Cherub Design

Hi, I'm new here and right now I know precisely nothing about boat design. I do have experience sailing HP dinghys. Combine this with my natural mechanical inclination and a desire to understand and build things, and I find myself in a situation familiar to many here: I'd like to design and possibly build a sailing dinghy. I know that I have a TON to learn about the entire process. I've read through a good bit of the threads here and have found out about DelftShip (formerly FreeShip, I think). I'd like to get started using this software and I plan on going through the tutorials. What I'd really like to do is get a Cherub design working in there. I think that working from an existing design would be best, possibly with zero changes. Short of buying a plan set from BloodAxe for over $100, what are my options? Any chance that someone has the offsets for a post '97 cherub design (is that even the right terminology, offsets?). I'm not sure when I'll be able to afford to build it, if ever, but working on designs in the computer is free and would surely be a great way to start learning about boat design and what goes into building and making these boats go fast. Thanks in advance!

J

 

join the club, i now know i knew less than i thought i did

 

If $100 is difficult for you to muster, then you're not going to like this boat building thing at all. Before you get comfortable with FreeShip or other design software. Learn the difference between what works and why, and what doesn't work and why. Software will happily draw up whatever you like, regardless of how unsuitable it may be for your needs.

 

I didn't mean to imply that $100 was going to be difficult to muster. I've got a ridiculous amount of money. In fact, a folded up Franklin is currently stabilizing the wobbly leg of my Steinway Grand where I routinely sit and savor some Courvoisier while gazing at one of the many members of my harem of exotic models frolicking on the polar bear rug, thinking to myself, "I wonder what the poor people are doing?" No, no, money is no object, but you don't get as fantastically wealthy as I am by throwing money away stupidly. In my opinion, spending $100 on plans for a boat that I don't intend to build would be unwise. Better to save that bill for lighting up a nice Gurkha. Besides, my understanding of the Cherub class was that they are nearly all homebuilt and designed and that the members were very helpful and sharing. For that reason I didn't think it'd be that hard to track down some offsets for one of the newer hulls. For what it's worth (get it?), I did manage to find some on the UK Cherub class site. I'll get busy getting those in Delft.

 

IF you want to build the ultimate class boat you need to learn about sailing, the class, sail and rig design, and than hull design. I think the best way to learn about boat design is to go out and sail in as many different similar sized boats you can, and study their hulls and rigging, it is also a lot of fun. Go hang out at sailing clubs and bum rides, rent or borrow as many different sail boats in the size class you can. Get to know other racers and serious hobby sailors, go out with them and compare their hulls, sail plans and rigs and how they behave differently. Also gather their opinions (do not put too much stock in that, but it can be useful to know what others are thinking and doing in the class).

This will give you a feel for how the different sizes and shapes affect the performance. the hull is only one part of the system, and not even the most complicated part. The sail plan, rigging and other parts of the system will likely give you far more trouble than the hull. And the single biggest factor, you own sailing skills, will be developing along the way. You have to understand, and have a feel for, seamanship and how all the various components work together before you can know what the optimum design will be.

Also, it would save you a lot of time and money in materials, for your first one, to just buy a set of current Cherub plans (if you can find any), and built that one first as your baseline. Or go buy a used boat. Than go out and use it a lot and learn it. Than you can use that hull as your "mule" to test out various rigs, sails, centerboards and rudders, and alterations to the hull design (caution: make only one change at a time or will not know what works and what does not). After a number of seasons of messing around with what is known to work, than you will be ready to experiment and design the ultimate hull. Not likely it will work the way you expect on the first one (no matter how much fancy computer analysis you do on it), so expect to evolve a new design, learning as you go. It always works out this way, I like experimenting too, but I have come to expect to build two or three examples before I am happy with it.

If this sounds like too much work, than just buy a competitive boat and enjoy using it. Going off in "innovative" directions without a good understanding of what you are facing is just a waste of time and very disappointing, you will just end up giving up on it after investing a lot of time, money and materials. So I suggest first study, participate, learn and understand what works good now, and than try to improve it from there.

