Tell me your thoughts on this chine area bubble

Discussion in 'Boat Design' started by aaronhl, May 5, 2024.

  1. aaronhl
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    aaronhl Senior Member

    I hope the pictures can tell the story well - I have a straight edge with no gaps for much of the high speed planing surface closer to the keel, as I move the ruler parallel of keel towards the chine, you can see a bubble/rocker form at about 1/4-1/3 the length of the hull...

    My concern is even though it's a warped design, the rear 1/4 of the hull should have the same deadrise?...Maybe the complex curves are confusing me...I believe the deadrise starts higher, then lowers, then goes higher again as you move to the bow...

    Another way I see some divergence is the keel is flat atleast for 1/2 the hull and you can see the chines curve upwards towards from the middle to the transom (side view)..

    Tell me what you think Thank you.

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    Last edited: May 5, 2024
  2. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    What is the background behind this model boat - did you build it yourself from a set of bought plans, or is it your design - or did you buy the model 'as is'?

    That 'bubble' in the last photo appears to be very slight - the deadrise in way of where your hand is will be very slightly curved, but are you worried that it will have a noticeable effect on the performance of the model?
     
  3. aaronhl
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    aaronhl Senior Member

    Good questions, this is a boat i am cutting up and modifying as the previous was too short and had too much convex... I was worried the bump would not make the boat too efficient, a flatter surface maybe making more speed and better handling if that makes sense. Come to find out I put the digital angle finder on it and the bump was about less than a degree on each side...I am now in the process of grinding it out and filling as the very edge of the transom deadrise is 22 degrees and i was able to find 22 degrees about 1/2 way on the hull before it increased towards the bow
     
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  4. wet feet
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    wet feet Senior Member

    You asked for thoughts;my initial thought is that you have little to be concerned about.It's obviously nice to have both sides identical but there are few boats in existence that are completely symmetrical-at least not if you look really closely.You don't give much detail about the extent of the alterations made to the hull and they may be much more significant than a tiny deviation from a perceived "ideal" shape in one comparatively small area.I'm guessing that the boat is destined for an outboard installation and would expect that a very small fraction of one degree on the trim adjustment would have more effect.
     
  5. Dolfiman
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    Dolfiman Senior Member

    I am not an expert but I believe that the usual design is : deadrise starts lower at transom (you indicated 22°), can be constant for about 30 to 40% of the length (the length which remains in contact with the water in the planing mode) then increases continuously to the bow ( in the range 50° to 60° ). The aft deadrise choice depends of your trade off seaworthy on chop/rough sea state versus speed on calm waters, typically from 24° (Ray Hunt V here below) - 22° (Glastron GT 150) to 7° (Rascal runabout).
    The Hunt Deep-V | Ray Hunt Design | Naval Architecture http://www.rayhuntdesign.com/deepv-questions-answers.php
     
  6. aaronhl
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    aaronhl Senior Member

    Yes exactly my concern was that the deadrise does not stay at 22 degrees for most of the rear of the hull, so I did form the plug so the dead rise is the same for most of the 1/3-1/2 rear part of the hull...
     
  7. aaronhl
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    aaronhl Senior Member

    Another issue I am running into with this build would be the chines, this is a high speed model it is 48" and will have a target speed for approx 60 mph...I have decided on straight chines to help with hull tracking...when I try to bend the wood to make the chine up in the bow area, the wood/chine does not stay parallel with the keel...to my eye if i make the chine straight, it actually is not parallel to to the keel in the bow area

    I say high speed model - do not want many chines or curved chines I believe to reduce friction - if you scale this model to a larger size like a 48 foot hull that makes it like a 200mph hull possible so the standard rules may not apply ??
     
  8. messabout
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    messabout Senior Member

    What will you use to power the boat? If you are expecting 60 mph you'll need some horsepower. Maybe a Zenoah gas or fuel engine? Model boat racer guys have a class similar to what you are building.
     
  9. aaronhl
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    aaronhl Senior Member

    Yes exactly we use 26 and 30 cc Zenoah gas engines
     
  10. fallguy
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    fallguy Senior Member

    Most likely, fairing/sanding passes were made along each side stern to bow or vice versa. And the result is the stern has been oversanded.

    You would not correct by grinding the rocker out, I’d say. But by adding back compound to the stern. Then be a little more careful about the sanding passes.
     
  11. aaronhl
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    aaronhl Senior Member

    I am glad you picked up on that because I was considering filling the transom area, instead i decided to grind out the bump because it ended up being on toutter area mostly at the chine, as I bought the angle finder from the transom to the bow i got 22 22 22 23 22 22 and then up from there so I knew i needed to grind the lump down. maybe I should of held on making the thread another day but sometimes it helps me document and think about it...

    Any idea on the strakes I can seem to get them parallel to the keel in the bow area, maybe its and optical illusion but ive been taking measurements...maybe they cuve them because it's easier to put them down that way
     
  12. aaronhl
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    aaronhl Senior Member

    I'm surprised how much finesse it need for fairing, it takes some skill putting body filler down, and when I do I typically put too much down. I finally got the surface I needed when I screeded instead slobbing filler down with the platic scrapers
     
  13. aaronhl
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    aaronhl Senior Member

    First pictures shows how the strake does not stay parallel with the keel, curving upwards towards the bow, the strake itself is straight though,
    Second pictures shows the strake equal distance from the keel, however appears to have a curve outwards as the strake itself is not straight
    Ur thouhgts??

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  14. fallguy
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    fallguy Senior Member

    You have to keep the strakes equidistant from the keel. If you ‘unzip’ the hull and broke it down to two sides of the hull bottom; you would be able to see better how straight things are unzipped.

    You could probably try it with paper. Just cut a paper template for each side of the hull. Then lay them down flat side by side and I think it’ll help you understand the shapes best. My guess is the keel opens forward.

    I’m not the expert on developable shapes. This forum boasts some experts in this area, but they don’t always respond to all questions.

    The strakes seem awfully wide in scale. How did you decide their dimensions and shape as well?
     
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  15. wet feet
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    wet feet Senior Member

    I'm curious about why those strakes are rectangular in cross section,most spray rails seem to have a triangular section.Similarly,I am interested in knowing why 22 degrees is the "magic" amount of deadrise and why 20.5 or 23 wouldn't work.
     
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