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The 70' Thames Sailing Barge


70' Peregrine-on-Thames - Classic Thames Yacht - Kasten Marine Design, Inc.
Aft View - Sailing
| Far Aft View - Sailing
Aft View Perspective | Forward View Perspective
Interior Plan | Interior Profile

Copyright 2012 Michael Kasten

The Concept

The request here was to see if an extremely shoal draft sailing "barge" could be created at around 70 feet on deck somewhat along the lines of the classic Thames Sailing Barge types, but built in steel with a fantail stern. A tall order it seems..!

These requirements have encouraged a long and low interior accommodation forward, with an aft "sunken" deck house, with binnacle and steering station right aft on deck. Given this request, it seemed best to take a pre-existing prototype and simply re-form it to the dimensions required for length, beam and draft. The Peregrine 82 prototype was perfect. For this new prototype I've used the design name "Peregrine-on-Thames" to reflect the parent hull form, and its current iteration. The links above show renderings of the preliminary model created with Maxsurf.

Thames sailing barges usually have a nearly flat bottom, fairly upright sides, and a hard turn of the bilge without much exposed keel. Ordinarily there are leeboards, as would be found on the 1800's and early 1900's Dutch sailing barges. Unlike the Dutch sailing barges, Thames sailing barges had a highly tucked up transom stern, with a big barn-door rudder and long tiller.

However I especially like the fantail stern for use with a simple and easily built single chine hull shape. A fantail stern echos the type of rounded stern more in keeping with the Dutch sailing barges, so it seemed a natural.

In order to get sufficient headroom with a draft of only around 3 feet, there should be perhaps 3 feet of freeboard, plus a cabin trunk on deck of maybe 24 inches in height. But it is also possible to do away with the side decks as on the Peregrine, so there is no actual "cabin trunk" but instead the cabin top is taken all the way out to the top of the bulwarks. In order to achieve the very shallow draft of only 3 feet, the bottom must be quite flat port to starb’d, or will possibly have only slight deadrise.

To achieve motoring with such shallow draft, ideally there will be twin propellers at the aft quarters. If a single propeller were desired for the sake of simplicity, it might be possible to extend the centerline keel farther aft to allow room for the propeller aperture. If that still turned out to be insufficient for the propeller, a fixed “nozzle” could be placed around the propeller thereby increasing the effective aspect ratio of the blades without having to increase diameter.

In order to provide for good sailing performance and safe sailing in terms of overall stability, it is extremely beneficial to have the Peregrine style flush-deck cabin top that extends from side to side at the height of the top of the bulwarks, i.e. no side decks. This provides greater reserve buoyancy, vastly improved large angle stability, and a much better chance of compliance with the EU – RCD with regard to the STIX rating in order to qualify for Category A – All Ocean, as well as extending the range of positive stability.

The traditional Thames Barge sail rig has a lot to offer in that regard, since it is low down but spreads a good amount of canvas. As an alternate, I also like the type of sail rig given to similar vessels in the Netherlands. There are many good examples of traditional Dutch and English sailing barges in Harlingen – one of my favorite harbors…!

An outside helm is easily arranged right aft, and is quite traditional for these craft. Given the request for a modest deck house, it seemed best to keep the house as low down as possible. My concept was that it should take the form of a “sunken” deck house with window sills just above the level of the flush fore deck, i.e. half buried into the raised fore deck. Below the deck house is the ideal spot for the engine / mechanical space, since it is not a requirement to achieve standing headroom there – in particular if the engine space is accessed from above.

The Preliminary Model

Because this request tweaked my curiosity, I took the trouble to model such a creature with a Length on deck of 70 feet, a Draft of 3 feet and a Beam of around 19 feet. Following are a few notes to explain the resulting model and its rationale.

Given the draft restriction, with a modest keel and a slight amount of deadrise, the model turned out to be quite light displacement. This points toward the possibility of using aluminum for the hull / deck / house structures. It is apparent that if steel were preferred but draft could not be increased, that the hull shape should be altered in order to accommodate the added weight. The most likely changes would be to introduce around 20 feet overall beam, and modify the underbody to have a more full shape with very little if any deadrise and less external keel.