Good luck, it looks like a fun class that allows experimentation (unlike a lot of class sailing rules). Keep us updated on your progress.

 

Thanks for the input Petros. I harbor no delusions of building the ultimate class boat. Whatever pile of dust and cloth that I (might) glue together will be lucky to be a slightly below average class performer. I'm afraid that I've given the wrong impression. Although I'm clearly no naval architect, I do have a respectable amount of sailing/racing experience and technical knowledge. Enough to know that the hull is but one small piece of the high performance puzzle. A benefit of an established class is that the rig is already sorted. I'd really just like to get some offsets for the modern Cherub designs if anyone has them so that I can see what they look like side by side in the computer. Perhaps with these, some books, and this forum a dim light of naval architecture understanding could be lit in my feeble mind. If I get even half serious about building the thing I would be pleased as punch to buy the plans for a boat that has gone through the development process. I might have mentioned my vast fortune...

Cheers,

J

 

Jack:

Sounds like you and I are in about the same position. I went through this exercise about three years ago, and eventually had a professional naval architect handle the hull design for the boats (2) I have built since (one completed - one in progress). I did play with Freeship and a couple other design tools myself, and I'm not unfamiliar with CAD tools.

What made me decide to leave the CAD to another was this:

• There were enough gaps in my knowledge that I felt any designs of my own that were built would incorporate errors and omissions
• The cost of having a professional take my design brief to a buildable boat was reasonable - the real cost is in the materials, tooling and time
• Performance (which was a important goal for me) is not a great first time designer objective

By all means have at it if you like .... but objectively assess your desire for a good outcome versus the commitment you can make to the project. There are good reasons why naval architecture and engineering takes several years to complete formal schooling and accreditation. It isn't a trivial subject matter, and other people have hit the nail on the hear - the tools are less important than the knowledge and experience. Building my boats has taught me a whole lot more than I thought - and any designs I attempt in the future will be far better than if I had built the first boat from my own design. Apprenticeship is a very important concept in this kind of work - and having a senior mentor to learn from can save you years of mistakes.

Good luck and have fun.

--
Bill

 

Bill, thanks a lot for your input. You've built a Falco, right? I was considering the Quetzal as well. Like I said, I don't know when (or if) I'll be in a position to actually build a boat. I'd be thrilled to build from an existing design. Getting the offsets in Delft is really just intended as an academic exercise. I know that contracting a NA to design a boat is quite out of the question though. Even accepting your wisdom about the benefits of such a pursuit, it is still a lot of $ that could be spent on an actual boat. Plus, the Cherub community is all about home build, home design, and I would think with that acquiring an existing, proven design from this community wouldn't be too hard. The main problem with building a Cherub stateside is that there's only one other one in the country that I know of, whereas the Brits all get together for "sticky weekends" and swap knowledge and manpower. Oh well, maybe these little skiffs will catch on around here. Thanks again.

J

 

You know Jack, your posting got me thinking about a long desire of mine. I reviewed the Cherub website and found the class idea interesting, but I could find no fleets in the USA. I like building and experimenting, but the few classes that allow that have become very costly go compete in (C-cat, moth, etch) because of competitors pushing the limits of materials.

There is the Puddle Duck class too, but you are limited to a real small and ugly hull, but I like the low cost idea. So how to create a class of sailboat racing that encourages creativity and innovation, but keeps the costs low?

A class that would allow class racing to be faster and more competitive with a bigger sailboat, at a low enough cost to open it up to many hobby builders and families that enjoy water sports. Anyone with a modest income could build several experimental hulls, sails, etc. without it becoming a financial burden.

I though about starting a thread on this topic to solicit ideas, but my thinking was a "box" design class (or classes) that only limits the structural material to wood or some such thing. Than i thought if we could get a store chain like Home Depot to sponsor the class, the rules would simply allow any materials that are only available from Home Depot (or something similar).

The rules would be simple: 14' overall length, 8 ft max overall width, 16 max mast height from lowest point of hull, CDX plywood hull, all structure; mast and boom(s) of wood (no reinforced plastic like fiberglass, graphite, kevlar, etc.) Sails must be of plastic tarp, house wrap (Tyvek), sheet plastic or similar.

