Bulbous bow addition

Discussion in 'Fiberglass and Composite Boat Building' started by Frosty, Aug 9, 2011.

  1. Frosty

    Frosty Previous Member

    Thank you very much Brian for your help. Yes I do have surface drives and the stern does noticably lift at about 20. The bow comes up too but the previous quick mod helped a lot.

    No they are not good photos Im afraid but were not really photos of the bow just the best I have. However there is enough to see the upper surface area that just begs to offer a down force. Many of there 38s had no bulbs but all the 44's have. They are a Crowther design. I have contacted Crowther some time ago but they want hundreds of dollars for calculations per hour.( I just wanted some advice from the designer)

    No the manufacturer does not use surface drives, but speaking to the foreman at that time I have information that they did the same thing as I did only more so. They had exactly the same problem as I do but the conventional drive with 100HP more is not as fast as mine.

    I live on Langkawi national geopark, connection to the island is by ferry. I would not be able to get foam sheet on the transport available.

    I can get foam locally from an air con man in AB mix Im told by boat builders here that this is fine.

    I thought the foam wrapping a television or washing machine was polystyrene and not suitable and melts in contact with polyester resin.

    Total removal--- tempting but im afraid she may float bow down, water drainage off the rear deck is close to reverse draining now.

    Taking all this into consideration I felt it would be best to modify and even fabricate some foils on the front to make sure it lifts. I am exited that this might increase its speed by loosening its grip on the water.

    Spray rails in the shape of a ducks beak has been fitted to the water line directly on the bow, this has helped but only if the breaking water is below this.
     
  2. Steve W
    Joined: Jul 2004
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    Steve W Senior Member

    FYI, there are polyester resins that dont eat polystyrene which can be used for the first coat.
    Steve
     
  3. Frosty

    Frosty Previous Member

    Thanks Steve there very well maybe special resins and purchasable some where!!

    I have A&B mix that's all I can get. The addition is very small I would think 1 sq foot would be enough to alter its sahpe into a more forgiving bulbous bow without having effect on trim.
     
  4. masalai
    Joined: Oct 2007
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    masalai masalai

    Go for it lad and good luck... Please post with images what you have done... (before and after shots.)
     
  5. Frosty

    Frosty Previous Member

    Thanks Mas ille have to have a go with what I know.

    Ive got here so I should be able to get there ---- my philosophy.

    As I have been offered no other way to my rib section mold apart from building slabs that I can't get ill carry on then!!

    Thinking allowed,- there is some mis calclulation that could evolve using slab , I mean where do I put the slab if I don't know what shape it should be be when the next slab goes on. Every slab would need maybe 90% cut out to cover the old bulb.

    I do everything in my head over and over until I have it done perfect. I can see all the way through a rib mould but slab I cant get passed the amount of work fitting each slab.

    I guess a lot of members think Ole Frosty knows everything he dont need help--not true.

    Thanks mas ille have a go.
     
  6. masalai
    Joined: Oct 2007
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    masalai masalai

    Make the slab about 1.5 inches thick with your A + B mix on site, shape the inside portion of each piece, then join and finalise external shape and work upward... then glass the faired and finished shape... Any thicker and matching to the existing hull shape will be too difficult... (it might make a big bubble where you cannot see it, near the skin of your boat...)
     
  7. Frosty

    Frosty Previous Member

    Yes I can see that, thing is dont have a plan or anything, like I can say it needs to be 18 inches wide. If I do a rib mould I might have a couple of goes at it till I not only like it but really like it.

    If it gets a bubble near the hull it wont matter because its getting glasses over anyway, sorry Im not arguing and its nice to toss back and forth ideas.

    At 1.5 inches thick I would need 10 slabs per side.

    I would need a mold to make the slab or slabs therefore I might as well make a mold for the bulb--No? So I would need to buy a flat PVC tray from the cheap shop!! OK can do that.

    Ille sit down with my feet up close my eyes and give it a run through.


    Edit Oh one other thing how do you stick the slabs together.
     
  8. masalai
    Joined: Oct 2007
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    masalai masalai

    Not all that difficult, start with the bottom 1.5 inch mold, do that and then sort of fix it in place (removable if it is a F@#% up) then make the sides a bit higher and do the next one, and so on... Then the whole mould does not have to be blindly done at one hit... Stage by stage... Stick the slabs with a bit of epoxy? or whatever you fancy...
     
  9. Frosty

    Frosty Previous Member

    I hav'nt had time to put me feet up yet and give it a run through but I tell you what Im warming to the idea. I was thinking I could buy some PVC trays (there is loads of them in the cheap shop) and they can be 3, 4 or 5 maybe 6 inches thick or make a few different sizes eh?

    My mind is running away now--maybe a 6 inch thick one planted right on the nose equal and parallel with the other side then what ever I do to one I do to the other. The bits I cut out would go on after and further up,Hmmmmm.

    And what about vertical build instead of horizontal or both interlocked in. Mas I think you've cracked it. That would mean I would have a 2 dimension bulb in just 2 hits.

    Yes yes vertical application thats the way first as thats the critical dimension.

    That would work! I like good a problem to solve when I go to sleep this will be perfect for tonight when the lights out and no one will talk to me for 8 hours, Oh shear bliss.
     
  10. masalai
    Joined: Oct 2007
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    masalai masalai

    Did you think you would be left to your own devices? - Think of all of us bored old farts, fingers poised over the keyboard, anticipating something to do and think about...

    On Australian Free to Air TV was a show on the seedy side of Thailand - lots of tall lady-boys posing for the cameras, lots of bar-girls screaming for their "one hour money" because the bloke said he was not interested and the bar-girl just hung around and the volunteer-expat-police who sort out the "issues" that arise in the streets of Pataya... Do not do drugs as there is ZERO TOLERANCE and the death sentence is popular...
     
  11. brian eiland
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    brian eiland Senior Member

    Last edited: Aug 15, 2011
  12. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    How about some canards, possably adjustable or better yet computer controlled to keep up with the continuous incidence adjustments?
     
  13. rwatson
    Joined: Aug 2007
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    rwatson Senior Member

    Also, watch the curved section underneath the bulb.

    Depending on the shape, you may get lots of suction downwards at high speed - like a reversed wing.
     
  14. Frosty

    Frosty Previous Member


    Yes yes that where I go drinking but I know the rules, been there 22 years, great init? Ille be there next Tuesday.

    One hour money????? they will do anything and shout anything for money.


    That lady boy--- was he a tall dark haired one,--thats David me mate, hes a motorcycle mechanic during the day, great bloke. --joke

    Was that "Linda Bar" by a big tree? or underneath and escalator?


    Yeah its all there mas but there are seedy film crews as well --seen em close down bars and pay for what ever they want to film, then send it to Australia where every one believes it.

    Metamphetamine ( ya ba) crazy medicine-- is rife amongst the Thai kids, but they are not in these areas these are for tourists, like Disney land.

    Believe it though its true, like Kings Cross Sydney except as mayhem it may look, its perfectly safe and all a big laugh. Cameras can lie-and very good at it too in that environment. Ille bet it did'nt show families with kids walking around.

    Now--back to Bulbous bows, the other type of bulbous bows.

    Mr Watson I am already getting down force, the top of the bulb is rounded more but does not give lift but makes it dive.
     

  15. masalai
    Joined: Oct 2007
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    masalai masalai

    I think that, - what he may be alluding to, - is that the bottom may also be a cause of the problem, - if - when at the appropriate speed, it induces a tremendous sucking force...

    - - can almost hear your mate at the train-station yelling "C'mon train!" in great anticipation...
     
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