Please remember that a displacement hull with a 30' Length of Waterline (LWL) will have a hull speed of 7.4kt or or 8.5mph. But most sailboats have a LWL that is noticably shorter than the overall length. For example, the C&C 35 or an Ericson 35 has a LWL of 27.5' with a hull speed of 7kt or 8.1mph. A An Ericson 38 and a Catalina 36 have a LWL of 30'.
Looking at 30' sailboats, a Pearson 30 and a Catlina 30 have a LWL of 25' with a hull speed of 6.7kts or 7.7mph. An Alberg 30 has a LWL of 21.6' with a hull speed of 6.3kts or 7.2mph. My Cheoy Lee Bermuda 30 ketch has a LWL of 24' with a hull speed of 6.6kts or 7.6mph
For this type of boat, the power requirements are more closely related to displacement. Our typical conversion recommendation is 1kW of drive for each ton of displacement. This size drive should get you to 90-95% of hull speed at full throttle. My Bermuda 30 displaces 10,200 lbs, and has a top speed of 6.1kts (92% of hull speed) at 5.1kW. These numbers hold true for auxiliary sailboats because they have pretty similar hull profiles.
Boats that are much lighter or have very differnt hull designs (kayaks, multihulls, etc.) have different speed results but for boats over about 3000 lbs, the power requirements stay pretty close.
Fair winds,
Eric
marina del Rey, CA
--- In electricboats@yahoogroups.com, KEN <rekkamurd@...> wrote:
>
> Â
> .... I sure like the potential hull speed of something 30ft, 8.5mph is decent if it'll do it.
> Â
> Â
>
>
>
> 4b. Re: 30 ft C&C/ Colombia 30
> Posted by: "KEN" rekkamurd@... rekkamurd
> Date: Mon Jan 23, 2012 10:21 pm ((PST))
>
> "roll your own".. funny expression no doubt, but pretty much what I had
> in mind pointing at the "monsterscooterparts.com" site, I dont know what
> kind of power requirements your 30 footers really need, the 24v 900 watt
> motors (1.2hp each) if 80% efficient is 1hp each..
> they spin about 2500 rpm and belt or chain joining em at whatever
> reduction would be simple enough. same for replacement if one takes the
> proverbial dump, theyre not spendy.
> if theres 3 of em and one comes unglued, still got the power of the
> other 2 and can limp it home? not that it'd be a long trip with your 1hr
> runtime requirement.
>
> --
> http://www.fastmail.fm - A no graphics, no pop-ups email service
>
No comments:
Post a Comment