Any designers want to tackle a new build idea?

Discussion in 'Boat Design' started by MinorThreat, Aug 11, 2024.

  1. MinorThreat
    Joined: Aug 2024
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    MinorThreat Junior Member


    Thanks for the advice, it's appreciated
    I think leaning towards both.

    Lash the hulls, and hard mount the pod to the frames.
    The poles and mast will connect to the
    Beams so the pod will give it strength
    The lashed hulls will allow a little movement not sure yet
     
  2. rob denney
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    rob denney Senior Member

    No problem. Next one will be in a month or so. If you are getting foam, you could also get glass, carbon, resin and consumables.

    Need to define "works". Gunboat performance is probably an unnecessarily high bar. It is unlikely due to the cost of sails, rigging, equipment to handle it, lack of length and the boat strengthening to take the loads high performance cats generate.

    Whereabouts in the tropics? I'm in Fiji, have had no problem with the recycled PET foam. I would not paint it anything darker than Fiji (sky) blue, though.

    The hull design is nothing special, there are plenty of boats to copy. The engineering is a different ball game for a light, fast cat and will cost a lot. Alternatively, copy what you can, guess the rest, develop it cautiously and beef up stuff that is too light, which is the design process for most fast, light low cost boats.

    All sensible. Amongst a lot of other things, you missed daggerboards and steering, which could easily cost more than the hulls and take longer to build. See above about spreadsheets. The design process for light boats starts with expected weight.

    That should rule out ply. ;-) I suspect the rig and rigging on that boat is at least double your total budget.

    If I design it to fit your criteria, it will be end up as a Harryproa when all the superfluous loads and equipment are removed from a catamaran. Also, my personal requirements (plus easy to sail and build, with good motion so my wife didn't get sick) for the original Harryproa are near identical to yours and a cat or tri did not meet these.

    We use tapered sockets for the beams. Solid, easy to build and quick to remove/replace. Boats with unstayed rigs and low performance cats can get away with hulls that move independantly (ie lashed), catamarans with high performance rigs need rigidity. Lashings are a pain; they stretch, take time to install/remove and are lumps on the topsides which get banged when coming alongside. On the plus side, they can be works of art, as we saw with the Marshallese proas.

    The pod can sit on and be located by the beams and separate from the hulls. This will mean it 'only' has to be strong enough to support it's loads, not try to stop the hulls from pitching independantly. The rear beam support will have to allow for the traveller, unless you have a much easier to handle, but slightly draggier, wishbone boom. See above re the desirability of a rigid platform. A lot of 'bamboo bombers' (no bridge deck performance cats) require stays to the bows and tight rigging (with consequent higher loads, bigger gear and more cost) to prevent the hulls pitching independantly.

    Carbon won't be much help with the pod. The areas you step on will need to be at least 400 gsm of glass or carbon, the rest can be as light as you want to go, also in either material. You are looking for strength and impact resitance, not stiffness, which is where carbon is useful. A pop top might be better than a solid roof if it is not connected to the hulls. Maybe something like the collapsible camping pod on the E25

    Bolts and other fasteners are a pain. They need beefing up/load spreading, the holes sealed with epoxy, often leak, cause rot in ply and if stainless are prone to crevice corrosion. There are very few places (none on the cargo proa, including winches) where they cannot be replaced with carbon tow or fibreglass rovings, the modern equivalent of lashings, without the blocks, stretch and hassle.
     
    bajansailor likes this.
  3. MinorThreat
    Joined: Aug 2024
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    MinorThreat Junior Member

    Thanks again for the good information. I'm researching max surf, to start designing my hulls. Lots of work to learn obviously but I'll get there
     
  4. MinorThreat
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    MinorThreat Junior Member

    I would be interested in your design, but on your site, I see a 25 with the pop up tent I like that, then they jump up into cruisers too big for me.

    If you had a design that's like the 25 but around 32 to 36ft I'm all ears. I do like the fact that when I build your design, I have. good cost option for the building materials.
     
  5. rob denney
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    rob denney Senior Member

    It's gratifying when someone is open minded enough to consider changing their mind when things are explained to them. Thanks.
    Have a look at the EX40 which is a previous version, but has all the information. The latest version is a work in progress on the web page as we are refining it based on a 43' version being built in Ireland. An interesting client (another advantage of designing boats that are different), he is infusing his own solar panels.
    A big advantage of a proa is that the length can be extended with little overall weight added and no change in righting moment. Consequently the rig can stay the same. There is scope to make any refinements you require, including reducing the hull length, but in the interests of speed, load carrying and seakeeping, I'd go with the longest hull that fitted into the workspace, marina or trailer.
    I'm not sure removing the cabin and adding a pod would be much of a weight or cost benefit, but we could certainly do the numbers and see. If a day/weekend racing version was required, the removable pod and minimal windward hull would be well worth a look.

