Sueños Mojados

Discussion in 'Boat Design' started by Saqa, Jan 11, 2015.

  1. Saqa
    Joined: Oct 2013
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    Location: Fiji

    Saqa Senior Member

    This is the seven month journey so far. It started when I asked a question about what type of boat can handle the sea conditions that I presented. Since there are no plans for sale for the resulting craft, no second hand vessels of that type in my location I have taken the path of making something myself and have a jolly old time at it

    I have settled on building two boats. The first will be this project, which will be a personal boat that I will use for finding and working new grounds and general exploring and fun. The second build will be a professionally designed boat along similar lines that I will use strictly for fishing charter operations. I have presented detailed SOR to Richard Woods and Jacques on the Bateau forum and good to see their interest in adding such a design to their lineup

    Thanks guys for steering me in the right directions in later discussions when I have asked for assistance with obscure materials and construction methods and possible software glitches and a couple of aspects that were beyond my ability to calculate. I am happy to report that the time you took to assist hasn't been wasted

    If there is anything that is helpful to anyone else in this project, you are welcome to use it and I would be happy to share. Also would appreciate any mistakes or problem areas being pointed out

    The Project
    Sueños Mojados - a paddock basher offshore fishing cat

    What I need from this boat
    1 - For tropical conditions
    2 - Can cross large choppy lagoons in comfort to run out past fringing coral reefs with breakers and travel out wards offshore along reef chains to fish each reef
    3 - At least 10 knot cruise ability and hopefully 15 knot
    4 - Open flat decks for all around fishing ability
    5 - Can be moored in poor water conditions on shallow flats, no worries about sustaining substantial damage from being pounded on rocky rubble at low water
    7 - Can be grounded anywhere I want to explore or have fun
    8 - Minimum amenities, is for personal use occasionally with my wife or a decky or fishing buddy

    Project is inspired by the Silver 29 production boat from Africa, I am aiming for a similar light displacement of around 1400kg and max around 1800kg

    I have selected HDPE as the build material with the option of foam filling the sealed hollow chambered hulls if needed. Its a material that I know fairly well in use and workability

    I am currently up to here, I have drawn one hull which will be reflected by a twin in a cat configuration

    Lines Plans one hull

    [​IMG]Lines plans by jonny.toobad, on Flickr

    Stats one hull

    [​IMG]Stats 1 by jonny.toobad, on Flickr

    [​IMG]Stats 2 by jonny.toobad, on Flickr

    Some 3D of single hull

    [​IMG]3D002 by jonny.toobad, on Flickr

    [​IMG]3D003 by jonny.toobad, on Flickr

    [​IMG]3D001 by jonny.toobad, on Flickr

    Profile of single hull

    [​IMG]Side by jonny.toobad, on Flickr

    Resistance calculations in Freeship

    [​IMG]Resist 1 by jonny.toobad, on Flickr

    [​IMG]Results 03 by jonny.toobad, on Flickr

    [​IMG]Results 04 by jonny.toobad, on Flickr

    Excel table of weights for pontoons
    [​IMG]Hull Plates Weights Table by jonny.toobad, on Flickr

    There will be three bulkheads in each pontoon creating four chambers. Each chamber will have multiple ring frames making for a usually rigid structure. I have drawn the bulkheads and frames in a drawing progie and have the dxf files but still trying to figure out how to calculate their mass

    Next will be concentrating on drawing the bridgedeck. This will be just a rectangular box so all the framework and panel mass will be easy to calculate. I have also started another weights table that will add boat weight and all inclusions like power, fluids, gear and crew

    I have another point that I want to address, something that I have been quite upset about lately

    Someone listing themselves as a NA on here claimed that I was leaching off the forum


    to that person I would like to say that at no stage I have asked about how to design or asked to be given ratios, calculations or equations. I have tried to do the hard yards by informally educating myself by searching and reading online papers and discussions including trying to understand helpful contributions in any topic that I raised. I was quite upset by the claims and since that person has already taken the effort of compiling all the topics that I have raised, I request that he submit how I could have possibly progressed to this stage of the project from a few general questions I have seeked assistance on when I have come across things like software glitches and unfamiliar material options and one hydrodynamic that is confounding me. demonstrate how is is possible to draw a design like this from the sum of the content of those topics that I raised without doing the hard yards of learning anything else
     
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  2. TANSL
    Joined: Sep 2011
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    Location: Spain

    TANSL Senior Member

    Dear friend, it is logical that you are very proud of everything you have done and it's amazing that you've got here. But, sorry to be a bit ashy, you've only just the easy part of a design. Be careful, or ask an expert to check your calculations, present and those who are still necessary, before taking anything as good.
    I wish you good luck, because you will need it.
     
