- My latest commission for an aluminum 48' with a ballasted - keel- centerboard.
- Very popular in France, and built by a few shipyards in aluminum, the model is known as "deriveur integral". True center boarder often ballasted, the raised board is totally integrated within the shape of the hull.
- This is still work in progress, and the above preliminary drawings have been upgraded and I have another version with a different interior, necessitating to review the lines, the board, and the displacement. Some of the revisited changes will be applied to the earlier version as above. See further down the updated version as of May 12, 2020
- Phase 1.
- Text: A shoal-draft cat-ketch. (The first draft, February 24, 2020).
- Over the past 30 years, there has been, especially in France, a special breed of boats. I am talking about the center boarders or if you prefer, swing keel shallow draft sailboats. What follows are generalities and my comments.
- The type has specifics; aluminum hulls and deck. Strong as hell and offshore oriented. Not a hard combination standing alone! But with a very shallow body hull depth and low ballasted centerboards the architecture and engineering present serious challenges.
- The general type is not unknown on this side of the Atlantic. As originated with the Monroe's Presto; Alice yachts and minced with the commercial skiffs of the 0ystermen. This was followed by the C.C.A racing rules, encouraging certain types of centerboards. So, with this new commission, I get the opportunity to study the question, raise a few others, and redefine the envelope.
- The Preliminary drawings shown are the first essentials to depict the vessel. More than usual time has been devoted to those drawings to satisfy the customer's wishes and at the same time, for me in my mind to develop a clear picture as we progress along. A boat like this one has conflicts in all directions and they need to be addressed as much as possible first hand, before getting out of hand altogether.
- So, we are following further with the specifications.
- The Sail Plan is divided. The request for a free-standing Cat-Ketch rig was the foremost first question to answer. It requires masts location, making sure about balancing the rig and the hull and the board and certainly trying not to screw up the interior plan in the first place. The choosing of carbon fibers for the mats is a step in the right direction, this in order to lower weight as much as possible for a yacht where stability is at a premium.
- Stability. How to have stiffness for this boat under with such a low static depth and with a divided ballast arrangement?
- Strength. Even though I am a little reluctant to park a 15T. boat on the sand, and certainly not over rocks, there is provision for it in the heavy scantlings for this all-aluminum hull and deck.
- Pilothouse and Deck saloon. Both nice features, but could make difficulties managing headroom, freeboard, and the rest of the Accommodation Plan; and still be attractive.
- So, follow me with the ongoing description of this project.
- Lines Plan. I went for several hull shapes; now number 12, aiming at a certain displacement since revised; hull depth, form, and functions to answer the many questions about stability righting moment, righting arm, and with the ability to build an aluminum hull in an effective manner.
- The hull form derives from many years designing chine hulls, and with this one, a real combination.
- First, the full bow above the waterline is important with a Cat-Ketch where the mainmast weight is located far forward.
- Second, the very wide shape of the boat is carried to the stern. Wide stern boats are unbalanced when they heel over, this is when my Gull/Stuka's wing at the back comes into effect. With a determined angle of heel, the stern will offer low drag, less wetted surface, and a planing platform.
- Third, there is a choice about the topsides where the hard knuckle chine can be substituted by a constant radius from bow to stern. It is an esthetic decision for people reluctant to adopt the look of hard chine boats.
- Such a wide hull needs twin rudders. The hull draft is not deep enough to make a viable proposition for a single rudder. So two rudders it is! As you heel over to, say 15 degrees the blade surface on the lee side double to give the necessary area to control the boat. I started with the installation of spade rudders, but I think it would be prudent to have full build skeg in front of the blades. I have to think more about it. The problem with steering will the backing under engine power where the water flow does not meet a turning rudder blade, you will have to anticipate the maneuver and a bow thruster is probably a necessity. One solution may be, that I have not seen before, is to build a small third rudder placed in the middle to achieve the result at a cost of more drag and complication with the steering system.
- A Fish view!
