Where Thwart Thou - Penboscot 14

[RumHead]

My Penoboscot 14 hull is now upright, ready to begin the seat installation. Noticed the thwart knees seem large and obtrusive - like they will really hurt if the boat heels and I lean back. Splitting the uprights, so to speak. I no nothing of engineering - I'm guessing the function of these thwarts is to hold the shape of the hull. They have nothing to do with supporting the seats. Could they be changed to something more butt-friendly as on the right side of the below pic?

http://tampa-bay-sailing-blog.com/wp-content/uploads/2009/08/thwarts.jpg

[Thorne]

Possibly -- if you put a support rail underneath like the example on the right.

[Candyfloss]

What you have pictured on the left is perfectly normal, but a little too intrusive for my taste.

http://pic50.picturetrail.com/VOL458/12377907/22018548/368205240.jpg

This is mine.

BTW, the grain orientation on yours looks wrong. The grain should run at 45 degrees across the knee.

Since this is a sailing boat I take it you have other bulkheads, floors etc. to support the shape? Just thinking outside the square, what's to stop you putting the knee under the thwart?

[Thorne]

Why not ask Arch Davis -- he's quite responsive to builder questions.

[RumHead]

Thanks - the pics I sent are not actually mine. Just ones I found while looking at how others have done it.
I will check with Arch.

[Yeadon]

The knees are to keep the gunnels from flexing while you row. They stiffen the rails considerably.

You could always make a bookended pair of them to support you as you lounge, and to offer extra stiffness. But they need to have plenty of long continuous grain between the rail and thwart or they will eventually fail.

I have that set up, but usually put a pad down over them anyways when I lounge. And lounging is very important, indeed.

[RumHead]

The knees are to keep the gunnels from flexing while you row. They stiffen the rails considerably.

You could always make a bookended pair of them to support you as you lounge, and to offer extra stiffness. But they need to have plenty of long continuous grain between the rail and thwart or they will eventually fail.

I have that set up, but usually put a pad down over them anyways when I lounge. And lounging is very important, indeed.

:)Exactly! I haven't even started on them and my first thought was "that looks uncomfortable!"
I have a lot of long narrow strips of mahagony plywood leftover from the planking. Was thinking I could laminate some.

[Thorne]

What do the plans call for? Looks like a job for solid wood to me...

I feel the same way about thwart knees -- even opened or participated in some threads about 'em. But there are a number of good reasons for including them (apparently) many of which are structural.

http://www.woodenboat.com/forum//showthread.php?t=55212
http://www.woodenboat.com/forum/showthread.php?p=2251438


With natural knees you could get away with something smaller, otherwise I'd get feedback from Arch and go on my merry way.

[RumHead]

What do the plans call for? Looks like a job for solid wood to me...

I feel the same way about thwart knees -- even opened or participated in some threads about 'em. But there are a number of good reasons for including them (apparently) many of which are structural.

http://www.woodenboat.com/forum//showthread.php?t=55212
http://www.woodenboat.com/forum/showthread.php?p=2251438


With natural knees you could get away with something smaller, otherwise I'd get feedback from Arch and go on my merry way.

Plans show knees near exact as the picture on the left.
Here was my response from Arch:
The knees both reinforce the hull, and help support the thwarts. However you could certainly make them as shown in the photo if you prefer them that way.

[Baltimore Lou]

Here's my Whilly Boat (Iain Oughtred design) I built about 8 or 10 years ago. These braces are laminated cherry. I always thought they added a neat sculptural curve to the boat's look.
http://pic60.picturetrail.com/VOL1673/12542239/22311829/372330657.jpg

[RumHead]

Here's my Whilly Boat (Iain Oughtred design) I built about 8 or 10 years ago. These braces are laminated cherry. I always thought they added a neat sculptural curve to the boat's look.


Very nice! Thanks for the the picture. I like that a lot, going to give it a try.

