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Rivers are often described as having a 'head of navigation', the furthest upstream point you can reach in a ship coming from the sea. Does this equally apply, regardless of propulsion method?

In particular, thinking about sailing boats, even small ones, it seems to me they might need more width on a river to be able to tack, or just generally respond to changing wind conditions?

I have seen it claimed that one of the reasons for the historical shift from ocean transport by sailing to steamship was because sailing ships had difficulty in the Suez Canal for that reason. Though that was large ships, and here I'm just thinking about small boats, suitable for operation by one or two people.

Do small sailing boats actually have more difficulty going upriver, than motorboats of the same size?

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    I believe it often depends on the draft. A sailboat needs a keel.
    – user2169
    Jun 27 at 12:12
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    A sailing boat also needs width to tack, but a motor boat can go directly into wind. "Regardless of propulsion method" - obviously a small rowing boat or canoe can go further, and can be carried past wiers where there is no lock, and I think it is is the presence of a lock (in UK at least) that determines the navigable limit. Jun 27 at 13:57
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    ...and a sailing boat isn't much use on many small rivers, because they cannot easily follow the rules of the river (pass port to port), and the frequent narrow-boats are not manoevreable enough to readily give way. Jun 27 at 14:04
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    The historical shift of ocean transport from sail to steam was probably driven by finance, needing smaller crews and being able to travel point-to-point and not have to rely on "trade winds" - not just the navigability of the Suez Canal. Steam became possible for trans-oceanic travel after 1815, but the Suez Canal was not opened until 1869. Jun 27 at 14:32
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    @ChrisH I meant the whether there is a lock. Jun 28 at 12:01
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The head of navigation is entirely subjective.

It depends on the type and the size of boats, which have different requirements. The river Thames in UK, for example, has several locations that limit navigation.

  • London Bridge was the traditional limit for tall ships due to their mast height

  • Richmond lock marks another limit, restricting the width of vessels

  • Further upstream Osney Bridge at Oxford has the lowest headroom on the Thames

  • Above St John's Lock at Lechlade the river is only suitable for very small boats

A sailing boat has more restrictions than a motor boat

  • It has a deeper keel so needs greater river depth

  • It has a taller mast limiting the bridges it can pass under

  • It needs width to tack, so cannot sail far on a narrow river

So a motor boat can definitely navigate further upstream than a sailing boat.

It is possible for boats to navigate between features they can't actually pass: a boat may have been delivered by road on a trailer and launched on the river. The general limit though, is when there is a change of level such as a wier or natural waterfall, and there is no lock to raise or lower the boat past it. Even where there is a lock, there is a width restriction, for example the lock at Richmond is only 2m wide.

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    +1, though my comment under the Q also addresses your example. Continuing that, the limit on the Thames for most river craft is Lechlade town, not the lock. You've got to watch out for decent-sized boats while swimming there
    – Chris H
    Jun 28 at 12:02
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    @ChrisH I had mentioned locks in the second bullet but I've extended the answer. Jun 28 at 12:07
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It is the motorboat. Definitiely

Draft
Any sailing vessel needs a mechanism to withstand sideways drift and heel. A yacht with an ordinary fixed keel will require at minimum 1.5-2m of depth but we are not limited to this. Draft is not only a problem in rivers but also in tidal areas so people have been creative by developing sailboats with retractable keels, twin keels and daggerboards mounted on the side which can reduce the draft to around 1m for sailboats carrying reasonable loads. Probably the most efficient hull with regard to draft can be found at beach cats which can sail in knee deep water if necessary.
By contrast, a motorboat does not require any keel, fins, etc. If is just limited by the depth of the screw and even that can be removed, for example in the swamp boats

Tacking
The draft of a swamp boat can already be considered full victory for motorboats but let us elaborate further on the topic of maneuvering. A sailboat can only sail at certain angles against the wind. Even a wider river will be a problem when the wind is blowing against you. Tacking may be possible but the VMG is considerably smaller than your speed through water. Additionally, on every tack the current will push one down, reducing the effectuve VMG even further. So already a rather wide river of 100m navigatable width will be a real problem for sail boats

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