Help drawing and design Texas Scooter boat

[Aransas Flats Rat]

Hello all I am wanting to build a sole purpose boat for shallow protected waters average depth 1-2’. The picture below is how I want it as per shape, looks and design other than all the deck clutter.

Most of these type boats have a flat bottom with pocket tunnel for enabling the outboard to be raised by a jack plate to run in shallow water.

Main purpose of the build will be for gigging flounder here in Florida.

Length: 17’ to 17’6
Width/beam: 7’
Draft: 4-8” acceptable
Freeboard 6-10”
No sheer/sides flush deck
Speed 20-30 mph
3 adults capable
Not sure on HP was thinking 50 hp

Motor and rigging weight: 500-600#

The displacement on this design was estimated at 2900 lbs.

I’m not stuck on a tunnel if it will affect the performance I can and have access to a outboard with a jet drive.

I have built three boats S&G and have completed a complete gut and rebuild.

Would like to build out of

Marine ply/laminate
Epoxy/glass

I would appreciate your help with drawing and design. Thanks so much.

 

[Aransas Flats Rat]

Sorry for my hogged drawings.

 

[Aransas Flats Rat]

Top view

 

[Aransas Flats Rat]

A few questions on figuring loads and what size materials

I was thinking

Hull
Bottom: 3/8 marine ply, 1708 both sides
Sides: 3/8 marine ply 1708 both sides
Deck: 3/8 marine ply 12 oz both sides
Frame/stringers
Egg create design not sure on size/thickness

Assemble as a S&G

Thanks

 

[Yellowjacket]

You'll need to add stringers and cross beams to support the bottom and deck, using plywood in an egg crate pattern will stiffen things up, but you have to decide if you want access to the insides or not. The problem is WHEN (note I did not say IF) water gets inside it'll create a mess. Even if you have no leakage you'll get condensation inside so it's best to have hatches and access and ventilation holes so you can get inside and check things out. As for stringers you'll need them to be about 12 inches apart on center line as a minimum. The problem you have is that you've got a pretty wide beam and a very flat bottom and no v in the front. That's fine for calm water, but when you go over wakes and waves it'll pound like crazy so the boat needs to be strong. If you make an egg crate inside it'll be plenty strong so that's a good idea. The stringers could be a 1x2, but the center stringer that runs down the center where you're attaching the two pieces of plywood are joined is going to be a 1x3 or 1x4. You'll also want to back up the center stringer with a 1x4 on edge to give it more stiffness. The 3/8 ply on the deck is a bit thin, but if you use glass on both sides and have the egg crate pattern at least 2' apart you should be ok. The design of the motor board is something you need to be careful with. With a low flat boat the motor board has a big moment on it. If you don't do that properly and spread out the load you'll have a lot of stress where it meets the transom and have problems with it. What I've described is more of a framed design as opposed to stitch and glue. If you go with stitch and glue you're going to need thicker ply and a different approach. A thinner skin and framing is more efficient in this case because you need support to stand on the deck. Stitch and glue is more appropriate for boats that you don't want any framing inside and you make up with the framing strength by making the skins thicker.
Those are some things to think about as you go forward with your design.

 

[Aransas Flats Rat]

Thanks Yellowjacket, that makes perfect sense and well appreciated.

On the stringers I was planing on doing full height from bottom to top and cap them with a 2x3 batten, on my Explorer rebuild it worked well. I used a router to cut a center grove and epoxied them to the stringers

Then I notch cut the stringers and epoxied in 1x3 for the deck supports 16” on center.

Was thinking of using 1/2” for the stringers but I am unsure if that thickness is proper. I would like some guidance in that area.

My thoughts on the bottom and side panel butt joints was to tape seems with two layers of 17 oz. if that is not a good practice please advise.

 

[Aransas Flats Rat]

On the motor board/transom I was thinking of using a standard type since I am leaning towards a outboard with a jet drive. If I buy a tunnel in it, it will be a minimal one. I’ve seen guys run Jet Drives without on and pop up in 6-8”.

So that ties into my thoughts of the full height stringers they would run from stern to bow and if I’m thinking right would act as knees and making it one unit. Of course the motor board would be well above the deck and I would bring transom knees from stringers through the deck.

Does that make sense?

 

[Aransas Flats Rat]

Also I completely agree on the deck access, I’m thinking of adding floatation in the event of a hull breach.

I would also like to take advantage of the hull space for a couple deck hatches for life jacket and anchor storage.

 

[Aransas Flats Rat]

Is there any software that you can input your numbers and come up with a displacement number. Thanks

I think I’m asking this correct, wanting to know draft ect.

 

[Aransas Flats Rat]

Weights I posted earlier are estimates so I thought I would post actuals to the best I can.

3 persons 500#
50 hp outboard jet drive 190#
Two batteries 140#
Console/cooler 100#
Other rigging 150#
Fuel 160#

Total loaded: 1240 lbs
Without persons: 740 lbs

 

[Aransas Flats Rat]

This the type of stringers I was thinking. Please these are from a previous build so dimensions are not to this build.

 

[bajansailor]

Re coming up with displacements, the easiest way, based on your initial sketches above, might be to simply divide the hull into a couple of blocks - the aft section could be assumed to be a fairly uniform rectangular section, where the volume would be length x breadth x draft.
The bow section has a bit more shape so here you could instead use side profile area x average breadth for a good approximation, doing this for different drafts as required.
OK, the volume of displacement when calculated this way is not going to be 100% accurate, but it will probably be better than 90%, and that should be close enough for your initial design iteration.
I say iteration, because invariably you will then want to change something, so you then re-calculate with the new dimensions.
Remember to include an allowance in your weight estimate for a good haul of flounder as well

 

[Aransas Flats Rat]

Just not sure how to figure loads from pounding. I leaning forwards 3/8 or 1/2. Stringers will be glassed as well

 

[Aransas Flats Rat]

Thanks banjansailor, I have kicked this thing around for 5 years lol.

I threw them in on the 150 lbs misc.

Ok so the boat as is length/width I came up with
Approximately 3000 lbs.

I feel like that leaves a lot of room for a few oops. I’m pretty much happy with the layout I just need to put it together. That’s a lot easier said than done.

 

[Aransas Flats Rat]

Next thing I need to figure out is the bottom,
Is this design better

or should it be straight as a normal flat bottom.

Again pics are for reference only and dimensions do not reflect this build.

Can someone explain the difference?