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Thread: A new Raidboat and Cruising Dinghy Design for the Home Builder

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  1. #1
    Join Date
    Jan 2010
    Location
    Wilhelmshaven, Northwest Germany, Jade Bay at the North Sea Coast
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    119

    Default A new Raidboat and Cruising Dinghy Design for the Home Builder

    Hello!



    In this thread I will start to design a new Raidboat (or Fast Cruising Dinghy) for home- and professional builders alike. It will be on the simple, fast and cheap side of construction with as few parts to be built as possible. But it will be but not a „simple as can be“ design to allow all the features that make sailing and cruising live safe and comfortable.

    On the sailing side it will be a fast and lively boat with a good overall performance and balance, able to sail many miles a day. Easy Daysailing with your partner and one kid is also a design target as well as racing on club races.

    For me Lightweight construction and -displacement is the key to reach the targets and also allows easy trailering and -handling on the beach.


    Safety is another important topic in this design. Recovery from capsize, self bailing cockpit and getting back aboard ... I will turn attention to these topics



    Concept Catalogue

    General
    This boat is meant to be a singlehander for cruising and cruising raids and can take up to two crew and a kid for daysailing. When sailing in club races it shall not automatically earn the red lantern.

    Length over all will be two sheets of plywood long, meaning a little under 16feet. So it will be a long and light boat for a single hander and therefore a fast one due to the long waterline.


    Safety:

    A raised floor for a self bailing cockpit after recovering from capsize, no bailing out water when sailing in strong winds and waves, no need for Elvström bailers, no wet sleeping bag when sleeping in the boat.

    No side tanks (a la 470 or 420) to allow the boat to sink in a little when capsized. This helps to reach the daggerboard from swimming to re-right the boat. It also makes the boat roll back more slowly, so that you can climb back into the boat in one rush as the boat becomes upright. The boat will stay at 90° heel when the mast is nearly parallel to the waterline and will have no tendency to become 180°.

    A safety ladder for getting aboard after capsize as well for taking a bath when anchoring.

    A sea anchor keeps the boat with the bow into the wind while reefing or capsizing.

    Water ballast will calm the boat down when sailing in strong winds and inceases the stability. It also helps to re-right the boat. Off course the ballast tank is empty in light winds and regattas.


    Performance and Balance

    Sharpie hull with flaring sides. Sharpie hulls offer good performance when designed with care. In a modern design like this one they have a slim waterline for low resistance and good planing abilities. The center of flotation is slightly aft of the middle to allow an effective trim from the aft sitting skipper. The flaring hullsides increase the sailing stability when sailed heeled and dampen the tendence to capsize. They also make hiking out more effective.

    Lightweight construction. The lighter the boat, the faster it is … so simple. Even if this design is a cruising dinghy and has to carry a lot of stuff beside the crew, for me performance is important. Take out all the cruising stuff and have some fun racing on club regattas. Overall boatwheight ready to sail but without cruising gear should be well under 90kg.

    Effective sail plan. Cruising Dinghys need a sailplan with a low center of effort and the ability to reef easily to make sailing safe. Singlehanders are suited best if they have only one sail to handle. I have chosen to use the balanced lug sail with a large sail area as the standard rig for my design. It can be trimmed very good to balance the boat upwind and is very neutral and effective when the wind is coming from the side or behind. Mast will be free standing without the need for shrouds.

    I know that a lot of sailors prefer the yawl rig for cruising so this rig will be an option in the plans. On the downside of this rig I see the building effort of 3 to 4 more spars and the cost of two sails instead of one. And the loss of efficency of the departed sail area, the increased wind resistance and the wheight of the aditional spars.

    The rig of the OK-Dinghy or other singlehanded dinghys is another option. Even the sails from a windsurfer can be rigged, but this would be a experiment on your own risk. Windsurfer sails cannot be reefed.


    Comfort

    Side decks for comfortable sitting and hiking out over a long time.

    Sleeping inside the boat is possible on the uncluttered raised floor and unter a custom deck tent. This is important in my home country as „wild“ camping is not allowed in Germany.

    Dry stores are under the raised floor in the forward part of the boat, reachable through watertight hatches in the floor. Here are fixed places for the anchor, water supply and other heavy gear that will double act as ballast. A step upwards in the raised floor brings here a height of more than 30cm (1').

    High sides for dry sailing in the sitting area midships


    Construction

    Construction will be sitch and glue, the fastest and most effective construction method for plywood. Every part you build will also be in boat later. No need to waste time and money on a buiding jig or temporary moulds. Okume marine grade plywood with 6mm, 5ply will be used for all parts of the hull. 4 frames/bulkheads plus stem and stern will form the transvers members. Only one stringer will be in the hull sides, mainly to be the base for the raised floor.

    The Sharpie Hull is the fastest and simplest hull to build and with it's three panel layout also the cheapest one to put together. There is nearly no waste in the panels

    The round Mast will be made from wood in the birdsmouth technique and rectangular sections for boom and yard.


    As far as I can see it now you will need 7 sheets of plywood and 12 – 15kg of multi purpose Epoxy for glueing, sheeting and laminating glasfibres.
    Opposite to 5 sheets of ply for a „simple as can be boat“ of the same 16 feet lenght. In my oppinion it is worth the extra effort.


    That's it for now!

    I'am open for comments and incitements. If you have other topics and ideas to be minded let me know and I will try to incorporate them into the design.

    Have fun! Michel
    Last edited by luckystrike118; 07-01-2019 at 05:11 AM.

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