Where to put holes in this bulkhead?

Discussion in 'Fiberglass and Composite Boat Building' started by leaky, Dec 11, 2021.

  1. leaky
    Joined: Sep 2008
    Posts: 224
    Likes: 14, Points: 18, Legacy Rep: 14
    Location: nh

    leaky Senior Member

    I need to create some holes in small sub deck bulkheads for engine intake. In the diagram basically I'm showing the bulkhead between two stringers, where the deck sits atop and is adhered both the to stringers and the bulkhead.

    The bulkheads are not normally there in these boats, probably aren't going to be loaded, just put them in because it seemed right, mostly I think their job is just positively assuring the stringers do not deflect (ie remain perfectly upright) without depending on the adhesion of deck to stringers. And they create deck support too of course.

    I haven't been able to dig up any guidelines that deal with this sort of thing but am striving to put the holes in the least impacting places. I feel like the two holes labeled 1 & 2 are the way to go because if anything stresses are compressing on center, and trying to push/pull the tops of the stringers together and apart.

    What do you think?

    20211211_121719.jpg

    20211211_145203.jpg
     
  2. TANSL
    Joined: Sep 2011
    Posts: 7,513
    Likes: 749, Points: 123, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

    Hole, wherever, with rounded corners and a reinforcing fringe.
     
    ondarvr and leaky like this.
  3. fallguy
    Joined: Dec 2016
    Posts: 7,797
    Likes: 1,735, Points: 123, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    Typically, avoid structural tapes.
     
    leaky likes this.
  4. TANSL
    Joined: Sep 2011
    Posts: 7,513
    Likes: 749, Points: 123, Legacy Rep: 300
    Location: Spain

    TANSL Senior Member

  5. leaky
    Joined: Sep 2008
    Posts: 224
    Likes: 14, Points: 18, Legacy Rep: 14
    Location: nh

    leaky Senior Member

    I'm thinking he means not to cut the tabbing out in the process?

    I think I'm basically just going to take a 6 inch hole saw and bore straight on center. That's a touch over the area I need, the bulkhead is about 17 inches tall, and I'll run so many layers of glass around and around inside, really to seal the core, a few sessions at it, sand the edges flush, makes a solid glass sleeve. End up with a hole pretty close to the middle 1/3 the height as far as the hole goes.
     
  6. kapnD
    Joined: Jan 2003
    Posts: 1,337
    Likes: 431, Points: 83, Legacy Rep: 40
    Location: hawaii, usa

    kapnD Senior Member

    Not too close to the edges, or each other.
    Also, stagger the pattern, and leave a holes’ diameter between holes.
    One big hole in the center might suffice.
     
    leaky likes this.
  7. Barry
    Joined: Mar 2002
    Posts: 1,880
    Likes: 530, Points: 113, Legacy Rep: 158

    Barry Senior Member

    1) Are there enclosed sleeping compartments on board?

    2) After you drill the holes for ventilation, where does the combustion air come from. Ie from within the bilge, or from other compartments of the boat?

    3) Confirm if the engine compartment is enclosed, with the exception of the air intake and compartment air exhaust of course.

    4) What horspower is the engine (engines)? The size of the intake opening is predicated from the manufacturer and if that is not available, there is a table that shows the EFFECTIVE cross sectional area required for given horsepower.

    5) Ultimately, you need to have the combustion engine air come from a vent attached to the outside of the hull. ( not from other compartments in the boat though if the attached compartment is deemed to be an
    "open to the atmosphere" compartment, PERHAPS this would satisfy ABYC guidelines. ( a side note- why would you want to satisfy ABYC guidelines- a) to keep the boat as safe as you can so that no one dies and b) enable a survey to satisfy insurance requirements)

    5b) You will need a duct and vent overboard as well. This is to permit dilution of fuel vapors, co2, co.

    6) You will require a blower exhausted to the outside of the boat
     
    leaky and fallguy like this.
  8. leaky
    Joined: Sep 2008
    Posts: 224
    Likes: 14, Points: 18, Legacy Rep: 14
    Location: nh

    leaky Senior Member

    For other holes, like a stringer where I can find some applicable guidelines I'm using the 1/3 and 2D rules, holes in the center 1/3, holes 2x the diameter spacing minimum (ie so 3 inch holes must be 6+ inches apart).
     
    fallguy likes this.
  9. fallguy
    Joined: Dec 2016
    Posts: 7,797
    Likes: 1,735, Points: 123, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    if it is a non-structural bh, there is no reason to reinforce, but you can't leave glass edges for chafing wires or hoses

    you can bond in pvc pipe as a chafe guard or make edge protectors with inner tubng to keep things protected from glass
     
    leaky likes this.
  10. leaky
    Joined: Sep 2008
    Posts: 224
    Likes: 14, Points: 18, Legacy Rep: 14
    Location: nh

    leaky Senior Member

    I raised the stringers to deck level, adding about 7 inches to the height including the flange you see in the pictures. This took stringers that were 5 to 15 inches tall or so (short aft, tall forward due to both deck pitch and banana bottom of hull combined together) and made them 12 to 22 inches. Bulkheads added here and there, and the deck adheres down to the flange.

    Some weight involved but eliminates framing and makes it seriously one structure. But the engine needs to breath somehow. Pilot house and cabin also has AC/heat and is of course enclosed, so engine air intake must be 100% isolated - ie no vents allowed in living space.

    Going with 1/2 square inch per HP, has 380 HP gas now but allowing for up to 550 HP diesel. Passages for air are being created where the engine will draw from under gunnels, using various objects that will exist as places to add vents where basically rain won't come in since the opening is a few inches under the gunnel but the engine can intake.
     

  11. leaky
    Joined: Sep 2008
    Posts: 224
    Likes: 14, Points: 18, Legacy Rep: 14
    Location: nh

    leaky Senior Member

    Thanks! Because I sand the edges flush after glassing inside its literally a perfect ring in there, nothing sharp, then I gelcoat to match the rest. I think even you guys who are very talented would give it the nod.
     
Loading...
Similar Threads
  1. fallguy
    Replies:
    6
    Views:
    1,391
  2. Bigtalljv
    Replies:
    13
    Views:
    1,804
  3. PennDude
    Replies:
    6
    Views:
    2,420
  4. sigurd
    Replies:
    7
    Views:
    1,600
  5. pleasedontsink
    Replies:
    2
    Views:
    2,162
  6. midcap
    Replies:
    3
    Views:
    2,371
  7. tunnels
    Replies:
    29
    Views:
    5,325
  8. Curious1
    Replies:
    6
    Views:
    12,525
  9. Ismotorsport
    Replies:
    27
    Views:
    4,688
  10. fcfc
    Replies:
    2
    Views:
    1,700
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.