Converting Carvel to cold moded

[Brumenschenkel]

I am looking at converting a traditionaly constructed carvel design ( William Atkins's Jabberwock) to either cold molded, or strip planked cold molded, or double planked with epoxy ala Paul Gartsides' Surprise.
Alas good shipmates I have had a tough time getting in touch with Billy to ask his advice.
I would also like to change the rig from a marconi sloop to a gaff sloop with topsail. Ideally I would Like to tabernacle the mast. I am assuming that I will end up with a slightly heavier hull, which can then be trimmed by removing ballast. Will I be able to get away with fewer frames? What other implications are there and what should I be weary of? Do I need to consider moving the mast to affect the center of effort? The rig is so bloody tall and designed for light weather summer days.Suggestions?

[John Gearing]

I think it's time to have something designed for you, to meet all of your requirements. You are talking about making a lot of changes to Atkins' design and of course with him being deceased, he can't advise. Time to get a designer or NA of your own to either design the changes or draw you a boat from scratch.

As for switching from carvel to coldmolded, I'd expect the coldmolded hull to be lighter, which would mean you could put the saved weight into additional ballast, down low (i.e. bottom of keel) where it will do the most good. Not only will this change heeling resistance, but will also affect things like roll rate, and even comfort or "feel". IIRC the book "The Gougeon Brothers on Cold Molded Boat Construction" has info on building coldmolded to carvel plans.

But first I'd advise talking to a good naval architect.

[Dick Wynne]

I would agree with John Gearing, as it appears you don't really want the design in question, but you can get a booklet defining strip-plank scantlings from MacNaughton (http://www.macnaughtongroup.com)
- in the absence of any formal authority on the subject.

[JimD]

Beautiful double ender. Even Atkin advises changing the sailplan if you intend to sail her in places where the winds can be strong so I see where your question comes from. I bet she'd be a looker with just a gaff main and no topsail. Just my very amateur opinion but I'd assume you'd want to leave the jib alone yet keep the combined CE very close to the same by playing around with the size and shape of the main or main/topsail combination. That much ought not to be too difficult
http://www.imagestation.com/picture/sraid200/p24f380e8496994d02fd0e9d6b8527ada/f08251fd.jpg

Edited to add: Hull weight and especially removing ballast is something I'd want a pro to sort out unless I felt very comfortable crunching the numbers to determine things such as CG, CB, stability curves and righting moments, and so on.

[ 01-19-2006, 09:55 AM: Message edited by: JimD ]

[Bob Cleek]

There are many boats which look very similar and have the parameters you seek. Even several by Atkin. It is a fool's errand to attempt to make the sort of major changes in construction and rig that you are contemplating, particularly when what you seek already exists in proven designs.

Some have built cold-molded or strip planked boats from carvel plans. Myself, I don't consider this a wise thing. As the sides of a stripped or cold molded hull will be monococque (one solid piece) rather than a multitude of moveable planks, the stripped or cold molded hull will transfer all of its stresses to the garboard joint where the hull sides meet the keel rabbet. This is a sure invitation to leaking and premature structural failure. A traditionally planked hull transfers stresses throughout its surface. A solid hull necessarily transfers its stresses to the "weakest link." A monocoque hull should be designed for such construction in the first place. Generally, this construction method is best suited to round bottomed, fin keeled sailboats in which the entire hull can be laid up continuously across the centerline.

There is no question that more abandoned boat projects ran onto the shoals because builders tried to pour all their "good ideas" into a boat that was intended to be built differently. There are thousands of proven designs, many even in the public domaine (free) which can be studied and picked over. Identify what you like about this design and what else you want that it doesn't provide, and then pick a proven plan. It is clear from your questions that you are not far enough into this game to start designing your own boat. (e.g., reducing ballast to accommodate additional weight is a major no-no if you want a boat to sail, or even float, as intended) Trying to reinvent the wheel isn't smart. Build a boat you know will sail when you're finished with her.

[ 01-19-2006, 03:33 PM: Message edited by: Bob Cleek ]

[RodB]

Similar post on this subject....

http://www.woodenboat-ubb.co m/cgi-bin/UBB/ultimatebb.cgi?ubb=get_topic&f=2&t=002807&p= (http://www.woodenboat-ubb.com/cgi-bin/UBB/ultimatebb.cgi?ubb=get_topic&f=2&t=002807&p=)

Bob Albers (alberwoodenboats.com) has built several traditioal designs in modern composite construciton...and can be consulted.

RB

[ 01-19-2006, 04:23 PM: Message edited by: RodB ]

[Keith Wilson]

It is a fool's errand to attempt to make the sort of major changes in construction and rig that you are contemplating, particularly when what you seek already exists in proven designs.Oh, come now - A fool's errand? Building the same hull shape in a different method of construction? Nonsense. It’s scarcely trivial; there are a lot of details to work out, but it is an entirely reasonable proposition to convert a carvel-planked hull to cold-molding. Cold-molding is generally stronger and lighter than traditional construction, so it is quite feasible to build it stronger than necessary without excessive weight, this makes a conversion fairly forgiving. Again, it needs to be done carefully by someone who understands the construction method, but IMHO it will result in a considerably better boat than the original. Bob, with all respect, when you talk about hull stresses it becomes quite obvious that you are a lawyer.

Small boats are not that damn complicated! Boat designers are not the elect of the gods, and a considerable amount of the structural engineering on older designs was done by rule of thumb and common practice. Remember that Billy Atkin designed one boat a month for Motor Boating Magazine for years; do you think he had time for elaborate stress calculations?

