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Self bailing designs
Posted by Hansen 
Self bailing designs
April 17, 2017 01:14AM
My understanding is that most self bailing boats have a raised floor (above the water line) so that the water which gathers in the boat will drain, either straight out the bottom as Sandy has recommended in previous posts, or out the sides above the water line.
Do most people completely seal the space between the false floor and the hull to keep it dry, or is it better to create "semi dry" hatches for repair access and storage?
Any guesses on "typical" height for the floor?
Thanks for the advice...
Re: Self bailing designs
April 17, 2017 05:12AM
Good questions. I hope to see others jump in.

I will say this:
Sealed off air chambers, like perhaps the space underneath a level standing platform in the front of an open fly fishing boat, are a very bad idea. I learned that lesson the hard way. Any permanently sealed chamber, no matter how large or small, will gradually fill with liquid water. Water vapor is a gas that can migrate through any thin fiberglass skin Plascore or plywood. Once through that vapor will eventually condense. And then the next thing you know your elaborately and meticulously made water proof air chamber is sloshing around with liquid water.

All such places need hatch lids or vent holes of one kind or another.


I have built only one decked boat so far in my career--my one man Dayak which is now going on four years old. For the first two years the deck was removable. It bolted down onto a fat closed cell foam gasket. For reasons I am a loss to explain I glued that lid down permanently when I added hinged locker lids in year 3. I already regret that move big time.

Bolt down decks work. And it is oh so convenient to be able to remove that lid a variety of contexts. The boat I'm working on now will most definitely have a bolt-down-onto-a-gasket deck.

25 years ago there was a creative and crazy white water guy here in Bozeman named Andy Lundstrum. He was a colorful character. He eventually got banned from Yellowstone Park for life for running the Black Canyon of the Yellowstone in a kayak. More than once, I think. Andy built a large wood strip Grand Canyon dory that had a foot thick floor made from wood strips sandwiched on top of and below 12" inches if poured in place foam. I don't think the wood strips worked out well. They were too prone to fractures traveling a long way out from impact points. His raised floor had fancy scuppers in it but they didn't work well. A horizontal surface 12" above the bottom isn't high enough. I think it should be all the way up, straight across from the top edge of the side panels.

Anyway Andy's scuppers never worked right. The boat did drain eventually but it spent too much time filled with a thousand gallons of water. He did run the Grand Canyon with it. More than once.

Most decked boats, in fact all that I've seen have the deck something like 4 to 6 inches down from a traditional wooden gunwale. That makes the whole top of the boat a giant water scoop that can momentarily fill with 50 to 100 gallons of water every time you punch a big wave.

If there was no gunwale at all and if the deck went from the top edge of each side panel directly over to the other side there would be no such 100 gallon water scoop on top. There would be no water to drain, except in the foot well depressions, which I plan to make as minimal as possible. Those are my thoughts.

I told Larry Hedrick about the no-gunwale idea and he made a face like he'd just swallowed a rotten oyster. I asked him why he didn't like the idea. Larry said "It wouldn't look right."

I rest my case. I'll be rowing with Larry in two weeks from today. On the Green. Larry will be rowing his Rio Verde, which is a stretched out Honky Dory. I'll be solo in a Dayak.
Re: Self bailing designs
April 17, 2017 02:51PM
So the bottom of the hatches would be the bottom of the boat (no raised floor) but the footwell decks need to be water tight (so the hull doesn't fill up) but removable (for maintenance). Is that right?
That puts a lot of faith in the seals on your hatch lids... expect a post in the future where I ask for help on that one... ;-)
Re: Self bailing designs
April 17, 2017 03:53PM
I'm not sure I understand your question. I'm talking about this.....I envision a boat much like this but bigger and longer with pointed ends and higher sides. Foot wells are depressions in the deck that allow you to sit lower down than totally on top of the boat. Pushing passenger weight down a bit (with foot well depressions and perhaps even a slightly lowered seat) lowers the boat's center of gravity. Too much weight too high makes any boat unstable.

Narrow boats (the Briggs) need the passenger weight as low and as close to the bottom of the boat as possible. Wider boats can have the same weight placed a little higher. A lot higher actually.

Depressions in the deck have to be drained somehow someway. I like straight down. This boat has no gunwale. The deck goes from side top edge to side top edge so there is no need for a gunwale. The rower's foot well drains almost instantly because the drain pipe is 4" inches wide, running straight down.

In bigger white water dories there is usually a front and a back seating area capable of holding two passengers each. Those are typically like giant depressions in the deck, that go all the way to the floor of the boat. In big water they fill up with a huge amount of water which can take a surprisingly long time to drain. Meanwhile the boat is unmanageable.

Reducing the size of the passenger depressions would help considerably. One way to reduce passenger depression volume without raising the boat's center of gravity is simply to make those passengers sit with their legs straight out, like a car seat, instead of straight down like a kitchen chair. Passenger seat depressions don't have to go from one side all the way to the other. Then could be two narrower side-by-side depressions in an otherwise flat deck, just wide enough to sit comfortably.

Re: Self bailing designs
April 18, 2017 01:35PM
Here's when I made my big mistake, gluing the lid down permanently. You live and sometimes learn. Bolt down onto a gasket decks are better than permanent. Maybe what a guy really needs is lever latches and hinges.


[attachment 1062 sPIC0722_One-man-lid.jpg]
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open | download - sPIC0722_One-man-lid.jpg (177.8 KB)
Re: Self bailing designs
April 21, 2017 04:19PM
I don't know about the flat top and no gunwale thing. I just can't seem to get past the look of it.

