feasibility of variable length hull/variable beam cat...

[black_sails]

Hello, I already posted my introduction post explaining possibly some of my wierdness if you search for it, and I wanted to ask people with more knowledge than i'm likely to ever have how dumb my ideas are. :^)


PROBLEM 1: I live inland. (Minnesota) I'd like to build a boat that I plan to use on lakes, including the Great Lakes. We generally like to haul our boats out of the water and bring them overland when it's winter since there's too many bad things that can happen left out on the lake.

PROBLEM 2: My lifelong dream is to sail on the big blue ocean in retirement. (at least ten years off i'm sure) I'd like a bigger boat. Or at least longer hulls and a wider stance on the same boat because you cant beat length for making big seas more tolerable.

SOLUTION? So I have this idea in my head of wanting to design and build a catamaran that I can still move overland but could literally be expanded once I got to the ocean. Not permanently - or i'd just build and put bigger cat hulls on it and such... no, genuinely designed to stretch out for sailing and scrunch up for road travel, storage, maybe even reduced docking fees when based on size??

The idea was in my head seeing adjustable length trailers for towing and making me wonder whether the ideas were feasible to implement on watercraft for the beam to start for stability. For length I don't yet know if hulls would telescope out on the ends, or just be modular like a front/center/rear section, the ends having a 180 degree hinge that lets the extra length fold in and under the boat (when the hulls are widened) and then locked inplace with whatever level of sturdiness the Computer Aided Design program tells me is needed for the shear loads and stresses under various sea states put on the end of the hulls.



I could probably build a much smaller version as a test (even just a 14-18 footer for lakes for where I am) and might but I don't know whether i'd learn that much more than a CAD program could tell me to scale up... the idea being an oceangoing vessel in terms of size/stability that can still travel overland to be stored in the dry. Or even convenient enough to change modes to avoid going through various locks in the future if I could get use of a semi flatbed in say Panama to move me overland, pretty sure the locks aren't cheap... what say you??

[GordMay]

➥ https://www.google.ca/search?q=foldi...H3NovHevTSgvAI

[AD28]

geez, NOBODY has EVER done this before...

Let me google that for you

Let me google that for you

[unclemack]

Rather than spending every spare minute from now until my retirement on the guaranteed frustrations of trying to make this work... I'd probably buy a cheap weekender and save hard for my last ever boat while learning & having fun now.

Never know what good things or bad things will get in the way of long-term plans

ps. Telstar folding trimarans are very affordable in the UK - must be something similar in the US I expect.

[barnakiel]

I think 100% doable with some technical glitches that would require sound prototyping. I think the problem is this niche may be very shallow. You may be working to the split paradigm of building something and then explaining to people why they want it. This is a lot more work than building something that people actually know how to use and why (pink dildos, chewing gum, dacron cloth, UHT milk, etc).

If you are seriously building one PLS, PM me and let me know how I could contribute.

Cheers,
b.

[DerekKelsall]

Providing you are not looking for the max living space and all the comforts of home, both cats and tris just lend themselves to variable geometry. The swing wing and folding tend to need some well engineered parts, but there are simpler sliding beam systems and rotating hull systems, which I favor and which are made by the boat builder.

In 1969 I build a 44ft. swing wing tri called Pula Tiga. About a year ago she came to grief on a Greek Island with crew missing, but the variable geometry had not given any problems during that time. Today we are working with cats - variable geometry with wheels. Simpler than you might think.

For further details - <derek@kelsall.com>

Happy boating,

Derek

[FSMike]

black sails -
As you can see, many variations of variable width multihulls have been produced. Variable length is a bit more difficult.

You might want to google "Phil Bolger's folding schooner".
I doubt that that design would stand up to the stresses involved in a larger boat, but I'm no architect.

[black_sails]

Originally Posted by AD28

geez, NOBODY has EVER done this before...

