New Project, Several Questions

Discussion in 'Boat Design' started by braun, Feb 16, 2011.

  1. braun
    Joined: Feb 2011
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    braun Junior Member

    hey,

    So a friend of mine convinced me to take my 12 foot aluminum, fix it up and refit ti to make it a better fishing machine that i will want to be out on rather than only using it a couple times a year to get a sore butt. So here are the plans:

    I am going to put out a section of the seats and take out all of the old flotation foam. fill the boat with water and find the leaks and repair them. I know a friend who may have this spray compound to seal the boat completely on the inside. I am a little hesitant about that but he said he has used it on the inside of airplanes that he has restored and it provides a nice seal to prevent leaks and isnt too thick. If he has it then i will do it but if not I wont. I am trying to keep to a budget on the project. I am going to be turning the front section of the boat into a casting deck with storage underneath. I will but putting floatation foam along the sides of the boat inside and all around the storage except along the bottom. If the boat were to ever leak or take on a little bit of water, i need it to run to the back for draining when the boat is taken out. I am going to turn the back section into a storrage area for the gas tank and a tackle storage. Lots of foam back there too. I am basically going to foam every where where i wont be storing stuff. I have certain plans for certain storage areas. For example. right at the front of the boat i am going to put a extra peice of alluminum across the top of the boat to use in the future for mounting a bow trolling motor. Directly bellow that is going to be a storage area designed for my battery for my future motor and electronics that i will be outfitting to the boat. I already designed that storage compartment to take up minimal room but it is kind of hard to explain. Before I build the decks I will be carpeting the sides of the boat that will be visable. The decks will be carpeted as well. If i am going to make this boat look good i midas well make it look classy. Because i will be carpeting the sides and deck it would be stupid to leave the one section where you will see the bottom of the boat bare. so I am going to put in a panel in that section(between the back bench and middle bench) that is carpeted are removable so i can open it up and see if there is water in the boat or so i can be sure the water is draining and what not. I will eventually draft some pictures of the plans and post them but for now you will have to visualize it.

    As for other things on the boat, i have already picked up a decent gps/sonar combo that i am going to make movable around the boat so I can have it where i need it. It will mount on a platform that i can put into the rod holder bases that i will be putting around the boat. I am going to be putting movable seats in so when we are driving the 2 people can be sitting on the back bench or sitting with there feet in the middle. facing eachother but when fishing we will have one person sitting on the front casting deck on the chair with an extention and one sitting on the lower panel between the middle and back seats on an extention. then of course lots of rod holder spots and other luxuries like cup holders. I might make storage totes inbetween those 2 benches as well. or nets that hold a fishermans stuff.

    So now the questions.

    the first of which is regarding the floatation foam. I know that the primary purpose of floatation foam is to keep the boat buoyant in the event of a leak or you take on water. But I was wondering if the foam was strategically placed can it be used to stabilize the boat as well. I dont see why not. For example i am focused on placing foam on the perimiter around the boat in hopes to provide more side to side stability. Additionally my boat always tends to sit lower in the back of the boat. I would really like to make it more even. Id get more stability out of it and also less of an angle when traveling if i can get my back end to sit up more in the water. I know the foam wont make a huge difference but the way i see it if the foam is below the waterline, it should help somewhat. think of it this way. If i were to take massive foam blocks and put it underneathe on the outside of the hull, the foam would lift it out of the water. Why wouldnt this be the same principal if the foam was inside the boat under the water line? Correct me if I am wrong.

    Next would be to ask do certain foams give better buoyancy? if so what kinds? i am looking to avoid pouring foams because i want to make it so everything can be dissassembled are removed incase i need to get at a leak or if i want to move things for better practicality.

    all other comments and questions are welcome regarding my project. I know I will come up with more questions as i go.
     
  2. gonzo
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    gonzo Senior Member

    To start with, leaks must be filled from the outside. They should be pushed against the crack or hole by the water pressure instead of away. If you put foam outside the boat, it will fall away in pieces as soon as you use it. Foam, for reserve flotation, needs to be in a place where it won't break away. There is usually more foam aft to compensate for the motor.
     
  3. braun
    Joined: Feb 2011
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    braun Junior Member

    I don't think you understood me at all. In no way, in any world, would I put foam on the outside of the boat. That is just ludacris. I was just talking about the theory of buoyancy. I just didn't realize that that would confuse anyone. What I had said is if I put my floatation foam INSIDE my boat below the waterline it should provide a positive floatation force there for providing more stability to the boat, correct?

    And yes I know that the boat leaks have to be fixed from the outside......... Sealing the boat with a spray compound would be an aditional measure taken AFTER the leaks are fixed. The leaks will all be along seams or from old rivets that need tightening. All would be fixed by tightening the rivets with a hammer and a block. Sorry I didn't clairify. But the fixing the leak part is not the part I have questions about
     
  4. JRD
    Joined: May 2010
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    JRD Senior Member

    Gonzo is correct (as is normally the case). The foam inside your boat will increase the reserve flotation. This will help you when your boat is sinking due to all the leaks.......

    Whilst this is sensible to do as a safety measure, it wont change the trim. Actually foam is heavier than air so it might make it sit 1/16th of an inch lower in the water infact, depending on how much you spray in there.

    The only way to make it sit higher in the water is to add more volume that is below the water line, and putting the foam on the inside isnt increasing the volume. To make the stern sit higher in the water you would need to make the boat wider or deeper in the stern sections. It probably sits wrong because someone has fitted a larger / heavier outboard engine than it was designed for.
    So the concept of putting foam on the outside could actually improve the trim.... until it all falls off.
     
