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Flatbottom Dory: Speed, seaworthy?



 
 
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  #1  
Old February 27th 04, 06:02 PM
Lloyd Sumpter
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Default Flatbottom Dory: Speed, seaworthy?

Hi,
I want to design and build a "riverboat" for the Fraser River, with some
.... "unique" design considerations (eg I want it to look ugly because it
will be on a "questionable" dock and I don't want it stolen!). Basically
I'm looking for something between an east-coast fishing dory and Bogie's
"African Queen". Something like Bateau Boat's FL14, but 16 ft, inboard and
probably not Stitch'n'glue.

Anyway, I need some anecdotal feedback: First, a 16ft boat has a
theoretical hull speed of about 5.5 knots. HOWEVER, I've seen many boats
(such as my 12ft alum) that exceeds hull speed without truly planing
(semi-plane?) Does anyone have some performance numbers for 14-16ft
flat-bottomed skiff as to how fast they go before planing? I'm looking at
maybe 6-10hp engine.

Second, I'm unfamiliar with how a flat-bottom hull performs in waves -
are they seaworthy?

Thanks for any comments, stories, etc!

Lloyd Sumpter

Ads
  #2  
Old February 27th 04, 11:20 PM
William R. Watt
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Default Flatbottom Dory: Speed, seaworthy?

"Lloyd Sumpter" ) writes:

Anyway, I need some anecdotal feedback: First, a 16ft boat has a
theoretical hull speed of about 5.5 knots. HOWEVER, I've seen many boats
(such as my 12ft alum) that exceeds hull speed without truly planing
(semi-plane?) Does anyone have some performance numbers for 14-16ft
flat-bottomed skiff as to how fast they go before planing? I'm looking at
maybe 6-10hp engine.

Second, I'm unfamiliar with how a flat-bottom hull performs in waves -
are they seaworthy?

Thanks for any comments, stories, etc!

Lloyd Sumpter


If you want a planing boat following might be of use ....
If you don't want the boat to plane it might still be of use ...
If you don't want a planing boat then it should be long and narrow for good
fuel efficiency.

TF Jones writes that a boat should plane with 1 hp for every 40 lb
displacement. That should give you some idea of now big an engine
you'd need.

Flat bottom skiffs and garveys plane good. The back end of the
boat has to be broad and flat. Sorry, I don't know how much flat
bottom you'd need to plane a given displacement.

Planing boats are not good in rough water. You need smooth water
to plane in. You can increase "seaworthiness" by giving the boat
high sides and higher bow with the sides raked to keep spray from
coming on board.

Flat bottom planing boats slap the waves. That can be pretty annoying for
some people. That's why "ocean" skiffs have "V" bows giving 'way
to flat bottoms aft. The "V" cuts the waves instead of slapping
them. There are lots of old plans for these plywood planing skiffs.

Any planing power boat needs a good strong bottom to take the pounding.

Feel free to copy and use the Skiff program under Boats on my website to
try different dimensions. Its not for planing hulls because it assumes the
rise in the bottom aft. You can use it for a dory by making the transom
very small, or anything you can imagine in between a dory and a skiff,
like a drift boat.

--
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homepage: www.ncf.ca/~ag384/top.htm
warning: non-freenet email must have "notspam" in subject or it's returned
  #3  
Old February 28th 04, 01:16 AM
Gordon
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Default Flatbottom Dory: Speed, seaworthy?

Basically, a flat bottom boat is always on a plane and can exceed "hull"
speed easily because of that.
As for ride, rough. Will pound at any kind of speed but plenty seaworthy
(most not good in a following sea) as evidenced by all the dories out there.
Gordon

"Lloyd Sumpter" wrote in message
news
Hi,
I want to design and build a "riverboat" for the Fraser River, with

some
... "unique" design considerations (eg I want it to look ugly because it
will be on a "questionable" dock and I don't want it stolen!). Basically
I'm looking for something between an east-coast fishing dory and Bogie's
"African Queen". Something like Bateau Boat's FL14, but 16 ft, inboard and
probably not Stitch'n'glue.

Anyway, I need some anecdotal feedback: First, a 16ft boat has a
theoretical hull speed of about 5.5 knots. HOWEVER, I've seen many boats
(such as my 12ft alum) that exceeds hull speed without truly planing
(semi-plane?) Does anyone have some performance numbers for 14-16ft
flat-bottomed skiff as to how fast they go before planing? I'm looking at
maybe 6-10hp engine.

Second, I'm unfamiliar with how a flat-bottom hull performs in waves -
are they seaworthy?