You could also have a 16'x8'x 20' tall two crew class, and perhaps a similar sized multi-hull class.

what do you think? How would you develop such a class?

 

Petros, the idea has a lot of merit. Personally, I'd skew more towards carbon/glass, mylar sails and all other things high-tech. However, it'd be really cool to see what kinds of hotrods people could build from simple commercial materials. I think you'd really like what Bistros has done here: http://bit.ly/2mivv I don't know if he's going to make Tyvek sails or get some 'proper' cloth cut, and the quality of wood he used is probably not available at the Home Depot, but it's way closer to your idea than most of the other homebuild boats. I suppose that I'd see this idea going more towards a one-off competition type of thing: box rule, only stuff from Home Depot, first across the line wins. That would at least be a really cool way to see what the creative folks come up with, and then maybe combine them into some type of 'class'.

 

The problem with the Home Depot idea is that you really don't control costs that well. I could buy lousy wood at Home depot and mill it into veneer, throwing away the stuff that isn't any good, I could then cold mold a hull with glue that really wasn't correct for the job, but I would sacrifice quality and longevity for performance, and I would out spend you and build a faster boat. So all you are boats that aren't worth the time and effort spent on them.

On Cherubs, there is a guy named Skip Kovacks who was building a Paterson 7a in Annapolis.
That would be a good place to start if your heart is set on a Cherub, Jim Champ and Andy Patterson also regularly contribute to these threads, so there are resources beyond what you can find at www.uk-cherub.org.
If you are more flexible about the boat you intend to design and build, here are other alternatives that have a US constituency. I am personally pretty invested in the International Canoe, which offers an interesting design space and very rapid boats. The nearest concentration of boats is in Annapolis. Because the rigs are smaller and there are no kites, the rig costs are more managable.
SHC

 

Thanks Steve, I saw Skip's photos on the Cherub page. Maybe that mold is still around? I'll try and track him down. I'm not even sure I'll ever get around to actually building a boat, I'm hopeful. I really would just like to get somewhat familiar with the software and since I like the Cherub so much I thought it'd be a neat place to start.

I think you're right about the Home Depot thing, but couldn't you just set a max amount of $? I guess that'd be hard to police, and it would possibly stifle creativity. Another problem would be hardware and lines. My Hope Depot is low on Vectran and Harken cheek blocks.

 

Personally speaking my time is too precious to waste it on poor materials. And sails made out of plastic tarp or whatever are so nasty to use and perform so badly that they would only lead to frustration. No matter matter what you build the hull out of spars gear etc is still going to add up to a significant sum of money so I want a result that I can be proud of and enjoy using...

I won't get much satisfaction from taking my boat to the sailing club and saying, look I built it myself, it looks like hell, is a pain in the neck to sail and doesn't go very well, but I saved myself 15% of the cost by using inappropriate materials...

Hullform software from Australia will let you download a cut down version that is more than adequate for designing a straightforward racing dinghy like a Cherub, and winning boats have been designed with its help.

 

I agree, further there is no way to regulate working harder. You can build a perfectly good 1930s era racing dinghy from Home Depot material, some things, like urethane glues are way better than what Uffa had to use, but it will not hold a patch to what can be dome with good stuff.
A friend of mine explained it this way: You will be spending several hundred hours building something. You are doing this for your amusement, curiosity, recreation and fulfillment. You should use whatever materials you WANT to use.
I don't use any hull design software, I prefer to just use Auto Cad and work out the sums with a few spread sheets. Probably dumb of me, but I have never been able to get any hull design software to do what I want instead of what IT wanted.
SHC

 

Thanks for the HullForm recommendation. The folks at UK-Cherub seem to be keen on this package as well. I'm going through it right now, seems a little less complicated than Delft.

I think Steve is right on with the Home Depot dinghy thoughts. Those are the reasons that I suggested it may be cool to just have a one-off Home Depot dinghy competition. Box rule with a $ limit. I suppose that it would really just devolve into a competition of who could build the best sail from Tyvek.

J