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Old 01-08-2020, 12:20   #1
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How many knots while motoring?

Watching a couple of Catamarans, including a Catana or Outremerand a Saona 47in the cape cod canal right now.

How many knots do you motor at? And how many RPMs?

What is your cruising rpm and speed? What is your top RPM and speed?

This question is valid for both Diesel and Outboard catamarans.

Thanks!
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Old 01-08-2020, 12:29   #2
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Re: How many knots while motoring?

When we motor I keep my diesel engines running at a minimum of 80% max RPM to keep them clean. In calm waters, one engine at 80% will have us doing ~7 knots.
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Old 01-08-2020, 13:19   #3
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Re: How many knots while motoring?

My Stiloetto27 would motor at 13 knots. The hull shape is semi-planing.



My PDQ 34 would go about 7.6, but cruised at ~ 6.8.
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Old 01-08-2020, 13:34   #4
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Re: How many knots while motoring?

42 foot with yanmar 3gm30's. Both engines at 2800 rpm in flat water is 7.1 knots
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Old 01-08-2020, 13:38   #5
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Re: How many knots while motoring?

2000 Leopard 45 with 56hp each side- one engine at 80% about 7kts, two engines 9 kts.
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Old 01-08-2020, 14:16   #6
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Re: How many knots while motoring?

Ok, this is great!!! Thank you. Keep em coming!

I have been all worried about getting 8 knots with a 30hp outboard. Thinking my worries are misplaced and there are plenty of other projects to work on instead.
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Old 01-08-2020, 14:18   #7
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Re: How many knots while motoring?

Lagoon 450, 2* Yanmar 54 hp, Flexofolds, One engine at 2400 rpm - 6 knots is what we normally did. If we can catch a breath of wind with the genoa up we still aim for 6 - 6.5 knots but drop the revs back to 2200.


Both engines at 2800 rpm - 9 knots if required. We only ever ran them at 3000 rpm once trying to get through a pass in the Exumas against an outgoing tide - we did SOG of 1.5 knots.


Obviously it also depends on how clean the bottoms are.


The fastest motoring SOG we did was through Hells Gate at 12knots +
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Old 01-08-2020, 14:28   #8
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Re: How many knots while motoring?

Quote:
Originally Posted by chris mac View Post
42 foot with yanmar 3gm30's. Both engines at 2800 rpm in flat water is 7.1 knots
Yeah, I was going to say 8+ knots for my TPI 42 at 3300 rpm. (which I hated!)
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Old 01-08-2020, 16:44   #9
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Re: How many knots while motoring?

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Originally Posted by Cheechako View Post
Yeah, I was going to say 8+ knots for my TPI 42 at 3300 rpm. (which I hated!)
We have pushed to almost 9 knots to fight currents(Ill advised trip into barnegat inlet) but I dont like pushing the rpm that high. We can run 2800 all day long
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Old 01-08-2020, 17:04   #10
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Re: How many knots while motoring?

prout elite 37,clean bottom 35 hp diesel.
8.5kt flat water,3200rpm,
cruise at 6.5kt,2200rpm
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Old 01-08-2020, 17:45   #11
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Re: How many knots while motoring?

Searunner 38 catamaran. Single Honda 15hp, cruising low 6,s, wot, mid 7,s.
TRT 1200, twin Yamaha 9.9ís. Cruising low 6ís, wot mid to upper 7ís
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Old 01-08-2020, 17:48   #12
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Re: How many knots while motoring?

60' 45t Seaton ketch, Ford Lehman SP135
7.5-8kts @1800, 9.5 -10 WOT in flat water
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Old 01-08-2020, 18:07   #13
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Re: How many knots while motoring?

Photo says it all. Not a breath of wind...Catalina 42
The jog was a break for a snooze.
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Old 01-08-2020, 18:26   #14
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Re: How many knots while motoring?

speed is really a component of water line length...LWL"...
...for your average 40' boat with a 36' water line length....about 7.8 knots, give or take....
to push that same 40' boat to 4-5 knots does not require much power....but to push it to 7.8 knots requires a lot of power....
in the same breath....motoring in a flat calm is nothing near the same as trying to motor against wind and current..
it's a complicated science, not easily explained in one paragraph.....don't be fooled into thinking you can get a lot for a little....doesn't work that way...
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Old 01-08-2020, 18:33   #15
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Re: How many knots while motoring?

https://www.facebook.com/warren.ward...8554298397881/
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