# 16' Flats boat build



## omegadef (Jul 10, 2011)

This is my first post here, but I've been lurking for some time, just cut into the wood for mine and a few buddies summer project. We'll be moving pretty quickly with this one.

More to follow.


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## omegadef (Jul 10, 2011)

Boat specs:
Design length         :     15.880 [ft]
Length over all       :     14.880 [ft]
Design beam           :      4.576 [ft]
Beam over all         :      4.571 [ft]
Design draft          :      0.250 [ft]
Midship location      :      7.940 [ft]

Volume properties:
    Displaced volume                       :        10.381 [ft3]
    Displacement                           :         0.297 [tons]
    Total length of submerged body         :        12.302 [ft]
    Total beam of submerged body           :         4.251 [ft]
    Block coefficient                      :        0.7941
    Prismatic coefficient                  :        0.8154
    Vert. prismatic coefficient            :        0.8702
    Wetted surface area                    :        52.756 [ft2]
    Longitudinal center of buoyancy        :         7.054 [ft]
    Longitudinal center of buoyancy        :        -7.205 [%]
    Vertical center of buoyancy            :         0.134 [ft]
Midship properties:
    Midship section area                   :         1.035 [ft2]
    Midship coefficient                    :        0.9739
Waterplane properties:
    Length on waterline                    :        12.302 [ft]
    Beam on waterline                      :         4.251 [ft]
    Waterplane area                        :        47.718 [ft2]
    Waterplane coefficient                 :        0.9126
    Waterplane center of floatation        :         7.652 [ft]
    Entrance angle                         :        48.779 [degr.]
    Transverse moment of inertia           :        67.095 [ft4]
    Longitudinal moment of inertia         :        518.68 [ft4]
Initial stability:
    Transverse metacentric height          :         6.597 [ft]
    Longitudinal metacentric height        :        50.101 [ft]
Lateral plane:
    Lateral area                           :         2.721 [ft2]
    Longitudinal center of effort          :         7.553 [ft]
    Vertical center of effort              :         0.133 [ft]


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## omegadef (Jul 10, 2011)

I ran hydrostatics on the hull for the entire hull length.

The chart wont come out right, but I've related the weights to their respective drafts.

1" 166lbs
2" 370lbs
3" 590lbs
4" 822lbs
5" 1060lbs
6" 1306lbs


With two people on the boat, we shouldn't ever be more than 4" draft, empty boat will sit at about 3", as designed.


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## omegadef (Jul 10, 2011)

Rough renderings, on the first image, the white part is the part that will be under water at the designed 3" draft.


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## omegadef (Jul 10, 2011)

Bottom of the boat is done.


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## omegadef (Jul 10, 2011)

Things are shaping up.


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## Brett (Jul 16, 2008)

Welcome to the forum...I like how you've started out.
No wasted time, right to the good stuff!
I love the smell of sawdust in the morning
and epoxy in the afternoon.

Don't mind me, I just like to watch... [smiley=popcorn2.gif]


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## omegadef (Jul 10, 2011)

Commence scarfing action.









Laid out









What better to clamp with than speaker boxes?


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## omegadef (Jul 10, 2011)

> Welcome to the forum...I like how you've started out.
> No wasted time, right to the good stuff!
> I love the smell of sawdust in the morning
> and epoxy in the afternoon.
> ...


Thanks, I like it here.


One of the guys thats in on the boat project works at a place that has a surplus of vinylester resin, so we're actually using that.

Also, the speaker boxes, my first and foremost hobby is car audio.


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## WhiteDog70810 (May 6, 2008)

Baton Rouge?  Cool!  Are you from there?  I grew up over off Gardere Ln. I am glad to see all the Louisiana guys showing up on here.

I like your boat's lines and I look forward to watching you work through the build.

Nate


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## omegadef (Jul 10, 2011)

> Baton Rouge?  Cool!  Are you from there?  I grew up over off Gardere Ln.  I am glad to see all the Louisiana guys showing up on here.
> 
> I like your boat's lines and I look forward to watching you work through the build.
> 
> Nate


I'm from Mandeville, but I'm here going to LSU. 

I'm getting excited, tommorrow I'll make the transom and get to filleting.


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## omegadef (Jul 10, 2011)

Tommorow gets transom and filleting.


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## oysterbreath (Jan 13, 2009)

Looking real good so far!
So are you using the v-ester resin in your S&G joints too?


