Shallow draft, wide beam, sailboat design. Comments good or bad welcome

Discussion in 'Sailboats' started by valery gaulin, Jan 18, 2019.

  1. valery gaulin
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    valery gaulin Senior Member

    Working on this design, Comments good or bad welcome.

    Lenght : 26 foot
    Beam: 13 foot
    Draft: 2 ft CB up, 7 ft CB down
    Displacement : Light 9 500 lb , cruising 11 500 lb
    Sail area: 600 sq. ft.
     
  2. JamesG123
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    JamesG123 Senior Member

    You might as well go foils or at least foil-assisted. All the cool kids are doing it.

    Whats with the chines in the bottom?
     
  3. valery gaulin
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    valery gaulin Senior Member

    JamesG123 the reason for the bottom of the hull as mainly 3 purposes. 1. It is a way to add headroom 2. A way to go aground when the tide goes out. 3. The chine will help for tacking ability, kind of like a mini shallow keel.

    No foil, anyway not with a pilothouse covered cockpit!!!
     
  4. messabout
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    messabout Senior Member

    If it is catboat then why not use the time honored cat rig?
     
  5. valery gaulin
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    valery gaulin Senior Member

    I love catboat single sail but for windward capability sloop work better. Also the giant boom and gaff of a catboat create problem.
     
  6. fastwave
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    fastwave Junior Member

    I would remove those chines. A normal smooth cross section will give you more volume for less wetted area. The you can reduce the rocker or the beam a little.
    In Addition it is better to create the lift with your nice keel instead of a very inefficient chine.
     
  7. valery gaulin
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    valery gaulin Senior Member

    You are right about everything. But it is a compromise those chine.

    1. It is a way to increase headroom inside.

    2. The bottom will be build to accept grounding when the tide goes out or for beaching.

    3. The bottom will have a large steel plate to act as ballast and for protection.

    4. The chine will help for course keeping when the centerboard is all the way up.

    Everything is a compromise. 26 foot lenght and 13 foot beam is also a compromise to create the most living space in a small sailboat. Also it should give a nice family experience with this initial stability for coastal cruising.

    The hull ratio are from catboats, actually very influuence by Harbinger catboat.
     
  8. sharpii2
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    sharpii2 Senior Member

    This is a very interesting design.

    I like the chine portion of the hull as a means of getting headroom and as a means of keeping the ballast low in the hull. A great idea if you're not trying to wring the most speed possible out of the hull. It may even be able to close reach with the board retracted.

    The one thing I don't get is why you have an aft cabin. The center portions of the hull have the most space. Those are also where most of the displacement of the hull is going to be. Usually, the cabin is where some of the heaviest items on the boat are. These include water tanks, food storage, and often the crew itself. Do you intend to use this boat as mostly a day sailor? My guess is that you put the cabin aft to avoid having the centerboard intrude into it.

    I believe you are wise in choosing a sloop rig over a cat rig. Actually, the cat rig is usually more weatherly. But it does have its vices. One of them is that the Center of Effort of the huge sail swings well outboard when the boat sails downwind. This effect, along with the shallow rudder most cat boats were equipped with, can cause some wild steering. The other vice is that, with a single sail, the boat has no sail up while being reefed. This can be very exciting when things start to get rough. The boat often finds itself in the trough of the waves in this condition. The working catboats were relatively small and used this rig to gain the most useable deck space possible. Larger boats of roughly the same proportions had a jib and were often referred to as "sloop boats". Joshua Slocum's famous Spray was a good example. Originally it was rigged as a twin-jib sloop (still called a sloop and not a cutter because the twin jibs were a very small portion of the overall sail plan). After crossing the Atlantic twice, he found the large main too difficult to deal with. So he shortened the gaff and the boom substantially and added a mizzen to make up for some of the lost sail area. He also found the long bowsprit and the twin jibs to be a bit of a handfull, so he replaced the twin jibs with a single one which was bigger but had less area than the twin jibs combined. This enabled him to shorten the bowsprit So his former "sloop boat" became a yawl, with a net loss of several hundred sf of sail.

    The exaggerated "bull nose"of the bow may be a good idea as it allows for a more gentle plan view curve for the bow.
     
  9. valery gaulin
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    valery gaulin Senior Member

    @ Sharpii2 :

    Thank you for your comments. The hull with the bottom of the hull shape with chine allow me to get 6'4" of head room, I measure 6'2".

