Rocker, length

[oldbuffpilot]

Been a little slow lately, more reading than posting or commenting. 3 weeks ago, I had open heart surgery 6 bypasses. At 77 it took some careful consideration to decide to do the surgery. But I did it and I am happy with the decision. I know some of you have had this procedure, I salute you it ain’t easy! So now I am walking around, doing some things, mostly sitting in the shop and scheming!
Here is my serious boat building question. I’m Happy with my latest water moccasin copy, BUT would like to lengthen the next build, no other changes. If I leave the side panel cutback, flare (forms), and add a foot to the length, will the rocker change because of the added length?
I know…. try it and see!!!! Trying to avoid that. Anyway you know who you are, come out of the wood work and give some advice!

Andy

 

[Kayak Jack]

Andy, I’m seriously glad you’re better. Jack

 

[PeteStaehling]

Can't help on your question, but heal well!

 

[oldsparkey]

Yes , a bypass is a really fun thing to do , been there and did not get the "T" Shirt. Take your time and heal properly then life will get back to normal , no matter how krazy it was.
I list my date of my bypass as a unofficial 2nd birthday. This way I can be either 08 or 78 depending on the circumstances.

 

[seedtick]

Yes it will change. Rocker depends on several things - the arc that cut out on the bottom of the sides, the width of the boat, the flare of the sides, and the length of the boat. I don’t know of any mathematical equation that ties them all together such that you can fix one parameter and calculate the others. That’s probably why the old time boat builders just built one or two styles of boats. Keeping everything constant and increasing the length will, I believe, increase the rocker. Think of it as a long lever arm. If midboat to stem is increasing, then keeping that angle and increasing midboat to stem distance will lift the stem further upward.

Another option is to build like Beekeeper where you fix the rocker and build around it

 

[oldbuffpilot]

Thank you. I suspected what you said, I actually am beginning to see the relationship and how it works. Thanks for reinforcing it!

 

[seedtick]

I suggest to folks who are trying their own designs or tweaking existing designs that they build a model out of cheap luan or Masonite. That way you can see the results without cutting up expensive plywood or planks. It also builds your confidence in your boat building skills

 

[PeteStaehling]

I suggest to folks who are trying their own designs or tweaking existing designs that they build a model out of cheap luan or Masonite. That way you can see the results without cutting up expensive plywood or planks. It also builds your confidence in your boat building skills

How big of a model do you typically build? I'd think that with luan or masonite it would need to be fairly large given the thickness of the materials, unless you have access to some quite thin stuff.

I built a couple models just for fun before committing to starting my pirogue, but didn't actually build them to the actual scaled size I wound up building. I sawed some thin veneers on the bandsaw and ran them thru the thickness sander so that they were pretty close to scale thickness even for a small model. It worked great for the simple curves of a UJ style pirogue, but may not for something with more complex curves.

I have a Jet 10/20 thickness sander that is set up with fine grit for musical instrument sound boards so it is easy to make quite thin stock with that and the bandsaw. I have also sometimes thinned down ply with the sander removing a layer or two. So if you had some scrap ply you could resaw and sand or just sand it to half it's thickness or less for a model.

 

[seedtick]

Half scale. Most pirogue sides about 12 inches wide and however long you want the boat. A half scale would six inches by a half length (6,7 or 8 feet). A 4 by 8 sheet could nominally give you eight sides or enough for 4 models. You don’t have to put the bottom on to check out the lines.

 

[PeteStaehling]

Half scale. Most pirogue sides about 12 inches wide and however long you want the boat. A half scale would six inches by a half length (6,7 or 8 feet). A 4 by 8 sheet could nominally give you eight sides or enough for 4 models. You don’t have to put the bottom on to check out the lines.

Ah, okay. When I was thinking model I was thinking much smaller. I think my first model was 1" = 1' or 1/12 scale and the next was 1.5X that big.

I can see a real advantage to your large models in that you can really get decent measurements off of the model. I wouldn't have space to keep the models, but I guess there is no need to.

 

[jdupre']

Models are the way to go. For an approximate answer, just continue the side profile shape of the rocker you have on the moccassin by adding the new length of that half of the boat. I'm sure that will put you within an inch or so of the finished rocker of the longer boat. If you're not super set on a specific side flair, you can do an awful lot of tweaking by adjusting the flair in or out to get the rocker you want.