designing a fast rowboat

Oar length link

Uncle Boats. You can check out my oarmaking page. There is the formula you need and some rules of thumb at the bottom of the page.

The formula give you about the right length. I would say for your boat and you size, ability, I'd start with the result you get and make a set of oars or have them made for that length. Row for a season and decide if you want a pair of harder pulling or easier pulling oars.

I typically have three sets: one all around set which were made exactly to the formula on my page. I have a shorter set (easier pulling) with narrow blades for upwind, choppy rowing conditions. I also have a set of 5" longer oars with bigger blades for downwind or calm rowing. In my fixed seat rowing I do not feather so the narrow blades are great when rowing upwind. Once I am off the wind, I switch to the longer oars.

 

Interesting point about using narrow blades for upwind work without feathering. The Arctic people who developed the kayak also prefer to use a narrow bladed paddle - called the Greenland paddle - which they do not feather. It is most efficient used with a traditionally-designed kayak with very little freeboard as the wind speed is lower closer to the surface.

 

I also use the Shaw & Tenney formula, i recently got it out of Wooden boat magazine.
The Hanningfield Skiff has two pairs of hollow Macon sculls i just altered & rebuilt & they are absolutely spot on, went for a family training row this afternoon and thoroughly enjoyed it. My boy is 14 & is really getting into it, makes me feel rather old & creaky tho!

 

oars

Thanks for all the info. I have four rowing positions so I am devising a way to have all the same beam width, something like a homebuilt folding oarlock block. I have several ideas, just trying to chose one that doesn't detract from the looks of the design. I don't know why I always have to complicate things, I guess that's just part of the fun!

 

You don't need exactly the same beam at each station. As long as it's within a couple of inches it should be ok.

 

I am already intending to stretch the rowing beam at the widest point, so would like to do the same with all. The widest beam is now 48" and I am going out to at least 56" ( 4" per side)

 

Ok, if you want to go that wide and you want to do it in four different places with equal width everywhere, the logical solution would be removable riggers that all pivot on a thwart/bulkhead at a given distance from the centreline. That way you can have one or two pairs of riggers and transfer them to the positions in use at the time. Would also be the cleanest looking solution IMO.

 

That is the direction I have been leaning towards, I have a set of plans for the Glen-L sliding seat and I am kind of modeling the riggers after that. Any thoughts on how wide the beam should be. The Glen-L diagrams call for 62" but I don't know if I want to go that wide. Right now the boat is fixed seat but that could change in the future. I'm not planning on entering any races, I mostly plan on using the boat for exercise as my knees don't like running anymore. Thanks Rob

 

That width (62") is pretty much standard for sliding seats. If your knees don't like running they may not like a sliding seat either, as that involves putting a fair load on the knees when they are flexed. Best to try one out on someone else's boat and see how you like it.

If you're rowing fixed seat you don't need anything like that much width. For fixed seat rowing anything upwards of four feet should be fine. Some people row with less beam (guideboats, for instance) but it tends to be not so good IMO.

 

Just thought I'd post up the results of my design spiral since I really (I mean really) have finished screwing around with lines now.

This is intended as a solo boat for a largish estuary, but with the ability to carry a passenger in good condtions. I want to be able to have the oars out of the water and look over my shoulder without the boat wanting to flop over. This means some (not much) positive metacentric height. I also want the metacentre to stay at the same height when carrying a passenger. That requires the flare above the solo waterline to be matched to the waterline beam and displacement. The midship section ends up being pretty tightly constrained by the requirements. I'll be having outriggers so am not worried about making the boat wide enough to have the rowlocks on the gunwales. Since I will mainly be rowing in sheltered waters I've used a straight keel line and fairly low freeboard.

I've included the out.mlt file for the lowest resistance hull I got from Godzilla in case anyone wants a basis for doing their own lines. Offsets are at the end of the file. Note that the underwater lines straight from Godzilla are not really suitable for building a boat from as they assume vertical topsides. However, they should provide a good guide to distribution of volume, etc. Godzilla only does calculations and offsets for the underwater portion of the hull, so freeboard and maximum beam can be whatever you like.

I used this out.mlt file as a guide for the lines I ended up settling on, but it's necessary to make intelligent allowances. My finished lines ended up being slightly better in terms of predicted resistance, but there's not much in it. Note that before running all the stuff through Godzilla I was thinking of another set of lines which were pretty sleek (basically a longer, narrower and more extreme guideboat). The lines I ended up have substantially lower predicted resistance without any reduction in stability. Since people seem to be getting good real world correlations with the output from Godzilla I'm confident the hull shape should be good, and it shows the value of checking your assumptions with some number crunching.

Anyway, out.mlt for the Godzilla series 7 hull is attached. Hope it's useful to someone. Also attached are the final lines I settled on for my purposes, along with the obligatory pretty picture and the resistance prediction graph for the 2 to 7 knot speed range. Now I just have to build the bloody thing.

 

I thought at first the forces of pushing and pulling were opposite and equal with a sliding rigger but I think I am wrong and their is some rocking fore and aft through the stroke cycle. I am thinking a little less comfortable with the same seat but it will probably never require a back rest.

My bow facing design (post #866) with sliding footstretcher and fixed seat cannot comfortably be operated without a lower back rest/support. You have the option as with the "Front Rower" of excerting as much pull with your arms or push with your legs as you care to. For me, and most, the legs win and you push yourself off a backless seat after a few strokes. If the support is adjusted right one can still lean back fairly well and their is some flex to help the return to the catch. At least thats how I remember it, it has been a while.

 

Comfort over Distance

The pics show where I'm at with my fixed seat/pin 17 footer(40" at gunwale). The seat is from a Concept 2 rower and rests on the bottom board. It does not slide (good luck trying!), but allows me to squirm enough to fine tune position. The cutout at the rear is critical to avoid chafe around the tailbone which I believe is due to rocking. The oars are 9' red maple. I put some spring into them.

I did a 3 mile race in 33 minutes(I'm 63) last summer, but usually cruise between high 3 and 5 mph on my gps depending on the wind.

 

I couldn't get through ten pages of this but I do know that an Adirondack guide boat of about 17', with overlapped spoon oars, rowed by a practiced rower, is very hard to beat. I know because there's one here in town that waxes everyone on the water except SALISH STAR, and she needs 4 rowers and a cox'n.

 

Fast? Rowboat

Thirty five years ago, a friend asked me to row with him in a first ever local race, having rowed quite a bit in my double ender as a youth I jumped at the chance. On race day I met up with him at the boat launch and he was towing the widest aluminum fishing boat I had ever seen that he had borrowed from some resort. He had to do a lot of talking to get me to row with him as I wasn't to keen on coming in last, but I finally swallowed my pride and we put it in the water. As it turned out the rules were that you had to sit side by side and all the skinny boats were absolutely worthless and the drift boats jump ahead on each stroke then stop until the next stroke, We won five years in a row in old no. 3. Year three we broke a oarlock at the start and there was never another race held.

 

oarlock

correction year six we broke the oarlock