Building the Strongback options in construction
JBB
lapstrake). The strong back is going up first. I saw a picture on
the internet of a strongback for a stripper canoe constructed like a
plywood box. It appeared to be 1/2 inch ply with internal frames of
2x4. The strongback box had legs but I guess it could be on trestles.
I would like to go this route, plywood is easier to find than 16 foot
perfectly strait boards.
a picture of an example is at
www.ministrycomputing.com/Kayak/WeeRobbie/4Dec00/scupper1.jpg
Can any one tell me what the pitfalls are?
JBB
Meindert Sprang
inflexible frame to put the moulds on. When you build up the hull, the bent
strakes tend to straighten and thus pull heavy on the strongback. I used two
67 x 44 mm beams for my Puffin (10ft lapstrake) and I noticed a slight
bending up of the strongback when the hull was complete. My next boat, a
15ft cold-molded hull, will have 2x8" beams as strongback, as specified by
the designer.
Meindert
www.customware.nl/boats
JBB <zmb...@flash.net> wrote in message
news:b14fddbd.01100...@posting.google.com...
JBB
lumber will bend in two planes and plywood will only bend in one.
This property of plywood should make a plywood box completely rigid..
JBB
"Meindert Sprang" <mhsp...@customware.nl> wrote in message news:<5j_u7.7381$fo2.8...@zwoll1.home.nl>...
> ...I used two
> 67 x 44 mm beams for my Puffin (10ft lapstrake) and I noticed a slight
> bending up of the strongback when the hull was complete. ...>
> Meindert
> www.customware.nl/boats
>
>
Bill Graham
frame. I used them to build 4 x 8 ply worktops for the shop and in
construction of a workbench. Rigidity is dependent on using glue on all the
frame/skin joints. As long as you plan to glue all the joints it should
work like a charm. The only draw back to my worktops and bench is they
sound like a drum when you hammer on them. Next time I'm filling the voids
with all those packing peanuts that seem to have no other use.
Jim Conlin
twist. If the floor's not flat and the stand is moved around, the boat'll
twist.
If a strongback bends a bit under the force of lots of planks, you can
counteract that by moving the supports under it closer together.
There's not a good way to counteract twist. Gotta prevent it in the first
place.
My strongback for small boats is a box beam of two 12' 2x4's and 1/2" ply
tops and bottom skins, glued & screwed in place. It may bend, but it won't
twist much. I don't like having permanently affixed legs because i like to
be able to vary the yeight of the strongback's underpinnings. When not in
use, it's screwed to the garage ceiling to keep it dry and flat.
For glued lapstrake boats, it's nice to be able to get at the inside of the
boat to scrape off epoxy squeezed out of the plank lap joints. Saves a lot
of work later. I've seen two styles of building frames which enabled this.
Tom Hill's frame consists of two light (1x6?) planks fastened together at the
ends and spread apart in the middle. Leaves a big opening in the bottom. If
you're going to build a glued lap boat, get Tom's book and video from
Woodenboat.
See also the "Building Ellen" series in Woodenboat issues 156-158 by John
Brooks and Ruth Ann Hill. Their frame is also open on the bottom. Don't
remember the details.
Have fun with your solo canoe. Bet you can't stop with just one.
Jim
Dale Gloer
same size.
Dale.
Meindert Sprang
news:3BBDA834...@ca.ibm.com...
> Don't kid yourself. Beams made from plywood aren't much stiffer in either
plane than dimension lumber of the
> same size.
Indeed. They would be even weaker, since almost half of the wood in plywood
has the grain oriented in the wrong direction when used as a loaded beam.
And across the grain, wood is some 20 times weaker than along the grain.
Meindert
Drew Daglish
full cut dry straight and strong . I attached the legs with black and
decker workhorse brackets to make the whole thing easily height
ajustable.
Have fun with your project Drew
Rich S.
news:3bbdb872...@news.execulink.com...
> My strong back is built with used lumber from a house wrecker it's
> full cut dry straight and strong . I attached the legs with black and
> decker workhorse brackets to make the whole thing easily height
> ajustable.