- The ballasted centerboard is next on the list with a question mark? With a boat floating in less than one meter of water, this apparatus has to be carefully studied. I went to several configurations to settle back on the Red Rooster arrangement; a Dick Carter Design of 1969 ( before my time there). Besides the straightforward parallel edges, this shape allows me to place, maybe close to 1.5T. of lead within the shell. I envision the total ballast at over 5 T. with as much as possible inside the board. A hydraulic system articulates the ups and down movement to the depth of 2.68M. A block and tackle arrangement is also available in case of system failure. A plate is lowered to close the gap left open when the board is down this, in order to minimize turbulence.
Note: The design has 2 different interior plans necessitating to review the board in particular and to be explained later.
- The Accommodation Plan. It is derived from a French sailboat appreciated by the client, with the particularity of having the navigation desk forward of the living area. Not unlike a set up on many powerboats. But we will start from the stern where we find port and starboard sleeping locations. One is larger than the other, the other being more dedicated to the possibility to install a bench and becoming a workroom with full headroom. Both cabins have
hanging lockers, seats, and drawers.
- Moving on forward on one step, the cabin sole on Starboard is going all the way forward on the same level. It includes the Head with separate shower, the Deck Saloon, and the Navigation Table already aforementioned. The place with full headroom is surrounded by the clear glass all around for a maximum of visibility and luminosity.
- The engine is located underneath the sole with good access for routine maintenance. Other machinery will find their place as needed and as specified. Notice the straight shaft and skeg protection. Also, that the settee berth is over the centerboard case giving the later more area and more efficiency going to weather when placed down.
- On the Port side, a wet locker with a seat to put boots on, a step down to the fore and aft 3,5 M. long galley area. You can do some serious cooking there! Going further forward, a step up to the Master (would it be?) cabin. With the usual arrangement first, on the port side a seat, hanging locker, a vanity table, and more storage spaces. On the Starboard side a large double berth with more cabinets.
- A watertight bulkhead divides this cabin from the bow area.
- The following drawing includes the up to date ( as of May 27, 2020) amelioration and changes affecting the new bow, the new configuration for the board, also a new chine line, and several other mostly small departure from the original preliminary drawings.
- The re-designed bow has seen many changes, the main reason being the handling of the anchoring systems and might see further improvement as we settle on the overall situation regarding the choice of anchors, windlass, and gears. One thing to note. If a plump bow is fashionable, there are drawbacks; it delivers a wet boat and offers challenges in not banging the hull when dropping the anchor. So, I welcome the latest hull lines with incremental overall improvements.
- The board has been enlarged and is deeper. The centerboard has a new case to handle the modification and the system to raise/ lower the board has been revised.
- Now on to Phase 2. April 15, 2020 updated to May 27,2020).
- No changes there, in terms of sail area, masts location but big alterations in hull lines, centerboard and of course the new or rather; the different Accommodation Plan. The later dictating and leading in modifications to both versions of the boat.
- Lines Plan.
Hull design tests led to the following major amelioration. The maximum Beam has moved aft, with some change with the transom , the deck lines became finer forward, towards the bow. The adjustment is made with further analysis of the weight and center of gravity in association with the new Interior; the new displacement figure increases the hull depth from the original. The construction plan and scantlings are justifying these changes.
- Centerboard.
The shape is modified to accommodate the new internal arrangement. Of course, the board is still ballasted and has less draft than the previous version (#199), but with more area and volume.
-Accommodation Plan.
Concentrated in the middle with another cabin located on its own, partially under the settee berth on the starboard side. A feature already presents on a couple of previous designs, but this time with the benefit of more available length. It shows a seat, hanging lockers, storage, and a large double berth. For the rest, starting in the stern, the cockpit and steering area are not modified. The portside cabin has a little less sole area but remains practically unchanged. The Starboard cabin is now more oriented to be a working place, with some machinery and direct access to the deck thru the cockpit seat. A single folding berth is still available. -Following, the navigation table is now placed aft instead of the forward position in the first interior version. Then, we come to the elevated Deck Saloon with, wraparound windows in a shortened pilothouse with seats and a table. The elevation allows for the centerboard trunk to be set higher given the added area to the board blade as mentioned before. Note: The Phase 1 interior will probably keep the original board shape or something close to it.
