Re: [bolger] Somebody stop me!
Chuck wrote:
Plotting the angle a vee bottom makes in order to be deep enough to
contain the batteries completely, though, I get about 30 degrees. I'm
not sure where that would float, but seems very tender to me, still a
novice boater.
Maybe taping on bilge strakes and a narrow flat bottom like a Gypsy
would be an improvement.
(There's an electric Gypsy described at
http://userweb.interactive.net/~jimkerr/sebtech.htm
that's said to make 6.2k (!) for 3 hours with a 24v 60# thrust MinnKota
and two 105 ah batteries like mine. My motor is half that in both amp
draw and voltage, so the range looks good.)
But I begin to think I'd need to be an architect myself in order to make
the new bottom work. No doubt it's saner to just build another boat and
not spoil the Windsprint.
This gives me renewed respect for how carefully a boat designer works compromise.
But I did have another thought on the step theme. What if I just built a
short teardrop keel, long enough to contain the batteries, but not
running all the way fore'n' aft? Say 4 ' long, giving only about 8 sq.
feet extra wetted surface.
A question for those with a better grasp of nautical mathematics than I:
Is friction proportionate to wetted surface, or does it increase
geometrically like volume?
A question for more experienced boaters: Would a short, double ended,
rectangular shape like this hanging off the flat bottom be dangerous?
And for the architects (includes both of the above): I'd think this
teardrop could have a dead flat bottom, but is it better to have a
rocker to match the hull?
Mark
> If instead of the step, you made the bottom into a vee, you would gain theYes! That makes me slap my forehead and say, "Why didn't I think of that?"
> space and buoyancy with a lot less of the friction.
Plotting the angle a vee bottom makes in order to be deep enough to
contain the batteries completely, though, I get about 30 degrees. I'm
not sure where that would float, but seems very tender to me, still a
novice boater.
Maybe taping on bilge strakes and a narrow flat bottom like a Gypsy
would be an improvement.
(There's an electric Gypsy described at
http://userweb.interactive.net/~jimkerr/sebtech.htm
that's said to make 6.2k (!) for 3 hours with a 24v 60# thrust MinnKota
and two 105 ah batteries like mine. My motor is half that in both amp
draw and voltage, so the range looks good.)
But I begin to think I'd need to be an architect myself in order to make
the new bottom work. No doubt it's saner to just build another boat and
not spoil the Windsprint.
This gives me renewed respect for how carefully a boat designer works compromise.
But I did have another thought on the step theme. What if I just built a
short teardrop keel, long enough to contain the batteries, but not
running all the way fore'n' aft? Say 4 ' long, giving only about 8 sq.
feet extra wetted surface.
A question for those with a better grasp of nautical mathematics than I:
Is friction proportionate to wetted surface, or does it increase
geometrically like volume?
A question for more experienced boaters: Would a short, double ended,
rectangular shape like this hanging off the flat bottom be dangerous?
And for the architects (includes both of the above): I'd think this
teardrop could have a dead flat bottom, but is it better to have a
rocker to match the hull?
Mark
Mark:
If instead of the step, you made the bottom into a vee, you would gain the
space and buoyancy with a lot less of the friction.
Chuck
If instead of the step, you made the bottom into a vee, you would gain the
space and buoyancy with a lot less of the friction.
Chuck
> I was taking a break from work today and the fatal flaw in this proposalconsideration.
> suddenly dawned on me. At this weight and speed, friction is the main
>
> The wetted surface of the 12' waterline hull is roughly 48 square feet.
> Rowing, one can feel an additional 4 by leaving a leeboard or rudder
> down. The step looks to be an additional whole sheet of ply, or 32
> square feet.
>
> To maintain my 3-4 knots , I'd need at least half again to twice as much
> power, I think, thereby killing the advantage of an extra battery.
>
> Alas. This looked like fun and would surely have been unique.
>
> Guess I'll have to make do with what I already have. If you could see
> my antique Audi, you'd know I have a knack for that.
>
> Thanks for letting me think aloud with you.
>
> Mark
>
> ------------------------------------------------------------------------
> Old school buds here:
>http://click.egroups.com/1/4057/10/_/3457/_/959581980/
> ------------------------------------------------------------------------
>
>
>
I was taking a break from work today and the fatal flaw in this proposal
suddenly dawned on me. At this weight and speed, friction is the main consideration.
The wetted surface of the 12' waterline hull is roughly 48 square feet.
Rowing, one can feel an additional 4 by leaving a leeboard or rudder
down. The step looks to be an additional whole sheet of ply, or 32
square feet.
To maintain my 3-4 knots , I'd need at least half again to twice as much
power, I think, thereby killing the advantage of an extra battery.
Alas. This looked like fun and would surely have been unique.
Guess I'll have to make do with what I already have. If you could see
my antique Audi, you'd know I have a knack for that.
Thanks for letting me think aloud with you.
Mark
suddenly dawned on me. At this weight and speed, friction is the main consideration.
The wetted surface of the 12' waterline hull is roughly 48 square feet.
Rowing, one can feel an additional 4 by leaving a leeboard or rudder
down. The step looks to be an additional whole sheet of ply, or 32
square feet.
To maintain my 3-4 knots , I'd need at least half again to twice as much
power, I think, thereby killing the advantage of an extra battery.
Alas. This looked like fun and would surely have been unique.
Guess I'll have to make do with what I already have. If you could see
my antique Audi, you'd know I have a knack for that.
Thanks for letting me think aloud with you.
Mark