> Have fun with your project Drew
I'm not 100% certain of the purpose of a strong back, but it appears similar
to the jigs used in building aircraft fuselages. In those, many builders are
using the prefabricated I-beam floor/ceiling joists which have OSB verticals
capped with dimension lumber. They fill the need for strong, straight beams
with the advantage of being light and warp resistant.
Rich
Dave W
every boat seems to want to be built higher off the floor than the
preceeding one. May have something to do with the aging of the knees.
"Jim Conlin" <con...@mediaone.net> wrote in message
news:3BBD46A4...@mediaone.net...
Jim Conlin
(nominal 2x10), so they'd be overkill for a 12' 30 lb. canoe. Being light,
straight and stable, they'd be an excellent choice for a larger project.
Not having permanently affixed legs makes the box easier to store between
projects.
Bob Perkins
It worked very well for me. I thought it was simple to build and very
strong. I used particle board because it was cheaper and very flat.
Bob
JBB wrote:
--
Regards,
Bob Perkins
http://people.ne.mediaone.net/bperkins1
Henrik Borg
I built my strongback for my 33 ft sailboat from a 12m by 180mm H-beam. The
beam is suported at the ends and in the middle by concrete mouldings to the
ground after that the beam was leveled. The only concern is if the ground
will move during the winter...
See my project home page http://vsrt.seglar.nu for more info.
Best regards
Henrik Borg
"Meindert Sprang" <mhsp...@customware.nl> skrev i meddelandet
news:5j_u7.7381$fo2.8...@zwoll1.home.nl...
jbb
I think you may be incorrect. The thickness of the beam is not element of
it's stiffness the thickness adds strength. It is the width that makes it
stiff. . In plywood, even 3 ply, if you had a 12 inch wide plank 1/2 to 3/4
thick it would be much stiffer than say a 2X6. It would be like trying to bend
a 12 inch X 12 inch board end grain to end grain. the board won't bend it will
split. if you laminated two boards or even one board with perpendicular grain
that would prevent the splitting and produce a very stiff board. As I said
earlier the thickness of the board does not add stiffness it adds strength.
The width of the board adds stiffness. I don't need strength . Stiffness and
straitness is what I am after.
With all that said I think I should not use the box beam. I need to be able to
get inside the hull during construction to make patterns for the planks and
scrape off oozed out epoxy. I will use a conventional strong back
JBB
Bob
something small like your boat, grab a couple of 1x6 boards for the top and
bottom of the "box". These boards need not be perfect. Butt blocks are OK
if you can't find boards as long as the boat.
Separate them with vertical pieces of 1x6 lumber every couple of feet, glued
and screwed using drywall screws. Make your box 6 or 8 inches deep. This
is just to get things in alignment for the next step. Working on an
ordinary floor will provide plenty of accuracy.
Now get some large pieces of corrugated cardboard from your local appliance
store and cut it into strips with the "grain" running vertically, i.e. at
right angles to the length of the beam. Squirt some cheap yellow glue on
the edges of your box and staple on the cardboard "sides" using a T-50 type
hand stapler. Trim the edges with a razor knife.
Use simple butt joints and continue until both "sides" of the box are
covered in vertical "grain" cardboard. You now have a very stiff and light
box to set on a pair of saw horses. It's quick to build and very cheap.
Glue and screw on cleats at each mold station.
The box need not be straight and a bit of twist is OK too. Of course,
perfect is nice, but you'll be leveling the mold at each station and
attaching them to the cleats (I use clamps for small boats) along with a
couple of tight wires through alignment holes so that the molds are all
perfect.
I like to recheck the level and alignment of the molds from time to time
throughout the construction anyway, don't you?
Bob
"JBB" <zmb...@flash.net> wrote in message
news:b14fddbd.01100...@posting.google.com...
brian whatcott
/snip/
>I think you may be incorrect. The thickness of the beam is not element of
>it's stiffness the thickness adds strength.
/snip/
>JBB
.er....
doubling the width of a beam doubles its stiffness:
doubling its depth quadruples (X4) its stiffness.
Brian Whatcott Altus OK
<in...@intellisys.net>
Eureka!
brian whatcott
the shear web - ideally, with best strength at 45 degrees to top.
Brian W
On Sun, 07 Oct 2001 10:21:34 GMT, "Bob" <boban...@worldnet.att.net>
wrote:
Brian Whatcott Altus OK
<in...@intellisys.net>
Eureka!