Thanks for any comments, stories, etc!

Lloyd Sumpter




  #4  
Old February 28th 04, 03:52 AM
Capt Frank Hopkins
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Default Flatbottom Dory: Speed, seaworthy?


Hi Lloyd,
I had a couple of flat bottom, plywood fishing boats as a kid growing up
on a lake. The 12' would plane with a 3 hp Johnson. The 14' would run like a
a scalded dog with a 15hp Merc. (Kiefhoffer)

I do recall that loading it up with 6 or 8 other kids kept in displacement
mode. Mostly due to the overload. Made a great bow wave!

Alas. the days of youth.
--
Capt. Frank

__c
\ _ | \_
__\_| oooo \_____
~~~~|______________/ ~~~~~
www.home.earthlink.net/~aartworks
"Lloyd Sumpter" wrote in message
news
Hi,
I want to design and build a "riverboat" for the Fraser River, with

some
... "unique" design considerations (eg I want it to look ugly because it
will be on a "questionable" dock and I don't want it stolen!). Basically
I'm looking for something between an east-coast fishing dory and Bogie's
"African Queen". Something like Bateau Boat's FL14, but 16 ft, inboard

and
probably not Stitch'n'glue.

Anyway, I need some anecdotal feedback: First, a 16ft boat has a
theoretical hull speed of about 5.5 knots. HOWEVER, I've seen many boats
(such as my 12ft alum) that exceeds hull speed without truly planing
(semi-plane?) Does anyone have some performance numbers for 14-16ft
flat-bottomed skiff as to how fast they go before planing? I'm looking

at
maybe 6-10hp engine.

Second, I'm unfamiliar with how a flat-bottom hull performs in

waves -
are they seaworthy?

Thanks for any comments, stories, etc!

Lloyd Sumpter




  #5  
Old February 28th 04, 12:51 PM
William R. Watt
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Posts: n/a
Default Flatbottom Dory: Speed, seaworthy?

"Gordon" ) writes:
Basically, a flat bottom boat is always on a plane and can exceed "hull"
speed easily because of that.


Shallow draft light displacement boats don't have much displaced water to
push aside. It doesn't take a lot of power to push them beyond "hull"
speed without actually planing. Canoes and kayaks are like that, and
shallow draft skiffs. Dorys have narrow bottoms and tend to sit too low in
the water to be really shallow draft. It doesn't take much to lift a
light displacement, shallow draft, wide bottom skiff or garvey onto a plane.

As for ride, rough. Will pound at any kind of speed but plenty seaworthy
(most not good in a following sea) as evidenced by all the dories out there.
Gordon


Its the narrow bottom, deeper draft, and high sides which make the banks
style dory more seaworthy. John Gardiner's "Dory Book" shows the 19 ft
inboard St Pierre fishing dory from the French islands in the Gulf of St
Lawrence. I think he wrote that the French government documented the plan
and made it avaiable cheap to the fishermen there.


--
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homepage: www.ncf.ca/~ag384/top.htm
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  #6  
Old February 28th 04, 03:30 PM
Backyard Renegade
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Default Flatbottom Dory: Speed, seaworthy?

crap, I just spent half hour addressing your questions and then my
google **** the bed... I will try again tonight, in the meantime see:
http://smallboats.com/stanley_sie.htm
Scotty, sorry
  #7  
Old February 29th 04, 07:10 PM
Backyard Renegade
external usenet poster
 
Posts: n/a
Default Flatbottom Dory: Speed, seaworthy?

"Lloyd Sumpter" wrote in message ...
Hi,
I want to design and build a "riverboat" for the Fraser River, with some
... "unique" design considerations (eg I want it to look ugly because it
will be on a "questionable" dock and I don't want it stolen!). Basically
I'm looking for something between an east-coast fishing dory and Bogie's
"African Queen". Something like Bateau Boat's FL14, but 16 ft, inboard and
probably not Stitch'n'glue.

Anyway, I need some anecdotal feedback: First, a 16ft boat has a
theoretical hull speed of about 5.5 knots. HOWEVER, I've seen many boats
(such as my 12ft alum) that exceeds hull speed without truly planing
(semi-plane?) Does anyone have some performance numbers for 14-16ft
flat-bottomed skiff as to how fast they go before planing? I'm looking at
maybe 6-10hp engine.

Second, I'm unfamiliar with how a flat-bottom hull performs in waves -
are they seaworthy?

Thanks for any comments, stories, etc!

Lloyd Sumpter



OK, a ten horse might get the 14-16 on plane but with effort and light
loads. You probably should look at a 15.
My 12 foot skiff noted earlier in the post planes at about 12 mph with
a load of me and another 300 lbs or so.
A pointy skiff blends in well, holds a tremendous amount of weight,