  3. Saqa
    Joined: Oct 2013
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    Location: Fiji

    Saqa Senior Member

    Thanks for wishing well TANSL, its not something I am going to start building in a hurry. Even then its just to throw at bad terrain. I am really interested in seeking formal education alongside this project too. But I don't want to wait 3yrs or more to start making a boat that I want to use next year. If this one doesn't work I'll just recycle it as something else, will make a fancy chicken pen on the farm :)
     
  4. daiquiri
    Joined: May 2004
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    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    Saqa,
    I didn't follow the thread in which you've been discussing your ideas, so I don't know if anyone has mentioned this.
    The deep wet transom of your hull looks excessive and will be a source of a significant drag force, especially at low displacement speeds. I don't see any data relative to wet transom immersion or area in your calculations, so I don't think it has been accounted for. I understand why you have introduced the wet transom, your maximum speed is pretty high. But nevertheless, it does look too deep and will penalize you a lots at lower speeds.
    Cheers
     

    Attached Files:

  5. Saqa
    Joined: Oct 2013
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    Location: Fiji

    Saqa Senior Member

    Daiquiri, I know what you mean. I shaped that area in lots of different versions and ran them through the resistance calcs in freeship. I didnt see any improvements in the results. Actually the performance degraded some if I lifted the bottom edge as draft increased a lot. I also have a few other reasons for ending up with that shape

    Firstly, The design draft I have chosen for the freeship calcs is in the middle of light and max displacement. The boat will rarely be running at max draft

    Secondly, the thing I forgot to mention in the first post above is that I will be experimenting with foils. Forward pair on the hulls and wings on the outboard working in tandem. I want to try different sizes and angles for lift assist and motion dampening

    Third, I am looking at max twin Mercury 40 EFI Bigfoots. At 100kg each I went on to draw max buoyancy only keeping a slight rocker

    Lastly I considered the kind of torque available of that pair and looking at the common 6m longboats with same power and very narrow waterlines here, I think I might be getting a lot planing assist. I have been reading up about design rations and the current S/L of 2.64 seems to back this in my limited understanding, I could be way off course but will understand more as my ability to comprehend grows and I can tackle more reading material

    To be honest I have been so focused on cruise speed that I neglected reading the lower end of the speed/power table when doing all that. I really should check it out some with this model vs another with a drier transom to see the performance hit in the 3-6 knot range where a lot of trolling is done
     
  6. waikikin
    Joined: Jan 2006
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    waikikin Senior Member

    Saqa, maybe you can utitilise a transom "pod" that fills in & sweetens most of the transom but leaves a step for release at planing speed, not sure how that would effect the transition performance & speed.
    Your boat name is cheeky.... reminds me of Wai Tadra

    Jeff.
     
  7. groper
    Joined: Jun 2011
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    Location: australia

    groper Senior Member

    Transom sterns will penalise you at slower speeds, however boats don't use bugger all fuel anyway at slow speeds! Optimise the design for high speed, which is where most of the fuel is burnt...

    Saqa, you need to understand the limitations of the software... The resistance calculations clearly don't model transom stern drag if the drag doesn't change much at low speeds without the transom. Most software packages , even the expensive professional ones, don't model transom stern drag very accurately. There is also the running sinkage and trim to factor in. The sinkage and trim varies a lot depending on the hull shape because it's largly influenced by dynamic lift- none of this is modelled in the software either. This is why it's better to understand principles rather than some random software output.

    If you have rise in the stern like you've shown, it will trim bow up running at speed because of the negative lift generated at the stern. This also causes more sinkage aswell.

    The other thing I don't get is your speed requirements.? You want it to be like the sliver 29, well it has a much higher cruising speed than your 10-15kt outlined in your first post? So do you want to do 20kts or not? With 2x 40hp and a good design, this should be no problem. Your hdpe scantlings are very heavy tho, like I said in your other thread, your hulls could be built much lighter. You only need a high density rub strip along the bottom edge for toughness and bashing it around on the coral etc but carrying 6mm hdpe up the hull sides and everywhere is pretty inefficient engineering which will cost you every time you fill her up...

    Have a look at the tornado sailing catamaran... It's built from thin tortured ply with aluminium crossbeams. The whole boat weighs less than 150kgs including the rig. It would be a good hull to scale up slightly, flatten off the rocker and give a bit more volume aft, and power with outboard engines at high speeds, hell they will do over 20kt powered with sails, never mind gasoline... So easy and cheap to build , they were extremely popular for years due to the excellent performance... The scantlings and plans are all over the web should you wish to see how they're built...
     
  8. groper
    Joined: Jun 2011
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    Location: australia

    groper Senior Member

    Ha , just found this...