Bob
> the shear web - ideally, with best strength at 45 degrees to top.
Well, yeah, but my cheap throw away cardboard only comes in the
unidirectional variety.<g>
So, I just run the corrugations in the vertical direction and let the shear
reaction do whatever the hell it wants to across the face of the cardboard.
Now I wouldn't use this beam to lift my wife's Blazer, but it certainly is
strong and stiff enough for building small boats.
Engineering students looking for extra credit might laminate two layers of
cardboard to produce a + and - 45 degree shear web, but don't expect me to
do that.
Bob
Bill Kreamer
cat-ketch sharpie, 20 feet long?
I'm thinking of using two bilge-located dagger boards, each with an angle of
attack to weather of maybe 3 degrees, and with a lifting foil shape. I
would set them at an angle to the boat's lines so that each board would
lift, carrying all the sideways load under certain conditions, so the boat
wouldn't make leeway. Drag would be reduced because the board is a more
efficient lifting body than the hull.
To tack, you would first put the weather board in, then put the tiller over
and remove the other board as you come head to wind (big tiller extension
when single handed, or just wait until you're squared away to remove the
weather board).
I would arrange the dagger blades to pivot between two cheeks like a rudder,
with the trio fitting into a wider-than-usual case. When fully down, the
cheeks are flush with the bottom. The wider case would let me experiment
with flow fences on the blade tips.
The case would have an angled after end to let the board pivot, either
intentionally or when it strikes bottom. There would be a detent in the
straight down position, another in an intermediate position. Hitting bottom
would override the detents. Pulling the board up would return it to the
intermediate detent, in which configuration it could be fully removed or
inserted.
How can I improve this? Thanks for all ideas/advice!
Bill
Bill Kreamer
have, if any, ahead of the sail plan center-of-effort of a cat-ketch
sharpie, 20 feet long?
Next, I'm considering using bilge-located dagger boards set at a 15-to-20
degree angle, because they are more efficient than (off-)centerboards. But
there is the problem of grounding out...
I could arrange the dagger blades to pivot between two cheeks like a rudder,
with the trio (cheeks plus board) dropping into a wider-than-usual case.
When down, the cheeks are flush with the bottom. The wider case would let
me experiment with flow fences on the daggerboard tips.
The case would have an angled after end to let the board pivot, either
intentionally or when the board strikes the bottom. There would be a detent
in the straight down position, another in an intermediate position. Hitting
bottom would override the detent(s). Pulling the board up would return it
to the intermediate detent, in which configuration it could be removed or
inserted.
Can you improve this? Or tear the idea apart for me? Thanks for all
ideas/advice!
Bill
Klaus
were something I considered and rejected as too complicated when I built my
boat.
I settled for a dual pivoting aft centre board(s) set up, imagine a standard
foil shaped centreboard split into two halves (port and starboard) and mounted
in the same case.
This set up does all you hope of from yours, is simpler, there's only one slot
in the bottom of the boat, albeit a long and 4" wide one, which has plastic
flaps to keep it closed and thus the slot turbulence down.
I used the lead and board area as designed for my boat with a single board,
something I would not recommend to figure out unless one knows exactly the
boats sail plan and underwater shape.
Having rotating aft board(s) the CLR can, of course, be changed by a fair
margin by raising or lowering the board(s) and thus the balance of the boat so
that she steers herself very well.
When fully down they are still carried swept back and do not catch weed. They
even deflect down the long craypot ropes hereabouts so I can run over them
without snagging. I have tested the grounding ability of this set up by
(unintentionally) hitting a reef, the board just pivoted up, slid over the
obstacle, lowered itself and we continued as if nothing did happen. Later
inspection revealed a very small scratch in the glass covered lead tip ( the
board(s) are NOT part of the boats ballast, the lead is there to make the
laminated wood boards sink).
If I'm lazy I leave both boards down and have surprised many a bigger boat when
they try passing to windward and find they cannot point as high after I
sneakily raised the leeward board :-)
Klaus
Bob
I used tandem, high aspect ratio centerboards. By moving the forward board
forward, I was able to open up the cabin area and provide a queen sized
sleeping area.
