Chesapeake Marine Design, llc
794 Creek View RD Severna Park, MD 21146
Hull Design Considerations
Unfortunately, going 18 knots in an electric boat for any length of time is all but out
of the question. The energy storage of batteries is not up to it for any length of time,
even with the most advanced batteries. About 80% of hull speed is the most efficient
use of power and weight capacity to carry the batteries needed for more than 8 hours
of operation. Higher speeds are possible (i.e. hull speed) for a few hours. Boats that
are designed for speeds higher than hull speed have a transom that is deeper in the
water. This deeper transom clears the water at high speed. At low speed, the water
doesn't clear and drags terribly. With cheap gas and high power, this isn't a problem.
With electric, a flat transom dragging through the water is horribly in efficient. This is
the paradigm that has to be accepted by boaters wanting efficient power. You can't
have efficiency and high speed with current technology. Going half fast will have to
be enjoyed for what it is. This is one among many shifts in cultural thinking that are
going to have to be made in the years ahead.
Primary factors that influence boat hull efficiency include waterline length,
displacement , surface area of hull and appendages and other hull shape factors.
Longer is faster.
SPEED LENGTH RATIO = V
= 1.34 theoretical maximum hull speed
= 1.2 most economical top powering speed
= .8 most economical for long range electric power
Lighter is faster for a give hull length.
DISPLACEMENT LENGTH RATIO =
> 200 heavy for electric boats
150 moderate, best range for electric boats
< 100 for small boats
Where displacement is in Long tons (2240 lbs) and LWL is in feet
Round hull sections have minimum wetted surface for given displacement.
Minimize appendage surface area. (e.g. skegs, keels, struts) They all c