Sueños Mojados

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

  1. groper
    Joined: Jun 2011
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    groper Senior Member

    Yeah, hence my previous comment... it would help if you turned on the volume distribution curve overlay on the images you post saqa
     
  2. DennisRB
    Joined: Sep 2004
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    DennisRB Senior Member

    Seems everyone is getting overly technical while missing glaring design VS SOR problems. If I have learned anything on this forum its to always look at your SOR when choosing any parameter of the design.

    I suggest that the aft bottom point of your "Tennant" hull is at odds with your SOR 5 and 7. I think a flat or curved bottom with no venerable corners or edges is a must. With the hull shown there will be accelerated ware in any material. HDPE kayaks ware through in this area easily even with a much less weight and less of a point, and they are not left moored permanently over rocky rubble!

    Yes I did see the pics of your last boat! It came out great , you should be proud. Some of the other posters should check out the thread before saying you have never designed and built a boat before.
     
  3. kerosene
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    kerosene Senior Member

    Point taken. I checked and it does look like a successful project. I wasn't aware of it.
     
  4. Saqa
    Joined: Oct 2013
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    Saqa Senior Member

    Groper, this is the screen shot of the progie I am drawing in

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

    I havent made any more changes to the lines yet. I am also trying to draw the more rounded chines like the 'Cambria' and without the CS feature. I am going to work on both styles and pick one of the two later

    Daiquiri
    I have narrowed it all around by scaling the beam. I have also included an inch wide spray rail by adding more chines. It runs from about half way up the bow down to the waterline about half way down the boat length. Its that curved line in the pic. If the model is rotated to view from below then its clearly visible. That step will also help stiffen up the side panel in the area heavy contact will be made with the chop. I'll post some closer pics of that area later

    Thanks Dennis, yup the whole family loves that boat too!

    Re this project. I have been thinking very carefully what materials the boat can be built with to best meet all those requirements. I kept coming back to PE although the was the fall back material

    Ply/glass
    I cant even begin to imagine how heavily I would have to overbuild it to remove the worry of getting just one nick through the glass that will allow moisture into the ply in any area below or above the waterline. I can use sacrificial wooden keel runners but they wont protect another area below waterline from coming into contact with a raised rock with oyster crust. Its likely that the runner would have to be attached prior to priming and painting to present a sealed surface

    My other worry is a scrape on the runner will cut through the surface finish into the wood. The wood is sacrificial but will the penetrated finish then be compromised and water slowly separate the paint from the base moving further onto the hull itself

    When the runner is due for replacement, that area will also need refinishing due to the tooling and work required to remove it and patching up around it. The ply plates are also a worry. I have recently helped repair a ply planga that had sat down hard on a rock rubble during falling did which was choppy in the same mooring area. the rubble had enough height to punch through 9mm quality marine ply. We had to take off the bottom finish to check how far the damage traveled, cut it out, patch in a replacement, fill in the edge with goo made from epoxy and wood dust, glass it on both sides with scraps of 450gsm db left over from my skiff and then refinish the entire boat bottom

    PVC foam/glass
    I have a fear that it will just get chewed up lot quicker then ply/glass, will require constant babying and not be the liberating worry free utility experience. It certainly will be a good choice around three years down the track with my development timeline of the mooring area

    Steel
    Too heavy and will rust if paint gets scraped. Will take time to rust through but removing rust to stop it from spreading and refinishing would become a priority that I dont need

    Aluminum
    Can be made to work, still be a lot heavier though. There is a 30' cat close by that was bought specifically for toughness for mooring on these flats that can go dry. Its a pig even with a pair of 200hp that are on it and is now put aside on grass looking for a buyer. I have been consulting with the foreman of that boatyard as he will be the welding guy if I ever build from alloy. We are setting this material aside for the moment due to material stress and fatigue reasons if built light enough for 40hp motors

    Plascore/glass
    This is my second choice. I like its rot free nature. If a cell gets pierced then no worries, that cell will fill with water but wont compromise adjacent cells. Worry is water compromising the finish around the damage. I have read that its quite hard to destroy over a decent area. I don't know if it will get chewed up like PVC will but I know how to plastic weld a patch into light hollow type plastic board material using an iron and drinking straws but reglassing and refinishing that area will again remove the utility nature of the boat. This material will be the best candidate for building the larger charter boat for the decent mooring over at the resort area from what I know of it so far

    HDPE
    If an area wears through or gets punched through, I can patch weld a piece back in. Plane it smooth and run heat over it to gloss it out, done. I think I can work with the Tennant design by welding on a sacrificial keel runner cut from 10mm sheet with 2" depth or so. To replace it I can cut and plane it off and weld on a spare cut and stored at build time. The possibility is also there to beef up inside that sharp skeg by fill welding in strips of PE

    The entire build and ownership period will be free from any time investment in filling/bogging/sanding/itching and bitching/priming/bogging/priming/painting......and waiting for glue to set!

