Design Issues for small, sail/human powered cruising boats

Regarding drain flooding cockpit when capsized:

My Marsh Duck had daggerboard with case open on top, in the floor of the cockpit, that acted as a drain. Occasionally in rough conditions a little water would splash up around the daggerboard and dampen the cockpit floor, but only a very small amount. The hatches weren't truly watertight, but even in the worst capsizes (during tests, including complete turtle, and my one unintentional capsize when cruising) no more than a gallon or two of water got inside the cabin and storage compartment. When I got her back upright (always within a couple of minutes of going over), there was never more than a little water in the cockpit (maybe a half gallon). On her side there was enough side-deck/hull floatation that the cockpit was still above the water. So she never sat low enough in the water for the daggerboard hole to flood the cockpit. I think the cockpit floor was only about 4 inches above waterline when loaded for cruising.

So, it all depends on your boat's design! More open boats, like Sea Pearl or Drascombe Lugger can swamp and be impossible to bail because water flows in through the centerboard trunk faster than it can be bailed out . . . personally, I wouldn't want a boat with that characteristic.

 

But only if the cockpit sole is below the waterline, which in this case, it wouldn't be.

 

I see the concept as somewhat of a dead letter.

Most of these rowing adventures seem to be record breaking attempts.

For such to be counted, the boat must be entirely powered by oars. Never mind it can go only where the prevailing winds and currents go.

One record, discussed on this forum, had a boat that looked like a dismasted long keel sailboat.

I saw that as sort of cheating. The keel added a lot of whetted area, so clearly wouldn't help rowing at all.

But what it would do is make for a far better controlled drift. Nevertheless, it was propelled only by oars, so I guess the record counted. This was probably as far as anyone could push the "rules".

Adding a sail of any kind would almost certainly be seen as going too far.

And if sails are let into the mix, how is one to determine just how much Sail Area is allowed?

At what point does the sail assisted rowboat become an oar assisted sailboat?

Sven Yrvin made an ocean passage in a sailboat with only about 43 sf of sail. He did it in 78 days. He never mentioned using human propulsion, except to maneuver in harbor.

My proposed boat would be roughly the same displacement as his 2nd Ex Lex, but would have a sail area that would be slightly greater.

I suppose that, with actively used oars, the voyage could have been made noticeably shorter. But adding more Sail Area could have the same effect.

I might play with the idea a little bit.

Part of the goal would be to keep the cost down. Since any record setting would be pretty much out of the question, this becomes mainly a intellectual enterprise.

I think that throughout history, a single oarsman was expected to propel no more than about 1,000 pounds of boat. So the more conventional oar setup was implicitly designed for such.

Now, asking the same oarsman to propel more than double that, may require the proportions of the oar lengths, blade Area, and even blade design to be reconsidered.

It may be better to have more oar strokes and bigger blade Area to move this much heavier weight.

A shorter loom length might also mean lower likelihood of snagging the water on the return stroke, especially in the conditions of a very uneven water surface.

I once saw a two metric ton Folkboat propelled two miles up river by two young men, using oars as paddles. I would say they were moving this boat at close to 4 kts.

It was something to see.

It is easy for me to imagine them using very short oars to do much the same job.

More on this later.

 

You have hit upon two important points I have wanted to make since Scott introduced his new direction with ocean crossing capability.
1 Ocean crossing rowboats are "stunt" focused and optimized -the major point being that any propulsion other than rowing constitutes failure. It brings the certainty that even with excellent athletic capability the speed will be slow. It also means that the ratio of time spent doing what it is designed for over the time it spends in storage is a pathetically small number.
The differences with Scott's SOR (and needs) are huge. He is designing something more versatile and useful for the common man.
2 Rowing as a means of propulsion brings lots of baggage in the context of a small boat.
-the position of the rower's weight relative to the water
- the reciprocating mass
-the secure space for those parts when not rowing and trying to do something else
-the clear space for all the moving parts -including the water->stability and waves.

The very path across the ocean is completely different for this design. Rowing stunts follow currents but avoid waves. Scott would undoubtedly follow favorable trade winds and avoid doldrums.