    [​IMG]

    And you also mentioned foils? Well they best you by 30 years or more...:D

    [​IMG]
     
  9. Saqa
    Joined: Oct 2013
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    Location: Fiji

    Saqa Senior Member

    Jeff, I am having a very difficult time drawing in freeship so I am doing it in another software then importing into freeship. That software wont allow me to make a model with steps. If I can get better at drawing in freeship itself then I might be able to play with that

    Groper
    Richard Woods is in the initial stages of drawing up plans for an offshore fishing cat built with optimum materials right now, something that might not only rival the Silver 29 but beat it in performance. I thot the Silver was good for 15 knot and it was the Custom 38 that was the performance master, I might have remembered incorrectly. Anyway, once Richard makes the plans available, I will be building that for the charter boat and it will be moored in good water conditions at a resort. It will be demountable so will be retrieved during cyclone warnings

    i know what you are saying about the overbuilding but I need a boat that can cop all the abuse that can be dished out. Thats why I dropped the performance aspirations for the 'flying tupperware'. Sometimes I have no option but to ground it up onto the shallow water bommies behind the outlaws farm. It will get hit by pangas and logs on the mooring. Hence the two builds. I can hope to optimise 'tups' to where she can have the best legs I can give her too!

    I have been playing on the water with a very similar foot print on the water. You are right about the bow up attitude. The boat is much shorter but has similar waterline beam and rocker and weight. With two up she is bow up and slow too. I fitted wing foils to the outboard and things changed dramatically. The nose came down, she picked up a lot of speed so she is doing 10 knots plus with only 8hp depending on the conditions offcourse, surprisingly slower in flat water then choppy conditions. She has a sharp leading edge and punches through the chop now wearing foils on the leg

    As an example, trolling a bomber...its has a very slow swimming speed, it blows out of the water at anything faster then slow winding speed. I cant troll it. The boat picks up too much speed for it without giving much throttle. I cant sit anywhere close to slow speeds, she gets up and gets moving so I have to keep modulating the throttle back to zero to troll

    I am taking the practical lesson from all that, that foils will work. Will keep boat level and damp motion
     
  10. Saqa
    Joined: Oct 2013
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    Location: Fiji

    Saqa Senior Member

    Is that one of Gary Dierking's boats? He moors his yellow one a couple of hundred meters away from my outlaws farm!
     
  11. Ad Hoc
    Joined: Oct 2008
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    Location: Japan

    Ad Hoc Naval Architect

    Hard facts tend to fall on deaf ears Daiquiri. Like so many that want to design their own boat, only listen to positive news, rather than hard facts.

    Indeed.
    Sounds like the student has become the master?? :D

    But sadly that takes time...and most, like the OP, who are chomping at the bit...haven't got the patience or time to learn such things. Yet just criticise others for merely suggesting it :p

    Indeed. Playing with free software without understanding what one is doing simply leads to a false sense of ability and thus not to be questioned...unless being positive. :eek:

    Design is not about emotions or pride...it is about objective facts and knowledge. 10 years of experience, still takes 10 years, whether one has a super fast PC or not!...that just makes poor design faster..that's all. And sadly too, the same old hurt pride too when one only wishes to listen to the selective positives not the hard facts. Pity...being objective and recognising one's limitations goes a long way.

    There are plenty about. Cheaper to buy second hand...
     
  12. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    One can be proud of what he has done, even if others despise hes work. No need to be too negative. Be naval architect is not everything in this life.
     
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  13. Saqa
    Joined: Oct 2013
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    Location: Fiji

    Saqa Senior Member

    Ad Hoc, I notice that you have not been able to substantiate your claims of leaching by demonstrating how is it possible to get to where I am with my project just from the sum of any topics I have raised to date

    I also notice an inclination from yourself to ignore any field trial and error work that I have taken on to find what will work for me for my one off build. I agree that formal education would be best but what you call chomping at the bit, I regard that as mucking around playing with stuff with lots of hands on work to see what will work

    I also notice that you are disregarding the 'proper' boat that will be designed by a professional and picking on the 'hobby' yet again
     
  14. JosephT
    Joined: Jun 2009
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    JosephT Senior Member

    Hello Saqa, you reference a successful design (Silver 29 from Africa). Do you have any pic or references to this design? If so, please post.

    Agree with the others that the flat stern may affect drag. You'll get better performance & less turbulence with say, a canoe stern. The only exception would be if this were a high powered catamaran that gets up on plane.

    It would help to get some references of this Silver 29 design you are trying to achieve.

    Cheers,

    Joseph
     

  15. Saqa
    Joined: Oct 2013
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    Location: Fiji

    Saqa Senior Member

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