Pulling boat seat location?

[Kudzu]

Did not want to sidetrack the other thread so just starting a new one. I have always had an interest in a Pulling Boat and Daves 'Ruth" has inspired me to design a SOF pulling boat.

I design and build SOF kayaks this is an easy transition. I have looked a few designs but nothing that doesn't need alternation to suit the SOF construction.

Designing the hull is pretty straight forward. I am not looking to race so a perfect hull not an issue. What I am stumped on is the placement of the seats. This will be fixed seats and I know in a kayak that the location is very important. I assume that rowing is not as critical but is still important for good performance.

I know you want the boat trimmed so the transom is not dragging under water. You don't want to be so far forward the bow digs in and stern is too high. But I am not sure Where to locate myself in the boat.

I assume you want to be seated in front of the LCB (LCF in Freeship) keeping your weight near the center of the boat and maybe slightly forward of it. I have a design I worked from and the seat is way in front of the LCB, over 2' on a 15' boat. This seems excessive to me but I admit I don't know, not having any experience with pulling boats. I am thinking this may be the two man position? Any one have an guidance there?

[Peerie Maa]

Two points to consider.
Pulling boats were designed to work, so the oarsman sits forward, passengers or kitbags went aft.
If you are alone, lifting the stern, especially a transom, out of the water will not slow you down.
If you might carry two or three passengers put a rowing thwart in forward as well.

[George Ray]

Not all in line with your design parameters but it's my two cents.

Assuming a constant load, I find that boat trim needs to vary with conditions and relative wind/sea. This can be achieved with a change in seating position or a shift of ballast. My favorite dingy interior is side tanks that leave a constant width alleyway down the center and an infinitely variable seat position sliding on ridges at edge of the tanks. For tiny vessels w/o centerboards this also allows space to lay down in the bilge.

[Andrew Craig-Bennett]

I agree with Nick; you will, in practice, almost always have some "shifting ballast" in the form of cargo, the anchor, maybe a passenger.

From somewhere I recall that another magic number is that the oarlocks should be 11" abaft the aft edge of the rowing thwart.

[Kudzu]

Shifting ballasts makes sense. But I am looking for some guidance as to where to start? A rule of thumb maybe?

Where should my seat/weight be in boat assuming flat conditions (or rough for that matter). Once I have a starting point that is close I can adjust it from there.

[Thorne]

You want to trim the boat so that it rides slightly bow-high with most load/crew options.

An interesting variation on the 11-12" oarlock/seat measurement is one I saw **somewhere** recently, showing a 14" angled measurement between the aft edge of the thwart and the oarlock -- which make a lot of sense.

This measurement varies a lot depending on rower size, arm length, oar length, cross-handed or standard rowing, use of cushions, etc. So if at all possible don't build the thwarts in place until you can get the boat on the water and test it with one rower and no crew, one rower and passenger, one rower and gear, etc.

I went through this with my Cosine Wherry, finally got thwarts and oarlocks positioned correctly -
http://www.woodenboat.com/forum/showthread.php?t=88766&highlight=cosine

[DGentry]

Hey Jeff -
I suspect there's a rule of thumb out there, but I can't remember if or where I read it. In any case, it's easy enough to take a gander at dozens of other established rowboats the same length as your design, and extrapolate from there. Duckworks has a good selection of designs you can easily peruse: http://www.duckworksmagazine.com/r/plansindex/pullingboats.htm

A fore and aft fixed thwart is another option.

Dave

[Andrew Craig-Bennett]

Jeff - your weight moves to quite an extent as you take a stroke. This is much more pronounced with sliding seat rowing, of course, but it is noticeable even with fixed seats.

[Clinton B Chase]

Jeff, This is a good question. In my pulling boats that I draw I put the seat from exactly amidships, or to be exact in the middle of the underwater volume (over center of buoyancy) or just forward of the center depending on the lines. If it is very full aft, with a transom, I would be inclined to put the thwart a half thwart's width to a full thwart's width forward of the center. In Drake, which is very fine aft, I put my thwart a half thwart width forward of the center of buoyancy with the idea that I'll have my bucket and a bag of stuff aft within reach. I usually have stuff in the boat, so I think of that as the movable ballast that gets my trim right. Best trim will change with wind, sea, and crew numbers.

