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Dayak questions

Posted by baldtexan 
Dayak questions
April 06, 2019 05:19PM
Sandy - I’m interested in seeing your new ideas for anchoring the dayak. One on my concerns was how hanging an anchor off the transom would affect the level of the boat. I would think a small flat section in the middle bottom and moving the rowers seat slightly forward (or make it adjustable) would take care of it. How would this affect the handling of the boat? A bit more front to back stability would be good, but I wouldn’t want to lose too much of the nimble handling characteristics. I will be using this for fishing small coastal tribs. It will most likely not see anything more than occasional very short sections of class III water.

I’m 50/50 at this planning stage on whether to glue and tape the deck down for better rigidity and water tight or fasten it down with a seal for later changes or repair. How did you treat the hull side edges so your deck had a good sealing surface when fastening down?

Re: Dayak questions
April 06, 2019 07:54PM
When I had the anchor hanging off the upstream end the Dayak trimmed backward too far. I could have moved the fixed seat forward but then it would be front heavy when I didn't have an anchor, as in white water situations. One way to fix that would be a quick-adjust rower's seat position. Just a small matter of engineering. I'm doing an 8 day San Juan River trip in a month from now. I won't be taking an anchor on an 8 day river camping trip.

Two season's back I cut a walled channel top to bottom through the boat, behind the rower, and dropped the anchor there. That had numerous problems. The worst was slowing the boat down dramatically. So I patched the hole. Right now I have no anchor mechanism at all.

Now I'm thinking about going back to the rear mount again, with a quick adjust rower's seat position. Steam is still coming out my ears.
Re: Dayak questions
April 06, 2019 11:56PM
It would be easy enough to make the seat adjustable a little forward and back. You stated that if you had made it for fishing that you would flatten it a little and raise the side height. Were you referring to the rear rocker? Would widening the transom an inch or two achieve this without affecting the maneuverability much? I wouldn’t think it would need much with just a small 15 lb. anchor out back. How would raising the sides affect the side to side stability with the rowers weight being higher?
Re: Dayak questions
April 07, 2019 01:55PM
For just a fishing boat I wouldn't bother raising the sides. It's slim and low but water almost never comes over the deck. Not much anyway. Except in big water. At Joe Hutch Wire Fence Three Fords and Coal Creek, in Desolation Canyon on the Green River, for instance, you do get you wet. They're all at the edge were class III is almost class IV except Joe Hutch. Which is a IV. I wish I had two more inches side height for that stuff.

Oddly I saw the biggest waves there last year when the water was relatively low. The closer to the big boulders the the fast part of the current is the bigger the waves. Six years ago when it was 38,000 feet it was an easier row. Everything was washed out and six feet down from the fast moving surface.

RE> the rocker. I made the plug with adjustable ribs and a straight line chine on cheap AC construction plywood. Then I made two Plascore side panels, laid them flat on the shop floor and marked them with a 3/4" inch by 3/4" inch long straight grained marking stick. Look for the page on "Reducing Rocker." I made the chine dish-out conservative at first. Cut it out. Put it on the form. Looked at it. Did it some more. Did it some more, little by little until it looked right. Then I marked and measured the underlying form, took it all apart and rebuilt it so the male plug matched the side panels I had gradually whittled out.

It's not a completely symmetrical dish. I wanted the center of gravity (my butt) to be a tad forward of dead middle, with the upstream end sweeping upward more so than the front. I didn't use software or calculations I used the seat of my pants, instinct and experience. I'm very happy with the boat. To do something completely new or to significantly modify something that already exists you have to take a chance. Or even many of them. I've had my share of failed experiments.

My absolute worst boat is still a good boat. I bad mouth it constantly (still have it). Friends finally get to row it and usually end up saying "I thought you said this was a shitty boat!" .......well it is. But it still rows better than most soft flexy commercially molded Chunkacraft fiberglass tubs.
Re: Dayak questions
April 07, 2019 02:11PM
RE> Understanding rocker, payload distribution and boat handling

I'm not saying I know everything. But I have learned some things.
No matter what the rocker profile if you have passengers out at both ends of the boat (fly fishing style) the harder the boat is to turn. Spreading the payload makes the boat a bit more side to side tippy too. I can't explain why. I don't even have a theory as to why. But it does.