Elsewhere, the fore deck is raised so there is no side deck and no cabin trunk. As noted, this benefits large angle stability immensely. As a sail boat, the deck house has been reduced in height (versus the 82' Peregrine), and the roof overhang has been abbreviated considerably.

The aft deck is at the height of the rub rail, and is intended to have a stout welded pulpit all around. I have assumed there would be seating all around aft at a height that would allow a reasonably good view around the deck house, with a binnacle and steering station right aft of the mizzen mast. Alternately, a good steering station could be located just forward of the mizzen for a less cluttered helm location.

The rig I’ve shown is very standard for a Thames Barge. This could easily become more like a Dutch barge rig, which I like quite a lot. Ordinarily the Dutch barges are cutter rigged, rather than the yawl rig as is most common among Thames barges. While the Dutch cutter rig is simpler, it also makes the main sail that much larger and less easy to handle, and it pushes the center of effort a bit higher, and that is not entirely favorable for such a shoal draft vessel…!


In this model, the engine room / mechanical space is below the deck house. Since there is no need for much if any headroom in the mechanical spaces if they are accessed from above, the deck house has been given a full 7 feet of standing headroom.

The deck house could be used to house a second, sheltered steering station. Or not...!

There are various options for the interior of a house like this, depending on where the entry is located. If the entry is located aft, then it is usually best to have bench seating on either side, or possibly a long counter to one side and dinette on the other side. At 70 feet of length, there is actually enough beam to accomplish that. Possibly the long counter could be the galley...!

Alternately, if the entries are located on either side forward, then a wrap-around dinette is possible in the aft end of the house.

Forward of the deck house, I have assumed the interior layout will be more or less the same as I have shown for the 61' Peregrine, the interior of which is shown there in Plan View and Profile View. A description is as follows...

Leaving the deck house, the companionway leads forward and below on the port side. To port of the companionway below is a long bureau, housing a laundry and hanging locker. To starb'd of that is a large U-shaped galley.

A large saloon is located forward of the galley. Two long curved seats along each side have a low "coffee table" between. At the aft end of the saloon seats is a cabinet / book case / sideboard.

Forward of the saloon to starb'd is a large head compartment, complete with a combination shower / bathtub... a very welcome device for living aboard! To port of the head is a guest cabin / ship-board office. It can be arranged to serve both functions, using a "berth-in-a-box" scheme, where the mattress hides in a large box, more or less the same height as a desk drawer. The desk-top is then arranged to fold up to reveal the bed inside the desk...

Forward of the head and office / guest cabin is a door leading to the master suite. Within the master stateroom are a pair of bureaus, one to each side, which also contain a pair of hanging lockers. Between the bureau lockers is a generous dressing area. A big double "island" berth is right forward, with the head of the berth forward. Another shelf / locker space extends across the ship just forward of the berth.

A bulkhead is at the forward end of the master stateroom, forward of which is a large fore peak for anchor rode, dock lines, fenders, etc. A hatch leads into the fore peak from the well-deck forward.

The interior described here is for long term living aboard for a couple. Guest sleeping is accommodated on the settees, within the pilot house, and if so arranged, within the convertible office.

The well-deck forward provides a good anchor handling spot. In between, there is an enormous foredeck area for sun bathing, where a simple awning would provide a bit of shade, or shelter from a tropical downpour.

The above described interior is merely a suggestion, but it does work rather well for this hull type. Naturally at 70 feet on deck, this model is wider and bigger than the 61' Peregrine in all respects, so there is much more elbow room and there is good flexibility with regard to just how the interior might take shape.

It is often said that there is no substitute for length when it comes to creating a generous living space. I believe this to be true.

