designing a fast rowboat

Crap. Delftship wont allow putting edges between the coordinate points. I wish he'd make his error messages a bit more helpful. "Operation not allowed" is not exactly informative.

 

Pfft. #$@%&! gfx apps. I'm going back to building my strongback. Can play with computers later.

 

Here is another midship section of a SLRS from John Gardner's "Building Classsic Small Craft" (waterlines at 135/225kg displacement).

The 20' Colon boat:

 

The midship section of the SLRS Annie resembles the Ellis Rangeley Boat (John Gardner BCSC) which is good for stability - not so much for speed.


SLRS Annie


Ellis Rangeley Boat

 

I got it to open. What are the numbers...I'm going to be lazy and ask for them.

Sure looks different from a Adk. GB. Is this boat pictured anywhere? Would be interesting to see the topsides, too. Width at the gunwale will be important for the rowing and oars.

 

The Rangely is much wider! But it looks the same...you could scale it and have the same result.


The savo is still my favorite. To gain some displacement for my big "section" I put a plank keel in...conceptual here..


Savo_MSsection_2 by Clint Chase Boatbuilder, on Flickr

 

Something along those lines would be the best way of getting the required area with minimum wetted surface.

 

Suppose I might as well throw in what I'm building. This has nothing to do with guideboats or the Blackburn. It's not meant to be the fastest possible fixed seat boat either. It's just something that has a range of characteristics I wanted for my own personal use. One of those characteristics was decent rowing performance. Another was good stability, both primary and secondary. LOA is 5.505 metres, BMax is 1.23 metres, with BWL of 0.708.

At the time I drew this, I didn't have any figures for guideboats. The boat I was comparing it with was the Herreshoff/Gardner 17 footer, since I know those well and knew what I wanted to be different.

I have overlaid the guideboat figures for two versions of Virginia (original 16 and stretched 18). Orange line is the Herreshoff/Gardner, green line is what I'm building, purple line is the original 16 foot Grant Virginia, light blue line is Virginia stretched to 18 feet.

Looks like my beast should be similar in resistance to a 17 foot guideboat at speeds over 4 knots. It loses out on wetted surface but has better wave drag. It'll have a lot more stability though. Metacentre with one person seated is 150mm higher than the guideboat, so GMT will be around 75% greater (assuming CG 250mm above baseline).

 

Rushton Saranac Laker (Atwood Manley, Rushton and his time in American canoeing)

Some renderings from my website:






From Vintage Canoeworks:

 

Flo mo, she is a beaut.

Only 7 1/2' oars though with 4-5" of hand overlap. But I like it. Have you looked into resistance?

 

The Virginia/Grant GB and the Saranac Laker/Rushton are very similar performance-wise. The Saranac Laker doing a little bit better at lower speed and Virgina at higher speed (might be due to the difference of prismatic coefficient of 0.55/0.56 and 0.57/0.59 respectively).

There is a significant difference in stability which will make Virgina more comfortable for most people.

The beam of the two boats is almost the same (at 39") and guideboat oars are typically 8' long for 16' boats (Building an Adirondack Guideboat, Olivette/Michne).

 

Are the differences in performance you describe based on actual in-the-water observations or on calculations? If calculations then which method was used?

 

Rushton's Saranac shows strong canoe influence - my first reaction to the picture was "that's the canoe I want to build" - then I noticed the beam . . a shade too wide for a solo paddle. Seems a bit skinny for oars however: is this a transitional design?

 

I just noticed something that the educated on this forum will already know.
After reading this.....

Ben Fuller on WoodenBoat Forum:

.....I repeated the resistance calculation for the AGB Virgina with a trim angle of 1° and 135kg displacement.

The effect is:

- slightly reduced wetted surface
- lower cp (0.55 instead of 0.57)
- slightly less resistance at mid speed - slighty more resistance at higher speed
- although the hull is symetrical the underwater body changes to a Swede-form

 

As much as I wish I could do actual in-the-water observations I refer to the calculations I did with ProSurf3 using KAPER for resistance calculation.