The forward trunk only split the berth for about a foot at the forward edge
of the berth.
The aft board trunk split the entire cockpit from the bridge deck aft to the
bulkhead forming the lazerette. I thought it might comprimize the utility
of the cockpit, but it really didn't cause any problems and proved to be a
good foot brace when sailing close hauled. By tying it in to the boat at
both ends, the trunk could be both light and strong.
The big advantage was that I could trim the sails for best effeciency and
then balance the helm by adjusting the boards a little bit up or down. I
was also able to strike the mizzen, retract the aft board completely and
sail along on the main and forward board only and still be in balance.
Of course, just like Mom said, "Son, there ain't no free lunch". The boat
was a bit slow in tacking with both boards full down, so I rigged the
pendant for the forward board so I could retract it quickly from the
cockpit.
In tight quarters when blowing a tack might prove embarassing or dangerous,
I could raise the aft board for a moment to start the tack, and then as I
came head to wind, let it down and quickly raise the forward board until
falling off on the other tack.
It sounds complex, but it worked just fine.
Bob
"Bill Kreamer" <kre...@mint.net> wrote in message
news:GO5x7.70$M6.2...@news1.news.adelphia.net...
William R. Watt
>
> I would arrange the dagger blades to pivot between two cheeks like a rudder,
> with the trio fitting into a wider-than-usual case. When fully down, the
> cheeks are flush with the bottom. The wider case would let me experiment
> with flow fences on the blade tips.
counter sink the head and nut on the pivot bolts into the cheeks?
daggerboards should be weaker than the trunk so they break before the
trunk does. if feasible it might be simpler to use disposable dagger
boards and carry a spare.
--
------------------------------------------------------------------------------
National Capital FreeNet www.ncf.ca Ottawa's free community network
website: www.ncf.ca/~ag384
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Klaus
cat ketch rig rather than the foreward and aft centreboards. My 26 N.I. sharpie
has a cat ketch rig and the first thing I noticed after launching her on the
maiden sail was the very different (from my previous sloop boat) tacking.
She would never spin on the spot as you can with a sloop rig but rather
sedately tack round, like a car taking a corner.
She even tacks under mizzen alone as long as the boat speed is over two knots
and the wind/sea state not too rough.
Klaus
Bob
> cat ketch rig rather than the foreward and aft centreboards. <<
Nope, the sluggish tacking was almost purely a result of the tandem
centerboards.
To help you imagine the situation, picture a sharpie with a full keel. Of
course, it wouldn't be a sharpie then, but you get the idea. When you
spread out the lateral resistance fore and aft, the boat is reluctant to
"pivot" as nicely as it does with a fin keel, or centrally mounted
centerboard.
It is true that spreading the sail plan out fore and aft will also slow down
the tack, but the effect is small compared with the underbody configuration.
IOW, something you might notice in a close tacking dual, but not something
that would normally inhibit the ability to successfully complete a tack.
The entire situation was made worse in my case because this particular 26
footer was traditional in appearance, but was of rather high tech
construction. The boat only weighed 825 pounds dry. She carried 750 pounds
of water ballast, but I often sailed her with no water in the tanks.
It would really scoot downwind in light conditions, but was particularly
difficult to tack (without manipulating the boards) when sailed at minimum
weight. An alternative maneuver was to ease the main at the start of the
tack, then sheet the main and ease the mizzen when passing through the eye
of the wind.
Bob
Klaus
on that boat :-)
My sharpie weighs about 2000 kg of which approximately 600 kg is ballast (500
kg lead+ batteries+ water in tanks).
Very comfortable to cruise in her.
Tacking ( competitively) means lowering the leeward board, putting the helm
over to let her tack, straightening helm, raising new leeward board - that's
it, no sail adjustment since main add mizzen run on full width travellers.
Tacking while cruising leaves out the CBboard raising/lowering since I leave
both down.
Klaus
Bill Kreamer
side-to-flat side) in the same slot? How much added lift to weather do you
get with one board down instead of both?
Wouldn't I do as well (aside from the bother of two cases) to use separate
port and starboard bilge boards, and give them a 3 degree angle to weather.
Of course, I could not sail with both boards down.
