Simple power catamaran?

Aaahhh...i see you really are one of those....the decminal places says....XXX..so it must be tue types.

Ok.

Thus just to reiterate (with direct quotation):

So, as "in the kind"....Hmmm..so either that means it is boat shaped or it is not. Well the OP again clearly stated these are "too inefficient".....thus one can concluded that the OP is either, looking at bricks that move through the water....which is why they are called bricks (vertical front/bows) or....surprise surprise, given a little bit of a pointy front, they are called....yup..boats. That's the funny thing about terminology, it all has meaning, not matter what you may decide to call it.

So, again exploring what the OP has said:

So those 2 designs that come close....please explain what is so obvious that these are cylinders with flat vertical front faces? This doesn't look a cylinder at all:

Nope...see above, or reread his first post.

You still have not explain what is obvious??..other than you clearly think a brick is called a boat. Does this mean you call a car, a house...because it also has four sides? :!:

 

Am I?

Hull shape discussion in this thread (that I've been party to at least) has been limited to a "boat shape" vs "aluminium cylinders".

Here is what the post of mine, that started you frothing at the mouth for no reason, was in response to (clearly quoted in my post):

I see no posts in this thread that suggest this does look like a cylinder.
I assume you're an intelligent person, so I can only imagine that you're pretending that you think these were the "aluminium cylinders" he was referring to when he questioned the difference between pontoon cylinders and "boat shapes", as he puts it.

See quote above.

I haven't said anything is "obvious".

I'll quote you again though:

 

Oh dear…seems we really are getting ones knickers in a twist over pointless semantics. But hey, each to their own and what floats their boat.

So an analogy has been given to try to explain what is required. But it is qualified by the very clear statement that certain cats use less power. Thus to any naval architect, or designer, this implies a particular direction from the outset. Thus one could, just could, throw in to the mix a literal interpretation, a cylinder.

But does that equate to the objective….less power, er nope. Even a child playing with foam blocks in the bath tub can see the difference a square block makes. Even a child would not call it a hull, just because it floats; its one and only SOR.

But, for the hard of reading it is clarified again:

So, the OP is trying to learn and understand…unlike others. Hence the clarification by myself an others.

And then also notes, this too:

Thus again, the OP clearly now understand what his objective is and what he wants. But for some reason you are ignore this.

Then we get YOU and YOU alone that wish to rabbit on about cylinders, as being the objective – despite the objective being very clearly stated several times and links given for examples - and understanding. Since you have made such a cause celebre about such a pointless position beyond what anyone actually wants, save for yourself. Why..no idea….however, please continue, as comprehension in an objective appear to be lacking somewhat.

Thus, you can call it whatever YOU like…but trying to convince people that a brick, should really be called a boat or at least a hull shape, just because you wish to debate decimals places, feel free. Since you’ve completely missed the point of ‘design’ and the SOR. So back to your own assumptions.

So again, your assumption/interpretationsare yours and yours alone of using a cylinder, since a cylinder is not designed for anything other than floating. Only those with an appreciation for things that float and move would understand this basic concept. Looking at decimal places does not lend itself to such analysis or critiquing.

Since the SOR, of sorts, has been given, again, here:

Doesn’t sound much like a cylinder to me..but hey….not everyone can imaging a brick with an outboard being less power than vessels already cited as examples.

So, you’re still advocating a cylinder as the solution then. Since anything else, with a pointy front, is called a hull and the pointy front but, is a bow. Aaahh..I say to-ma-toe...you say TOOO-matoe...

Otherwise, why not use a house…it too has vertical front sides, why not use that…satisfies YOUR SOR..not sure about anyone else’s though.

Since the OP has made it abundantly clear what he wants, and again given here:

http://bateau.com/studyplans/EC24_study.htm?prod=EC24

Still want a cylinder that satisfies?...ops my bad....a boat shaped hull - but in reality is just a floating cylinder. But why get bogged down in semantics eh?

 

"Party barge" is used to market pontoon boats. Maybe American slang.

http://www.808boats.com/boats_suntracker.html

Unsure the debate is over a cylinder drum with no bow. Or probably the midship section being cylindrical, a pontoon boat "party barge", a cylinder with the front 4' shaped into a pointy bow.

 

It'd be extremely difficult to not throw in a cylinder, as the OP has explicitly mentioned comparing actual boat hulls to cylinders, and contemplated using an old pontoon instead of a boat.

You're waffling - this doesn't address anything I've said, which is: yes, the difference in shape between pontoon cylinders and boat hulls has a significant impact on resistance.

The OP brought up cylinders, not me.
I specifically addressed a post of his, nothing more.

I'm quite sure I'm not the person here with cause celebre about a position no-one else is interested in discussing!

I don't think for one second a brick, or a pontoon cylinder, should be called a hull shape. Honestly no idea why you think I do, nor why you keep mentioning it.