[almeyer]

I used laminated thwart knees on my Penobscot 14 - a little more trouble to make than knees from sawn stock, but worth the effort, in my opinion. Note the "backer block" against the sheerstrake so you have some real wood to secure the knee to. The knee shown is a replacement - the original knees cracked after the boat was bounced around like a rag doll during Hurricane Ike, but I consider that a pretty extreme load.
Al

http://im1.shutterfly.com/media/47b9da34b3127ccec68bc163988d00000060O00ActHLVi5bt2 IPbz4E/cC/f%3D0/ps%3D50/r%3D0/rx%3D550/ry%3D400/

[RumHead]

I used laminated thwart knees on my Penobscot 14 - a little more trouble to make than knees from sawn stock, but worth the effort, in my opinion. Note the "backer block" against the sheerstrake so you have some real wood to secure the knee to. The knee shown is a replacement - the original knees cracked after the boat was bounced around like a rag doll during Hurricane Ike, but I consider that a pretty extreme load.
Al



Great tip on the backer block - thanks!
Were you in the boat during the hurricane? Was it tied to a dock?

[Mrleft8]

I laminated Mahogany for the thwart knees on my Catspaw dinghy very much like the picture on the right, for the same reason that you posted this thread. The ones prescribed by the plans looked horrible. I also used a 3/8" radius router bit to round over the edges except where they meet the thwart and hull.

[RumHead]

After studying the pics, I'm wondering if I could mount the knee on the side of the seat, instead of the top - as in my crude addition to this pic.

http://www.pyratsail.com/images/knees.jpg

[Candyfloss]

Or better still, recess a pair into the edges of the seat.

[Robert L E]

How about something like this?

http://www.woodenboat.com/forum/attachment.php?attachmentid=566&d=1250796670

[RumHead]

How about something like this?

http://www.woodenboat.com/forum/attachment.php?attachmentid=566&d=1250796670

It looks great - but I think by what I've gathered is the knees support the the gunnels while rowing and other hull stress. So they need to have more curve, can't be an L shape. Am I making sense or should I have some more rum?

[Robert L E]

It looks great - but I think by what I've gathered is the knees support the the gunnels while rowing and other hull stress. So they need to have more curve, can't be an L shape. Am I making sense or should I have some more rum?

I was thinking that it would be two pieces, the vertical, having straight grain, would transfer stiffness to the gunnel, and if extended below the seat give a place to attach a knee for seat support.

Bob

[Mrleft8]

I think I'll invent a wheel now.....Anyone interested in a wheel? ;)

[almeyer]

Just my opinion, but I like the traditional style much better. I got inspiration to use the laminated knees after looking through John Gardner's Building Classic Small Craft. You should really get a copy of this book, or at least borrow one, and look through it. The Penobscot 14, even with it's modern construction techniques, is still a pretty design that lends itself well to classic details. As to function, I haven't found the laminated knees to get in the way after almost 5 years of very serious use (almost every weekend between March and November, with the exception of last year). When I row solo, I'm sitting in the middle of the center thwart. With crew, I sit on the forward thwart and have enough room. The gentle shape of the knees doesn't cause any discomfort when I scoot over to one side. When sailing, I'm on the windward side bench, so neither of the thwarts are an issue.

As far as the hurricane, the boat was strapped to it's trailer, and the trailer was hitched to the truck. When the hurricane first made landfall, the wind was strong enough to pick up boat and trailer and swing it around 90 degrees to the truck. After the eye passed and the wind shifted direction, the wind picked up the trailer again and swung it around 180 degrees. By the time the storm was over, the trailer hitch had come off the ball - the only thing holding the trailer to the truck were the safety chains. Sometime during all this commotion, the centerboard was lowered from the fully retracted position to partially lowered. The partially lowered centerboard then banged against the keel rollers and bunks as the trailer was being tossed around, resulting in a cracked plank and cracked thwart knees.
Al

[RumHead]

I appreciate all the imput very much - helped me make some decisions. I'll post pics of the finished knees hopefully in a few weeks.
Thanks again everyone.