Monday, August 20, 2012

Re: [Electric Boats] Lewmar bow thrusters & intro

 

OK $10,000 is a tad high but not as bad as you contend. I will admit to thinking a turnkey battery system with support from the seller.
 
A pile of bare batteries do not make anything safely usable. This is a small open boat and everything has to be safe when wet.
 
A Cal 30 has a hull speed a bit over 7 knots this boat has one a bit over 5 knots  (water line 15.75 feet)..Your 5 knots is right at 2/3 hull speed.
 
I'll stand by this boat needing close to 4,000 watts to do 5+ knots.  And something like 2000 watts for 2/3 hull speed.(3.5 knots).
 
How would you size and configure something with a range of 30 miles at 3.5 knots including housing, fuses, etc. Figure 15,000 watt hours.
 
 
Sent: Monday, August 20, 2012 8:36 PM
Subject: Re: [Electric Boats] Lewmar bow thrusters & intro
 
 

10,000 dollar in lithium batteries would be a 38kw bank at 48 volt and 800 AH.  I doubt he would need a bank that large and that he could fit it in a 17 foot boat and still have room for himself.
 
Even if by some magic he needed 100 amps (4800 watts) to push the boat to 5 knots, he would still get 8 hours of travel time.  Let's be serious here,  his boat will need nowhere near 100 amps to reach hull speed.  Could we at least stay a little inside reality here?  
 
A cal 30 only needs 2.4kw to reach 5 knots.  With a 3000 dollars lithium bank (9.6kw) he could travel 100% hull speed and go for 9 hours easy.  At 3 knots he could probably go 24 hours strait.
 
 




On Aug 20, 2012, at 4:40 PM, Edward Bachmann <edbz@hotmail.com> wrote:

 
The question is how much will you want to spend on batteries.
 
The Penobscot 17 is a pretty boat with a hull speed around 5.3 knots.
 
With $10,000 invested in lithium batteries, you could travel all day and a long way long way at something like 2/3 hull speed (<4 knots).
 
For a total investment of under $3,000 you will find the useful range/speed limited to around 1/3 hull speed (<2 knots).
     (Figure a Torqeedo 1003 with an extra battery pack)
 
You might get another knot or two out of a twin hull design of the same length. Something like Slider might be fun for two people.  http://slidercat.com/blog/wordpress/?page_id=2
 
 
Sent: Sunday, August 19, 2012 1:38 PM
Subject: [Electric Boats] Lewmar bow thrusters & intro
 
 

Hi

I'm a new member with aspirations to build an electrically powered boat to cruIse the coastal waters around Oahu with one passenger. I live on the North Shore of Oahu.

•The boat
Haven't started building yet, but am pretty committed to a Penobscot 17 from Arch Davis (archdavisdesigns.com). The theory being that an easily driven sail/row boat is a good candidate for electric construction, and the 17 is large enough to be comfortable and handle some chop.

• The power
Lots of questions and options here. I have read with interest the many discussions of inboard vs outboard vs trolling motor comparisons. However, I haven't seen (but may have missed, you guys have _lots_ of posts--interesting, but a bit daunting) discussion on thrusters for primary propulsion. Nothing definite yet, but would appreciate discussion of the Lewmar 185TT from WMJ Marine (wmjmarine.com). Don't want to exceed hull speed, but don't want to be "full throttle" the entire time I'm out.

Any feedback?

Stan

 

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