Do some boats have a cabin but no sole or floors?

[Thames]

I was taught by a boat builder that you can't just walk around on a bare hull - boats need a cabin sole and some flooring to spread the weight of the crew, and to make the whole structure more rigid.

However I have now seen some respected designs for microcruising boats that have no sole or flooring. I've included photos of each build to show that they have no cabin sole.


First Matt Layden of Florida's Enigma 360 - stitch and tape 9mm/6mm plywood glassed, displacement c.420lb, LOA 12' beam 3'3" draft 6".





Second Sven Yrvind of Sweden's latest boat which he has just sailed from Ireland to Madiera. It has a 2" thick foam core in a fibreglass sandwich. 16' LOA, 4'3" beam, ~10" draft, displacement c.1800lb.





Matt Layden's only published design is the Paradox which does have a cabin sole. It's roughly 14' LOA 4' beam 9" draft displacing 1400lb:




How can the boats with no cabin sole be strong and rigid? Possible explanations:

• they gain extra rigidity from the convex shape of the planking, and they all have some rocker

• they only have approximately 3' headroom so crew must sit on the hull, spreading the weight more gently

• they're narrow beam so the unsupported surface is not large

• Yrvinds boat is a 2" thick foam core sandwich so this may add extra rigidity and spread point loads

Are there any guidelines for the size of boat that can be built like this?

[Lister]

If the plan show the crew walking on the inside part of the bottom planking, they are not "Respected designer". Keep this term for real designer.
Lister

[Thames]

They don't walk on the inside of the bottom planking because there is no standing headroom, they can only sit. But they can stand if they have the hatch open.

[Mick@itc]

Hi
Bob Oram's designs have no sole in the hull cabins and he is an excellent designer. He is a minimalist in terms of design and reduces his design to what is needed, no more. This results in a comfortable and easy to sail cat.
Mick

[philSweet]

If the plan show the crew walking on the inside part of the bottom planking, they are not "Respected designer". Keep this term for real designer.
Lister

Well, this ought to get some people's attention. I would submit Bill Crealock's Clipper Marine designs as a counter example. Not my personal favorites, mind you.

[viking north]

On our grand banks dorys we walk directly on the floor --it all depends on the rigidity of the material used. 2 in foam core is certainly rigid and warm also especially in these North Atlantic waters.

[CatBuilder]

Some comments below.... in red.

Originally Posted by Thames

How can the boats with no cabin sole be strong and rigid? Possible explanations:

• they gain extra rigidity from the convex shape of the planking, and they all have some rocker

Yes, some rocker will make any flat surface stiffer. Don't forget the arch from architecture. Although, thinking about it a bit more, the "arch" of rocker is upside down and not contributing to stiffness at all, except stiffness against external water pressure.

• they only have approximately 3' headroom so crew must sit on the hull, spreading the weight more gently

• they're narrow beam so the unsupported surface is not large

• Yrvinds boat is a 2" thick foam core sandwich so this may add extra rigidity and spread point loads

This is probably the biggest reason. Try making up a sheet of something with an adequate skin on it and 2" of 6lb Corecell. You could drive a tank over it and it wouldn't break.


Are there any guidelines for the size of boat that can be built like this?

[Thames]

Thanks for the useful comments.

It would seem that the rocker combined with the bend in side panels stops the boat flexing around as much as a cuboid shaped hull and gives it more external strength.

But the 2" thick foam core sandwich construction will enable the hull to take more point loads from the inside (as well as increasing strength for external point loads and overall stiffness).

It's amazing how the Enigma 360 can take the loads on the inside, having only a 9mm plywood bottom with no added support. It must be ok because it was one of the first finishers in the Ultimate Florida Challenge, a 1200 mile coastal/river race around the whole of Florida. I suppose it is only 3'3" wide so perhaps can go unsupported.

[DCockey]

Originally Posted by Lister

If the plan show the crew walking on the inside part of the bottom planking, they are not "Respected designer". Keep this term for real designer.
Lister

Some of Phil Bolger's designs use the inside of the bottom as the sole. Guess he's not a real designer.

[Easy Rider]

That would be a problem only on a very light boat. My 16' open outboard was designed to walk on the inside of the hull. Works fine if there's no water in the bilge or if one has boots on. Floors are mostly to keep your feet dry or to provide a flat surface to stand on or (usually) both. Later models of this boat have flat floor boards.

[LP]

Floors on traditionally built watercraft also tied the frames and keel together. They carry tension loads from the frames and bear the keel loads, tranmitting the loads to the frames and thus to the planking. The added benefit was that you could add your cabin sole to the topsides of the floors. Point loading on traditional hull planking is to be avoided. Todays sheet materials can handle point loading a whole lot better than pieced together plank hulls. Granted, point loading needs to be acounted for in the hull scantling.

[lewisboats]

Most (not all but most) of the boats that don't have floors have other structure filleted in (bulkheads, bunks, lockers etc) that reduce the amount of open area (span) that carries the load. Added to that...a point load on a curved piece of sheet material fixed by vertical members (basically an open topped box with a curved bottom) isn't going to cause the sheet to form a compound curve...it usually can't. The one exception is when torturing the ply and that is done during construction using very thin materials.

[Lister]

Originally Posted by DCockey

Some of Phil Bolger's designs use the inside of the bottom as the sole. Guess he's not a real designer.

I don't consider him a great designer, but yes he was real designer.
Walking inside the bottom on a offshore sailing boat is not a good idea. On a plywood epoxy sharpie going around the pound it is an other story.
Lister

[PAR]

Lister, Bolger was one of the greats, with nearly 700 designs to his credit. Unfortunately, he's mostly known for his eclectic nature and square, common man's designs, which is sad really, considering the volume and scope of his work.

The use of a sole is largely a matter of available space. A 16' pocket cruiser, carrying a 150 square ft. sail plan and a small cabin to hide from the rain, can't afford kissing off several inches of sitting headroom, just to have a proper sole. An 18' powerboat cruiser with a cuddy, may just have enough internal volume, particularity if it's round or V bottomed, to warrant a sole.

As to it being a good idea to walk on the planks, well, yes and no is the answer. If you have a relatively small, traditionally built lapstrake or carvel, you should try to keep you feet on the frames or stringers. These planks weren't intended to bear weight in this fashion and you could easily pop fasteners, if not actually crack a plank. On the other hand, this type of build would likely have some sort of sole, be this a simple grating or slates over the frames or a full blown sole.

Conversely, many small craft are intended to have the bottom planks walked on. I have several designs just like this and the additional loads this imposes was considered in the scantlings, during design development.

It's difficult to second guess the engineering approach a designer may have incorporated into a particular project. I have a design that Eric is familiar with, that has the crew walking directly on the bottom planks. The boat is a rock under foot, underway or at rest and this was my intention when I drew it up.

Lastly, the old builder that told you that walking on the planks was wrong, is correct, sometimes. Bundling designers into a lump, because they don't meet his expectations, is a rather narrow minded, if absurd view and should be taken with a grain of old salt. When he was a lad, this was very true, but modern building methods have surpassed even this guy's expectations, so he needs to try to keep up at the very least or qualify each comment like that with a "in the old days" prefix.

[BATAAN]

It seems that one is sitting in the bilge, so the least bit of H2O and your pants are wet and your sleeping bag.
Sole/floorboards separate the wet bilge from dry feet one would hope.
Flexible closed cell foam liner would substitute, getting you a little out of the wet.
But if your boat is tiny, eliminating all but the absolutely necessary is kind of like an ultralight airplane in that you leave everything off but what you really need, and some boats don't need floor timbers or a sole, but most benefit from them.