. Your comfortable fishing seat will also be in the way as you will have to sit offset to properly control the motor, so make it something you can move out of the way when you need to travel. Make your seat tanks as sealed flotation and you should be good to go. I would tape the chines and all joints if you aren't in a very rocky area, otherwise 'glassing to the waterline should be fine, so long as you really seal all exposed plywood edges and protect the wood with plenty of paint (the lighter color the better).

Here's one of mine:


Sorry for the image quality, it was a scanned in Kodak instant picture

Steve

 

Steve, thanks for the tips....

I thought about the back seat being to close, you definitly confirmed it for me, though I didnt think about seating position being slightly offset.

3/8" on the sides also sounds like a good idea, I would think mostly because of the length and the potential for tourque with three adults in the boat. Thicker sides would help with that.

I have noticed that most designs that I have seen have a buldge on the bottom right under the bow. Can you or anyone be a little more specific. Is this even what your refering too?
If we use the bottom of my current design which is all on one plane as a start how far below that plane would the area below the bow drop? From for to aft how far would it go?
Check the attachment, I tried to do a simple drawing....is this what your talking about?

What about a double keel vs a single keel? Again the idea is two short long keels may provide two advantages beyond the obvious. Two place outside near the chines might help protect the bottom, provide more surface area for a relitive minimum amount of drag and might help provent quick rollovers in the even somone leans over the sides. Ok that was three......
I guess my questions are....what are the rolling tendincies on a flat bottom boat?
I havent seen any designs like this so I find it hard to belive that I thought of somthing new.....

Thanks again...

 

gotta add this to appease the software as it doesn't recognize my additions inside of the quote...sheesh!

Oh, and a good profile of the bottom is for the curve to run 1/4 - 1/3 of the boat length back from the front, curving smoothly into the bottom...something like this:



Steve

 

"Two or even three will help stiffen the bottom and keep it from oil canning, but you don't want a lot of surface area...it equals more drag, requiring more power. 2x2" strips or even 1x2" are plenty. Beam and depth, along with flare to the sides prevents turtling. A wider beam gives greater initial stability, but with straight or slight flare, ultimate stability is reached soon after heeling starts (depending on the depth of the sides). With increased flare (like a dory), stability increases as the boat heels right up to the time the gunnel goes under (you are pushing a wide vee into the water as opposed to a narrow or acute one). So a beamy (waterline) with lots of flare should be the ultimate...but not quite. You trade off for additional drag, more weight requiring more power to push it, a sturdier trailer to carry it, etc.
You must also watch out for over powering the boat and trying to take sharp curves, as a flat bottomed hard chined boat will trip on the chine when pushed too hard in turns...nasty business."

I got most of this....but the phrase "oil can"?

Also.... Turtling?...Roll over?


You said.....You must also watch out for over powering the boat and trying to take sharp curves, as a flat bottomed hard chined boat will trip on the chine when pushed too hard in turns...nasty business."

The soulution to this would be to angle the gunnels more? Is there a perfered way to calculate the angle of the gunnel?

I chose 4' because it's 1/2 an 8' sheet of ply, thus cutting it in half gives me 2 fully usable pieces. But I think we could figure out other uses if I cut it longer.

 

Oil canning... like pushing in the bottom of an old oil can...it pops in and out again. Happens with flat bottom craft a lot of the time.

turtling, yep rolling over, turning turtle.

Has nothing to do with the gunnel (gun wale...outer or inner strip along the sheer or upper edge of the side panel). It has to do with the sharp corner where the bottom meets the side...the Chine. Tripping is where the edge grabs the water and flips over. On Vee bottomed boats and on round bilged (or chined) boats this is much less of a problem. Vee bottoms tend to lean into the turns and round bilged flat bottoms will tend to slide rather than dig in. 4 ft is fine...wide enough for stability and narrow enough to drive reasonably efficiently. You could angle out (Flare) the sides more to give additional stability when leaning over the side to bring in that 12 pounder. Increasing that beam at the gunnels to 4.25-4.5 ft gives you quite a bit more righting arm when leaning over the edge.

Steve

 

Thanks for all your help on this.

I think im going to make the beam 4' and the gunnel 8" wider.

As far as the keel goes, I considered making a double keel on the outsides of the bottom. Seems like this would just promote the tendincy to roll over in a turn you were talking about. I might do 2 keels (1"x 2"x 10')but Ill place them more inward. I dont think I have a lot to worry about flipping as the chance this boat will see an outbord is slim. Even if it does a 10hp is probably the most I will ever use.

I have had some other advice to use pre-exsiting designs from a book called "Instant boats". If I was going to make a boat I was sure would see an outboard w/ more than 25hp I would proly follow that advice. Part of this endevor is to build the whole thing myself (with some tips from those who know).

Thanks again for all your help.....If I ever get the thing done...Ill let you know how it goes.

 

Good Luck

Steve