--Clint

[Dick Wynne]

I agree with Nick; you will, in practice, almost always have some "shifting ballast" in the form of cargo, the anchor, maybe a passenger.

From somewhere I recall that another magic number is that the oarlocks should be 11" abaft the aft edge of the rowing thwart.

And you want the thwarts on at least 40" centres, about 43" if you can get it, or your kidneys get a bashing from the rower behind on the forward lean, if you're all doing it properly. You might get by with less in boats where the seating positions are staggered as in some whalers.

[Kudzu]

Here is what I have in mind. This is the still very rough and a lot of refining to do. I hesitate to post it it needs so much more work.

For example I am pretty sure I will stretch it out to 16-17 foot. It looks tall to me and I expect to lower the gunwales. But you see where I am going and that I don't really have transom.

http://kudzucraft.kudzupatch.com/designs/Mabel/scooter1_Linesplan.gif

Clinton what you said is what I was thinking. It seems logical to keep the weight somewhere near the center of the boat or just forward of it. But logic isn't always right. ;)

This will be primarily a single person boat. I am sure I will have an occasional passenger and expect sometimes I will be the passenger with someone new trying it out. Might rarely be two of us rowing but I think that would be very rare. So I do want to have the option of adding thwarts as needed. So I am thinking removable thwarts. Maybe being able to remove the center one and install two for when I do have a passenger. Or just moving one and installing a second?

Since I will single hand 99% of the time I really want to keep the weight low for ease of loading. I have a kayak trailer now and would like to be able to carry it from the water and load it on the top rack.

Haven't thought this far ahead but I might want a fixed thwart in the bow or stern for launching? Lots to work out but that is half the fun.

[Thorne]

As Andrew points out above, rowing will create a certain amount of pitch -- and even more in a SOF build. So you'll want the boat longer than usual, and probably put the thwarts a bit lower if possible.

How does it work to use software for ply strakes for SOF design?

[john welsford]

Can I suggest that you find the longitudinal center of bouyancy, to place the rower and maintain the boats trim the after edge of the seat goes 25mm forward of that point, the seat ideally for old folks with sore backs should be between 160 and 200 mm above the rowers heels and for a fixed seat rowing boat that may be used in rough water the feet need to be around 350 apart. For an average 1775 tall male the rowlocks should be 330mm aft of the after edge of the seat and 200mm higher than the seat and the stretcher ( footrests) 730mm aft of the after edge of the seat.
If designing from scratch I try to put the LCB at around 46% of WL aft of the forward end of WL. Prismatic Cf needs to be around 52%

Hope that helps

John Welsford


Did not want to sidetrack the other thread so just starting a new one. I have always had an interest in a Pulling Boat and Daves 'Ruth" has inspired me to design a SOF pulling boat.

I design and build SOF kayaks this is an easy transition. I have looked a few designs but nothing that doesn't need alternation to suit the SOF construction.

Designing the hull is pretty straight forward. I am not looking to race so a perfect hull not an issue. What I am stumped on is the placement of the seats. This will be fixed seats and I know in a kayak that the location is very important. I assume that rowing is not as critical but is still important for good performance.

I know you want the boat trimmed so the transom is not dragging under water. You don't want to be so far forward the bow digs in and stern is too high. But I am not sure Where to locate myself in the boat.

I assume you want to be seated in front of the LCB (LCF in Freeship) keeping your weight near the center of the boat and maybe slightly forward of it. I have a design I worked from and the seat is way in front of the LCB, over 2' on a 15' boat. This seems excessive to me but I admit I don't know, not having any experience with pulling boats. I am thinking this may be the two man position? Any one have an guidance there?

[Kudzu]

As Andrew points out above, rowing will create a certain amount of pitch -- and even more in a SOF build. So you'll want the boat longer than usual, and probably put the thwarts a bit lower if possible.

Good info and totally possible!


How does it work to use software for ply strakes for SOF design?

Never tried it, but I think the design phase would work. Just have to keep SOF limitations in mind as you went. For example you need to bend a stringer along the line of each panel. So you wouldn't want anything really twisted that would be hard to bend into shape. No concave shapes that the skin wouldn't conform too.

What I question is if the software would give you offsets at each rib/frame location? If you could get offsets at the locations you specify, I would think it might work.

