new subscriber/ electric auxiliary
Hello Bolger fans,
This site was one that popped up while I was researching electric
boats. Bolger is one of my favorite designers. The recent thread on
electric auxiliaries caught my attention.
My dream project is to build an electric auxiliary trailerable
coastal cruiser/ gunkholer. The concept is a 24ft lwl 26-28ft loa
hull displacing 4500-6000lbs. All up trailer weight not to exceed
6000lbs.
A modified version of Bolger's box keel designs such as long micro
or Seabird 86 would work well for this. The keel would be opened to
the interior of the boat and batteries would replace the lead shoe
and water flooding ballast of the original. I am partial to his
Moccasin design and it derivatives.
A 5-6kw rated electric drive running off a 48-60v 400 amp hour
battery bank would provide 2 hours of run time at 7 knots at 50%
discharge. This would increase to about 10 hours run time at 5 knots
under power alone. One could realistically expect a 50 mile a day
cruising range with a 50% reserve under power alone. Motorsailing at
5 knots in a light 4-5 knot breeze would triple that range. A 30 amp
shore power connection at a marina would recharge the system
overnight. For more remote cruises one could carry a 2kw portable
generator for emergency use. Solar power and regeneration from the
engine in breezy sailing weather could keep the bank topped off if
usage wasn't too heavy.
The total weight of the batteries and motor would be around 1600lbs.
The overall efficiency of the electric drive itself is in the 80%
range including mechanical losses. With an efficient prop and a low
drag displacement hull design the system would be putting out about
7hp/1500lbs of thrust at the prop at 7 knots boat speed. The current
drain at 60v would be around 90 amps. This compares with an overall
efficiency of about 20% at best for an outboard motor. Equivalent
performance from an inboard diesel installation would require a 20hp
rated diesel engine. The overall cost of the electric installation is
roughly equal to an inboard diesel installation.
Depending on intended use, an electric auxiliary can be a practical
if expensive option.
Regards,
David Rasberry
This site was one that popped up while I was researching electric
boats. Bolger is one of my favorite designers. The recent thread on
electric auxiliaries caught my attention.
My dream project is to build an electric auxiliary trailerable
coastal cruiser/ gunkholer. The concept is a 24ft lwl 26-28ft loa
hull displacing 4500-6000lbs. All up trailer weight not to exceed
6000lbs.
A modified version of Bolger's box keel designs such as long micro
or Seabird 86 would work well for this. The keel would be opened to
the interior of the boat and batteries would replace the lead shoe
and water flooding ballast of the original. I am partial to his
Moccasin design and it derivatives.
A 5-6kw rated electric drive running off a 48-60v 400 amp hour
battery bank would provide 2 hours of run time at 7 knots at 50%
discharge. This would increase to about 10 hours run time at 5 knots
under power alone. One could realistically expect a 50 mile a day
cruising range with a 50% reserve under power alone. Motorsailing at
5 knots in a light 4-5 knot breeze would triple that range. A 30 amp
shore power connection at a marina would recharge the system
overnight. For more remote cruises one could carry a 2kw portable
generator for emergency use. Solar power and regeneration from the
engine in breezy sailing weather could keep the bank topped off if
usage wasn't too heavy.
The total weight of the batteries and motor would be around 1600lbs.
The overall efficiency of the electric drive itself is in the 80%
range including mechanical losses. With an efficient prop and a low
drag displacement hull design the system would be putting out about
7hp/1500lbs of thrust at the prop at 7 knots boat speed. The current
drain at 60v would be around 90 amps. This compares with an overall
efficiency of about 20% at best for an outboard motor. Equivalent
performance from an inboard diesel installation would require a 20hp
rated diesel engine. The overall cost of the electric installation is
roughly equal to an inboard diesel installation.
Depending on intended use, an electric auxiliary can be a practical
if expensive option.
Regards,
David Rasberry