International Canoe hull design

[Steve Clark]

Gaijin lines.pdf
For the general amusement.
The recent trend is toward increasingly fine waterlines forward and enough reserve buoyancy aft to allow the helmsman to be about 500mm further aft than previously possible. This reduces speed lost in wave encounters but still allows enough volume to prevent going right down the mine when running.
In light air, it is necessary to move way forward to keep the fat ass out of the water, even so the lower wetted area ( pointier stern) boats are faster. The cross over is just about at 6-8 knots TWS, or once the flow starts breaking cleanly off the stern.
Construction is in a female jig, so foam and composite, tortured ply, and strip are all options.
SHC

[JRD]

Nice drawings Steve, thanks for sharing them. Have you built one of these already or is this hot off the press?
Is this intended to be sailed with the assymetrical kite, or just main and jib?

[sean9c]

Just curious (I don't know anything about anything) Is the LCB on current designs in about the same place? Or has thinning the bow and filling the stern moved it forward?
Thanks

[Doug Lord]

Thanks, Steve. Can you post any renderings of the boat?

[Steve Clark]

3 views.
Helmsman is such a big proportion of the displacement that the LCB pretty much follow him around.
SHC

[Doug Lord]

Thanks !

[BobBill]

Somewhere, in the back of my bean, I read similar comments concerning cat hulls, but alas I did not keep that mag...might have been old One-Design Mag, before Offshore was added, so it is dated. Could have been Rod McAlpine-Downey comment. Do not recall now, dang it.

[waynemarlow]

Any idea of the hulls weight fully ready for sailing excluding rig and seat.

[Steve Clark]

Class minimum weight for complete boat less sails is 50kg.
Too get there, the finished hull with seat carriage has to be in the 25-28 kg range.
The wt/m^2 was based on what is normal in the A Class.
This is "pretty easy" to achieve out of foam and carbon and "pretty hard" to achieve out of plywood. I have built 7 boats to the new rules, The 3 carbon foam ones were on weight, the 4 plywood ones were 5-10 kg heavy. Others have been closer with plywood than that, so clearly I need to rethink some of the scantlings.

SHC

[Doug Lord]

Steve, where do you see the major areas of development under the new rules?

[CutOnce]

Originally Posted by Steve Clark

Class minimum weight for complete boat less sails is 50kg.
Too get there, the finished hull with seat carriage has to be in the 25-28 kg range.
The wt/m^2 was based on what is normal in the A Class.
This is "pretty easy" to achieve out of foam and carbon and "pretty hard" to achieve out of plywood. I have built 7 boats to the new rules, The 3 carbon foam ones were on weight, the 4 plywood ones were 5-10 kg heavy. Others have been closer with plywood than that, so clearly I need to rethink some of the scantlings.

SHC

Steve:

Interesting. There are probably more issues at play than just the scantlings.

Plywood implies joins and seams, which makes fillets and taping come into play. The same area of the hull in foam/carbon would have no "extra" material. I don't doubt your choices in the slightest regarding structure and materials and I doubt you made anything bigger/stronger/heavier than experience had taught you. I watched your development of the plywood egg-crate sliding seat (and saw you come back to the dock with a slightly underbuilt one in pieces), so I know you don't err on the side of Soviet design.

There is a bit of a skill+/cost+ divide between the two methods as well. I have no trouble with imagining my ability to build a plywood version, but I know I lack experience to execute a well-done foam/carbon hull. People like me who live on the cheap side of the tracks (priorities) will probably opt for less expensive execution on the non-hull components as well. So many plywood builders would be paying a weight penalty for both plywood and non-Gucci choices are well. If I had been smart I should have offered a week or two of free labor as an intern/sweeper at the Lab of Luxury years ago.

I should have listened to Willy and you five years ago when you guys were gently trying to steer my interests to the IC. Now I'm dealing with early onset arthritis and I don't know if I've got the dinghy time left to start a new project. There are days my elbows refuse to unlock. I hate the thought, but I think my skiff/trapeze days are running out.

