Cedar Strip: hull form & oilcanning

[Qayaq]

How about this solution to oilcanning. A full 1"x5" board wedged and screwed under the seats and thwart. Just picked up this boat to do some evening and weekend paddling for my remaining 3 weeks in Sweden. Believe it or not, this is about the best boat I've found for less than $500. I'm calling it the Red Devil. Oh yeah, and it leaks.

 

[memaquay]

Whew, I know it's not right to call another man's canoe down, so I'll just call it unique. Those Swedes better stick to cheap furniture making.

 

[sailsman63]

No Title

Qayaq well... it seems like it would work... somehow. Are you sure that the locals aren't having a laugh at the expense of the out-of-town guy? Hope you get to enjoy your paddling.

Alan Gage Well, tried out DelftShip. You were not kidding about the learning curve! I think mostly it's because they don't use standard shortcuts/conventions for some fairly basic stuff, and their modeling tools are really lacking when it comes to creating a new hull form from scratch. Anyway...

I've got a delft model of what I'm looking at attached here. Anyone who wants to play around with it, feel free.

If you have the name of the software you are using for stability, I'd be somewhat interested in the results. I found another free program, supposed to be more for smaller ships/boat that does do stability calcs, jSDN, but have not downloaded, as I really don't want to mess with another new program unless it has lots of advantages.

One thing to note about this design: I did experiment with adding a more arched bottom, to add a little below-waterline fineness, but it appears that the difference in resistance is minimal, at least in the 0-5 knot speed range. If anyone has another thought on that subject, feel free to tell me.

 

[Alan Gage]

Polycad is the software I use for stability calculations. It's free but if I remember right you have to e-mail the creator for a passcode to unlock it after downloading. It's supposed to be a powerful hull design program in its own right but I was completely lost with it and couldn't get it to do the most basic functions. I didn't find a "help" section and there are very few good tutorials on it.

But there is this youtube video, which introduced me to the software and how to perform stability calculations. I don't have speakers on this computer so I can't listen to it but if I remember right the fella has a pretty stiff accent and it can be hard to understand him. But it's a simple enough process and following his steps should get you there.

https://www.youtube.com/watch?v=MzFI-dlmllE

I'll see if I can open your attached file in delftship.

Alan

 

[Alan Gage]

I wasn't able to open your file, it locked up the file every time I tried it. I'm not sure why.

If you're already familiar with CAD programs we might find the program confusing for different reasons. Me because I had no experience with any sort of computer drafting (other than straight lines when designing my house) and you perhaps because it doesn't respond like other CAD programs.

When I open a new file I enter my parameters for length/width/draft and then edit the generic hull they build. Closing in the transom gave me fits at first but after doing it a couple dozen times it became quick and easy. A big breakthrough was realizing that points can be set to "corner points", which, if I remember right needs to be undone on one of the transom points. Or maybe it's that you need to turn it on for the uppermost point at the end of the stern? All I really remember is that it twisted my tail for a while.

You can do a lot with just the basic adjustment points given in the generic model. I try to do everything I can with those and only add control lines as needed. The fewer control lines the better for most things. When I add more, especially the ones edited in the "bodyplan" view it tends to get messy in a hurry. You can do a lot just by where the control lines are placed. I worry about the rough hull shape first before I get too carried away getting the tumblehome exact. Come up with a quick below water length, width, and general hull shape you're happy with and then start working the above water components into it.

Thankfully there are a lot of Delftship users out there who have posted tutorials or forum questions and it has a decent "help" section. It can still be very frustrating trying to find what you need though, most information is based on sailboats or ships.

A couple things that jump out to me on your initial design:

I think the bottom should be rounder with a more gradual transition to the sides. I think that would improve looks, feel, stability, and speed.

The knuckled tumblehome doesn't have to remain constant from bow to stern, it's normally tapered. Gives it a nicer look and keeps flare where it's needed most and tumblehome is needed least.

I believe you said you don't have a canoe at present and that will make things harder. I've got a whole shed full and while I didn't copy any of them it sure was helpful to look at hulls of various lengths, widths, and shapes to see how things were shaped and what the dimensions were at certain points (e.g, how wide 24" from the bow, how far down does the tumblehome start, etc). You definitely start looking at boats with a different eye.

