Kudzu Craft

SPEED VS WEIGHT

I have seen comments made by some people that they thought a lighter weight boat was faster than a heavier boat. While that made sense I wanted know just how much difference there was. Was it really enough to even be noticeable?

I started with a kayak design I call Basic Boat. It is very simple design with plumb bow and stern. It is hard chined and the bottom has a shallow V shape and approximately 1-1/4” of Rocker front and back. This is a realistic design but probably not a great paddling boat. Basic Boat was kept simple so that if I wanted to change length, width or other factors so I could compare the differences, the changes in the boat would be minimal. For this test I used the 15' version.

The calculations are based on the assumption that the kayaks speed is directly related to the amount of resistance of the water against the hull. Less resistance the faster it will go with the same amount of force. Other forces such as wind and waves can play apart but we are ignoring those for now.

I started with a total weight (boat and paddler) of 150 lbs, then I increased this by 25 lbs increments and charted the resistance numbers using FreeShip software and the Kaper Resistance figures calculated by the software.

By using the same hull shape and only changing the total weight any differences you see in the number will be because of the change in the displacement. This way you can see how much difference there would be in the same boat at different weights.

THE RESULTS

Lets start by comparing the boats speed if you were exerting 2 lbs of force on the hull. Looking at the numbers you can see that a 150 lbs displacement the boat would be traveling at 4.0 mph while at the other extreme, the 250 lb. Displacement would be traveling at 3.7 mph (rounded number) or .35 mph difference. Not a huge amount but over an hour or two it does mount up.

Since the idea was to compare boats, I think it is more realistic though to look at 25 lbs difference. That is a big difference in boat weight. Looking at the 175 lb vs 200 lb displacements the difference is .11 mph. I doubt most paddlers would ever notice that slight a difference

With Basic Boat your going to loose about 1/8 of a mile per hour for ever 25 lbs you add. I would assume that other boat designs would be similar. Of course variations in hull shape will have behave differently.

The average flat water paddler I have encountered travels in the range of 2.5-3.5 mph. Some stronger paddlers can average 4 mph, very few can maintain and average speed of 5 mph or faster for any length of time. So I am not talking about sprints.

Now the disclaimers.
The software doesn't give me numbers at exactly 2 or 3 lbs resistance. It calculates at .1 knots so the numbers are not exact. I chose the number closest to the desired resistance, that's why I have the exact resistance listed in the chart.

My software calculates in knots and I converted these to MPH.