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## omegadef (Jul 10, 2011)

Thanks, I did all of that today by myself for the most part, my little brother helped me hold the side while I stitched them up. 


Thats the plan, I'm not foreseeing any problems from earlier tests.


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## CapnK (Jul 6, 2011)

Looking good. Did you do the design yourself?


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## omegadef (Jul 10, 2011)

> Looking good. Did you do the design yourself?


I did indeed.


I just spent 2 hours waiting to be helped at home depot. I was about to kill someone. Transom soon to be applied.


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## mhinkle90 (Feb 24, 2011)

cool build and nice fabric on the speaker box ;D

keep the pics coming!!!


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## omegadef (Jul 10, 2011)

Bad picture, but, transom is in, almost completely filleted from the inside, and back stringers/deck support system in.


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## firecat1981 (Nov 27, 2007)

did you fillet it with the sides warped by that center support in the picture? if so that may lead to some issues later on as it will want to retain that shape. The fillets will be much stronger then you would think.


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## omegadef (Jul 10, 2011)

The picture makes it look really bad, but in reality they are only about 1/4" out from where they should be, applying very little force to the nose brings them right back in line. 


I need to figure out how I want to do the livewells and whatnot... I guess I dont really NEED to, but thats what I'm worried about.


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## omegadef (Jul 10, 2011)

I'm having an issue with deciding upon transom thickness....

I'm currently at 3/4", but will definitely need to increase it.

I have two available methods, stacking 3/4" ply or a sandwich of 3/4" ply and 2x4 to have a final thickness of 4.5". is that too much?


Anyone have some input? I've actually never been on a boat less than 20ft that wasn't a bass boat, so I'm a little lost here....


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## firecat1981 (Nov 27, 2007)

4.5"  Are you hanging a 300hp e-tec off it, lol.

I over build my transom, It is 1 inch thick (1/2" meranti ply laminated together) and a extra 1/2" clamping board at the top. You need to shoot for about 1.5" if you are using a clamp on motor (anything 40hp and under), but only for the top 5-6 inches, for the rest the 3/4" ply, assuming it's good ply with few voids, should be good for up to that assuming your motor well is designed right.


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## omegadef (Jul 10, 2011)

I just did a bunch of rough statics work on the transom piece.
I chose a random acceleration of 0-30mph in 7 seconds
With how I plan to brace the transom to the stringers, each stringer will have 337 lbs of compression in them, with the diagonal braces seeing 238 lbs in tension. 

Each stringer is good for 25200 lbs of compression, so I think we'll be alright at 1.5" thick and the support system I have planned


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## Andrewp (Jul 23, 2010)

re: transom design ....

What FC said about measurements .... I was concerned about compression of the ply, so I went with a solid oak plank where the motor clamps down onto the transom (inside and outside). I seem to recall others (maybe it was FC) who used a plastic laminate cutting board as the brace. Plenty of options, just watch the overall width. When I braced mine, I over-did it and the motor would not fit over the brace! Had to shave off some of the oak to allow the motor to slide in place .....


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## omegadef (Jul 10, 2011)

Heres a rendering of my transom design.


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## omegadef (Jul 10, 2011)

Also, here's the chine line import file I used for freeship. 

There was minor tweaking done after it imported.


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## ksm330 (May 12, 2011)

All looks good, but keep in mind, you might get more strength and eliminate weak spots on your transom knees by just cutting a taper from the top of the knee to the stringer runner in one piece.  This way you can laminate the piece as a whole.  With youre criient design, this will make lamination difficult, if not impossible.  Also, you are creating more work and possibly over building.  Think of it this way, with 2 pieces of lumber to create your "knee" brace, you are infact open for hard spots along the hull skin anywhere those points touch.  believe it or not, even with a small outboard, stress on the hull skin, specifically where the planing surfaces are, is quite strong.  To eliminate this, you need to get rid of hard spots and points of concentrated pressure when torque is applied. 

The fact that there are 2 sistered pieces of lumber on either side of the strigner is going to create some very specific points of pressure to absorb the bulk of the stress.  If you built it as one piece, say using 2 pieces of ply laminated together (or even one pice of 1/2" or 3/4") and laminated on each side with structural glass, no you improve strength, reduce weight and if bedded properly, you eliminate the hard spots.

Please take this for what it's worth, just an opinion.  No criticism here.

All in all I like what I see, just maybe re-think your transom knees.  Just my opinion.  Very cool this is all yours by the way...


