Solo daytripper - design ideas

[sailsman63]

More stuff to think about....

Jim Dodd I've tried sitting on the bottom, and even with back support, its just not my thing. I like to be about 3-4 inches off the bottom at minimum. Perhaps this is due to the sheer height that I've been dealing with. I wouldn't be kneeling to lower my Center of Mass. I'd use the stance more for active precision maneuvering, such as snaking through tight channels. This would be forward of my seated position, but probably leave my mass a little higher.


Alan Gage We are definitely looking at the same size class here. You've got a flatter bottom and harder chines than I'm considering.

I did end up reducing the WL beam to 24" and I have to say that the lines seem a lot more graceful that way. As I expected, I lost about 17# of design displacement, which means that I'm right at the design load, if I can keep the build down to the 30# range. An extra 1/4" draft brings me back to about 200# displacement, but I don't need room for a canoe dog.

Question: You've designed asymetric hulls before. I have what I thought was a fairly significant difference in rocker profiles front and aft, but I see that the lateral Center of Area is only back from hull centerline about 3." Does this seem about right?

 

[Muskrat]

24" at waterline is very narrow. That's slightly narrower than John Winters Barracuda for example. Which if you're not familiar is a pretty extreme speed hull. I haven't opened your hull up in delftship yet, but just based on the numbers and hearing its got a fairly rounded bottom, I'd consider bumping the wl beam up closer to 26" if you ever want to relax and not worry about keeping the boat upright.

 

[Alan Gage]

24" at waterline is very narrow. That's slightly narrower than John Winters Barracuda for example. Which if you're not familiar is a pretty extreme speed hull.

I built a Barracuda and can say that it isn't nearly as tippy as you'd think. I actually find the stability quite comfortable and if I'm going out for a relaxing day paddle it's usually the boat I grab.

EDIT to add that all else being equal (hull width and profile) a 17' canoe should have more stability than a 14' canoe.

You've got a flatter bottom and harder chines than I'm considering.

I noticed that too. I was going for a bit more stability and shallower draft with a larger load. This boat might see some light tripping as well. If I remember right my 3" waterline was 26". Have you run any stability calculations on yours? I haven't had a chance to open your file in Delftship yet.

Question: You've designed asymetric hulls before. I have what I thought was a fairly significant difference in rocker profiles front and aft, but I see that the lateral Center of Area is only back from hull centerline about 3." Does this seem about right?

I don't pay much attention to those numbers but yes, I believe that's in line with some of the boats I've done.

Alan

 

[sailsman63]

Thanks for the thoughts. Sorry that I have not responded sooner. I've had stuff just go nuts - spent two weeks training into a new job (second in three months) and the weather has been nice, so I didn't want to spend it all in front of a computer.

@Muskrat: I suspect that part of stability issues would come from weight distribution. I'm not too far off a Bell Flashfire, which I actually found rather nice.

@Alan Gage: No stability calculations, but metacentric height, which is an indicator of initial stability, seems a lot like my tandem.

New file up: https://drive.google.com/open?id=0B8dhNVBeB9VTZGc3TGtmNllTS0k

I've dropped the sheer line a bit, and worked on smoothing out the hull design. Still showing a hard knuckle, but I'm still mulling that one over. If I did something else, I would probably hand-loft on the form stock.

This is a true asymmetric, not just a differential rocker. It should trim fore-and-aft with just a little shift of weight to adjust for paddling conditions. I've found that I'm heading toward a slight V-shape in the stems, though I'm keeping the bottom rounded in the center of the hull.

 

[stripperguy]

sailsman,
Which version of Delftship did you use?
I can't open your latest model in my version 9.10 (301)

 

[sailsman63]

I just let the auto-upgrade run last week, I'm on 9.12 (303). Delftship seems to be one of those programs that does not care much about format compatibility....

 

[stripperguy]

I looked it over..what was your design displacement?
Are you still gonna add some sheer to it?
And I guess you like that knuckle, so do I. That feature serves many functions. That design feature was why I was initially drawn to the Kite...