Design Constraints

I found it quite interesting to create this model in order to investigate what a 3’ draft limit would require. This is by no means a “final version” since there are many tweaks to be made based on the preferred material of construction, etc. Also, the rudder should be larger and possibly the aperture eliminated in favor of twin propellers, one under each quarter.

A centerboard could certainly be used rather than the usual Thames barge leeboards. I think a generously sized CB could be hidden below the saloon table (see the interior Plan View). But if leeboards are preferred, the tall bulwark of this model would suit them well.

The displacement of this model is right around 30 long tons, which as noted above will mandate rather a light structure. Although displacement can be increased as noted above in order to accommodate a steel structure, if we assume a lightweight structure there are a few interesting results...

One of the challenges with extremely shoal draft – besides having enough headroom throughout the interior – is to achieve adequate stability. The tendency is that a shallow draft boat will be extremely stiff and therefore very well able to stand up to her sail, but often there is not much “range” to the stability curve, which often disappears completely beyond around 80 to 90 degrees.

I was curious about this, so I ran the model through a quick hydrostatics analysis. With the raised flush fore deck, if the VCG can be kept within a given range (depending on the eventual hull form and displacement) there is likely to be well over 120 degrees of positive stability with this model, and… there will be extreme stiffness under sail.

This kind of hull form has a generous water-plane, which provides very adequate reserve capacity for fuel, water, and stores. Overall though, systems must be kept as light as possible. Therefore, we should assume there will be no elaborate systems, no separate generator, no water maker, nor all manner of other stuff. Instead we should assume there will be a very adequate 24v DC system; that tank capacities will be kept to the minimum required; and that construction materials will be chosen for lightness.

One can also save quite a lot of weight by using light weight interior structures, such as honeycomb panels for the joinery flats wherever they are practical. One such material is Nida-Core, possibly the most cost effective among the HC panels. Nida-Core is easily laminated to thin plywood skins, producing very stiff and light interior joinery panels.

It has been quite informative to check this out. In other words, rather than simply reply to this inquiry with a glib “yes we can” I thought the request sufficiently challenging to actually “want to know” for myself whether it could be made to work. As it turns out, yes such seemingly conflicting ambitions are achievable..!


Sail area as modeled is around 1,500 square feet in the lowers, with around 2,200 square feet total. Though I've shown a very traditional Thames Sailing Barge sail rig on this model, many other sail rig options are available. For example, the Chinese Junk rig would also be an ideal choice. To see an example please have a peek at the cat ketch junk rig drawn for the 50' Renegade.

This hull form was originally derived from a marriage of two well known sailing types - the sharpie and the skipjack...! Therefore an enlarged sharpie schooner rig would work well. Or possibly a skipjack rig in yawl format. Or a long and low gaff schooner rig possibly like a Tancook Whaler rig... Many options indeed...!

For the best balance under sail, it could turn out to be favorable to arrange tandem centerboards in a way that would not interfere with the accommodations.


So far the 70' "Peregrine-on-Thames" is a prototype design - one which can serve as inspiration for slim water, whether for river cruising, canal travel, or all around gunk-holing among the reeds... With a nearly flat bottom, taking the ground presents absolutely no drama.

The adventure with the Peregrine series of desgins has been to nail down a style that provides a timeless classic aesthetic; generous interior accommodations without crowding; a low profile for canal cruising; a hull type that lends itself to economical construction; an easily driven hull form; and an overall presentation that would "fit-in" regardless of where the yacht may be found, whether that may be in the South China Sea, the South of France, or the riverine estuaries along the English coast.

I believe such a vessel has considerable merit for permanent living aboard, intimate charters, and long range cruising...!

70' Peregrine-on-Thames - Classic Barge Yacht - Kasten Marine Design, Inc.
Click for Larger Image

Other designs in the "Peregrine / Renegade / Moxie" Family:

36' Molly | 43' Moxie | 49' Quinn | 50' Renegade
61' Peregrine | 82' Peregrine | 100' Amazon | 164' Peregrine
60' Pennywise Trimaran | 70' Peregrine-on-Thames