A Newbie's Greeting and A Couple Questions

[ArmchairDeity]

Hello all, I am new to the forums and actually rather excited to have found you all. I have a lifelong fascination with boats and water, am an avid fisherman and have had a million ideas for different boats over the years.

I guess my main question is this: do you guys answer one-off hobbyist sorts of questions, or is this mainly a forum for pros in the watercraft design world? I have a particular project in mind but I need some information before I just go off to do it, but I have no local source for answers... am I in the right place?

Thanks to all in advance, even for a "hey, you're not in the right place" sort of answer.

Jared

[Guest625101138]

Ask away and understand you will likely get many opinions. You have to weigh what makes the most sense by sorting the science based opinions/answers and simple preferences.

Rick W

[masalai]

OK, I'll bite? law your ideas and vision out and you will surely get many and varied views and opinions, at some stage someone may suggest you leave this thread (having served its initial purpose), and re-establish again elsewhere in the forum where the readership is more in tune with your needs and aspirations.

Good luck, and keep an open mind...

[Landlubber]

Well there is no shortage of Armchair Admirals, but we have never seen a higher rankiong "official" actually ask anything before.....welcome to the site, hope we can help somehow. Your humble servant.

[ArmchairDeity]

You guys are one of the more friendly forums I've been to. That rocks. Let me forewarn you, however, I am going to do my best to use the "right words" for all the nautical stuff (displacement, draught, gunwales (pron. gunnels aye!) etc.) and I'll probably get a lot of it wrong. That's never stopped me before tho... heh... and I'm totally open to correction.

OK, let me start by saying I've really sunk my chops into this project... I'm sort of determined to make it work come hell or high water just because, umm, well... yeah. Just because. Because I think it's a cool project I guess, and because it should be fairly cheap and a great way to be inventive and creative.

So I used to have a pet alligator (who now lives in a crocodilian refuge) and she lived in a 300 gallon stock tank. As I was looking at the stock tank after she left us, I realized: it's the right size, shape, and material for a boat! I mean the thing is made of high-density polyvynylclorithaneide or something like that and it's built to _hold_ water, so it should hold water out, right? SO, there are 2 issues.

First of all, it's 26" tall, and 6'4"x3'1" on the "deck" and 6'9"x3'6.5" at the gunwales. My concern is that it wouldn't have enough of a draught to be stable and yet is entirely the wrong shape to be stable with no draught at all. Based on my calculations, it will support about 1 ton (300 gallons or 2500 lbs gross displacement), but it weighs 100 lbs or less. Now, I'm sure that there's some formula based on dimensions and weight to calculate stability, but my guess is that this thing is gonna tip itself right over unless I put about 600 lbs of rocks in the bottom. Otherwise it's going to be like trying to float an empty shampoo bottle standing upright.

So I'm looking at outriggers. I found a set of 8' pontoons with bullet tips that would run about $168USD/side. I plan on welding up my own struts with matieral I already have... I was thinking about using PVC, but as brittle as the stuff is I'm just not sure. What I'd really like is just a cylinder made from high-density polyurethane... although something like this would work too:



Turn them sideways and mount them tight to the sides of the boat... it just might work. Anyway, I am wondering if there are any stability suggestions. I was also thinking it might be better to mount them on struts away from the boat (kind of a trimaran with a _really_ fat, umm, maran, in the middle) and that these struts might even be better off being adjustable, so they could be raised and lowered based on the load of the boat.

The other issue I have is propulsion. I want to build the most efficient propulsion system I can. I've had suggestions from a $99 electric trolling motor to gas engines, etc., but what I'd really like to do is put a DC electric pump in the boat with an inlet at the front and a reduced-diameter nozzle at the back... yeah, like a jet-based system. I'm assuming that I have to have enough capacity to remove the equivalent displacement of the boat per distance travelled. That is, if the boat displaces 3 cu feet of water and I want it to move 1 inch in 1 second I basically have to be able to run 3 cu feet of water/sec thru the system, yes?

I hope not, but I am afraid that by now you probably think I'm a babbling idiot... but I really appreciate any input you've got and I look forward to hearing back from folks. Thanks in advance for both your interest and your patience!

PS - Attached is a very rough 3D CAD approximation of the tub I did using Google's SketchUp software. it's not exact, but it's close to the tub I have.

[masalai]

Your human powered amphibian seems unique

[ArmchairDeity]

While I thank you for the compliment, that's not my amphibian... I just want the floats off it for my own project.

[Guest625101138]

What are your expectations of the motorised stock tank?

Are you intending to see if you can make something that will float and move through the water or do you intend to travel somewhere on a specific water way? Things to consider:

1. What is the purpose of the boat -

2. How much do you want to carry -

3. What speed do you envisage -

4. How will you transport boat to water -

5. What is your budget -

Your idea of efficient propulsion is incongruous with a motorised stock tank. An efficient boat starts with an efficient hull design and your stock tank does not meet that criteria.

Rick W