are very stable for fishing and such, a 14 footer will hold two to
three kids on one gunnel and still not near flip over, they can be run
all day long at a strong hull speed with a 5 horse or even a three on
a lake, a 14 will still row nicely with properly sized oars, beach
nicely...
A pointy skiff of typical design with flat sides and bottom will plane
off easily and can be a lot of fun but for practical use, you will not
spend to much time on plane. At high speeds you will get somewhat if
not all the way airborne which is waaaaaaay cool, but these boats do
not "fly" well and a slight yaw and roll means you catch a sharp edge
in a wave and abrubtly turn or in extreme cases roll (which btw is not
as bad as it sounds if you are prepared for it and just out playing in
the waves), at plane you can have a condition called "chine walk"
which can lead to rollover, flat sided pointy skiffs are very wet
boats and if you or your fishing partner are sensitive to being wet
all day, do not build one, even in a slight breeze at hull speed you
get spray in most typical instances. Flat bottom skiffs slap, even at
slow speeds (typical with little rocker) and on plane this slapping
means catching edges and putting up spray. Flat sided pointy skiffs
don't usually have a lot of bearing up front so they tend to dive into
or through waves, taking a lot of water... especially when you don't
expect it like the 9yo decides to go up front abruptly for chips and
the dog decides to join her at about 8 mph... nice wooden swimming
pool in the middle of the lake!
Ok, sounds like I hate these boats, on the contrary, I have made my
business on them. I just like to see that folks who get them, know
what they are getting in to. Did I say, these are wet boats, period!
That being said, here is what I would do if I were you and still want
a pointy skiff:
Go with the 14 footer. Make it 6.5 to 7 feet wide in the center and 6
inches narrower in the transom. Cut a couple of pieces of 1/4 inch
plywood and lay them lengthwise, tack em' down. On one end draw a
point 20 inches up and put a nail in with 1/2 inch left visible. Go to
the other end, come in two feet (for a 14 footer) and put a nail 28
inches up in a similar fashion. Connect the two nails and lay a line.
Cut out your side panels and butt joint them together, cut back wider
ends (bow) 30 degrees and the stern say, 10-15 degrees. Take a four
foot 4x4 and knock off two chunks at 30 degrees and make a stem.
Sharpen the stem and drive it into the ground at a 30 degree angle,
where you will build your hull and attach your side panels to it. Make
a 24 inch high transom or 2x4's and 3/4 inch plywood and attach two
stakes to it temporarily so you can drive it into the ground, 14 feet
from your stem! A ten degree rake from bottom to top of transom
should do for 10 degrees sides at the transom. Make a quick jig of
scrap to wrap the sides around see:
http://rbbpix.com/images/stanley_sie_03_450.jpg
If you wish your chine logs (1x4, where sides will meet bottom) to be
inside of the hull, make notches in your jig to accept the 1x4's, make
the notches oversize and use wedges later to make up for the spaces.
Using whatever means possible, wrap the side panels around the jig and
attach to the transom, now it starts to look like a boat! Apply your
chine logs, inside or outside, yes outside, looks funny like you
wanted and it is actually much easier then trying to size and force
inside gunnels without long ends to hold on to and remove later as in
outer chine logs. Many Bolger boats have the "logs" on the outside of
the hull, anyway, attach your chine logs.
Well, seems simple don't it and it just begun. Anyway, stay tuned as
tonight I will try to get to the bottom, seating, flotation,
motormount etc. For now, it is beautiful out there today and I got an
itch...
Scotty
  #8  
Old February 29th 04, 08:14 PM
[email protected]
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Default Flatbottom Dory: Speed, seaworthy?

On 29 Feb 2004 11:10:25 -0800, (Backyard Renegade) wrote:
OK, a ten horse might get the 14-16 on plane but with effort and light
loads. You probably should look at a 15.


Main thing though, he wants it to go "pooketa-pooketa-pooketa".
Is it possible to do that and plane at the same time?

Rick
  #9  
Old February 29th 04, 11:01 PM
William R. Watt
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Default Flatbottom Dory: Speed, seaworthy?

) writes:

Main thing though, he wants it to go "pooketa-pooketa-pooketa".
Is it possible to do that and plane at the same time?


definitely, if he doesn't mind doing the "pkta-pkta-pkta" himself while the
boat does the planing.

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