Wider is better than narrow. Boats started off as 48" inches wide not because that was the ideal width, they were that way because that's how wide plywood is. That's why the first boats had 48" inch bottoms with 16' foot side panels. When they finally gave in and started to make bigger boats they scaled that up and mde boats with 17 or 18 foot side panels that proportionately had the same bottom width.

My HD has 16' foot side panels and a 56" inch bottom. That really is wide. You have to row it in big water to appreciate how good it is. I need to spend a day munging numbers with a calculator, so someone can make a bigger one, made with 18 foot side panels. The Briggs is made with 19' foot side panels (or there abouts) and it STILL HAS A 48" inch bottom. The Briggs is a side to side tipping machine.

For maximum handing and stability you want the passengers sitting side by side close to the middle, with the rower as close behind as possible, with the oars just missing the front seats by a few inches. Now the payload is centered on top of the middle. It turns easier (a lot lot more easier) and it's more side to side stable.

I made my last boat with a relatively flat bottom. I wanted to be able to use my 20hp Merc. It works as a row boat and as a motor boat. But it does both poorly. I should have built a Rapid Robert. Better yet I should have kept my Honky Dory and built a V-bottom lake boat. I don't much like Rapid Roberts either. Compromise do everything boats are always disappointing. Hot rod specialty boats, designed specifically for how you use it most, make you smile.

For nimble handling in scary water you need rocker that matches the payload distribution, which needs to be as close to the center as you can make it. And you want it wider than tradition tells us. Wider than plywood tricked us into building in the first place.
Re: Dayak questions
April 07, 2019 03:24PM
Side flare and side shape is the topic I'm least certain of. I met a guy in Wyoming who built an otherwise nice-looking decked drift boat with straight up and down sides. I know I don't like that.

But what and how is best.........isn't clear.
The more side flare the less the boat reacts when you get suddenly sideways to a fast current...IE less "chine dip"

But no matter how much flare you have there is a point when when the boat will flip.

Rounded "tumble home" sides are an idea I've thought about but never tried.

Rounding the deck upward radically, on a whitewater boat, or leaving the deck flat but building a "Creature Craft" like arc overhead is something I'd like to explore. Cross-ocean rowing dories are supposed to be self righting. They tend to be decked but open in the middle, so you still row, but have "cabins" at either end with rounded roofs that pooch upward a lot, so they turn back over if temporarily flipped. Trouble with that is you can't see where you are going without side mirrors like a bicycle.

Some kind of a Creature Craft arc over a decked Grand Canyon dory would be a relatively easy experiment nobody has done yet. So. Somebody out there. Pick that low-hanging fruit.
Re: Dayak questions
April 07, 2019 05:00PM
My hull has a 4’ long bottom section with straight sides before tapering more conventionally to fore and aft. It does not change the curve of the gunwale. It does appears to slightly reduce the side flare in the middle section of the boat but I haven’t actually measured it. I don’t have enough experience rowing different drift boats to know how it affects the maneuverability of the boat because I also reduced the rear rocker a bit, but it does keep the boat level front to back greatly lessening the effects of weight distribution. I think I’m over thinking this as the Dayak can be built with all significant weight centralized around the rower seat and moving that forward a little should reduce the effect of an anchor hanging off the transom, but I may build a couple of scaled models for comparison, one with a small flat section on the bottom out of curiosity.
Re: Dayak questions
April 07, 2019 05:18PM
Yes a lot of boats have a "flat spot" in the middle. My current not-yet-finished boat does too. Actually what I'm building is not dead flat in the middle. It has some but not much rocker in the middle 4' feet. And then gradually more rocker as it gets further from the middle.

What I was negatively alluding to while blabbering above was about really flat boats, that flat in the middle and almost flat out at the ends. I built my compromise "row it or motor it" boat that way and.......wish I didn't.
Re: Dayak questions
April 07, 2019 05:23PM
How does that middle flat spot affect the maneuverability of the boat?
Re: Dayak questions
April 07, 2019 11:04PM
Don hill had a flat section in the middle of his bigger boats. And they were good boats. Rowed well. I don't think the flat spot was anything more than an artifact from stretching a shorter boat out to longer. I don't think it gains performance in any way. I prefer to scale up proportionately, so the middle is almost but not completely flat, and so the chines are never completely parallel.

Perhaps my preference is just a quibble. Don made good boats.
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