designing a fast rowboat

[Clinton B Chase]

Latest on Drake, 17'3" Faering

Here is the latest. Thwarts are 5" above floors (6" for fwd thwart/mast partner) This will place my weight low in boat and allow for the 1" butt pad. The next major decision is how far aft of seat to place oarlocks. I have mocked up the rowing station a few times. At this point the center of the oarlocks is 12 1/4" aft of the aft edge of seat. That feels pretty good. The oarlock spread is 57" so I can use quite long oars. That is the other big decision but I will probably end up making several pair anyway. So the first set will be 9'1 3/8" according the Shaw and Tenney formula. Any thoughts on oar length? I am getting some of the finest spruce money can by so I do want to get the right length. If 9'1" is a bit short these can become my easy-pulling, upwind, choppy water set of oars. They will have spoon blades about 5" wide. The blade length will be at least 36". I'll taper them to a max of 2 1/4" near the handle and down to 1 1/8 x 1 5/8 oval near the blade.

Any thoughts are welcome. Enjoy that shot of the nice light coming in...can you just make out the rang in the lower half of the picture?!

Cheers,
Clint

 

[DickT]

The rolling transverse wave is my concern. Both hulls have very little or no rocker and the same 16' wl length. My boat at 17' has some overhang. I think my seating position has the aft 75-80% of the keel line (which is pretty much dead straight) about an inch high at the stern at rest and about level when pulling. I didn't want to load it too to much to the stern, but am now having second thoughts. I'm wondering if shifting more immersed volume aft at the expense of drag on the keel might help.

I printed out your Godzilla hull on post 256 a shortly after it turned up and have looked at it a bit. I don't have as full ends as you show nor have I cut back the bow.

 

[DickT]

First post above was in reply to Rick.

I like your faering a lot Clint. You've included the ribs in the ends that I keep hoping I don't need. I really prefer long oars. I had a pair I made from 10' spruce 2x4 stock on a pretty heavy stretched(18') Norwegian pram I built 25 yrs ago. I didn't feel they were at all too long, even with all the weight of the motor and sail rig. I'd experiment a lot with oarlock position. I'm wishing now I hadn't mortised and epoxied mine in place after they came loose in a race last year.

 

[Guest625101138]

The rolling transverse wave is my concern. Both hulls have very little or no rocker and the same 16' wl length. My boat at 17' has some overhang. I think my seating position has the aft 75-80% of the keel line (which is pretty much dead straight) about an inch high at the stern at rest and about level when pulling. I didn't want to load it too to much to the stern, but am now having second thoughts. I'm wondering if shifting more immersed volume aft at the expense of drag on the keel might help.

I printed out your Godzilla hull on post 256 a shortly after it turned up and have looked at it a bit. I don't have as full ends as you show nor have I cut back the bow.

Dick
I am travelling this week but if you like and can get Godzilla to generate the optimum for your conditions.

You need to have some idea of the power level you can produce or speed in the existing boat. I would need something to draw the existing boat from.

Certainly trim is worth playinf with.

I repeat the hull if post #256 is for 250kg. I expect yours will be less than this so the bow and stern will be finer.

Rick W

 

[nordvindcrew]

oar length

Clint, we use 8'11" oars on a 54' oarlock spread, so you should be right in the ball park. 12 1/2" from thwart to oarlock sounds close, but people and boats vary. If it feels good to you, it is a good place to start. Ours are 17 1/2 " aft ofvthe thwarts. We like to really bend into the catch and lean back at the finish of the pull. We row a SLOW cadence with long pulls.

 

[nordvindcrew]

skin on frame

Ive got the rails fabricated, transom installed and the fore and aft deck beams in place. next is to laminate the keel and stem. this boat gets built from the gunnels down. Once the keel is in then steam in the ribs, shaping them by eye and with some battens to help. Next, install longitudinal stringers and finally the skin. Don't know if I'll use canvas or ballistic nylon, depends on the price. Can't begin to guess on the finished weight, but hoping for 60/70 pounds. I really need a boat I can row on some of the beautiful days when my brother is busy doing something else like working. It will also allow me to do some races in more distant locations when I have to row single. Length is 16', beam is 41 1/2" depth is not locked in yet but will be about 13" midship. I've got a set of spoon oars 8' long that should be about right. There's a race on a local pond July 26th that I'm hoping to be ready for.

 

[Clinton B Chase]

Jeff, is that 17 1/2" from aft edge of thwart? Wow, that would be big...I will try it b/c I also like long, slow pulls.