But on the plus side, each would have a narrower slot, and a better location
(at the bottom of the boat when heeled). They would have a 15-20 degrees
outboard slant so as to be upright at that heel angle. They would be longer
and narrower than the old style, and would be sailed pointed straight down,
pivoting for light air, sailing downwind, tacking, or to clear a fouled
line. Because of location and shape, they could be 25-35% smaller than
usual. All told, a lot less drag.
- Bill
--
Bill Kreamer
Sol-Air Company
129 Miller St.
Belfast, ME 04915
Tel 207-338-9513
Fax 603-853-9339
mailto:kre...@mint.net
"Klaus" <K.Suss...@curtin.edu.au> wrote in message
news:3BCA47EA...@curtin.edu.au...
William R. Watt
>> > Nope, the sluggish tacking was almost purely a result of the tandem
>> > centerboards.
>> >
>> > To help you imagine the situation, picture a sharpie with a full keel.
> Of
>> > course, it wouldn't be a sharpie then, but you get the idea. When you
>> > spread out the lateral resistance fore and aft, the boat is reluctant to
>> > "pivot" as nicely as it does with a fin keel, or centrally mounted
>> > centerboard.
this reads like TF Jones' description of tacking a catamaran. One hull
pivots while the other sails around it. Good catamarans don't tack as well as
good monohulls.
however bilge keel are popular in the UK. look at G Atkin's design of a
twin bilge daggerboard weekender that won last year's amateur design
contest at www.duckworksmagazine.com.
Bob
cruising
> on that boat :-)<<
Well, it depends on what you mean by cruising. When we were stuck living in
St Louis, my wife and I used to stash an old car at the Miami airport. We'd
fly down, drive to the FL keys, where we kept the boat in a back-water
marina on it's trailer. In a few minutes I'd have the unstayed rig in the
boat and be ready to go down the boat ramp.
We have explored Florida Bay for as long as 10 days at a time on this boat,
going ashore for ice or drinks at a bar, but spending all of our sleeping
time on the boat anchored out, and we did most of the cooking on board.
We would take her out into Hawks Channel in moderate weather, but never
thought about crossing the Gulf Stream, for example.
However, we're old farts now. In my younger days I certainly would have
considered going to the Bahamas, which is not to say it would be prudent.
The boat was light, but not lightly built, if you know what I mean. It was
a fiberglass foam cored boat with minimum systems and water ballast,
intended to be easy to tow behind a small car and suitable for "camp out"
style cruising. It did this perfectly.
Although it was not a live aboard boat by any means, we certainly did a lot
more cruising than many of our friends in much larger keel boats.
Bob
Andrew Moore
<kre...@mint.net> wrote:
> First question is, how much lead should a board
> center-of-lateral-resistance have, if any, ahead of the sail plan
> center-of-effort of a cat-ketch sharpie, 20 feet long?
The CLR and CE should line up may just a touch forward to
make for automatic rounding up if you fall of while single handing.
I'm reading between the lines a bit here but if you are looking at
compensating for the comman wheater helm problem in cat boats
you have the wrong cause. This ploblem is caused by the transfer
of the sails forces to the hull by the mast, which is very far forward.
When the boat is sailed upright this causes the bow to nose dive
some what which is why cat boats are usually very full in the bow.
When the boat starts to heal over this force attempts to drive the bow
up into the wind. Sloops, Ketches or any boat with a mast stepped
farther aft provides some hull in the water to help keep the boat
tracking straight mind you it can still be a problem sometimes. The
solution is to opt for a boat with a mast stepped further aft or sail the
boat flat. This can also be a problem in very wide boats so talk to
some the local hot shot racers they are used to sailing boats flat it is
not so bad once you get use to it.
>
> Next, I'm considering using bilge-located dagger boards set at a
> 15-to-20 degree angle, because they are more efficient than
> (off-)centerboards. But there is the problem of grounding out...
Can you make them centerboards or pivot board?
>
> I could arrange the dagger blades to pivot between two cheeks like a
> rudder, with the trio (cheeks plus board) dropping into a
> wider-than-usual case. When down, the cheeks are flush with the bottom.
> The wider case would let me experiment with flow fences on the
> daggerboard tips.
Looks like you have considered centerboards or pivot boards.