Go to manufacturer's websites and look at boats you think you might like. Pay attention to how they're shaped. Look at woodstrip plans available online. Greenval and Bear Mountain many times show a small image of the lines. Look at how they're shaped at the bow, center, and stern. You certainly don't have to do it exactly like them but they do know what they're doing so if your lines look similar to everyone else's you can't be completely off base.

I'm attaching a couple files from the boat I'm building now with the sharply shouldered tumblehome. Hopefully you can open them. One version is nearly completed but I haven't added the shear strip yet. I save that as a final step since it's a simple matter of "extruding" the top edge up 7/8", or whatever height you want, and it makes it a lot easier to edit the hull before that's done. You just need to keep in mind as your designing that the hull will get about 1" added to the depth.

The second file is the completed hull with the shear strip added. There are probably some other minor hull tweaks in there too.

Ok, it says the second file is too large. I'll try it in a separate reply.

Better yet let's scrape the file upload all together. Send me a PM with your e-mail address and I'll just send them to you.

Alan

 

[sailsman63]

No Title

I wasn't able to open your file, it locked up the file every time I tried it.

Huh... Odd. I just downloaded from here to check for issues, and was able to load fine. Did you extract the .ZIP first?

you perhaps because it doesn't respond like other CAD programs.

Not so much CAD, per-se, but modeling programs. Subtle difference. I could provide quite a list of things I don't like about the UI, but the main ones are: no good way to select multiple control points, No on-screen visual feedback scaling, no way to scale around center of selection. Also, you should be able to start with a blank screen and just add a few points, create a curve from them, and you're off. Had to import what I had through a non-standard text file, and even then, It didn't integrate those curves into the model, it used them as a suggestion for creating a surface the way it wanted to. Oh, well. Back to canoes!

I think the bottom should be rounder with a more gradual transition to the sides.

Think you might be right. Posting an updated picture of what I could do. Keep in mind that, even though I'm experimenting on the computer, I might be modifying an existing set of forms, and the curve shown earlier is what I have built already.

I'll run the hydrostatics tomorrow to see what difference that made, if any.

knuckled tumblehome doesn't have to remain constant from bow to stern, it's normally tapered.

Do you mean in a transverse direction? Or vertically? I'm attaching the "buttock" lines for the latest iteration. The last foot or so of the hull on each end is at full flare, though I could probably ease that out closer to the center.

the boat I'm building now with the sharply shouldered tumblehome.

This was intended to be the one from the "Solo Expedition" build thread, no? I've very much enjoyed that thread - convinced me that a sharp knuckle is do-able in strips. One of the reasons that my plan has the tumblehome feathered so close to the ends, is I want the gunwale curve to be more sweeping. You have that section near the center that is nearly straight... not quite what I'm going for here.

I need to get offline for a while. Thanks for the feedback!

Luke

 

[Muskrat]

I agree with Alan. The bottom is very flat. The second rendition looks better in that regard. I also was unable to open the file in DelftShip. Nothing happens when I try to open it. DelftShip shows that its trying to open the file, but nothing ever materializes. I agree with Alan on the tumblehome too. The tumblehome knuckle is too bulky the length of the boat. The knuckle should meet the sheer line at the bow and stern and gradually flare to its full extent. Also, if I'm looking at it right you have over 4.5" of rocker? That is a lot of rocker unless its only going to be a downriver boat. Can you tell us what the sheer heights are? I suspect they may be a little much for the width of the canoe. Take a look at Wenonah's Solo Plus for an idea of basic dimensions. Also, Northwest Canoe has free plans. They come as a .pdf, but you can put them as a background image into a CAD program and get the measurements fairly easily. Like Alan said, get as many lines of reference boats as you can. One last thing, maybe I missed it, but can you give us a displacement at a couple different water lines?

Isn't designing fun? I have over 12 major reworks of the design I'm currently working on. Looking back, my first couple renditions were terrible, but it has really taken shape after a couple months of on and off work.

 

[Alan Gage]

I have over 12 major reworks of the design I'm currently working on. Looking back, my first couple renditions were terrible, but it has really taken shape after a couple months of on and off work.

Isn't that the truth! Every time I make significant changes to the design I save it as a new version, starting with V1, in case I make it worse and need to back up a step. I usually end up with about a dozen and when I'm all done I cringe when I go back to look at the first few.

