designing a fast rowboat

Launch

Here are some shots. My plan was to row past an Island on which there is a school that my wife works at. Missed her by a few minutes...would have had better pictures.

I was very happy with her performance and extremely pleased with her looks in the water. The pros: she is fast (I will have to wait and see just how fast after more time on the water), she is very comfortable (the oars, the spread, the handle height in the pull, the oarlock placement was all dead on...fit like a glove). The bad was that I placed my foot cleats too far aft and didn't have good pressure on my feet in the last part of the pull. Easy enough to fix. She handled the wind really well...it was gusting up to 20 kts at one point and I was very happy that the windage wasn't too bad at all. The stern does blow off -- not badly -- but requiring some correction. I know I was trimmed well because I had my friend sight in profile the waterline marks. With me, oars, a bag of gear, and a 12 pound anchor she floated right on the DWL! When I put the anchor just aft of my feet she sat stern down about 3/4-1", which is what I thought one wanted. I rowed that way the whole time. If there is a breeze on the beam I definitely notice the stern fall off...could be a lot worse! (i.e., the boat rounds up a little...such that some extra pressure on the windward oar will keep her on track) But I don't have enough experience in other boats to know if this was in the range of normal or not. Jeff, what say you? At this point I just plan to row more and experiment and if it really ends up being a consistent thing, should I add some depth to the outer keel/skeg? It'd be easy to laminate some strips on and add 1/2 inch and inch. At what point does this add drag? What is your experience with this issue Jeff and is it possible to have none of this effect....in other words a boat that is neautral in a cross wind? I guess I'd rather have it blow off at the stern rather than the bow getting blown off as it helps get one up wind, in a way. My o. keel/skeg is about 1 7/8" deep at its max before it turns up into the sternpost. I drew it to be 2", but to get a nice fair curve I recall shaving a bit off there. I'd appreciate thoughts. Look forward to having you row her and tell me what you think, Jeff.

Cheers,
Clint

 

drift

Clint, in my opinion, you are probably pretty near right on. I think the only hard and fast test is in an absolute cross wind. If you don't blow off then you are balanced. It seems to me that the amount of skeg or keel necessary to maintain a straight course depends on the angle you present to the wind. What might be right for broadside would be too much if the wind is off your bow quarter. If you aren't fighting it too much, leave it alone, or try a temporary extension to your keel/ skeg or do as we did and jury rig a small rudder to test and find out how much is needed to hold a course. We added a 2" deep X 1 1/2" wide keel to the Nordfjiord and the drag was tremendous. The only cure there will be to cut out the bottom and build in a new bottom with a much deeper Vee. For some reason, wetted surface in a Vee bottom doesn't seem to induce as much drag as it does in the added keel. Of course, this is all "seat of the pants" stuff and not backed up by any facts. Drake looks great, get us some shots of you rowing her and get a GPs so we can know how much speed she is willing to give you. The GPs is also a great way to analyze rowing technique. If the sensitivity is good, you can instantly see if you are making more speed or not.

 

Jeff, I don't think I am far off either. I started the row with a downwind leg and the boat was a champ...it was only when I was in the cross wind that I noticed the effect...it may be that it is fine.

This all has me wondering about the keel on these faerings and the drag they must create. My outer keel is 3/4" at the forefoot and 1 7/8" before the keel turns up into the s' post. What would the effect be if I reduce the draft of the keel and kept it deep at the skeg portion...wouldn't that reduce drag? Another question I have is: if one were to sit across the wind with out moving, and then be rowing directly across the wind, what is the most desirable behavior from the boat...would one expect a balance boat/not have one end or the other blown off more?

I'll try the GPS. Again, I can't tell how fast she is because the wind was blowing 10-20 most of the time. When I got into the lee of the East End of Portland and the wind was calm...she took off. Upwind I was pleased with how well I could power her through the chop and into the wind. It isn't the lightest boat (I have to get a scale and measure her...my guess is 135lbs) but it clearly has enough "way" on here to get through chop...something I really like in a rowboat. If there wasn't enough skeg I would think upwind is where I would really feel it (the boat would want to round up right?...I have not seen that effect, yet). I'll try the GPS...have to get it working with the computer map software -- I am weak at these things.

Clint

 

The center of dynamic pressure moves forward with speed.

Therefore the boat will find an equlibrium position when merely drifting that is different to its balance when underway.
A zero camber foil at 90 degrees angle of attack will have a centre of pressure at the centre of surface area, whereas the same foil, unstalled will have a centre of pressure at 25% mean chord - Big difference....

