Weight and speed

B

bshillam

Member
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/vi ... 2337980157

https://www.facebook.com/toddshillam/vi ... 9030058485


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.
 
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.
 
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
 
colbysmith":2t56hagd said:
... 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
Click to expand...

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.
 
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.
 
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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