 

Skyak, you make very good points! Sailing, for me, is the primary propulsion. Rowing complicates things, but still seems the most efficient means of auxiliary propulsion other than motors that I don't want. In ocean crossing, rowing would primarily be used when there is little or no wind, for example, to cross the doldrums as quickly as possible if they cannot be avoided.

 

Your direction in hull design -lightweight, long, very narrow -is more suited to double paddle. I think the reason the rowers are pushing you to beamier designs is that rowing demands that the sweep of the oars be parallel to the water around, even when that is the side of a wave. Skinny kayaks and baidarkas stay vertical with double paddle. There is also something important in facing forward in waves, seeing what is coming and reacting. Oars have more leverage, but in the context of an ocean crossing the waves will win that war by attrition.
Somewhere on one of your threads I made a point about how the optimal dimensions for a fast human powered boat depend on the power output of that human. You might want to check yourself out on a rowing ergometer. I think it will point you toward something a little shorter and wider like the rowers have been pushing and it might make a better sail foundation.
The reason I love human and natural powered craft is that it grounds the design in something everyone can appreciate -their own power output. If you leave out human power there is no answer to "why not make it bigger?".

 

An oar auxiliary powered sailboat all but demands a center cockpit.

It's usually at or near the mid-point of the boat where the sheer is lowest.

The lower the sheer is, the shorter the oars can be. And I think short oars are called for to move a relatively heavy vessel (say one metric ton or more).

Shorter oars are like the lower gear ratios for your car. Longer oars are like the higher ones.

Lower gear ratios are needed to get you car moving. The higher ratio ones keep it going. But your car has plenty of horsepower. Your body doesn't. This being so, you have almost no hope of getting a heavy boat moving fast enough to make switching to long oars practical.

As the oar length gets shorter, the blade area should probably increase. But the bigger the blade area, the greater likelihood of the blade snagging the water on the return stroke. To lessen this risk, the blade planform probably should be changed from a rectangular tip to a triangular one.

I have even considered using a short sweep instead of a pair of oars. This is going to be the auxiliary power for the tiny sailing scow I'm building.

The advantage of this system is that there is only one side that needs to be watched, but this comes with a certain loss of efficiency, since now propulsive power is off to one side. Rudder correction will be needed to keep the boat going straight. I can imagine using both arms to pull the sweep. It can be moved to the other side of the boat to avoid fatigue, and to use the body muscles more evenly.

Another idea I have had is to make the blade curved in section. I am considering using a 3 inch pvc pipe, cut in half down the middle, as a blade. This way, if the blade snags the water on the return stroke, it will affect forward progress less.

 

1) Sliding seat?

2) Heavy, flexible PVC has no place on an oar. You really need to study and understand the basics which have been pretty well worked out.

 

Double paddle works well for a 24 to 28 inch beam kayak, and OK up to perhaps 36 inch beam. Beyond that, not so well! And sliding-seat rowing is significantly more powerful.

Using sail when there's wind reduces the "rowing in waves" problem, though doesn't eliminate it. And yes, facing the direction you're going is good. I rowed my Marsh Duck in significant and quite steep waves (once when mast broke). That was challenging, but OK. I think that ocean swells would be easier.

Longer provides greater hull speed.

Narrow reduces wetted surface and resistance.

Fore-aft weight balance can be challenging in ultra-light boats because crew weight is a large percentage of gross displacement, so when crew sleeps in a cabin, but rows in the cockpit, this must be managed. Greater length makes it more manageable.

Re "why not make it bigger", there are MANY advantages to small and light beyond feasibility for human power. Some that I appreciate include: ease of transport on cartop, by bicycle, and in other ways (across Panama on a pickup rather than dealing with canal requirements?); ability to more easily manhandle in launch, beaching, moving above high tide, etc. There are also the issues of cost, maintenance and storage which tend to be much less and easier for a smaller boat. Not to mention that smaller boats end up being used much more than larger boats, because they are easier to use and deal with.

Boats always involve compromise! We each must decide what might work best for our purposes!

 

1.) Maybe. But it seems to me that the purpose.of a sliding seat is to lengthen the stroke. IIRC, such is used primarily on racing shells, where the rower must propel about 200 lbs or less. Combined with the narrow beam of the shell and the extended outriggers, this makes a lot of sense. The oars can be quite long.

But with a much heavier boat (8 to 10 times as heavy), I'm not so sure.