You could very well shave some keel off forward in small increments until you find an ideal amount so the boat is fairly well balanced across a range of different angles to the wind, when underway at typical speeds.

Once this is obtained you will find that when merely drifting the bow tends to fall off somewhat - it will no longer drift at close to 90 degrees to the wind.

It is important to remember that some keel is necessary, not just for 'directional stability' or 'tracking', but rather to reduce leeway.

There is an optimum amount in between so much keel that it is itself a lot of resistance and so little keel that the boat does so much leeway that the hull itself is creating a lot of resistance (due to going through the water at an angle)

 

T, This is helping me understand things. I just got back from a fabulous row. The boat feels great and the stern coming off line is minor. It happens in a direct cross breeze and when the breeze is aft or forward a little of amidships. The current messes with the experimentation. I still need to row in slack current, b/c I think with a strong keel, the current makes the boat turn into the current as well. Also the waves seem to increase the effect...the stern gets pushed down stream of the waves. I noticed that alot at one point. Many variables.

You mention the center of dynamic pressure moving forward...that definitely explains what I notice: across the wind just floating the boat is balanced; when I start going is when the stern comes off the line. With weight aft, it helps but only slightly. Overall the effect is mild, but still there requiring an easy amount of correction. So what would be the course of action: shave a little off from forward to aft of midships and/or add some skeg? Or not bother. Jeff what would you do, too?

Cheers,
Clint

 

If you feel the leeway angle is fairly insignificant and you have ascertained this is indeed so up to the windiest cross wind you're likely to row in, then shave some off, as you've obviously got enough lateral resistance and can probably afford to lose some of it.

If on the other hand you don't want to have any more leeway you should add a similar amount at the stern as you take off the bow. If you feel less leeway is better then just add at the stern.

There is also another trick which is to give the keel a rounded shape forward and leave it sharp and square aft (gradual transition obviously, use a hand plane) . This is more subtle so make sure the planform of the keel is just about right before bothering with that. This will make the keel 'bite' a little less where it's rounded off compared to where you leave it crisp and sharp.

On the current; In most situations current is completely irrelevant. I know it might not seem that way but it is.
The only time current will affect you is if there is turbulence within it (eddies etc) and in your case where the keel is quite rockered you have an advantage over straighter keel designs in that you dominate directionally with the oars better compared to if you had more 'bite' at the ends.

The only other thing the current will do and this has no effect on balance either is affect the waves. Wind against current- choppy abrupt steep slow moving waves,, wind with current- long low glassy fast waves.

Bottom line of course is balance when under way, boat attitude when drifting is usually fairly irrelevant in your type of boat anyways. Besides, trim when drifting can be anything you like (won't affect performance) so you can just sit a bit forward and find the position at which the boat will drift at 90 degrees to the wind, and therefore drift as slowly as possible.

 

Some photos

Jeff, T-cubed, et. al.

Here is my keel shape. That is about 3/4" forward to 1 7/8" deep aft. I based it on other faering outer keels.

After my row I am thinking that some modification wouldn't hurt but I want to take my time...this is just to give you a better picture of it. Does this look like what was on your boat, Jeff? T-cubed, I was thinking it couldn't hurt to laminate on some strips to build up the skeg portion and then fair that in to the sternpost and in the meantime fair it into the rest of the keel but shave a little off from the forefoot back to around the aft seat station. I may want to go for one more row with someone else to see if it is not just me being overanalytical and sensitive as this is my first design. I also want to gain a better sense of the boats speed and leeway and see if this keel is being a drag. But you thoughts seeing the pictures would be great.

added:
Well I decided to do the mod b/c I have nothing else to do...so any thoughts? I drew a line in on my plans and addedmore skeg, about + 3/4" and may shave off 3/16-1/4" from the rest. This would shift the CLR aft. In that 2nd picture it would look like: less keel back until the skeg section where my Dad is: the keel would run straight back and then curve quickly into sternpost. So more of a skeg and slightly less keel.