Alan

 

[Alan Gage]

It looks like your hull is starting above the "base line". I think it needs to touch the base line at its lowest point (bottom of the center of the hull) for measurements and calculations to be accurate as I believe it's basing shear height, rocker, draft, etc from the baseline.

Alan

 

[sailsman63]

No Title

Thanks for the Comments!

Muskrat

I also was unable to open the file in DelftShip. Nothing happens when I try to open it.

Version Compatiblity issues?

Thanks to the pointer to NorthwestCanoe. I'm grabbing several of their plans just to take a peek.

The knuckle should meet the sheer line at the bow and stern and gradually flare to its full extent.

Is the for Asthetic reasons, or am I missing something more?

Alan Gage Is correct about the arrangement of my baseline. Long story, I've fixed now & updated pics posted here.

Now some numbers:

13.25" Sheer Midships (Deeper than I intended, by about 1.25")
18" Sheer @ stem. (very in line w/wenonah Solo Plus)

4" DWL

28.75" BeamWL
32" BeamMax

1" Rocker @ 2' from stem. (John Winters & Stewart River - compare to their version of Chestnut Pal)
2.75" Rocker @ stem.

Displacement:

392# @ 4"
457# @ 4.5"

200# @ 2.4" (Solo: Me + Boat + day gear)
Expect it to be a bit more lively this way.

This is really starting to be a rather different boat from what I started with... I'm having a bit of fun with this, but I'd rather be building!

More numbers, extra WLs, etc. linked to a fileserver. Also trying to put the delftship file there, in case it's something to do with the zip process.
https://drive.google.com/folderview...9BamdnaWp3cG9MZms3VG9ZaUU5ZDZaUFE&usp=sharing

 

[Muskrat]

OK, I downloaded the latest version and I'm now able to open up the latest file from your drive folder.

The knuckle fading into the sheer is mainly for aesthetics, but it also allows the hull to flare out farther back, giving better wave shedding. Most waves that dump into the boat happen about a 1/4 to 1/3 of the way back from the stem. The longer you can keep the flare the drier the ride. Save the tumblehome mainly for the middle, especially for a narrow canoe like this one, there wont be any problems reaching the water from the bow or stern seat. Just from eyeballing it, I'd raise the knuckle at the center about an inch and then gradually curve it up to meet the stems.

Now that the baseline is set correctly, I'm feeling better about the other measurements. That's still quite a bit of rocker. Your stems will be barely poking out when you're solo.

I'll let Alan critique any further, as I am working on boat designs other than canoes and this is about my familiarity limit when it comes to canoe shape.

If you haven't got it already, John Winters has a great book, The Shape of the Canoe, available on a CD in .pdf format. You can get it through Greenval.

 

[Alan Gage]

It's starting to look pretty good. How have your resistance and stability numbers changed? The "GZ" reading given at the top of the Bodyplan view is a quick indicator of stability. I believe it's mostly indicating primary stability but it's nice to have something right in front of you as you make changes. Figuring out how it relates to real life is another matter.

I think the tapering tumblehome is mainly for aesthetics as well but I really do think it looks nicer.

Your stems are very sharp at the bottom curve. You might see what it looks like rounding them a little more at the turn. Racing boats that are meant to go straight tend to have sharp stems like that but most general purpose canoes have a much rounder profile. I think this will have large affect on maneuverability. Last weekend I was talking to Jim Dodd and he mentioned he once heard David Yost say the rocker right at the stem is what really matters and from my experience I'd tend to agree. I think you could have a perfectly flat keel line and still make big differences just by changing the shape of the last couple feet at the stem.

Sounds like you're starting to have fun with it. I found it pretty addicting. Don't feel locked in on using or modifying the forms you already have. If you're going to the trouble of building an entire canoe $50 worth of plywood and a few hours to cut out forms is nothing.

Alan

 

[sailsman63]

Thanks, Muskrat.

​

Most waves that dump into the boat happen about a 1/4 to 1/3 of the way back from the stem. The longer you can keep the flare the drier the ride

Worth remembering. I'll be thinking about fading the knuckle back to flare closer to center. May also try fading it up but I personally like having the hard line at the same distance below the sheer, or maybe a touch flatter, just from a looks perspective.

