"Sal's Dad" wrote in message
...
I modified my Bolger Diablo along those lines - It had a 20" transom, and I
wanted to run a "short shaft" outboard. It worked ok 90% of the time, but
ventilated like h3!! when accelerating. So I cut a notch out of the
bottom - maybe 2 or 3" high into the transom, 16 " forward into the bottom
panel, and 8" wide. Sort of a mini-tunnel. I'm sure this causes a
small degradation in performance, but gains me a few inches of draft.

I'm sure you could take any skiff design, with a flat bottom, and play
around with this. I would start with a really deep tunnel, and high
transom. If that seems too much, just cut down the transom (and glue foam
into the top of the tunnel) until you get the desired performance. You
might be surprised.

But, if you are going to cut a big notch in the bottom, make sure there is
enough bottom left at the transom to provide lift. Maybe extend the
panels out beyond the transom, on either side of the tunnel - you can
always cut them off. If there is a good high-speed tunnel design for
home-builders, I haven't seen it. Atkin had a bunch of low-speed tunnels,
you might take a look at the Atkinboatplans.com website for ideas.

Sal's Dad

That's basically what I figured. What I am really looking for is a shallow
water runner for an outboard. I suppose I could go with an air cooled mud
motor, but I already have a couple regular outboards. I looked at
converting one to jet, but there is no jet available for one, and the jet
available for the other is pitched for a smaller motor. My motor over-revs
with it.

I'll look at the Atkin designs. I'm figuring if I get this the way I want a
28-35mph top speed is all I can expect. That's about what I get out of my
current shallow water boat (16' flat bottom jon). 28 with one motor and
35-37 with the other. (gps speeds)

I'm not sure what you mean by "semi tunnel" but I built an Atkin Rescue
Minor with fully protected prop and rudder. Or you can modify the
transom of any skiff to give you a bit of a tunnel effect with an
outboard - at the loss of some "lift".

There are some "tunnel" designs for running an outboard a few inches
higher that just have a small tunnel at the rear of the boat. When I was
really reading a lot about boat building a few years ago I recall reading
about some of them.



--
Posted via a free Usenet account from http://www.teranews.com

On Mon, 10 Dec 2007 00:14:16 -0600, cavelamb himself
wrote:


THere have been at least a million aluminum airplanes produced. All
were riveted. Wonder why?


Lowest bidder?


not hardly.

Best fastener for the material.

Rivets were the best fastener for ships until they started welding
plates (then a few Liberty ships sank before the subs got 'em.)

Brian W

On Mon, 10 Dec 2007 20:48:04 GMT, Brian Whatcott
wrote:

On Mon, 10 Dec 2007 00:14:16 -0600, cavelamb himself
wrote:


THere have been at least a million aluminum airplanes produced. All
were riveted. Wonder why?


Lowest bidder?


not hardly.

Best fastener for the material.

Rivets were the best fastener for ships until they started welding
plates (then a few Liberty ships sank before the subs got 'em.)

Brian W

Most of the high strength aluminum alloys are not weldable.

See Materials specification for 2024 - one of the more commonly used
aircraft alloys:

Welding

Welding may be done by use of resistance welding or inert gas
consumable electrode arc method. However it must be noted that, in
general, welding by any means is NOT recommended for this alloy
because of the degradation of corrosion resistance that occurs as a
result of weld heat. A repeat heat treatment should be done if welded.

Bruce-in-Bangkok
(Note:remove underscores
from address for reply)

On Tue, 11 Dec 2007 16:58:38 +0700, Bruce in Bangkok
wrote:


Rivets were the best fastener for ships until they started welding
plates (then a few Liberty ships sank before the subs got 'em.)

Brian W

Most of the high strength aluminum alloys are not weldable.

See Materials specification for 2024

Bruce-in-Bangkok

I marvel that people thinking about aluminum sheet invariably think of
2024. There are stronger materials now available, but weaker
materials are often useful. But one other factor mitigating against
welding is the top coat of soft aluminum which helps the sheet resist
corrosion.

Brian W

On Tue, 11 Dec 2007 16:58:38 +0700, Bruce in Bangkok
wrote:

THere have been at least a million aluminum airplanes produced. All
were riveted. Wonder why?


Lowest bidder?


not hardly.

Best fastener for the material.

Rivets were the best fastener for ships until they started welding
plates (then a few Liberty ships sank before the subs got 'em.)

Brian W

Most of the high strength aluminum alloys are not weldable.

Yes, of course. There are weldable alloys that make a very nice boat
and they are easily weldable if the plates are thick enough. Rozema in
Seattle makes a nice forty foot power boat. Yacht or oil skimmer, same
fittings and workmanship. The same good cabinet latches are on the
workboat. There are otters living under the building and you can watch
them from the breakroom.

Casady

For boatbuilding, you will want to use the 5000 and 6000 series alloys. See
Pollard's book, Boatbuilding with Aluminum
http://www.amazon.com/Boatbuilding-A.../dp/0070504261
.. NEVER use aircraft or other alloys, especially for use in salt water.

These alloys, down to about 3/16 thickness, can be welded. 1/8 is trickier,
and lighter gauge requires very specialized knowledge, experience, and
equipment, generally not appropriate for small-scale boatbuilding.


See Materials specification for 2024 - one of the more commonly used
aircraft alloys:

On Tue, 11 Dec 2007 07:47:00 -0600, Brian Whatcott
wrote:

On Tue, 11 Dec 2007 16:58:38 +0700, Bruce in Bangkok
wrote:


Rivets were the best fastener for ships until they started welding
plates (then a few Liberty ships sank before the subs got 'em.)

Brian W

Most of the high strength aluminum alloys are not weldable.

See Materials specification for 2024

Bruce-in-Bangkok

I marvel that people thinking about aluminum sheet invariably think of
2024. There are stronger materials now available, but weaker
materials are often useful. But one other factor mitigating against
welding is the top coat of soft aluminum which helps the sheet resist
corrosion.

Brian W

The question was about why airplanes were riveted and I believe that
2024 is still used in the aircraft industry although I think it is all
alclad, as you say.


Bruce-in-Bangkok
(Note:remove underscores
from address for reply)