If it turns out that it would be useful, a track can be installed on the sides of the cockpit seats, and the rowing seat can have wheels to fit into this track. The seat can then be easily removed and stowed when not in use.

2.) As for the PVC half-pipe oar blade, I don't see how it would be much heavier than the typical wooden plank blade, which must be somewhat thick, as it must deal with bending moment across the grain. Oars are often made out of a single, wide, thick plank. I see this as a terrible waste of wood. Mine would be made with plywood blades, if they are going to be all wood. The loom can then be two tapered boards glued together.

The loom will extend to the tip of the blade, or nearly this far. The blade will be attached to the loom so it faces forward, so there will be a squaring moment on the pull stroke. The PVC half-pipe will merely replace the plywood blade.

I doubt there will be enough bending moment to open up the curve significantly.

I am by no means an expert on rowing arrangements. I only have two formulas for length of oar, seat distances, and seat heights, that I got from magazines I have read.

I'll use them as my starting point.

 

Oars. I don't have a lot of experience with them yet but that will change soon. I do have kayak experience and experienced kayakers agree a quality, lightweight paddle is more important than the boat, within reason of course.
PVC is a heavy, flexible product, the exact opposite of what is needed. Sitka spruce and carbon fiber are generally considered to be the best materials in their classes. I am building some 9' 6" oars from Douglas fir using CLC plans. You will never see a knowledgeable rower using a split pipe, regardless of material, or PVC on oars.
You worry about wasting wood but the useless PVC oars you will discard are even more wasteful. You need to get some time on the water to cool down your half-baked ideas.
Sliding seats. Here are pre-production images of the boat I am having built. Note the tandem sliding seats. It has a self-bailing cockpit FWIW.
https://ghboats.com/wp-content/uploads/2021/06/8.jpg
https://ghboats.com/wp-content/uploads/2021/06/7.jpg

 

Sliding seat is mostly about using the strength of the legs (big muscles) to drive the boat, really using the entire body, not just arms and back. That's the reason ocean rowing boats always use sliding seats - for the power!

Due to old back injuries, I can use fixed seat rowing and double blade paddling for only limited amounts of time, while sliding seat rowing is no problem.

 

Also note that the inboard length of oars in sliding-seat rowing provides leverage, greater force (power) out at the blade.

 

I think these are two healthy criticisms of my approach.

Yeah, I'll admit mine are somewhat half-baked ideas. But I intend to test them on myself before recommending them to others.

Two points I left out in my goals are:
1.) That I want to really limit the length of the oar(s), and
2.) I want to try out my ideas as inexpensively as possible.

The boat I am building (see JoeBoat Alana thread in the sailboats forum) is primarily a sailboat, but has a somewhat shorter rig, to be supplemented with human propulsion.

Now to oar length. Oars typically must be double the Beam of boat, plus some, to be useful. On my 3 ft wide boat, this would require 6 ft oars, which would have to be stowed somehow while sailing. This can be a bit of a hassle, especially if I want to use my boat for angling.

But oars need to be so long, so the oarsman can sit in the center of the boat, and have the oar blades immerse at a decently shallow angle.

This is why I'm going to a short sweep. With that, I need the center of thrust as close to the side of the boat as possible. This gives a powerful incentive to make the sweep shorter. The shorter sweep will be much easier to stow. And I will need only one of them.

The hull design, a straight-sided scow, will benifit from this system, as it will heel towards the side being propelled from. This will lengthen the waterline, and present a "V" section to the water, which will reduce whetted area.

All of this, of course, is not only highly experimental, but not terribly efficient either (for the size and weight of the boat it's being tried on). My hope is that, if it works tolerably well, it can be scaled up. But it's very likely to fail.

There will be a pair of oarlocks installed, just for this possibility.

The loom will then be disposed of and replaced by new ones, long enough to make proper oars. So I don't want invest a lot of time and money making it. I probably will use a plywood blade for my first version.

I will use only about 15 inches or less of PVC pipe, if I go that route.

Such can be repurposed as fenders for my bicycle.

Half-baked ideas are where innovations come from. Much more often than not, they fail.

But, sometimes they succeed.

And my temperament is such that I want to try them.

 

I understand building a boat on a tight budget. I've been there and my biggest mistake in the process was not using proven, time-tested methods.