[Thorne]

I'd say that John has the definitive answer above -- he's the experienced designer after all.

As for the software I don't have the faintest clue. But I suspect that the plank layout is 90 degrees off what most SOF layouts are, so everything would be WAY off...

[DGentry]

What I question is if the software would give you offsets at each rib/frame location? If you could get offsets at the locations you specify, I would think it might work.


With Carlson's Hulls, at least - and likely many others - the program will give you offsets for frames at any positions you specify, as well as offsets for the transom. It works great. Plank layouts are irrelevant, as the skin will naturally assume the shape that the frames and stringers dictate (excepting big hollows, as noted).

It's my belief that many multi-chined, or round hulled small boats can be easily adapted for SOF construction, traditional or otherwise. My RUTH, while not a previously established design, is similar in conception to about 4 or 5 wooden pulling boats that I know of, and was an experiment to prove my hypothesis - successfully, I like to think.
SOF adaptations of classic canoe designs are another, more common, example of this (i.e. my see-thru Wee Lassie).
I've got a few other conversions in mind for future builds.

Single chine dinghy designs are not so suitable if they have large flat expanses that would result in too much unsupported skin. Clearly, a hull the size of a kayak is OK, though.

Sorry, thread drift!

[Kudzu]

Since John gave all that good info I think a little Thread Drift is fine. Besides me and you think a lot alike when it comes to SOF. I have some other boats in mind to add to the kayaks. A canoe will probably come quicker than this one. But this is a boat "I want".

Of course I also want to build the the other kayak design I have done, and finish the one I am building and....... You get the picture. Not enough time for all the boats that interest me.

[Kudzu]

BTW, I realized I only said this in passing. Thank You John! This was the information I was looking for. Saved that and printing it out and putting in my Book of Knowledge!

[Clinton B Chase]

John's info was great confirmation of others' intuitive rules of thumb. But remember to mock up the rowing station and get in the boat and feel it. Rules of thumb are not as handy with seat height, oarlock placement, etc...because we are all different heights and widths with differing rowing styles. For example, I like to really stretch into the catch and don't finish with too much layback. I'll grab my measurements from Drake and put them up. Remind me if I forget. I think if we have a bunch of rules to design from we are better off.

[George Ray]

John Gardner "Classic Small Craft You Can Build" and Howard Chapelle "American Small Sailing Craft" would be two places you could peruse venerable designs (w/ tables of offsets) and see what has worked in the past.

[john welsford]

BTW, I realized I only said this in passing. Thank You John! This was the information I was looking for. Saved that and printing it out and putting in my Book of Knowledge!

No problem, I enjoy rowing fixed seat boats and once I got one of my early boats right put that in my book of useful things. But like Clinton says, its really a beginning and it pays to mock the boat up so you can taylor it to your particular physique and style.

Good luck with the boat.

JohnW

[Ben Fuller]

I have found the trickiest bits is setting things up so the boat does not weather cock, hunt to windward, gripe or what ever you want to call it. Interesting example: the Gardner LFH boat was designed to go in one direction with two, the other with one. The stems were skeggy enough so that the stern stem had to be trimmed down an inch or two below the bow. Whitehall style hulls often suffer from this problem as in old ones the traditionally you always had a passenger. Perfectly double ended boats like the ducker which have no skeg and not much stem shape have to be weighted to the stern and I find that sitting just aft of amidships is about right. On a fast dory we had a removable seat between two fixed seats for rowing solo. A really big round sided dory 21" that we measured had 4 rowing stations. We found that you could not row 4 people; three people had choices as to where to put their weight

As people wrote above a seat in the middle of the boat works pretty well solo most of the time but there will be times that weight is needed in the stern. If a design has the oarlocks in the middle of the boat I suspect that it might be gripy

[Clinton B Chase]

By gripey, Ben means that it will want to round up into the wind. This is worst when the wind is on the beam...if you ever felt like you've been rowing really hard with one or and hardly with the other, that is a classic case of the stern being blown off. Really common in dories, which are unbelievably trim sensitive. The moment you get the weight aft such that the transom is in the water providing a skeg effect (a little lateral resistance) then less gripe.

