Scale down?

Hi all, this is my 1st post here. I have a question for all you smart guys. I have fell in love with a 78' AL sailboat that I in no way can afford to buy. But I do have a large shop with lots of equiment and feel capable of building it in a smaller version. I am thinking of a 54.5' scale down, just multiply all dementions by .7 . The designer does not sell plans, so I would be free wheeling this project. I would scale down everything by .7, mast size, room sizes, engine, hull, sails, keel, everything. Will this work? Will it sail or will I end up with a 54.5' anchore? I dout a NA would reduce someone else's work for me. Please give me your thoughts.

Thanks much
Zultar

 

Headroom problems? Unless you are really short, I would think you'd hit your head on the beams a lot (assume 6'6" headroom in the original, to be generous, would make 4'6" or so in the "new" one)
And that's just for starters ;-)

 

I will lower floors making less space underneath them, I hope

 

You have to use different scalefactors for length/beam/area/volume etc. Even an anchor will not be scaled linear....
If you don't have the plans....how do you gonna scale it down.. ;-)
rgds/Olle

 

Thats why i'm asking, your saying using .7 lenth and .7 beam wont work?
And why would I care about volumes? Sails will be .7 of original, that wont work?

 

as a satrter...if length is scaled by factor L (in your case 0.7) sailarea is scaled by L^1.85, Beam L^0.7, wetted area L^1.63...ect....you will end up with a new design..
Just try to scale it extrem, like 0.5, and then compare to other designs in that range and you'll see what happens.

 

Scaling down, as you've suggested would make the design in question very close to capsizing at the launch. You just can't use a multiplier and go for it.

As the hull form goes down in size it's length to beam ratio must go up to maintain the stability needed to float with the decks facing up.

Typically, you can scale length up or down by re-spacing the sections + or - 10%, 15% at most with few problems. This works much better going up in size then down. Beam and draft would remain the same.

There are some noteworthy scaling formulas, but not within the frame work of a discussion board, but a thorough knowledge of the design process.

You need to approach this from a different tack, try finding the elements of the design you have fallen in love with and look for a design that has them or could be made to have these qualities. Then get that design or have one done for you.

If you are at the stage in your building experience, where a 54' yacht is a doable thing, do you really want to hijack, modify and/or butcher someone else's work? A yacht of this size is a very demanding, long term project, needing years to complete, and barrels of cash. Building a patched together, bandage of a design, doesn't seem cost effective in the long run. In fact rather foolish, unless you'd not be sailing farther from shore then you can swim . . .

 

Darn, well thats why I asked. Thanks for the info, so find a design I like or pay someone to design what I want. I purchased plans from Bruce Roberts for his 45'er but upon building the frames from the full size paper patterns and seeing the rust I could not bring myself to continue. The hull was far from fair and he does not sell mylar patterns so I guess it's back to rethinking the whole idea. The design's I see for sale are very old tech and want something newer in style. Like 54' of waterline on a 55' boat, mizzin and main, ect.

 

Bruce Roberts has a very good reputation, his designs, quite sound and Roberts designs up on the resale market don't last very long before someone grabs it.

Steel hull building is all about rust. Let it rust. No kidding, let it rust, it will protect the framing and plating, besides you'll not be able to build fast enough to get it coated, before it begins. Loads of rust and scale is normal in this construction method. There comes a point in the build (later then you've gotten) to deal with this.

At the stage you've described, having built the frames, the hull shouldn't be fair (I'm assuming they got erected on the backbone) Building accurate frames helps the fairing process a great deal, but you'll get to that point in the construction, if you keep plugging at it (according to the plans)

Roberts has a very helpful bunch of builders, most of whom are available for comment on his web site. They've been pooling their resources for a long time and the method has worked well for them.

Building a boat isn't instant gratification. Frankly it's a painful way to learn about yourself and the ones who love you. BUT, if you have written a Ph.D. dissertation, remodeled a house, raised a child or anything else that doesn't give this instant gratification, then you certainly can build a boat. If you've never carried through a large project you can still build a yacht, but I'd strongly recommend you think smaller, say under 35'. This would help keep things moving along and the risk of failure is not as great, as the end is closer and possibility in view. It's very easy to get bogged down building a too large of a boat.

That said, yes the "stock" designs are dated, this is why they are offered this way. Stock design sales amount to very little for a designer. Some companies like Glen-L and Roberts sell a bunch of plans and they, I'd think, are making money, but for the most part they sell plans, maybe some kits and their design staff if out of house or dead.

Custom design work isn't that expensive, when the big picture is observed. Aside from the few dozen real notable folks currently designing and getting a fine premium for their effort, many less notable, but quite capable people can set you up with a good set of plans, though they may not have a AC winner in their portfolio. Mylar plans sets are usually unnecessary and very expensive to produce. The last set I had plotted off cost me over $1,200 and you can guess what I charged the client. This was a simple set, and not really needed by an experienced builder. In a yacht of this size, you'll need experience building large yachts. Most builders don't bother with the plans so much as the design brief and a lofting of the sections from the offsets.

What is your building experience in sailing yachts over 20 tons? I've got a 50' schooner (43 tons) in my yard now, I've been beating at it for a few years now. I just launched a 33' gentleman's racer, have a 23' daysailer just rolled over and a 15' daysailer just being lofted. These are all my designs and my construction, I have a small crew of skilled guys I use as often as I can and pump out a few boats a year. How about you?

For what it's worth, no builder has built a completely symmetrical or completely fair hull . . . regardless of what their brochure says.

 

Building in aluminum won't solve the problem with fairness on the hull. Working with plating is similar in all metals. Steel can be much easier because you can fair it with a torch. The metal distorts with heat and changes shape. With aluminum it is not possible. Also, about your question on scaling down: All the scantlings will change. How do you plan on calculating all that? If you are making a new design, it's OK to take ideas or looks from others, but keep in mind that there is a lot of engineering to do.

 

scaling down

i asked similar questions about my 1/3 model of an america's cup racer. there are formulas for scaling down. some of them are found in the discussion in "sail area vs ballast" thread. you might try reading this thread; it was an education for me. best of luck with your project.