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  1. #121
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    I wouldn't put foam under the floor either. Bouyancy under the floor makes your boat far more likely to roll and float upside down if you swamp it. All that water is sloshing around in the cockpit above an "air tank". If the buoyancy is high under the rear deck and the water can flow quickly into the underfloor compartment it lowers the centre of gravity and the boat is far less likely to roll. That gives you time to pump it out too. I see this with fisherman. They roll their boat at sea and all they have to hang onto in the open ocean is the bow eye. I would rather be sitting inside my swamped boat, floating the right way up, waiting for someone to figure out I am missing. This is far more effective with a high sided boat like yours than a low sided boat with a heavy powerhead jacked up high in the air. And yes..... I have rolled a boat full of water while racing …

  2. #122
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    Way back on page three, when you were asking about a big star crack in the hull, Xstream wisely suggested in post 32:- "
    The "star" crack might be at the end of a stringer or bulkhead making contact with the hull on the inside." This is a common problem. And you have created this scenario with the transom knees. If I had to do it the way you have done it I would run those knees under the floor into the aft floor width bulkhead. You have done the same thing in the bow by cutting the centre stringer short in the bow, but you will get away with it because it butts into the forward bulkhead.
    I would not finish the centre stringer short of the transom, even though it does tie into the small bulkhead between the knees. That part of the hull can have a lot of pressure on it when running fast and you are leaving it unsupported.
    Especially on re-entry!
    Sound like overkill? Are going to be pushing hard in the open ocean?
    The worst place to have some flex is in the last couple of feet of the running surface on a fast boat.
    You have done some great work but you are letting yourself down with some small but important structural details.
    Last edited by GregAdams; 07-30-2018 at 03:00 AM.

  3. #123
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    Quote Originally Posted by GregAdams View Post
    Way back on page three, when you were asking about a big star crack in the hull, Xstream wisely suggested in post 32:- "
    The "star" crack might be at the end of a stringer or bulkhead making contact with the hull on the inside." This is a common problem. And you have created this scenario with the transom knees. If I had to do it the way you have done it I would run those knees under the floor into the aft floor width bulkhead. You have done the same thing in the bow by cutting the centre stringer short in the bow, but you will get away with it because it butts into the forward bulkhead.
    I would not finish the centre stringer short of the transom, even though it does tie into the small bulkhead between the knees. That part of the hull can have a lot of pressure on it when running fast and you are leaving it unsupported.
    Especially on re-entry!
    Sound like overkill? Are going to be pushing hard in the open ocean?
    The worst place to have some flex is in the last couple of feet of the running surface on a fast boat.
    You have done some great work but you are letting yourself down with some small but important structural details.


    I see what you are saying, that star crack up that you are referring to was more than likely an impact with a trailer bunk or something similar, there was no stringer or anything near it and nothing pushing on it from the inside. I understand where you are coming from with the rear of the boat, however in that area is almost 3/4 inch thick of glass, the boat was made from 2 layers of 1708, then we added a fresh layer of 1708 and then 5 layers overlapping transom to the pad and of course the two layers of 170-8 tabbing in the knees too the hull as well, I don't think strength in that area is an will be an issue. Are you suggesting that I cut the points off of the knees that touch the bottom of the hull?

    This is a picture of sharkeys boat, his drain area is the same, that boat has been really beat up and raced hard, jumped etc and has no issues at all. That's how most of these bullets are built when they are rebuilt.






    Last edited by TwzteD; 07-30-2018 at 08:47 AM.

  4. #124
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    Are you suggesting that I cut the points off of the knees that touch the bottom of the hull?
    No. I am suggesting running the knees forward to meet the next bulkhead would be a good idea.

  5. #125
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    It would add a lot of stiffness to the bottom running short stringers fwd from the knees tied into the bulkhead. The bottom could flex at the knees fwd. contact points when landing from a jump. One thing for sure, it wouldn't hurt.

  6. #126
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    Quote Originally Posted by XstreamVking View Post
    It would add a lot of stiffness to the bottom running short stringers fwd from the knees tied into the bulkhead. The bottom could flex at the knees fwd. contact points when landing from a jump. One thing for sure, it wouldn't hurt.


    I do agree, wouldn't hurt, but would you still add them if the Knee/Stringer extensions were only 1.5-2" tall? that's all the room there is under the floor, reason we went with the single stringer down the middle.. I don't mind adding them but im trying to save as much weight in the back as possible and I didn't think a 2" tall x 3/4 stringer would do much. See what you are saying about the points of the knees if it flexes could possibly poke a hole or crack the bottom at the spot, adding them in wouldn't add much weight but and i could do it if it would actually help. would coosa be nessacary or h80 work?
    Last edited by TwzteD; 07-30-2018 at 11:43 AM.

  7. #127
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    I would think either coosa or h-80 would work. Short is ok. All they will do is stiffen the bottom and spread the load out to the bulkhead. How much does the bottom move if you walk around in that area? And how thick is it?

  8. #128
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    Quote Originally Posted by XstreamVking View Post
    I would think either coosa or h-80 would work. Short is ok. All they will do is stiffen the bottom and spread the load out to the bulkhead. How much does the bottom move if you walk around in that area? And how thick is it?
    It does not flex really at all when walked on atleasit I can't see it, the bottom is 3 layers of 1708 not counting any overlapping, the pad is at least 4 layers due to overlapping and them more newar the knees and transome. I don't mind adding them I can make some templates up to see

  9. #129
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    Sounds like it's fairly solid. The short knee extensions will help to keep flex to zero and give a bit more strength overall. The bilge area will be made stronger when you glass in the bulkhead and the floor. This is an example of why it is good to have several sets of eyes on a project. Greg Adams knows his stuff and caught something that could have been a problem in the future. Being the boat is only 13' long the short distances between the stringer and bulkheads won't allow much flex or twist once the floor is glassed in.

  10. #130
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    The floor is a structural member. The stringer in that situation behaves like the web in an I Beam and the hull and floor are the top and bottom flanges of the I Beam. It may well be that your hull is so thick that you don't need to do it. But having the knee and the aft bulkhead finish at a 90 degree angle and having 270 degrees unsupported around that point is not ideal.
    On the positive side I am a big fan of solid laminate hulls with solid laminate stringers for very lightweight and tough hull bottoms

  11. #131
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    Quote Originally Posted by GregAdams View Post
    The floor is a structural member. The stringer in that situation behaves like the web in an I Beam and the hull and floor are the top and bottom flanges of the I Beam. It may well be that your hull is so thick that you don't need to do it. But having the knee and the aft bulkhead finish at a 90 degree angle and having 270 degrees unsupported around that point is not ideal.
    On the positive side I am a big fan of solid laminate hulls with solid laminate stringers for very lightweight and tough hull bottoms
    so I did some measuring last night and looks like its about 15 / 16 inches in legnth and a little less than 3 1/2 inches of height, could i get away with using H80 for this also? im sure Coosa is a lot stronger, im really trying to keep weight out of the back. the engine is already alot for this boat.




  12. #132
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    I would ask Xstream about Coosa. I haven't worked with it.
    Can you get away with using less glass with the Coosa?
    The end result may be similar weight wise .
    The job of the stringer there is to transmit the shear stresses in the "I Beam" to the floor and hull.

  13. #133
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    You could use either coosa or H-80 The weight difference between the two for that small amount of material is ounces.

  14. #134
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    Quote Originally Posted by XstreamVking View Post
    You could use either coosa or H-80 The weight difference between the two for that small amount of material is ounces.

  15. #135
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    Will be using coosa for sure.

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