The only person who ever considered a cylinder is the OP. You need reminding, again, apparently:

Don't worry, I can post the above quote as often as you forget it.

Non sequitur. You must be reading something other than what I'm writing.
I've never advocated a cylinder to any degree.
On the contrary, I explicitly pointed out to the OP that the shape of a pontoon cylinder would be detrimental to performance.

 

Hmmm....oh well :!::!::!:

It's 35c outside and 90%+ humdity...i'm off to cool down. Shall i go float in a boat or a cylinder.. on the beach??

Most likely!

 

That was me mentioning cylinders in reply to the OPs post about cylinders. I don't see your problem:

 

if i can revive this thread for a question rather than start another thread
The hull shape attached the proposed shape and its effects, sorry no 3D modeling here.
I have tried to show the removal of width and replace with depth as mentioned above as slenderness very slender. so replacing displacement from width to depth
Proposed say a small boat of 6-7 meters aluminum lightship 1500kg with 200hp
would this hull have a much higher drag due to the surface area below waterline.
The aim would be to achieve smooth ride in very choppy conditions at speed
or is there a limit to this effect with handling please explain pro's and con's
Thanks
Givit

 

I built a very narrow trimaran on that principle.
http://www.boatdesign.net/forums/projects-proposals/historic-home-made-tri-41690.html

Yes. Without doubt. The drag would be significant. 200hp on 6-7 metres is not a sound idea. The weight on a 7 meter narrow hull like this would be crazy. I had a 6hp on my 18ft tri, and that was as much as it could carry in some conditions.

The centre hull was so narrow I had to put "pods" extending to fit myself in it.

The ride through choppy water was very smooth. I had then to build up the foredeck to prevent taking water on board.

On the whole, quite successful.

But, this is all old hat. Every style of catamaran you could ever think of has been tried, and its really down to picking an existing design that fits your "needs".

Cat/Trimarans have a lot of benefits, but they don't carry big loads, especially heavy motors.

 

I'd suggest that you don't slim the hulls high up, slim them in 3 stages so the top third is the same as the normal hull, assuming you are intending to employ hydrofoils to make up the difference in lift.

 

Thanks
The sea conditions proposed would be flat to 1-1.5m seas and or 1-2m swell and try to average 20+knts. yer probably over estimated Power but would see 70 to 90hp a side.
I want to peirce waves then lift (equalize momentum) thru the middle giving a good AOA to next wave. the foils are mainly for lift and as suspension into the face of a wave, cavitation around the foil is not critical as i dont want hard landings. Foils are set 1-2vdegree deflection and retractable for less effect. 20 foot long and the rear shape much like a standard power cat not too thin.

As mentioned MrE step/planning/ deflecting stages i agree to be necessary this also adds strength by form.
Nice looking tri Watson. but this this would be for offshore power white knuckling. we have been doing a set 40 mile round trip in a mates 18" ali mono hull even standing at transom my back and heels can take no more.as younger fellas we sucked up impact and spray with beers(too old for this s**t now) the trip is fun now to make it comfortable. plus the 18 mono has destroyed its self from the inside out, well we destroyed it.

Next when i get home download a free (easy to use)hull designing program and not so much cad *******paint. suggestions? maybe a 1m 1/6 scale foam glass rc version to trial

 

You can work out the hydrostatics with something like Freeship, if you have a couple of months "play time".

Usually also a waste of time. I would go up to 1/3 scale for any kind of testing not in a proper tank, just so you can easily get at least get engine performance characteristics easily. Tank testing is thousands of dollars a day, so that probably isn't going to happen.

If you are serious, you really need to bite the bullet and get a qualified NA onto the job, or find an existing design to suit.

 

Way too experimental to be making a boat like givitago envisages, the odds of it working well without a vast amount of trial and error is not good. You are stepping into unknown territory in too bold a way, I think. And scaling is very tricky, dynamic effects are out of whack with bouyant lift as you scale down

 

All valid points
Yes to go ahead defiantly sit down with NA and mock design plan, nut out feasibility and correct ball park figures.
Even if based on proven hull design and manipulated to slightly thinner deeper hulls wave piercing bow, (So a proven design manipulated to just outside or on threshold of stability without foil assist) I would be so bold use as test craft.
The modular foil system i envisage can be removed an run as a standard boat.
This requires rectangular sections cut into each hull approx 1m long x 150mm high x full width of hull, a strong box section formed within the ribs and bulkheads (cassette). The experimental foil module or a sealed flotation section insert. all that is required is 2 hyd supply points to the cutouts. Then experimental sections inserted, removed, modified etc.
These foil section are Ali plate sections driven by simple rams as such would be home built, modified, experimented with cheaply as hobby by myself.

Bold experimentation is required for any concept to come to fruition.
But how much do we invest as a hobby is the question, all we can do is minimize risk.
any ideas what the going hourly rate is to talk to a Naval architect