simple boat design 8-10ft

[hobbybuilder]

Here attached is the frame construction of the boat.
Simple foam with carbon fiber composite as structure frames.
Let me hear from your opinions:

[Toot]

I like the idea and the size.

But am I interpreting your drawing correctly, that you intend to use CF tubes? Don't bother.

All you experts, correct me if I'm wrong here... but as a boat gets smaller, the design becomes "easier" because the thickness necessary for puncture resistance becomes a much larger portion of the necessary structural strength.

In other words, FRP over foam, alone, with just a couple bulkheads, probably ought to get you all the strength you need in a boat of that size.

Unless you're talking about a 50mph+ hydro or something. If you're talking about needing roll-over protection and whatnot, then that changes things dramatically....

[messabout]

If your aim is to build a novel boat then go for it. Creativity is a blessed attribute so I like your free thinking approach.

If you want a boat to build and use in the conventional manner then build a pram or three panel skiff of plywood and epoxy. Lots more practical, more useful, cheaper, faster build, better resale value, and more.

[marshmat]

What is the boat's intended use? This more than anything will determine how suitable your ideas are.

[hobbybuilder]

it will be use for experimentations on different type of engines and speed testing. That cage frame will be needed in case there's serious accidents.

[SailDesign]

hobbybuilder,
The cage frame may be the CAUSE of serious accidents, especially at speed. If the hull is only attached to the frame at the nodes, there will be numerous hard spots with little structure to spread the impact loads into the skins.
What structural design experience do you have? I ask only because your approach is very car-influenced, but a boat's structure needs very different treatment.
That said - I like the fact that people are thinking outside the box - just as long as they have looked inside it first, and have realised why things are usually done the way they are.
Steve

[Toot]

It's awfully tiny. What range of hp are you thinking it would have?

I'm not a fan of CF tubes. They are difficult to bond and don't give you nearly the strength of steel. CF tubes are rarely used in structural applications except as individual pieces (fishing poles, club shafts and such). I've seen some bike frames built that way, but am skeptical that such tubes live up to the strength potential of the fabric. Generally, CF that isn't dead-stright gives up a lot of its strength such that you aren't much better off than with fiberglass.

Then there's the issue of escape. You can swim out from under a boat- and that task is made easier if there aren't a lot of tubes and obstructions in your way.

I agree with the point about localized stresses- another reason for sandwich core construction or straight up FRP for a one-off boat such as this. Remember, the entire hull, not just 4 points, are taking the stress on a boat.

[hobbybuilder]

Im designing my own jet system as well. I dont know the size of the engine but what I have in mind is a motorcycle engine...500cc or so. It would be a fun experiment.

[Toot]

By developing a propulsion system and a boat simultaneously, I suspect you would not so much be killing two birds with one stone as you would be throwing two stones at one bird... and neither with very much accuracy.

Build a basic, no-frills boat out of fiberglass and foam. This type of construction is great for making changes and modifications as your needs dictate. Then try to get your propulsion system to work... and then optimize the boat around your propulsion system. But, truth be told, by the time you're done, the odds are you'll have an inferior boat with an inferior motor...

But you'll learn a lot, so it may not be money wasted.

[hobbybuilder]

...to be safe, i'm going to build a r/c version. Perhaps a 1/6 scale see if it actually works, then ill do a full frabrication of the boat.

[Toot]

I don't see how an r/c version is going to tell you much about the safety aspects. I mean, come on... a one foot model , versus an 8 foot boat (plus driver) that weighs 400lbs?

Models can tell you quite a bit if you account for scale effect and perform your tests appropriately, but an r/c scale model just isn't going to do much good. Right now, I'm designing an aircraft.. but I'm not going to build a model first... I don't have the sophisticated equipment necessary to learn anything significant from a scale model. Seriously, you'd better off spending the time that you would invest in the model and read some extra books instead. Besides, your real problem is going to be with the structure... and the "scaled" structure won't tell you diddly-squat about that- there is no such thing as "scaled-strength" epoxy. It will all boil down to your fabrication expertise and weird little unimaginable things that a truly experienced designer/builder will have seen before- or perhaps know enough not to even attempt.

Bear in mind, this is coming from someone who's never designed or built a boat, but I am sorry to say you seem in way over your head. Purchase a few books on boat building. Then a few books on design. And read them. Or for pete's sake, at least pick up a few engineering texts. Figure out why things are normally done the way they are before you try to reinvent the egg.

I can tell you don't have an appreciation for the differences between what you are undertaking and other things you have done in the past. That's what my sig line refers to- I know a lof of stuff that is transferable to boat building/design, but I'm continually amazed by things I *think* I know which are totally inapplicable to boat building for reasons I never imagined. I sense you are in the... *ahem* same boat as I... in that respect. Good luck.

[hobbybuilder]

lol yea.

[Joe6]

You need to go and look at the underside of a jet-ski or similar fast small craft. The performance of this hull will be a disappointment.

Joe

[messabout]

The good people at Yamaha, Kawasaki, Honda, Suzuki, Polaris, etc have far more resources for developing jet powered small craft than individuals do. In short; this has already been done by very smart people who have strong incentives for making theirs better than the competitors.

If you merely want to go fast, you can design/build an outrigger type hydro with surface piercing prop. Power it with a motorcycle engine of your choice. For example: A Suzuki GSXR 600 will make more power than you can use. There are plenty of others that are capable of producing 100+ HP as well.

Go to the pond where the RC nitro powerboaters are having at it. You will see that they have developed their boats to an astoundingly high level. The FE (fast electric) guys have done the same. As a matter of fact an FE holds the worlds model speed record.

[djwkd]

thing is,'fun experiments' have to be thought over carefuly before being carried out.someone who drove in a high powered boat once hit a six foot fish in his boat,this seriously injured him,and even with a one foot fish if you hit it at high speed you could get knocked out of the craft.