Boats with Flat Hull Shapes

[potomac]

Other threads have explored flat hull shapes and a recurring theme tends to be the limitations of such hulls in both comfort and performance. One frequent poster, who shall remain unnamed but whose name might rhyme with Flames McSullen, feels so passionately about the subject that every time it comes up, he points out their lack compared to more "evolved" round hull shapes to the point where it would seem such hull shapes are not worth building. Is this an oversimplification or is it true? And if true, why are they still being designed? I know build-simplicity might be sighted, but highly respected (even beloved) designers seem to incorporate flat hull shapes into their designs. John Welsford uses it from his smallest to his biggest, the SCAMP and the Penguin are flat or use large flat sections. Iain Oughtred has utilized flats all the way up to his sharpie Haiku. I know Oughtred's use is in a a sort of directed way, (his take on a dory or a sharpie), but that is not the case with Mr. Welsford's. Now James (whoops- the cat's out of the bag) tends to be a quiet, shy, somewhat reticent type, so he is unlikely to respond here (though I wish he would), but I am curious what people think and just how detrimental the use of flat sections is. I'm hoping to limit this discussion to sail or oar type boats as power designs could easily merit their own thread.

[wizbang 13]

yes, wizbang, my ol powerboat, lands hard when air born for more than a second or three, even when landing on water. so there.

[James McMullen]

I don't know what you are insinuating. I love big flat panels. The more the better. Just think of all the flat planes and hard chines on your typical seal, dolphin or mackerel.

[James McMullen]

I'm stealing that line about Flames McSullen for my new Bilge alter-ego, by the way. I love it!

[darroch]

Always consider the nickname a new iteration might bring, 'Flamer'...

[potomac]

I get what you are saying James, (dolphins, etc.), and it makes complete sense to me. But why are these brilliant designers still going down that road? Also, I thought you were a fan of SCAMP (given its obvious limitations).

[Ian McColgin]

It's an argument that can only be carried out by a combination of limiting the design brief past pointless and letting all prejudice rip. It makes sense to look at specific designs and even compare comperable designs as you might compare a pleasurized peapod to a gunning dory, but any general case is west to stupid and south of pointless.

[Spokaloo]

I like your thought Ian, let's expound from a single design:



Reasons for the flat bottom:

Construction time of 3 weeks of part time work
Flat interior walking/work area that runs all the way to the sides
Stable beyond necessity
Beaches bolt-upright and easy to board from shore
When run aground, you can hop over the side and easily push her back into deeper water.
Takes weight well while remaining shallow drafted.

These are all facts that I know quite well, as this thing gets used and abused daily. Just did 3 hours of water sampling this morning.

Yes, in a chop over a foot tall, we have to slow down. That's a small price to pay for being able to get across a sand bar or mud flat easily.

E

[James McMullen]

Okay, here's what the deal is as I see it: all boats are compromises. (and let's be clear from the start that what works for displacement boats is an entirely different issue for what works for planing hull forms) Although the curvy shape is ideal, in many cases it is useful to incorporate flat planes from a purely practical standpoint for building. For example, a lapstrake hull is a compromise that allows relatively thin and flat planking boards to be fastened to each other in a relatively rounded fashion. A multi-chine stitch and glue hull is another example of such a compromise, where the planking material which comes in convenient 4x8 flat panels can be assembled into a close approximation of that ideal, rounded form.

There are certainly times when the curve is subtle enough that it might be a worthwhile simplification to substitute a flat panel for that portion of the boat. That's what you see all the time in boats designed for building out of plywood, or sheet aluminum, or plate steel or some other form of flat panel material. But it's an artifact, not a feature.

My own particular predjudice against over-simplified hull shapes was hard and bitterly earned through the several dozen boats of this nature I built for myself before I figured out what I really required. It is not a knee-jerk reaction or the result of armchair theorizing. For example, the only person I have ever met who built more Bolger Instant boats than me was Harold Dynamite Payson himself.

But that doesn't mean I don't ever use flat panels when it's not appropriate. I have a couple of stitch and glue sea kayaks, a stitch and glue skiff, and three different lapstrake boats right now. But they're all approximations of convenience for the construction method.

What works for a powerboat that has power to waste is not necessarily good at all for a boat that relies on the relatively minuscule amount of power available from human muscles. If you're planning to burn calories rather than octane to propel your boat the little things add up.

[potomac]

And planes easily to boot. The flat hull or hull section as being incredibly valuable to modern, relatively fuel-efficient planing boats is not lost on me at all. I guess I'm interested in discerning if the flat sections are a hinderance or a benefit, (or a bit of both), in other types of hulls like sail boats. Dories aside, as their history and purpose, and the reasons behind the original designs through their evolution is well documented in other threads, why would Welsford make SCAMP flat bottomed or Penguin for that matter, if indeed it is detrimental? Maybe it isn't. Maybe it's much ado about nothing. That's what I'm trying to understand here. It's completely possible, by the way, that those designs aren't the least bit flat and I'm misunderstanding what I'm seeing in pictures. I don't own the plans of either boat. If neither of those boats has a round-bilged counterpart for discussion sake, how about Redmond's Whisp and a similar round bottomed rowing skiff?

