designing a fast rowboat

[DickT]

17' Rowboat

Here's two more pics.
Dick

 

[nordvindcrew]

keepin on keepin on

First, Wow! another Faering. Cool and so good looking. Congrats on a fine job. Where do you row? Team Nordvind is on the skids recently. Both of us has had minor health problems and haven't rowed enough to be in good shape. That is looking up and with luck and Gods grace, we'll be back in good shape for fall. Our 20' Nordfjiord is in my back yard and scheduled for major bottom surgery to put a lot of deadrise back in that was lost in the building process. We're rowing the 16' 8" Nordvind now. Today, we had her at 5.3 knots on the GPS for a long way on the Herring river and out behind the sand spit of the North River. We can't keep up that pace long enough for a race, but the stamina is coming back. Today, I laminated the gunnels for my 16' skin on frame single. Guesstimating about 50/60 lbs finished.Rough dimensions are: 16' LOA, 42" beam, keel to sheer midships 12". This all I have, as this boat is built by eye as you go. Will post pics as soon as there is anything that looks like a boat. There's a new local race on fresh water July 26th, hoping to be ready for that. Who knows, could happen. Look way back in this thread for pics of the model to get an idea of what it will look like. Major differance will be to lose the canoe stern and add a very small wedge shaped transom.

 

[DickT]

I was out this am on a small lake nearby(3rd time this year) and was able to average over 5 on my gps. The surge was 4.8-5.3 upwind and somewhat better downwind, though I was losing oomph after a 40 minutes or so.

The dimensions on mine are very close to your skin on frame. I have a 16' WL and 30lbs more weight. In hindsight, I would have made mine a little fuller in the ends.

Dick

 

[charmc]

Dick,

Just curious; are you able to maintain directional stability in windy conditions? Your smooth, nearly flat midsection is offset by sharp entry/extreme deadrise angle fore and aft. I was wondering how she fairs in the wind.

 

[DickT]

It's about the same as a kayak. Flat water and upwind/downwind is pretty good. On Lake Champlain in a 15mph crosswind with some fetch I'm often working one oar twice as hard as the other. I've tried moving where I sit fore and aft to optimise lee helm/ weather helm, but am also usually getting one end or the other pushed into a trough by quartering waves. So I gave up trying to beat it, and have tried to set my weight so that the bottom(which has no rocker in the aft 13-14 feet) is evenly immersed. I'd welcome any advice as to whether that's the best overall approach and would also consider bottom surgery or a rudder if it seemed worth it.

 

[charmc]

A very shallow keel, similar to that found on aluminum canoes, might help. I found that improved performance in wind and waves for a canoe I used to paddle along the Maine coast. Nordvincrew/Jeff is the senior rowing boat surgeon around here, though , so I'll await his comments.

 

[charmc]

BTW, that's a great looking boat!

 

[nordvindcrew]

Surgeon?

hell, wood / fiberglass butcher is more apt. I'd try a jury rigged rudder first and consider a keel or skeg second. We got much better directional stability with a long, shallow keel, but felt that the drag was too much. I've been very interested in the rudder systems on kayaks. Being able to raise and lower the rudder is a plus and a foot pedal to steer with would work if it could be made to hold a heading without constant tending. I plan on a fairly long skeg on the skin on frame boat and only enough keel to protect the fabric. On the Nordfjiord, we're hoping that the greatly increased dead rise plus a sharper entry will help to keep us tracking better. I've made a set of wooden oars out of cedar. They are very light, but seem like they might be too flexible. Every one who has tried our composite oars with aluminum shafts screams about how stiff they are and that there is too much shock on the arms at the start of the pull. We're used to them, but the wood oars will be a good experiment. The cost was OK too; $0.00 for material ( Damaged fence posts) and just some good woodworking time shaping them and straightening the finished product. Charlie, tried to get the Row hard bunper sticker, they aren't stocking them. Will try to see if I can find them. Need one for my new car. Jeff (Nordvindcrew)

 

[DickT]

I got my wife a really nice rudder system from CLC for her kayak for her birthday, but she's since torn a ligament in her knee and hasn't been able to try it. I was considering doing a knockoff for my boat, because I think that's probably the way to go.
My oars are 9' red maple with flex built in as described in Steever's great oar book from Mystic.