It is tricky, no doubt about that. If you can build some flexibility into the boat...like do not permanently glue things in until sea trials, then all is better. I'd put the seat dead center and get out rowing. You can use a different thwart for sea trials, then make the final thwart one your location is set, depending on how it is made fast into boat. In a dory or boat with permanent frames, you would cut the notch later and make the seat cleat wide enough to handle movement of seat fore/aft after sea trials. If you will definitely have stuff/crew in boat, I'd not worry and use this material as movable ballast.

[JohnC]

Clint - I thought I read somewhere that you were about my height (6'5")
I'd be interested in hearing what distances you like from thwart to oarlock and thwart to floor.
I'm still planning to build the boat I discussed here (also SOF) :
http://www.woodenboat.com/forum/showthread.php?t=92942&highlight=what+size+gunning+dory%3F
The load requirements are less now so its about 16' LOA and I hope to start building in a couple of weeks.

John

[Chip-skiff]

I'm 6'4" and long-limbed, and use a 14-inch distance from the rear edge of the thwart to the rowlock. Fortunate, the Wolf Goddess (my mate) is also long-armed and legged, so any adjustment can be accomplished by a shift of the arse on the seat.

In the event the boat will be rowed by different-sized persons, the simplest tactic is to build two mounts for the locks, say at 14 inches and and at 11 inches. I've seen driftboats with two or three mounting holes for the locks. These are from Boulder Boatworks, in Colorado:

http://www.boulderboatworks.com/photos_boat_kits/02260020.jpg

These are plastic, but you could do the same thing with oak and bronze sockets. They also sell lifts for the locks:

http://www.boulderboatworks.com/photos_boat_kits/oar_towers.jpg

Besides the thwart to floor to lock dimension, the length of your oars also determines the final geometry.

[CapnJ2ds]

John Welsford has it right - and he's got a lot of rowing miles under his bum!

My two cents' worth ......

If your boat suits it, three rowing positions is a good idea.

Some one above has already mentioned trimming ballast, and I've read somewhere (Pete Culler?) that working dories carried a "dory stone" for the purpose. Currently I use a 10 litre plastic container of water (Whe I remember to chuck it in); water has the advantage that you can empty it out when not needed. I'm also told you can drink the stuff in an emergency, but haven't tried it meself.

Children, suitably trained and restrained can make good "bionic ballast", being able to move themselves to the right location. The disadvantage here is that the blasted do-gooders get their knickers in a knot if you turf the kids overboard when no longer needed.

A good and good-sized dog is probably the best bionic ballast. My old Gordon Setter took well to going forward when we went upwind and aft when going downwind. The disadvantage was that when he assumed the traditional "Noble Dog" pose in the stern sheets his height of eye was greater than mine and people tended to assume he was the one in charge.

'Tany rate, a little trimming ballast is a big help with griping etc in a breeze.

Your boat looks pretty good to me at this stage - your proposed stretching the length will almost certainly make her even better.

[Kudzu]

LOL love your comments. But no kids to chuck overboard here. I have a dog that would probably love to go but he wouldn't sit still long enough. He understands sit. That means make his bum hit the ground and then jump up an stare at you thinking "OK, I sat. Whats next? Can we play, want chase me? Lets go!"

Thanks for the comments on the boat. I have worked some more on it. stretched it out to 17'. Cleaned up the lines some and made it 'prettier' to my eye. Calculated the Stability and was surprised it was as high it was. Of course compared to a kayak it may just look 'high'.

Also redid the transom pulled the keel down to work as a rudder. It needs a bit of work to make sure that the fabric will wrap around. That or add a keel strip after the boat is skinned.

[Kudzu]

Previous John replied to my question about fixed seat rowing locations. I have printed this out and saved it. Designed a boat around/using this info and found myself day dreaming about sliding seats and maybe putting one in the boat instead of fixed seats. Or maybe both just making them removable.

I have a pretty good idea on the sliding unit itself but I find I am back to questioning the locations of everything in the boat. Any rules of thumb on sliding seats and placements of everything?



Can I suggest that you find the longitudinal center of bouyancy, to place the rower and maintain the boats trim the after edge of the seat goes 25mm forward of that point, the seat ideally for old folks with sore backs should be between 160 and 200 mm above the rowers heels and for a fixed seat rowing boat that may be used in rough water the feet need to be around 350 apart. For an average 1775 tall male the rowlocks should be 330mm aft of the after edge of the seat and 200mm higher than the seat and the stretcher ( footrests) 730mm aft of the after edge of the seat.
If designing from scratch I try to put the LCB at around 46% of WL aft of the forward end of WL. Prismatic Cf needs to be around 52%

Hope that helps

John Welsford

[Tom M.]