    She will be heavier then if built from foam and such. But she will be around the same size and power as the Silver 29. If I can keep off all the flab that is built as amenities on the Silver and bring this project in around the same weight as the Silver, then I can be pretty confident that the performance will be good enough to at least cross the lagoon in good time and travel up the reef chain and back

    Kero
    I hope you don't take my reply above addressed to Dennis as arrogant and refusing to listen to good advice, please read it in the way intended being my reasoning towards choosing PE as the build material regardless of all the advice towards other materials. Some of the other materials will be a fine choice once I have the mooring sorted

    All this work and building should be good clean fun both at personal and familly level and nothing can take away from that at the end of the day

    Mr E
    Bula!
     
  5. Saqa
    Joined: Oct 2013
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    Saqa Senior Member

    Some more work on the model. Improved a few things

    Draft 35cm @ 800kg per hull
    Waterline beam 61cm
    DL ratio 38
    Prismatic coefficient .59
    Transom height 20"
    Skeg height 12"
    Skeg offset from transom 24"

    [​IMG]LP by jonny.toobad
    [​IMG]COB by jonny.toobad
    [​IMG]Profile by jonny.toobad
    [​IMG]Plan by jonny.toobad
    [​IMG]BP by jonny.toobad
    [​IMG]73D001 by jonny.toobad
    [​IMG]73D002 by jonny.toobad
    [​IMG]73D003 by jonny.toobad
    [​IMG]73D004 by jonny.toobad
    [​IMG]73D005 by jonny.toobad
    [​IMG]73D006 by jonny.toobad
    [​IMG]kg by jonny.toobad

    Frames and bulkheads are estimates bases on transom size as I still haven't figured out how to find their weight. I have picked up 40kg by going longer and taller from the original hull model. Still have 825kg to play around with towards the bridgedeck, electronics, controls and such and still come in under the Silver 29s max displacement figure
     
  6. Mr Efficiency
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    Mr Efficiency Senior Member

    Starting to look interesting !
     
  7. Saqa
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    Saqa Senior Member

    Bula Mr E, I hope interesting means I am on the right track. I am starting to think that the Tennant design is better suited to much deeper draft designs then this. The boat will have to be built and loaded on the heavy side to keep that waterline!
     
  8. Richard Woods
    Joined: Jun 2006
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    Richard Woods Woods Designs

    I just re read this thread. Unfortunately it is very difficult to get the right tone in emails and forum posts, especially when compared to a face to face conversation.

    I certainly do appreciate the help you gave me regarding what you would like to see in a fishing boat. I also got comments from many other fishermen, fishing in other waters for different fish. Some disagreed with your comments and I tried to compromise on all of them. But even so I know that the requirements are so different that one boat will not suit all. Which is why I have always said that there will be several different deck layouts based on the same hulls.

    Although I have never personally caught a fish I have studied a lot of fishing boats round the world. For example, I am currently in the Baja, Mexico, which, as you know, is a major sports fishing area during the summer. The fishing boats are laid up now, so a few days ago I went round the boat yards. Out of maybe 100 sports fishing boats I looked at not one had a deck layout that allowed you to walk round the whole boat while fishing. Indeed few allowed you to get on the foredeck at all.

    In my earlier post I said you would not be interested in scaling up a 25ft powercat, particularly as you didn't want to start with my Jazz 30 hull. Judging from your later posts that still seems to be true, as you are continuing to do your own thing.

    I also commented that it seemed strange that you would draw a detailed lines plan when you don't know what material you will build your boat in. Again, it seems you still don't know. Wood, foam sandwich and plastic boats will all have different shell weights and, even without knowing what deck/cabin layout you are planning, I think I am right in saying it's not the way professional designers would approach your project.

    Hope that clarifies my views

    BTW I am now in the final stages of negotiations to have the Jazz 30 built as a production boat in Europe. More news here when it comes to fruition.

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
  9. Saqa
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    Saqa Senior Member

    Richard, your earlier post reads as an address to others in the thread, it is not addressed to myself. That and the content sets the tone. The content is regarding the work I am doing on my project which makes me the subject of your address to the others. I read that as an attempt at derision

    This is why those of us jigging and popping need a more appropriate layout. This is the fasting growing segment of the bluewater scene and we have to use what is available. A large number of bluewater boats do offer foredeck to cater for the popping guys but these are monohulls that running some big horses making for huge charter costs. You are a very well traveled person, I can supply you with a good number of operations that you can checkout

    I gave you the closest form that is related to our sport being the American tournament bass scene. These boats are all flat deck

    This is a conclusion that you have drawn, I have only said that I want to look at a better perspective drawing of the Jazz to see if I can customise on that

    In this thread here and on the thread I started on Beteau re the Cat22 which turned into the Jazz thread, I have mentioned multiple times that I will be making two boats. I listed one as the Jazz that will be the charter boat as it is professionally designed structurally and suitable for conveying paying guests as well as a second boat that is a explorer for my personal use and needs to be utility for rough terrain which is the project of this thread here. Since then I have added building the Cat22 to the timeline as well as I require a small trailable boat for customers for the business I am setting up

    This is another thing that I have specified in this and the Jazz/Cat thread.