I know! I'm a genius! ^O_O^

I've never heard of either of those search terms before associated with cats and didn't know that 'demountable' or 'folding' were the terms i'm looking for. However that's not quite what I had in mind...

I'm wondering something larger in scale and ocean going, able to handle larger seastates including accidental ones you can't get out of the way of and wondering how far the idea can be pushed. 6 foot seas in a 30 footer i'm told is pretty rough going, 6 foot seas in an 80 foot catamaran with wave piercing hulls is not much of a big deal. When i'm told that's pretty common sea state for oceangoing passages i'd like to see what I can do about that.

My goal is to stretch the hulls out "as long as I feasibly can" to get some of the wave averaging effect that only length can get you (50ft? 70ft? 90ft?) but primarily having that in the hulls. Think a man on skiis. :^) I'm not building an "80 foot boat with the room of an 80 footer" but more like a 30-40 foot liveaboard boat with the cat hulls of closer to an 80 footer. By spreading the weight bearing into length instead of wider cat hulls i'm hoping drag might also be less improving efficiency too. (the narrowness i'm hoping overcoming the increase in wetted area, though I haven't run calculations on it yet there may be points of diminishing returns)

Because of shear forces on superlong cat hulls under rough conditions if you make a mistake or get caught off guard, i'm wondering if I could even convert between "longest hulled passagemaking mode" and "shorter hulled survival mode" (potentially along with the third "minimum footprint possible" for just floating in the marina at the 40 foot dock price instead of the 80 foot dock price).

I mean I want the long hulls and wide stance to stabilize the waves but at some point if they're too long (if the idea is taken too far) the weight added for strength starts to defeat the purpose of efficiency. It might have to be that things compact in a bit or hull extenders remove so they don't get broken off if bad planning (or if it were a sail only vessel unable to move fast enough) means being stuck in rougher conditions than planned. Wouldn't have to reduce the floatation, they might just be put in a position (like folded back alongside the center part of the main hull, so it almost looks like four hulls if the extension is all on the front) to reduce the risk of shear loads tearing the cats off.

The discussion about trailering is more just wondering out loud how far the idea might be taken... the end result might require a class 8 truck but still technically be overland moveable, which might be fine as after some oilfield driving I might end up owning one. (i'm wondering if moving by truck overland in Panama would be cheaper than going through the Panama locks or something though, even if in "hulls compressed" mode to take less space up) Or I might be curious how far the idea could stretch and still be Class 8 moveable. But trailerability is not the only reason - I think this is a design i'd like considered whether it was a 40 foot great lakes cruiser, 80 foot ocean going, or 160 foot megayacht.


If youre thinking i'm nuts, the biggest issue is more how far the idea is taken rather than existing at all. I'm sure a Catamaran that widens from 8 feet road hauling to 12 feet stability is no big deal, but wonder whether that idea can still work at 16 feet or 20 feet wide before too much weight is added to have proper strength. (I suppose at some point modular boats that can break down/be hauled in two chunks become possible - but again diminishing returns) I'm sure a Catamran with small hull extenders that goes from a 32 foot long roadgoing mode to 42 feet for a little more stability isn't going to push the limits of engineering, but one at 64 feet potentially would. This is sort of a feeler to see if anyone has done THAT before/not just implementing the idea but pushing it to what I see as an evolved form. Length+width = stability and comfort, and thus a good i'd like to pursue, without ending up with some critically dangerous flaw obviously.

[Redreuben]

Harryproas are are good example of modest accommodations on long waterlines, they can decrease beam for docking, but variable length is a big ask. Probably best bang for your waterline $$
Check 'em out.


Sent from my iPhone using Cruisers Sailing Forum

[black_sails]

Originally Posted by unclemack

Rather than spending every spare minute from now until my retirement on the guaranteed frustrations of trying to make this work... I'd probably buy a cheap weekender and save hard for my last ever boat while learning & having fun now.