    Designing your own hulls should be a lot of fun. I look forward to the result. Any help required, let me know.
     
  6. gonzo
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    gonzo Senior Member

    Do you have any engineering background to be able to calculate any structure? Copying a moderate performance boat is very different from trying to copy a high performance design.
     
  7. MinorThreat
    Joined: Aug 2024
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    MinorThreat Junior Member


    I'm learning how these hulls are designed and what's required to make a good hull shape.

    Please shew away troll, I'm not trying to copy anything thxs
     
  8. MinorThreat
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    MinorThreat Junior Member


    I looked at the ex 40, not allot of info? Unless I looked in the wrong place, all I read was plans in the working

    Have a link to the old 40 plans with more details?
     
  9. Tiny Turnip
    Joined: Mar 2008
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    Tiny Turnip Senior Member

    upload_2024-8-14_15-29-58.png upload_2024-8-14_15-29-58.png
     
  10. MinorThreat
    Joined: Aug 2024
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    MinorThreat Junior Member

    Thxs. I missed the link.

    So. Group opinions

    How would this ex40 work for extended trips from Miami to the Bahamas, crossing the gulf stream? I just don't know enough about proa's to know the sailing ability's in the area I will be sailing in.

    Thxs
     
  11. Rumars
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    Rumars Senior Member

    Let's return to reality here. Making a light hull in (ply)wood has been solved by the Gougeon's a long time ago, all you have to do is read the book. Doing better in wood involves real engineering and expert builders, something that's definitely not in your budget.

    Going fast is a question of SA/D ratio. Gunboats are all above 35, so that's your benchmark.

    You can thoroughly forget all of Wharram's propaganda. Fast cats have to be rigid and use good sails. In real life a bolt and nut is also much cheaper then 50ft of hightech line for a lashing.

    For overall hull shape look at any racing cat in the size range you desire. Realistically any slab sided, fat and flattish stern will work. All you have to decide is how much rocker, if the transom is immersed or not and above water bow shape. Those are difficult enough decisions, no need to go into the more subtle things.
     
  12. MinorThreat
    Joined: Aug 2024
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    MinorThreat Junior Member


    Thanks. So how do I start figuring out the below waterline shape?

    The ply work I got the experience to do right.

    The carbon tube experience I have also.

    I helped build a pre preg mono back when...

    I have zero design experience..

    See my photos in my first post, let me know your best guess on how these hulls are shaped under the water line?
     
  13. MinorThreat
    Joined: Aug 2024
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    MinorThreat Junior Member

    Here is the photo, my thinking is, these hulls will be more then needed, if I can get similar shapes. I really.like the look of this boat. I need to simplify the rig. Reduce cost...i loose performance, understood...but that's okay. That's why I was as thinking a wharram TYPE SAIL
    With upgraded materials.

    Allot of people are poo poo'n the soft sail. But when I look at some of the more modern racing types sails and rigs, they are similar...close enough that with upgraded shapes, (the fall off in performance is substantial) it will be good enough to offer a nice sailing experience.
    I tend to think it is. If sized right. And.the cost plummet's to reasonable.
     

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    Last edited: Aug 14, 2024
  14. MinorThreat
    Joined: Aug 2024
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    MinorThreat Junior Member

    artemis-racing-catamaran-ac-50-desk-model.jpg


    Before anyone wants to come explain the major difference between this sail and a wharram save the o2

    My point is if you look at this fact,
    there is a middle ground between these two rigs...I think with a little work I can get 60% of this sails performance.
    Which is fine by my wants and needs. And I will keep the price reasonable doing it.

    I plan to find it
     

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  15. MinorThreat
    Joined: Aug 2024
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    MinorThreat Junior Member

    Here is the most recent wharram his newest design before his passing

    It might be faint, but I see some similarities
    Mast is wood, doesn't have to be
    The top gaff is wood doesn't have to be
    It doesn't have a boom, could have one
    Sail material is dacron doesn't have to be...
    Added the black wharram sails photo. Look at those beut'z
    Still working on this idea with study
     

    Attached Files:

    Last edited: Aug 14, 2024
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