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  5. JRD
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    JRD Senior Member

  6. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    You said you "were to take massive foam blocks and put it underneathe on the outside of the hull, the foam would lift it out of the water." What did I misunderstand?
     
  7. braun
    Joined: Feb 2011
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    braun Junior Member

    Ok thats basically what i wanted to know. So in no way will i get any additional buoyancy by placing extra floatation foam beneath the waterline inside the boat. That link was actually pretty cool and a great idea. Definately something to consider. Thanks alot guys. The boat, as far as i know, Is running its original 9.9evenrude. Both are really old. the boat doesnt sit that low when still its more driving the front lifts up alot. it might be due to all the extra water inside the boat running to the back though too. lol. I think once i get the leaks all solved and before i start refitting it i will need to drop it in some water just to see exactly what it is doing. I am also now thinking of geting a 14ft instead of the 12 to refit. the extra room wouldnt hurt in the long run and i think i know where i can get my hands on the 14. a little sad though cause the 12 was my grandfathers.
     
  8. braun
    Joined: Feb 2011
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    braun Junior Member

    i was talking in theory of buoyancy in attempt to try to explain why i thought foam on the inside of the boat undeneath the water line would give me extra buoyancy. In essence applying the reasoning of having it on the outside below the water to being the same as having it inside below the waterline
     
  9. CaptBill
    Joined: Jan 2010
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    CaptBill CaptBill

    Hi Braun,

    The foam won't affect how she floats unless you put it on the outside. Doesn't matter where you place it within the boat either. No difference other than weight distribution.

    Your key concern, if the intent is to make it unsinkable, is to minimize weight. Over-building is a common mistake. You have the good intention and say "let's do it right and make the floor 3/4 ply instead of 1/2 ply", as an example. Then come to find out, in reality, 1/2' plywood is WAY overbuilding, if building like you describe. In fact, glassing over solid foam is quite ample with a solid foam-core backing. My Boston Whaler doesn't have a wood floor. Simple glass over THICK foam. The beauty of is is that if you can set the floor a juuuust above the water line...she has continually self bailing. Your drain plug is two wide open drains into the water. Not saying it can be adapted to your boat right offhand. They need to be 'beamy' or wide to accomodate that feature, I imagine.

    As far as the leaks go . You should just plan on a simple, effective philosophy..."coatings are your friend". You need a good liquid sealer that can penetrate all the paths the water wants to take. First primer coat is key. Then you build up the layers. The water you fill the hull to check for hole needs to be the water coming out of your pressure washer as you prep for the coatings. Gaping holes are all you care about addressing. The coating system will handle the rest. This needs to be done (to the bare aluminum) well before anything like foam get in the way.

    Need a good coating that is a good match for you aluminum. I think this could be the hot ticket for your first move...

    http://www.epoxyproducts.com/aluthane.html
     
  10. rasorinc
    Joined: Nov 2007
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    rasorinc Senior Member

    Stryofoam boyance billits can be made in any size and can be encapsolated in a canvas wrap or some such product that will hold up to fresh or salt water. These would go on the outside of the sides or your boat held in place by heavy snaps or twist type fasteners. A cubic foot( 1728 cubic inches ) of stryofoam will float 55lbs. Then a 14" x 10' x 5" thick would float 486 lbs per side. Take them off and store in garage for the winter. Get a cloth solid enough to prevent UV rays hitting the stryofoam. I priced out a special cloth that is made to wrap Navy stuff, stored on deck where waves would hit it and it did not tear. I'll search to see if I can find the company. You want them to end just above the water line--I estimated 14". I've had stryofoam unwraped under a pier now for 35 years with no wear just muscrat bites. They are protected from the sun by wood decking.
     
  11. CaptBill
    Joined: Jan 2010
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    CaptBill CaptBill

    A good set of fins for that 9.9 motor will fix your issue of the bow rise, I would bet. She is probable struggling to get on plane, maybe prop height is an issue.

    The Davis Dolphins worked great for a dingy that was bad about the bow rise. Worked like a charm.
     
  12. braun
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    braun Junior Member

    What do you mean fins? do you mean like the aqualisers that were posted in the thread already?
     
  13. CaptBill
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    CaptBill CaptBill

    The fins simply slide onto the small 'wing' extrusion just above the prop. The fins are simply much larger 'wings'. They are highly engineered of coarse to address this issue which is common. Your lightweight hull allows the stern to try and catch up with the bow, because it's so light. The larger wing pick you up on plane no problemo. Common problem, easy solution. Really improves the handling.

    With all your plans, were I you, I would consider while I was at it to add an extended motor mount to set the motor back 12' or so. Free up the aft space while improving performance.
     
  14. braun
    Joined: Feb 2011
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    braun Junior Member

    I get what you mean. just different terminology. Its a planer board. ya nice thing about those is they are also fairly cheap. definately will be a consideration. Im really starting to rethink some of my plans. not that i think they wont work but more that i dono if it will really satisfy what i want. I have a friend who did thsi to his boat. I need to take a good look at his boat. I wasnt planning on using 3/4 ply for anything but i still worry about the integrity of 12. Still need to reinforce it and what not. definately need to think it through
     

  15. CaptBill
    Joined: Jan 2010
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    Location: Savannah,Ga

    CaptBill CaptBill

    [​IMG]

    These are your 'standard issue fins'. Many other available too.
     
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