Bilge Maintenance in Flat Bottom Steel Boats

I am considering various general design issues for a near future live-aboard boat. For various reasons, I’m leaning toward a flat-bottomed hull constructed of steel. My preference would be for an “open” design rather than fully raised decks, with a self bailing sole above waterline. However, I’m concerned about how one could reliably dry out and maintain the bilge to avoid damage from rust and corrosion. Can anyone offer knowledge/experience with this? For example, how does one manage to fully pump out a bilge when the hull is flat, so it doesn’t have any straightforward, obvious collection point? I’m guessing there are some standard design elements used to help deal with this, but I haven’t come across them so far. I’ve thought about a fully open bilge, so at least I can entirely see what’s going on with the water, but it would need to have enough flotation to float upright if swamped in that case and I’m skeptical there are boat designs of that type in a size useable for a live aboard. Thank you.

 

For drainage you would make limber holes (mouse holes) through all the frames on both sides of the hog, from front to back, and also inside the chines of a flat bottom, then whatever way/attitude your boat floats, water will run to the lowest point, and be pumped or sponged out, along with leaves, dust, and tiny garbage. A slight dead rise to the bottom reduces it's chances of being suctioned down into mud when beached on a muddy shore. Fully open bilge lets water and rain flood in. Inspection ports are easy to fit, with waterproof seals, and can be made of clear plastic. Buoyancy tanks can be included in the design, so a swamped boat doesn't sink. Lose a bit of space, save a lot of boat. See wooden sailing dinghies for ideas, eg. the plywood Mirror.
You could have put this post/question in your main thread, to keep all your info together. We don't care how long or involved / convoluted a thread is, as long as you get all your questions answered. And then take heed.

 

Are you still thinking about a long and lean monohull which was discussed in your other thread in this link below?
Hull Design Choices for Very Fuel Efficient Live-aboard https://www.boatdesign.net/threads/hull-design-choices-for-very-fuel-efficient-live-aboard.70865/

Can you remind us please what waters / cruising grounds you intend to use your liveaboard boat in - will it be on the inland waterways of the USA, or coastal, or will it have to be capable of crossing oceans?
+1 re Seasquirt's suggestion to have some deadrise on the hull bottom, rather than having it completely flat.
If you do build in steel, then it would be sensible to use steel plate and sections that are already shot blasted and painted with primer. You then just have to paint the welds and finish with top coats, rather than having to worry about blasting the whole interior of the boat.

 

Thanks for the info and the recommendation re combining topics in a thread.

I understand the concept with the limber holes and inspection ports. Unclear on one thing - you mention sponging up water in a bilge. How would one do that other than in a fully open bilge? Is it common to have some open access areas? I could see why it could be helpful to have some way of really cleaning out the bilge, since it seems bound go get mucked up over time.

The point about a little deadrise to help avoid sticking in the mud is interesting. I hadn’t thought of that. I had considered having some kind of ballasted twin keels/bilge keels having read that they would help improve roll behavior while motoring. Thinking they could have a flattish bottom in some way to help avoid digging in too much.

Including buoyancy features seems a great idea to me. I made the mistake of canoeing with neither lashed in, watertight gear nor flotation bags a couple of times and learned my lesson the hard way. This boat will be a lot more costly than a canoe (and much harder to retrieve if sunk ).

 

Originally, I was discounting the idea of a long, lean hull, thinking I need to give up the higher displacement speed (or lower fuel for a given speed) in order to have a boat that will not roll too much and be comfortable at sea and anchor. However, based on a variety of feedback on here and further reading up, I’m reconsidering that

I had thought to offset the propulsion/fuel/power challenge of a beamier, shorter boat by including some sort of sail rig to use at times. I like the sail idea also because there are conditions when it would gove a better ride than motors. It may still be a fair idea, but I’m wondering if I can really find a way to stow the sail and mast so it doesn’t penalize my solar generation of electricity. Unless the sail is quite small, that may be tough and if it’s too small it may be pointless. I’m starting to think it might be better to stay completely focused on optimizing for motoring and maximizing my solar and maybe utilize 1-2 gas outboards as auxiliary/get home propulsion instead of a sail rig. I could even include a kite rig if not too costly. Wouldn’t always be appropriate, but would be sometimes and wouldn’t block the solar panels.

Maybe I can find some good approaches to enhancing comfort of ride at sea and comfort at anchor without giving up the long, lean displacement hull approach. I’ve read twin/bilge keels can help a lot with roll and there are other things like paravanes I could look at. Any advice in the area of improving comfort and seakeeping with a long, narrow monohull will be appreciated.