 

[jarmo.hakkinen]

Design for the Sulkava Race 2009

Very interesting thread you folks have here. I'm in process of designing a rowboat for two rowers for Sulkava race 2009, and I've found some useful information here. Does anyone have practical knowledge about the minimum value for metacentric height for a boat measuring 6,49*1,22*0,13 meters, weighing 190-195 kg loaded. I have a feeling, that my design could come a bit tippy, for the MC height is only 0,607 meters.

 

[Guest625101138]

Very interesting thread you folks have here. I'm in process of designing a rowboat for two rowers for Sulkava race 2009, and I've found some useful information here. Does anyone have practical knowledge about the minimum value for metacentric height for a boat measuring 6,49*1,22*0,13 meters, weighing 190-195 kg loaded. I have a feeling, that my design could come a bit tippy, for the MC height is only 0,607 meters.

You should do cross curves to see that the boat has positive righting up to about 45 degrees if you want to be real comfortable. I would think a KMT of 0.6 would be reasonable. You really need to determine the height of your CofG and if it is under 0.6m then it will sit OK for initial stability. Ideally the righting moment improves as it heels - up to the point of flooding of course.

Rowing sculls have a KMT around 0.1m. They are stabilised by the oars. The racing kayaks are maybe 0.2 to 0.3m and are marginal at rest but you sit really low. It is possible to stand in an ocean kayak and they have KMT around 0.45.

Hence the answer is not clear cut. It depends on how twitchy you can live with. It depends on how low you sit. When sitting upright on the floor the height of your CofG is roughly belly button.

One way is to compare with a boat you have tried out.

Rick W.

 

[DickT]

Transverse Wave

Went out rowing this morning with a friend who has a glass Adirondack Guideboat. We have about the same 16' WL, but it was disappointing to me to see how much less wake he had at the same speed as me. I didn't bring my GPS, but I start to develop a transverse wave at about 5mph; I didn't see any of that from his, even at faster speeds. He said my wave seems to start by the oarlocks. I know I'm still trimmed a bit bow down, but am not sure whether that's the cause. I have to move the oarlocks to check. I'd appreciate any thoughts.

 

[Guest625101138]

Went out rowing this morning with a friend who has a glass Adirondack Guideboat. We have about the same 16' WL, but it was disappointing to me to see how much less wake he had at the same speed as me. I didn't bring my GPS, but I start to develop a transverse wave at about 5mph; I didn't see any of that from his, even at faster speeds. He said my wave seems to start by the oarlocks. I know I'm still trimmed a bit bow down, but am not sure whether that's the cause. I have to move the oarlocks to check. I'd appreciate any thoughts.

Compare the rocker of the two boats. I expect the Guideboat will be close to dead straight.

Compare the waterline length with respect to the overall length on the guideboat. I expect they will be the same thing. Now do the same measurements for yours.

Go back to post #256 and see what Godzilla produces for the lowest drag hull (albeit with chines for planking).

Rick W.

 

[Guest625101138]

I should add the NVC-6IA at post #256 is designed for 250kg. For lighter displacement it would be slightly different but still flat rocker and still maximum waterline length with respect to overall length.

Rick W.

 

[Guest625101138]

It you were comparing the diagonal waves from the hull then these do not take a lot of energy to generate. The high energy wave is the rolling transverse wave following behind the hull.

The fineness of entry or bumps along the waterline can generate diagonal waves.

The easiest way of doing an accurate comparison is to get a GPS, strap on a heart rate monitor and go rowing in calm. Hold a steady heart at a normal working level for about 1 hour. Do this in both boats and you will have good data for comparison.

Rick W.