Now about drains. You will need big through hull drains. 1/2 or 3/4 is not going to get the water out fast enough. From now on I will put in 1 small drain and use inch scupper flap drains just above the. In places where scuppers are not practical use 500 GPH or up to 1000 GHP pumps. 1 10 Amp hour batter gets me through a 2 week trip down the Grand canyon. A spare will cover the whole trip. I have a pump up front to drain what water does not go out the scuppers.

When you put the boat underwater and every compartment is full the gunwals, the water has got to go and fast. Trust me I know. You can't move a 1000 pound boat with another 50 gallons of water in it.

I'm with Sandy on the issue of sealing things. Water has a way of finding it's way in. If you fill with foam it will soak it up. A closed compartment under a floor is just a place for mold etc. Kept things open so air can get in there after a trip and dry it out.
Re: Self bailing designs
April 21, 2017 05:58PM
I've been thinking about this for a while and trying to put my question into better terms so it makes sense. I think the missing part of the question is tangential to my other post re: coolers. Larry's recent reply helped me to articulate my vision better.
When I talk about decking a boat, I'm not envisioning a deck with depressions as Sandy described - I've always visualized it the other way around - more like built up storage compartments that surround seating areas, footwells, drop in cooler / kitchen boxes etc. If you look at it from that perspective you end up with a lot more areas that need to be pumped or to self bail and a continuous floor starts to make sense - at least in my mind.

I see two ways of doing it - and maybe at least one of them is stupid but I don't know... I'm new to all of this so that is why I'm asking.

Method one - deck the top, put depressions into the deck for the footwells and seats etc as Sandy described. If the depressions can stay above the waterline, they can "bail" through holes in the hull or bottom of the boat. Sounds easy enough. But considering what I said above about the amount of negative space in the deck and it starts to look like one big depression which could start to look a lot like a floor... also consider that even factory manufactured aluminum dryboxes often leak when submerged. Since a hatch failure in a flipped boat would allow the boat to fill completely with water and maybe even sink - that puts a lot of pressure on your hatch lid design.

Method two - build a raised floor that is semi-permanently attached (I thought permanent, but that has been answered above) . Probably bolt it down over a gasket just above the waterline - since you wouldn't be getting in and out of it multiple times a day, this could be a bomb-proof connection that is less likely to fail than a hatch lid. Above that, you would have your bulkheads, deck, and hatches but essentially the boat would act like a self bailing raft. Any water that comes into the footwells or through the hatch lids etc would stay above the "floor" and would bail through the drains above the waterline. This way, there is permanent floatation below the floor. I do realize that through the plumbing for the bailing mechanism, the water would then have free access into your hatches and that might be a problem... but it seems like with scuppers, and if the drain holes are above the water line you may be ok. You can also pack in dry bags like your are in a raft but maybe that defeats the purpose. Either way, the floor seems like it provides a margin of safety by having a built in air pocket that isn't subject to leaks caused by getting in and out of it several times a day.

I'm probably overthinking it, but it helps to try to spell it out...
Thanks.
Elliott
Re: Self bailing designs
April 22, 2017 01:07AM
I think you have a good idea. It makes sense too. If you can visualize it you can build it.

I still like the sit on top kayak idea, with sitting well depressions deep enough so the center of gravity isn't too high. No gunwale. Deck goes from side top to side top, like a Dayak blown up to a full size boat with an 18' foot gunwale.

You mentioned the idea of locker lids flying open at a bad time. Lids need a latch mechanism of some kind. I built flush latches into my Dayak but they don't work worth a shit. They don't seal tightly and they need to be adjusted a lot. Lever latches that pull the lid down tight are a much better idea, I now think.

Larry Hedrick has latches of some kind I think but he also uses blue nylon NRS raft straps over top of the lid from side to side. Those aren't coming off no matter what. I've been in and rowed Larry's boat. It could swim upside down after capsizing and the hatch lids aren't coming off.

You have a different vision and it's a good one. That's the cool thing about designing and building your own. You get it your way.
Re: Self bailing designs
April 24, 2017 03:40PM
You made the comment "above water line", try to remember that the water line is not always in the same place. I can Deso a thousand times and in almost every trip, the boat will draw 4-6 inches of water. The Grand Canyon is another story. I have had the boat under water more then a few times. Plus waves can roll over the bow plenty of times too. I once screwed up and went into the wall at Granite. Even though I managed to stay in the boat, next thing I know I still have 1/3 of the rapid to go and the foot well is full to the top, the front area is full to the level of the deck. 350 pounds of people in the boat and coolers, beer, 100 pounds of drinking water, and God knows what else and I had the same situation at Hance another time and had at least 200 yards to go. All of a sudden the drains are now below water level and the boat is too heavy to row it and it has an extra 400 pounds of river water in it. It's so low in the water it's not going to drain out for 10 minutes. That is why I say pumps are the way to go. We have got to get water moving out so the boats starts floating higher and the gravity drains can start working faster. If your deck has lots of drop in areas for cooler, dry boxes, passengers front and back that makes space where another 200-300 pounds of water can hide.

The comercial operators take 1 rower and 4 passengers in their boats, but the bulk of the gear hauling is done with big support rafts. On our private trips day 2 in the roaring 20s we have to day with big rapids all day and the boats are very heavy. It takes a week until food, beer, ice drinking water loads start to lighten up. We are floating low for the first few days.
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