Floor or no floor?

Discussion in 'The Beach' started by stapletm, Aug 27, 2012.

  1. stapletm

    stapletm Established Hydrodyner

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    Boat Model and Year:
    1970, 18' Outboard, 1974 18" Outboard
    So, I'm well into the restoration of my second 18 footer. I put restoration of my first 18 footer on hold when I found core damage, and I happened to find my second 18 footer which I thought was in better shape, largely because it was a newer hull with the stringer floor, which my 1st early model did not have. Ironically, when we pulled out the soft stringer floor, then wet foam, then wet stringers, sounding with a hammer revealed this one had core damage as well. I chose to proceed with this as a hobby, as I'm not sure I could ever justify core repair otherwise (which proved considerably larger than the hammer sounding would have me believe). I'm well into that, and will post it with photos as a new restoration thread in the fall when I have more time.
    My question for now though, "floor or no floor?" is regarding whether or not, once my core repair is completed, it is worth rebuilding the stringer floor as well, as I’ve read there is no hull structural integrity requirement to the stringer floor. What is the value added? I know it makes a flatter floor surface, but you give up about 6 inches in the middle, of cabin space in a low boat, and introduce back in a floor and stringer section that rotted in the first place, not to mention the additional expense and weight. Opinions appreciated!
     
  2. markbano

    markbano Hydrodyne 18 Specialist

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    Probably the biggest single value of the double floor is the fact that it provides a surface to screw things like seats into so that you are not creating holes for water to get into the core. Without the floor, you will just be srewing into the core and making new water channels into the core again.

    The second benefit of the floor is the floatation foam under it. This will make the difference in terms of nuetral flotation and safety, as well as keeping the boat off the bottom of the lake if you get waves over the back, or a lot of rain, or both. This, in turn, may save your engine from being under water.

    From a structural standpoint, and having rebuilt one of these boats myself, it seems almost impossible that the second floor would not add structural rigidity to the boat. It absolutely adds rigidity.

    I genuinely do not know if the post-1970 boats designed with the second floor had a different fiberglass layup for the hull. I would be nervous about not re-installing the second floor in any boat that was made originally with it. It may be that the late 60's boats had a heavier duty floor - either thicker balsa or more layers of glass or both. I just don't know.

    Finally, the floor will allow you to use a modern seat. Otherwise, you would need to make custom seats to be up high enough.

    That is my $.02

    Good luck with your project!

    Markbano
     
  3. jim

    jim Hydrodyne 18 Specialist

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    The older boats that were built with no floor had a double layer core.

    2MERCS boat is an 18 twin rig with inlines and has a partial floor to mount the seats. I believe it has full length stringers, but no floor in the aft section of the boat. The advantage is that the rot often starts at the stern. That boat also has a deck and transom mounted tow hook.

    The later boats did not have foam under the floor because it is also a source of trapped moisture. I believe these boats had more foam under the gunwales, the foredeck, and the aft deck. The advantage of the high mounted foam is that is does not tend to pick up moisture and helps the boat float upright.

    jim
     
  4. markbano

    markbano Hydrodyne 18 Specialist

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    My 73 had foam under the floor, but it was open cell foam. You can now get closed cell foam that does not fill with water. That's what I used under my rebuilt floor.
     
  5. stapletm

    stapletm Established Hydrodyner

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    Thank you gentlemen! Did I not read in more than one spot on this site that the stringer floor added nothing to the structure (although I do take your point Mark)? Not sure I like the idea of screwing into wood even on a stringer floor. For the seating I think I'll build fiberglass pedestals to screw into no matter which floor way I go. May even glass in aluminum bolting plates.
    Do like the idea of flotation foam up in the under the gunwales, the foredeck, and the aft deck as opposed to down in the floor.
     
  6. markbano

    markbano Hydrodyne 18 Specialist

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    my boat was built originally with foam in all of those places . I don't think it is an either/or situation . However , you have to be able to put the boat upside down to put foam under the gunwales. It gets poured in as a liquid and then expands.
     
  7. stapletm

    stapletm Established Hydrodyner

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    Food for thought, thanks. My goal for this year is to get the new balsa core in and encapsulated. I should finish the main accessible repair area this weekend, then pop the top to finish the very front and very rear. Then there's the transom. I have a bit of time to consider where I'm going with the final floor design.
    As mentioned, I will put a work to date thread into the restoration section when I have time in the fall, or sooner. Thanks for the advice/oppinions.
     
  8. GaDyne

    GaDyne Established Hydrodyner

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    That is correct that the older boats with no flat floor had a double layer balsa core. There are several dynes around here with a partial flat floor only where the seats are and they have no stringers and the single layer core. I liked my 72 O/B with no floor better than the flat floor. My 79 had foam under the floor between the stringers and there is alot of foam under the gunwales and front deck. My 72 had no foam at all, don't know why but it never had any.

    Ashley
     
  9. stapletm

    stapletm Established Hydrodyner

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    1970, 18' Outboard, 1974 18" Outboard
    Thanks Ashley, I’ve been thinking about this a lot as I'm refinishing the glass over my repaired Balsa floor, and curiously, I have been thinking about only building the false flat floor up a bit in the front where the front seats are, and carefully slope it back into the deck, as the back is so flat anyway. If I did that, I'd likely build that layer up only a little, maybe 2 inches where the original was about 6, so net gain of 4 inches in the boat. Tricky part will be what to use as it would likely go from 2 inches out to nothing on the sides in such a short span. Would love to sculpt (fair?) out a light composite panel to encapsulate in there, but I haven’t seen anything appropriate, plus the sculpting would be extreme. Given the sharp angle, you’d almost want to use a filler to do the job, but again, I haven’t seen anything appropriate (light yet strong and flexible).
     

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