Bill Kreamer
larger main, well forward, and a slightly smaller mizzen. I've decided to
use regular bilge boards (off-centerboards), like lake scows, instead of off
center daggerboards; they are more convenient when you bottom out, plus
easier to handle in the boat.
I guess I'm confused about the interaction between CE and CLR. I think (my
first mistake?) a boat needs a light weather helm that increases moderately
along with wind speed. Does anyone else share my confusion about why a
sailplan CE leads the CLR (of board + hull). How does having the CE lead
the CLR produce the desired moderate weather helm? Doesn't it? Shouldn't
it?
I went to the net to get some advice, which I found at
http://home.clara.net/gmatkin/therules.htm (thanks to Gavin Atkin). Here's
a summary of the opinions on balance, (the ones that seemed to relate to
sharpies):
· CE should be right over CLR or an inch or two ahead - John F Sutton
· CE should lead CLR by 12-14% LWL (centerboard craft) - John Teale
· 7-11% lead (shoal full-ended centreboarders), + moveable mast - Norman L
Skene;
and from him also?:
CE of a boomless sail is some way aft of the drawn position
· 11-14% lead (ketch) - Dave Gerr
· CE over CLR ( flat-bottomed boats) - Jim Michalak
· 7% lead conventional sloop) - L Francis Herreshoff; and from him also:
as boat heels, depending on bow sharpness, water-flow from
leeway may turn bow to wind.
a wide shallow boat will tend to head up to the wind on heeling.
Increasing draft in a sail moves the effective centre aft.
a divided sail plan's effective centre of effort moves less.
Looks like CLR should be anywhere from right over CE, to leading CLR by up
to 14%. Your kind correction of any of my favorite misconceptions would be
very much appreciated. Then I can decide on a good location for a
daggerboard on my 20' sharpie, and avoid too much rework, I hope.
My sincere thanks to you all. -Bill
"Andrew Moore" <amo...@hfx.eastlink.ca> wrote in message
news:20011019.194247...@hfx.eastlink.ca...
Bill Kreamer
forward, and a mizzen only slightly smaller. I have elected to go with
regular bilge boards (off-center centerboards) rather than off-center
daggerboards.
I'm pretty confused when I see the sail-plan CE leading the centerboard CLR
by 15% of LWL in some similar boats (the CK17 has been mentioned). It seems
like it would give a dangerous lee helm under some conditions.
I went to the net to get some advice, which I found at
http://home.clara.net/gmatkin/therules.htm (thanks to Gavin Atkin).
Here's a summary of the opinions on balance, (the ones that seemed to relate
to sharpies):
· CE should be right over CLR or an inch or two ahead - John F Sutton
· CE should lead CLR by 12-14% LWL (centerboard craft) - John Teale
· 7-11% lead (shoal full-ended centreboarders), + moveable mast
- Norman L Skene;
and from him also?:
CE of a boomless sail is some way aft of the drawn position
· 11-14% lead (ketch) - Dave Gerr
· CE over CLR ( flat-bottomed boats) - Jim Michalak
· 7% lead conventional sloop) - L Francis Herreshoff;
and from him also:
as boat heels, depending on bow sharpness, water-flow from
leeway may turn bow to wind.
a wide shallow boat will tend to head up to the wind on heeling.
Increasing draft in a sail moves the effective centre aft.
a divided sail plan's effective centre of effort moves less.
I need some guidance here. I'm not sure what really happens with CE and
CLR. I think (first mistake?) a boat needs a slight weather helm that
increases moderately along with wind speed. Do some others also share my
confusion about why we see some sailplan CEs leading the CLR (of board +
hull)? How exactly do you get the desired moderate weather helm with the CE
leading the CLR?
Your kind correction of any of my favorite misconceptions would be very much
appreciated. Then I can decide on a good location for the board(s) on my 20
' sharpie, and avoid rework, I hope.
My sincere thanks to you all. -Bill
"Andrew Moore" <amo...@hfx.eastlink.ca> wrote in message
news:20011019.194247...@hfx.eastlink.ca...
William R. Watt
>
> Increasing draft in a sail moves the effective centre aft.
>
so does increasing wind speed
Once you put the bilge boards in the boat you can still adjust the
balance by moving or changing the angle of the mast and by changing
the size of the rudder blade.