....a certain amount of pitch -- and even more in a SOF build.

Thorne I don't follow the logic here. Seems to me that pitching is all about distribution of volume. Why would SOF increase pitching?

[Thorne]

I meant to say rowing double, although fixed seat rowing usually creates some pitch too. When you push with your feet against the floorboards or whatever and bend forward and then back on the pull, this makes the boat pitch somewhat. With two rowing it pitches a lot more, making longer length better not only for longer waterline, but to reduce pitching.

[john welsford]

The centre of gravity of a man seated to row is about on the after edge of the seat. Place that on your c/b and you'll be about right.
The centre of bouyancy in a conventional fixed seat rowing hull should be at about 48% of wl aft of the forward end of the wl.

John Welsford


Did not want to sidetrack the other thread so just starting a new one. I have always had an interest in a Pulling Boat and Daves 'Ruth" has inspired me to design a SOF pulling boat.

I design and build SOF kayaks this is an easy transition. I have looked a few designs but nothing that doesn't need alternation to suit the SOF construction.

Designing the hull is pretty straight forward. I am not looking to race so a perfect hull not an issue. What I am stumped on is the placement of the seats. This will be fixed seats and I know in a kayak that the location is very important. I assume that rowing is not as critical but is still important for good performance.

I know you want the boat trimmed so the transom is not dragging under water. You don't want to be so far forward the bow digs in and stern is too high. But I am not sure Where to locate myself in the boat.

I assume you want to be seated in front of the LCB (LCF in Freeship) keeping your weight near the center of the boat and maybe slightly forward of it. I have a design I worked from and the seat is way in front of the LCB, over 2' on a 15' boat. This seems excessive to me but I admit I don't know, not having any experience with pulling boats. I am thinking this may be the two man position? Any one have an guidance there?

[Clinton B Chase]

John, thanks for sharing your rules of thumb...I find myself using them to check my boats!

Hull type is important. A trad. dory needs to be trimmed down in the stern to get the skeg effect happening. A double ender like a faering, I find that I like to move fore/aft on the thwart to adjust where my cg is relative to cb. In the St Lawrence River Skiffs, the rower's thwart was extra wide so the boat can be trimmed and so one could row the boats from either direction (i.e., switch bow and stern when rowing single or double, depending). Here is a photo of the SLS..

http://farm6.static.flickr.com/5251/5464924532_4739755efc.jpg (http://www.flickr.com/photos/clintchase/5464924532/)

[Kudzu]

The centre of gravity of a man seated to row is about on the after edge of the seat. Place that on your c/b and you'll be about right.
The centre of bouyancy in a conventional fixed seat rowing hull should be at about 48% of wl aft of the forward end of the wl.

John Welsford

Once again, thank you for sharing!

[Ian McColgin]

You'll no doubt have two stations minimum - one forward for rowing with a passenger and one just abaft amidships for rowing solo. You may well want a third a bit further aft for doubles rowing with one person in forward station and one aft.

There's really quite a bit of possible movement fore and aft of the spot that puts your torso at optimal postition with the oarlocks. This is nice in a weight responsive pulling boat when rowing solo since you can position yourself - usually at least 6" easy travel here - to trim the boat for the angle of the wind, shifting forward to go up and aft to head off, with the ideal position just where the boat will track nicely across the wind.

Since you never want the boat really bow heavy, this means that the leading edge of the center station rowing thwart should be at or a couple inches abaft the center of buoyancy for boat with one person standing. I find the easy way to check that position is to (before thwart placement) to stand in about in the middle holding a line that someone can pull me sideways, or if the current and a mooring or pier head are convenient perhaps stand such that the boat hangs athwart the current. This helps make up for the fact that when I make a boat, given accidents of stern sheets, duck boards and other things that add weight at the ends, the boat is never quite as an analysis of the plans would predict.

If you're going to err, have the center station's thwart a bit too far aft since a boat eternally bow down will gripe and be most unpleasant.

G'luck