I am kicking myself b/c I established my seat height that felt right -- I like to feel like I am sitting IN the boat...so the top of midship thwart is 5" off the floorboards. I went ahead and glued the cleats in and made a perfect thwart to fit. Now it seems like with the oarlocks and oarlock pads clamped on that the height between oarlock and seat is a lot...it feels like my hands will be high when I get in, but I am also not holding the actual 9'2" oars in my hand, which will change their angle down to water and this perhaps make my hands lower (I've been mocking up with a couple of 6' sticks as oars)....any advise beside don't glue the oarlock pads in place until after a sea trial. When I put the sleeping pad plus pad from sliding seat under me butt it lifts me up 1"+ and that feels better. So for rough seas I can take that out and get my weight way low. Otherwise I can always shim myself up with the butt pads which feels great to the butt...for those long days on the water. Suggestions based on your experience RE: height from oarlock to seat...I am 6'6" tall.

Cheers,
CLint

 

[DickT]

Dimensions of your boat are similar to mine, but you'll be at least 20lbs lighter. I use 9' oars and can hold over 6mph on my gps for a few minutes but am pulling up a pretty good wave train. I think fuller ends as in Rick's 256 post would help. I moved everything to trim further aft and tried it out this evening, but didn't get the left oarlock right.

 

[Clinton B Chase]

See...I have my thwart just forward of the midship frame. I have found in nearly all the boats I have rowed to be stern down. I'll usually row with a picnic anchor and extra oars, plus a sail rig so that gear will help me trim right if it is off. I am going to put bright tape on the stem and sternpost at the waterline so someone viewing from the dock can tall me if I am trimming on the DWL.

I was just rowing the boat in my shop with my shorty oars and ralized, as I have before, that it seems that the oarlocks should be placed such that in the middle of my stroke where, presumably, the most power is being generated, that the blades should be at a certain place in the water where the most thrust is...a little forward of amidships? Where is that spot? Then the oarlocks could be moved such that in the middle of the stroke the blades were at that spot. Doesn't that make sense? Jeff, what do you think?

Cheers,
Clint

 

[KJL38]

Hi everyone, I've been reading these posts with great interest as I am currently building an Adirondack Guideboat.

Nordvincrew, have you seen this website about building a skin on frame guideboat http://www.capefalconkayak.com/adirondackguideboat.html His fifteen footer weighs 42#.

Kelvin

 

[nordvindcrew]

thrust

Clint, I'm not sure where the most power gets delivered to the water,but we think that the part of the pull from were the oar is at right angles to the boat, until the final snap at the end is where the power gets to the water. to us, the first part of the pull is to accelerate the oar to boat speed and the last is to accelerate the boat. We like to have a high pull with the handles coming in at a height that is mid way between your belly button and shoulder, or a bit higher. High pulls help you get your oars up to clear rough water on the return to the catch. Too low and you'll be fighting the oars scraping your thighs as you try to get the oars out of the water to clear even a minimal chop. That guide boat site is fantastic! to get a completed boat like that in two weeks you must really have to know exactly what you are doing. i've got the keel in my new boat, laminated a stem and bent in some temporary ribs and stringers to verify the shape. Looks sweet, hope it rows as good as it looks while it's upside down on a building jig. RE being 6' 6" tall, that translates into a long, efficient pull that you should be able to use to good advantage. The low seat is the right way to go also; lowers the center of gravity and helps on your stroke, both catch and pull.

 

[nordvindcrew]

elusive quest for speed

we rowed Sunday with perfect conditions. 5 knots was easy with bursts to 5.7. Try that in a race with wind and waves. this was with our smaller boat, the Nordvind with a 15.5' waterline

 

[DickT]

What's your surge range per stroke? With my gps I'm trying to keep the low end high, if that makes sense. Upwind I'm 4.8-5.3, calm 5.4-5.7, some pretty cool surfing bursts over 6 downwind,(I can't keep that up for long). Steever's book talks about using weight shift to narrow the range.

 

[nordvindcrew]

surge range

What's surge range? we row somewhere around 20 strokes per minute. We try to co-ordinate our breathing with our pulls. lLong pulls with oars that are 8' 9" on 50" spread oarlocks. poweris applied with emphasis on the last couple of feet (at the tips) to pick up speed. We can get up to over 7 knots for a short burst (1/4- 1/2 mile) at the start of a race, but it's a real killer if done too long. Haave to stay up front but not kill yourself in the proicess. Pasing in a race is a demoralizing prospect when it takes 1,2 a mile or more if your opponent is rowing almost as well as you are.

 

[DickT]

I learned about surge from Andrew Steever's great book on oars available from Mystic Seaport($15). The boat is rhythymically accelerating during power and decelerating during recovery. I notice a range of .3 to .5mph if I stare at my gps. Since wavemaking resistance increases with speed, you would ideally want to keep your speed as even as possible because the added drag of the high speed bursts is not offset by equivalently less drag in the lower speeds of recovery. This argument can be used to justify a short, fast stroke rate, but there are also good arguments for long and hard. Steever says upper body weight shift can be finessed to damp out the extremes(if you think about it it makes sense), but it's easier said than done.