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## firecat1981 (Nov 27, 2007)

You did remember to angle the transom back 14 degrees right? Cause the picture looks like it it set at a 90 degree angle to the hull bottom.
Also you are over thinking this and over building it, all you are doing is adding alot of weight and it won't add much more stregnth. Build a proper motorwell, it will do much more for the design and function as it can house much more. Look through Bateau.com and see how other did theres, in most cases the stringers and motor well are build out of 1/2" sometimes less.


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## ksm330 (May 12, 2011)

Nice point, dont forget to rake the transom if you are going to hang an outboard on it.


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## omegadef (Jul 10, 2011)

I'm not sure I follow what your suggesting fully...can you elaborate?


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## omegadef (Jul 10, 2011)

Transom is set at 90 degrees....

I planned to get a jack plate, I was under the assumption that it would do the angling for me....


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## ksm330 (May 12, 2011)

> I'm not sure I follow what your suggesting fully...can you elaborate?


I think we are both suggesting the same thing basically.  Using hard lumber for the stringers is fine (typically in larger boats) but you might have a better fit with cutting your stringers out of a pice of ply, slicing together as needed for length.  you will get plenty rigidity and eliminate points of contact that create hard spots.  What you have looks plenty strong, but may be over built as well as create weak spots on the hull.  look at this...

http://forums.bateau2.com/viewtopic.php?f=12&t=24726&start=10

about half way down the page you will see a pic of a stringer on frames waiting for planking.  exactly what we are proposing.  Laminate those ply stringers with some biax and they will be almost bullet proof.  Glue them to the hull on a bed of thickened epoxy to eliminate hard spots and you are good to go.  

as for the transom rake, your 90 degree angle should have some negative angle in it, even if you are using a jack plate i would recommend it.  you can add transom rake by using a wedge, but since your in the infancy stages of the build, why not just build it in?  your transom should be at an angle greater than 90 to your planing surface, say at 98  -  104 degress, at your preference based on wetted surface and desired trim. You can even go more on the angle if you want, remember, most outboards have several adjusting holes to set the angle of attack at the desired trim, if your transom is 90, your prop will be pushing you bow up too great even at the lowest setting. Fixing now is easy, all you would need to do is trim the bottom edge of the side panels (on the stern) to create the rake, then your sheer line wont change. Now is the time to do it BEFORE you glue and skin it.


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## Brett (Jul 16, 2008)

Transom rake can be built to any angle you desire.
However, if mounting an outboard, the recommended angle is from 13 to 15 degrees aft from vertical.
This angle allows best use of the tilt bracket or power tilt of todays outboards.
In order to find the best transom angle for a small outboard,
set the trim pin at the middle adjustment and measure the angle
from the anti-ventilation plate to the mounting surface.
This angle will allow the most adjustment of running trim.
It allows tucking in for lift/hole shots and trimming out for speed.


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## firecat1981 (Nov 27, 2007)

> Transom is set at 90 degrees....
> 
> I planned to get a jack plate, I was under the assumption that it would do the angling for me....


Jack Plates are designed to lift straight up in line with the transom, so if your transom is set at 90 degrees, then so will your JP. You need to angle the transom back for your outboard to run correctly. When I called Yamaha and Merc before my first build they both told me there motors are designed for a transom angle between 14 and 15 degrees so I built it at 14.5.
I'd like to say it is your boat and you can build it as you wish, but this is something that really needs to be fixed now before you continue.

I'm not trying to be a jerk, but where did do the research on your design? Did you read through all the tutorials on bateau and other sites? Trust me when I say planning up front will save you from a disaster on the back end!


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## omegadef (Jul 10, 2011)

I fully agree that this needs to be addressed, I have to redo the transom anyway, I just wanted to make sure I was doing what needs to be done. 


I did tons of research but it never occurred to me that the transom would be set at an angle....


Thanks for the help guys.


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## SilentHunter (Jun 14, 2010)

diggin the build so far. cant wait for it to be done!


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## omegadef (Jul 10, 2011)

I never explained the transom issue fully, the reason it had to be redone anyway was because I had done so many prototype designs prior to settling on this one that I had gotten them confused when it came to the transom shape.

Remember how the front bowed out? thats because the transom/brace sides were supposed to be at an angle and I thought they were square like in some of the other designs I had cooked up.

Needless to say, they will be taken out and redone. Probably wont have any more work on this until after next week though, its finals week for my summer class.


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