The Atkins themselves designed several boats with alternate rigs. Putting a slightly shorter gaff rig on this boat seems a perfectly reasonable thing to do.

So, my advice, (which is probably worth about what you paid for it): Read the Gougeon Brothers’ book; it’s the best introduction to epoxy-glued boatbuilding there is. Ruel Parker’s book isn’t bad either. Look at as many plans for other similar cold-molded boats as you can. Then if you still think you want to go ahead, pay to have somebody competent at least look over your ideas and ensure you aren’t doing anything too dumb. That’s a nice boat, it would still be a nice boat cold-molded.

[JimD]

It's a centerboarder, btw

http://www.imagestation.com/picture/sraid200/pdea761eb2e4882f0fe1da7b1784afef2/f08137e7.jpg

W Atkin said this about the sail plan.


The rig was designed for use in the average summer weather we have on the western end of Long Island Sound. If Jabberwock is to be used on the Lakes, and other certain sheets of water where it blows hard, reduce the height of the mast and the sail area. But, good shipmates, don't do this by guess and by gum. Drop me a line first.

[Bob Cleek]

Well, if it's a centerboarder, you may be able to pull it off, but why bother? I'll bet that if you went through Atkin's design catalog, you'd find exactly what you are looking for, gaff rig and all. Fact is, Atkin did design a boat a month for MoTorBoaTing and a lot of them were "retreads" of earlier designs. Still and all, cold molding a boat designed to be built easier, cheaper and faster traditionally doesn't make a whole lot of sense to me, but it's your time and your money.

[Brumenschenkel]

Thank you all for your input.My reasoning for modern hull construction was to ease maintainence, and maintain the hull integrity while sitting atop a trailer. I am sure the rig can be modified sith the help of a competent designer.

I have been through all of Atkins comparable designs, and many others buy numerous designers, Nothing has haunted me like Jabberwock, many come close, but in the nd I keep coming back to this design. Pat Atkin has reccomended a gentleman to advise me on the proposed changes. I will post an update following a discussion with him. I will do it right or not at all!

peace

[JimD]

The hull is certainly the right shape for trailering. And as you say traditional carvel doesn't like trailers. I've probably gone through the Atkins' website a hundred times and there really isn't anything else that comes very close to her. Nor have I seen a similar more contemporary design for cold molding. Under the circumstances I can see why you'd want to go to the extra trouble to modify her for cold mold or strip plank.

[ 01-20-2006, 12:14 PM: Message edited by: JimD ]

[Keith Wilson]

You might consider glued-plywood lapstrake; that hull shape seems at first glance like it would look good in lapstrake and would be fairly easy to plank, and it would stay tight on a trailer. It's about the same size as some of Iain Oughtred's designs.

[Brumenschenkel]

Bingo! on the plywood lapstrake idea. I actualy talked to Joohn Brooks and Ruth Ann Hill, authors of Gued Lapstrake wooden boats about this idea and they were very helpful. Ultimately they suggested the prudent move of consulting a Naval Architect. I imagine lapstrakes would only ehance her pleasing form. So I am not mad! Oh did I forget to mention Billy Atkin rated her displacement at 8,725#.gulp! Here in lies my next concern. I know it acan be done and has been done with boats of this displacementbut.... Most of the ones I have seen are keeled boats which are certainly trickier to trailer launch. Jaberwock has her hull form going for her, I have the rig to haul her I am only short on the trailer. I feel better already.

cheers

[JimD]

You may yet prove to be mad and a lot of folks come and go on this forum with their flash in the pan ideas that go nowhere. But it does look like a feasable idea and she would look lovely in lapped planking.

[chrisk]

So, I am curious on how things turned out with your Jabberwock project ?

It's a tempting design for trailer sailers like myself, though that 8725# takes one back a bit.

Thanks
Chris Kottaridis (chriskot@quietwind.net)

[RodB]

As I said above, Bob Albers, who is a mechanical engineer and a professional builder, has built several older traditional carvel designs in strip/cold molded...and is presently doing that exact thing with Murry Peterson's Schooner "Susan".

http://www.woodenboatvb.com/vbulletin/upload/showthread.php?t=51863

You can email him bobalbers@purelyonline.com


Mr Albers seems to cut the number of frames at least in half, and usually the hull is lighter...and a bit more ballast is added. He certainly has the design skills to analyze a design and massage it around to make for easier construction for strip coldmolded building.

Personally I would want someone with his experience or an NA to go over a design that I was translating to modern epoxy composite methodology.

Good luck,

RB

[Canoeyawl]

A lovely vessel… It would be an interesting exercise to calculate the weight differences in the two hulls. If you have the plans they can be reduced to cubic feet of materials. At a glance it seems a fairly symmetrical hull and the ballast placement can probably remain in the same position even though the ratio may change a bit. The difference in weight and placement of the rig will have some bearing on that decision.
It is common for owners / builders to change rigs to suit. No sacrilege there in my opinion.
I am an advocate of lapstrake plywood but the cost may be prohibitive. My guess would be one would want at least 5/8-inch material for that job and good Mahogany ply that size would probably be $3 or $400/sheet. Cold molded construction may offer a better economy in materials.
These changes don’t seem huge to me and I suspect an N.A. will be able to counsel you with no problems… simply find one with an eye towards traditional boats that you like.