That's still quite a bit of rocker. Your stems will be barely poking out when you're solo.

Yes, I may have to cut this back a bit. The last one, the problem was that there was too little rocker. (measured ~1.25") A solo paddler, maybe a bit larger than myself, couldn't break the stems free by rolling even when he wanted to... balance in all things!

Alan, Stability (at least, initial stability as measured by "MetaCentric Height" has increased. 1.58' VS. 1.43'

Resistance @ 5 knots (Kaper numbers) is reduced by about 8.1% (11.5 oz.)

Racing boats that are meant to go straight tend to have sharp stems like that but most general purpose canoes have a much rounder profile.

One of the things I liked about my last build (where I got those stems from) was that when trimmed flat and reasonably loaded, it would track straight as an arrow. I'd be willing to consider such a change, especially since I've read that such sharp stems can get caught in a wave and make you broach if out in a bit heavier weather. (We all know that the weather report is never wrong, don't we? ) I'd just like to understand what I might be trading off.

once heard David Yost say the rocker right at the stem is what really matters and from my experience I'd tend to agree.

I've read similar from some articles of John Winters' that are posted on the greenval site. Again, one of those trade-off points.

 

[Alan Gage]

Thanks, Muskrat.

Yes, I may have to cut this back a bit. The last one, the problem was that there was too little rocker. (measured ~1.25") A solo paddler, maybe a bit larger than myself, couldn't break the stems free by rolling even when he wanted to...

One of the things I liked about my last build (where I got those stems from) was that when trimmed flat and reasonably loaded, it would track straight as an arrow.

So you're hoping the sharp stems will track nicely when paddled straight ahead and that a good deal of rocker will break them free when heeling? It will be interesting to see how that works out. If you can get the Polycad software to work it will show you the water line on the hull at whatever angle of heal and load you choose so you can see when/if the stems break free. It also shows how much righting resistance there is at that angle of heel.

Like you said, it's all a balancing act.

Alan

 

[sailsman63]

So you're hoping the sharp stems will track nicely when paddled straight ahead and that a good deal of rocker will break them free when heeling? It will be interesting to see how that works out.

Do I note a bit of skepticism? Don't blame you. When put like that, it does seem a little... reaching. Still might be worth trying sometime.

Three new tweaks, in progression, added tonight. Same shared google drive folder: I've pulled back some of the rocker, and tried softening the stem line a bit. A larger proportion of the rocker is now concentrated near the stems, and the softer line should reduce the "tripping over the stems" effect that I have read about, and that on reflection was present in my previous builds, though I didn't really understand the cause then.

Have not yet tried any of these in Polycad yet (tomorrow's project) But I think I'm getting close to what I will actually build.

Also did some tweaking on the topsides. Muskrat was right about the knuckle being too blocky. I readjusted the flare so that three feet of each stem are fully flared. didn't quite look right (3a) until I faded the knuckle up towards the sheer. (3b) I may also re-fair those curves in the morning, when I'm fresh.

The wetted hull changes have increased DWL displacement by 9% (!!?!!) and also upped estimated drag by a small fraction. Any thoughts on how to fine this out without losing the entire shape and proportions?

 

[Alan Gage]

Do I note a bit of skepticism? Don't blame you. When put like that, it does seem a little... reaching. Still might be worth trying sometime.

While I am a little skeptical I didn't mean it to sound like that. I really am interested to see how that plan would work out. Part of the fun of designing your own boat is to draw up somewhat off the wall ideas.

Alan

 

[Jim Dodd]

It looks like your having fun ! Nothing gets me more excited, than building a new design !
Or seeing someone else's design and build !
Keep at it boys !

Jim

 

[sailsman63]

Alan Gage Have you ever had issues importing to PolyCad? I've got PolyCad 10 here, in trial mode. I can get the list of importers, but they are all greyed out. Cannot select one. Is the trial license feature-locked or something?

 

[Alan Gage]

I didn't have any issues with it. Have you gotten the unlock code? I don't think I used it at all until I'd unlocked it (still free).

Alan

 

[sailsman63]

I did not get the unlock code. Frankly, I was intending to just run in trial mode for a few days, and then probably un-install when done. May have to re-think that.