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digger
Joined: 02 Nov 2003
Posts: 496
City/Region: Spokane
State or Province: WA
C-Dory Year: 1993
C-Dory Model: 22 Angler
Vessel Name: C-Sik
Photos: Snoopy-C
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 Posted: Wed Feb 16, 2011 5:05 pm Post subject: |
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| Using the kicker to get you home is also quite different than using a kicker for trolling. At higher rpm's a single cylinder kicker works as a "get you home" motor, but a low rpm's, a single cylinder motor really rattles the boat and can be quite annoying. I personnally prefer a 2 cylinder motor, whether it is 2 or 4 stroke -- the 4 stroke is best to minimze breathing the blue air. Ron |
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Matt Gurnsey
Dealer
Joined: 11 Nov 2008
Posts: 1532
City/Region: Port Orchard
State or Province: WA
Photos: Kitsap Marina
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| Posted: Thu Feb 17, 2011 1:12 pm Post subject: |
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| starcrafttom wrote: |
So a 3 hp will get you to hull speed but if you are in a 6mph current you are not going any where. But a 9.9 might be able to overcome a 6mph current and still get you to hull speed or at least near it.
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Okay, maybe I need some schooling here  , but here's my understanding.
We all agree that Hull Speed is the maximum theoretical speed of a boat at displacement speed through the water. Square root of Waterline Length x 1.34.
In other words, a 22 C-Dory will have a hull speed of about 5.76 mph (square root of 18.5 is 4.3x1.34). That is the maximum speed at displacement through the water. Beyond that the hull must acheive a planning attitude to run "over" the water, not through it. 
Now, if you are going against the current, you will be moving at a through the water speed of 5.76 mph. If there is a sizable current against you, you will be going backwards.  Unless you have the horsepower to acheive speeds above the hull's displacement speed.
So when we talk with people about kicker motors, and they bring up speed against the current- it doesn't matter. Hull speed is hull speed. Against a six mph current you will be standing still  (0 mph speed over ground) in a 22 C-Dory. With the current you will be making more progress, as the current is pushing you, but the speed through the water is still 5.76 mpg. (In theory you will be doing nearly 12 mph.) 
There are passes up in the north Puget Sound area that have very strong currents, and displacement trawlers have to plan the traversing of these areas so they aren't going against the current, because they will be unable to make progress over ground. 
The Tacoma Narrows is the same way. You can have a 10 knot current running through there, and a displacemet vessel will not be able to make headway against the current, even though they are moving 6-10 knots through the water. 
Now, can a 9.9 push a 22 C-Dory faster than hull speed? I don't know, but I doubt it. I do know it will burn more fuel, cost more, and weigh more.
We had a 24' boat in our shop, an I/O powered deep V fishing machine. I can't remember if it was a Skagit Orca or Sea Sport, but it was that type of boat. The owner has outfitted the boat with a 25 horsepower Yamaha kicker, on a very expensive aluminum bracket that he had custom built, because nobody had aything available that would handle the weight of the Yamaha. 
If you look at the prop of the outboard, you notice that all of the paint on the outer edge of the blades is burned away from cavitation. And it makes sense, because once he acheives hull speed using the Yamaha, he can keep giving it throttle, but he can't get much more speed- so something has to give.
In this boat's case, the prop breaks loose, and begins slipping and cavitating. The exploding air bubbles burn the paint away. So the owner could have gotten the same speed out of his kicker if it had beena 9.9. In fact, the High Thrust 8 or 9.9 might perform better, because the larger prop has better contact with the water, and is less likely to slip.
I suppose he could have gone with a 25 horse High Thrust (if one had been offered then), but even it's gonna start slipping as it pushes the boat to hull speed, and attempts to go beyond. 
The area where more horses will help is in a wind, because the wind affects the vessel, but not the speed through the water.
At least that's my understanding. But I'm willing to be educated on this. 
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Matt Gurnsey
Kitsap Marina
www.kitsapmarina.com
360-895-2193
(888) 293-7991 |
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rogerbum
Joined: 21 Nov 2004
Posts: 5927
City/Region: Kenmore
State or Province: WA
C-Dory Year: 2008
C-Dory Model: 255 Tomcat
Vessel Name: Meant to be
Photos: SeaDNA
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| Posted: Thu Feb 17, 2011 1:38 pm Post subject: |
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| Matt Gurnsey wrote: | <stuff clipped>
At least that's my understanding. But I'm willing to be educated on this. |
Matt - you're correct (of course) and you're the one doing the educating in this case.
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Roger on Meant to be |
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thataway
Joined: 02 Nov 2003
Posts: 21385
City/Region: Pensacola
State or Province: FL
C-Dory Year: 2007
C-Dory Model: 25 Cruiser
Vessel Name: thataway
Photos: Thataway
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| Posted: Thu Feb 17, 2011 4:54 pm Post subject: |
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Matt,
Well put and excellent examples.
_________________
Bob Austin
Thataway
Thataway (Ex Seaweed) 2007 25 C Dory May 2018 to Oct. 2021
Thisaway 2006 22' CDory November 2011 to May 2018
Caracal 18 140 Suzuki 2007 to present
Thataway TomCat 255 150 Suzukis June 2006 thru August 2011
C Pelican; 1992, 22 Cruiser, 2002 thru 2006
Frequent Sea; 2003 C D 25, 2007 thru 2009
KA6PKB
Home port: Pensacola FL |
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Tortuga
Joined: 01 Apr 2008
Posts: 320
City/Region: Ventura
State or Province: CA
C-Dory Year: 1994
C-Dory Model: 22 Cruiser
Vessel Name: Tortuga
Photos: Tortuga
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| Posted: Fri Feb 18, 2011 2:28 am Post subject: |
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| Quote: | So when we talk with people about kicker motors, and they bring up speed against the current- it doesn't matter. Hull speed is hull speed. Against a six mph current you will be standing still (0 mph speed over ground) in a 22 C-Dory. With the current you will be making more progress, as the current is pushing you, but the speed through the water is still 5.76 mpg. (In theory you will be doing nearly 12 mph.)
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This is exactly right. I spent years sailing a Ranger 26 in San Francisco -- the boat weighed about 5000 lbs and had a 6 hp auxiliary outboard. It would push the boat at hull speed (about 6 knots) all day and night -- but if I had a good ebb tide I would appear to be sitting still in the water while Alcatraz rock came cruising toward me . I learned to limit my crossings to slack tide when possible. The Tohatsu 6 seems to do the same for my CD 22.
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Tortuga
Ventura, CA |
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