Never know what good things or bad things will get in the way of long-term plans

I'm undecided what to do between "now and retirement" though I explained all my motivations in my intro post. :^)

Originally Posted by barnakiel

I think 100% doable with some technical glitches that would require sound prototyping. I think the problem is this niche may be very shallow. You may be working to the split paradigm of building something and then explaining to people why they want it.

If you are seriously building one PLS, PM me and let me know how I could contribute.

Well I wouldn't be building it for anyone else (though I wouldn't care if anyone else also built one - I just want this for me, call it open source for anyone else), this would be a custom job just for myself. It's also quite a ways off (if you look at my intro post elsewhere) but it's one of several plans i'm taking my time to explore. The nearest big sea to me is the great lakes, and I could still theoretically sail it out to the atlantic and then south whether or not it's overland haulable, but variable geometry for seastate comfort is still something i'm interested in and it seems like an idea that doing more = getting more.

Originally Posted by DerekKelsall

Providing you are not looking for the max living space and all the comforts of home, both cats and tris just lend themselves to variable geometry. The swing wing and folding tend to need some well engineered parts, but there are simpler sliding beam systems and rotating hull systems, which I favor and which are made by the boat builder.

Well it's not for max enclosed living space. (although large deck space to stretch out on would be fun) My plan is to first decide on whatever enclosed living space I want to start with, and then see how long and widely spread I could make the hulls under it capable of being. I'm aware bad things can happen to any boat, including specific to their design (cats can capsize, monohulls sometimes roll 360 under the same conditions) but I at least don't want something to fail due to fundamentally bad engineering itself.

[belizesailor]

How often do you foresee making this transition between inland/ocean? Awful lot of work/expense/complexity for an ability you might not use often.

Bigger does not necessarily equal more seaworthy. All those connections/joints give Mother Ocean plenty of potential failure points to work on. Friend of mine circumnavigated on a Tiki 21...compare that to something like the "Flyin' Hawaiian" (though I understand you plan to properly engineer your boat).

[Stumble]

The width hung has been done, so wishing the limits there you are just dealing with application of existing ideas.

Altering length I just can't see. It isn't as easy as biting on a new section of hull, there are a lot of issues with keel placement, mast placement, rudder placement that would need to be changed as well. Possibly you could build a boat in sections, a bow section, keel section, rudder section, interior hull section, and add more interior hell sections to increase the length....

Frankly I am having a hard time wrapping my head around it. The connections maybe by massive ring frames, lots of bolts, quick connects for electric, fuel, and water....

This would be a massive engineering project to be honest. So how many millions do you want to spend to build a couple hundred thousand dollar boat?

[barnakiel]

It is always amazing to listen to people who will go full monty.

From my brief conversations with people who actually build the best boats in the sailing world, massive prototyping is a norm there.

Build it break it build it break it build it break it ... all in the era when these guys have huge computers at hand that can solve very complex structure/material questions using methods like Monte Carlo and other relatively complex tools.

And then you meet someone who is going to build a big completely innovative boat at home.

;-)
b.

[leftbrainstuff]

General purpose solutions invariably suffer from the tradeoffs being more dominant than the benefits.

As an engineer I see many complex and complicated design elements in your concept. The cost and time to resolve thise issues is significant. Far greater than the cost to buy two vessels I suspect.

For example a corvette pickup truck is both an inferior sports car and an inferior pickup truck.

A simple model I developed to assist inventors to quickly assess ideas before investing time and effort is this. Is it both radically better and radically different? If so it is innovative. Your idea meets the radically different test but probably not the radically better test. This makes it just different. Change itself is always a hard thing to sell. Based on this assessment I would not invest.

Why not buy a boat now and then sell and buy a cruising boat later?

Take a look at kayaks that are modular. You'll see the challenges in a vessel that is significantly simpler than what you propose.

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[siamese]

A boat that gets longer and wider? Maybe you can get Viagra to sponsor this thing.