The minimum weight for the new design IC's seems to be set a little too low for the average garage ply builder to hit target, so unfortunately the arms race will result in a divided class separating the rich from the poor (at least theoretically). I know the differences on the water are completely dependent on the person sailing, but psychology can't be ignored. If you and Chris Maas are straining to hit plywood weight targets, the average garage builder hasn't got a chance.

What are your thoughts on cedar stripping and weight on this hull? Do you think a 3mm strip hull with carbon could achieve better results than plywood? Basically, by avoiding plywood could a foam/carbon competitive hull be arrived at by increasing labor? Maybe my fear of foam/carbon construction is unfounded and I'm looking for a solution to a problem that isn't valid.

Just a thought.

--
CutOnce
(Bill in Ottawa)

[BobBill]

Why not acquire a large block of suitable foam. add structure, glass up and so on?

Is that possible?

[CutOnce]

Originally Posted by BobBill

Why not acquire a large block of suitable foam. add structure, glass up and so on?

Is that possible?

As I tell my clients, anything is possible. Probability is another issue entirely.

Optimal composite construction techniques are achievable in less than optimal facilities, but require a minimum level of equipment, skill and non-recurring engineering and tooling expense.

First, some method of achieving a surface from which to mold the desired part is required. The typical method is to construct a male pattern/part, prepare the outer surface and make a female mold from that part. With further surface and structural prep, the female mold is used to create the final product.

Builders usually take quite a bit of time creating the original male pattern - because mistakes with this are repeated on every copy made. Symmetry, fairness and avoiding hollows and release problems have to be considered. So basically, you are building a complete, perfect hull that isn't often used as a boat. Serious people like Steve use 3-D CNC equipment to generate femaie molds directly from CAD files.

This "as close to perfect as possible" male plug is used to create a female mold. Using a female mold means to the external surface of the final product is optimized and will match the mold. As this is the surface in contact with water, you can see why people use female molds more frequently than male. After all this, no one wants to have major work re-fairing a hull pulled from the mold.

Creating the material layup schedule, fitting core material and then achieving a final composite structure with just enough resin (for light weight and maximum strength) requires skills (& equipment) I don't have right now - vacuum bagging, resin infusion etc. Avoiding extra work on the internal surface requires the use of peel ply. Once the part is pulled, optimal results are achieved by curing the part in a suitable temperature controlled oven.

From what I can see, good results start from:
- optimized CAD output from naval architecture software,
- CNC production of parts (2-D stations for cedar stripping a plug) or female mold components (a order of magnitude larger CNC required)
- superior mold preparation and surface prep,
- quality composite layup schedule, core material and resin,
- vacuum bagging / resin infusion,
- post cure ovens

All this is before you start dealing with internal structure, adding bulkheads, decking etc.

It is never as easy to do as it is to talk about. Experience and skill is more important than all of the above. Someone like Steve Clark can produce high quality parts in his home shop that many composite manufacturers in optimal facilities will envy - but I doubt my ability to do so.

--
CutOnce

[DCockey]

I talked to John Lindhal, a successful builder of A-cats, about his method of using carbon fiber / epoxy over closed cell foam strips to build the hulls. The hulls are done in two parts. For molds he uses female plywood station molds, cut by CNC router, at 12" or so spacing (may be closer). The foam strips are laid into the mold, very similar to the way a wood strip hul would be built. The inner surface is then covered with carbon fiber and epoxy. I saw a sample and thought he used vacuum bagging but he said it was just knowing how to use a squegee. After both hull parts have the inner carbon fiber / epoxy in place, they are glued together with carbon fiber / expoxy along the seams on the inside. Then the outside is covered with carbon fiber / expoxy. It sounded like he usually gets below the A-cat minimum weight and has to add ballast.

[DCockey]

Website with photos of John Lindahl's method: http://lindahlcompositedesign.weebly.com/lr4-build.html