[James McMullen]

Potomac, a boat like the Scamp really isn't the least bit "flat" in the way that a simple sharpie or crude, slab-sided Banks dory is. It merely has a wider bottom panel before making the turn of the bilge. That bottom plank is flat only in the athwartships plane, it is rockered fore and aft. This is not the same thing as a square sectioned boat. If Mr. Welsford had designed the Scamp for cedarstrip construction instead of glued lapstrake plywood then you wouldn't see that same flat panel shape, you'd merely see a lightly curved part of the sections amidships.

Turns out I've actually built a Redmond Whisp skiff myself. It's okay. . . for a skiff. I wouldn't have one ever again myself though. . .

[kenjamin]

There's something to be said for minimum draft!

[johnw]

Did someone mention simplified shapes?



Sharpies might not make the best row boats, but they are quite good for their purpose. They spread to a number of areas where fishermen were using round-bilged boats and displaced them, because they were better for some purposes. They were often faster, shallower, and better load carriers for the effort it took to build them and sail them. When they were introduced to the Carolinas, there was a race between one of the cutters then in use and a sharpie under conditions considered to favor the cutter, and it was left far behind. Accounts of Egret's introduction to Florida emphasize how impressed people were with her handling, not with her ease of construction.

It's horses for courses, of course. If I rowed as much as Flames does, I'd not be nearly as happy with my sharpie. But for a day sailer, she's quite good.

[johnw]

There's something to be said for minimum draft!

And for a straight run and minimum deflection angle on a planing boat.

[IanHowick]

Okay, here's what the deal is as I see it: all boats are compromises. (and let's be clear from the start that what works for displacement boats is an entirely different issue for what works for planing hull forms) Although the curvy shape is ideal, in many cases it is useful to incorporate flat planes from a purely practical standpoint for building. For example, a lapstrake hull is a compromise that allows relatively thin and flat planking boards to be fastened to each other in a relatively rounded fashion. A multi-chine stitch and glue hull is another example of such a compromise, where the planking material which comes in convenient 4x8 flat panels can be assembled into a close approximation of that ideal, rounded form.

There are certainly times when the curve is subtle enough that it might be a worthwhile simplification to substitute a flat panel for that portion of the boat. That's what you see all the time in boats designed for building out of plywood, or sheet aluminum, or plate steel or some other form of flat panel material. But it's an artifact, not a feature.

My own particular predjudice against over-simplified hull shapes was hard and bitterly earned through the several dozen boats of this nature I built for myself before I figured out what I really required. It is not a knee-jerk reaction or the result of armchair theorizing. For example, the only person I have ever met who built more Bolger Instant boats than me was Harold Dynamite Payson himself.

But that doesn't mean I don't ever use flat panels when it's not appropriate. I have a couple of stitch and glue sea kayaks, a stitch and glue skiff, and three different lapstrake boats right now. But they're all approximations of convenience for the construction method.

What works for a powerboat that has power to waste is not necessarily good at all for a boat that relies on the relatively minuscule amount of power available from human muscles. If you're planning to burn calories rather than octane to propel your boat the little things add up.

James,

I'm curious to hear where you see the Goat Island Skiff (yawl version) fits in your sail and oar universe. I'm guessing my boat has a ready to go weight a bit less than half of Rowan, but doesn't give up much in the way of waterline length, beam, freeboard and full sail area to your Oughtred double ender with the big overhangs. (All up weight with rig, oars, anchor etc on board is 75 kg or so)

I realise overhangs have their uses, and weight is a good thing in itself in many situations, especially going to windward when it is getting rough.

On the other hand, even with the extra wetted surface area of the flat bottom, rowing has got to be easier with half the water to push out of the way for each boat length travelled, and off the wind in rough conditions it's going as fast as you want with next to no sail up.

Comments on downside of the flat bottom beyond the obvious extra banging and more abrupt motion in some conditions?

Comments on the plusses and minuses of going light and absolutely minimal sail versus heavier and more sail in heavy conditions when not hard on the wind?

I have the ability to add sand or water ballast in the centre of my boat, though I haven't tried that yet, could easily double the weight of the boat with a few bags of sand.

Ian

Mik and John Goodman getting a reef in on the Texas 500:

[johnw]

At the speeds one rows a boat, I suspect wetted surface adds as much drag as weight.

[wizbang 13]

I started out in a Seabird Yawl.
When she heeled over, her so called faults melted away.
My Lightning? not so much.