Re: Leeboard pivot
Our Brick weighs 75 pounds or so. I think in your weight calculations,
you forgot to subtract all that framing wood that could be eliminated.
Plus you could drop off maybe 3 inches of bottom width and some on the
vertical corners etc without having to overlap that outside framing. Of
course the tape and epoxy weigh a little bit. I calculate that the taped
version would require maybe 12 pounds less wood. And you could make a
pivoting leeboard without framing or guards (since the side of the boat
is flat) and save another couple of pounds. Then you could leave off or
shrink the bottom skids (since the bottom is now thick enough by itself)
and save another 5 or 7 pounds. So this is all SWAG (Scientific, wild
a....)but I think you could come back down about 20 pounds! (Assuming
the glass tape doesn't weigh much.) But our hull weighs 75 pounds with
luan so I'm wondering if your hull weight is optimistic? Or did you
weigh it? But to my mind, this is all guesswork.
Michalak (http://homepages.apci.net/~michalak/15feb03.htm) seems to
think you lose 5 lbs or so per sheet by going to taped seams, but the
Brick has heavy framing so I think my estimate is close.
Still all guesswork.
I've also heard of 5/16" MDO, but I suspect it's a rare item.
you forgot to subtract all that framing wood that could be eliminated.
Plus you could drop off maybe 3 inches of bottom width and some on the
vertical corners etc without having to overlap that outside framing. Of
course the tape and epoxy weigh a little bit. I calculate that the taped
version would require maybe 12 pounds less wood. And you could make a
pivoting leeboard without framing or guards (since the side of the boat
is flat) and save another couple of pounds. Then you could leave off or
shrink the bottom skids (since the bottom is now thick enough by itself)
and save another 5 or 7 pounds. So this is all SWAG (Scientific, wild
a....)but I think you could come back down about 20 pounds! (Assuming
the glass tape doesn't weigh much.) But our hull weighs 75 pounds with
luan so I'm wondering if your hull weight is optimistic? Or did you
weigh it? But to my mind, this is all guesswork.
Michalak (http://homepages.apci.net/~michalak/15feb03.htm) seems to
think you lose 5 lbs or so per sheet by going to taped seams, but the
Brick has heavy framing so I think my estimate is close.
Still all guesswork.
I've also heard of 5/16" MDO, but I suspect it's a rare item.
>Mark wrote:
>
>
>>> The Brick does flex and make strange noises when it gets windy. I wonder
>>> how heavy a 3/8mdo Brick done with taped seams would be?
>>
>>
>>>> >Lincoln,
>>>
>>>
>
>With the 23 pounds/ sheet 1/4" pine ply and cedar framing, my bare hull is 70 pounds. Half
>again on the ply, a little lighter for the tape, and cancel out the difference between the
>paper's extra weight and less paint puts it in about the 100 pound range.
>
>That's just to the edge of cartopping, especially for a short boat, but easy on the
>lightest trailers.
>
>Mark
>
> The Brick does flex and make strange noises when it gets windy. I wonderWith the 23 pounds/ sheet 1/4" pine ply and cedar framing, my bare hull is 70 pounds. Half
> how heavy a 3/8mdo Brick done with taped seams would be?
> >Lincoln,
again on the ply, a little lighter for the tape, and cancel out the difference between the
paper's extra weight and less paint puts it in about the 100 pound range.
That's just to the edge of cartopping, especially for a short boat, but easy on the
lightest trailers.
Mark
The wood problem I was referring to is this:
If the 3 layers are all the same thickness, then the middle layer will
be flimsy and floppy (i.e. the sheet will bend and break very easily
across the grain of the outer faces. If you want comparable stiffness in
both directions, optimal outer faces for one layer of plywood are thin.
For optimal strength in both directions, thin but not quite as thin. For
two layers of ply glued together, the optimal outer faces will be twice
as thick. All this goes away if you glass, but I can't see glassing a
Brick. I did the numbers on this a while back but I don't remember. My
impression was that normal luan was close to optimal face thickness for
equal stiffness in both directions, but you could just measure the
stiffness of a square piece to see if this is true. Anyway, I solved the
floppiness problem on a boat I built by glassing the floor.
The Brick does flex and make strange noises when it gets windy. I wonder
how heavy a 3/8mdo Brick done with taped seams would be?
If the 3 layers are all the same thickness, then the middle layer will
be flimsy and floppy (i.e. the sheet will bend and break very easily
across the grain of the outer faces. If you want comparable stiffness in
both directions, optimal outer faces for one layer of plywood are thin.
For optimal strength in both directions, thin but not quite as thin. For
two layers of ply glued together, the optimal outer faces will be twice
as thick. All this goes away if you glass, but I can't see glassing a
Brick. I did the numbers on this a while back but I don't remember. My
impression was that normal luan was close to optimal face thickness for
equal stiffness in both directions, but you could just measure the
stiffness of a square piece to see if this is true. Anyway, I solved the
floppiness problem on a boat I built by glassing the floor.
The Brick does flex and make strange noises when it gets windy. I wonder
how heavy a 3/8mdo Brick done with taped seams would be?
>Mark wrote:
>Lincoln,
>
>Your 25% theory works too.
>
>I've used what I think is a rather good grade of radiata pine mentioned here, brand
>Arauco. 3 voidless layers and ext glue.
>
>But I'm not sure what problems you mean. The main one so far is that, though square and
>built with the straightest lumber I could find, the boat was actually more trouble to get
>into free standing alignment than one with more conventional curves; not that same
>tension, you know? Even with the top corners on, it needed clamping to a building table
>till the bottom was firmly on.
>
>Bolger calls it, "Flimsy" if driven hard. Is that what you meant? Or is there something
>else worth taking measures to prevent.
>
>Pivots all around would be worth while.
>Mark
>
I should have been clearer. I think both reasons can be valid at the
same time.
same time.
>Richard Spelling wrote:
>
> Lincoln Ross wrote:
>
>
>>> That sounds like a good reason, but I see another one. The lift on a
>>> symmetrical lifting surface acts at approximately 25% back snip
>>
>>
>Going to the source:
>http://tinyurl.com/os0v
>"About all that's left to do now is to find a pivot point that will allow the leeboard to retract fully under the upper guard"
>
>My method, in files, is a refinement of this, and will find the exact position for both the way you want it to sit veritcaly, and
>the way you want it to sit when retracted.
>snips
>
>
>