    The material for this project is HDPE, the benchmark is the Silver and the deck and layout weights I need to match performance is the difference between my plastic hulls weight and the fully rigged weight of the Silver

    The material for the Jazz I had listed as would like to build with plascore or PVC foam

    I have spent a ton of words on why I do not want wood or ply so why do you state that I do not know which material I wish to use?

    You are right, not a professional approach, lol I am not a professional and doing the best I can with what I can learn

    I hope the other two fellas pushing the design can run with the acceptable layouts on your form. I do not appreciate the manner you took here with my personal project and that I cant work with someone like that
     
  10. Saqa
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    Saqa Senior Member

    Groper, I am using Hydronships Freeship plus v3.4

    On their site they have some heavy blurb about the resistance calculation abilities of the extra development they put into Freeship using hydronship modules. Do you know if their calculations give any meaningful results? Even for comparing two different variations of hull lines?
     
  11. groper
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    groper Senior Member

    hmm...

    You will notice that if you compare 2 hulls of differing lines, but same overall length and displacement, that the resistance will not be very different. As i said before, the most influential design parameter on resistance, is displacement to length ratio. Please stop and read that again, then think about what it means.

    Now as to meaningful results...

    the software resistance calculation doesnt account for transom drag.

    It doesnt account for dynamic lift - and you could welll be operating in at least semi planing regime rather than pure displacement.

    You dont really know what your propulsion efficiency will be based on propeller loading, speed etc

    Your best method of estimating speed vs horsepower, is to search for similar boats which have the same displacement to length ratio and likely to operate in similar modes, with similar propulsion devices - such as the prowler cat if your considering the canoe stern etc Then look at what speeds they are getting with their installed engines. As the prowler is quite alot heavier than yours, but its also longer, use its displacement to length ratio as a constant. Adhoc has posted a displacement to length ratio vs resistance graph on bdforums many times in other threads, you could extrapolate off it using your displacement to length ratio and the prowler cat as a yard stick and likely get far more accurate results than the software provides...
     
  12. Saqa
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    Saqa Senior Member

    The Silver 29 at max displacement seems to come closest. Power is the same. I dont know its waterline beam. Looking at the rake on the bow I estimate it has similar or a bit less waterline length then my model. I estimate its DL be around 37 too so it would be the one to compare to

    Re the canoe stern, I cant workout if that is suitable for my boat. Especially since I want to use front/rear tandem foils for pitch dampening.

    I cant help but think that the hull will Initially squat when throttle is opened and that will bring even zeroed foils into a positive attack angle and that will lift the transom lower edge clear of the water surface, I dont know what this will mean to the flow of water to the prop with the CS

    I have almost finished drawing a AC45 type shape but with no rocker in the rear two thirds length or so in two versions. One with round chines to the transom and one with chines getting sharper in the back third. Draft on both is 8" and DL 37 with waterline beam 65cm

    With 40 to 60 horses per hull and DL of 37, seems ok, are these good numbers? Reminds me of another point I asked earlier. The weights of the 40 and 60 are the same and the 60 can be had with 25" shaft

    So I think it comes down to 20" shaft plus CS stern or 25" shaft plus regular stern with 8" draft

    Are there any disadvantages going 60 other then price?
     
  13. Saqa
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    Saqa Senior Member

  14. Saqa
    Joined: Oct 2013
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    Saqa Senior Member

    I mentioned previously that I am still working on refining the lines and investigating the Silver 29 shape as well as something almost as sleek but with a very low draft. I have tried to draw a shape like the silver

    [​IMG]sil001 by jonny.toobad
    [​IMG]sil002 by jonny.toobad
    [​IMG]sil003 by jonny.toobad
    [​IMG]sil004 by jonny.toobad
    [​IMG]sil005 by jonny.toobad

    Stats
    Design length : 8.839 m
    Design beam : 0.865 m
    Design draft : 0.380 m
    Water density : 1.027 t/m^3
    Displacement : 0.835 tonnes
    Total length of submerged body : 8.457 m
    Total beam of submerged body : 0.627 m
    Prismatic coefficient : 0.6946
    Wetted surface area : 7.305 m^2
    Longitudinal center of buoyancy : 3.699 m

    The immersed depth of the transom is 13cm. I think I can use strip plank tech to build the shape by using lots of frames

    I still feel inclined towards something with similar waterline beam but almost half the draft though. The wetted area has gone up quite a bit on this. One more shape left to show, something along the lines of racing cats types but with hull rocker optimised for power instead of sail and draft of 20cm. That will be hard chine based that can be softened during build
     

  15. kerosene
    Joined: Jul 2006
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    kerosene Senior Member

    are you dragging the transom so deep to get enough buoyancy in the aft or are you hoping for lift?
    Sorry if I missed it in this thread just curious about the hull shape choice (displacement shaped belly with flat section on top).
     
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