 

[sailsman63]

I was targeting something in the 180#-200# range at the three-inch waterline. This would be a light build, shooting for about 30# for the hull weight.

Add sheer? Where along the hull were you thinking? I dropped the stem sheer to 15" rather than the 17" that I started with, perhaps that is a bit too low. I may also raise the midships sheer a bit.

I like the results of the knuckle. Case in point, I was able to paddle my (Much wider) tandem from the midships position today. (Forgot my ballast bag) Not the most comfortable station, but without the knuckle, it would have been impossible. I'm less enamored with building and glassing that sharp edge. I'm considering that whole area a work in progress, more so than the rest of it at this point.

 

[stripperguy]

Looking at you model, I'm measuring 10.62 inch amidships...The sheer line does have a beautiful sweep to it though.
24 inch at design load should be fast enough for that length. I'm curious to see how it might track.

 

[sailsman63]

That matches my measurement as well. I've gone back and checked - my tandem is 12.5" deep midships. Would you expect me to have issues with the lessened sheer? I can smooth out the sweep if I have to at just about any height, though right now, everything just seems to "flow."

Hopefully, it would track reasonably well. It's balanced on a bit of a cusp, very small shifts of weight make significant shifts in trim, and therefore in the underwater shape as well.

I've got the Lateral center of area behind the center of buoyancy, which should tend to balance toward forward motion. I also have the hull shape such that more of the rear half of the lateral area nearer to the stem, so that it has more leverage. Odd that delftship does not have a good way of graphing this, or of running numbers at several trims.

I'm not necessarily looking for a hull that needs no steering, I just want to not have half my effort go into correction...

Trimming forward will have a more balanced hull form, for better maneuverability. (about .45 Degrees should give me an inch difference in trim...)

That hard knuckle, though, has me fussed. It runs all the way to the stems on this hull. I know I can do it, not sure if I want to... I'm trying to figure a way to soften it just a hair. What would you say to a trio of half-width strips right on the knuckle? One hardwood, flanked by two cedar, just to make a tighter radius than normal strips can handle, to avoid that sharp, sharp edge.

 

[stripperguy]

I wouldn't worry too much about the sharp knuckle, it's easier to strip and blend than you might imagine. I would be more concerned with the sharp radiused blend from the knuckle to the sheer. In my experience, that's the tricky part. I've never been a fan of mixed species stripping, sanding is too inconsistent.
As far as sheer height, it's got a really nice sweep. At almost 29" max beam, you'll probably stay dry during any healing. And at 13 ft, the hull will likely rise and fall along with any rollers, as opposed to a longer hull's slicing, but you still might take water over the sheer in big water....I just went back and reread your initial goals---I think you've got a winner!!

When will you start? I think I would like to build a similar, smaller version for my granddaughter. Unfortunately (or luckily?) I'll soon be homeless, so new builds will have to wait.
I'm anxious to hear how it handles on the water.

 

[sailsman63]

When I get my shop situation figured out to (partial) satisfaction?....? I'm not keen on a 45 min drive every time I work on a build, and I am having a hard time finding space to rent nearby.

I'm glad you like the sweep. I just realized that the 29" max beam is only 3" narrower than my tandem... This may mean some re-thinking, as reach over the gunwales in center station is one of the things that I'm trying to make easier. I think I can lose about an inch without affecting the submerged form... though this leaves me with a much less aggressive flare above waterline. see new upload.

You're right that the cutout above the knuckle is small. I'm looking at 4.5 or five strips at midships. I've done a sharp knuckle line before, and I'm wondering if this one might actually be easier. The knuckle actually extends to the ends of the hull, while in my tandem it faded out about a third of the way in. The fade transition was hard.

I generally do include some walnut accents, and for certain points the harder sanding is an advantage!

I would like to get this one built and tested in a reasonable time. If it works well, I have a friend that might enjoy a duplicate.

 

[sailsman63]

stripperguy You may be getting some reports on the hull performance fairly soon. I've just begun posting a build thread for this hull (Went a little different direction on the build.)