- We already talked about the Middle cabin with its own access door on the Portside.
- Continuing on to Port, the aft seat and the wet hanging locker has been replaced by the galley all the way forward to the Head and Shower. Ahead of the Main bulkhead, the cabin has not been modified.
- The above concludes the evolution of the design for the time being. May 27,2020
(to be continued).
-Ref: TYD #240
- The Swing keel for this model is outside the body in a retracted or extended position, whether up or down and with only its articulation inside the hull. The keel shape results in a high aspect ratio foil.
- The swing keel.
- Finisterre is a keel centerboard and made good use of it. With the ever-present pressure to reduce draft, retain stability and performance; the combination is appealing. But what sort of keel? What sort of board? There is nothing new about what I am proposing, but I think it will go well for this type of craft.
- The ballasted keel-board articulates to a variable geometry. Essentially, with three positions; all the way down to 30 then, to 45 degrees and all way up for a total depth of 5' from the waterline. This ballast arrangement is deep when you need it. The question of ultimate stability is always raised with wide boats. Finisterre was also a "Study in Beam" case at the time. - By paying attention to the location of weight, with a conservative displacement to start with, the stability will be there in the first place. Shape the deck superstructure with some volume and camber, incorporate a pilothouse bubble then you reach ultimate stability, or rather instability if you have the misfortune to find yourself upside down.
Ref: TYD# 271
- Aluminum Sloop. 40'. New "Blue Water Ship". Shallow draft cruising boat. Charter boat for up to 10 guests and crew. Daggerboard.
- L.O.A 12.2M x L.W.L 11.56M x Beam 4.67M. x Canoe Body Depth 635MM. x Draft 2.44M x Displacement 10T440 x Sail Area 917 Sq/M.
Read more? " L'aileron" on Search.
- On a smaller note, and on a smaller scale, this 30' sled with swing keel is the next topic. I have a lot of affinities with the shape of the boat in the first place; being of very light displacement and very straightforward in all forms. A light, fun, fast swing keel sailboat! Built with plywood, the boat is assembled by using every element; bulkheads, frames, and longitudinals all for a purpose.
- The interior is of a classic, almost old fashion layout delimited by structure and the construction of the keel case. To adhere to the Sport Boat avocation, the cockpit is large and wide open. You can see more about the boat on an earlier Blog: L'Aileron.
Hull no.1
Hull No. 2
OLDER DESIGNS.
Ref: TYD#216.
- Wood. Utility sailboat based on Commodore Munroe's principles. Shoal draft ketch with the rare qualities attributed to His type of boats. Adapted to the Florida Strait, the Bahamas, and other areas with shallow water. An optional external ballast keel increases the range for offshore sailing. A leeboard version is also available. The Gunter rig and free-standing spars are very much in line with the overall concept.
- Loa. 32' x Lwl. 30' x Beam 10'-6" x Canoe Body Depth. 30". Draft: Leeboards 4'-6"; centerboard 5'-6" x Displacement 11,287Lbs.
Wing Maran.
-Ref: TYD#243
MOUSE
- Ref: TYD#253.
19'-6" strip plank or cold-moulded wood. Centerboard with 4" draft. Sitting headroom. Cat-Yawl rig.
SEA-SHELL
- Ref: TYD#946.
31'. plywood Coastal Cruiser, daggerboards, gaff rig; 6'-4" headroom. L.o.a 30'-11"x L.w.l 27'x Beam 9'-9"x Draft 2'-0"/5'-3"x Sail Area. 520 Sq/Ft. Displacement. Light 9000Lbs.
TEN-TEN.
- REF: TYD#284. Having designed many so-called "Lobster Yachts"; I thought that a hybrid alternative power and sail could be interesting. L.O.A 46'; 14M.
Ten knots under power, 10 knots under sail.
SEAWEED.
- Ref: TYD#940. Centerboarder.
Ref: TYD#962. Lifting Keel.
- To be continued.
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