Cedar Strip: hull form & oilcanning

[sailsman63]

No Title

And I thought that I had the design finished!

I had actually started lofting lines to form material, and realized (actually, my dad pointed it out - always good to have another set of eyes!) that the chines seemed a little sharper than I intended. I pulled down one of my old forms, and he was right. Attaching here a drawn line, compared to the last design I had posted, and to what I am now going to build.

New delft file up, this is what I am going to build! Probably cut forms today, and yes, there will be a build thread.

https://drive.google.com/open?id=0B8dhNVBeB9VTUjZBUWV5X2QxRW8&authuser=0

In the images, the purple line is center form for my last canoe. Current design I am designating KnuckledCanoe3d "The Experiment"

static stability looks to be right about the middle of the designs I've been goofing with, 1.47 ft metacentric height.

4" WL right on 400#
2.4" WL for 200#, so solo and trimmed flat, I should just have the entire hull to the stems wet.

 

[Alan Gage]

Way to go! Can't wait to see it start to to take physical shape.

How did you get the forms out of delftship? The only way that worked for me was to export the entire lines plan as a .dxf and then delete all the lines I didn't need in Rhino. Then shrink the forms to account for strip thickness, close them on the top side, and cut out the bow and stem forms from the entire hull profile. A lot of work the first time. Not so bad the second time.

Alan

 

[sailsman63]

I went a little more old school. Don't have access to CNC, so will be bandsawing.

- Export stations.
- Open the text file, translate the fractions of feet into inches. (You get to throw out most of the numbers here - only really need 8 points or so, and that includes some to define the knuckle.
- Measure out your points right on the form stock. A carpentry framing square is great for this.
- Fair with a spline (bandsaw blade works well in tighter spaces)
- Make sawdust!

Luke

 

[Alan Gage]

No CNC for me either but I like to print out full size forms and transfer them to the plywood with carbon paper. I didn't have any luck importing the text file into other programs and receiving anything usable, though I'm sure that's my inexperience rather than a fault with the software or method.

How did you get a profile for the stems? I didn't see anywhere that Delftship gave that.

Alan

 

[sailsman63]

I didn't have any luck importing the text file into other programs and receiving anything usable,/QUOTE]

Well, I didn't import to other software either. didn't think it was worth a special script for something I only do once in a while. I just opened the text file and ran through manually with a calculator, typing in another file as I went. I'm spacing the forms 18" so not all that many to do - total of five unique stations.

Have not done the stems yet, but will probably just take some measurements off the side view, as the stem profile is pretty simple. On thing that I need to decide (soon) is how I'm going to build the stems. I've done stemless before, but has trouble with a clean finish inside. Was going to do an inner stem, but after seeing you flotation tanks, I'm wondering if that is the way to go? Have you had any concerns about slow seepage into the tanks?

Luke

 

[Alan Gage]

On thing that I need to decide (soon) is how I'm going to build the stems. I've done stemless before, but has trouble with a clean finish inside. Was going to do an inner stem, but after seeing you flotation tanks, I'm wondering if that is the way to go? Have you had any concerns about slow seepage into the tanks?

Luke

No worries about leakage into the tanks unless I do some serious damage to the bow/stern, they're sealed up tighter than a drum. Also a good chance I'll punch a hole in them and add a hatch for some dry storage. I think the tanks will be nice but they were also more work. Whether or not I use that method again will depend on the intended usage of the boat.

Stemless seems like the easiest method to me. Using an inside stem, like on my current build, was easier in some ways and harder in others. I'm not sold on it yet but will probably try it again to give it the benefit of the doubt. Tough to say how easy/hard something is when you've only done it once. I think a tapered stem gives a much nicer appearance to the outside of the hull but I sure think it looks ugly on the inside.

Alan

 

[sailsman63]

Well, I managed to fall out of my last canoe twice. Luckily, both times right at shore. The second pretty much completely swamped it, and I realized that a little reserve flotation would be a good thing, as if this had happened out on the water, I would have been in trouble. Hence the curiosity about the float tanks. From what I gather, 1 Cubic Foot of airspace would provide about 64 lbs flotation, though I doubt bow and stern tanks would approach that...

When I've done stemless in the past, I ended up with the photo linked. The other canoe I filled with epoxy and wood flour. Neither meets what I would prefer. When I've considered using an inner stem, I would pretty much do the whole stemless thing, interlock and all, but with a backer inside so that I have a radius to run the glass around, if that makes any sense...

 

[Jim Dodd]

I feel flotation chambers are well worth the effort. In moving water, they can be life saving. I guess that's why the Coast Guard requires all commercially made boats to have flotation.
I also prefer stemless construction, I find it to be, every bit as strong or stronger than a canoe built with stems.A few layers of cloth, saturated with resin, seals and adds plenty of strength to the inside stem, without a lot of weight.

Good luck on your build !

Jim

 

[Guest]

Well, I managed to fall out of my last canoe twice. Luckily, both times right at shore. The second pretty much completely swamped it, and I realized that a little reserve flotation would be a good thing, as if this had happened out on the water, I would have been in trouble. Hence the curiosity about the float tanks. From what I gather, 1 Cubic Foot of airspace would provide about 64 lbs flotation, though I doubt bow and stern tanks would approach that.

A couple of friends were doing a day trip in an empty carbon Bell Prospector with miniscule float tanks. That was a loaner canoe for review from Bell and several of us had kind of laughingly notes the wee size of the float tanks before launching.

