economical coastal cruiser

What's wrong with Star Trek?

 

A 12m cat would not be an outrageous or even distasteful consideration. Does anyone believe one can be built for less than the price of two boats?

 

Quite how you can say that any of those are comparable in anything but size is beyond me...
Graphite has 4 permanent berths, 2 showers, a microwave, a galley and saloon / cockpit with space to rival most 40 footers. It can comfortably accomodate its crew for extended cruises, offers a range of well over 400nm and carries 400l of water. There are separate batteries for starting and house loads (2 x 120AH). Whilst it wasn't a major design objective, it has a top speed of 32 knots, so the far greater slamming loads must be accounted for when considering the stucture.
I don't have a problem with justifying the construction choices for Graphite. Suffice to say that I examined all the available options and the strip-plank hull came out trumps. I don't have the figures in front of me, but from memory, the hull shell (topsides and bottom) totals just 350 kg of the total weight, so even if you can manage to make a considerable % saving, the effect on the total will be minimal. The bulk of the rest of the boat is made from foam or balsa cored composite panels, so major weight reduction there would be difficult.
Now - yet again - let me say, Graphite is intentionally conservatively specced in terms of scantlings & I am not suggesting you can't build a similar boat that weighs less. But the only way you will do so in any meaningful way will be to have 'less' boat.

 

No

 

I agree. A boat weighing only 2000 to 2500 lbs will be a lot less boat, not simply different scantlings.

 

OK, now that Will and I seem to agree again, as we usually do, and I'm not taking things personally (sorry, that was inappropriate, and my only lame excuse is that I had the flu for a MONTH).

Sandy, I think you hit the nail on the head with the suggestion that a spreadsheet is needed to first figure out how much all the stuff you want to take along actually weighs.

One fellow told me that you should not start really designing until you've identified the absolute minimum you want in the boat. Its all the extras that drive the cost and weight, and not simply the hull and deck.

And yes, I think this is in fact something every boat design needs from the beginning, and it gets maintained throughout the design and build process.

Anyone care to start?

 

I'm piddling around with the idea, but I'm not very adept with spreadsheets. I think the idea can be expanded a bit to a list of options and costs in dollars, weight, man hours, added structure and systems. I'm thinking of a question and answer concept that starts with the buyer/builder's broad goals and limits, such as finances, time, trailered or kept in water at a dock or mooring, cruising area, realist berthing, and so on. Part of the table would include parameters that can be set for the cost of resin, the price of an engine, and the size of fuel and water tanks, etc.

It's beginning to sound like a book, too. I think that arriving at a total weight of accumulated crap/bare necessities, and some idea of the type of vessel envisioned, we could calculate the approximate size and complexity.

Gazing deeper into my fishbowl/crystal ball, I could see this quiz working for a boat shopper too. Fred the fish just looks back at me like I'm off my meds. He thinks my time could serve a higher purpose by dropping a few food flakes
in a convenient location....

Pretty wild, huh?

 

There's a challenge to make a hull like that into a practical boat, and not looking like something from Star Trek. I'm not convinced that it cannot be done though.


Stability under way could be done with out the drag of a set of Amas.

Think of a simple Maurice Griffiths style center board case made 3x wider than usual.

A well shaped board could have a simple ram to give it a slight angle of attack , voilla roll stability, with out huge hydraulic fins sticking out the side.

Go fast , need less drag,pull 3/4 of the board up.

Run aground? no problem with $10K fins holing the hull , the board simply does what it does on sailboats for 500 years.

There would be no outside unusual shapes required .

FF

 

Do you mean dynamic roll stability control? On my budget?

 

FF,
I've searched the net best as I can to understand what a Maurice Griffits style center board is, without success. How is it different from a normal center board?

Erik

 

Gee. Erik, it should be obvious! A normal centerboard is easier to find on the net.

 

Dynamic roll control does not need to be astronomically expensive. The least expensive Naiad system is less than $15000 USD. A roll-your-own could be substantially cheaper:

Imagine using moth foils. These generate 200+ lbs of lifting force. Thye are mechanically controlled by a wand that kisses the surface of the water: when the foil is deep, the wand causes the foil trailing edge tab to be pushed downward, increasing lift. For a fully mechanical system, a couple of moth T foils mounted perhaps at the transom outboard corners so they would kick up on impact. The cost of a moth T foil is about $2500 USD. Buy two, that's $5K. The mechanical control won't lead to zero roll, but could lead to greatly reduced roll, and its easy to tweak and play with.

Or, one could use the computer you'll probably have onboard anyway, add a USB IMU (inertial measurement unit) for less than $1000, write a little control system, add some motor controllers and motors, and then actively control those foils.

If you've never been on a boat with active roll control, you will be amazed. A typical installation results in ZERO roll up until the seas get amazingly wild, at which time you might see a few (like 3) degrees of roll in, say, 10 foot beam seas. It really seems like magic!

I think its highly likely that a NAIAD system is cheaper than amas, and for certain stabilizers result in MUCH less roll motion than amas.

When you are anchored, use flopper stoppers to get just a few degrees of low rate roll.

Or, use a planing V bottom for dynamic roll control. The dihedral stability at even low planing speeds is very noticeable. Try sailing a planing dingy like a Laser, 505, Windsurfer: at about 6 knots, as the boat is starting to plane, it gets MUCH more stable.

I've gone around and around on this, within the constraints of 8.5 foot beam for trailering. Cat, Tri (really, augmented thin monohull), displacement, planing, ...

I think that the simplest, cheapest to build and to own over long term, is a VERY light planing V bottom monohull. If its very light, then planing can occur at essentially displacement speeds, so you always get that dynamic roll stability. At anchor, use the flopper stopper. Its the simplest structure: most internal volume per unit surface area. Its therefore the lightest, all things being equal (surface area equals weight and cost, so minimize!).

How light? Use that spreadsheet, try to always choose the simplest: e.g., the minimum number of engines is one, so choose one. Minimum number of heads is one, so choose one. And so on. Then figure on 0.5 to 0.7 lbs per square foot for the hull and deck and bulkheads and stringers and floors (you can achieve 0.5 lbs pretty easily). Then just design to fit that weight.

I find that the design needs to be a stepped bottom with a pad, just to get the displacement down to the design displacement.

 

Eric: its Maurice Griffiths, who passed away in 1997. He wrote a book that inspired many British readers to build their own boat: sort of like Phil Bolger did for the Hippy Boomer generation.

U4ea32: I thought I was the starry-eyed far-sighted dreamer here! But that is what Forums are for. You suggestions are interesting, but a little bit of a stretch for someone who admires Dave Gerr's 1920's-looking DR Northwest Cruiser. Getting a bedroom, 3/4 bath and kitchen up on foils would be challenging to say the least!

 

Sandy,
I may be mistaken but I don't think he is referring to foils. Think of the Lulworth mentioned in Gerr's book with a flat spot aft to ride on.

 

Oh, I was not suggesting being up on foils, just using the foils for roll control.