My intended use range comprises the river, lake and limited coastal cruising one would encounter around the North American “Great Loop,” but I’d love it if I could cross to the Bahamas or even do some limited travel in the Carribean or say get over to Newfoundland eventually with a lot of patience and careful consideration of weather. I don’t have any ocean crossing ambitions however and will be fine if those bigger crossings I mentioned end up out of reach (although the Great Lakes might not be so very different at times).

One of those Michelin WISAMO inflating wingsails with a telescoping mast that stows fully away would be handy, but I suspect that might cost more than the hull itself.

Thanks all.

 

Talking about long, narrow live-aboard motor yachts made me think about reading years ago (when I first started thinking about living on a boat) about the Dashew “FPB” designs.

SetSail FPB https://setsail.com/

Long Thin Boats Are Cool https://www.morganscloud.com/2012/09/08/long-thin-boats-are-cool/

 

Bilge keels can sink in mud, and with a flat bottom section will turn into anchors as mud flows over the tops of them. May be ok on sand but probably not sticky mud. Inspection covers can be hinged for quick easy access, over a bilge pump, and easy access for a hand sponge, or a squeezing mop type sponge if too deep to reach by hand. Clear inspection covers will mist up or show drips of condensation if water is in the bilge; you will almost never have a bone dry bilge. A short mast and small sail helps on motorsailers to reduce roll while under way, flopper stoppers help at anchor, and many other systems exist. A lifting centerboard also helps but takes up cabin space. Two lifting centerboards, at the sides, allow more space, but lee boards give maximum cabin room, and shallow access, but no hull support when on the bottom.

 

@seasquirt thank you for the feedback. When I don’t get stuck on that mud flat one day in the future, I’ll owe you.

 

I don't know if there has been a boat that kept a dry bilge. Don't skimp on surface prep and coatings, and be thorough with your maintenance.

 

I would consider a pair of short masts, side by side in tabernacles near the bow. For wind up to about 110 degrees from the bow, use only the leeward sail, balanced by a board under the bow. Further downwind, use both sails. Close to dead downwind, use them in a V configuration, for self steering. When a mast is not in use, fold it down in its tabernacle. Being on the side, they will not fold down on top of solar panels and shade them.

Then you might want to see this:


The mast is quite light because the lines it holds up are control lines that don't pull hard. The load bearing lines are at deck level.

 

What sail rig types do you think might be most readily/effectively used this way? Do you think that the 14-16 foot beam of a monohull would allow these sails to be spaced far enough apart? One additional utility I could imagine would be to keep some open viewing area down the centerline, at least if the sails were relatively tall and skinny in shape.

Thanks.

 

I stole the idea from Sven Yrvind, who uses a balanced lug.


For easy reefing and stowing away, look up Matt Layden's roller reefing design:




I wrote a short article for the AYRS journal Catalyst #42.

You need the distance between the masts to be at least twice as much as the portion of yard or boom that is in front of the mast. You'd need very long yards and booms for that to be a problem. Yrvind manages on a quite narrow boat.[/QUOTE]

 

Thanks. I’ll look for some more articles/videos re Sven Yrvind and become more familiar with the use of those sails. You’re certainly right that using smaller sails and increasing total sail area by using multiple sails could make it easier to stow them away in a manner that doesn’t impact my solar panel array. Kind of like leeboards not using up interior cabin space the way a centerboard does. If I keep them individually small, it would also be less challenging to make the masts unstayed. Might not produce a lot of power, but then again, you read about people sometimes sailing with little more than the mast up in a lot of wind. And part of me feels like every boat that plans to get far from shore should have some form of sail on board.

 

Right away, I found Yrvind’s discussion of shallow draft boats for open ocean sailing, and his view that emphasis on sailing to windward is more important for racing than cruising, to be interesting subject matter (since shallow draft is important to me). I don’t really think I’ll ever want to cross an ocean, but even for shorter passages, nearer land, the principles involved have relevance. Or, to put it another way, I’m even less likely to ever want to race than I am to venture into open water.

I’m also interested by the inclusion of a mizzen on one or more of his boats. Seems like it could have several very practical utilities.

 

Regarding your original question, I would consider some slope in the bilge to be a very necessary part of design, as well as some sort of sump from which to pump out. Even a small keel bump will be beneficial towards corralling the bilgewater to a pump out point. Sponging out the bilges will be extremely tedious, and a never ending career, and will definitely cast shade on your desire to cruise!