Pram Design Help Wanted/Needed!

Hi All!

I'm wanting to build a ~10pram for hunting with my dog 'round lake/marsh margins and for  crossing the river and mellow water anchoring and fishing.  I weigh 220#; dog=100#; gear 50-100#.  So, I'm looking for something to safely float ~400-450#.

I'm thinking that I need a compromise.. neither a river runner, 'nor a long distance racer.  I just want to paddle/row ~100-200yrds to get where I and others can't go with waders.

This is modeled so that the wide transom is headed downstream, when drifting; or when rowing somewhere, the narrow transom it headed in the direction of travel.

I first modeled a Hudson Springs Pram:  http://www.duckworksbbs.com/plans/messer/hudson_springs/index.htm

I modified it by raking back both transoms, for river use.  I then widened the sides and freehand cut a bottom out and created the sides and transoms to fit.

I don't know how to use the FreeShip software.  I might figure out Hull.  But I need some sound advice on how to modify what I have.  I've attached pics.

1"=1'   So the bottom=8", or 8' long;  Bottom is 45" wide;  Narrow transom is 27" at bottom;  Wide transom is 40" at bottom;  Beam is~ 66";  Transom top to top is 9'10.5"; Sides are ~18-19" actual height/width and just shy of 10' long.

There's some rocker in this, but not much.  I'm thinking I could easily narrow the narrow transom some and a touch on the wide transom.  I'm thinking that this is way overbuilt for the weight I've given above.

Could I go narrower than 45" overall?  I've seen prams from 38.5" to 48" wide.  Could I go a little shorter on the side height?   I'm really open to all ideas!

Many thanks!   Ken

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Permalink Reply by Ken Shindledecker on November 5, 2013 at 11:17am

Thanks Tungsten!   Great ideas.   I remember seeing Warren Messer on YouTube doing such things: 

http://www.youtube.com/watch?v=wvfdEMHIp80  http://www.youtube.com/watch?v=wVQrPYnwySg  

Who's "Guy"?... How/where do I find the calcs?

I downloaded some things, a number of years ago, along the lines you're talking 'bout designing your pram.  The started with a dory and cut off one end to make a skiff; then cut off the other to make a punt/pram.  It was on some Boatbuilder's site.

I may flatten my design out in the downstream, just a bit from yours, to have more length on the water and still take some mild chop/small waves, if necessary.

I wouldn't go any narrower than 43"... still thinking 45",, but could be convinced to go to 48".

What do you think of "plascore"??

Permalink Reply by tungsten on November 5, 2013 at 4:53pm

"Guys wooden boat" Look on page 2, somewhere in the 565 replies is the formula.

Permalink Reply by Ken Shindledecker on November 5, 2013 at 5:08pm

Eeeeeeeek!!!!    http://en.wikipedia.org/wiki/Catenary

I remember in some of my readings over the years, 'bout curves and the geometry of boat design.

Here's another pram design I had looked at: 

Montana Pram  http://www.butlerprojects.com/boats/montanapram/

I really like that straight section you put in your boat!

Permalink Reply by Ken Shindledecker on November 5, 2013 at 9:24pm
Permalink Reply by Lawrence E. Long on November 6, 2013 at 5:33am

Ken:  Go to Wooden Boat Magazine and search for plans for the "Nutshell Pram".  9'6" OAL, 4'4" beam, 100lbs.  Glued Lapstrake const(like my Peapod)  Have seen them with 3 POB- might save you "reinventing the  wheel" Glued lapstrake const makes a very rigid boat for the weight.  Can be used with low hp outboard rowed or sailed if you want to build it with a centerboard.

Good Luck

Permalink Reply by Ken Shindledecker on November 6, 2013 at 9:44am

Thank you, Lawrence!

Yes, I do like the looks of the Nutshell and it would be great, if only for lake/pond use, but I'd also like to use it for gentle, rocky bottom river use... and the Nutshell has a V-hull at the narrow transom end.  The bottom IS flat and it has a lot of room.

http://lunenburgdoryshop.files.wordpress.com/2011/08/img_6418.jpg

http://lunenburgdoryshop.wordpress.com/tag/nutshell-pram/

Do you know if this would handle somewhat like a drift pram, in the river?  I understand that a drift pram, like Dave Z's is a true river pram and I couldn't expect the same performance as it, but how maneuverable and initially stable would this boat be in river situations?

Thanks again, Lawrence and All.

Ken

Permalink Reply by Ken Shindledecker on November 6, 2013 at 1:28pm

So, in looking at jon boats and some prams, much of the side panel has been taken out to raise the narrow transom...One doesn't need to do this with the back end of a drift boat...

Maybe because the sides of these boats are more perpendicular and the floor straighter, so they produce less rocker/rise? 

Doesn't that narrowed side panel delete the floatation and lessen the length on the water, too?

Here's a nice pram, but too, it's one transom "appears to me" to be higher than necessary: 

Permalink Reply by tungsten on November 7, 2013 at 6:38am

Why not do Dave Z's boat in SnG?I thought someone on here did just that awhile ago.Maybe just reduce the rocker a little and maybe some side hight to save weight.

Permalink Reply by Ken Shindledecker on November 7, 2013 at 7:09am

I will research that.. thank you!  Dave's is a beautiful boat and solid.  I would need to really strip it down and find ways to stiffen it.. perhaps as Messer has done with the triangular pieces replacing ribs.  I was also thinking of running ash strips around the inside of the boat, to set the seat(s) on, which would also stiffen the sides.

Is your boat a full 48" bottom?

Thanks again!... Ken

Permalink Reply by Dave Z on November 7, 2013 at 10:25am

Thanks for the comments. The drifter pram design was a stroke of luck if I may say so.  I built that thing after one model iteration. Im trying like hell to scale it up into a larger version and having a hard time!

 

Ron Shealer has built it in S&G.  He is on this forum somehwere!

Permalink Reply by Lawrence E. Long on November 7, 2013 at 7:05am

Ken:The great pictures of the Nutshell  from NS  are classic plank on frame construction.  Building S&G will cut some weight and have a "cleaner" interior.  Just guessing here- but the slight "V" might make it more maneuverable on a river.  Jason Cajunes  famous drifters have curved "up stream" transoms said to reduce river push on a flat transom.   My cousin uses a Nutshell as a dingy behind his 32' sloop and sails from midcoast ME to the Canadian border  so I guess it can handle some waves.

Good Luck 

Permalink Reply by Ken Shindledecker on November 7, 2013 at 7:18am

Cutting the end off this Rapid Robert and replacing it with a transom and flattening out the bottom, would also be a possibility:  http://home.clara.net/gmatkin/rapidrobert/rapidrobert.htm

http://storage.ning.com/topology/rest/1.0/file/get/2309596886?profi...

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