Making A Fast Rowboat Faster

portacruise · Jan 21, 2013

After a certain length, reasonable hull shapes have negligible effect. Discussion was in human power boats section comparing rounded vs. squarish hulls.

Maybe consider the other aspects as some have mentioned. Weight of the men, windage increase/decrease, and adding deck, might be more significant. Optimize oar shape, weight, leverage and technique to the men, read the water for favorable eddies, waves, if such exist, etc. Propeller propulsion is theoretically more efficient than oars if such is allowed

Porta

Tallman said: ↑

I've gotten to the point in building Ken Bassett's Firefly Double where I need to decide if I can make the hull shape faster. It's not an ideal speed shape to begin with, but it's what I have, and I want to optimize it. The boat is 23' long (stretched a bit from plans, per Ken) and 39" wide at the sheer; the bottom planks -- it will float essentially at the chines or slightly above -- are 6" wide at stern and 14" wide at widest beam. I hope to keep it under 100 lbs before adding the two Piantedosi sliding seat rowing rigs.

As two strong, experienced oarsmen will be powering this, hopefully in open water races that can last 3 hours and cover 20+ miles, even a few percentage points of speed will make a huge difference. My understanding (and I've tried and have zero ability with hull programs, hence my posting with primitive cardboard models) is that while skin friction drag goes up with speed, the wave drag goes up much faster. With two rowers, I'd like to maximize waterline length and -- I don't know the term here -- bring the water smoothly together at the stern, per a racing shell, Guideboat, etc. Given the power moving the boat, I expect it to hit max wave drag speed pretty easily and so wish to raise that bar as much as possible.

The original plans called for a wood skeg per the shape labeled #1. It's unclear to me if the skeg is thick enough to count as added waterline length in terms of adding a little top end speed.

I was wondering if a fuller stern section -- #2 cardboard piece -- would work; the mock-up is messy but is meant to approximate grafting a single racing shell stern piece to bottom so that the flow is continuous from where the rocker curves down through to the stern.

Intuitively, #3 seems faster: a tapered "fuller" skeg shape that makes the end slipperier, like a Whitehall or wherry stern.

The #4 is hard to see but is essentially a smaller version of #3 and might not be in the water as much given the rocker of the bottom.

In all cases the fuller skegs would be very light/buoyant foam/glass/ply constructions to minimize added weight and ideally add a little buoyancy. This is not a workboat and will be carried to and from water, and treated like, a delicate racing shell.

A racing shell fin will be installed about four feet in from the stern so it's not important that the tail section provide guidance.

I hope this is clear and would love to hear any opinions on what might work best.
Thanks much,
Tallman

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Making A Fast Rowboat Faster

portacruise Senior Member

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