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Weight and speed

 
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bshillam



Joined: 21 Aug 2007
Posts: 782
City/Region: Bellingham
State or Province: WA
C-Dory Year: 1981
Vessel Name: Heaven To Me
Photos: My Heaven
PostPosted: Sun Oct 03, 2021 11:28 am    Post subject: Weight and speed Reply with quote

What a difference adding another six hundred pounds can make, WOT went from 30 to 24 MPH. Here's a videos of yesterdays trip with four souls aboard.

https://www.facebook.com/toddshillam/videos/402052337980157

https://www.facebook.com/toddshillam/videos/646339030058485


Knocked six off the top end. The engine also sounded more strained. I wouldn't however re-power just for a few MPH gain. This one only has 120 hours on it. Nice ride, felt a little heavy on the stern, tried to trim down w/ tabs. I think a foil on the engine would make a huge different to help bring the bow down.
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jkidd



Joined: 23 Oct 2006
Posts: 1609
City/Region: Northern, Utah
State or Province: UT
C-Dory Year: 2007
C-Dory Model: 22 Cruiser
Vessel Name: Voyager
Photos: Voyager (JK)
PostPosted: Sun Oct 03, 2021 11:59 am    Post subject: Reply with quote

I get an error saying the video isn't available.
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Jody Kidd
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JamesTXSD



Joined: 01 Mar 2005
Posts: 7444
City/Region: from island boy to desert dweller
State or Province: AZ
C-Dory Year: 2007
C-Dory Model: 25 Cruiser
Vessel Name: "Wild Blue" (sold 9/14)
Photos: Wild Blue
PostPosted: Sun Oct 03, 2021 1:38 pm    Post subject: Reply with quote

Years ago, I used to belong to a MacGregor Power-Sailor group (a few boats before the C-Dory)... testing on that boat (26' relatively flatish hull in the stern) showed a 1mph drop in top speed for every 100 additional pounds onboard.

It pays to keep your boat as light as the usage will allow. When we used to keep our CD-25 at our dock at home, I rarely had more than 1/3 fuel onboard for day-tripping. There is an easy-access fuel dock across the ICW, and at 7 pounds per gallon, that fuel weight makes a difference. Didn't make sense to me to burn additional fuel just to carry fuel around. Cruising is a different situation, though, so you have to plan for the performance for that additional weight.
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colbysmith



Joined: 02 Oct 2011
Posts: 4523
City/Region: Madison
State or Province: WI
C-Dory Year: 2009
C-Dory Model: 25 Cruiser
Vessel Name: C-Traveler
Photos: C-Traveler and Midnight-Flyer
PostPosted: Sun Oct 03, 2021 2:57 pm    Post subject: Reply with quote

Same issue as Jody, video not available. I also think it makes a difference on where the additional weight is loaded. I do a lot of cruising, so will start out with full fuel and water tanks. But I do notice the difference as fuel and water are used. Colby
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ssobol



Joined: 27 Oct 2012
Posts: 3362
City/Region: SW Michigan
State or Province: MI
C-Dory Year: 2008
C-Dory Model: 22 Cruiser
Vessel Name: SoBELLE
Photos: SoBelle
PostPosted: Sun Oct 03, 2021 7:07 pm    Post subject: Reply with quote

colbysmith wrote:
... I also think it makes a difference on where the additional weight is loaded. I do a lot of cruising, so will start out with full fuel and water tanks. But I do notice the difference as fuel and water are used. Colby


Loading the boat can make a big difference. Loading a bunch of weight in the stern or cockpit and then having to use a lot of trim tab to get the boat to cruise properly is going to affect the boat 2x. Once for the weight and once for the drag of the tabs.
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T.R. Bauer



Joined: 17 Nov 2007
Posts: 1726
City/Region: Wasilla
State or Province: AK
C-Dory Year: 1993
C-Dory Model: 22 Cruiser
Vessel Name: C-Whisperer
PostPosted: Mon Oct 04, 2021 9:35 am    Post subject: Reply with quote

Yup....600 pounds is going to make a big difference. The boats really scoot along with 90-100 hp with a light payload. Heavy.....not so much. I can't say mine is always loaded heavy, but when it is I'm wanting about 50 more hp.
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Foggy



Joined: 01 Aug 2013
Posts: 1518
City/Region: Traverse City; Northern Lake Michigan
State or Province: MI
C-Dory Year: 2014
C-Dory Model: 26 Venture
Vessel Name: Boatless in Boating Paradise
Photos: W B Nod
PostPosted: Mon Oct 04, 2021 5:16 pm    Post subject: Reply with quote

Not too hard to figure out.

Speed on water is directly proportional to power, inversely
proportional to weight. Variables are craft length, beam,
trim and hull shape.

To know the numbers for any, experiments are required.

Aye.

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