They capsized while attempting an attainment on a deep narrows. When they dumped it the canoe vanished from sight and didn’t reappear for several minutes, by which time I was convinced that we would never see it again. By the time it finally resurfaced 100 yards downstream I was busy thinking about just how I was going to explain this to Bell.

Float tanks, bags or some other auxiliary floatation is good.

 

[memaquay]

Interesting conversation....I have yet to see a stripper sink without float chambers. Mine have all floated pretty well the various times I dumped them. The majority of construction material is wood. As for innies and outies...Alan, the inner stem is a thing of beauty, very nautical and reminiscent. However, without an outer stem, the inner is a lonely ugly red-headed step daughter. You need to have them both to achieve the look. Mine are made out of cedar, and only add about 10 ounces total for the pair, by the time they are shaped and sanded.

I dunno, I find float chambers to be unsightly; stems, on the other hand, excite me. To quote Lady Gaga, Baby I was born this way.

 

[Guest]

I have yet to see a stripper sink without float chambers. Mine have all floated pretty well the various times I dumped them. The majority of construction material is wood.

Wood of course provides its own floatation, same as the foam core in an RX canoe. The carbon Prospector in that episode needed more flotation than was provided by the Lilliputian float tanks. The current took it deep and held it long, and when it finally resurfaced there wasn’t much of it showing above water.

An inch of black hull peeking above water was hard to spot that far downstream. I counted it as a couple of lessons learned; the advantage of float tanks in composite boats and, while I like the look of carbon, it is hard to spot at a distance in a rescue.

 

[Jim Dodd]

I've dumped a couple of my strippers, where little more than the gunnels showed above the waterline. My western red cedar must have been denser. I believe it was my 5th stripper before I wised up on flotation.
I'm building much bigger flotation tanks for my Kevlar hull.

Jim

 

[sailsman63]

I have yet to see a stripper sink without float chambers. Mine have all floated pretty well the various times I dumped them.

As for innies and outies...Alan, the inner stem is a thing of beauty, very nautical and reminiscent. However, without an outer stem, the inner is a lonely ugly red-headed step daughter. You need to have them both to achieve the look. Mine are made out of cedar, and only add about 10 ounces total for the pair, by the time they are shaped and sanded.

Floated high enough to self-rescue in the water? My canoeing includes small to big-ish lakes where there is no handy shore just a dozen yards off.

Took a look at one of your build threads to see how you do your stems. I'd always figured that if I was going to do an outer stem, it would be hardwood & outside of the glass.

 

[memaquay]

Most people who build with an external stem enclose it in glass. The benefits are primarily for capping the ends of the strips and also providing an anchor for the brass stem bands. I used to use hardwood, but found it to be redundant. I have self rescued both my solo (osprey) and the 17.5 foot winisk. In my mind, if you want really good floatation for immediate self rescue, floatation bags are the answer. Not sure how much small chambers are going to provide, most of my white water buddies use bags.

 

[sailsman63]

Well, had a thought and did a little math.

Per deltship, wetted surface at 12" draft (right at the gunwales) for my design is 49.614 Sq. Ft.
At 1/4" thick, the hull material volume comes out almost perfectly at 1 cubic foot, which displaces ~62 lb. water. This means that, at my estimated build weight, the fully swamped canoe would just support itself right at the gunwale line.

Gear will probably change this a bit, depending on how dense it is, and whether it is tied inside the hull, but even a small person would be able to drive this canoe fully under. Means I need something, whether bags or built in. I would probably not use this on a regular basis, unless to practice right next to the dock, but It's really a piece of safety equipment, and I should figure out how to do it right.

Fortunately, that is a decision that can wait until later in the build, but I do need to decide on the stems.

I probably won't do an outer stem like memaquay Because then I loose the sharp, almost knife edge entry of a stemless build. (I really like that look) If I go with an inner stem, at least as I pictured it, It would be more of a pre-placed cedar filet, rather than a structural member. Only purpose would be to provide a smoother surface to run the glass around, without all the weight of a epoxy-and-sawdust putty, which is always painful to work with anyway, and never looks right in those large quantities.

Jim Dodd I was impressed with your fleece-resin trick on the Pearl. But what I would really like to know is: How did you get your glass to lay into the stem as well as you did? When I tried this, I had bubbly, choppy job for an inch or inch and a half back from the stem. Had to cover it somehow, hence my current dilemma...

Or would I be better off laying a bias-cut piece in independently, coming back along the sides for 6" or so, then run the main glass over it by
~3"? Thought here is that with a smaller piece, I can take the time to do it right, without worrying about what I'm doing to the entire inside layup and wetout?

 

[stripperguy]

For what it's worth...On larger boats (17 ft and longer) I typically have decks that are about 24 inches long and fully sealed bulkheads. Even so, I make sure the inside of my stems are well covered in glass. My hulls are usually so narrow at the stems that I can't sand them so well, scraping alone is usually OK. Those fully sealed chambers go a long way to increase buoyancy of a fully swamped hull.
And fillets of epoxy inside the stems? Why not? I have been using Cabosil thickened epoxy for aover 15 years and it really does the job.

 

[Jim Dodd]

Sailsman

I should have someone there to take pictures while glassing the inside side stems !
I cut my main layer cloth, big enough to over lap in the ends.
The cloth is folded back, and saturated. I lay in one side, and use a scrap strip , that is sanded to a chisel type edge. I use this to work the cloth into the ends, and smooth it out, one side at a time. Then the other side is laid over top.
The strip is used like a long putty knife.
It varies, but I try for at least a 2" overlap.
Wear long sleeve gloves.
Jim