For most props the most efficient pitch ratio is 1.5 times the prop diameter
The biggest diam prop with that ratio will give you the best option.
A gearbox lets you optimize that further and two pulleys and a toothed belt are usually cheaper than a bunch of cells
From:
Sent: Tuesday, 22 November 2011 6:40 AM
To:
Subject: Re: [Electric Boats] Re: stupid question about props
It gives me a starting point. I had noticed in looking at props that "oversquare" seems to be common. What is on the boat now is an 18" two blade, not sure of the pitch. The
What's a good source for props?
On Mon, Nov 21, 2011 at 2:31 PM, Eric <ewdysar@yahoo.com> wrote:
Hi Chris,
The pitch question is harder to answer, it completely depends on your boat, drive and reduction ratio.
That said, I think that some people here, myself included, have switched to "oversquare" props where the pitch is greater than the diameter with great success. I went from a 2 blade 13 x 10 to a 4 blade 13.5 x 15.5 prop. You can see pictures in this Yahoo group in the photo folder "Eric's Serenity". You can see that 13.5" is really pushing the limit for my boat's aperture.
http://groups.yahoo.com/group/electricboats/photos/album/1967401930/pic/list
Here's a brief excerpt from sometihing that I posted on Oct 1 this year that discusses the differences in slip for my old and new propellors.
"When you're dealing with displacement auxiliary sailboats, even the good propellers run at slip rates above 35%. If you look at the propeller calculators from most of the propeller manufacturers, the typical figures for displacement sailboats are around 50-55% slip. Here's the figures that came from my boat, before and after:
"Doing the calcs, the old prop showed 39% slip at 3kts and 58% slip at 5.5kts. The new prop observed performance calcs to 27% slip at 3kts and 37% slip at 6kts...."
It's not a direct answer to your question, but I hope that this data helps.
Fair winds,
Eric
--- In electricboats@yahoogroups.com, "Chris" <cxguldi@...> wrote:
>
> I keep reading "get the biggest prop you can find" Wouldn't pitch be more important?
>
> I can fit up to 21" if the prop is 21 or 24 inches and the pitch is the same wouldn't I be getting the same from them? What part of this equation am I missing?
>
> I don't think I have read anything about prop pitch so how do I know what pitch to get?
>
--
Chris Guldi
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