    Now the aft cabin over the cockpit area is like a hard top bimini slash dodger. The reason I am drawing a permanent cabin over the cockpit is for many reason. 1. Good protection from the sun. 2. Good protection if it rain or get cold 3. A place to put solar panel 4. Could also collect rain water. 5. Could also be use to calculate stability. 6. The cockpit will be design to be an extension from the interior of the sailboat, were we mainly hang out and eat meals.

    Also I decided to design a hard top cabin over the cockpit from the beginning of the design because when I see all the sailboat at my marina with those huge full enclosure bimini/ dodger type of structure, It just make most sailboat look like **** because they were not design from start with the bimini enclosure.

    Why this design? It is mainly an exercise to see how much of a sailboat I can design with a 26 foot max lenght for my family of 5 (3 kids) for weekend cruising around Montreal Area. In Quebec. Futher down the road, when the kids are gone, being used for the great loop, ICW, Florida keys and if I am brave a jump to Cuba.

    Why 26 foot max? Because my home insurance can cover a boat with a max lenght of 26 foot and a motor of up to 25 hp.

    Actually it is not shown in the drawing shared above but I have fitted a 25hp high trust outboard on the transom. Easy maintenance and should be adequate for this type of hull.
     
  10. sharpii2
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    sharpii2 Senior Member

    Your cockpit covering would have to be heavily reinforced if it is expected to add to ultimate stability. Such may not be worth the added weight and top hamper cost. I once thought of such a scheme which would have a substantial amount of floatation in the top and would have a roll cage like support system. The high walls would be expected to be breached. Allowing such would remove considerable side loads from the support structure, which would hopefully improve its chances of surviving a roll over. But such a buoyancy system would increase the height of the top substancially. On a boat as wide and heavy as your design, the top would need to be even thicker to be effective. The walls should probably be made of fabric held by snaps.
     
  11. valery gaulin
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    valery gaulin Senior Member

    @sharpii2

    Yes you are righ about strenght, forces and everytjing else.

    I was already planning to run the bulkhead up to the cabin top but I will see when I make finite element analysis if it makes no sense weight wise.

    Thank you for the input.

    I think that the force needed is to hold the boat completely up on it roof top! The strenght needed is in direct relation on the amount of buyancy yoi want the cabin to contribute to the stability.
     
  12. sharpii2
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    sharpii2 Senior Member

    This is true. But even more effective at preventing a complete capsize would be adding buoyancy to the mast. This could be filling the hollow mast with low-density foam. If your boat was ever turtled (ended up completely upside down) it would not likely recover. This is because of your design's sectional proportions (too much Beam for the sectional height). So keeping it from doing so should be a major design concern. The deep, sharp chines may help trip the hull in the instance of a breaker hit abeam. But they also dampen the roll, slowing the capsize down. They may slow it down to such an extent that the breaker's energy is expended before the boat flips.

    But in the event of a capsize, the top of the mast will hit the water before any buoyancy you put in the awning top can be effective. If the mast stays hollow, it can fill with water all the way to the point the boat completely turtles. At this point, recovery is all but impossible. But if the mast cannot fill with water, it can act as an outrigger float and resist further capsize. The buoyant awning top would certainly help too.

    What material are you planning on building the hull out of?
     
  13. valery gaulin
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    valery gaulin Senior Member

    @sharpii2 : thank you for the input!

    I dont't even know if I will build it!!! I am just having fun drawing it! But if I build probably it will be a mix of Cedar strip planking and cold modled plywood epoxy.
     
  14. trip the light fandango
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    trip the light fandango Senior Member

    The the rear cabin helps the craft point to wind, easier steering when adrift etc.
     
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  15. philSweet
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    philSweet Senior Member

    The centerboard arrangement you depicted is very impractical and doesn't balance the sail plan (look at the aero lead of a Cal 28 profile by comparison). Please post some drawings of that CB, housing, and mechanisms. I think you are going to be seriously disappointed when you realize what a board that can deliver 70,000 ftlb or so to the hull will look like. Maybe get the area right for starters, then figure what chord you need to fair in the required thickness. Then you will see that you can't really use 7' draft in a 26' boat. Even five feet is a lot. If the board is ten inches thick, and you go with a 15% thickness section, you need 5'6" of chord. Since the boat isn't road transportable, just go with a fixed keel, take the space savings out of the beam, and realize that you will have as good or better performance with a well done keel at 4'9" or so.

    Box keels really don't do very well hydrodynamically. They just don't produce the lift of a narrower full keel of similar profile. You can certainly build down a 26'er, but you would normally do it with modest beam and modest displacement.
     
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