Cheers,
Clint

 

keel mods

Clint, I'd go with what t cubed tells us. He knows the technical things that I don't. Just remember that you are close to good and don't make changes without a lot of thought. All my boats have minimal keels, on the Nordlys (SOF boat ), it is full length, 3/4" wide by 1/2" high with rounded edges. it goes back into a skeg that is, or will be when I make the change, 3-1/2" high, tapering forward for 3-1/2' till it blends into the keel. The keel is mostly there to protect the canvas bottom, and then to give directional stability. If I ever get her into the water and get some serious time in at the oars, I'll let you know how it all works. It is far better to have the stern fall off than fight to keep the bow up into the wind. Your keel looks huge to me, but is typical of faerings. I would guess there is quite a bit of drag there but compared to a keel/ skeg, it might not be too different in area of wetted surface. Sunday, we did our annual Pearl Harbor Day Row. There were only three boats; us with the Nordvind and two couples with Seth Pressons' Atlantic 17 ( take a look at his web site ). We rowed up river on the North River against a 2 knot current for 3-1/2 miles, took a break for a libation and rowed back. The weather was cold, in the low 30s' with light but steady snow falling. The river was very pretty with the marshes and pines all snow covered. It was a good row even with so few boats and when it was done, it felt good to get home, get some dry clothes on and reflect on what an idiot I must be to be out rowing in the snow when I have to work in it every day. Oh well, I never claimed to be sane.

 

Clearly, you both offer great experience and I appreciate it. I realized that I can't do much wrong by doing the modifications. It is a gut feeling; I may be wrong, but we are talking about wood and epoxy: anything can be done. I am taking down the keel a little over all and adding about 7/8" to the skeg region. I fit is too muc, I'll shave some off until I have it right, then put the bronze strip back on. One of my gut feelings is that the whole thing is offering a bit of drag so shaving down and adding a little to the skeg won't hurt...rather the extra wetted surface be in the skeg. I hope the weather warms a little so I can try my experiment this weekend.

Jeff your 3/4 x 1/2" high keel is that one the faering type boat you have? I wonder about these boats and the tradition of that heavy keel...it must have been directly from the fishing boats wanting the keel to help them in the waves and open water and provide lateral resistance for sailing. It is interesting to compare them to the dory where the whole bottom immersed and the chined provided that lateral resistance and boy you sure notice when the fore-aft trim isn't right! Fascinating how different these two boats -- the faering and the dory -- are yet their purpose, for fishing, is very much similar.

Will post pics of the changes tomorrow for you guys to smile or cringe at

Cheers,
Clint

 

keel

the 3/4" X 1/2" keel is on my SOF boat The "Nordlys". She has a rounded bottom and the kel is there first to protect the canvas then to add directional stability. On my test row with out the keel, I could, somehow, keep her going straight but only with constant attention. With thekel and skeg it should be much more forgiving. Only time on the water will tell me how right it is. The faering style "Nordvind" in its' original form had no keel but had a sizeable skeg. The moderately deed vee bottom and skeg combined to give us a boat that tracked pretty well. The fiberglass version has a wineglass transom and the extra run of the bottom aft has replaced the skeg. Stability is about the same. The stern does fall off in a cross wind, but not so much that we can't control it esaily

 

I have shaved the keel about 1/4" down and want to fair it into the addition layers glued to the skeg. At this point the skeg is 2 1/2" deep...keep going maybe to 2 1/4" deep and try there? My hope is I take a little drag out of the keel and put it into the skeg area where it will be useful to keep my stern on track. I guess I am surprised at how much skeg I needed.

Clint

 

Ive been following this thread for some time now and must say I found it very interresting. Im from sweden and here we have races with an old type of fishing boat called "skötbåt". The boat is rowed by 4 or 5 oarsmen depending on local rules and an old type of sail rig is also allowed. The races are between 7-25 miles. We are currently looking for new boat and I was woundering if someone could help me define what quality's to look for?
here is a picture of the old boat

 

What a gorgeous boat. How much does that weigh? The first thing is to make the boat light, but ultralight may not exactly make it the best in a sea. One aspect of Drake I love is that it has some weight (Yes, I still have to weigh it guys) so it just slices right through the chop going up wind, quite exciting. The others will surely have more to say. I will add more as they chime in. Have you seen my lines plan. It should be in this thread somewhere. I will try to find it.

 

rules?

Seconding Clints comment, that's quite a boat! If you are racing, then there must be rules. Are you limited to that style or can you row something else? The picture reminds me of a surf dory of the type used for lifesaving here in the 19th century. For a new boat, go for long, narrow and reasonably light and you can't go far wrong. Good luck with your search

 

Shearwater 18

Hi all .There is an interesting discussion over at http://www.woodenboat.com/forum/showthread.php?t=89176&page=2
About a two man boat for SFbay. The Wooden Boat site would not let me post this photo so I put it here